Radioactive Waste Disposal into the Sea

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No . 5

Radioactive Waste Disposal

into the Sea|

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jI N T E R N A T I O N A L ATOMIC ENERGY AGENCY

V I ENNA 1961

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R A D I O A C T I V E - W A S T E D I S P O S A L I N T O T H E SEA


The following States are Members of the International Atomic Energy Agency:AFGHANISTANALBANIAARGENTINAAUSTRALIAAUSTRIABELGIUMBRAZILBULGARIABURMABYELORUSSIAN SOVIET

SOCIALIST REPUBLIC CAMBODIA CANADA CEYLON CHILE CHINA COLOMBIA CUBACZECHOSLOVAK

SOCIALIST REPUBLIC DENMARKDOMINICAN REPUBLICECUADOREL SALVADORETHIOPIAFINLANDFRANCEFEDERAL REPUBLIC

OF GERMANY GHANA GREECE GUATEMALA HAITI HOLY SEE HONDURAS HUNGARY ICELAND INDIA INDONESIA IRAN

ISRAELITALYJAPANREPUBLIC OF KOREALUXEMBOURGMEXICOMONACOMOROCCONETHERLANDSNEW ZEALANDNICARAGUANORWAYPAKISTANPARAGUAYPERUPHILIPPINESPOLANDPORTUGALROMANIASENEGALSOUTH AFRICASPAINSUDANSWEDENSWITZERLANDTHAILANDTUNISIATURKEYUKRAINIAN SOVIET SOCIALIST

REPUBLIC UNION OF SOVIET SOCIALIST

REPUBLICS UNITED ARAB REPUBLIC UNITED KINGDOM OF GREAT

BRITAIN AND NORTHERN IRELAND

UNITED STATES OF AMERICA VENEZUELA VIET-NAM YUGOSLAVIA

IRAQThe Agency’s Statute was approved on 26 October 1956 at an international

conference held at United Nations headquarters, New York, and., the Agency came into being when the Statute entered into force on 29 July 1957. The first session of the General Conference was held in Vienna, Austria, the permanent seat of the Agency, in October, 1957.

The main objective of the Agency is “ to accelerate and enlarge the contribution of atomic energy to peace, health and prosperity throughout the world” .

© I A E A , 1961Permission lo reproduce or translate the information contained in this publication may be obtained by writing to the International Atomic Energy Agency, Kaerntnerring 11, Vienna I.

Printed in Austria by Paul Gerin, Vienna September 1961


SAFETY SERIES No. 5

RADIOACTIVE - WASTE DISPOSAL INTO THE SEA

REPORT OF THE A D H O C PANEL CONVENED BY THE DIRECTOR GENERAL OF THE IAEA

UNDER THE CHAIRMANSHIP OF MR. H E N R Y B R Y N I E L S S O N

IN FEBRUARY 1960

INTERNATIONAL ATOMIC ENERGY AGENCY Kaemtnerring, Vienna I, Austria

1961


THIS REPORT IS ALSO PURLISHED

IN FRENCH, RUSSIAN AND SPANISH

RADIOACTIVE-WASTE DISPOSAL INTO THE SEA, IAEA, VIENNA, 1961

STI/PUB/14


F O R E W O R D

Preventing pollution of the seas from the discharge of radioactive wastes has been recognized as an international problem of considerable magnitude. In April 1958 the United Nations Conference on the Law of the Sea adopted a Convention on the High Seas, Article 25 of which provides that every State shall take measures to prevent pollution of the seas from the dumping of radioactive wastes, taking into account any standards and regulations which may be formulated by the competent international organizations. The Conference also adopted a resolution recommending that the IAEA pursue studies and take action to assist States in controlling the discharge of radioactive materials into the sea.

Later the same year, a Panel of experts was invited by me to meet in Vienna to study the technical and scientific problems connected with radioactive waste disposal into the sea, and Mr. H. Brynielsson of Sweden was designated Chairman of the Panel. Representatives of the United Nations, the Food and Agriculture Organization of the United Nations, the World Health Organization and the United Nations Educational, Scientific and Cultural Organization participated in the work of the Panel.

After a second series of meetings in 1959, the Panel completed its study, setting forth the result of its work in a report dated 6 April 1960, which has been submitted to the Agency’s Scientific Advisory Committee and to Member States for their information.

The Panel’s report is now published in the present volume of the Agency’s Safety Series in the form in which it was submitted by the Chairman of the Panel.

I should like to add that the report represents the views of the experts participating in their individual capacity in the work of the Panel. It is offered as an information document and it should not be regarded as an official statement by the Agency of its views or policies in relation to the subject discussed.

September 1961 Director General


T A B L E O F C O N T E N T S

Preface ............................................................................................ 8c h a p t e r I. Introduction..................................................................................... 9c h a p t e r II. Existence and Extent of Radioactive-Waste Problems . . 15c h a p t e r III. Approach to a Solution of the Radioactive-Waste Disposal

Problem .................................................................................. 24c h a p t e r IV. Maximum Permissible Exposure to Radiation from

Disposal of Radioative Waste into the S e a ........................ 32c h a p t e r V. Nature of the Marine Environment.......................................... 37c h a p t e r VI. Practical Evaluation of Typical Waste-Disposal Problems 53c h a p t e r VII. Control Measures ...................................................................70c h a p t e r VIII. Conclusions and Recommendations .................................. 74

Appendix- I. Data on Typical Radioactive W a stes........................... 80Appendix II. Data on Maximum Permissible Concentrations . . . . 85Appendix III. Chemical Properties of Sea-Water and Resultant

Geochemical P r o c e s s e s ....................................................88Appendix IV. Marine Biological D a t a ........................................................ 92Appendix V. Monitoring, Sampling and Analytical Technique . . 95Appendix VI. Mixing and Exchange P ro ce sse s ....................................100Appendix VII. Discharge of Radioactive Effluent into a Coastal-

Water Region (Example Computation) ...................133Appendix VIII. Packaged-Waste Disposal-Site Evaluation (Example

Computation) .................................................................... 143Appendix IX. Radioactive Wastes from Reactor-Powered Ships

(Example C om putation)....................................................158


P R E F A C E

The views expressed in this Report represent the joint results of the Panel members acting in their capacity as individual scientists. Thus they are not necessarily an expression of the opinion of any body or authority with which the Panel members may normally be associated in the course of their employment.

The Appendices are largely the work of sub-committees or individual members of the Panel and do not necessarily represent the views of all members of the Panel with respect to matters of detail.


CHAPTER I

I N T R O D U C T I O N

United Nations Conference on the Law of the SeaThe possibility of undesirable contamination of the sea from disposal of

radioactive wastes lias become a matter of growing public concern. In November, 1956, the United Nations Scientific Committee on the Effects of Atomic Radiation initiated limited studies on the possibility of radioactive contamination of the sea from such disposal. As a result of this preliminary study it was able to report (Report of the United Nations Scientific Committee on the Effects of Atomic Radiation (1958) pp. 14, 38):

“ Radioactive waste. .. The Committee has not given any detailed consideration to the

technical aspects of these problems, but from the information available it is clear that there is no general population hazard from this cause at the present time. The Committee realizes that these problems may become of importance in the future and considers that the release of radioactive wastes should be made a matter of international co-ordination and agreement.” . . . (p. 14).

“Radioactive wasteThe discharge of radioactive waste in countries with nuclear reactors

has not led to appreciable radiation exposure of populations, . . . however, . . . this subject (should) be kept under review. It is important that work should be actively continued on methods of minimizing environmental contamination from these causes.” (p. 38).At the United Nations Conference on the Law of the Sea. (1958), con

cern with pollution of the sea, which had originated in connection with release of oil, was extended to include pollution by radioactive materials. As a result, it was decided to propose the inclusion of the following provision relating to the disposal of radioactive waste in the Convention on the High Seas (United Nations Conference on the Law of the Sea, Official Records, Vol. II (1958), pp. 22, 138):

“Article 251. Every State shall take measures to prevent pollution of the seas

from dumping of radio-active waste, taking into account any standards and regulations which may be formulated by the competent international organizations.

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2. All States shall co-operate with the competent international organizations in taking measures for the prevention of pollution of the seas or air space above, resulting from any activities with radio-active materials or other harmful agents.”The Conference, at its Tenth Plenary Meeting, adopted a Resolution on

the pollution of the high seas by radioactive materials, which reads, in part (United Nations Conference on the Law of the Sea, Official Records, Vol. II (1958), pp. 24, 144):

. the International Atomic Energy Agency, in consultation with existing groups and established organs having acknowledged competence in the field of radiological protection, should pursue whatever studies and take whatever action is necessary to assist States in controlling the discharge or release of radio-active materials to the sea, in promulgating standards, and in drawing up internationally acceptable regulations to prevent pollution of the sea by radio-active materials in amounts which would adversely affect man and his marine resources.”

The International Atomic Energy Agency ad hoc Panel on radioactive waste disposal into the sea

The programme of work recommended by the Preparatory Commission of the International Atomic Energy Agency in 1957 included the proposal that the Agency should undertake studies and consider the formulation of regulations governing waste disposal into the sea. To implement this programme, and in conformity with the recommendations of other United Nations bodies, an ad hoc Panel on Radioactive Waste Disposal into the Sea was set up in October 1958 under the chairmanship of Mr. H. BRYNIELSSON, of Sweden, to advise the Director General.

Members of the Panel were:Dr. Bo ALER, Physicist Prof. Dr. F. BEHOUNEK, Physicist Mr. P. COHEN, Chemist Dr. A. K. GANGULY, Chemist Mr. H. HOWELLS, Physicist Dr. C. A. MAWSON, Biochemist Prof. D. W. PRITCHARD,

Oceanographer Prof. N. SAITO, Radiochemist Mr. J. B. SCHIJF, Hydraulic

EngineerMr. Ing. VESELY, Chemical Engineer

SwedenCzechoslovakiaFranceIndiaUnited Kingdom CanadaUnited States of America

JapanNetherlands

Czechoslovakia

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In addition, the following representatives of United Nations Organizations took part in the work of the Panel:

Mr. A. DOLLINGER, Economist Mr. T. LAEVASTU, Fisheries

Hydrographer

Dr. P. TAILLARD, Radiologist

Mr. M. YOSHIDA, Engineer

United Nations Food and Agriculture

Organization of the United Nations

World Health Organization of the United Nations

United Nations Educational, Scientific and Cultural Organization

The Secretary of the Panel was Mr. G. W. C. TAIT of the International Atomic Energy Agency.

The results of the studies of this Panel are given in this Report.

Purpose and scope of the ReportThe Report offers recommendations which could serve as a basis of inter

national agreement to ensure that any disposal of radioactive waste into the sea involves no unacceptable degree of hazard to man. It is drafted for all who have responsibilities or interest in the problem of radioactive waste disposal at sea. The body of the Report is intended to ensure that such persons are adequately informed on the broad aspects of the problem. It is hoped that those more technically concerned with waste-disposal operations will find material in the Appendices which will guide them in a safe and efficient manner in their work. It should be noted that any special considerations of all eventualities which could arise from accidents is beyond the scope of the present Report. Finally, it is intended that the conclusions should be read on the understanding that they would be subject to modification and change in the light of the growth of knowledge in this field.

Basic scientific concepts

R a d io a c t iv e n u c l e i

The atoms which form matter are conveniently visualized as being composed of a group, of elementary particles (neutrons and protons) forming a compact core, or nucleus, held together by very strong forces, and an external diffuse region in which electrons are held by much weaker forces. Because of the relatively vast forces within the nucleus, the amounts of energy associated with possible nuclear changes, or disintegrations, 'are

11


much greater — usually by a factor of 1 000 000 or more — than energies associated with changes in the outer areas of atoms. (Chemical reactions and temperatures normally at man’s disposal only affect the outermost electrons).

Each nuclear grouping is characterized by a resultant electrical charge which is some integral multiple of the charge of a single proton. A specific nuclear charge is associated with each element. The number and arrangement of external electrons derive from the nuclear charge and, in turn, largely determine the chemical properties of each element. Of all possible arrangements of the elementary particles which, grouped together, form nuclei, only a limited number are stable groupings. These are the naturally- occurring stable nuclei. Other nuclei contain excess energy which can be released by a spontaneous rearrangement of the nucleus. These are unstable nuclei. Incidentally, such unstable nuclei form atoms chemically indistinguishable from corresponding stable atoms. Atoms with the same chemical properties, but differing nuclear composition, are called isotopes of the same element, and those with unstable nuclei, radioisotopes. Alternatively, when attention is directed to nuclear properties alone, the radioisotopes are often referred to as radionuclides.

The discovery of nuclear fission resulted in the production of artificially radioactive elements in two ways. The fission process itself gives rise to very radioactive matter, since the splitting of an only slightly unstable large nucleus into two, results in new nuclei which are highly unstable. These are the nuclei of the fission products. In addition, neutrons escape which, when captured by stable nuclei, cause the latter to become unstable. This resulting radioactivity is referred to as “ induced radioactivity” . These two processes have led to the production of very great quantities of radioactive matter compared to that previously available in the form of the naturally-radioactive elements, such as radium, of which only 1.5 kg was in use in 1953.

The nature of radioactive elements may, perhaps, be best understood if we consider that in all nuclei the constituents are in continuous motion. In the radioactive nuclei the arrangement is not absolutely stable and a more stable arrangement can be achieved by release of energy. However, such a transition is only possible during a certain fraction of the nucleus’ pattern of internal motion, or we may say that the transition has a certain probability of occurring over a unit interval of time. An alternative way of looking at the. same phenomenon is to say that we do not know when any particular nucleus will undergo a transition to a more stable state with release of energy, but that we can assign an “average life” to such a nucleus. An equivalent mathematical expression is to speak of the “half


life” of a group of radioactive atoms, that is, the time interval in which half the nuclei originally present have undergone transition, or “ decayed” . Radioactive isotopes are usually characterized by their half-life.

N u c l e a r r a d ia t io n a n d b io l o g ic a l e f f e c t sThe energy released during the nuclear “ transition” , or radioactive

“ decay” , appears in the form of radiation. The energy carrier may take a number of forms, for instance, alpha, beta or gamma rays. From the point of view of biological effects these rays, or carriers of energy, only differ materially in the ease with which they will pass through matter. The final effect in tissue, or the individual cell, is the same. The absorption of radiation results in ionization and excitation, with the breakdown of the water contained in the cells into chemically-unstable components, i. e. the “ free radicals” , which, in achieving chemical stability, in turn damage important constituents of the living cells. The significance of this final chemical action results from the large ratio that the nuclear energy carried by the radiation bears to normal chemical energy. As a result, about 100 000 of these chemically-active “free radicals” are produced by each individual particle of nuclear radiation, in coming to rest in the cells of living tissues.

Radioactive material can be dangerous to man for the following reasons:(1) The release of energy, since it arises from rearrangement of the

nuclei of atoms involving very great internal forces, is not subject to regulation by means at man’s disposal.

(2) The released energy is often in the form of radiation which can penetrate readily available protective devices.

(3) The energy, being in highly concentrated form, can arise in dangerous amounts from quantities of matter so small that they will evade control measures normally applied to dangerous substances.

(4) The energy, on being released in living tissue, acts in an indiscriminate fashion, and deleteriously, on the fundamental constituents of all cells in such a way as to make protective measures generally ineffective.

S ig n if ic a n c e o f r a d ia t io n

Such dangers must be considered as matters of degree rather than kind, since all living tissue is normally exposed to some amount of high-energy radiation coming from naturally-radioactive material present everywhere (including the human body) in small quantities, and to cosmic radiation.

This latter consideration is particularly important, since devices for detecting nuclear radiation are extremely sensitive. With many other forms

13


of hazardous exposure which affect man it is possible to recommend that there be no exposure, since available detecting devices usually fail to respond below a certain level. The problem has been to develop a detecting device which is sufficiently sensitive to respond to the minimum degree of hazard which is notably dangerous. When this degree of sensitivity is reached, instrument development often ceases. Any degree of hazard less than the accepted minimum permissible is indicated as “zero hazard” . With nuclear radiation this is not the case. In general, even a simple detecting device, such as a Geiger-Miiller counter, will respond to amounts of radiation commonly present in nature so that the instrument always shows some “background” . For this reason control of radioactivity must always be on a quantitative basis and the term “no activity” is meaningless. This illustrates a point frequently overlooked, that measurement has meaning only in terms of the instrument which is used.

The activity of a radioisotope is often characterized by the disintegration rate, which is expressed in the unit “curie” . A “ curie” is defined as 37 thousand million disintegrations per second and is approximately the rate of disintegration for one gram of radium. This unit does not take into account the nature and energy of the radiation emitted by the radionuclide in question. For measuring radioactivity a useful range of physical instruments exists which respond to the physical phenomena produced by such radiation. Fortunately, the biological effects and damage produced can usually be related in a simple fashion to such physical measurements. The biological effects are dependent on the amount and nature.of radiation energy absorbed in the tissue. The biologically-effective dose, which is the product of the total energy absorbed in the tissue and a factor representing the relative biological effectiveness of the particular type of radiation, is designated in “rem” and dose-rates in units, such as “rems per year” .

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CHAPTER II

E X I S T E N C E A N D E X T E N T O F R A D I O A C T I V E - W A S T EP R O B L E M S

Nature of wastesC la sses o f w a st e s

The discovery and use of nuclear fission has led to the production of large quantities of radioactive substances. In general, the bulk of these are merely a by-product of the fission process and constitute a waste product from the moment of their formation. Other radioactive material which has useful application eventually becomes waste when the purpose for which it was made has been fulfilled.

The nuclear-energy industry produces high-activity, intermediate-activity, low-activity and so-called non-active wastes. The different categories are not sharply delineated. “High-level wastes” have been defined elsewhere [1] as those with “ concentrations of hundreds or thousands of curies per gallon” whereas “low-level wastes” have “concentrations in the range of one microcurie per gallon” . It is evident that between these classes of waste must lie a wide range of wastes of intermediate activity. The waste can be solid, liquid or gaseous; combustible or non-combustible; aqueous or non-aqueous.

The range of properties of radioactive wastes is so great that two different approaches to waste treatment exist. In general, the more radioactive and dangerous wastes are subject to concentration and containment while the less dangerous wastes are often diluted and dispersed. By its nature waste disposal into the sea is predominantly an example of the latter approach and would therefore be considered chiefly in terms of low-level wastes. However, to the extent that containment may be achieved, either by non-destructible packaging or placement in sites possibly offering isolation over long periods of time, it could be considered to be based on aspects of both approaches. To some degree it might therefore be possible eventually to extend sea disposals to wastes other than those of strictly low activity.

The present practice of waste management is to contain the high- and intermediate-activity wastes in storage tanks on land. Low-activity wastes are discharged into the ground or, in some centres, released through pipes to the sea, either directly or after treatment, or they are fixed in concrete or in packaged containers, some of which are disposed of in the sea. Although radioactive wastes occur in many different forms, some order can be achieved by considering them in relation to the operations from which the arise.

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W astes f r o m o r e t r e a t m e n t a n d r e f in in gInitial refining and beneficiation processes are an important source of

low-level wastes. At the processing stage, the steps include crushing, grinding, washing and chemical operations. Wastes from ore processing include wash waters, waste solids and process liquids. After recovery of uranium by chemical processes, the waste liquids contain daughter products of uranium. The refining processes also contribute non-active wastes which may prove to be a greater hazard to the environment than the radioactive matter.

W a stes fh o m r e a c t o r o p e r a t io n s on l a n dRadioactive wastes can arise from land-based reactors in several ways.

In early reactors the primary coolant was simply passed through and returned to the environment. If air was the coolant no problem of sea disposal could occur, except possibly in connection with any coolant filters used. With water as a coolant, impurities originally present in the water supply, or arising from corrosion, acquire induced activity in passing through the reactor and could appear as radioactive waste. Under normal operating conditions such radioactivity is usually relatively short-lived. Radiophosphorus (P32) is probably one of the most important contaminants because of the biological significance of phosphorus.

In more modern reactors the primary coolant is in a closed system linked by heat exchangers to the secondary coolant. The latter will only carry radioactive wastes if the heat exchangers develop defects. However, radioactive wastes in the form of fission products can enter the closed circuits through failure of fuel cladding, or other mechanical failures. In such closed-circuit systems the coolant is purified, using such devices as ion exchangers and associated filters on side streams. The exhausted filters and exchangers must be disposed of as radioactive waste.

The great majority of the radioactive-waste products are present in the spent fuel from the reactor. Customarily, the radioactive material is transferred to the fuel-treatment plants, where it appears as highly-active waste. However, in certain reactor systems it might not be considered economic to recover the spent fuel. Such highly-radioactive fuel elements would provide a high-activity waste-disposal problem.

W a stes f r o m r e a c t o r s o p e r a t e d at seaThe primary wastes from ship reactors will arise in connection with a

shore fuel-treatment plant and are similar to those produced by land-based reactors. Wastes peculiar to nuclear shipping include those radioactive materials contained in the excess volume of coolant which is displaced

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at warm-up. This may contain both radioactive corrosion products and fission products in low concentrations. In addition, there will be operational wastes from leakage of various reactor systems, laboratory effluents and decontamination wastes. In general, contaminated solutions are purified by passage through ion exchange columns so that the ion exchangers contain the bulk of such actual radioactive waste material.

W a ste f r o m ir r a d ia t e d f u e l t b e a t m e n t in s t a l l a t io n s

The vast majority of radioactive materials and resultant wastes come from the nuclear fuel used in reactors. On a comparative basis the radioactivity from all other sources is small. There is an important difference between the high-activity wastes, originating from the first stages of chemical processing of irradiated nuclear fuel as currently practised, which are concentrated and represent more than 99.99 ®/o of the total activity of the fission-product wastes, and the other types of wastes which are much less active and occur in much larger volumes.

The activities associated with present-day primary wastes, formed by dissolving irradiated fuel in chemical processing plants, are of the order of 1000 c/1. The use of longer irradiation times, or treatment by new processes, could raise this figure by an order of magnitude. The primary waste solutions differ considerably in chemical composition, depending on the process used. They are all highly corrosive. From the chemical point of view the non-radioactive reagents used in the treatment process completely dominate their behaviour. However, their high radioactivity will generate heat, especially when the material is held in large bulk. The radiation itself may have deleterious effects in degrading organic substances, and possibly even leading to dangerous gas formation or other phenomena. These wastes are contained but their existence should always be borne in mind.

In addition to these high-level wastes, low and intermediate wastes result from certain operations in the processing of irradiated fuel. The intermediate wastes are either placed directly into storage or are pretreated to produce further low-level wastes and separated wastes of higher activity suitable for storage.

W a ste f r o m u ses o f r a d io is o t o p e s

The radioactive wastes which arise from the industrial, agricultural, scientific and medical uses of radioisotopes also occur in many different forms. However, in practically all circumstances they will be of intermediate- or low-level activity.

A major nuclear-research centre may produce a wide variety of radio

17


active waste including, typically, about 100 m3/yr of solid objects contaminated to low or intermediate levels of activity, and 1000 m3 of water a day contaminated to a low level.

High dilution of the wastes, or the presence of appreciable quantities of inactive solids, acids or complexing agents, often causes difficulties in the treatment of wastes. Laundry wastes may be particularly troublesome, since the agents used to dissolve or suspend the active material make its subsequent removal from the effluent more difficult.

A hospital using small quantities of short-lived radioisotopes may not always produce wastes of sufficient radioactivity to justify any special disposal methods. Certain research laboratories may also come into this category.

Animal experimentation can cause special problems due to the difficult nature of cadavers from the disposal point of view. However, the level of activity is trivial in regard to sea disposal.

Quantities of radioactive wastes

P r e s e n t s it u a t io n

An estimate of the rate of radioactive-waste production can be made in the following way. For all practical purposes the total radioactive waste is that contained in the spent fuel from nuclear reactors. Within very narrow limits the fission-product yield is directly proportional to the thermal power of the reactor and a simple conversion factor gives grams of fission products in terms of energy generated. It is, therefore, only necessary to estimate the world nuclear-energy production at any time to know the corresponding yield of waste.

One source of confusion in designating quantities of waste is that due to the continuous radioactive decay. The activity of a quantity of waste- fission products, when expressed in curies, is continuously decreasing, so that it is necessary to know the time since formation and, to a lesser extent, the time of irradiation in the reactor, for adequate designation. However, the measure of danger of waste-fission products is largely given by the content of long-lived fission products, such as 28-yr strontium (Sr90). Over a period of several years this does not change in the way total activity does, but rather remains proportional to the original weight of fission products and, therefore, to the thermal power of the reactor in which it is produced.

The following numerical example is provided. One gram of fuel undergoing complete fission would give about 1 MWtu for one day. Remaining as waste will be one gram of fission products. At one day after removal from the reactor (assuming a 100-day fuel cycle) the activity will be about

18


10 000 c, of which 3 c or 0.02 g will be the critically-dangerous isotope Sr90. After 3 yr the total activity will have fallen to the order of 10 c while the Sr90 content (and resultant hazard) will remain practically unchanged at about 3 c, since it takes 28 yr for the Sr90 activity to decrease to half its value.

Estimates of the present-installed nuclear capacity must be conjectural, since a large part is connected with military programmes, but can be something of the order of 10 000 MWth- On this basis, the present total waste production would be of the order of magnitude of 4000 kg of fission products a year, or 10 Me Sr90. The bulk of this is contained in stored waste solutions. These high-level waste solutions are probably being produced at the rate of about 50 000 m3/yr at present, but improved treatment methods will probably yield waste solutions concentrated to a higher degree in the immediate future.

Estimates of wastes, other than the highly-active stored solutions from the primary processing of fuel, are more difficult, but a rough estimate is possible. Even here the great bulk of wastes released to the environment comes from the fuel-treatment plants. They represent incidental and accidental by-products of the treatment process, which are considered uneconomic for further processing or storage, and of sufficiently low hazard to permit some form of environmental release. At most fuel-treatment centres the proportion between the activity of total wastes and that of wastes released to the environment, which represents a balance between costs of further processing and costs of environmental protection and monitoring, ranges from ten thousand to one up to a million to one. It is usually considered worthwhile to reduce the concentration of the critically- dangerous 28-yr strontium (Sr90) to a proportionately greater degree before release. On these considerations, the total release of fission-product wastes to the environment is at present probably not more than about V2 kg/yr.' This would have had an initial activity of not more than about 5 X 106 c one day after removal from the reactor, but the Sr90 content should be well below 1000 c.

Another approach is to consider the commercial production and distribution of radioisotopes. By far the major production is radio-cobalt (Co60) of which about 106 c/yr is produced in the form of sealed sources. If this were released as waste, the resultant danger might be comparable with the low-level by-product waste from fuel processing. However, by its nature this material would not be released as waste to the environment in the normal course of events.

Other radioisotopes not in the form of sealed sources, such as those used in medicine, which would be released to the environment, represent hazards many orders of magnitude less than those discussed. The total

2’ 19


O

TAILINGS FROM MILLING PERMANENT CONTAINED STORAGE ENVIRONMENTAL DISPERSAL

VFig. 1

Schematic representation of the origin and the relative amounts of radioactive wastes.The cross-sections of the various streams symbolize the relative amounts of radioactivity. The maximum permissible levels for human consumption are used for the comparison of different radioisotopes. For details see

Chapter II.


quantity of these materials distributed is probably of the order of a few thousand curies, of which the bulk is radioiodine (I181) and radiophosphorus (p32) The toxicity of such materials would correspond to less than 10 c of 28-yr radiostrontium (Sr90).

Finally, the production of radioactive wastes from ore processing- should be considered. The most serious hazard here is the contained radium. On the basis of a uranium production of 100 000 metric t/yr the radium (Ra226) in the wastes could amount to 30 000 c/yr. This could be a major radioactive-waste problem in the environment. In the case of thorium production, the content of mesothorium (Ra228) must be considered. Fortunately, however, due to the chemical nature of radium and the ore treatment process involved, nearly all this activity is returned to the environment in a chemically-inert form dispersed throughout large volumes of mineral solids at a safe level.

Further data on typical wastes reported in the literature are given in Appendix I (see Fig. 1).

A m o u n t s e x p e c t e d in t h e f u t u r e

Estimates of future waste production are largely dependent on corresponding estimates of world nuclear-power development. Any precise time scale appears unrealistic. However, it is possible to foresee two stages of future development. The first is the point to which current plans will materialize. A recent press estimate, based on compilation of published plans, and corrected for non-reporting countries, would give a total installed power of 200 000MW on the maturation of present programmes. The next stage would be that at which atomic energy becomes a major source of the world’s energy needs.

In the former case, there would be about 60 tons of fission products a year. This represents, after 100 days’ cooling, nearly 70 000 Me of activity, which is already one tenth of the natural radioactivity in all the oceans of the world. The latter case is even more speculative, but probably corresponds to a fission-product waste production of at least 1000 metric t/yr.

The estimate of future secondary waste production is even more difficult. However, certain arguments permit estimates within broad limits. A proportional increase paralleling that for power production might at first appear reasonable, but it is held that this would represent an extreme upper limit.

In the case of chemical processing, the secondary waste can be viewed as arising from imperfect processes. The ideal processing system would provide only two effluent streams, one containing all the radioactive material in a highly-concentrated form suitable for storage, and the other

21


very low-activity effluent presenting no disposal problems. As technology improves the proportion of activity in the secondary streams (now about one ten thousandth of that in the primary streams) will become even less. A further consideration is that the present secondary wastes from processing are sometimes not subject to further treatment where the environment has been used for their disposal. It might be expected that at present sites the environment is often being used close to its capacity. The amount of secondary wastes will therefore be unlikely to increase as fast as the use of nuclear power.

In connection with radioisotope production, while the use of sealed sources will undoubtedly increase, the use of dispersible isotopes leading to waste production may not increase in nearly the same proportion. For example, it is not unreasonable to believe that, while greater medical knowledge will increase the use of trace amounts of radioactive agents for diagnostic purposes, the more crude use of larger amounts in internal medicine may even decrease.

Radioactive-waste disposal as a problemOn economic grounds, man customarily releases non-radioactive wastes

to the environment wherever produced. It is only when some resultant hazard or disadvantage arises that more carefully thought-out methods of waste disposal are used. Historically, producers of wastes have often only reluctantly applied safe methods of disposal when the effects of uncontrolled release have damaged strong interests or outraged public opinion.

The subtle and persistent nature of the hazards of radioactivity, however, make it more desirable in this field that safe waste-disposal practices be initiated from the beginning. If one waits for harm to be manifested, the consequences could affect large numbers of people over long periods of time, with little hope of corrective measures undoing the harm. Consequently, when adopting a waste-disposal method, and also before any extension is made of the use of a certain waste-disposal practice which is safe in a present situation, a careful evaluation of the future consequences, in particular the international implications, should be made. In this context both the immediate local aspects and the effect on more distant areas must be taken into account in evaluating the safety of the method. The investment of capital and effort in one line of development may make its replacement very difficult. Therefore, advantage should be taken of the fact that, at the present time, radioactive-waste disposal is a relatively small .problem and various methods may be explored without too much concern as to their immediate economics so that, if and when the problem assumes major proportions in the future, methods of disposal will economically meet the same very strict standards of safety.

22


The uncontrolled release of radioactive wastes at their point of production is eliminated • as a possibility when the expected rate of production is compared with the recommended permissible levels in the environment. Possible exceptions in suitable situations are the tailings from the milling of ore, and the effluents from hospitals using istotopes for diagnostic purposes. In the former case, the non-radioactive properties of the waste may make some control desirable.

It is therefore necessary to choose a method of waste disposal which provides appropriate control. The wide range of properties, and the amounts of wastes already considered, make it most unlikely that any single method of disposal will meet all needs. Rather, each class of waste must be considered separately.

The purpose of this Report is to consider the utilization of the sea as a recipient of low- or intermediate-level radioactive wastes.

R E F E R E N C E[1] JOINT COMMITTEE ON ATOMIC ENERGY, CONGRESS OF THE

UNITED STATES, Hearings on Industrial Radioactive Waste Disposal (1959).

23


CHAPTER III

APPROACH TO A S O L UT I ON OF THE R A DI OA C T I V E - W A S T E DISPOSAL PROBLEM

General features of acceptable radioactive-waste disposal methodsRadioactive waste is an unavoidable accompaniment to the use of

nuclear energy. As its radiation properties cannot be artificially destroyed, it has to be safely disposed of in some way. When considering different methods of disposal, the first principle must be the safeguarding of man against the damaging effects of radiation. Only if this has been ensured may other considerations be allowed to come into play. The established practices of high-level waste storage with no environmental release are in accordance with this principle. The Panel has also observed the principle of first safeguarding man when considering the use of the sea for the disposal of low- and intermediate-level radioactive waste.

The sea as a site for radioactive-waste disposalBecause of its tremendous capacity, the sea appears attractive as an

environment for the application of the dilution and dispersal technique of waste disposal. It is evident that there is a limit to the capacity of the sea to disperse and dilute radioactive materials since man should continue to have unrestricted opportunities for the harvest of marine products. Present knowledge of the sea is not sufficient to provide for a precise evaluation of this capacity, though order of magnitude estimates can be made and are useful in serving as guides in delineating the scope of the problem which will be considered in detail later.

Maximum permissible concentrations of the various radionuclides in seawater, which may result from waste disposal into the open sea, can be determined, using reasonably conservative assumptions regarding man’s utilization of the sea. Such determinations are made in Appendices VIII and IX, and indicate that the concentration of the most hazardous isotopes, including, for example Sr90, in those layers of the sea harvested by man (the upper 1000 m) should not exceed about 10-9 [xc/ml as a result of waste disposal into the deep sea. If waste materials introduced into the sea were distributed uniformly throughout the volume of the world oceans, this suggested maximum concentration would be reached at equilibrium if only about 1 */o of the Sr90 produced by the possible future fission of 1000 metric t/yr were introduced into the sea.

As will be discussed in greater detail in Chapter V, the sea is stratified, with some restriction on the exchange between the deep waters of the

24


ocean and the upper layers utilized by man. Over a large part of the ocean area located in mid, and low latitudes, the disposal of waste into the deep waters would provide some retention time during which radioactive decay would result in lower concentrations occurring in the upper layers at equilibrium than in the deeper waters. At present there are two divergent views among oceanographers regarding the average retention time for a water particle in the deep layers (below, say, 1000 m) in the sea. One group holds that this residence time is rather short, of the order of tens of years, while the other group has presented arguments favouring retention times of the order of hundreds of years. Assuming a simple two- layered model of the ocean, and taking a short retention time for the deep- water layers of 50 yr, computations indicated that less than 2 % of the fission products from the fission of 1000 metric t/yr could be placed in the deep sea without having the concentration of Sr90, arising from such disposal, exceed the suggested value of 10~9 iic/rnl in the upper layers. On the other hand, if the alternative view is taken that the retention time for the deep-water layers is more like 500 yr, computations indicate that about 7°/o of the fission products from the considered future power production could be placed in the deep sea. In view of the fact that only a rather low degree of confidence can be placed upon the various factors which must enter this type of computation, consideration at this time of the deep sea as a recipient of any considerable fraction of probable future quantities of high-level wastes, does not appear justified. Such consideration must await further extensive studies and research into the nature of the sea. Further, even in free disposal of all wastes into the open sea were safe, it is by no means clear that it would be economic.

Attention will therefore be concentrated on the evaluation of the sea and, in particular, specific sites for the disposal of selected and limited radioactive wastes. The chief purpose of this Report is to determine under what conditions limited radioactive waste disposal into the sea does not result in more than negligible hazard. The assessment of the relative economic merits of different methods will be largely left to the user.

Maximum permissible levels to man from sea disposalsThe concept of negligible risk is achieved by setting maximum per

missible levels of radiation for various segments of the population. Such maximum permissible levels are chosen so as to result in no amounts of damage which are considered unacceptable by the International Commission on Radiological Protection (ICRP) [1,2]. Due to the intensive study that has taken place on this problem, the degree of damage considered unacceptable is far less than the public is subjected to from other hazards of life. Nevertheless, such a maximum permissible level of ex

25


posure is not necessarily desirable and should be reduced as close to zero as technically and economically feasible. Such maximum permissible levels as have been published for the radiation exposure of man are inclusive, and do not differentiate between different sources or routes, except in the broadest fashion.

One characteristic of such maximum permissible levels is that they are selective with respect to the group of persons exposed. Different values are set as the maximum for occupationally-exposed individuals, persons in certain restricted groups, and for the average and maximum exposure per person in a large population. Although the recommended figures differ considerably, they actually represent about the same small degree of hazard to the community as a whole in each case. The permitted level in the case of general population is probably the most appropriate for sea disposals, which produce widespread effects of an international character. The limited group figures may, however, be more appropriate in special cases of strictly limited hazards, which are confined to nationals of the country making the disposal.

Even when the maximum permissible radiation level to which man can be exposed has been set, there is little or no guidance as to what fraction of this can be allocated to waste disposal in the sea. Out of the permissible exposure to the population as a whole, an allocation can be made for occupational exposure, but the unallocated remainder includes not only effects of waste disposal in the sea but also radioactive contamination in drinking-water, food and air, and exposure from such devices as television sets and wrist watches. It could reasonably be argued that the allocation between the various modes of exposure connected with man’s economic welfare might be made on the basis of the contribution they make to such welfare. For example, if nuclear power becomes a significant source of energy and if waste disposal into the sea were a significant contribution to the development of such power a higher percentage of the residual unallocated permissible radiation level might be assigned to contamination in the sea, than if such disposals were not of major importance.

Routes from wastes to manThe fate of radioactive material introduced into the marine environment

is initially dependent on the physical and chemical form in which the material occurs at the time of introduction. Relatively rapid changes in physical and chemical properties can take place when such material is brought into contact with sea-water.

The initial mechanical dilution of the wastes by the receiving water

2 6


depends upon the manner of introduction. The initial mechanical dilution is desirable to reduce the density difference between liquid wastes and surrounding water, and thus favour subsequent turbulent diffusion.

Transport of waste material by currents in the sea, away from the source region, and simultaneous turbulent diffusion, spread the radioactive components into an ever-increasing volume of sea-water.

The content of radioactive substances in sea-water is reduced by two processes. The first is radioactive decay. The second method is by physical and chemical transfer (including biological mechanisms) between the seawater and the surrounding bottom sediments and shore areas.

Radiation from radioactivity external to man can come from the seawater itself, from contaminated beaches, and from contaminated fishing gear. Radiation to man from internal radioactivity is most likely to come from marine products used as food, although contaminated sea-water, spray and beach sediment could also be absorbed.

The various radioisotopes are indistinguishable in behaviour from the stable isotopes of the same elements in the same form present in sea-water. The initial ratio of radioisotopes to stable isotopes in sea-water will be preserved in the biota living in equilibrium with the water and thus all through the food chain to man (provided, of course, that there is no extraneous introduction of material of different isotopic composition into the food chain).

The uptake of activity by various groups of biota, such as shellfish and fish used as food, can eventually lead to internal radiation exposure to man. The product consumed by man is not usually the first organism assimilating radioisotopes from the waste. The nature and behaviour of the individual members of the food chain may therefore be highly significant.

To facilitate computations, the ratios of the concentration of elements in sea-water, and in various biological materials, are determined. The concentration ratios will also be representative for the radioisotopes of the same elements.

A third route by which radioactive contamination in the sea might affect man would be by the disturbance of the marine ecological system. According to present knowledge, and with the rates of release of radioactive material considered allowable on the basis of an evaluation of the direct exposure of man, the danger of such disturbance does not appear to be likely. Therefore, in the evaluation procedures dealt with in this Report, the considerations will be confined to the processes leading to exposure of man. Further research into the possible effects of waste disposal on the marine ecological system would be of value.

27


When the routes from the sea-products to man are studied in connection with a particular waste-disposal problem, it will usually be found that a very great number of such possible routes exist. However, one or two may prove overwhelmingly significant compared with the others.

Calculation of the allowable rate of disposal of radioactive wasteAt this point the preceding arguments are reviewed, as they apply to

the calculation of permissible disposal rates. The evaluation of the suitability of any particular marine locality as a receiver of nuclear wastes ideally involves the precise, step-by-step consideration of all factors affecting the possible return of radioactive material to man. The general procedure in evaluation of permissible disposal rates is the same, whether the evaluation concerns, for example, the selection of the position of an outfall discharging low-level liquid effluent from a chemical processing plant, the selection of suitable disposal areas for packaged wastes, or the consideration of the suitability of a given harbour, or harbour approach, to receive low-level liquid wastes from nuclear-powered ships. Understanding of many of the physical, chemical and biological processes involved is, however, far from complete, and further research is recommended to provide more adequate foundation for the determination of the capacity of any particular marine locale to receive nuclear-waste materials without undue risk to man.

Figure 2 presents such a step-by-step procedure in schematic form. The starting point is the total allowable dose to man from all sources. The arrows between blocks on the diagram indicate the course of the procedure used in the evaluation.

The first step involves both the determination of the portion of the total allowable level of exposure that is allotted to sea disposal and of the fraction of this allotment assigned to the particular site considered.

The next step is the consideration of various routes which the radioactivity can take in reaching man from the marine environment. Here an evaluation of the uses man makes of the specific marine environment is required. The possible danger of direct radiation, the harvest of sea-food, the possible contamination of fishing gear and the possible contamination of beach sand, are some of the items which should be considered at this stage of the study.

The determination of the maximum permissible concentrations of the various significant isotopes in those parts of the marine environment (i. e. the sea-food, the bottom sediments, and the shore material) which constitute the routes by which radioactivity may reach man from the sea, then follows. From consideration of the factors by which the biota, the

28


MANPORTION OF TOTAL ALLOWABLE DOSE ALLOCATED TO THIS OISPOSAL SITE

lROUTES TO MAN FROM THE MARINE ENVIRONMENT E.G. EATING SEAFOOD; CONTAMINATION OF FISHING GEAR, DIRECT CONTACT ON BEACHES

MAXIMUM PERMISSIBLE RATE OF INTRODUCTION OF NUCLEAR WASTESI1 CTO THE PARTICULAR MARINE LOCALE )

PHYSICAL AND CHEMICAL FORM OF WASTES AT RE - INITIAL MECHANICAL DILUTIONLEASE ANO MANNEROF DISCHARGE 1

AOVECTION AND TURBULENT OlFFUSION C INCLUDING EXCHANGE WITH ADJACENT MARINE ENVIRONMENT)

MAXIMUM PERMISSIBLE CONCENTRATION IN PARTS OF THE MARINE ENVIRONMENT :E.G. SEAFOOD / BOTTOM SEDIMENT, BEACHES CONCENTRATION FACTORS

FROM SEA WATERS TO PARTSOF THE MARINE ENVIRONMENTWHICH PROVIDE THE ROUTESTO MAN

TRANSFER OF RADIOACTIVE MATERIALS FROM SOLUTIONS OR SUSPENSIONS

IN THE SEA WATER TO BOTTOM SEDIMENTS

MAXIMUM PERMISSIBLE CONCENTRATIONS IN SEA WATER

Fig. 2Step-by-step procedure for evaluating a marine waste disposal site


suspended matter and the sediment, concentrate the various elements from the sea-water, it is then possible to arrive at the maximum permissible concentration of the various isotopes in sea-water.

The final steps involve evaluating the changes in the concentration and distribution of radioactivity which may be brought about by:(a) transport of radioactive isotopes between bottom sediment, biota,

suspended materials and sea-water;(b) transport by sea current and dispersion by turbulent mixing both

within a given marine environment and between adjacent environments;

(c) initial mechanical dilution, influenced by manner of discharge.In this procedure the physical and chemical form of the wastes at the

time of their release must be taken into account.The end result is an estimate of the maximum rate of introduction of

radioactive material which will lead to a concentration of such material in sea-water which does not exceed the maximum permissible level.

Experimental verificationThe very considerable number of assumptions which have to be made

to permit calculation of permissible rates for sea disposal make such calculation of value only as a guide. In addition, in many cases there will not be sufficient information on which to base reliable assumptions. It is clear that, if any confidence is to be placed on the results of such computations, they must be supported by experimental studies.

Fundamental research will often be needed to establish the validity of the various hypotheses underlying the scheme of calculations. These will, in turn, need to be verified on a step-by-step basis by experiments under field conditions approximating those expected to be met in practice. Extensive environmental and biological studies will be necessary to identify all factors of interest. Statistical and economic studies will be necessary to establish the pattern of man’s use of relevant marine resources. Experimental releases of simulants, or of actual wastes, on a limited scale must be followed to verify the mechanism of dispersal when such a mechanism is an essential factor in determining the safe limit. Finally, a system of monitoring must be established, including adequate routine checks on the routes to man which are considered significant, plus spot- checking of other possibilities to ensure that nothing has been overlooked or misinterpreted.

Effects of additionIn any evaluation procedure along these lines, due attention should be

given to the fact that more than one isotope may, and in general will.

30


contribute to the total radiation. The population may also be simultaneously exposed to radiation from more than one source of food, or external radiation, of marine origin. It is evident that the sum total of the combined radiation exposures should not exceed the maximal permissible dose set for the particular segment of the population considered.

The general derivation of formulae to take into account these additivity considerations is an extremely complex problem, but in a practical case it will usually be found that several of the terms are negligible and that the computations may be limited to two or three major components of the total radiation. However, it should be noted that radiation affecting the general population from other sources than waste disposal into the sea has not been included here but must be allowed for separately.

R E F E R E N C E S[1] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION,

Report of Main Commission, Pergamon Press (1959).[2] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION,

Report of Committee II, Pergamon Press (1960).

31


CHAPTER IV

M A X I M U M PERMI SSIBLE EXPOSURE TO R A DI A TI ON FROM DISPOSAL OF R A D I O A C T I V E WAS T E INTO

THE SEA

Mechanisms and types of exposure

To decide how much radioactive material may safely be placed in the sea it must first be known how much radiation may be absorbed by man and other organisms without causing more than negligible harm. Such radiation may come from outside (external radiation) or from within the body (internal radiation). Internal radiation arises from radioactive elements which are deposited in the tissues of the body or are passing through the gut or lungs. Contamination of this kind may enter the body in the air we breathe, in food and drink, or by absorption through the skin. To set limits to the amount of radioactive waste which can be placed in the sea, it is necessary to consider not only the effect of radiation arising from the sea-water, beach sand, fishing gear, etc., but also the effect of internal radiation which could result from ingestion of radioactive food taken from the sea, or the breathing of air contaminated by sea-spray. The relative importance of these and other effects depends on the local circumstances.

The effect of radiation exposure on man will depend to some degree on the nature of the group exposed. The following categories of exposure groups have been distinguished by the ICRP [1],

A. Occupational exposure.B. Exposure of special groups:

(a) Adults who work in the vicinity of controlled areas but who are not themselves employed on work causing exposure to radiation;

(b) Adults who enter controlled areas occasionally in the course of their duties but are not regarded as radiation workers;

(c) Members of the public, including children, living in the neighbourhood of controlled areas.

C. Exposure of the population at large.D. Medical exposure.

For the purpose of this Report persons who, because of special habits, belong to a small group using marine products from the neighbourhood of the disposal site, are regarded as members of group B (c).

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Maximum permissible levels for different exposure groupsRadiation exposure may be divided broadly into two aspects: exposure

of the individual and exposure of the population at large. Both the nature of the exposure groups and the organ or organs affected must be taken into account. A major distinction of significance to waste disposal is between individuals, limited groups and the population as a whole. This arises because of the nature of genetic damage. It is held that an average amount of radiation acceptable by individuals of a small group without constituting a genetic risk could, if given to members of the population at large, cause unacceptable effects. This leads to the concept of maximum permissible genetic dose to the population as a whole.

In the case of radioactive-waste disposal into the sea, radiation exposure will, in general, be limited to a small fraction of the whole population. Consequently, in the foreseeable future, the likely extent of radioactive- waste disposal into the sea would not contribute significantly to the genetic dose of the whole population. It then follows that the critical control as far as the problem of waste disposal into the sea is concerned, is the resulting radiation exposure of the individual, rather than the genetic dose. The above consideration can be expected to apply to waste-disposal procedures that result largely in localized contamination and in which significant contamination is only experienced by the nationals of the country making the disposal. However, if persons are exposed who are not nationals of the country making the disposal, the limiting average genetic dose should apply to individual exposure.

In accordance with the ICRP, workers engaged in waste-disposal operations in controlled areas (i. e. under radiation safety supervision) should not accumulate significant exposure (e. g. exposure to whole body or gonads) in excess of a mean rate of 5 rem/yr starting at the age of 18. Within this limitation, a maximum rate of accumulation of dose not in excess of 3 rem during any period of 13 consecutive weeks is permitted. High rates of accumulation, however, should be avoided as far as possible, especially in the case of women of reproductive age. In addition, special limits and conditions are set for emergency situations. Workers included in groups B (a) or B (b) should not be exposed to more than 1.5 rem/yr. For the individual of a special group, and also for the individual in the population at large, the dose is specified as a maximum limit of 0.5 rem/yr.

The ICRP has proposed a minimum permissible genetic dose to the whole population of. 5 rem. This means that the dose to the gonads from all sources, other than natural background and irradiation given in medical procedures, averaged over the whole population and including occupational and special groups, shall not exceed 5 rem at the mean age of child?

3 33


bearing, which is assumed to be 30 yr. The suggestion is made by the ICRP that the national regulatory bodies should decide what fraction of the total permissible population dose should be allotted to persons occupationally-exposed to radiation, to special groups, such as those living near atomic establishments, and to the general population, leaving a reserve for future developments. An example is given in which 1.0 rem is allotted to occupationally-exposed workers, 0.5 rem to special groups and 2.0 rem to the population at large, leaving 1.5 rem as the reserve.

The size of the special group, relative to the size of the whole population, at which the genetic dose becomes more significant than the exposure of the individual, will depend on the apportionment of the genetic dose which is allotted to the special group and upon the variance of individual exposures.

A calculation of the permissible size of a special group can be made if the average exposure of the group is known. If there are N people in the whole population, and the apportionment for a special group B (c) is D$o rem, then that group may receive up to a total dose of D30 X N “ rem” over a 30-yr period. If the average gonad dose within the group is D rem/yr, and there are n people in the group, the total dose accumulated by the group will be:

n X 30 X D “rem”Hence: D30 X N = n X 30 X D

, n Dan and —N 30 X D

This is the fraction of the whole population that can be permitted to be in this group.

If the size of the special group is large, the maximum permissible dose to individuals in the group may need to be less than the 0.5 rem/yr recommended for individuals of group B (c). Such lower dose limits can be calculated as follows: If we have a special group to which is apportioned a genetic dose of D30 rem, and this group constitutes a fraction nIN of the whole population, the average permissible annual gonad or whole- body dose D to an individual member of the group must be less than

D = _ g * em/yr.30 X n/N y

For example, if D30 = 0.5 rem and n/N = 0.1 (i.e. 10% of the whole population) then D = 0.17 rem/yr. If the distribution of dose should be very uniform throughout the special group, this latter limitation could prove more limiting than the individual maximum permissible dose of 0.5 rem/yr.

34


In some cases radioactive waste will be disposed into the sea in such a way that its effect will bear on more than one nation. These cases, by their nature, can only be considered in terms of exposure of the population at large. Consequently, the limitation of exposure must depend upon the genetic effects. We cannot use the whole genetic dose to the population for waste disposal of this type, so a fraction of this dose must be included in the apportionment to be used to cover disposals into the sea, the effects of which extend beyond national boundaries. It is recommended by this Panel that the national regulatory bodies of countries using substantial amounts o f marine products should assign 1/25 of the genetic dose, i. e. 0.2 rem, for this purpose.

The figures for maximum permissible doses for different exposure groups include external and internal radiation, but not radiation received from natural background and from irradiation of patients in medical procedures. The maximum permissible dose is the maximum dose of radiation which involves a risk that is not unacceptable to the individual and to the population at large. On the basis of the maximum permissible doses for different organs and exposure groups the “maximum permissible concentrations” o f radionuclides in air and water are calculated and recommended by the ICRP [2], The maximum permissible concentration of radionuclides or of mixtures of radionuclides in air or water is that concentration which, if a person continues to breathe the air or drink die water for 50 yr, results eventually in the accumulation of a “maximum permissible body burden” of radioactive material. The maximum permissible body burden of a radionuclide is that amount of the nuclide distributed within the body which will deliver a maximum permissible dose of radiation to the “ critical ■organ” . The critical organ is considered to be that organ of the body receiving the radionuclides, damage to which results in the greatest damage to the body as a whole. It should be noted that the maximum permissible concentrations in water tabulated by the ICRP are not directly applicable to contamination of sea-water, but refer specifically to water supplying man’s needs, either for drinking or as a constituent of food.

No maximum permissible doses or concentrations have been defined for organisms other than man.

Possible contributions to radiation exposure from disposal of wastes into the sea

The natural background radiation varies a great deal from place to place ■on land, and is an environmental hazard to which man has always been ■exposed. Natural radiation to man on the surface of the sea is considerably less than to man on land. Food taken from the sea will probably be the major source of contamination transferred from the sea to man.

3 “ 35


In considering any disposal scheme it will be necessary to determine the types of food (e.g. fish, crustacea, shell-fish, seaweed) which are taken from parts of the sea that could be affected by the disposals. It is also necessary to know the maximum amounts of these foods which are normally eaten by individuals, and the concentration and nature of the accumulated radionuclides.

Many products, other than food for human consumption, are taken from the sea. Examples are, salt and other chemicals, animal foods, fertilizers (such as fish-meal and seaweed) and even sea-water itself, which is used in some places for medical purposes. Contamination of beaches could contribute to the irradiation of workers on the shore and people who use the beach for recreational purposes. A complete evaluation would even include sea-spray contamination of beaches and land within a few milesof the sea-shore. However, this should be unimportant in most cases.Generally, contamination in the vicinity of a disposal area would be considered to affect only limited groups coming under category B (c). Contamination of fishing-gear (from the bottom and from the sea-water) would reasonably apply to group B (a).

It will usually be found that one, or at any rate only a few, radionuclides are predominant in setting the maximum permissible discharge rate of waste into the sea. However, this should not be relied on too much, because the composition of wastes, the feeding habits of populations, the sites of fishing grounds, and many other factors change. Control of disposal areas and regions affected by disposals will always be necessary in order to ensure that maximum permissible exposures to the population are not exceeded.

A more detailed treatment of maximum permissible exposures is given in the “ Recommendations of the International Commission on Radiological Protection” [1,2]. An abstract of part of this material is given in Appendix II.


Report of Main Commission, Pergamon Press (1959).[2] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION,


36


CHAPTER V

Physical properties affecting waste disposal

D iv is io n o f t h e sea in t o z o n e s

With respect to the physical processes pertinent to the problem of radioactive-waste disposal, the marine environment may be subdivided into three zones:(1) The nearshore areas, including the intertidal zone of the open coast,

and areas which are partially enclosed by land, i. e. harbours, bays, estuaries, lagoons and passages separated from the open sea by fringing islands.

(2) The continental shelf and overlying waters. The continental shelf is the submarine rim of a land mass. For the purpose of this Report, it is considered to extend from shore seawards to a depth of about 400 m. From its edge outwards, a markedly steeper slope descends into the deep sea. The width of the shelf varies from a few miles, as along the coast of California and some of the Japanese islands, to over 100 miles, as off the North Atlantic coast of North America. It may also contain fairly large marginal seas, such as the North Sea and the South China Sea.

(3) The deep sea beyond the continental shelf. For our purpose, an important further subdivision of the deep sea and the outer continental shelf may be introduced. In the upper layer of variable thickness (10 to 200 m) the water is mixed by various processes due to wind and seasonal changes of temperature. A density gradient of variable sharpness and thickness separates this mixed layer from the water below. The density gradient constitutes a barrier which impedes change between the mixed layer and the deeper water.

T h e n e a r s h o r e a r ea

In coastal waters, both currents and mixing processes are more intensive than in other regions of the sea. Currents, either due to large-scale oceanic circulation patterns, local winds, tidal motions or a combination of these, usually follow the main trend of the coastline. They may have velocities up to a few meters per second. Moreover, in many coastal areas the shallow water is subject to considerable variations in level as a result of tidal motions and wind action. These conditions also give rise to intensive mixing, both vertically and horizontally. Complicated flow patterns brought

NATURE OF THE MARINE ENVIRONMENT

37


about by irregularities in the coastline and in the depth contribute to horizontal mixing and to the bodily displacement of relatively large bodies of water.

Although the conditions in the nearshore areas favour the mixing processes, there are factors which may oppose a rapid dilution of a contaminated effluent. The shallow depth, by its very nature, limits the volume of water available for dilution, because, after fairly rapid mixing over the entire depth, further diffusion is confined to the horizontal dimension. Moreover the diffusion is impeded by the presence of boundaries. Whereas in the open sea the diffusion can extend in all directions, a straight eoast limits the process to an arc of 180 degrees. In an embayment the arc is still narrower, and within an estuary even more so. If an outfall were to be located in a partially-enclosed basin, an equilibrium concentration of radioactive isotopes would be established, the level of which would depend on the exchange of water between the basin and the adjacent environment. In such a case the rate of exchange, which can be expressed as the renewal rate of the water in the basin, is dependent on the width and the hydraulic characteristics of the connection between the basin and the adjacent water.

Another feature of the nearshore areas that may be important from the point of view of waste disposal is the mobility of the sea-bed material in many coastal environments. The mobile material, which may vary from gravel to fine sand and mud, is subject to displacement in fairly large quantities by the action of currents and waves which, in these shallow waters, extend their action through the entire mass of water down to the sea bottom.

In the vicinity of river estuaries the sea-water is, to a certain extent, diluted with fresh water. This may give rise to stratification as a result of differences in density. Subject to the intensity of the mixing processes, stratification is generally more marked in the estuaries than off the coast. Where stratification occurs, the mixing is reduced by the transition zone between the layers of different density impeding the exchange of water between the layers. On the other hand, these density differences aid the establishment of large-scale circulation patterns.

T h e c o n t in e n t a l s h e l f

The waters of the continental shelf exhibit intermediate conditions between those found in the nearshore environment and those of the deep sea. There is great variation in vertical stratification, with large areas being well mixed from surface to bottom, while other areas show strong vertical stability. The waters of the continental shelf exhibit less seasonal fluctua

38


tion in properties than the nearshore region but, on the other hand, show more variation than the deep sea.

Tidal currents are relatively weak over most of the continental shelf. Three processes provide the predominant motion in the waters of the shelf. Along coastlines of high fresh water run-off, the waters of the inner continental shelf have lower salinities than the offshore waters. This density difference produces a current flowing parallel to the coast and directed so that the shore is on the right-hand side of the current in the northern hemisphere and on the left-hand side of the current in the southern hemisphere. The outer parts of the continental shelf generally exhibit a flow related to the large-scale ocean current patterns. Finally, wind-induced motion contributes significantly to the current pattern throughout the shelf area.

As a result of the various factors influencing the motion of the shelf waters, the flow of the waters of the inner shelf is frequently directed opposite the flow over the outer shelf. Thus, along the Atlantic coast of South America, the waters at the outer edge of the shelf flow southward with the Brazil current while the inner shelf waters flow northward.

Such counter-flows produce large-scale eddy motions which favour the dispersion of any introduced contaminant. The wind produces the major mechanism for turbulent mixing over the shelf. Since this meteorological parameter is not constant, the intensity of mixing in the shelf waters shows considerable time variation.

Finally, there is understood to be a special phenomen of infrequent occurrence in connection with currents on the sea-bed. This is the turbidity current. It is believed that a slide of the bottom material may result in the dispersal of suspended solids in a layer of water close to the bottom. This suspension, or slurry, because of its increased density, may then flow great distances at high speeds with the resultant turbulence keeping the entrapped solids suspended.

Such a turbidity current, although of infrequent occurrence, could be highly significant with respect to packaged-waste disposal since, because of its violence, solid material could be carried for some distance across the ocean bottom.

T h e d e e p sea

The major part of the ocean volume (about 75% ) is filled with cold water, at a temperature between 1 °C and 4 °C, which originates in the high latitudes of the North Atlantic, South Atlantic and possibly also in the Antarctic regions south of the Pacific Ocean. This large volume has a remarkably constant salinity of about 34.7 g/kg. In the middle and low latitudes, a layer of relatively rapid density-increase with depth and hence

39


large stability, called the pycnocline or thermocline, separates this so-called “ deep” water from the surface layers. The surface layer of the open sea is of variable thickness, from 10 to 200 m thick, and is almost uniform in the vertical distribution of temperature and dissolved solids. Because of this uniformity, the surface layer is frequently called the “ stirred” layer or “mixed” layer. The surface layer constitutes about 2 % of the total volume of the world oceans, and the intermediate layer of relatively large stability comprises about 20°/o of the total volume.

Any contaminant introduced into the surface layers will be rapidly mixed vertically. This rapid vertical mixing results primarily from two processes:(a) Convection, which is produced when the density at the surface is

sufficiently increased, either from a decrease in temperature or an increase in salinity, so that the surface water sinks and mixes with the sub-surface layers.

(b) Wind stirring, which produces turbulent mixing in the surface layers. The effect of such stirring decreases with depth and is dependent on the magnitude of the wind velocity. Stability, caused by increasing density with depth, decreases the effectiveness of wind stirring.

The depth of the mixed layer, and the degree of homogeneity within this layer, are dependent upon the intensity of convection and wind stirring.

An indication of the rapidity of vertical mixing in the upper layer is shown by the results reported by R e v e l l e , F o l so m , G o l d b e r g andI saacs [1], These investigators report that, when fission products wereintroduced at the surface, the activity became uniformly distributed over a surface layer thickness of 100 m in approximately 28 hr. Further vertical mixing into the pycnocline layer below 100 m was extremely slow.

Any contaminant introduced into the surface layers of the deep seawill be transported away from the area of introduction by surface currents, which, in general, extend throughout the entire depth of the mixed layer. The major features of the important surface-layer currents of the world’s oceans have been studied for many years and are well known (S v e r d r u p , J o h n so n and F l e m in g [2 ]) . The large-scale permanent currents, such as the Gulf Stream, the Kuroshio and the Equatorial Current systems, transport vast quantities of water and actively disperse the waters of a major segment of the mixed layer throughout the area of each ocean basin in a relatively short time. Thus, the volume of water flowing through the straits of Florida in the Gulf Stream in a 15-yr period is about equal to the volume of the upper 500 m of the entire North Atlantic. It therefore

40


appears likely that no area of the surface layers of the world oceans can be considered to remain isolated from the rest of the surface waters for any length of time.

During transport by currents, any contaminant introduced into the surface layers will be dispersed horizontally by turbulent diffusion. Some evidence indicates that the intensity of such horizontal diffusion is fairly constant throughout the open ocean area. The rate of dispersion depends upon the magnitude of the coefficient of eddy diffusivity. This coefficient varies with the dimensions of the dispersing contaminated volume. Appendix IV to this Report summarizes our present knowledge of the processes of turbulent diffusion.

The result of this process of diffusion is the reduction with time of the maximum concentration of any contaminant introduced into the ocean, and a corresponding spread of the introduced material over a continually increasing area. Thus, F o l s o m and V i n e [ 3 ] report experiments which indicate that 1000 c introduced in the surface layer as essentially a point source in an open sea area having a “mixed” layer depth of about 5 0 m would, after 4 0 days, be spread over 4 0 0 0 0 km2 and have an average concentration of about 1 .5 X 1 0 ~ ' ° uc/ml.

Within the intermediate layers of relatively large, vertical stability, any introduced contamination would be confined to a relatively thin layer, since vertical mixing is greatly suppressed. Horizontal spread would occur, but at somewhat less rapid rates than in the surface layers.

In deep water, movement and mixing are considerably less intense than in the surface layers. However, during the time taken for dispersal of the deep waters over a vertical distance of 1000 m or more, horizontal dispersion will have occurred throughout much of each ocean basin. Thus, any contaminant introduced into the deep water of the ocean would be dispersed through a very large volume before spreading upward into the surface layers (S t o m m e l [ 4 ] ) .

E x c h a n g e o f w a t e r s b e t w e e n t h e v a r io u s s u b d iv is io n s o f t h e o c e a n s

The rate at which a contaminant may be introduced into the sea without undue risk to man, depends not only upon the rate of dispersion within the particular marine locale used for disposal, but also upon the rate of exchange between the waters of that locale and the adjacent environments. The diluting water for the nearshore area originates over the continental shelf, and a given area of the shelf waters must also exchange with adjacent shelf waters, as well as with the waters of the open sea. The surface layers of the deep sea will ultimately be exchanged with waters of the deep layers.

41


The process of exchange between adjacent water bodies can be considered from two extreme aspects. For simplicity, assume that the marine area in question can be considered as a tank of water connected by two pipes to a much larger tank representing the adjacent, larger water body. First, consider the case where the pipe in which water flows from thelarge tank into the smaller tank enters at one end of the small tank andthe pipe in which outflow occurs is located at the other end. If no intermixing of the inflowing waters with the waters resident in the tankoccurred, then the inflow would simply replace the waters in the tankand there would be a linear rate of renewal, or exchange of the water in the small tank. However, if instantaneous and complete mixing occurred between the inflowing water and the resident water, then some of the outflow would consist of water which had just entered. In this case the rate of exchange follows an exponential law rather than a linear one and, theoretically, this process could never renew all the resident water in a small tank. However, it is possible to determine the time interval required to renew any given fraction of the water present initially.

The actual process of exchange in the sea is somewhere between the two extremes discussed in the previous paragraph. It so happens that the time interval required to replace 50% of the water present at any given instant is very nearly the same for both processes. Hence, a convenient measure of the exchange rate is the time interval required to replace half the water resident in the subject water body. This time is sometimes referred to as the “half-life” of the water body.

In the nearshore environment the process of exchange between the embayments, harbours and estuaries on the one hand, with waters of the open coast on the other, is extremely variable, so that the water of some nearshore areas is replaced at a relatively rapid rate (half-life of the order of a few days) while other areas have very long exchange time (half-life of the order of several months). The processes which control the rate of exchange are tidal motion, density-induced current and wind- induced currents.

The major processes that contribute to the exchange of waters of the continental shelf with waters of the deep sea are the permanent currents which are related to the distribution of density and the wind-induced motion. As an example of the time intervals involved, it is estimated that about one year is required to replace 50% of the volume of the water of the continental shelf of the Atlantic coast of the United States between Cape Hatteras and Cape Cod with water from the open sea.

At high latitudes convective motion extends to great depths, and here exchange between surface layers and deep waters may be quite rapid. The exchange between the deep waters and the surface layers at mid


and low latitudes is restricted by the relatively stable intermediate layers. The deep water which sinks at high latitudes spreads throughout the deep ocean basins and slowly ascends through the pycnocline into the surface layers over the large ocean areas found at mid and low latitudes. Present estimates of the rates of such upward motion range from 2 to 5 m/yr. In addition to this direct vertical flow, some exchange takes place between the surface layers and the deep waters by mixing through the stable pycnocline.

The whole problem of mixing and exchange processes in the sea ranging from molecular scale to world-wide currents is fundamental to the problem of waste disposal. Appendix IV provides a more detailed study of these phenomena.

0

Chemistry of sea-waterSea-water is a complex solution of a variety of dissolved salts contain

ing some suspended inorganic and organic material. The major ionic constituents dissolved in sea-water in order of decreasing concentration are chloride, sodium, sulphate, magnesium, calcium, potassium, bicarbonate, bromide, borate and strontium, which make up more than 99% of the total dissolved solids. The quantitative relationship of these ions is nearly constant. Therefore, if one of these components is chemically determined, it gives a measure of the total amount of the dissolved salts in the seawater. The total amount of the salts is commonly expressed by salinity which, for practical purposes, can be defined as the mass of the dissolved salts in unit mass of water (g/kg or %o). The salinity of the sea-water ranges approximately from 33 to 38°/oo.

Sea-water contains many elements as minor constituents. As compared with the major constituents, these show much wider variation in their concentrations, connected closely with physico-chemical phenomena and biological activity taking place in the sea.

The chemical forms in sea-water of some minor constituents are known. Nitrogen is present as ammonia, nitrate and organic compounds. Phosphorus is present as inorganic and organic phosphates. Silicon is found in the form of soluble silicate as well as colloidal silica. Some part of the carbon occurs as organic compounds. Various other elements are mainly present in sea-water as colloidal, or particulate forms. The elements of groups III, IV and VIII of the Periodic Table tend to be present as suspended material. In connection with this, some guide is given as to the physico-chemical state of various elements in sea-water by an experiment carried out by G r e e n d a l e and B a l l o u [5 ] (Appendix VII).

Gases from the atmosphere are dissolved in sea-water. In addition to these gases, ammonia, hydrogen, and sometimes hydrogen sulphide,

43


methane, some other hydrocarbons and radon are present as minor gaseous constituents in sea-water. The concentration of oxygen in sea-water varies with the temperature, salinity and biological activity in the sea-water mass. The equilibrium is dependent on various physical, chemical and biological conditions in the water mass.

Various radioactive nuclides are found in sea-water. Besides well-known radionuclides such as K40, Rb87, uranium, thorium, radon and their decay products, several nuclides produced by cosmic-ray-induced nuclear reactions are present. Among them tritium and radiocarbon (C14) are important. According to L ibby , sea-water contains 0.2— 1.5 tritium atoms per 1018 hydrogen atoms. The specific activity of radiocarbon (C14) in various forms of carbon in the ocean shows some fluctuation depending on the location and the depth of the'water-mass, and is increasing at a measurable annual rate as a result of weapon tests. Its present value for the surface layers of the sea is approximately 15 disintegrations per minute per gram of carbon.

A knowledge of normally-occurring geochemical processes in sea-water gives a general background for the understanding of the processes by which radio-elements introduced in sea disposals are distributed by dispersion, sedimentation and biological uptake. The physical states and valency distributions under equilibrium conditions depend upon various factors, such as alkalinity, salinity, oxygen content, temperature and chemical constituents available for reaction. The trace radioelements, when present as ionic species, follow the corresponding non-radioactive element in the normal chemical reactions in the sea by one or other of the following processes: adsorption, mixed crystal formation and ion exchange. When present as particulate dispersions and floes they are formed by simultaneous •precipitation and coagulation under favourable pH conditions, and are distributed by gravity, by transport or by biological uptake.

Chemistry of bottom sediments

As illustrated in Fig. 3, sedimentation takes place in the sea. Solid particles and colloidal matter introduced by rivers tend to be removed from sea-water by flocculation and subsequent sedimentation. In addition, certain elements dissolved in sea-water may be accumulated on the sea bottom by chemical precipitation and by other means. As a result, a variety of marine sediments are formed at the bottom of the sea.

The rates of sedimentation for some deep-sea sediments, such as red clay, have been roughly estimated by geochemists using the ionium-radium method, the recently developed ionium-thorium method of chronology, and by other approaches. It has been reported that the rates are of the order of millimeters per thousand years. The corresponding rates on the con-

44


RIVERS AND ICE

TRANSPORT BY WIND

DISSOLVED GASES LIGHT ENERGY I BIRDS AND MAN

HALMIRQBfSES.

WAVE ACTION .'?'

SEDIMENTATION

V SOLUTIONL * —j f 4 — i----------- ; c- -------------- -

* _•_ J_ i PHOTOSYNTHESIS

CHEMICALPRECIPITATION

V.. i

i DECOMPOSITIONj a ^ V esS f w io ^ t

n e r g y I qi

^ rre^ TTRANSPORT BV CURRENT TURBULENT MIXING

PLANTS PHYTOPLANKTON

-|a n im a l s [:

( UDIFFUSION

ELEMENTS IN TRUE SOLUTION IN DEEP WATER

SEDIMENTATION AND (DECOMPOSITION

BY BApERIA TRANSPORT BY ANIMALS i »

I i n

VOLCANIC a c tio n!

SORPTION I BY SEDIMENT SURFACE

, t I REOISSOIVINGI FROM SEDIMENT

1BURIED IN S E D ® e K ^ A » v :?Kr:- ,• \ ;

Fig. 3Scheme of major physical and geological processes in the sea

Physical (mainly dynamic) processes -------------- Biological processesChemical processes -------------- Combined processes


tinental shelf are probably of the order of tens of centimeters, whereas the rates in shallow water will be much higher and vary considerably, depending upon the local conditions.

The main constituents of the sediments in the near shore originate from the weathering of rocks on land or on the shore. On the continental shelf some fine sediments, such as blue mud, are found in addition to sandy sediments. The remains of certain marine plants and animals are also found in the sediments of both areas.

The deep-sea sediments, which cover the largest portion of the sea bottom, contain components which can be divided according to their genesis into three principal classes:(1) Lithogenous components arising from the weathering of rocks and

from volcanic debris (quartz, volcanic glasses, etc.).(2) Biogenous components, mainly composed of skeletal remains of marine

plants and animals (calcium carbonate, siliceous material, apatite, etc.).(3) Hydrogenous components originating from the dissolved or suspended

matter in sea-water (clay minerals, ferromanganese minerals, phillipsite, etc.).

The deep-sea sediments are usually more fine-grained than those in the near-shore area and on the continental shelves, and play an important role in the removal of elements dissolved in sea-water. In particular, the following mineral species are significant for the uptake of elements in sea: skeletal apatite phases; phillipsite; ferro-manganese minerals and other clay minerals. The skeletal apatite phases tend to absorb heavy alkaline earths, rare earths and certain heavy elements, such as uranium. The phillipsite especially takes up, by ion exchange, some metallic ions with high charge and large radius. The ferromanganese minerals have a three- layer structure, with the outer layers composed of manganese oxide and an inner disordered layer of hydrous manganese oxide or hydrous manganese oxide and hydrous ferric oxide. This structure is very suitable to pick up a number of transition elements existing in trace concentrations in sea-water, such as nickel, cobalt, zinc, copper, cadmium, lead, radium and thorium. In fact, many elements are remarkably concentrated in such sediments as manganese nodules. The ion-exchange properties of clay minerals are also important in regulating the amount of elements in sea-water. For example, sodium in clay minerals is replaceable by potassium in sea-water. In addition to cations, the anions, such as phosphates, in sea-water are sometimes taken up by sediment minerals. The uptake of elements by the nearshore and continental-shelf sediments is generally not so pronounced as that by the deep-sea sediments.

In connection with radioactive-waste disposal into the sea, it seems

46


extremely important to know the average time during which an element stays in the water column before removal to the sea bottom. Such time is given by the calculation of the so-called residence time of an element in the sea. The residence time in years is defined by T =A/(dA/di), where A is the total amount of the element in suspension or solution in the sea, and dA/df is the rate of introduction or removal of the element to or from the sea-water. In this calculation, a dynamic equilibrium with respect to the distribution of chemical elements in the sea is assumed. The calculated values obtained by G o l d b e r g and A r r h e n i u s [6] are given in Table VI of Appendix III.

The alkali and alkaline earth elements have residence times of the order of 10e— 10s yr, while other elements, such as iron and aluminium, have rather short residence times of about 100 yr. The values of residence time seem to be important to predict the behaviour of radionuclides introduced into the sea as wastes. For example, strontium has very high residence time (1.6 X 107 yr) compared to the half-life of the longest-lived radioisotope (28 yr). This means that the rate of removal of strontium-90, the most hazardous fission product, from sea-water by marine sediment is very low.

Some numerical values relating to the chemistry of sea-water are tabulated in Appendix III.

Biology of the seaThe rate of uptake, accumulation and dissemination of elements by

marine organisms (biota) depends on the type of organism, their living and feeding habits, physiology, age of the organisms and on the specific environment. The characteristics of marine biota which are pertinent for the problems of disposal of radioactive wastes in the sea are described under the heading of appropriate groups (Fig. 4).

M a r i n e b a c t e r i a

Marine bacteria are chiefly associated with particulate matter in the sea. Their main ecological function is the decomposition of organic matter. Besides taking up substances from the decomposable organic matter, they can also take up dissolved elements from sea-water directly. As the increase and decrease of bacterial populations in the sea are rapid, they can cause equally rapid changes in the content of specific elements in solution. After the phytoplankton bloom, high standing crops of bacteria can take up much activity if it is present in the form of a radioisotope of an element subject to uptake by the bacteria present. This will normally be released again shortly after the death of the bacteria and decay of the plankton detritus. For example, it is generally agreed that marine bacteria

47


GO

Fig. 4Food relations in Marine Ecosystem

1 Organic detritus2 Seaweeds3 Benthic animalst Cod** } ^ emersal6 Megaloplankton (large zooplankters)

7 Zooplankton (e. g. calanus)8 Phytoplankton9 Small pelagic fish (e. g. herring)

10 Large pel&gio fish (e. g. tuna)11 Whales12 Man


are the main producers of vitamin B12. As this has an appreciable cobalt content the bacteria can also accumulate any Co60 present. The abundance of marine bacteria is higher in coastal waters than in the off-shore waters, and higher in surface waters than in deep waters. There is also usually an accumulation of bacteria in discontinuity layers.

P h y t o p l a n k t o n a n d s e a w e e d s

Phytoplankton and seaweeds are the producers of organic matter in the sea, using solar energy and taking the nutrient salts from sea-water. They can concentrate the radioactive elements at a high rate.

The uptake of elements varies with the growing seasons of the plants and is at a maximum during the period of intensive growth. The uptake is more rapid in light than in darkness (e. g., more rapid in the surface layers than in deep water).

Phytoplankton is not normally used directly as human food. However, it is consumed by zooplankton, by some filter-feeding fish, and by bottom dwelling (benthic) animals. Because of the high concentration rate of trace elements and their associated radioactive isotopes by phytoplankton, it can serve as a general indicator of the levels of introduced radioactivity in the sea. Because of the need for light energy for growth, the bulk of the standing crop of phytoplankton is found in surface layers. The maximum depth of the occurrence of attached seaweeds is about 90 m in clear waters and much less in turbid waters (average 30— 60 m). There are great seasonal variations in the standing crop of phytoplankton in medium and higher latitudes. There is usually a high peak population in early spring and a smaller peak in early autumn.

Some of the larger seaweeds are used directly as human food, or indirectly as fertilizer for food crops. In some regions they may provide an important part of the diet.

Z o o p l a n k t o n

Zooplankton uses phytoplankton as food and will take up radioactive isotopes, along with the corresponding inactive element, mainly through this food chain. Elements are also absorbed directly from the sea-water. Some organisms are selective feeders, feeding on smaller zooplankton organisms. However, the feeding habits of zooplankton can vary considerably. Also digestive and metabolic processes are selective with respect to the uptake of many elements. Some zooplankton organisms are used directly as human food (e. g., squids, euphausides) in certain areas.

4 49


B e n t h o s

Benthonic animals spend most of their life on the bottom. Some of them have commercial importance (oysters, lobsters, shrimps, etc.). Benthonic animals can take radioactive isotopes by: (a) food, (b) direct absorption from sea-water, and (c) by contact with the bottom. The benthonic organisms can be divided by feeding habits into (a) filter feeders (filtering sea-water and mud suspension), (b) detritus feeders (collecting organic particles actively or passing mud through the digestive tract), and(c) “hunters” (eating other benthos animals). Some of them (e. g., shrimps) get part of their food from the water-mass, as they make active feeding migrations into the water above. The standing crop of benthos varies considerably on different bottoms. The availability of organic matter in the sediment and the depth of the water also determine the standing crop of benthos. Mobile benthonic organisms may have seasonal migrations in temperate and high latitudes, into deep water during the early winter and back to shallow water during the spring.

P e l a g i c f is h

Some small pelagic fish (surface-dwelling fish) feed on plankton and some even feed selectively on specific planktonic organisms. Large pelagic fish usually feed on smaller pelagic fish. Depending on the feeding habits, the amount of radioactive isotopes taken with food generally decreases with successive stages in the food chain. However, even vertebrate predators may concentrate some elements (e. g. Cs137) to higher levels than those found in their prey. Certain elements can be taken up by absorption and adsorption through skin and gills as well as through the digestive tract. The rate of uptake is usually greater during the feeding season (spring) than during the rest of the year.

D e m e r s a l f is h

Demersal fish (e. g., plaice, rays, etc.) spend part of their life on the bottom and feed partly on benthonic animals. However, they will take part of their food from the water-mass, as they usually make diurnal “up and down” migrations. Therefore, the uptake of radionuclides by demersal fish depends greatly on the living and feeding habits (i. e. how long they spend in contact with the bottom and how great is the proportion of food which is taken from the bottom). Some demersal species are rather stationary (e. g. plaice) and some make considerable horizontal migrations (e. g. cod). The variations in a standing crop of fish in a given locality depend mainly on seasonal migrations and aggregation during the spawning season.

50


S e a b ir d s

Sea birds can take up radioactive isotopes with food. Little data are available on this subject. Birds feeding on intertidal animals during low tide, close to the disposal sites, could be expected to be of most concern.

M ig r a t i o n s o f m a r i n e a n i m a l s a n d p o s s ib l e t r a n s p o r t o f r a d i o a c t i v e i s o t o p e s b y m a r i n e o r g a n is m s

Phytoplankton has no mobility of its own and is carried around in the sea by currents. However, through sinking (or occasionally by rising to the surface) it can carry elements into the deeper layers (or up to the surface). There is usually also an accumulation of phytoplankton in the discontinuity layer (pycnocline).

Many zooplankton organisms have diurnal migrations from the deeper layer to the surface layer, or from the deeper layer to the pycnocline and can transport elements by these migrations. In addition, there are large seasonal migrations for spawning purposes from the deeper layer to the surface involving vertical movement of as much as 2000 m.

Many benthonic organisms have diurnal migrations into the water mass from resting places on the bottom. Added to this, considerable seasonal migrations of mobile benthonic animals along the bottom may occur (e. g. into deep water during the winter and back to shallow water during the summer).

Pelagic, as well as demersal, fish have, in most cases, both diurnal migrations in depth and seasonal migrations between spawning and feeding grounds. These migrations vary by species and even by locality for the same species. Speeds up to 70 sea miles in 24 hr have been recorded.

F o o d c h a in s i n t h e o c e a n s a n d f r a c t i o n a l t u r n o v e r r a t e

A significant factor in any quantitative study of food chains is the food coefficient. This is the fraction of food consumed which is retained to form tissue. An average value of one tenth is often used. Since all elements do not respond to metabolic processes in the same fashion, individual concentration factors for elements with radioactive isotopes of interest must be known. In addition, it is sometimes of interest to know how many times the standing crop is renewed during a year. A generalized food chain is illustrated in Appendix VIII.

Data on biological observations pertaining to the sea are also tabulated in Appendix IV.

51


R E F E R E N C E S[1] REVELLE, R. R , FOLSO M , T. R., G O LD BERG , E. D. and ISAACS, J. D.,

“ Nuclear Science and Oceanography” , Proc. UN Int. Conf. PUAE, 13 (1955) 371.

[2] SVERDRUP, H. U., JOHNSON, M. W . and FLEM IN G, R. H., The Oceans, their Physics, Chemistry and General Biology, Prentice-Hall, New York (1942).

[3] FOLSOM , T. R. and VINE, A. C., ‘ On the tagging o f water masses for the study of physical processes in the oceans” , Nat. Acad. Sci. Wash., Publ. No. 551 (1957) 121— 132.

[4] STOM M EL, H., “ The Abvssal Circulation of the Oceans” , N ature, 180 4589 (1957).

[5] G REEN D ALE, A. E. and BALLOU , N. E „ “ Physical State o f Fission Product Elements follow ing their Vaporization in Distilled W ater and Sea W ater” , USN R D L Docum ent 436 (1954) 1— 28.

[6 ] G O LD BERG , E. D. and ARRHENIUS, G. O. S., “ Chemistry o f Pacific Pelagic Sediments” , Geochem. et cosmoch. Acta, 13 (1958) 153— 212.


CHAPTER VI

PRACTI CAL E V A L U A T I O N OF TYPICAL W A S T E - DISPOSAL PROBLEMS

Liquid effluents in coastal watersS e l e c t i o n o f s i t e

Coastal waters are a possible disposal region for low-level radioactive wastes. They may be particularly suitable for the disposal of liquid effluents through a pipeline from shore-based plants. In fact, the possibility of sea disposal may be a large factor in originally locating the plant.

It is probable that a number of possible sites will at first be proposed. Selection will be based on such factors as the source of the radioactive waste and the economics of the transport of the liquid waste to the disposal area. Ultimately, feasibility studies will reduce the choice of the disposal area to one or two possibilities. At this stage a detailed examination will need to be made of the sites remaining. The aspects which need to be considered are outlined in general terms below. (A hypothetical case is evaluated in Appendix VII to provide a guide to the method of carrying out such an investigation.)

P h y s ic a l f a c t o r s r e l a t i n g t o t h e n a t u r e o f t h e c o a s t l i n e

Certain physical features characteristic of a coastline are of special importance for waste disposal in coastal waters.

Lowland coasts usually presenting straight, or approximately straight stretches of coastline, and ria formations are often associated with movable, in most cases alluvial, shore material such as shingle, sand or mud and with a gradually shelving profile. Such coasts are subject to degradation and aggradation. Conspicuous features are likely to be river mouths, lagoon outlets or man-made constructions, such as harbour moles and groynes.

Coasts consisting of resistant material, such as fjord coasts, coasts dominated by land structure and coral formations, usually present a more irregular coastline marked by headlands, bays and coves. Although movable material may be accumulated and form beaches within bays and other sheltered parts, on the whole steeper profile will be found with greater depth close inshore.

Together with the shape of the coastline, the depth configuration has an important influence on the current pattern. Depth is also of major importance for the scale and intensity of mixing processes. The sea bottom

53


may consist o f rock, gravel, sand, silt, clay or organic material, or a com bination o f two or more o f these materials, and its nature may influence the waste-disposal problem in a number o f ways. Roughness is a source o f friction to currents and increases turbulence, and hence diffusion. The nature and com position o f the bed material affects living conditions for flora and fauna. In so far as the bed material is transported by currents and wave action, it may contribute directly to the m ovem ent o f radioactive material. The nature of the sea bottom is also important from an engineering point o f view (construction of a pipeline).

M e t e o r o l o g i c a l a n d o c e a n o g r a p h i c f a c t o r s a f f e c t i n g c o a s t a l d is p o s a l

Site evaluation for coastal disposals requires a detailed study of local m eteorological and oceanographic conditions. M eteorological conditions may affect the sea in a number o f ways:(a) Variation in temperature may lead to stratification of the water;(b) Changes in atmospheric pressure may give rise to variations in water

level and resultant water movements;(c) W ind may set up or lower the water level, engender currents along,

towards or from the coast, and raise waves;(d) In many locations variable m eteorological conditions will introduce

an unpredictable element in the physical characteristics o f the sea, w hich will com plicate evaluation o f the physical processes affecting the release of waste.

Sea currents are ultimately the result of large-scale w ind action on the ocean surface and o f horizontal differences in water density. A long a given stretch o f coast, however, a current may be in existence without any immediate relation to local conditions. As far as the coastal waters are concerned, the direction o f such a current is, usually, parallel to the general trend o f the coastline. Around headlands and in bays counter-currents may, however, be a predominant local feature. M any coastal currents are subject to seasonal variations, due to dependence on large-scale windfields and the inflow of fresh water from rivers (monsoon conditions).

In many locations tidal variations of the water level and tidal currents will be the most important water movements affecting waste disposal. They are periodic and, although subject to variations o f monthly and even longer duration, follow well-established laws. As they are predictable, they can be incorporated in a mathematical m odel for quantitative treatment. The rise and fall o f the water level has its direct influence on the depth, and hence on the currents and mixing processes; it also gives rise to filling and emptying currents of estuaries, bays, lagoons and other bodies of

5 4


coastal water. The tidal currents displace huge quantities o f coastal water as a whole. In and around estuaries, around headlands and in bays they may give rise to com plicated flow patterns, contributing to large-scale dispersion and creating intensive turbulence. Such currents may transport large amounts o f bed material, either by traction along the bed or in suspension. Close to the coast and in restricted cross-sections, tidal currents are predominantly to and fro. Further out at sea they may be rotary. A net flow in one or the other direction along the coast may also result.

D i f f u s i o n a n d d i s p e r s a l p r o c e s s e s

In most coastal waters, natural diffusion and dispersal processes o f different scales of m agnitude and intensity are going on simultaneously. For the present, the initial diffusion brought about by the m ethod of release is not considered specifically.

Further diffusion resulting from the turbulence associated with the local current can be treated by theoretical and empirical relationships which have been established w ith a fair degree o f accuracy. Hough estimates can be made as to this effect w hich is related to the depth and the flow velocity and to some extent is dependent on the bottom roughness. The rate of diffusion increases rapidly with increasing depth. Unless the water is very deep, in most cases the “ flow turbulence diffusion” spreads out any contamination over the entire depth in a relatively short distance. H owever, if the water is stratified due to salinity or temperature differences, the transition zone betw een the separate layers o f water will be a zone o f low eddy activity and hence im pede the exchange of water betw een the layers. The diffusion mechanism of the local current may be increased by additional turbulence stirred up by the w ind associated with wave action.

W hen this first turbulent mixing process has passed through its initial stages, other processes may com e into action. They may be due to different causes. In particular the wind, when directed towards or from the coast, sets up a circulatory current system consisting o f a surface drift in the approximate direction o f the wind, accom panied by a compensatory current in deeper layers. Such a current pattern m ight contribute effectively to both horizontal and vertical diffusion. On the other hand, either a surface drift or a bottom current towards the coast m ight tend to carry contaminated water to the shore. Another manner in w hich the w ind may create turbulence on a larger scale is due to the inhomogeneities in the windfield both in time and space. These may give rise to eddies superim posed on the main flow. Such eddies may also be a result o f inequalities in depth and in bed roughness and, o f course, o f the reaction o f the cur

55


rents to islets, isolated rocks, reefs and irregularities of the coastline. Irregularities on a still larger scale, such as bays, estuary mouths, etc., w ill give rise to diffusion processes associated with flow patterns of corresponding magnitude.

Finally, whole masses o f contaminated water can be carried away bodily from the environment by tidal flow or coastal current. As tidal flow on the coast is, in most cases, to some extent a reversing process which, moreover, may be strongly influenced b y wind, this should not be taken for granted without careful verification.

The diffusion and dispersal processes are usually highly dependent on local conditions. M oreover, as far as w ind-induced motion occurs, they may vary quite considerably from one time to another in the same locality. Therefore, even if a com plete and quantitative accurate understanding of their nature should exist — which is not the case — no generally valid rules can be established for their evaluation. In any given case, a thorough study should be made of the nature, effectiveness and variability of the diffusion and dispersal mechanism active at a particular site.

C h e m i c a l a n d b i o l o g i c a l f a c t o r s

Although, as discussed above, physical considerations will determine how material released at a disposal site w ill be carried away and dispersed, chem ical and biological factors may be o f even greater importance in determining the extent to w hich the dispersed radioactivity may return to man.

Chemical changes w hich occur when the effluent mixes with the seawater are o f fundamental importance in determining the extent to which the radioactivity adsorbs onto suitable surfaces, eventually settles to the bottom as sediment, or remains in a form to be concentrated by bacteria and phytoplankton. From the point o f view o f these chem ical processes, com plex as they are, the chem ical properties of ocean water are sufficiently constant that any particular effluent will show the same chem ical behaviour at all sites. On the other hand, small changes in the nature o f the effluent may be highly significant in determining the chem ical result o f the mixing process. In general, however, the chemical result o f mixing processes is indicated largely by the chem ical form of the corresponding elements naturally present in sea-water. This is discussed in Chapter V.

Biological processes are highly variable from site to site. Further, such processes are usually the key links in the chain from disposal to man. A com plete biological evaluation of the site is therefore fundamental to its assessment.

Both chem ical and biological processes tend to concentrate specific ele

56


ments (and thereby associated radioisotopes) in some particular phase or organism. If the material or object in w hich the activity is selectively concentrated tends to com e into contact directly or indirectly with man, these biological and chem ical effects are unfavourable to waste disposal, while if this material tends to be withdrawn from man’s environment, the effect can be considered favourable.

G e n e r a l u t i l i z a t i o n o f m a r i n e e n v i r o n m e n t

Prior to any discharge o f radioactivity to coastal waters, an assessment must be made o f the ways in w hich man makes use of the marine environment. This assessment must cover the utilization o f the seashore, the sea-bed, the sea and all it contains. It is convenient to consider the follow ing headings:

(1) Use of the shore for living or pleasure;(2) Use o f the shore for industrial purposes. Sand and shingle may be

rem oved for industrial purposes and parts o f the shore may be directly used for building;

(3) Use of the sea-bed, possibly leading to the contamination of fishing gear and o f such equipm ent as dredgers. There will be additional problems if land reclamation is likely in the area;

(4) Industrial uses o f sea-water, such as the extraction o f magnesium, the evaporation o f salt water in salt pans and provision of cooling water for industries;

(5) Sea-food, including fish, shell-fish, seaweeds and salt. Under these separate headings there are three aspects of this problem . Sea-food may be harvested locally and eaten locally, it may be harvested locally and transported to remote areas and then eaten, or finally, the sea-food may have m oved some distance from the point o f possible contamination before being harvested;

(6) Other uses o f marine products, including the production and use o f alginate from seaweed and the use o f sea products as fertilizer;

(7) Special local methods o f using the marine environment, including problem s w hich have not been dealt with under the previous six headings.

Although these headings cover the methods by w hich man uses the marine environment, it is not possible to put them in order o f priority, since this w ill depend on special local conditions. Significance of a method o f use o f the marine environment may also depend on the nature o f the discharge. In all these assessments special problem s, such as the interaction

57


o f waste discharge with local releases of sewage, and the possibility of sand and spray being blow n inshore, must also be considered.

E x p e r i m e n t a t i o n f o r s i t e s e l e c t i o n

An overall assessment of the nature of the marine environment, o f its utilization, and of the nature and magnitude of the wastes, will indicate that certain features require detailed quantitative study which can only be provided b y practical experimentation. On the other hand, this assessment will also suggest, on purely theoretical grounds, that many o f the problem s are insignificant in a particular case and need not be considered. W here the total quantity o f waste for disposal is small, calculations may demonstrate that all the problem s are insignificant. In such a case, if the margin o f safety is considerable, the elimination of experimental studies prior to discharge may be justified. H ow ever, some form o f monitoring, once discharge takes place, w ould always appear desirable because o f the m any unknown features in any waste disposal into coastal waters. C on tinued favourable results o f such monitoring could, of course, justify a gradual decrease in the frequency o f tests.

The precise form o f necessary experimental work will clearly depend on the local circumstances, but work in the follow ing fields has on occasion been found to be necessary:(1) Transport and dilution processes. Quantitative studies of diffusion

processes o f marine currents and tidal flow using hydrographic techniques may be needed.

(2) Concentration processes, including deposition and adsorption of radioactivity onto sand and m ud or onto surfaces, such as harbour in stallations, and biological uptake processes. W ork at tracer level in laboratories will give some information in these areas, but field work with experimental discharges may ultimately prove necessary. L aboratory work will be useful in limiting the scope o f field experiments.

(3) Use of environment. Quantitative studies o f some values used in the preliminary assessment may w ell be required. Sociological studies o f the habits and behaviour of the population potentially exposed may be required in this connection. Biological field studies may also be required to establish the importance o f various food chains and to obtain information about the migration of organisms within these chains.

A combination o f theoretical assessment and o f experimental work can be used to indicate not only the suitability o f one site relative to another, but also the maximum permissible rate of discharge which it is feasible to allow at any particular site.

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Packaged and solid wastes

P r e s e n t p r a c t i c e

Solid radioactive wastes form a class which is often considered suitable for sea disposal. Such materials are at present almost entirely o f low or intermediate activity. If disposed of by burial on land their bulk, and uncertainities as to the exact degree and nature o f contamination, make it necessary to withdraw large areas o f land permanently from other use. This is only justifiable in areas with sufficient waste land. Storage w ould be relatively costly with respect to the contained radioactivity. Their general low activity, on the other hand, does not provide insurmountable transport problems. It has also often been found convenient to package small quantities o f liquid wastes and include them with the solids for sea disposal. Such disposals are carried out by several countries and appropriate safe practices have been recom m ended by scientific bodies and have resulted in appropriate regulations by countries concerned. In general, recommendations and practice do not include high-level wastes for such sea disposal. H ow ever, it should be noted that, at this time, the limited occurrence o f highly-active waste and econom ic and technical problems o f transport and handling eliminate any demand for disposal o f highly- active packaged waste.

It is the established practice o f all States to contain high-level wastes in tanks on land, but this storage is, in general, in conjunction with plants engaged in the processing o f spent fuel. Future technical advances may result in sufficient increase in efficiency o f fuel utilization that chem ical processing of the spent fuel elements w ould not be an econom ic requirement. It is also possible that means will be found to econom ically fix high- level wastes into solid, non-leachable form. In such cases, a primary requirement could be to provide thermal cooling for the solid wastes, and the deep sea might then appear as an attractive medium, far rem oved from man, for the disposal of high-level wastes. Contra-indications could be high costs o f transport, limitation on effective monitoring, and the inability to take corrective action if a mistake is discovered. There is insufficient knowledge o f the circulation and diffusion in the deep sea to allow any positive statements to be m ade regarding disposal there o f high-level wastes. If the utilization o f that environment ultimately appears desirable, it is recom m ended that an adequate research program me be first carried out so that the required basic data on the physical, chem ical and biological processes connected with disposal in the deep sea may be available.

The evaluation o f the suitability of a given marine locale as a receiver o f packaged radioactive wastes must take into account several factors peculiar to this form o f disposal. The disposal is not continuous nor made

59


from a definite fixed point, but rather in the form o f discrete increments spread over the area o f the designated disposal site. The packaging provides a certain period o f containment prior to actual release to the environment, during which radioactive decay w ould occur. The radioactive materials released when the packages ultimately fail will initially be in close contact with the bottom , where processes o f sorption by the sediments may restrict dispersion and remove activity from the water, whileincreasing the radioactivity in the bottom sediments. Materials introduced in solid form may not immediately release their contained radioactivity when exposed to sea-water, but rather may be subject to slow leaching.

S e l e c t i o n o f d i s p o s a l s i t e

The choice between disposal in coastal waters, or in the deep sea offthe continental shelf, w ill depend on several considerations. Coastal waters involve lower direct costs, since transport and handling in connection with disposal far from shore can be a severe problem . Further, location, control and monitoring of sites on the continental shelf are easier than in the deep sea. M ore is known o f the processes o f transport and dispersion in coastal waters than in the deep waters of the open sea. On the other hand, what is known o f physical, chem ical and biological processes leads to the con clusion that the bottom o f the deep sea can safely receive m uch greater quantities of radioactive wastes than can be allowed on the continental shelf. Finally, packaged wastes resting on the deep sea-bed are much less likely to affect commercial fish or foul fishing gear than in the case of shallow coastal disposals.

In the selection of the marine area or areas to be utilized as packaged waste-disposal sites, consideration must, as in other cases, be given first to the factors affecting the safety of man, and secondly to econom ic con siderations. The choice o f a site on the continental shelf should only be m ade on the basis o f detailed analysis o f the factors affecting the return o f radioactivity to man; and the rate o f disposal in any site must be limited to an amount which will not result in any undue hazard.

In general, the first steps in evaluation will involve the selection from a number of possible sites o f those most suited for safe disposal of packaged wastes. The factors w hich must be considered in such a site selection are:

(1) Probability o f accidental recovery of packaged solid waste by man. A site w ould not be suitable for packaged or solid waste disposal unless it were highly im probable that accidental recovery w ould occur;

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(2) Utilization of a site by man directly in the harvest o f marine products, or indirectly in the use made o f the area b y organisms which are harvested by man for food in adjacent areas;

(3) Nature o f bottom sediments with respect to the uptake o f the activity from the water and im pact damage to packages;

(4) Transport by currents from the disposal area, with particular concern for the shoreward-directed flow;

(5) Rate o f turbulent diffusion in the waters over the site;(6) Rate o f exchange o f waters o f the particular marine subdivision con

taining the site with other subdivisions of the marine environment.

It is evident that disposal sites must be selected in areas not used for bottom trawling or other types o f bottom fishing, and w hich are unsuited for future utilization. Areas crossed by submarine cables are likewise undesirable. This requirement is best satisfied by selection o f sites in water having depths of 2000 m or more. W here the continental shelf is wide, making the transport o f wastes to deep waters very costly, disposal sites might be selected on the shelf, provided the area has too rough a bottom for trawling or is otherwise unsuitable for bottom fishing, but yet serve as spawning or nursery areas for important commercial species. Such sites would evidently be less suited for waste disposal than areas w hich are not only unsuited for fishing, but also are not important nursery or spawning grounds. The area should be so located, or have bottom conditions such that w ave transport w ould not carry the package out of the designated site — particularly towards the shore, or towards adjacent fishing areas. The depth should, in any case, be sufficient that bottom sediments, which m ay becom e contaminated, w ould not be transported shoreward by currents or w ave action.

The predominant current pattern over sites located on the continental shelf should be directed away from shore, or at least parallel to the shore, with no com ponent towards the land. Turbulent diffusion should be intense so that any activity released from the containers w ould b e rapidly diluted to safe concentrations. Rapid exchange of the coastal waters, containing the disposal site, with the open sea is desirable. On the other hand, disposal sites located in the deep sea should be in areas where there is a minimum o f exchange of the deep waters with the surface layers and with the waters o f any adjacent continental shelf. Thus, submarine canyons located on the edge of the continental shelf are generally less suited for disposal sites than the deep waters in the true ocean basins, since the deep waters o f the canyons more readily exchange with the waters o f the continental shelf.

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Once the most suitable sites have been selected, the maximum rate at w hich packaged or solid radioactive wastes may be introduced without undue risks to man must be determined. This evaluation should follow the general approach discussed earlier in the Report. As pointed out, only a portion o f the maximum permissible dose to man w hich is allotted to the results of peaceful uses o f nuclear energy may originate from sea disposal and of this not all can b e necessarily allotted to packaged-waste disposal, since the human population concerned may receive contaminated marine products resulting from other types of waste disposal. Thus, for a particular packaged-waste disposal operation the additive effects of radiation from all marine sources must be considered.

Because o f the limitations placed on the selection o f the disposal site in regard to possible accidental return o f the waste to man’s environment, there is very little likelihood o f risks due to direct radiation or contamination o f beach sands. The primary route for return o f activity from the disposal site to man w ould be through ingestion o f sea-food. The maximum permissible concentration o f activity in the sea-food harvested from the affected area is determined on the basis of its allocated contribution to the permissible dose.

The next step is the use o f known concentration ratios for the uptake by harvested species, o f elements corresponding to radionuclides involved in the disposal operations. Such concentration ratios depend on species, age and season. The most restrictive concentration ratios for the species involved are customarily used in planning allowable disposal rates. Such considerations determine the maximum permissible concentration of radionuclides w hich may exist in sea-water o f the area affected by waste disposal operations. In making this determination, care should be taken that the additive effects o f the several radionuclides involved are included. On the basis o f a determination of the rate of removal of the introduced elements by uptake on the bottom , o f the effects of transport by currents, and o f dispersion by turbulent diffusion, an estimate can then be made of the maximum rate of disposal. In such a pre-use evaluation it should be assumed that the package will break immediately after disposal. After sufficient actual experience is gained on the life o f the containers, this latter factor may be em ployed in a re-evaluation o f the safe introduction rate.

Other sections of this Report present discussions o f the environmental factors w hich influence the physical, chem ical and biological processes pertinent to the evaluation outlined above. Appendix VIII presents a

E v a l u a t i o n o f t h e s a f e m a x i m u m h a t e o f d i s p o s a l

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detailed example o f the evaluation o f the suitability of a particular marine locale for packaged-waste disposal.

P a c k a g e d e s i g n

Materials. It can be expected that packages containing significant quantities o f radioactive waste should be made o f dense material and they should be made strong enough for safe handling. For sea disposal, how ever, it is often desirable to have the additional quality o f resistance to attack by sea-water, and the material must be reasonably cheap and easy to fabricate. G ood quality steel drums can be expected to resist corrosion for about 10 yr and a good quality concrete o f low porosity will remain intact in sea-water for at least as long. Steel drums are frequently used for form ing the concrete containers, and both the concrete and the steel can be regarded as protective. It is desirable that concrete used in packaging b e o f good quality and of low porosity if it is intended to resist breakage on im pact with the sea-bed and to withstand the destructive action o f sea-water. It should not be regarded merely as weighting material. W hen concrete is used, the thickness of the concrete betw een the waste and the outer surface should be sufficient to prevent rupture of the package on impact. Other suitable material can be used to provide the needed weight. Unprotected packages of baled waste should not be disposed of in the sea.

Density. A ll solid wastes disposed o f into the sea must be sufficiently dense to sink immediately. This end should not be difficult to achieve since the density o f sea-water at sea level does not exceed about 1.03. However, precautions must be taken to see that the contents of a broken package will not rise to the surface. Packages and their contents should be sufficiently dense to ensure that they are not readily m oved along the sea-bed b y currents. It is recom m ended that light materials, such as cloth and paper, should be incorporated into concrete within the outer protective package, and that the density o f all packages disposed o f in deep waters should not be less than 1.2. W hen disposals are made on the continental shelf the density should be at least 1.5.

Voids. I f a package containing voids or compressible materials is sunk in deep water it is likely to collapse under pressure or to develop zones; o f weakness w hich w ill eventually lead to cracking o f the surface. Packaged wastes should contain the minimum of voids. This can be ensured by incorporating the contents in concrete or asphalt. I f voids cannot be filled in any way, the container must be made sufficiently strong or pliable to remain intact under the pressure encountered at the point o f disposal.


(The pressure in the sea increases by one atmosphere for each 10 m of depth.)

Strength against impact. Packaged wastes will suffer impact at the surface o f the sea, and again when they hit the bottom . The terminal velocity of a concrete block in sea-water is likely to be about 5 m /sec, but for a block containing wastes with an overall density of 1.2 the velocity w ould be about 2 m /sec. If the bottom is hard there will be a considerable impact. Packages consisting o f concrete in 200-liter steel drums w ould be likely to withstand this impact, but large “ coffins” made of reinforced concrete m ight w ell be broken. It is recom m ended that the designers of packages should take into account the effects of impact with the sea bottom, and that reinforcements should be included when this is necessary.

Prevention of leakage. The possible leakage of liquids from defective disposal containers should be prevented, preferably by solidification with cement or other suitable material, or at least by an impervious secondary lining.

Examples of current practice. Diagrams of containers used in the United States o f America for sea disposal are given by A. B. J o s e p h in USAEC docum ent W ASH -742 (1956).

O t h e r f o r m s o f s o l i d w a s t e

Pieces o f contaminated equipm ent too large for disposal in concrete drums or “ coffins” should preferably be dismantled or cut into smaller pieces. W hen this is impracticable and the material is not resistant to corrosion, the equipment should be covered in a resistant material. The coating should be sufficiently robust to resist im pact on the sea bottom and should be applied to all surfaces accessible to the water. The irregular form o f such objects may make them particularly liable to recovery by fishing gear, etc. All such wastes containing dangerous amounts o f radioactivity should only be disposed of in deep water. (The maximum depth o f commercial trawling is approaching 1000 m.)

Experimental materials for the permanent fixation of radioactive wastes are being developed in many countries. They are usually glasses, ceramics, or micas in which fission products are fixed either physically or by incorporation into crystalline lattice. Many o f these products have very low leaching rates, though few have been tested adequately in sea-water. D isposal o f highly-radioactive wastes in such a form is com plicated by the large amount o f heat produced by radiation so that deep-sea disposal has been suggested. Very little is known of the long-term effects of radia

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tion and transmutation on the leachability o f material o f this kind. The disposal o f concentrated wastes into the sea in this form cannot be recom m ended in our present state o f knowledge, but it is recognized that this may be possible with further development.

Ship problemsS p e c i a l f e a t u r e s o f r a d i o a c t i v e - w a s t e d i s p o s a l f r o m s h ip s

An adaptation o f the approach o f Chapter I I I can be m ade for waste disposal from nuclear-powered ships. This is based upon the principle that any release o f radioactive wastes from nuclear-powered ships should be made in such a w ay that there is no resultant limitation on man’ s harvest o f products from the sea, taking into account the follow ing special considerations:

(1) The source of wastes is not stationary, but moves through a variety o f marine environments. The most restrictive segment o f the marine environment from the standpoint o f suitability as a waste receiver will usually call for regulations concerning the operation o f nuclear- pow ered ships. H owever, wastes unsuitable for discharge in some segments o f the sea may be stored on shipboard and discharged when the ship is passing through areas w hich have the capacity to receive them safely.

(2) The significant wastes are not discharged as a continuous effluent, but are released as discrete amounts o f activity. Evaluation may take the form o f an allowable amount o f activity in a single release from a nuclear-powered ship, and a permissible number o f such releases per unit time in a given segment of the sea.

Operating regulations must be based on the most restrictive consideration regarding the return o f radioactive materials to man, since nuclear- pow ered ships may traverse all types o f marine environments. The general suitability o f any segment o f the sea to receive wastes from nuclear- pow ered ships is determined on the assumption that ships will enter regions that supply the major protein requirements o f a significant-sized population, and that the sea-food utilized by such a population will have a maximum capacity for concentration of activity from the sea-water. O n the other hand, any specific evaluation of the suitability o f a given harbour, for example, to serve as a base or major port o f call for nuclear- pow ered ships, should include a study of man's actual utilization of that particular area.

The nature o f the wastes to be expected from nuclear-powered ships has been presented in Chapter I I. At present any detailed discussion must

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be based on a very limited number of ship reactors which have been studied. The sources of radioactive wastes which might be discharged to the marine environment from a pressurized-water reactor system are:(a) The expansion volume of primary coolant during warm-up of a pres

surized water reactor;(b) Operational leakages from various components of the primary and

auxiliary systems, wastes from the laboratory, from sampling, from equipment decontamination and showers and laundry wastes associated with the reactor plant;

(c) Ion exchangers which remove corrosion products from the primary coolant.

P r o b l e m s p e c u l i a r t o s h i p p in g

In describing the properties of the ocean, a division was made on physical grounds into nearshore areas, the continental shelf and the deep sea. The risk of radioactivity reaching man depends markedly on the physical, chemical and biological processes affecting the waste released in any particular part of the marine environment traversed by the nuclear-powered ship. Therefore, from the point of view of waste disposal from ships, a rather different division might be considered desirable and has been proposed elsewhere. (National Academy of Sciences — National Research Council, United States of America.) However, it appears possible to provide adequate guidance with respect to present needs by carrying out a study of ship disposal in terms of areas of the oceans defined solely on physical criteria. Suitable criteria are:

Zone A (nearshore area). Harbours, estuaries and inshore waters within two miles of the coastline.Zone B (the continental shelf and coastal area). The area seaward from two miles offshore to the 400-m depth contour, or to 10 miles offshore, whichever is more seaward.Zone C (the deep sea). Those areas of the open sea more than 10 miles from the coast and having depths greater than 400 m.

B a s is o f c a l c u l a t i o n o f s a f e d is p o s a l l i m i t s f o r s h i p p in g

In Chapter IV it was pointed out that, for the foreseeable future, waste disposal will, in general, affect special population groups rather than the population at large, and the critical dose-rate will usually be that to the individual of 0.5 rem/yr. This criterion will apply to the nuclear-powered ships problem only in the case of Zone A (nearshore area), where waste

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disposal will directly expose only a relatively small fraction of the whole population. In the case of Zone B (continental shelf and coastal area) and Zone C (the deep sea) it is more likely that international utilization of marine products will require the use of the genetic apportionment of 0.2 rem, as recommended in Chapter IV. The significant route whereby activity associated with waste disposal from nuclear-powered ships could return to man is through the ingestion of sea-food. The determination of the partial maximum permissible concentration in sea-food which may result from nuclear-powered shipping may be made in the following manner. The basic tabular data employed are the maximum permissible concentrations in water for the various radioisotopes recommended by the ICRP. These m p c values are based upon an assumed rate of intake of water per individual of 2200 ml per day. Individuals who obtain their full protein requirement from sea-food would ingest approximately 1500 g per week. Thus, one step in obtaining the partial maximum permissible concentrations in sea-food from the given m p c values is to obtain a factor, which gives the ratio of drinking water ingested per week to sea-food ingested per week.

The next step in the procedure is to obtain a factor representing the ratio of the permissible annual dose for the population groups which might be exposed to the effects of sea disposal from nuclear-powered ships to the permissible annual dose for occupational workers.

Zone A. The portion of the population which might be affected by nuclear-ship operation within Zone A (inshore and estuarine areas) is usually a small fraction (less than 10°/o) of the whole population and can be considered included in the special group B (c) (see p. 32). The whole population genetic dose arising from the allocation to special groups is taken to be 0.5 rem and there is no necessity for further allocation to cover this requirement in the case of exposure arising from ship operation in Zone A. Nuclear-ship operations must be controlled within Zone A, both to maintain the contribution to the genetic dose within the special group allocation of 0.5 rem, and also to keep the individual maximum permissible dose below 0.5 rem/yr.

Zones B and C. Here the recommended apportionment from the whole population genetic dose for sea-disposal problems of an international character applies. In Chapter IV it is recommended that 1/25th of the genetic dose, or 0.2 rem over the average reproductive life, be allotted to sea disposal having an international character. Nuclear-powered shipping appears to be a primary source of waste problems having international implications. Thus, it seems reasonable to assign a significant apportionment of the 0.2 rem to nuclear-powered shipping.

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Having estimated ppc’s in marine food organisms, ppc’s in the seawater can be obtained if the factor by which food organisms concentrate the isotope in question in their bodies from the water is known. For a population which receives all its protein requirement from sea-food, assumptions are made of the contribution from different items of diet. The partial maximum permissible concentration in sea-water, for each of the zones, is then obtained by dividing the ppc values for sea-food for each of the zones, for each isotope, by the corresponding concentration factor.

R e s u l t s o f t h e a p p l i c a t i o n o f t h e a b o v e c o n s i d e r a t i o n s t o t y p i c a l

PRESENT-DAY NUCLEAR-POWERED SHIPS

Calculations on the above lines have been carried out for representative present-day nuclear-powered ships and are presented in Appendix IX. Below is a summary of the findings:

The waste to be disposed of at sea in connection with nuclear shipping will depend upon the design of the reactor, and ancillary equipment used. It is only possible to deal with currently-proposed ship propulsion units, but it can be assumed that such wastes will be of low, or intermediate activity for the present. Radioactive waste materials that might be introduced into the marine environment from presently-designed ships powered by pressurized-water reactors include low-level liquid effluents originating from warm-up expansion volumes and leakage of the primary coolant, plus intermediate-level wastes contained in spent ion-exchange resins.

Ships will traverse regions of the sea that are unsuited as safe receivers of nuclear wastes. However, over much of the open sea traversed by trade routes conditions are suitable for the discharge, without undue risk to man, of amounts of activity associated with the normal operating wastes from nuclear ships. In order to obtain maximum initial dilution of the radioactive wastes discharged from nuclear-powered ships, such wastes can be introduced into the turbulent propeller wake while the ship is under way.

Harbours, estuaries and other inshore areas appear unsuited for the discharge of spent ion-exchangers from nuclear-powered ships. Many harbours could, without undue risk to man, receive the low-level liquid effluent associated with the warm-up expansion volume and normal leakage. However, some harbours of poor flushing character would be unsuited for such release of activity. Closed harbour basins are unsuited for receiving wastes. The degree to which a particular inshore area can be utilized as a receiver of low-level liquid wastes from nuclear-powered ships can only be judged upon a specific study of the area in question. All discharge of radioactive wastes from ships in harbours and other nearshore areas should be in conformity with conditions laid down by the local authority.

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Zone B, the continental shelf, and coastal area, from two miles offshore out to the 400-m depth contour, or 10 miles from shore, whichever is farther seaward, has adequate capacity to receive safely the low-level liquid wastes arising from normal operations of nuclear-powered ships. Spent ion-exchangers should not be released from nuclear-powered ships in this zone.

The open sea, more than 10 miles from shore, and having depths greater than 400 m, can receive the low-level liquid wastes and the intermediate- level wastes from the spent ion-exchangers resulting from normal operation of nuclear-powered ships, without undue risk to man.

6 9


CHAPTER VII

CONTROL MEASURES

Monitoring, and standardization of monitoring techniques

E x t e n t o f m o n i t o r i n g

The term “ monitoring” in the nuclear-energy field is ideally applied to those measures taken to warn against radiation hazards or other likely occurrence. Individual measures, to be effective, must form part of a carefully considered overall programme, which forms the basis of any system of control measures. As a general principle, whenever radioactive waste is discharged into the environment it is necessary to monitor the environment. Consequently, it is important to consider the nature of such monitoring programmes in the particular case of disposal to the sea.

An initial theoretical evaluation of the suitability of the site as a disposal area is needed before discharge of radioactive waste. This evaluation will provide a broad guide to the nature of the pre-operational measurements required to give reference data for the monitoring programme which, in turn, will influence the nature of subsequent control.

The monitoring required will be dependent on the quality and quantity of the waste discharged and on the nature of the disposal site. If there is little direct impact on man, or if the quantity discharged is so small that theoretical evaluation established safe conditions under all visualized possibilities, then the extent of monitoring can be small. For such reasons it is impossible to specify a monitoring programme which would apply to all sites, and each will need to be judged on its merits.

M o n i t o r i n g p r o c e d u r e s : s t a n d a r d i z a t i o n

The disposal of radioactive waste to the sea may have effects of international concern, and there is, therefore, an obvious need to standardize the techniques employed in the monitoring process so that interpretation of the data collected may be uniform among the nations concerned. The presently-accepted best methods of making these measurements are discussed in Appendix V. Standardization and inter-comparison of monitoring methods are also dependent on the availability and interchanges of suitable standard samples in support of the accepted measuring techniques.

Pre-discharge measurements will usually be necessary to indicate the normal levels and fluctuations of the natural background, and give a basis for the evaluation of measurements provided by the monitoring programme, as such fluctuations are of a seasonal character. The effects of

70


fall-out, or activity due to existing neighbouring nuclear-energy centres, may also contribute significantly to background. Such measurements can also be of value to provide data for legal or public relations problems which may eventually arise.

A comprehensive monitoring programme will be required unless theoretical assessment has established categorically that the proposed rate of discharge is well within safe limits. If sufficient radioactivity is available which could in any way lead to hazardous sea disposal conditions, a monitoring programme is necessary both to ensure compliance with the regulations and to check that regulations are adequate to their purpose.

Measurements of environmental activity resulting from waste discharge can be used for two purposes: either they can be part of a research or study programme to establish safe limits of discharge or, at a later stage, provide the basis of a routine monitoring programme indicating any departure from normal acceptable environmental conditions.

Prior to the discharge of radioactive waste at a selected site, both theoretical and experimental data will have been used, possibly in conjunction with field measurements of dilution processes, to estimate the permissible rate of discharge. It will be necessary to verify this estimate by direct measurement in the field, which can only be done by discharge of the particular radioactive waste at a very low level, yet of sufficient activity to enable monitoring to be effected. The precise nature of this control experiment can only be decided at the time. Subsequently, a cautious approach may, if necessary, be made to the permissible discharge limits.

A routine monitoring programme should be prepared for the site once the fundamental data, relating activity discharge rate to sample activity, has been established. In the beginning, the permissible discharge should be well below the estimated maximum permissible rate. It is suggested that every effort should be made to maintain a constant rate of discharge, averaged over approximately one month, and the rate should be maintained at this level for about twelve months, during which time intensive measurements should be carried out in order to test the original estimate of the relationship between discharge rate and sample activity.

Increase in the rate of discharge of activity must be made in progressive steps, safety of release being established at each step. Since there may be considerable seasonal variation in the uptake of activity, a period of at least twelve months of monitoring should intervene between steps. Continued monitoring, after reaching the acceptable discharge rate, serves not only its normal purpose of warning of errors of operation or abnormalities of the environment, but also indicates the presence of uncon

71


sidered factors, or long-term trends, and, despite uninterrupted negative results, can be of value as a demonstration of the adequacy of the safety measures.

N a t u r e o f s a m p l i n g r e q u i r e d

It is difficult to specify the number and types of samples needed to implement a monitoring programme, and this applies even more strongly to the frequency at which these samples should be collected. A broad guide is here provided. It may be necessary to take regular samples from the sea-water, sea bottom, fish, shell-fish, seaweeds and phytoplankton of the locale of disposal. The extent of the area sampled will depend on the nature of the disposal site and other factors, such as magnitude of the disposal process.

The frequency with which samples are collected for analysis is dependent upon the disposal rate, but a high rate of sampling will be needed during the experimental period of disposal to determine maximum safe utilization, whereas at a later stage samples may be taken less frequently when disposal limits have been established. As a guide, sampling frequencies of the following order are typical of current practice:(a) seaweeds, phytoplankton, shellfish — alternate weeks;(b) fish and crustaceans — monthly;(c) sea-bottom deposits — alternate months.

This is not intended to provide a comprehensive sampling programme; in the case of deep-sea disposal, for example, samples taken once or twice a year might be adequate. Further guidance will be found in Appendix V.

The response and efficiency of counting equipment to be used depends upon the nature of the sample, and the interpretation of results may depend upon the specific activity of the sample. Further, intercomparison of procedures between laboratories necessitates submission and interchange of common samples. As a result, calibration and standardization of monitoring procedures demand standards characteristic of material normally evaluated, rather than non-specific radiation standards.

R e g i s t r a t i o n

Registration, including reporting of the results of any relevant monitoring of the disposal of radioactive wastes at sea, is necessary to ensure that disposals are in conformity with agreed national or international requirements. In addition, registration can serve a variety of other useful purposes, e. g. alleviation of public concern over safeguarding an important part of man’s environment; establishing that the use of the sea for radio

72


active-waste disposal is carried out in an orderly and planned fashion; discouragement of the development of questionable practices; discouragement of unnecessary multiplication of disposal sites; means for fisheries authorities and others with recognized interests to demand any protective measures felt necessary; and aquisition of data for evaluating the desirability and safety of continuing disposals.

A distinction may be usefully made between recording individual disposals, and international registration. All significant quantities of radioactive wastes deliberately released into the ocean or into waters entering the ocean (including the discharge of radioactive wastes from nuclear ships, and the performance of scientific experiments which involve significant amounts of radioactive contaminants) should be recorded as to nature and amount. Compilation of key data from such records should be registered at a collection centre, the essence of such registration being that significant data are made available to all those who are legitimately concerned.

Although original records may be on a national basis for convenience, eventually registration or compilation of reports should be on an international basis, since a large amount of the disposals will necessarily be in international waters, and may affect the interests of nations not responsible for such disposals. Besides the quantity, registration should indicate the general nature of disposals and any facets which could pose special problems for users of the oceans; ease of preparation and practicality should be borne in mind in setting up registration procedures.

The various methods for the collection of basic data could be left to national governments; however the following suggestions may be useful:(1) Continuous disposal by pipeline to be subject to control involving

periodic or continuous sampling.(2) Agencies disposing of packaged wastes to do so under licence neces

sitating adequate reports of such disposals to a government authority.(3) Disposal from nuclear-powered ships to be reported in a special log

book giving estimates of quantity and position of discharge.(4) Periodic reports from nuclear ships to be made to the country of

registration.(5) Particulars of the incoming voyage to be made available to each port

authority in a similar manner to arrangements at present in force for reports of oil release at sea.

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CHAPTER VIII

C O NC LUS I ONS AND R E C O M M E N D A T I O N S

ConclusionsRadioactive waste is unavoidable in the utilization of nuclear energy

and has to be safely disposed of in some way. The first principle must be the safeguarding of man against damaging effects of radiation, and only those waste disposal methods should be considered as do not involve any risk which is unacceptable either to the individual or to the population at large. Consequently, when adopting a waste-disposal method, and also before any extension is made of the use of a particular waste-disposal practice which is safe in the present situation, a careful evaluation should be made of future consequences, and in particular any international implications.

The Panel has carried out an assessment of safe conditions for radioactive-waste disposals to the sea. The recommendations of the ICRP have been accepted as the basis of the safety assessment.

To make this assessment it has been found convenient to divide the problem into two aspects:{a) Waste-disposal operations which may be regarded as only affecting

the nation concerned. An example of this can be certain waste- disposal operations into coastal waters.

(b) Waste disposal which may affect a number of countries, and so may be regarded as having international implications. The waste arising from nuclear-powered ships on the high seas comes within this category.

In the first of these cases it is considered that the radiation exposure will, in general, be limited to a small fraction of the whole national population. Consequently, for the forseeable future, waste disposals of this type would not contribute significantly to the genetic dose of the whole population. The critical control will therefore be the radiation exposure of the individual in this group. If, however, the size of the group exposed in this way becomes large, then the genetic dose to the whole population arising from exposure in the special groups could become the limiting feature.

For the second case — waste disposal which could give rise to exposure of more than one national population — the controlling factor must be in terms of the genetic dose which could be received by the various national populations involved. The ICRP has recommended that the genetic exposure of the whole population should be limited to less than 5 rem (over

74


a period of 30 yr). This is intended to include exposure from all sources other than natural background and medical procedures. It has further been recommended that the proper apportionment of this total genetic dose will depend upon circumstances which may vary from country to country and the decision should therefore be made by national authorities. This apportionment will allow for the particular case of waste disposals which affect only one nation. However, for a case of disposal which may have international implications, it is necessary that, for those nations which utilize large amounts of marine products, a fraction of the genetic dose should be apportioned to this possible source of exposure. It is recommended that this should be l/25th of the genetic dose (i. e. 0.2 rem).

At present the release into the sea of high-level wastes from irradiated fuel cannot be recommended as an operational practice as we do not know enough about the properties of the deep sea. It is possible that means may be found to fix the high-level wastes into solid, non-leachable forms. Should the utilization of the deep sea ultimately appear desirable for the disposal of such waste, an adequate research programme has to be carried out so that the required basic data on the physical, chemical and biological processes in the deep sea may be available.

Wastes of low, and intermediate activity may safely be disposed of into the sea under controlled and specified conditions. All such radioactive wastes disposed of into the sea, with the exception of those incidental to the operation of nuclear-powered ships, should be released into designated disposal sites in conformity with the conditions specified for the particular site.

In evaluating a disposal site a number of factors must be considered. Once the permissible radiation exposure level to man arising from sea disposals is set, it is necessary to find the numerical relation between the rate of discharge and the resulting exposure to man. In this evaluation all significant routes have to be taken into account. A study should be made of the various ways in which the population that is potentially exposed makes use of the marine environment. A complete biological, chemical and physical evaluation of the environment of the site is fundamental to this assessment. A thorough study into the nature, effectiveness and variability of the dispersal and diffusion mechanisms at the site should be made.

The very considerable number of assumptions which have to be made to permit calculation of permissible rates for sea disposal make such calculation of value only as a guide. If full confidence is to be placed in the results of such computations they must, in general, be supported by experimental studies, such as releases of simulants or of actual wastes, on

75


a limited scale. If, however, the margin of safety is considerable, the elimination of experimental studies prior to discharge may be justified.

A system of monitoring should be established, including adequate routine checks on the routes to man which are considered significant, plus occasional checks of other possibilities to ensure that nothing has been overlooked or misinterpreted. Standardization of the techniques employed in the monitoring is desirable to permit intercomparison of data between the nations concerned.

All sites referred to above should be designated by a responsible national or international authority according to international agreements. This authority should set out conditions of use for the disposal site adequate to ensure that no unacceptable degree of hazard to man arises. It should provide for any necessary monitoring of the area to verify that safe conditions are maintained and should collect all necessary records of disposal to maintain an adequate knowledge of the state of the disposal site.

It is further concluded that all authorities setting up disposal sites in the sea should provide the information necessary to maintain an adequate international register of radioactive-waste disposal into the sea. This register could be maintained by the International Atomic Energy Agency.

The waste to be disposed of at sea in connection with nuclear shipping will depend upon the design of the reactor and ancillary equipment used. It is only possible to deal with presently-proposed ship propulsion units but it can be assumed that such wastes will be of low, or intermediate activity for the present. Radioactive-waste materials which might be introduced into the marine environment from presently-designed ships powered by pressurized-water reactors include low-level liquid effluents originating from warm-up expansion volumes and leakage of the primary coolant, plus intermediate-level wastes contained in spent ion-exchangers.

Nuclear-powered ships will traverse regions of the sea which are unsuited as safe receivers of nuclear wastes. Therefore, such ships should be provided with facilities for temporary storage of waste products. On the open sea conditions are suitable for the discharge without undue risk to man of amounts of activity associated with normal operating wastes from nuclear ships. In order to obtain maximum initial dilution of the radioactive waste discharged from nuclear-powered ships, such wastes can be introduced in the turbulent propeller wake while the ship is under way. Ion-exchangers should be made of material that will sink when introduced into the sea.

Harbours, estuaries and other inshore areas appear unsuited for the discharge of spent ion-exchangers from nuclear-powered ships. Many harbours could, without undue risk to man, receive the low-level liquid effluent associated with warm-up expansion volume and normal leakage.

76


However, some harbours of poor flushing character would be unsuited for such release of activity. The degree to which a particular inshore area can be utilized as a receiver of low-level liquid wastes from nuclear-powered ships can only be judged upon a specific study of the area in question. All discharge of radioactive wastes from ships in harbours and other nearshore areas should be in conformity with conditions laid down by the local authority.

The continental shelf and coastal area, from two miles offshore out to the 400-m depth contour, or 10 miles from shore, whichever is further seaward, has adequate capacity to receive safely the low-level liquid wastes arising from normal operations of nuclear-powered ships. This area of the sea is not recommended for the release of spent ion-exchangers from nuclear-powered ships.

The open sea, more than 10 miles from shore and having depth greater than 400 m, can receive low-level liquid wastes and the intermediate- level wastes from the spent ion-exchangers, resulting from the normal operation of nuclear-powered ships, without undue risk to man.

The conclusions and recommendations of this Panel are based on the knowledge available at present and must be subject to continued re- evaluation in the light of the rapid accumulation of new data. The necessity for further research and development work in all fields of importance to waste disposal is strongly emphasized. The universal nature of these problems requires international effort.

RecommendationsThe following recommendations are made:

(1) At present, the release into the sea of highly-radioactive wastes from irradiated fuel cannot be recommended as an operational practice.

(2) Wastes of low, and intermediate activity may safely be disposed of into the sea under controlled and specified conditions.

(3) The most recent Recommendations of the International Commission on Radiological Protection should be used as a guide for the assessment of the safety of proposed radioactive-waste disposal into the sea.

(4) Only waste-disposal methods should be considered which limit the radiation dose to that which involves a risk which is not unacceptable to the individual and the population at large. The interpretation is made that one twenty-fifth of the genetic dose to the population as a whole, arising from the peaceful uses of nuclear energy, should be allocated to radiation received from marine sources beyond national control.

77


(5) All radioactive wastes disposed of into the sea, with the exception of those incidental to the operation of nuclear-powered ships, should be released into designated disposal sites in conformity with conditions specified for the particular site.

(6) Release of radioactive wastes from nuclear-powered ships should be made in such a way that there is no resultant limitation on man’s harvest of products from the sea.

(7) Each waste-disposal site should be designated by a responsible national or international authority. This authority should set out conditions of disposal for the site adequate to ensure that no unacceptable degree of hazard to man arises. It should provide for any necessary monitoring of the area to verify that safe conditions are maintained, and should collect all necessary records of disposals to maintain an adequate knowledge of the state of the disposal site.

(8) All authorities setting up disposal sites in the sea should provide to a suitable international authority, information necessary to maintain an adequate register of radioactive waste disposal into the sea.

(9) The International Atomic Energy Agency (IAEA) should maintain this register and should receive:(a) Notice of the licensing requirements of all sea-disposal areas

set up by national authorities or by international bodies according to agreement by the national authorities. This information should be supplied to the Agency a sufficient time prior to the establishment of any disposal site, to permit transmission to interested parties and the receipt of any pertinent comments or representations.

(b) Annual reports on the state of such sites, including any change in licensing conditions and information as to the quantity and general nature of disposals in the past year. An itemised report is not necessary, but an estimate of the total activity, and the nature of the more hazardous single disposals, regarding packaging, content, and maximum activity, should be included.

(c) The monitoring programme and all relevant scientific findings.(10) The IAEA should provide for any necessary standardization of

monitoring techniques.(11) Radioactive wastes disposed of from nuclear-powered ships should be

entered in a record maintained on the ship and available for inspection by port authorities. A suitable abstract of the record should be transmitted annually to the authority of the country of the ship’s registration for forwarding to the Inter-governmental Maritime Con

78


sultative Organization (IMCO) which should work out, jointly with the IAEA, an effective registration and compilation of radioactive- waste disposals from nuclear-powered ships.

(12) All disposals from ships in harbours and national waters should be in conformity with conditions laid down by the local authority. In international waters disposals should be in conformity with conditions specified in the licensing of the vessel or provided by the appropriate international authority, whichever is more restrictive.

(13) The IAEA, in collaboration with other international organizations concerned, should at appropriate intervals review the problems connected with radioactive-waste disposal into the sea.

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DATA ON TYPICAL R A D I OA C T I VE WASTES

A careful examination of the literature will show the difficulty of defining typical radioactive wastes. The composition of wastes varies widely with process, site and occasion. In general, it is felt more will be learned by study of the particular situation to be dealt with than by reference to the literature. However, a few examples of wastes quoted in the literature are given below. In general, intercomparison of data from various reports is almost impossible because of the lack of clear information as to the exact nature of the figure reported and the units used.

Ore processingWastes have been of concern chiefly because they are often produced

in arid regions where any contamination of available water is undesirable.Wastes from uranium mills (order of magnitude by inspection of avail

able reports) [1— 25]:

Appendix I

Reactor coolantsFrom corrosion of structural materials, highly variable concentrations

of Mn56, Co60, Fe59, Cr51, Fe55, and Na24 with a total output of long-lived products of between 1 and 10 c/MW yr [1,3,4].

Spent fuel processing (primary wastes from solvent extraction) [5]

V o l u m e p r o d u c e d :

Natural U about 5 1/kg.Enriched U about 500 1/kg.

Nitric acid concentration up to 7 molar depending upon process. Activity 100 to 1000 c/1.Heat production up to 5 W /l (after 100 days’ cooling).Present wastes in storage (United States) about 4 X 10s 1.Cost of storage (United States) $ 0.2/1.

URa226

Th234 + Pa234

10~° [ic/ml 10 7 (xc/ml 10-7 (xc/ml 10-c lie/ml

Wastes from thorium production [2]:Total activity 10 i: |xc/ml.

80


Appendix I

Low-level wastes from major nuclear-energy centres [5]

The following Table (Table 2 in the United States Atomic Energy Commission Report No. w a s h 742) shows the diversity of low-level waste operation, even among roughly comparable operating groups:

T a b le I“LOW-LEVEL LIQUID-WASTE DISCHARGE DATA

Invest Approx. Annual

Type o fment in Volume Operating

SiteTreat D is Total Curies and

MaximumTreatment ment and

Release Facilities

chargedp e r

Year

Discharged(*) Moni - toring Costs

($ 1 0 0 0 ) (1 0 6 gals) (X 1 0 3) ($ 1 0 0 0 )ANL Depends on

Specific Waste 143d) 47BNL Evaporation 307 1 2 0 (2 —3)(2> 64FMPC Calcination 2458 90 329H APO D ecay Storage 1559 7668(5) 2096

(Since '44)60

K A P L Evaporation 932 .126 65LASL Co-ppt 356 14 139N RTS D ecay Storage 2436 420 1.7

('55 and '56)78

ORNL None 100(3) 159 75(Since '48)

230

R ockyFlats Evaporation 602 40 136SRP Decay Storage 20 0 .8

(Since '55 and '56)444

W A P D Evaporation 114 137(4) — (2) 62Total $ 9007 8841 2173.5 $ 1607

* Activity discharged without further control.(1) The cost of the evaporator, ion exchange and co-ppt plants not included.(2) To sea burial in packages.(o) Estimate for 3 discharge pits at $ 24,000 each, (1) discharge line at $ 15,000 and $ 10.000

for monitoring stations. Does not include obsolete evaporator planl.(4) Includes infiltrated storm water.(5) Includes condenser cooling water not normally radioactive.”

Solid and packaged wastes

The production of solid and packaged wastes by a major research centre can be indicated by French experience at Saclay (plus Fontenay-aux- Roses).

6 81


The wastes can be divided into several groups:(a) sludges from the purification of liquid radioactive effluents.(b) waste in drums

(i) combustible waste from laboratories: paper, rubber, wood . . .(ii) non-combustible waste from laboratories: glass, scrap-iron . . .

(c) loose solid waste (piping and various items of contaminated equipment).

In five years, the research centres at Saclay and Fontenay-aux-Roses have produced:

group (a): 40 m3group (b) (i): 210 m3group (b) (ii): 320 m3group (c): 160 ms.

Laboratory wastesThe discharge of mixed types of activities from laboratory sinks and

drains is an important source of low-level wastes. The volume of wastes varies from 50 000 gal [6] to 500 000 gal [7] per day and activities range as high as 10-4 uc to 10-5 ac/ml. These wastes are generally of low solid content and contain mixed activities (alpha, beta, gamma) and have a wide spectrum of radio-elements and non-active pollutants. Most of the wastes mix with the sewage and the biologically-toxic elements might harm organisms feeding on the sewage [8]. An analysis of the gross characteristics of liquid laboratory wastes of Argonne National Laboratory is given below [9]:

Appendix I

T a b l e IITYPICAL ANALYSIS OF LABORATORY DRAIN WASTES

Averageflow

Gal/hrp H

R adioactivityi i c / c m s

Alpha Beta

16 — 32 2 .2 - 6.5 0 - 4 .6 X 10- 8 1 .8 -7 .1 X i o - ?2 7 -9 3 2 . ! ) - 5.8 1 .0 -5 .7 X 10 -’ 1 .3 -8 .2 X 10~ 61 8 -3 5 3 .5 -1 0 .4 1.3 —4.0 x 10- 7 3.7 —6.3 x 10~ 5

Besides liquid effluent a wide variety of solid wastes are accumulated: paper, glass, equipment, rubber tubings, gloves and overshoes, metal and porcelain ware and other articles which are contaminated in use.

8 2


Appendix I

Increasing use of radioisotopes in industry and medicine constitutes another source of low-level wastes. Open sources used in medicine and biochemical studies are mostly Au198, I131, P32, C14, Ra D, Na24 and Th. These are also used in the study of metabolic processes through animal experimentation. In addition, these studies produce wastes composed of excretions and cadavers.

The use of radiogold in the treatment of cancer in London [10] releases about 250mc/d of waste to the sewers. Reviewing the use of I131 and P32 in some selected cities in the United States it is claimed [11] that the discharge of I131 and P32 wastes from hospitals will be amply diluted by city waste waters to values of the order of 10-7 (ic/ml before they join the public waters. In industry and medicine sealed sources of.Cs137, Co60, Sr90 and Ru10li are used for radiography, teletherapy, thickness gauges, static eliminators, etc. Such sources ultimately call for disposal as contained wastes.

Laundry wastesAn estimate of inactive and active laundry wastes at Shippingport

has been given by L a p o i n t e et al. [ 1 2 ] .These effluents contain mixed activities and non-active toxins and

substances like Be, Cd, Pb, fluorides, soaps, detergents, acids and, chelating agents. The effluents also contain solvents, such as “ stoddard” solvent, petrol, carbon tetrachloride, and heavy metal soaps in emulsified form when dry-cleaning is done.

Non-active wastesThe nuclear-energy industry also produces non-radioactive toxins in the

effluents very much in excess of the maximum allowable concentrations for drinking water. They are mostly soluble fluorides, nitrates, sulphates, beryllium and ammonium salts.

R E F E R E N C E SThe extreme range of wastes produced even in smaller operations requires

reference to the original literature for any sound appreciation of the problem. The following list o f references is provided:

[1] JOINT COMMITTEE ON ATOMIC ENERGY, CONGRESS OF THE UNITED STATES, Industrial Radioactive Waste Disposal (1959).

[2] KAMATH, P. R „ and PILLAI, K. C„ AEET/HP/RWD/1 (1958) (restricted).[3] GOPINATH, D. V., Radioactivity build-up in reactor coolant water,

AEET/HP/TH/1 (1958).

Use of isotopes

6* 83


[4] ROCKWELL, T. and COHEN, P., “ Pressurized Water Reactor (PWR) water chemistry” , Proc. UN Int. Conf. PUAE, IX (1955) 423.

[5] UNITED STATES AEC, Status Report on Handling and Disposal of Radioactive Wastes in the AEC Program, Wash. 742 (1957).

[6] RODGER, W. A. and FINEMAN, P., “ A complete waste-disposal system for a radiochemical laboratory” , Nucleonics, 9 6 (1951) 56.

[7] KRAMER, H. P. et al., “ Radioactivity in surface water” , J. Amer. Water Works Ass. (Nov. 1958),

[8] JENSEN, E. C. et al., “ Problems facing state agencies in handling treatment and disposal of radioactive wastes” , 2nd Nuclear Engineering and Science Conf., Philadelphia, Paper No. 57, NESC 92 (1957).

[9] RODGER, W. A. et al., “ Disposal of radioactive wastes at Argonne National Laboratory” , Eighth Industrial Waste Conf. (May 1953).

[10] SADDINGTON, K. and TEMPLETON, W. L., Disposal of Radioactive Waste, George Newnes Ltd. (1958).

[11] RUCHHOFT, C. C., “ Decontamination and the disposal of radioactive wastes” , Radioisotopes in Industry, Ed. John B. Bradford, Publ. Reinhold Publish. Corporation (1953).

[12] LAPOINTE. J. R. and BROWN, R. D., “ Radioactive material control” , Ind. Engng Chem., July (1958).

[13] WOLMAN, A. and GORMAN, A. E., “The management and disposal of radioactive wastes” , Proc. UN Int. Conf. PUAE, IX (1955) 9.

[14] ANDERSON, C. R. and ROHRMAN, C. A., “ The design and operation of high level waste storage facilities” , Proc. UN Int. Conf. PUAE, IX (1955) 640.

[15] HATCH, L. P. et al., “ Processes for high level radioactive waste disposal” , Proc. UN Int. Conf. PUAE, IX (1955) 648.

[16] REINHARD, G. M. and GLASS, D. W., “ U-refinery waste and clarification” , Chem. Engng Prog., 52 9 (1956) 360.

[17] PELANGE, R. C. et al., “ Radioactivity .in stream pollution” , Ind. Engng. Chem., 48 10 (1956) 1847.

[18] GILBERT, F. W., “ Decontamination of the Canadian Reactor” , Chem. Engng Prog., 50 5 (1954) 267.

[19] GORMAN, A. E., “ Disposal of Atomic Energy Industry wastes” , Ind. Engng Chem., 45 12 (1953) 1673.

[20] GEYER, J. C. et <al., “ Low level radioactive waste disposal” , Proc. UN Int. Conf. PUAE, IX (1955) 19.

[21] TSIVGOLOU, E, C. and TOWNE, W. W., “ Sources and control of radioactive water pollutants” , Sewage industr. wastes, 29 2 (1957).

[22] BEARSE, A. E. et al., „Thorium and rare earths from monazite” , Chem. Engng. Prog., 50 5 (1954) 235.

[23] VOZNESENSKY, S. A. et al., “ Decontamination of dilute low-activity effluents from radiochemical industries” , Proc. 2nd UN Int. Conf. PUAE 18 (1958) 123.

[24] BOLSHAKOV, K. A. et al., “Pilot plant for decontaminating liquid laboratory wastes” , Proc. 2nd UN Int. Conf. PUAE, 18 (1958) 127.

[25] TSIVOGLOU, E. C. et al., “Waste characteristics for the Resin-in-PuIp Uranium Extraction Process” , Proc. 2nd UN Int. Conf. PUAE 18 (1958) 174.

Appendix I

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Appendix II

D A T A ON M A X I M U M P E R M I S S I B L E C O N C E N T R A T I O N S

Those responsible for estimating permissible rates of discharge in connection with a waste-disposal system require reliable numerical data on permissible levels of radiation and permissible uptake of radioisotopes in man.

Subject to the concurrence of the responsible authority in each case, the published recommendations of the ICRP provide the best available guide. In carrying out calculations to serve as a control on waste disposal, the official publications of the ICRP should be consulted [1,2]. An abstract of some of the recommendations most pertinent to problems of radioactive waste disposal into the sea are given below. It should be noted, as shown in Chapter IV, that the average annual dose of radiation which may be received by individuals in a special group forming a stated proportion of the population may be limited by the resulting genetic exposure of the whole population.

Maximum permissible concentrations in water and air

The ICRP Report on Permissible Dose to Internal Radiation, Table I, shows the maximum permissible concentrations (m pc) in water and air for individual radionuclides. These concentrations are given for a 40-hr week and also for a 168-hr week (i. e. continuous exposure). For occupational exposure a man is assumed to work for 5 days per week, 50 weeks per year, and to have a working life-time of 50 years. The calculations are based on a “ standard man” (defined in the ICRP report) who consumes 1100 cm3 of water during an 8-hr working day and 1100 cm3 during the remainder of the day. This includes the water contained in food, which is assumed to be equally contaminated with the drinking water. The standard man breathes 10" cm3 of air during an 8-hr working day and 107 cm3 during the remainder of the day.

O c c u p a t i o n a l e x p o s u r e . The m pcs for air and water given by the ICRP are primarily intended for application to persons occupationally exposed to radiation. The concentrations to be used for control purposes (underlined in the above-mentioned ICRP Table) are calculated to ensure that the dose of radiation to the tissues resulting from the continued intake of contaminated air or water over a long period shall not exceed the values given for occupational exposure. If there is external radiation to

85


the organ the m pcs must be reduced by the factor (D-E)/D, where E is the external radiation in rem/yr and D is the annual maximum permissible dose (m pd) in rem. For an intake of a mixture of radionuclides, calculations are made which are dealt with below.

E x p o s u r e o f in d iv id u a ls in s p e c ia l g r o u p s . The special groups B (a) and B (b) consist of non-radiation workers who work near to, or occasionally enter, a controlled area in the course of their duties. If such a worker receives no external radiation during working hours, the m pc in air or water of a nuclide that will deliver a dose of radiation to the gonads or blood-forming organs shall be 3/10 of the occupational value for the 40-hr week. For group B (c), consisting of members of the public who live in the vicinity of a controlled area, the m pc in similar circumstances shall be 1/10 of the occupational value for the 168-hr week. If external irradiation does occur as a result of operations in the controlled area, these values are reduced by the factor (D-E)/D, where E = annual dose in rem from external sources and D = 1.5 for groups B (a) and B (b) and0.5 for group B (c). If there is no significant irradiation of the gonads or blood-forming organs, the m pc for groups B (a) and B (b ) shall be 1/10 of the m pc value for occupational exposure of an individual with the same work period per week. The m pc for group B (c) shall be 1/10 of the occupational m pc for the 168-hr week.

E x p o s u r e o f t h e g e n e r a l p o p u la t io n . The m pc for the individual member of the general population is 1/10 of the occupational m pc for the 168-hr week. It is tentatively recommended that 1/100 of the occupational m pc for continuous exposure based on the total body should be used as the average m pc for a general population. This would not lead to a greater genetic dose than 1.5 rem in 30 yr. If neither total body nor gonads is the critical organ, the m pc is 1/30 of the occupational m pc for continuous exposure.

M ax im u m p e r m is s ib le d a i l y in t a k e . The water intake of the standard man is 2200 cm:,/d. The maximum permissible concentration of radionuclides in water (m pc,,;) has been defined above for continuous intake. For practical purposes the maximum permissible daily intake (|ic) of a nuclide by mouth is taken to be 2200 X mpc,,- provided that there is no other source of radiation.

Mixtures of radionuclides

Contamination of air and water will usually be in the form of mixtures of radionuclides. Each nuclide contributes part of the permissible dose

Appendix II

86


Appendix II

to any organ. To determine whether the total radioactive material in the mixture is within permissible limits, the individual concentrations must be known and calculations must be made to estimate the fraction of the permissible dose that is contributed by each nuclide. This requires considerable analytical work which cannot be done easily or quickly. For this reason the ICRP has drawn up Tables of Maximum Permissible Concentrations of Unidentified Radionuclides (m p cu ) for air and water (Tables III and IV of the Report of Committee II, ICRP, on Permissible Dose for Internal Radiation).

If nothing is known about the composition of contamination in water, the m pcu is 10“ 7 l i e /ml for a 168-hr week occupational exposure. If Ra220 and Ra228 are not present in significant amounts the m pcu is 10_6[xc/ml. Absence of Sr90, Pb210, Ra220 and Ra228 make 6 X 10-6 |xc/ml permissible, and so on. Thus, if the contamination of certain dangerous radionuclides is known to be small compared with their m pc values, these Tables give a rapid means of determining the minimum m pc of the mixture.

If the radionuclides in the mixture have a high m pc, the m pcu values are likely to be too restrictive. In this case, or if the m pcu value is near to that observed in the environment, it may be necessary to carry out a radiochemical analysis of the mixture and calculate the actual dose of radiation delivered to the individual organs and to the whole body by all its constituent organs. The general principle of this calculation is as follows:

For each organ likely to be affected by the components of a mixture, the fraction of the m pc contributed by each nuclide is obtained by dividing the concentration in the air (or water) by the appropriate m pc. The fraction of the m pc contributed by external radiation is added to the sum of the fractions contributed by the nuclides. The total must not exceed unity. This calculation must also be done for total body, since irradiation of several organs may be equivalent to total-body irradiation. For details of the necessary calculations the reader is referred to the Report of the ICRP Committee on Permissible Dose for Internal Radiation.


Report of Commission, Pergamon Press (1959).[2] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION,


87


C H E M I C A L P R O P E R T I E S OF S E A - W A T E R A N D R E S U L T A N T G E O C H E M I C A L P R O C E S S E S

Appendix III

T a b l e ISUMMARY OF REPO RTED VALUES FOR T H E ELEM EN TA L

CO NSTITUENTS OF SEA-WATER [1]

Element -Representative value (mg/1)* Element Representative value

(m g/1)*

H 108 0 0 0 . K r 0.0003He 0.000005 R b 0 .1 2Li 0 .2 Sr 8 .Be Y 0.0003B 4.8 ZrC 28. NbN 0.5 Mo 0 .0 10 857 000. ToF 1.3 R uS e 0.0003 R hNa 10 500. PdMg 1 300. A g 0.0003Al 0 . 0 1 Cd 0.000055Si 3. In < 0 .0 2P 0.07 Sn 0.003S 900. Sb < 0.0005c\ 19 000. TeA 0 .6 I 0.05K 380. X eCa 400. Cs 0.0005Sc 0.00004 Ba 0.0062Ti 0 .0 0 1 La 0.0003V 0 .0 0 2 Ce 0.0004Cr 0.00005 Pi-Mn 0 .0 0 2 NdFe 0 .0 1 SmGo 0.0005 EuNi 0.0005 GdCu 0.003 TbZn 0 .0 1 DyGa 0.0005 HoGe 0 .0 0 0 1 ErAs 0.003 TniSe 0.004 Y bBr 65. Lu

(K r u m h o lz , G o ld b e r g a n d B oroughs . )N ote: T h e content o f certain elem ents varies tw o orders o f m agnitude or m ore. F or exam ple,

the iron content o f Japanese coastal waters.

8 8


T a b l e I ( c o n t d . )

Appendix III

Element Representative value (m g/l)* Element Representative value

(m g/l)*

H f Bi 0 .0 0 0 2Ta PoW 0.0001 AtR e Eli 9.0 X 10-15Os FrIr R a 3.0 X 10“ nPt AcAu 0.000004 Th 0.0007H g 0.00003 Pa 0.003T1 < 0.00001 UPb 0.003

* ( K r u m h o l z , Goldberg, a n d Boroughs . )

T a b l e IICONCENTRATION OF THE MAJOR CONSTITUENTS OF SEA-WATER

OF STANDARD CHLORINITY

Ion Content (g/kg o f water o f 19°/00 chlorinity)

c i - - 18.97Na+ 10.55so 4— 2.65Mg++ 1.27Ca++ 0.40K+ 0.38h c o 3- 0.14Br 0.065H 3B O 3 0.026Sr++ 0.013

T a b l e IIITHE NORMAL RANGE OF CONCENTRATION FOR DISSOLVED GASES

IN SEA-WATER

Elem ent Content (ml/1)

OxygenNitrogenTotal carbon dioxide ArgonHelium and Neon

0 - 1 0 8 - 1 5

3 0 -6 0 0.2—0.4

1.2 X 10~4 — 1.8 X 10- 4

89


Appendix III

T ab le I V

NATURAL RADIOACTIVITY IN THE SEA [2]

NuclideConcen-tration(g/ml)

Specific activity

(d/sec ml)

Total amount

in oceans (Mt)

Total activity in ocean

(Me)

Potassium-40 4.5 X 10“ 8 1.2 X 10- 2 63 000 460 000Rubidium -87 8.4 X 10-* 2 .2 x 1 0 ~ 4 118 0 0 0 8 400Uranium-238 2.0 X 10“ 9 1 x 1 0 ' 4* 2 800 3 800Uranium-235 1.5 X 10" 11 3 X 1 0 '6* 21 1 1 0Thorium -232 1 0 - 11 2 x 1 0 ' 7 * 14 8Radium-226 3 X 10~ 18 3 x lO "5* 4.2 x 10-“ 1 1 0 0(Carbon-14) 4 x 10“ 17 7 X 10' 6 5.6 x 10~ 5 270(Tritium )** 8 X 10- 20 2.5 X 10' 5 1.5 X 10-» 12

* Activity of nuclide and daughter products. ** Only in top 50—100 m of the ocean.

T able V

SOME EXPERIMENTAL DATA ON THE PHYSICOCHEMICAL STATE OF FISSION PRODUCTS IN SEA-WATER [3]

Element Ionic(% )

Colloidal(% )

Particulate(% )

Cs 70 7 23I 90 8 2Sr 87 3 10Sb 73 15 12Te 45 43 1 2Mo 30 10 60R u 0 5 95Ce 2 4 94Zr 1 3 96Y 0 4 96Nb 0 0 10 0

It should be noted that the distribution between the different states has reference only to a specific laboratory experiment [3]. However, this may serve as a rough guide on the equilibrium state of dispersed fission products in general.

90


Appendix III

T a b l e VIRESIDENCE TIME OF SOME ELEMENTS IN THE OCEAN [4]

(Goldberg and Arrhenius, 1958)

Element Am ount in Oceans (g)

Residence-time<yr)

Na 1.47 X 1 0 “ 2 .6 X 1 0 sMg 1 .8 X 1 0 21 4.5 X 1 0 7Li 2 .S X 1 0 17 2 .2 X 1 0 7Sr 9.8 X 1 0 18 1 .6 X 1 0 7K 5.3 X 1020 1 .1 X 1 0 7Ca 5.6 X 1 0 20 8 .0 X 1 0 “U 5.2 X 1 0 15 6.5 X 1 0 5Zn 1.4 X 1 0 1S 1 .8 X 1 0 5Cu 5.2 X 1 0 16 6.5 X 1 0 4Co 7.0 X 1 0 14 1 .8 X 1 0 4Si 5.2 X 1 0 18 1 .0 X 1 0 *Mn 1.4 X 1 0 ^ 7.0 X 1 0 3Fe 1.4 X 1 0 u 1.4 X 1 0 2Ti 1.4 X 1 0 15 1 .6 X I 0 2Al 1.4 X 1 0 1C 1 .0 X 1 0 2

The residence time in years of an element is given by the equation T — As/(dA/cU), where A5 is the total amount of the element in suspension or solution in the oceans and dA/dt is the rate of contamination. The values given by Goldberg and Arrhenius are shown in this Table.

R E F E R E N C E S[1] KRUMHOLZ, L. A , GOLDBERG, E. D. and BOROUGHS, H., “Ecological

factors involved in the uptake, accumulation and loss of radionuclides by aquatic organisms” , Nat. Acad. Sci. Wash., Publ. No. 551 (1957) 69—79.

[2] REVELLE, R. R., FOLSOM, T. R„ GOLDBERG, E. D. and ISAACS, J. D., “ Nuclear Science and Oceanography” , Proc. UN Int. Conf. PUAE, 13 (1955) 371.

[3] GREENDALE, A. E. and BALLOU, N. E„ United States National Radiological Defence Laboratory, Document 463 (1954) 1228.

[4] GOLDBERG, E. D and ARRHENIUS, G. O. S., “ Chemistry of Pacific pelagic sediments” , Geochim. et cosmoch. Acta, 13 (1958) 153— 212.

91


Appendix IV

Representative data on marine biology, useful in evaluating uptake and food-chain relationships, is given in the following Tables:

Table I gives some average assimilation rates and food coefficients. The food coefficient is the fraction of the food consumed which is converted into tissue.

Table II gives figures on concentrations of phytoplankton and zooplankton in various parts of the sea and at different seasons.

Table III gives the fractional turnover rates for selected groups of marine biota. It is given as the ratio of the yearly production to the average standing crop.

Table IV gives estimates based on a variety of sources for the content of various elements in the selected biota and also resultant estimates of concentration factors. However, it should be remembered that a wide range of highly specific concentration factors can occur.

T a b l e ISOME AVERAGE ASSIMILATION RATES AND FOOD COEFFICIENTS

M A R I N E B I O L O G I C A L D A T A

Assimilated food converted to tissue

<%)

Foodcoefficients

Zooplankton 70 0.05Benthos (average) 30 0 .1

Herbivores benthos 25Carnivores benthos 50

Fish (average) 10 0 .1Plaice 6Carp 40

T a b l e I I

QUANTITATIVE RELATION BETWEEN PHYTOPLANKTON AND ZOOPLANKTON

Locality TimeBiomass

phyto-plankton

(m g/m 3)zoo

plankton

R atio o f phytoplankton to zooplankton

A ctic Seas W inter 410 52 8 1Spring 2410 1 2 2 2 0 [ 1 ]Summer 560 230 2.5 I

Barents Sea Late Spring 5 0 0 -6 0 0 140 4 [1, 2]SW North Sea February-March 27 241 0.1 [3]Off Plymouth Yearly average 1 2 0 60 2 [4]


Appendix IV

T a b l e III

SOME FRACTIONAL TURNOVER RATES OF MARINE ANIMAL GROUPS Total annual production (average standing crop)

Phytoplankton 10— 100 (about 30% daily)Zooplankton 2 - 30Benthos 1 - 3Fish about 1 (varies considerably from stock to stock)

T a b l e IV

AVERAGE CONTENT OF SOME ELEMENTS IN MARINE BIOSPHERE (mg/g of biomass) AND THE CONCENTRATION RATIOS ’

Element Marinealgae

P h ytoplankton

Z oo plankton Fish

Orders o f magnitude o f concentration ratios* (the

most com m on values are in italics)

(Watercontent) (80% ) (90% ) (80% ) (75%,)

Nitrogen 5 4.3 2 0 30 50 000 to 300 000Sodium 10 3 1 0 .1 to IPotassium s 3 o 1 0 to 2 0Caesium 5 x 10“ G 2 x 1 0 - 5 2 x 1 0 “ 5 1 to 10Calcium 4 1 ( ? ) 0.4 1 to 10Strontium 0.15 0.07 0.007 1 to 2 0Magnesium 0.4 0.3 0.3Phosphorus 2.5 ( ? ) 0.55 1 .6 1 .8 10 0 0 0 to 1 0 0 0 0 0Sulphur 4 2 4Iron 0 .1 0 .1 0.05 0 .0 1 1 0 0 0 to 10 000Nickel 0 .001 0.001 0 .0 0 0 2 100 to 500Cobalt 2 0 0 to 10 0 0 0Copper 0.005 ( ?) 0.006 0 .0 1 1 000 to 5 000Zinc 0 .01 ( ?) 0 .1 0.025 1 0 0 0 to 20 000Radium 2 x lO ' 11 l x l O - 1- 1 x 10-1- 1 to 1 0 0Cadmium 0.0006 1 0 0 0 0Iodine 0 . 0 1 - 1 0 .0 0 2 0.00015 3 to 20 000Manganese 0 .0 0 2 -0 .4 0 .0001 0 .0 0 2 25 to 10 000Aluminium 0 .0 1 2 0Titanium 0 .0 0 1 1 0 0

* Amount present in a unit weight of the biomass divided by the amount present in a unit weight of sea-water.

1 Broad estimates from various sources.

93


Appendix IV

R E F E R E N C E S

[1] ZONKIVITCH, L. A., “ Fauna and biological productivity of the seas” (in Russian), Sovetsk. Nauka, Leningrad, I— II (1947, 1949).

[2] JASHNOV, W. F., “ Plankton productivity of the southwestern part of Barents Sea” , Trans. Inst. Mar. Fish., USSR, 4 (1959).

[3] KREY, J. “Plankton und Sestonuntersuchungen in der siidwestlichen Nord- see auf der Fahrt der ,Gaul3‘, Februar-Marz 1951” , Ber. deutsch Komm., Meeresforsch., 8 2 (1953) 136— 153.

[4] HARVEY, H. W., “ On the production of living matter in the sea off Plymouth” , J. Mar. biol. Ass., 29 (1950) 97— 137.

94


Appendix V

MONI TORI NG, SAMPLING AND A N A L Y T I C A L T E C H N I Q U E

Sampling for radiation monitoringS e a - w a t e r

It is desirable that all background and routine monitoring include chlorinity determination. Systematic determination should be made at a grid of fixed stations with chlorinity and temperature being determined at various depths. From such measurements conclusions can be drawn on the stability, mixing and movement of water masses. Collection of seawater and its analyses is described in various publications [1 ],

B o t t o m m a t e r ia l

The nature of bottom substrata in the disposal area is usually found, using short gravity corers. If more than one kind of sediment is found close to the disposal site, the different types of sediment should be monitored separately. The surface layer of the sediment (2-cm thick) should be used for radiochemical analyses. Corers are unsuitable for the sampling of the sediment surface. In soft bottoms, Mortimer’s mud-and- water sampler could be used for this purpose. For sampling harder bottoms spring-loaded snappers are useful.

P l a n k t o n a n d o t h e r s u s p e n d e d m a t t e r

There are practical difficulties in separately sampling suspended matter and phyto- and zooplankton. A partial separation of inert suspended matter and plankton is achieved by two parallel samples: one with a millipore filter and the other with a fine quantitative plankton net.

A technique for sampling suspended matter (and part of the plankton) follows:

Millipore 'filters are “conditioned” to constant weight in a vacuum desiccator containing a H2SO4 solution of such concentration as to give a vapour pressure of 60°/o saturation at 20 °C. The filters are then weighed and kept in numbered Petri dishes; 0.5— 2 liters of water to be sampled is filtered with suction through the filter. The filter, and the material on it is “ conditioned” again in the same vacuum desiccator for at least 24 hr, and weighed. The difference in weight gives the amount of suspended matter on the filter. The filters are used to measure the gross activity of retained suspended matter.

For special measurements of radioactive isotopes in phytoplankton,

95


greater quantities of plankton are needed, and should therefore be sampled with a Clarke Bumpus sampler fitted with a No. 20 net. The concentration per cubic meter of water should be computed. The collected plankton should be measured by displacement volume, filtered and dried. Normal preservation of plankton with formalin is not desirable because part of the radioactive isotopes, contained in the plankton, can be lost in the preserving solution.

S e a w e e d s

Seaweeds should be collected with a commercial seaweed dredge from localities where they are, or might be, harvested. As there are differences in activity in different parts of the seaweed (e. g. fronds and tops of leaves), these differences should be determined.

F ish

Fish should be collected by experimental gear close to the disposal site, or in packaged-waste-disposal areas. Fish caught at a greater distance from the disposal site can be collected from commercial catches. Special attention should be given to (a) less migratory demersal fish close to the disposal site; and (b) plankton feeders which might have been feeding in, or close to, the disposal area.

M o l l u s c s

Shellfish should be collected with a dredge in the vicinity of the disposal site. Both small and mature specimens of molluscs should be measured, as the smaller ones grow rapidly, and the accumulation of radioactive isotopes in them might be different from that in the full-grown adult.

C r u s t a c e a n s

Crustaceans can be caught with traps (lobster) and with dredges (shrimp). Catches should be made in the immediate vicinity of the disposal sites, and also in deeper and shallower water, according to the expected migrations.

Cross counting of activity in marine samples

S e a -w a t e r

Although the sea-water contains various radioactive elements, the level of activity is so low that only the activity of radioactive potassium (K40)

Appendix V

9 6


Appendix V

is detected by ordinary counting techniques. The use of extremely large samples and special low-level counting techniques would make it possible to detect the activities of other radionuclides. Normal sea-water contains 3.8 X 10~4 g K/ml giving 29 beta rays and 3 gamma rays per second per gram K.

If radioactive contamination of sea-water arises, however, normal counting techniques can be used effectively. Underwater gamma counting could detect gross gamma contamination quickly. Beta counting of samples is better for detecting trace activities. The scavenging of sea-water is very effective to measure trace activities. The addition of scavengers, such as iron plus barium, or yttrium, and the subsequent precipitation of mixed ferric hydroxide and barium sulphate or yttrium oxalate, can remove most of the active elements from contaminated water. By this means the radioactive nuclides in water are concentrated in small amounts of precipitate. If necessary, radiochemical analysis of individual nuclides can then be made by standard methods.

S e a -b o t t o m m a t e r ia l s

The gross alpha, beta and gamma counts are made on dried sea-bottom samples. The solution obtained by acid-leaching of the samples can also be subject to counting. The activity of the shallow-sea sediments is generally low, and is comparable with ordinary sedimentary rocks. It is recommended that the sediment be separated according to particle size and each fraction counted. Some long-lived isotopes tend to be concentrated in the sediments. It is advisable to analyse for such isotopes in the bottom materials at appropriate intervals, at least once a year.

P l a n k t o n

The gross alpha, beta and gamma counts are made on dried or ashed samples. The ashing should be carried out at low temparatures to avoid the loss of volatile compounds.

S e a w e e d sa m pl e s

The gross alpha, beta and gamma counts can be made on dried or ashed samples. The ashing should be done at temperatures below 600 °C. The seaweed contains considerable amounts of potassium and the amount of K40 in various seaweeds should be carefully determined on non-contaminated samples in a background survey.

The analysis for radioiodine in seaweed is important if there is any

7 97


possibility of contamination of sea-water with active wastes containing radioiodine. Consideration must be given to the short half-lives of iodine isotopes. Edible products and chemicals prepared from seaweed must also be checked for gross activity.

F is h , c r u st a c e o u s f a u n a a n d s h e l l f is h sa m p l e s

The gross alpha, beta and gamma counts can be made on dried or ashed samples. If the size of samples is large enough, similar counts are made on selected tissues, such as skin, eyes, visceral organs, gills, muscle and skeleton. In the case of crustaceous fauna and shellfish, flesh and shell are counted separately. Special attention should be given to the bones of smaller fish, which might be consumed by humans, in which the strontium content should be measured. Both small and mature specimens of shellfish should be measured, as the smaller ones grow rapidly and the accumulation of radioactive isotopes in them might be different from that in the full-grown adult.

Radiochemical analysis for isotopes of major interestThe complete radiochemical analysis of individual isotopes in the marine

samples is difficult and time-consuming. It is usually sufficient to analyse for selected isotopes which are important in evaluating the level of radioactive contamination in the marine environment. For the present purpose, the isotopes of greatest importance are Sr90, Cs137, Ru106, Co60, Zn65, Feoi), Ce144, I131 and Pu238.

There is a variety of methods available for the analysis for these isotopes. With a homogeneous solution containing these isotopes, ordinary radiochemical separation procedures can be applied. However, pretreatment of the marine samples is needed before radiochemical separations can begin.

The details of such pretreatment and separation procedures are available in the literature [2, 3, 4, 5, 6].

R E F E R E N C E S

[1] U. S. NAVY HYDROGRAPHIC OFFICE, Instruction manual for oceanographic observations, H. O. Publ. No. 607 (1956).

[2] FOOD AND AGRICULTURE ORGANIZATION AND W ORLD HEALTH ORGANIZATION (OF THE UNITED NATIONS), “ Methods of Radiochemical Analysis” , FAO Atomic Energy Series No. 1 (1959).

Appendix V

98


Appendix V

[3] WHITNEY I. B., Manual of Standard Procedures, Analytical Branch, HASL, United States Atomic Energy Commission, NYO-4700.

[4] KOOI, J., “ Quantitative determination of Sr-90 and Sr-89 in water” , Anal. Chem., 30 (1958) 532.

[5] BARRACLOUGH, J., The determination of radio-ruthenium in sea-weed ash, IGO-AM/W-70 (1958).

[6] KHAN, B., SMITH, D. R. and STRAUB, C. P., “ Determination of low concentrations of radioactive cesium in water” , Anal. Chem., 29 (1957) 1210.

99


M I X I N G A N D E X C H A N G E P R O C E S S E S

A general account of the physical dispersive processes which would affect wastes released into the sea is not readily available. A review of the theories developed in connection with mixing and exchange processes in the sea has been provided by J. C. S c h o n f e l d and P. G r o e n and is reproduced here as Appendix VI. The theoretical approaches are developed to the stage of providing guidance in making numerical calculations. Application is made to several practical examples.

Appendix VI

1. Introduction.2. Sectional treatment.2.1. Introduction.2.1.1. Transient state, steady state.2.1.2. Closed systems and open systems.2.2. Closed system.2.2.1. Simplest case: the whole system one “ section” .2.2.2. Two sections.2.2.3. General case.2.3. Open system.2.4. The parameters.3. Continuous treatment.3.1. Introduction.3.1.1. Necessity for a statistical approach.3.1.2. Autonomous and non-autonomous turbulence.3.1.3. The problems of scale.3.2. Mathematical formulation of the diffusion problem.3.2.1. Basic equations.3.2.2. Boundary conditions.3.3. Micro-scale diffusion.3.4. The differential diffusion concept.3.4.1. Application of the similarity principle.3.4.1.1. The exponential distribution.3.4.1.2. The error-function distribution.3.4.1.3. The superposable distribution.3.5. The neighbour diffusion concept.3.6. The integral diffusion concept.3.6.1. Solution by Fourier transformation.3.6.2. Some special solutions.3.6.2.1. Incidental point release in a resting medium.3.6.2.2. Continuous release in uniform flow.

Examples of application:Continuous point release in a bayMixing in an estuary ...................................Continuous point release in coastal waters Incidental point release in deep ocean

(sectional treatment) (sectional treatment) (continuous treatment) (continuous treatment).

100


Appendix VI

The water in the sea is practically always in motion; hence mixing and exchange processes are going on continuously. The stirring motions range from the Brownian movement of the molecules, through all kinds of turbulent eddies, to the large-scale circulations associated with the major current system of the oceans.

If an effluent is brought into the sea, it will at first form a small cloud, which will start to diffuse under the action of small-scale motions, such as: the turbulence engendered by its own introduction into the environment and thereafter (in particular in coastal waters) the flow turbulence of currents of tidal or other origin, provoked by the bottom friction.

After the cloud has started to spread out by the action of these processes, swirling and eddying motions of a larger scale begin to exert their influence. In general, a pattern of motion of certain dimensions will not affect a cloud of much smaller size, except by moving it about as a whole. However, as soon as the cloud assumes a magnitude comparable to the pattern of motion itself, it is liable to be divided into several parts, each of which will again grow in size and be subject to a similar process. At the same time the diffusion patterns of smaller scale will tend to mix the separate parts of the original cloud with the surrounding water which is not yet, or is to a lesser degree, contaminated.

The rate of diffusion is in first approximation proportional to the concentration gradient of the property considered, which may be physical (e. g. heat) or chemical (solution). In molecular diffusion the rate of proportionality — or diffusivity — is a constant, determined by the physical and chemical characteristics of the medium and of the property (elements) concerned. The concept of constant diffusivity may also be used in such cases where mixing is provoked predominantly by eddies of small dimensions as compared to the size of the cloud. Such a limitation to the scale of the eddies may be present, for instance, in currents in shallow water, where the depth sets a limit to the vertical development of eddies, and the bottom friction to the horizontal development. In such cases we are confronted with micro-scale diffusion (sect. 3.3.). Although in this case the diffusivity is independent of the distribution of the property, it is not necessarily constant in time nor the same at every spot, or in every direction; it may be inhomogeneous and anisotropic.

When larger scale patterns cannot be disregarded, we must take into account an increase of the diffusivity with the length scale, that is to say, with the distance between moving elements, or with the size of the cloud

1. Introduction

101


under consideration. It should be borne in mind that in this line of thought the “local” concentration has to be taken as a statistical average, or as an average in a volume related to the scale of the diffusion pattern. Mixing processes of this type are classed as macro-scale diffusion (sect. 3.1.3.).

In what precise manner the diffusivity is a function of the length scale is at present still a matter of conjecture. Several authors, basing themselves on recent developments in fundamental studies of turbulence, arrive at a diffusivity proportional to the 4/3 power of a length parameter. Others (sect. 3.1.3.), have postulated a linear relationship, and they present observational data which appear to be in satisfactory agreement with their theoretical findings. Quite possibly, different relationships are valid for different mechanisms of generation of the diffusion-eddy-field. In sect. 3.6. also, a more general formulation of the relationships involved is presented.

Whatever the type of relationship the diffusivity follows (constant, linear, or otherwise scale-dependent), the mathematical treatment consists of establishing a differential equation, or a set of such equations, based on the transport of contaminant. A solution of these equations, either analytical or numerical, must then be sought in combination with the boundary conditions prevailing.

This type of treatment deals with physical processes acting continuously in space and time throughout the region under consideration, and also with gradual variations in concentration. This will here be called the ‘continuous’ treatment, which can be applied only in the absence of abrupt changes, either in the nature of the processes or in the concentrations. If these occur a different, and in a sense, simpler treatment is indicated. This is the case if the environment consists of a number of interconnected cells, sections or compartments, in each of which the distribution of contaminant is homogeneous and between which there is an abrupt variation in concentration. At the transition from one compartment to the next there is, in addition to the convection, an exchange of contaminant, the quantity of which is determined by the product of the difference in concentration, and an exchange factor which may either be a constant, or a function of some parameter derived from the hydrodynamic conditions. This will here be called the ‘sectional’ treatment.

This treatment mathematically takes the form of a set of equations, each derived from the conservancy of contaminant in a section, which are linked by the exchange conditions between the sections. In simple cases (few sections) they can usually be solved without great difficulty;

Appendix VI

102


Appendix VI

in complicated systems they can be adapted to processing in a digital, or analogue, computer.

The application of the sectional treatment is not restricted to such cases where the cells are delimited more or less naturally, as in the case of a chain of bays or lagoons with relatively narrow connecting passages, or the different layers in a vertically-stratified medium, but it can also be applied to a continuous system like an estuary, which is then, for the application of the method, divided into a number of relatively short sections. As the size of the separate sections decreases, the model approaches to the continuous model in the limit of infinitesimally small sections.

Although in principle the sectional treatment might be applied to any diffusion problem, it is most advantageously used in cases where the physical conditions naturally suggest a division into suitable compartments, or where an adequate model by a relatively small number of sections can be obtained.

Other cases will require too fine a mesh of cells for convenience and the continuous treatment is more advantageous. This applies, for instance, to a pipeline release in coastal waters, unconfined except by the shore, and to release in the deep ocean, as long as stratification does not enter into the problem.

In some cases a combination of the two methods may be required. Such a case is encountered, for instance, with a release into an embayment, or otherwise partly-confined body of water, having restricted communication with the open sea. Here the diffusion within the embayment itself (supposing that its size and hydrodynamic conditions do not warrant the assumption of homogeneous distribution) is of the continuous type. Moreover, there is an exchange with the open sea through the mouth of the bay, which has to be dealt with by the sectional treatment (two-section system). Another example occurs where difference in density as a result of salinity or temperature difference gives rise to stratification into two or more layers. In the transition zones between these layers turbulence, and hence, mixing, is impeded. Here, within each separate layer, diffusion of the continuous type will be active, while the interaction between the layers is subject to sectional treatment.

103


2. Sectional treatment2.1. I n t r o d u c t i o n

2.1.1. Transient state, steady stateThe main problem is to find, for any given sea area, the steady-

state distribution of concentration of the substance Q under consideration, since the underlying, problem is a problem of safety and since, with stationary sources, the final steady-state will have the highest concentrations.

2.1.2. Closed systems and open systems

The body of water considered may be, oceanographically, a “ closed” system or an “open” system. By “closed” , we mean that the system has no communication with sea regions outside it, for example, the whole- world ocean. “Closed” does not mean that there is no inflow from rivers or no evaporation. An “open” system does have such communication(s) as, for example, a marginal sea or an estuary. To treat the problem of an “open” system it is necessary to have some boundary conditions valid along those boundaries where the system is open, e. g. a given concentration of the substance Q along such a boundary.

2.2. C l o s e d system

Let the system be subdivided into n sections, each of which is treated as a whole. The sections are numbered 1, 2 . . . k, . . . n.

The mass of Q within a section will be called qu, the mean concentration is pa- — piJVh; where V/,- is the volume of section k. Changes of p and q may be brought about by the following processes:

1. Input from a source. The rate of discharge into section k will be called jk.

2. Transport to (from) section k from (to) an adjoining section k' by a regular unidirectional current. The rate of transport (positive if from k' to k) will be called

3. Transfer from (to) an adjoining section k' by mutual exchange (eddy exchange). The rate of transfer by this process is called iwk-

4. Decay causes a loss of Q. The rate of loss by decay in section k is -4- = qkh, where r is the characteristic decay time of the substance Q (half-life time = 1 n X r). Any loss by sedimentation is supposed to be included in »*.

Appendix VI

104


Thus, for the rate of change or qu we have the follow ing equation:

" — S ik'k + 2 ik’ k — g_kh + ik- (1)

For the steady state w e have

S Vfc + 2 ik’ k ~ Qklt + jk = 0- (2)k ' k '

2.2.1. Simplest case: the whole system one “ section”

In this case there are no transport and exchange to be considered and equations (1) and (2) becom e simply:

= j k — qkjr (transient state), (3)

U — Qkh = 0 or qk = j h r, p k = j k t I V k (steady state). (4)

Thus, in the steady state, the total mass o f a radioactive substance present in the w hole w orld ocean, or in an isolated basin, is r times the rate of discharge.

2.2.2. Tw o sections

Between two sections, 1 and 2, there will be an exchange o f Q at a rate proportional to the difference o f the mean concentrations p i and p->, so that w e have:

*12 = -&12 (Pi — Pi), (5)?2X = *12 = -®12 (Pi P i ), (6)

where Ey-> ( = £ 21) is a factor of proportionality w hich may b e called the exchange factor. It is only dependent on general oceanographic factors.

If an average net transport o f water from one section to the other is present (this is only possible if the first one has a surplus of precipitation, plus runoff, over evaporation) w e have a transport of matter 712 proportional to the volum e transport Si2 from section 1 to section 2 and w e may write

j 12 “ $ 1 2 Pli, (7)where P12 is a concentration lying somewhere between p\ and p2. Writing

P 12 = Pi + £1 2 (Pi — Pi) = (1 — £is) Pi + h i Pi (0 < £ia < 1), (8)we have

/1 2 ~ ^ 1 2 (1 £12) Pi £12 Pi* (9)?21 = ~ jli , (10)

Appendix VI

105


so that the com plete equations are as follow s:

Gi = {p2 ~ Pi) _ 512 [(1 _ + 5i2 pi] ~ - ^ r ~ + ji ’ (11)

G2 “ (Tr = Ei°- Pi ~ p^ + Si2 ^ i2 Pi + ^ ~ ^ p^ ~ + ?'2-The equations for the steady state are obtained by putting the left-

hand members of (11, 12) equal to zero. If, moreover, S12 vanishes, we have

— (E,2 + F j/t) Pi + E u p 2 + ^ = 0 (13)-£’12 Pi — (-Eis + F 2/t) p 2 + 7, = 0, (14)

the solution of which is:

v - jl + . T (15)Pl + F 2~1^ 12r ( F 1 + F 2) T’ ( 5)

v ~ j2 + F»~1-E» T ^ + *'■> . T (1C)Pi F 2 + F i-1 E 12 r (Fj. + F 2) T- ( 0)

An example of this case is the system o f the world ocean as com posedof a mixed upper layer and the deep lower layer, separated by the mainthermocline. This m odel has been successfully used for studying the distribution o f radiocarbon in the ocean (the whole m odel has three sections in this case since the atmosphere is also part o f it).

2.2.3. General case

T he formulae for the general case can now be easily written down. First w e establish the follow ing relations (which are analogous to equations(5), (6), (9), (10)):

The rate of transfer k' to k by exchange is

H'k = Ek’kiPt' ~ Ph), (17)Ek'k = Ekk' being the exchange, factor betw een sections k and k'; the rate o f transfer by unidirectional transport from k' to k is

1k' k = ^k' k [5fc' k Pk' + (I ~ ?jfc’ k) Pfc]> (1®)Sk'k = —Skk' being the volume transport from k' to k, whereas, since ik'k = —jnk', w e can write

0 < lkk- = 1 - U ’k < 1 - (19)

By substitution in equations (1) and (2) we now obtain the follow ing sets of equations:

Appendix VI

106


Appendix VI

V k — Sfc' -®*!' k (Pk‘ ~ Pk) +

+ S-sV * K ii'tP t ' + (! — 5*-*)p*] — VkPkh + h:>(20)

( 2 1 )

(steady state)

The sums S are to be taken over all those sections k' w hich communicate k’

with section k.

The above equations are linear and can easily be handled by means of a digital or an analogue computer. (For the latter method, p may be replaced by a potential, q by a charge, i and j by electric currents, V by a capacity, 1 /Ewu and l/S/,-7,- by resistances. The m odel becom es especially simple if all Sk’k are zero.)

2 .3 . O p e n s y s t e m

In an open system one or more sections are connected with sea regions outside the system, where given p-values are supposed to prevail, which put boundary conditions to the system considered. Such an outside region is, e. g. a sea or an ocean which is so large in comparison with our system that it gives, outside the boundary involved, a value of the con centration which is independent o f the p -values inside the adjacent section of our system and w hich thus plays the role o f a boundary value.

If there are m o f such boundary values, w e number them from n + 1 to n + m (n being the number o f sections o f the system) and call them simply pr w ith k' running from n + 1 to n + m. Then w e can formally use the same equations (20) and (21) as before, bearing in mind that now

k runs from 1 to n,

and that the values o f p/,- with k' n are the given boundary values.

A m o d e l s im ila r t o th is o n e ( b u t w i t h o u t r a d i o a c t i v e d e c a y ) h a s b e e n s u c c e s s f u l ly u s e d in e s t u a r y s tu d ie s , a m o n g o t h e r s b y D o r r e s t e i n [4 , 5 ] ,

b u tfc' runs from 1 to n + m,

107


who, moreover, devised a practical technique of com puting solutions of the equations for the non-stationary distribution of concentration, by means o f matrix calculus.

2 .4 . T h e p a r a m e t e r s

The follow ing parameters are supposed to be simply given:r = 1/ln 2) X half-life time of the matter Q considered.■jk = rate o f input o f Q into section k.V * = volum e o f section k.

Pk' {k' > n) = boundary value of concentration p.S/c'k ~ volum e transport towards section k from section k’ or

(;c' > n) across the boundary o f section k with the outside region where pn' is given.

T he follow ing parameters must have been determined either empirically, e. g. from the observed steady-state distribution of some conservative property of the water, or by theoretical calculation follow ing the “ continuous” treatment:

■E/c'ft = exchange factor betw een sections k and k' or across an open boundary o f section k.

I — — mixing ratio of the water at the boundary betweensections k and k' or at an open boundary o f section k.

D o r r e s t e i n [4 ] determined values of £/„■■* for his 13-sections m odel o f the Ems estuary (German-Netherlands border) from an average salinity distribution, whereas he put each £u'k equal to 1/2. This is reproduced in more detail as Example 2.

3. Continuous treatment3.1. I n t r o d u c t i o n

3.1.1. Necessity for a statistical approach

Diffusion in the sea is predom inandy provoked by turbulent stirring motions. In this context we may consider as turbulent motions such variable motions as those w hich are not known in detail, but which are characterized by statistical mean values.

The necessity for introducing this concept follow s from the fact that a good deal of the stirring motions in the sea are only known in a substantially statistical way, like the eddies generated by bottom friction

Appendix VI

108


Appendix VI

or by w ind action. In some cases, however, the statistical approach may also prove applicable to motions, like the tides, known systematically rather than statistically.

H ence we are able to predict the distribution of an effluent brought into the sea in a statistical way only.

If, as a mental experiment, w e release suddenly a definite amount of radioactive matter at a definite site into the ocean, the matter will spread out so that, after a definite time lapse A t, and in a point at a definite distance r from the point o f release, a definite specific radioactivity (concentration) is encountered.

W hen w e repeat this release (the remnants o f the first release are supposed to have been discarded) and determine again the concentration at the same point at distance r, at a time interval £\t after the release, w e shall generally find a somewhat different value, ow ing to the fact that the stirring motions in the ocean have not been exactly the same as in the first experiment.

By repeating the experiment a great number of times, w e arrive at a series o f values for the concentration considered, the average o f which approaches the statistical mean concentration.

A serious handicap to the study o f oceanic turbulence is the severe limitations to repetition o f experiments such as depicted above. Fortunately, it is sometimes possible to substitute more practicable averages for the requisite statistical averages. In the field o f a continuous source, for instance, averages over a long period o f time approach to the statistical average. In other cases, averages over regions o f space may serve.

3.1.2. Autonomous and non-autonomous turbulence

The generation of the stirring motions which are capable of provoking diffusion may be either entirely autonomous, or the distribution o f the diffused property may affect the stirring motions. An example o f the latter situation is the diffusion o f salt in a salt w edge, where the vertical density gradient attending the salinity differences betw een the layers may have a considerable influence upon the developm ent o f the turbulence.

The turbulence is autonomous when the diffused property is irrelevant to the dynamics o f the diffusing medium. W hen the diffused property is not neutral in this sense, the turbulence may, none the less, be treated as autonomous, provided that the concentrations of the diffused property are so low that their influence upon the moving medium is negligible.

109


The present investigation will be confined to the case of autonomous turbulence.

3.1.3. The problems of scaleW hen the stirring motions occur predominantly in patterns o f dimensions

which are small, as com pared with the cloud of matter, the distribution of w hich we are studying, the diffusion in such a cloud can be treated adequately by equations similar to the classical Fickian equation of molecular diffusion. This will here be denoted as micro-scale diffusion.

In many cases, however, eddy diffusion takes place b y stirring motions (eddies) in patterns of w hich the dimensions may no longer b e considered as small com pared with the dimensions of the polluted regions, i. e. macroscale diffusion. Then w e are faced with tw o questions:

First, w e must find an adequate mathematical formulation o f the diffusion transport vector in terms of the distribution o f the concentration.

Second, w e must know the law according to which the diffusive pow er of the eddies varies with their scale, and w e must determine the numerical values o f the parameters involved in this law.

The approach to the first question has been pursued mainly by three conceptions o f the eddy-diffusion mechanism. They will be discussed hereafter in the follow ing order:

A. The differential diffusion concept. T he diffusion transport is then formulated in terms of the gradient o f the local concentration.

B. The neighbour diffusion concept. Instead of the local concentration, its autocorrelation is introduced as “ neighbour concentration” and the diffusion is formulated in terms o f “ neighbour diffusion” ( R i c h a r d s o n [12]).

C. The integral diffusion concept. T he diffusion transport is formulated in terms o f integration of the local concentration ( S c h o n f e l d [14]).

The scaling law has to be adapted to the concept in which it is applied, but the form is much the same in all three concepts and can generally be assumed as functional relations betw een diffusivity parameters and length parameters. As to this relation the follow ing possibilities deserve special attention:

(a) In the ideal case of a hom ogeneous system in which the largest eddies are driven by external causes and the smaller eddies are feeding on the larger eddies, there being a statistical equilibrium between them, the theories of Kolm ogoroff and von W eiszacker-Heisenberg may be applied, leading to the law:

K = constant 14/3

Appendix VI

110


Appendix VI

where K is the diffusivity parameter and I the length parameter. A law of this type has been proposed in meteorology and oceanography by Richardson. Observational evidence has been produced by R ic h a r d s o n , S to m m e l [15,16], I n o u e [6] and O z m id o w [11].

(b) When smaller eddies are not only feeding on larger eddies, but also receiving a more immediate stimulus, the diffusivity will increase more slowly than with the 4/3 power of the length parameter, or decrease with it. S v e r d r u p [18] has forwarded the hypothesis that in a large interval of scales, the diffusivity parameter in the oceans is approximately proportional to the length parameter. J o se p h and S e n d n e r have supported this proposal by observational evidence.

(c) When mainly smaller eddies are stimulated externally, so that eddies larger than, say, L are negligible, and L is small compared to the dimensions of the bulk of the polluted water, the problem can be simplified appreciably (micro-scale turbulence; cf. section 3.3).

There is still a great lack of knowledge of the numerical values of the eddy diffusivity. We must expect, however, that the diffusion is rather widely variable according to the locally and temporarily prevailing conditions, such as the depth, the vertical stability, the tidal currents and the wind.

Therefore an investigation of diffusion in a particular sea region should be based as much as possible upon data collected in that particular region.

3.2. M a t h e m a t i c a l f o r m u l a t i o n o f t h e d i f f u s i o n p r o b le m

3.2.1. Basic equations

• The distribution of a radioactive substance introduced into the sea is defined by diffusion (mainly eddy diffusion), advection and decay. This may be described mathematically by the equation

V V s r n I xt t = ¥ - T - ^ r (U* + p v *] -

a 3 (22)- -J L (Uy + p vt) - (Vz + p

Here x and y are the horizontal and z the vertical coordinates. Moreover p, vx, vv and vs are statistical averages of concentration and velocity components over an ensemble of possible distributions of equal a priori probability.

I l l


Furthermore, Ux, Uy and U2 denote the components of the eddy diffusion transport vector U, which is the statistical average of the product of the random variations of p and those of v.

When clouds are considered with dimensions small compared to the tidal excursion path, the tidal entrainment enters into the convective term p v. If, on the other hand, clouds are considered with dimensions great compared to the excursion path, the dispersive effect of the tidal stirring enters into the vector U.

Finally Y denotes the rate at which the substance is introduced into the sea per unit volume and per unit time, whereas t is the decay time constant again.

When clouds are considered with horizontal dimensions great compared to the depth, we may also take averages over the full depth and ignore the z-co-ordinate:

T7 - " F f i {U- + p ’ ■> - i f tV- + 1231In case there is an interface of great stability (thermocline) at a certain

depth, the system may be split up into two (or eventually more) layers, each obeying an equation of type (23). These layers are treated as separate sections in the sense of the preceding part. The exchange between them can be introduced by an additional term in equation (23).

In certain special cases, where the body of water may be treated as a channel (e. g. in many estuaries), the problem may be reduced to a onedimensional form, at least in first approximation.

3.2.2. Boundary conditions

Along the boundaries of the region considered, the following conditions must be satisfied.

1. When no substance passes through the boundary (closed boundary) the component of the transport vector normal to the boundary vanishes:

U n + P v n = 0 . (24)

We may generally assume that vn = 0 at a closed boundary, so that the boundary condition reduces to

V n = 0. (25)

This type of condition is pertinent, e. g., to the bottom (if precipitation on the bottom is ignored), to the surface (if evaporation to and precipitation

Appendix VI

112


Appendix VI

from the atmosphere are ignored) and, in two-dimensional problems, to the coast boundaries of the sea.

2. Along an open boundary the normal component Un may be given, or the concentration p, or a relation between Un and p.

A special problem arises when substance is introduced into the sea in a relatively small region from whence it spreads throughout the sea. Inthat case Y = 0 everywhere except in the small region just mentioned.We can then integrate (22) over the region co, and, assuming that co is so small that W f~T + “ ]da:d2/dzJ j J T J

to

is negligible as compared toj = ^ V Ax Aij Az, (2 6 )

<0we arrive at:

55 Und o + ^ p v nd a = j. (2 7 )a - a

Here a denotes the boundary surface of the region co and Un and vn the components of the vectors U and v normal to a. The equation (27) states that the outward transport across the surface a equals the source strength /.

3 .3 . M i c r o - s c a l e d i f f u s i o n

Since the concept of micro-scale diffusion is mathematically the most simple proposition, we shall start by expounding this briefly.

Eddy diffusion generally tends to carry substance from places with greater, to places with less, concentration. Hence, the transport vector U at a point depends on the concentrations in the vicinity of this point from whence the substance can reach the point by eddy convection.

Now let eddies greater than L be of negligible influence and let L be relatively small (we shall specify this below).

Then let L be so small that L times the -second order derivatives.of-p with respect to x, y, z, i. e. !i2'pl~bxl, Wp/Tsxhy etc., are negligible - with, respect to the first order derivatives. We can.then describe the distribution in the vicinity of a point sufficiently by the values of p, ’hp/'dx, and4)p/~bz at the point considered, and the diffusion transport is then .supposed to be defined by

8 113


Appendix VI

Ux = K XX i piX + K Xy i p

+ K Xz~bp D 2

uv K-yxi piX + Kyy

i pi y + K VZ

dp'bz

Uz ^zxi pi X + Kzy

i pi y + K ez

Dp£)Z ’

(28)

(29)

(30)

where the coefficients Kxx, KXy etc. have definite values at the point considered, and hence are functions of x, y and z in general.

When there is no preference to clockwise or to counter-clockwise rotations in the eddy field, the diffusion tensor K is symmetrical:

x y y x i ^ x z K y z K z y • ( 3 1 )

In an isotropic eddy field the coefficients Kxy etc. are zero andK xx = K „ = K zz = K. (32)

When the eddy field is, moreover, homogeneous, K is constant throughout the whole field. In that case the diffusion equation (22) reduces to the Fickian equation

— = Y - - K V2 p - (p vx) ------ — ( p v J ------ — (pvz) (33)r 3a: r iy y ® iz

where V 2 is the Laplacian operator. In this case molecular diffusion may as well be included.

The equation (33) may also appear in a form reduced to two dimensions or to one dimension.

As an example of two-dimensional micro-scale diffusion we mention the case of a very shallow sea with a regular coastline and bottom configuration, in which the water is moving by the action of a regular field of forces, for instance, the earth's gravity and tidal forces. The currents generated by these forces are affected by bottom friction which causes turbulence in patterns limited substantially to dimensions not much greater than the depth.

When the substance is dispersed horizontally over distances large compared to the depth, the bottom friction turbulence may be considered as micro-scale turbulence.

We reduce to the two-dimensional case by averaging over the depth, and then can put

K „ = K + « K ^ - ^ ~ ; K vy = K +

K xv = a K(34)

114


Appendix VI

Here a is a coefficient less than unity, v = -r v„L , andK = fi a v, (35)

where a is the depth and jj coefficient, for which we may roughly put0,003.

The values a and fl are not known with great precision and this can justify us in neglecting the diffusitivity terms with a, which leads to a rather great simplification in the differential equation.

Irregularities in the shape of the sea bed and in the field of the driving forces (wind) may cause appreciable eddies of much greater horizontal dimensions than the depth, giving rise to eddy diffusion on such a large scale (macro-scale turbulence) that the concept of the present section is no longer adequate.

3 .4 . T h e d if f e r e n t ia l d if f u s io n c o n c e p t

It is always possible to define a set of coefficients KXx, Kxv, etc., in every point (x, y, z) in such a way that (28), (29) and (30) are satisfied. The matrix K, however, will then generally depend, not only on the diffusive eddy field, but also on the distribution of the concentration p. Hence, it is in general not possible to solve the diffusion equation on this basis, since K is not defined before p (x, y, z) is known and p cannot be solved without K being given.

In special cases, however, we can avoid this difficulty by making plausible assumptions on the K-coefficients.

A valuable clue to such an assumption in the case of a cloud of substance is the insight that actually the most effective eddies are those in which the dimensions are comparable to those of the cloud (R i c h a r d s o n , 1926). This follows from the consideration that the much smaller eddies are ineffective, as they cannot intermix over great concentration differences, whereas, on the other hand, the much larger eddies will rather displace the whole cloud than scatter it.

3.4.1. Application of the similarity principle

The above consideration can be rendered in a more exact formulation if we confine ourselves to the special class of solutions which represent clouds remaining similar in shape throughout the time.

We shall illustrate the calculus for the case of a cloud with rotational symmetry in a two-dimensional isotropic field. We ignore the advection

s* 115


and the decay, and assume that after t = 0, no more matter is introduced. In that case the diffusion equation reduces to

l>p 1 5 ( _ Tr Dp'it. r hr

We now suppose that the distribution can be described by a function of the form

* = w * ( t t ) ■ 13,1where b denotes a length parameter characterizing the size of the cloud; b is a function of time to be defined below. It is also noted that the total quantity of substance,

CO CO

M = j p 2 7ir dr = C (i?) 2n R dB, ‘ " (38)0 0

where R = r/b, is independent of the time I (we suppose that R <[> vanishes for R infinite so that the integral is convergent).

The clue is now to assume that K is of the form

K — B (b) ■ H , (39)

Appendix VI

where B -is a function of the cloud size defining the intensity of the diffusion and H a function characterizing the spatial distribution of the diffusive effect..

Substitution from ( 3 7 ) and ( 3 9 ) into ( 3 6 ) reduces this equation to

T i { JiIr<s>S} + ii7 |- + 2i,“ 0’ (40>on the necessary condition that

b ^ = B ( b ) . (41)

These equations can be solved, provided we can make rational assumptions on the functions B and H.

When the scale law of the turbulent field is of the formK = K 1 1” , (42)

w i t h n , f o r in s t a n c e , 4 /3 ( R i c h a r d s o n , S t o m m e l , O z m i d o w ) o r l (S v e r d r u p ,M a c E w e n [ 1 0 ] , Jo s e p h a n d S e n d n e r [ 7 ] , P r i t c h a r d a n d O k u b e ) o r 0 ( m ic r o - s c a l e ' d i f f u s i o n : F i c k ) , i t is r a t io n a l t o a s s u m e

B — B t bn. (43)

116


Appendix VI

Integration of (41) then yields2 - n __________________

6 =• ]f (2 — n) b x (t -^77). (44)

This defines the expansion of the cloud and accordingly the decrease ofthe concentration in the centre: C b~'2 (0).

The form of the cloud is closely connected to the function H. Severalspecial forms have been applied.

3.4.1.1 The exponential distribution

The assumption that the diffusivity is a power function of the distance r from the cloud's centre,

K = B j rn, (45)

can be reduced to the proposition of the preceding section by putting (43) and

H = ( y ) " = (46)This leads to solutions of the form

».2 — n

C (2—n)&2 n ! ah \p = — e 1 (47)

where b is the function of the time defined by (44). The constant C isdefined by integrating C over the whole cloud and equating to the totalquantity released, M.

More in particular this yields for the linear law (n = 1):

p = _______ ^ _______ e ~ . (48)v 2 7T k s ( ( - t0y~ K ’

This solution was first derived, by M a c E w e n and afterwards, on somewhat different assumptions (cf. 3.4.1.3.) by J o se p h and S e n d n e r . The constant K\ is a measure for the velocities of the stirring motions: the diffusion velocity.

In the case of the 4/3 power law we arrive at

„ = ______________ M _____________ - 4/9 * , « - « . ) (4£hp (128 tc/243) (t - h Y 1

w h ic h is t h e f o r m u la d e r i v e d b y O z m i d o w .

117


Appendix VI

3.4.1.2. The error-function distributionWhen we start from the assumption that, at any moment, the diffusivity

is constant throughout the whole field, whereas its value K varies as a power function with the increasing dimensions of the cloud, we can put (43) with

H = 1. - (50)

Then we arrive at the distributionr*

M ~■ (5_^

This represents a Gaussian distribution with a standard deviation b ]/ 2,where b is given by (44).

When n = 1, this yields the distribution

v = M e ~ (6 2 )P 2 A V (t - <„)2 ( '

w h e r e Ki m a y o n c e m o r e b e in t e r p r e t e d a s a d i f fu s io n v e l o c i t y . T h e a b o v ed i s t r ib u t i o n h a s b e e n a p p l i e d b y P r i t c h a r d a n d O k u b e .

3.4.1.3. The superposable distributionIn a diffusive field with autonomous turbulence the distributions of a

diffusible property satisfy the superposition requirement. This involves that, if the distribution for the instant fo is known, the distribution at a later instant t^ > to can be defined by the integral

co

P (t, y) = 55 d ®0 d 2/o V (*0. ®0, 2/o) Pi (< — <o» * — V ~ 2/o)> (53)— CO

where pi (t, x, y) denotes the distribution a time lapse t after a releaseof a unit quantity at the origin. (53) holds good, provided firstly, that theturbulent field is homogeneous, and secondly, that no new quantity is introduced during the interval from to to t.

More in particular (53) is valid if p (to, xo, yd) represents the cloud of substance produced by a unit release in the origin at time zero, so that the function pi has to satisfy

OOPi (t, y) = JS d ?/0 pi (t0, x0, </o) Pi (t — h, x — xw y — y0) (54)

— 00for any pair of values I > la > 0.

Equation (54) can also be interpreted as follows:

118


Appendix VI

The unit release function pi (t, x, y) represents the probability density that a particle launched at the origin at time zero will be found at the point (x, y) after the interval t. Then (54) states that this probability can also be defined by considering all the possible intermediate positions (xo, yo) at the time to, and meanwhile formulating the probability that the particle reaches the point (*, y) by such an intermediate position (xo, yo).

When the superposability condition is . imposed upon the self-similar distributions (assuming isotropic turbulence), the following proposition is arrived at in case of the linear scale law ( S c h o n f e l d , 1959):

h “ t ( 1 + -&) = ¥ < 1 + s , >-This yields the distribution

„ _______ 1 /miP 2 n (B 1 2 + r2)3/2 ' '

This can also be deduced by the integral diffusion concept (cf. (67) for1/r = oo, where W stands for D\).

J o se p h and S e n d n e r have followed essentially the same line of thoughtas in the above probability discussion. That they have arrived at theformula (48) instead of (55) seems to be the result of an inadmissible simplification.

3.5. T h e n e ig h b o u r d i f f u s i o n c o n c e p t

The first attempts to deal with diffusion in the sea were based on the Fickian diffusion equation (cf. 3.3.). When it became clear that the influence on the scale cannot be well taken into account by this approach, R ic h a r d s o n (1926) devised his neighbour-diffusion concept.

This concept leads to considering the autocorrelation of the local concentration distribution as a property subject to diffusion. In three dimensions the autocorrelation or “neighbour concentration” is defined by

CO

q (|, rj, £) = j p [x, y, z) p (x + £, y + rj, z + £) t\x d y d «. (56)— CO

It is then postulated that this function obeys an equation of the form

+ (5,)where F is a function of I = |; + i f + t 1, provided the turbulent fieldis isotropic and homogeneous.

119


The neighbour-diffusion concept is usually applied with a 4/3 power law.for the relation between the neighbour diffusivity F and the neighbour separation I.

The local concentration p is not uniquely defined by the neighbour concentration q. Hence the application of the neighbour diffusion concept must practically be confined to symmetrical distributions.

A more serious objection against the neighbour diffusion concept lies in the fact that it does not satisfy the superposability requirement, at least not with a power law for the function F (Z).

Appendix VI

3.6. T h e i n t e g r a l d i f f u s i o n c o n c e p t

The eddy diffusion transport in a point (x, tj, z) consists essentially in the eddy advection of substance from points in the vicinity. In the integral concept (S c h o n f e l d ) it is now assumed that eddies of the size I will, on the average, carry in the point considered substance with concentrations comparable to the mean concentration to be found on a circle with radius I about die point considered. Since eddies of all possible sizes contribute to the diffusion transport, we arrive at the following formulation of the transport

CO

U X = ^ V (x — { , y — >b z — 0 -J- d f d JJ d f , (58)— co

or in two-dimensional casesCO

U x = ^ P (x — € , y — v) - j d £ d »7- (59)— CO

Here I = )/ f 14 + i f + C2 or 1/12 + rf and, in case of homogeneous isotropic turbulence, W is a function of I only. Similar expressions for Uy and eventually Uz are valid.

The quantity W can be interpreted as a diffusion velocity. Hence, when the 4/3 power law ( R i c h a r d s o n ) for diffusivity is adopted, we have to put W proportional to the 1/3 power of I. When the linear law isadopted (S v e r d r u p ) we should put W constant. The micro-scale conceptis arrived at when we suppose that W = 0 for I > L, where L is smallas discussed in section 3.3.

120


Appendix VI

3.6.1. Solution by Fourier transformationA practicable method of solution of the integral diffusion equation for

an infinite sea consists in using the Fourier transform of the concentration function:

etc.,where Vx denotes the Fourier transform of vx, like I' denotes that of ty. Moreover

An alternative interpretation o f the integral diffusion concept is arrived at when w e proceed as follow s:

We start from the Fickian equation (33) and apply the Fourier transformation, observing that in a homogeneous field or turbulence the diffusivity K cannot be a function of x, y and z. Hence we arrive at an equation of the form (61), with K standing for B.

Then we consider that o represents the spatial frequency of the Fourier spectrum and hence I/a-is a length measure of the Fourier components. Accordingly, we can introduce a length-scale dependence in K by putting it equal to a function B of o.

When we can solve (61) we 'find the distribution p by an inverse Fourier transformation.

CO

P (A ,/<, v) = 555 p (x, y, z) + M + vz) d a Ay dz. (60)— CO

The diffusion equation then reduces to

OD

\}.VX . P ] = 555 A v x (/. - Au M - Ml, V - V,) P (Aj, /h, Vl) d Ax d/.(l dv, (62)— CO

B(a) = (63)o

or, in the two-dimensional case,

oHere 1\ is the Bessel function of first order whereas o = ]/ ?r + (x2 + v-or |/A2 + |x2.

121


When two or more eddy fields, independent of each other, are engaged simultaneously, we have to define B (o) for each field separately and then the sum of the B's has to be introduced into (61).

This applies more in particular to the combination of microscale diffusion characterized by a constant diffusivity K, with macro-scale diffusion characterized by a function B (a). In that case B (a) in (61) has to be replaced by B (a) + K.

Appendix VI

3 .6 .2 . Some special solutions

We shall here reproduce a few elementary solutions (S c h o n f e l d [ 1 4 ] ) , which are useful in studying problems of radioactive-waste dispersion.

We confine ourselves to the case that the macro-scale diffusion follows the linear scale law, so that W is constant. Then

3.6.2.1. Incidental point release in a resting mediumWhen a quantity M of substance is released very rapidly in a very

small region, we may schematize this as a release in a single point (say x = y = z = 0) in a single instant of time (t = 0).

There is supposed to be no advection.In case of macro-scale diffusion following (65), the distribution of p is

then found to beM “ 7 W t

V 6 (IF2*2 + r 2)2 ’ ( *

where r = \j x2 + y2 + a2.When the substance is suddenly released uniformly spread along the

3-axis at the linear density M' we obtain

_ M ’ ~ 7 W tV 2 * 6 (WH* + r2)3/2 ’ ( J

(two-dimensional point release). Now r = [/ xi + y ’.In case of a release in the yz-plane at a uniform density M" per unit

area, we have

M " ~ 7 W t . . . .W T ^ ’ (68)

(one-dimensional point release). Now r = I'd.

122


Appendix VI

In case of micro-scale diffusion the solution becomes

t 4 El

P - ^ n e (4 7t K t ) nl 2 ’(69)

where M„ = M, M' or M" and n = 3, 2 or 1 in the three-, two- or onedimensional case, respectively.

The combination of macro- and micro-scale diffusion is more complicated to calculate. For the two-dimensional case the concentration in the centre of the cloud has been calculated:

l ' n w * t_______ e 2 2 K2 2 K

i w n2 K

M' W 2i TT K 2

WH 2 K

1(70)

W -t2 i r +

Here (I‘ is the error integral.

3.6.2.2. Continuous release in uniform flow

We consider a continuous release at a rate M per unit time in a medium moving uniformly in the ^-direction at a speed v.

The solution has been calculated for the two-dimensional problem with linear macro-scale diffusion and ignoring the decay. In that case

_ M/_______________ W_____________P — 2 tz y w 2 + [ (]rW- + v*)r — v x Y (71)

where M' is the rate of release per unit time and per unit length alongthe z-axis.

In case of micro-scale diffusion the corresponding solution is

M' T, ( r v \P ~ ~2tz~K 6 2K M W (72)

where Ko denotes the Bessel function Ko (z) = i ^ i Hiy]> (i z).

323


Appendix VI

E x a m p l e 1

Continuous point release in a bayIn a bay, having restricted communication with the open sea, a radio

active effluent is released from a pipeline at a constant rate of activity of / curie per month. The volume of the water in the bay is V ms, the rate of exchange with the open sea is Ei m3 per tide. The rate of decay of radioactivity is characterized by a half-life of n days.

We suppose perfect mixing in the bay, and hence a homogeneous concentration of radioactivity throughout its volume. This concentration at a given time is indicated by p.

If the concentration of radioactivity in the open sea is zero, we have a special case of the two-section system of para. 2.2., so that the equations (11, 12) take the form

Here E is the exchange of water between the bay and the open sea per month, equivalent to Ei, and t is the half-life in months, equivalent to n.

If the release is assumed to commence at the time t = 0 and the initial concentration in the bay to be zero, the solution is:

The concentration increases at a gradually diminishing rate up to an asymptotic value, determined by putting t = °o. This final concentra- • tion will be

The concentration will be half this value after a time, given by:T

Numerical application:

j = 100 curie per month x = 1 month

124


Appendix VI

V = 10s m:i (e. g., 100 km2 surface area at an average depth of 10 m)El = 5 X 107 m3 per tide orE = 3 X 109 m3 per month (this rate of exchange would, for instance,

arise from a 25% exchange of the tidal volume with a tidal range of 2 m).

The final concentration of radioactivity in the bay is then found to be:

p•=•^^ra?W = 25xl0Jc'm•Half this value will have been attained after about 5 days, which

means that the concentration will be practically at its final value within a relatively short time.

In this case the dilution as a result of the exchange with the open sea is three times as effective as the decay. The two effects would be equivalent at a half-life of 10 days instead of one month.

E x a m p l e 2

The spreading of matter in the water of an estuary"'For the purpose of describing the longitudinal spreading of any quan

tity of dissolved or suspended matter, or of the water itself, along a steady-state, vertically-mixed estuary with periodic tides, a mathematical model is used which is, in principle, similar to that presented by S to m m e l (1953) [16],

It is essential in the present treatment that no details of tidal scale are considered. The variations within a tidal cycle are left out of consideration; all quantities studied refer to a given phase of the tide. The tidal currents are not used explicitly, but the whole tidal mechanism goes into one parameter, the mixing parameter or exchange parameter, which enters into the equation that governs the spreading of matter.

This equation is a linear difference equation expressing the variation of the concentration of matter in the water as the sum of two effects, that is, advection by the residual current and exchange by turbulent and tidal mixing.

The total volume of water is split up into a finite number of segments, numbered 1, 1, . . . k . . . , with volumes V*, and mean concentrations p* of the matter considered. The change of mean concentration in a time-

* This example was provided by an investigation by R. D o r r e s t e in [5],

125


interval A t (preferably one, or one-half tidal cycle) is supposed to be given by the linear difference equation:

Vk A P k = At £ 2 |-2_'SV 7; (Pk' + Pk) + -E'Ak (Pk‘ ~ ’

where the sum is to be taken over all segments k' (normally two) that border on the segment k considered and p/s and pjc refer to the beginning of A t ; the constants Sk'k represent net water fluxes towards k and the constants Ek'k are exchange factors. For a one-channel estuary, Sk'k equals the river flow and Ek'k can be estimated from stationary mean salinity distributions. Sk'k A t and Ek'k A t should always be much smaller than Vk- The sea and the river are also considered as segments with, respectively, infinite volume and zero salinity.

The problem is now: from a given initial distribution of concentration of the matter considered, to compute the distribution of concentration over the various sections at any later moment. The difference equation makes it possible to perform any such computation stepwise. The idea of the computational technique proposed here is the following:

We introduce a number of basic initial distributions, such that the concentration p is zero in all sections, except in one, section m, where it is 1. The distribution of concentration which develops from that initial distribution is called ym/c (t).

Once the values of ymk are known for a certain time-interval f, for every m and k one can compute the distribution of concentration at the time t from any given initial distribution, since any initial distribution of concentration can be built up as a linear combination (superposition) of our basic distribution. The distribution of concentration to be computed for the time t will then be the same linear superposition of the functions ymk(t), or:

Pic (t) = 2 P m (° ) Vmk (<) •m

One has only to compute the values ymk{t) in order to solve any problem of spreading of matter over the region considered in the time-interval t.

The yHift(t)-values form a matrix || y(t) ||, an example of which is shown in Table I. This example has been taken from an investigation of the Ems estuary by the author and is valid for t = 8 tidal cycles. From the definition of ymk(t) it is clear that ymk{o) is the unit matrix, where all elements are zero except the diagonal elements, which are unity.

Appendix VI

126


Appendix VI

T a b l e IEMS-ESTUARY W ITH SIDE-BASIN

Values of ymk (t) for t — 8 tidal periods (in parts per 1000)

k -> 13 12 11 10 9 8 7 6 6 A 6 B 5 4 3 2 1m1

Sea Basin R iver

13 = sea 1 0 0 0 302 74 18 5 2 0 0 0 0 0 0 0 0 012 0 444 241 95 40 17 6 2 1 0 1 0 0 0 011 0 179 372 255 151 82 36 17 7 3 8 3 1 0 01 0 0 52 179 260 229 168 97 57 30 18 34 14 5 1 09 0 16 80 172 2 0 0 183 134 96 64 48 65 32 12 2 08 0 5 34 99 144 157 143 121 99 89 89 50 2 2 5 07 0 2 1 2 48 89 1 21 140 139 140 140 H I 59 34 11 06 0 0 5 28 62 1 0 0 136 151 174 184 124 81 43 15 0

6 A basin 0 0 1 10 29 57 94 119 163 186 90 54 25 7 06 B 0 0 1 6 2 1 48 90 1 2 2 182 218 8 8 49 2 1 5 0

5 0 0 1 5 13 2 2 33 38 39 40 38 32 21 10 04 0 0 0 2 7 15 24 29 34 25 37 40 32 16 03 0 0 0 1 5 1 2 22 29 24 2 1 49 62 54 30 02 0 0 0 1 3 9 21 30 21 16 65 94 89 50 01 = river 0 0 0 0 2 7 24 50 2 2 12 2 0 1 430 641 848 1 0 0 0

The y;«/i(t)-matrix has a further property, which makes it possible to compute it for any time _N A t (where N is an integer) from the one basic matrix y„,k(At). To show this we first show

Vmk ( 1 2) Vmv ( 1) yvk ( 2) >V

orII y (k + h) II = II y &) il • II y (t2) II,

according to the multiplication rule for matrices. From this result it follows that

|| y (N t) || = || y (t) || N .

Consequently, the difference equation need only be used for the first step, that is, to compute the basic spreading matrix ymk{ A t). All further computations can be performed by means of the latter formulae.

Whereas the horizontal rows of the matrix (m = const.) show how the water of one particular section (m) will be spread over the other sections after a time-interval t, the vertical columns (k = const.) show how the water which is now in one particular section (k) was distributed over

127


the other sections a time-interval t before. In other words, where this water came from and how it was composed, quantitatively. In order to show this, we consider the water that was in section m at time-f. Of this water, the concentration in section k at zero time is ijmu (t-); or ymkit) is the fraction of the water in k that was in m a time interval 1 before. From this result it also follows that

S Vmk ( 0 = 1 .m

By taking sums, the fraction of the water present in an arbitrary combination of segments which will, after time t be, or which was before time t, in another arbitrary combination of segments, can be readily calculated from the t/ms-values. In this way one can, for instance, compute the time needed for, say, half of the water of a particular part of the estuary, or of the whole estuary, to be replaced by other water.

Finally, similar considerations can easily be held for the river-water and the sea-water, as components of the estuary water, separately.

E x a m p l e 3

Continuous point release in coastal water

This example refers to a continuous release of radioactive waste near the coast of a shallow border sea, where tidal currents, mainly parallel to the coast, prevail.

The waste is supposed to be introduced into the sea, for instance by a pipeline, at some distance from the shore, in such a manner that a rapid vertical spreading in ensured. This requires, especially when the waste is different in density from the receiving water, a dilution to such a degree as to prevent the waste from either sinking to the bottom or floating upon the surface.

A rapid initial dilution can be obtained by forcing the vvaste out into one or more strong jets'1'.

After leaving the nozzle, the jet begins to intermix with the environment. In the first stage of this intermixing the uniform cross-sectional distributions of the velocity and of the concentration, prevailing in the nozzle, are remodelled into approximately Gaussian distributions. The first stage extends on a length of some 5 do, where do is the nozzle diameter.

* Cf. [I] where further publications on the subject are quoted.

Appendix VI

128


Appendix. VI

After this stage, further intermixing results in widening of the jet, attended by decreasing of the velocity and of the concentration in the axis of the jet, according to

_ P do _ a do „^axis — — “ — > 5axis — ~ « *

Here x is the distance from the nozzle along the axis of the jet, do is the nozzle diameter, vo and so are the velocity and concentration respectively in the nozzle, and a and j3 are constants ( a ~ 5.5; fi ~ 6.2).

When the effluent has a density different from that of the environment, the axis of the jet follows a ballistic curve which, for a roughly horizontal jet, is given approximately by

, ~ , « Qo — Qi 2 gy — x tan 0 + ~12 /S2 q0 v02 d0

where 0 is the angle between the nozzle axis and the horizontal (0 1),Qi the density of the effluent and go that of the environment {go— pi ^ Qo)-

These formulae enable us to calculate the concentration in the axis of the jet when it attains either the bottom or the water surface.

In fact, the concentration will be lower than the value thus calculated, because of the additional diffusion by the environmental turbulence.

Where the jet becomes exhausted, the environmental turbulence takes care of the further diffusion, so that at some distance down-stream, the effluent is spread from bottom to surface.

In order to pursue the further dispersion, we shall now assume that the waste is introduced uniformly spread from bottom to surface along a vertical line.

The waste is dispersed by the combined action of advection and diffusion. We shall here ignore the natural decay.

The advection is primarily by the tidal currents, and, secondly, by drift.As to the diffusion, we can count upon the bottom friction turbulence

in the tidal current, which we shall treat as micro-scale turbulence. It is to be expected, however, that there will also be larger-scale stirring motions. Anyhow, the horizontal tidal excursion movement will more or less contribute to the dispersion of the waste. In addition there will be wind-driven circulations.

The micro-scale diffusinity can be defined byK = y a v ,

where a is the depth, v the velocity of flow, and y a coefficient for which we may put 0.003.

129


Appendix VI

In the case of macro-scale diffusion we have even less information, not only as to scale law, but also as to numerical values.

It must, moreover, be assumed that the diffusion is greatly variable according to the local and temporary conditions, especially meteorological. The most unfavourable conditions from the safety point of view, are usually those of little diffusion. In that case we must preponderantly consider calm weather conditions.

In the absence of better evidence we may adopt the linear scale law which, in the integral diffusion concept, takes the form

WB = •2 n aThe value of W should preferably be deduced from observations on the

spot. If these are not available, W has to be conjectured. There is evidence (Joseph and Sendner) that in deeper water 10-2 m/sec is a fair estimate, but in shallow water we should generally count upon smaller values, for instance 10~3 m/sec.

In the beginning the dispersion of the waste is predominantly defined by the advection by the tidal current and the micro-scale diffusion by the frictional turbulence in this current.

As a result of the entrainment the waste forms a trail downflow from the releasing point. This trail expands transversally by the diffusion, as represented by the formula

M v f r v ~\2 2* M . w J ’

where M is the rate at which the waste is introduced per unit time (cf. para. 3.6.2.2., formula (72)). The concentration in the axis of the trail is (somewhat overestimated) approximated by

M M 5 Mfix is — ------- ■ — — — — .

a f4 tz K v x 1 4 tz fi a3 v2 x ][a3 v2 x

This demonstrates the influence of depth a, velocity v and distance from the releasing point x, upon the concentrations in the trail, and in particular the favourable influence of a greater depth.

As a result of the tidal oscillation, the waste returns to almost the same position after every tidal period. Consequently, the water into which the waste is released may already have been contaminated more or less by the waste released in previous periods. This contamination forms the waste background, which we estimate as follows:

130


Appendix VI

We look apart for the moment from the tidal advection and count upon the micro-scale diffusion only. We suppose, then, that we release the waste periodically in portions MT every tidal period T. One such portion gives concentration at the point of release which, after n tidal periods, amounts to

M T4 7r K n T a

The whole waste background would be the sum of the contributions of ail previously-released portions:

2 M Tn=1 4 7t K n T a

However, the series n "1 is divergent, which shows that, if there is only micro-scale diffusion and no advection, the contamination would accumulate indefinitely.

Admitting that there will also be macro-scale diffusion, we find that one portion after n tidal periods gives a concentration

M T W 2 ___________ 1________8 iz K a W 2 n T ( W2 n T( W2 n r y

I 2 K )2 Kat the point of release. Summing this over n yields (with a somewhat overestimated approximation) the waste background

M T r, , „ 2 K4 7x K T a

It is to be noted that even a very small value of W is sufficient to ensure a convergent build-up of the waste background. The numerical value of W is then of relatively little influence upon the level of the background. If, for instance, K = 10-2 m2/sec and W = 10 * m/sec with T = 4 X 104sec, we obtain

M TPbg = 4-6 4tx K T a ‘

When W decreases to 10-5 m/sec the background level is only doubled.The waste is not only taken up and down by the tidal current, but it

is ultimately carried away by the drift current u.We look apart from the tidal entrainment and the micro-scale diffusion

by frictional turbulence. The concentration from a continuous release in the drift current is then given by section 3.6.2.2., formula (71):

M W^ 2 7to fTF2 -f M3[(fT P -f u2) r — wa] •’

9* 131


In the axis of this “ trail” we encounter the concentrations

Appendix VI

Paxis —M

2 7r a W x|f W2 + u- -f u

1{W2 + u2It is important to note that the drift current u, which is usually a rather variable agent, is of relatively little influence, so that we can always be sure that the concentration at a distance x from the releasing point, is not greater than:

M7t a W x

The concentration may even be appreciably less, since here we have entirely ignored the favourable influence of the micro-scale diffusion, which is more important as W is less.

The above considerations are of an explorative character. For more thorough information we refer to the list of literature, especially to the work of Whipple (Exercise Mermaid).

R E F E R E N C E S[1] ABRAHAM, G., Univ. California, Inst, of Engng. Res., Rep. 138-2 (1959).[2] BATCHELOR, G. K.; Quart. J. Roy. Meteorol. Soc., 76 (1950) 133— 146.[3] BOWLES, P., BURNS, R. H., HUDSWELL, F. and WHIPPLE, R. T. P.,

Exercise Mermaid, E/R 2625, Atom. Ener. Res. Est., Harwell (1958).[4] DORRESTEIN, R., Proc. Int. Oceanographic Congr. New York (1959).[5] DORRESTEIN, R., “A method of computing the spreading of matter in

the water of an estuary” , Disposal of Radioactive Wastes, Int. Atom. Ener. Agency, Vienna, 2 (1960) 163.

[6] INOUE, E., / . Meteorol. Soc. Japan (2nd Ser.), 28 (1950) 420—424.[7] JOSEPH, J. and SENDNER, H., Deutsche Hydrogr. Zeitschr., 11 (1958)

49—77.[8] KLUG, W., Beitr. Phys. frei. Atmos., 30 (1958) 137— 142.[9] LAUWERIER, H. A., Appl. Sci. Res., A 6 (1956) 197— 204.

[10] McEWEN, G. F., Trans. Amer. Geophys. Un., 31 (1950) 35—46.[11] OZMIDOW, R. W „ Akad. Nauk. SSSR, 120 4 (1958) 761— 763.[12] RICHARDSON, L. F.; Proc. Roy. Soc., (A) 110 (1926) 709— 727 and 214

(1952) 1— 20.[13] ROBERTS, O. F. T „ Proc. Roy. Soc., (A) 104 (1923) 640— 654.[14] SCHONFELD, J. C., “ Diffusion by homogeneous isotropic turbulence” ,

Rijkswaterstaat, Water resources and hydraulic research, Report Fa-1959-1.[15] STOMMEL, H., J Marine Res., 8 (1949) 199— 225.[16] STOMMEL, H., “ Computation of pollution in a vertically mixed estuary” ,

Sewage and Industr. Wastes, 25 9 (1953) 1065— 1071. Contribution No. 640, Woods Hole Ocean. Inst.

[17] SUTTON, O. G., Micrometeorology, Ch. 4 and 8, New York-London (1953).[18] SVERDRUP, H. Y., Scripps Inst. Oceanogr., Oceanographic Report No. 1

(unpublished).

132


Appendix VII

DI S C HARGE OF R A D I OA C T I V E E F F L U E N T I NTO A C O A S T A L - W A T E R REGI ON

(Example computation)

1. Introduction

This Appendix is a guide to a method of estimating the maximum permissible discharge rate of radioactive effluent into coastal waters. The problem is complex and highly dependent on both the nature of the effluent to be discharged and of the locale of the discharge point. For these reasons a generalized solution to the problem cannot be made, consequently a simple model has been chosen and a solution for this simplified case is presented. In this way it is possible to demonstrate the approach to such problems and the principles of the method adopted.

On introducing the radioactive effluent at the discharge point into coastal waters, there will be physical processes operating to produce a reduction in the activity per unit volume of the radioactive waste. These processes will be dependent on a number of factors, such as the method of injection of the effluent into the sea, the depth of water and the tidal conditions (see Appendix IV). These hydrodynamic factors having been dealt with, the expected radioactive concentration in the sea-water at any point of interest may be calculated for a given rate of effluent discharge.

Calculation of maximum permissible rates of discharge of radioactive effluent will depend directly on the maximum permissible levels of radiation exposure applicable to individuals or groups exposed as a result of the discharge. The basic criteria are provided by the International Commission on Radiological Protection. This aspect is discussed fully in Chapter IV of the main Report, but for completeness the application to the particular problem of waste disposal in coastal waters is discussed below.

2. Maximum permissible radiation exposure levels arising from waste disposal in coastal waters

In dealing with the overall problem of radioactive-waste disposal into the sea it has been found convenient to divide it into two aspects:(1) Waste-disposal operations which may be regarded as only affecting

the nation concerned;(2) Waste disposal which may affect a number of countries, and so may

be regarded as having international implications.Disposal of radioactive liquid effluent into coastal waters may be an

133


example of the former of these two classifications. Such a disposal technique will, in general, give rise to radiation exposure of a small fraction of a whole national population without contributing significantly to the genetic dose of the whole population. In this example the critical control is assumed to be the radiation exposure incurred by the individual member of the group exposed. This group is regarded as one of the groups B (c), referred to in the ICRP recommendations, and for the purpose of this Report includes persons who, because of special habits, use marine products from the neighbourhood of the disposal site.

The limiting “whole body” exposure for the individual in the special group of the population B (c), as recommended by the ICRP, is 0.5 rem per year. The size of the special group, relative to the size of the whole population, at which the genetic dose becomes more significant than the exposure of the individual, depends on the apportionment of the genetic dose which is allotted to the special group and upon the variance of individual exposures.

This may be illustrated as follows: if the genetic dose apportioned to the special group is D 30 rem, and this group constitutes a fraction f. of the whole population, the average permissible annual gonad, or whole-body dose, D rerri, to members of the group must be less than

D30 rem/year 30e

For example, if D 30 is 0.5 rem and e is 5®/o of the whole population, then D would be 0.33 rem/yr. If the distribution of dose should be very uniform throughout this special group this latter limitation would at this stage prove more limiting than the individual maximum permissible dose of 0.5 rem/yr.

Summarizing, the radiation exposure control in this case of radioactive waste disposal in coastal waters is 0.5 rem/yr for the individual members of the special group who live in the neighbourhood of, or use marine products from the area affected. If this group should become large, then the control becomes a genetic one and the control value may be calculated as shown above (see also Chapter IV of the main Report).

3. Model computation of discharge limitsSome basic assumptions must be made before starting such a calculation,

and in this case it is assumed that the radioactive waste which has to be discharged consists of only two radioisotopes, strontium-90 and ruthenium-106. It is required to find the maximum permissible discharge rate

Appendix VII

134


Appendix VII

for such an effluent into the coastal-water region. The point of discharge is assumed to be a pipeline from the coast into the sea.

It is evident from the main text of the Report that such discharge limits will be dependent on the nature of the coast, since this will determine the possible routes whereby the radioactive material discharged may aSect man. These effects may be direct, due to external irradiation of the populace, who may work and live in the neighbourhood of the discharge area, or indirect, due to internal irradiation arising from contamination of marine foodstuffs collected in the area. It is impossible to consider all such aspects in this example computation, since there are so many variables dependent on the particular utilization of the marine environment (see p. 57). In order to make this simplified estimate of maximum permissible discharge rates, it is assumed that the discharge is to be limited to contamination of fish, edible seaweed, shore sand and sea-bed mud. The discharge rate will hence be limited by the most restrictive of these items in terms of uptake of activity and effect on man.

3.1. D e r i v a t i o n o f m axim um p e r m is s ib le l e v e l s in t h e m a r in e b io t a

For the example taken, we are concerned with the possible contamination of fish, edible seaweed, shore sand and sea-bed mud by two radioisotopes, strontium-90 and ruthenium-106. The first step is to calculate the maximum permissible levels of contamination of these items of the marine environment for the two radioisotopes concerned.

3.1.1. FishThe maximum permissible level of contamination will obviously depend

on the rate of consumption of fish and study will need to be made of the eating habits of the special group that consumes the fish obtained from the coastal waters concerned. This study will yield a figure for the average quantity eaten daily per individual of this population (say a; g per day). The ICRP recommendation for the maximum permissible concentration of a radioisotope in water is related to the average daily intake of water by standard man. This is assumed to be 2200 cm8, so that the (MPc)water X 2200 is the maximum permissible daily intake of the radioisotope concerned. From this data we may calculate the maximum permissible level of contamination of fish for the two radioisotopes which we are considering:

Strontium-90. ICRP maximum permissible concentration in water for occupational workers is 10~B c/cm3.

135


Appendix VII

Therefore maximum permissible daily intake =10 ' 6 x 2.2 x 103 jxc = 2.2 x 10- 3 fie Sr9».

For exposure of the special group concerned this has to be reduced by a factor of 10, so that the maximum daily intake of strontium-90 must be limited to less than 2 X 10~4 jxc. If this intake is to arise from eating contaminated fish at the rate specified above, then the maximum per-

2 x 10-4missible concentration of strontium-90 in the fish will b e ------------- [ic/gof fish.

Ruthenium-106. By an argument similar to that given above the maximum permissible concentration of ruthenium-106 in fish will be 2 x 1 0 - 2------------- /ic/g of fish.

3.1.2. Edible seaweed

The approach in this case is similar to that presented in section 3.1.1. Suppose again that the study of eating habits reveals that the average quantity eaten daily by an individual in the special population of seaweed eaters is, say, b, g per day. Then, for

Strontium-90. The maximum permissible concentration of strontium-902 x 10-4in the edible seaweed must be limited to ---- ------ iic/g of seaweed, the

method of reasoning being identical with that given formerly.

Ruthenium-106. Again, the maximum permissible concentration of2 10-2

ruthenium-106 in the edible seaweed must be limited t o ----- ------ uc/gof seaweed.

3.1.3. Shore sand

Contamination of shore sand as a result of the discharge of the radioactive effluent into coastal waters could give rise to direct irradiation of individuals on the beach. Here again a study of local habits is required in order to establish the length of time normally spent on the beach. Suppose that such an investigation shows that no individual spends more than Ce hours per year on the beach. Exposure due to the mixture of beta and gamma radiation will depend on the nature of the mixture, but is here assumed to be limited to 1.5 rem/yr.

136


Appendix VII

The dose-rate at the surface of a semi-infinite volume of uniformly contaminated sand is

1.85 X 104 S E MeV/sec gwhere S = specific activity in (rc/g,

E = mean energy of radiation in MeV per disintegration.

This is equivalent to 1.07 SE rad/h from such a source.Consequently, the maximum permissible level of beta/gamma contami

nation of the sand will be1.5 , _ 1.4

1.07 E C j LClg'

The mean energy of the radiation for the particular case considered may be assumed to be about 0.7 MeV and hence the maximum permissible level in sand will be 2/Ce uc/g beta/gamma activity.

The method of performing this calculation will depend on the nature of the contaminants and the solution given represents one such approach.

3.1.4. Sea-bed mud

Radioactivity on the sea bed is not a direct hazard to man but, because of the possible contamination of fishing gear, a limiting value has to be set. The contamination level on the fishing gear is likely to be an order of magnitude or more less than the level reached on the sea bed. Consequently using the data obtained in 3.1.3., a conservative limit for activity of the sea-bed mud may be set at 20!de uc/g beta/gamma activity, where de is the time in hours per year spent by fishermen in handling fishing gear used in these coastal waters.

4. Permissible activity levels in the sea-water

The activity levels reached by the components of the marine environment given in para. 3 will be related to the specific activity of the sea-water and there may be biological and chemical processes operating which will make the specific activity of these higher than that of the surrounding water. The concentration ratios involved in this way will depend primarily on:

(1) the particular element of which the radioisotope is present in the sea-water, and

137


(2) the medium (plant, animal, etc.) which is causing the concentrating process.

There will be other factors, such as seasonal variations and the nature of the general marine biota, which will also affect the situation. Values for these concentration ratios can be found by a survey of the literature or by direct laboratory experiment to determine the uptake values. Such ratios have to be used with caution since there are many factors which may be negligible in effect at one locale and yet may be important in another. Since the purpose of a computation such as this, however, is to determine the approximate permissible rate of discharge, it should be possible to ascribe an upper limit to these concentration ratios sufficiently accurate for this purpose.

Suppose, then, that the concentration ratios are as indicated in Table I.

Appendix VII

T able I

Medium Radioisotope concentrated Concentration ratio*

Fish Strontium-90 AsRuthenium -106 Ar

Edible seaweed Strontium-90 B sRuthenium -106 B r

Shore sand Beta/gam ma activityStrontium-90 1 GRuthenium-106 |

Sea-bed mud Beta/gam m a activity 'Strontium-90 1 Ruthenium-106 J

D

* Concentration ratio being defined as:Activity per unit mass of medium

Activity per unit mass of sea-water for the radioisotope concerned.

If we now apply these ratios to the maximum permissible concentration values derived in para. 3 we may calculate the maximum permissible specific activities of the radioisotopes in the sea-water based on the limiting activities in the various media considered. This may be conveniently displayed in Table II.

138


T a b l e I I

Appendix VII

Medium RadioisotopesMaximum permissible level in

Medium(f*°/g)

Sea-water(s*°/g>

Fish

Edible seaweed

Shore sand Sea-bed mud

Strontium-90 Ruthenium -106 Strontium-90 Ruthenium -106 Beta/gam ma activity Beta/gamma activity

2 X 10-4K- 2 X 10_2/a8- 2 x 10_4/6,- 2 X 10 -a/6l 2/C ,20 Id,

2 x lO-'IA'fli 2 x 10- 2IA Tai 2 X 10_ 4/B 86j 2 x 10-2/.BA 2/C •20ID . de

5. Maximum permissible rates of dischargeIf we now use the data available from the hydrodynamic study it is

possible to calculate the maximum permissible activity per unit volume of the radioactive liquid effluent released at the discharge point into the sea. The dilution ratios for such a discharge will be dependent on the relative location of the media considered, for example, the distance from the discharge point to the shore, for the shore sand and for the edible seaweed, if it grows on the shore-line.

In this way it is possible to obtain maximum permissible rates of discharge for the radioisotopes, limited by the various media considered above. Suppose that such a calculation gives the following results, as indicated in Table III.

T a b l e I I I

Radioisotope Discharge lim ited byM aximum permissible

discharge rate* (c/d)

Strontium-90 Fish D aEdible seaweed D f

Ruthenium -106 Fish K *Edible seaweed D Uu

Beta/gamma activity Shore sand Sea-bed mud

DoDd

* The method of deriving the values in this column is as follows: Suppose that the meanconcentration of strontium-90 in sea-water in the fishing zone considered is a factor F lessthan that of the activity per unit volume of this radioisotope in the effluent being discharged.Then, from Table II the maximum permissible concentration of strontium-90 in the discharged effluent must be: (2 x 10-*lAsa ) F //c/cm 3. If, then, the rate of discharge of thisradioisotope is V m3/d Dsr = (2 X IO-V-^ol) F V c/d.

139


The minimum values for the maximum permissible discharge rates given in Table III will control the discharge, assuming individual radioisotope discharges to occur. In practice, it has been assumed that both strontium-90 and ruthenium-106 are to be discharged together, and consequently it is necessary to consider the additive effects of simultaneous discharges of both radioisotopes.

6. Additivity aspects of simultaneous discharges of two radioisotopesIt is now necessary to consider the combined exposure effects due to

contamination of the marine food by the presence of more than one radioisotope.

Let the discharge rate beD Sr c/d of strontium-90

and Dliu c/d of ruthenium-106 where DSrand DRuare less than the smallest values derived from Table III.

Consider the particular case of the fish-eating population. They will be subjected to internal irradiation due to the presence of strontium-90 and ruthenium-106. The critical organ for strontium-90 is skeletal bone and for ruthenium-106 the gastro-intestinal tract.

(a) Limitation of discharge in terms of irradiation of the bone of fish eatersFor strontium-90 the critical organ is the skeletal-bone, whereas for

ruthenium-106 die limitation which has to be applied in .terms of bone irradiation is 100 times less restrictive than for irradiation of the gastrointestinal tract.

Hence, for this case the relationship required is:DSr , Dnu Dlr "r 100 £>*u < 1

the terms being defined above, and in Table III.

(b) Limitation of discharge in terms of irradiation of the gastro-intestinal tract of fish eaters

D Sr f ) Ru

500 DlT + < 1 '

The maximum permissible rate of discharge of strontium-90 may, in this case, be increased by a factor of 500, because the critical organ considered

Appendix VII

140


Appendix VII

is the gastro-intestinal tract. Similar limitations may be derived for the section of the population who are regular seaweed eaters.

(c) Limitation of discharge in terms of irradiation of the bone of seaweed eaters

J>Sr I)liu 1 D f ' 100 D f n '

(d) Limitation of discharge in terms of irradiation of the gastro-intestinal tract of seaweed eaters

pSr i 1)11,1500 D f' D f u < 1 ’

If the population of fish eaters also contains seaweed eaters then the limitations will take the form:

/ DSr UKa \ / J)Sr DJiu \\ D®1' 100 D ®" / \ Z)*r 100 D f u I <

and/ £>Sr X>Bu \ / D '!u \( 500 + I \ 500 Z)fr + J j f 1 ) <:

The maximum permissible rate of discharge will then be specified by: (a) the minimum levels quoted in Table III, as the upper limit for individual radioisotope discharge; and (b) the most restrictive of the limitations given by the inequality expressions quoted above for simultaneous discharges of both radioisotopes. Both these conditions must be satisfied to meet the requirements of providing safe discharge rates.

If the special group exposed, as a result of these discharges, becomes large relative to the whole population, then the control will pass from that required for individual exposure to the genetic dose which the population receives as a result of the exposure of the special group. This would modify the maximum permissible daily intake values quoted in 3.1. to fit in with the approach presented at the end of para. 2 of this Appendix.

7. ConclusionsThis Appendix presents one possible approach to the problem of setting

limitations to the maximum permissible discharge rate of radioactive liquid

141


Appendix VII

effluent into a coastal water area. The case considered only involved two particular radioisotopes, but it may obviously be extended to embrace the discharge of a whole range of radioisotopes by an extension of the method demonstrated.

It is evident from these calculations that a considerable amount of data must be collected before the estimate can be made, and that the precise values of some of the parameters concerned will not be known. Consequently, it is important to emphasize that the approximate estimates of permissible discharge rates obtained by this method of calculation should only be used to provide the basis from which an experimental discharge programme may be planned. It is only in this way that safe use may be made of coastal water disposal sites when significant quantities of radioactivity are being discharged.

142


Appendix VIII

P A C K A G E D - W A S T E DISPOSAL- SI TE E V A L U A T I ON (Example computation)

In this Appendix, an example evaluation of a packaged-waste disposal- site is presented. A hypothetical, though representative set of conditions is taken in the evaluation. The approach used here is not presumed to be the only method which might be employed, though the major items which should be included in any actual site evaluation do receive consideration in this approach.

Hypothetical initial conditionsIn the hypothetical case treated here we assume that a coastal section

of a country has developed some use of nuclear power and radioactive isotopes for medical purposes, research and material testing. This use will inevitably result in the production of a certain amount of low-level waste products which will include contaminated clothing, papers, rags, glassware from laboratories, and other disposable equipment. Isotopes no longer useful for the research or testing programme for which they were produced also require disposal.

Assume that burial of all the low-level wastes so produced is not practical. Sea disposal of packaged low-level waste is suggested, and an evaluation of the risks involved in such disposal is therefore required. There are two ports along the sea coast, which we will designate as Port A and Port B, at which facilities for packaging of low-level waste materials and loading of the completed packages onto disposal vessels can readily be developed. The continental shelf along this coast is quite wide, extending for about 150 miles off-shore. One object of the evaluation is to find the nearest site suitable for disposal.

General criteriaA suitable site for packaged-waste disposal must satisfy the following

general criteria:(1) There must be a negligible probability that the packages will be

accidentally recovered by man.(2) There must be a negligible probability that natural processes will

lead to a movement of the packages outside of the designated disposal site.

(3) There must be a negligible probability that natural processes will lead to a premature rupturing of the packages in the disposal site.

143


(4) There must be a negligible probability that material released, when the packages, finally do fail, will be carried in any significant amounts to the shore.

(5) Natural processes of advection and diffusion must provide for sufficiently rapid dilution of any released wastes so that the level of activity taken up into the food chain will not exceed allowable amounts.

While each prospective site will be subject to an individual evaluation following the general approach given in Chapter III, the criteria listed above provide a set of conditions which control the selection of several prospective sites from which the most suitable can be chosen on the basis of the more detailed evaluation.

First of all, the site must be in an area not used and not conceivably usable for bottom trawling or other forms of bottom fishing. It should not be in a cable area, or in any area in which man’s activity might result in accidental recovery of the packages.

The site should not be closer than ten nautical miles from shore. This rule will generally satisfy the criterion that the concentration of activity which reaches shore be at an insignificant level. However, each prospective site should be examined in detail from this standpoint even though more than ten miles from shore.

The bottom depth should be such that wave action will not lead to movement of the disposed packages.

Maximum permissible dose-ratc from all sources for the population potentially affected by the disposal operation

For the purposes of this example evaluation, we consider that the population can be divided into two groups. One group comprising only a small percentage of the total population involved is considered as a selected group which, because of its particular habits of utilization of the marine products from the area, may be classed in the same category as neighbours to a nuclear installation. The criteria which will control the maximum permissible dose-rate to this group would then depend on the apportionment of the genetic dose made by the national authorities and on the size of the special groups, as discussed in Chapter IV. If the fraction of the population which comprises the special group is small, then the maximum permissible dose-rate to the individual of the group applies; that is, 0.5 rem/yr. If the size of the special group exceeds a certain value, which is dependent upon the apportionment of the genetic dose.

Appendix VIII

144


Appendix VIII

then the maximum permissible dose-rate averaged over the individuals of the group must be computed as indicated in Chapter IV (see p. 32). Assume for this case that the special group is a sufficiently small fraction of the population so that the maximum permissible dose-rate to the individuals of special group B (c) applies.

The maximum permissible dose-rate averaged over the remaining, much larger part of the population, is determined simply by the apportionment of the genetic dose to the population at large. For this example evaluation, it is assumed that the portion of the genetic dose of 5 rem allotted to the population at large is 1.5 rem. The maximum permissible dose-rate averaged over the general population is, then, 0.05 rem/yr.

The maximum permissible concentrations (m p c) of radionuclides in water as recommended by the ICRP serve as the starting point in this evaluation. The maximum permissible dose-rate for the members of the special group would not be exceeded if the m pc values for this group were set at one-tenth of the corresponding values for continuous exposure to occupational workers. For the general population, the above assumed maximum permissible dose-rate would not be exceeded if the applicable m pc values were set at one-hundredth of the corresponding values for continuous exposure to occupational workers. Treated below are the methods of utilizing these values in computing maximum permissible concentrations in the various segments of the marine environment which constitute possible return routes to man.

Determination of the portion of the maximum permissible dose which may be allotted to packaged-waste disposal

It is presumed, for the purpose of this example evaluation, that exposure of the population to activity resulting from land-based operations is, at the time of the evaluation, only a small fraction of the permissible exposure. However, in view of the likely increase in use of nuclear energy, it is probable that the contamination level of the air and fresh water will increase with time. An evaluation of this probable increase indicates that about two-thirds of the permissible dose for the population must be reserved for the air and fresh water. Thus, 30°/o of the permissible dose- rate is, in this example computation, assigned to the marine environment.

There are, however, other potential sources of nuclear-waste disposal to this coastal region. Thus, we presume that a chemical processing plant is planned which will utilize all the allotted capacity of one segment of the coast and up to 10D/o of the allotted capacity of the coastal area in

10 145


general. The development of nuclear-powered ships will require the reservation of another 10°/o of the allotted capacity of the coastal waters for waste disposal from that source. Thus, the portion of the maximum permissible dose which may be allotted to packaged-waste disposal for these coastal waters is given by

30°/o - (20 °/o X 30 % ) = 24 %>.

In view of the uncertainties involved, this figure is rounded off to 20°/o for this example computation.

Appendix VIII

Routes to manThe general criteria placed upon site selection for packaged-waste

disposal limit the possible return routes to man to the marine products harvested from the area. In this hypothetical example we presume that the coastal area considered supports a rather extensive fishery for both fish and crustacea.

It is presumed that an investigation shows that there exists a number of local fishing centres along the coast, each of which supplies a selected local population with sea-food. These selected groups each utilize seafood to supply about two-thirds of their protein requirement, and thus consume about 1000 g of sea-food per week, though a few members of these groups consume as much as 1500 g of sea-food per week. Since the limit on the dose for the special groups is an individual one, this higher rate of consumption must be used in the evaluation. The coastal area as a whole also supports a fishery which supplies the general population, which consumes about 150 g per week of fish products obtained from these coastal waters.

The ICRP recommendations relative to the m pc values for drinking water are based upon an assumed intake rate of 2200 ml of water per day. The ratio of the weight of this amount of water to the weight of the average daily intake of fish can be computed for each of the population groups. For the special group in this example evaluation, this ratio is given by

2200 x 7 1500

and for the general population by2200 x 7

= 10

= 100 .150

This ratio will be utilized later in the evaluation.

146


Appendix VIII

The first step in the selection of sites is the procurement of good bathymetric charts of the region. An example of such a chart has been prepared for the hypothetical coastal area being considered here, and is shown in Fig. 1. The depths entered on this chart are in meters below mean low water. Contours are entered for 20 m, 40 m, 100 m, and 1000 m depth.

The packages to be employed are to be steel drums of about 210-liter capacity, or reinforced-concrete containers of about the same capacity. The containers will have no voids and will have a density of between 1.5 and 3.0, depending upon the density of the waste material mixed with the concrete or other solid filler in the container.

Experiments should be conducted, or the information otherwise obtained from previous experiments, to determine the magnitude of the oscillatory motion associated with surface waves which would be required to move the packages which will be employed. We presume, for the purpose of this example computation, that such information is available and indicates that an oscillatory motion of about 10-sec period, involving peak velocities of approximately 0.3 m/sec will just begin to move the proposed packages.

A statistical analysis of storms off the subject coast indicates that the maximum significant wave heights to be expected are of the order of6.5 m with a wave length of about 100 m. Such a wave field would produce a peak oscillatory velocity on the bottom of about 0.35 m/sec in water 25 m in depth, and 0.25m/sec in water 30 m in depth. Thus, the disposal areas should be 30 m or more in depth.

As discussed previously, the disposal sites should not be located in areas where trawling or bottom fishing of any kind is carried out. The next step in the preliminary site selection then requires the collection of information on the fishing industry. We presume that the government agency responsible for the management of the fisheries of this coastal region has available information on the location of areas which are unsuited for trawling or bottom fishing. Marked on Fig. 1 by cross-hatching are the locations of “ tear-up” areas, where the bottom roughness prohibits bottom trawling. In this case these areas also have no value for other types of bottom harvest. The “non-fishing” areas are indicated only for depth greater than 30 m, since shallower depths are otherwise unsuited as disposal sites. Trawling is limited in this coastal region to depths less than 2000 m, so that the area with depths greater than this is also suited for disposal sites from this standpoint.

The currents for the region are known to be generally parallel to shore,

Preliminary site selection

10 147


Sample of bathymetric chart for disposal-site selection

148


Appendix VIII

and to flow southward over most of the shelf. There is some indication from readily available data that during a portion of the year a sinuous flow pattern develops, with a component towards the coast in some areas. However, for the example evaluation, we presume that the indications are not sufficient to eliminate any of the three possible disposal areas on the shelf from inclusion on the preliminary list of disposal sites.

A ten-by-ten-mile area in the centre of each of the non-fishing regions is then designated as a possible disposal site, subject to more detailed evaluation.

Detailed evaluation of the proposed disposal sitesThe purpose of the detailed evaluation is twofold; first, to provide

assurance that the sites selected on the basis of the preliminary evaluation are indeed suitable as disposal sites and, second, to determine the probable rate at which packaged wastes may be introduced into the sites without undue risk to man.

The preliminary investigation has firmly established the lack of fishing in the area concerned, and also the negligible possibility of any package being carried from the disposal sites by natural processes. The major items requiring further investigation are the processes of advection and turbulent diffusion.

A d v e c t iv e pr o c e sse s

Quite extensive observations of the currents in the vicinity of both the northern and southern sites are available from information on ship’s drift, as well as direct measurements obtained in past oceanographic studies by survey vessels. The region around the central site, and particularly just to the south of that site, is lacking in information for the winter half of the year. Available information shows that the summer-season exhibits flow parallel to the coast at all sites; however, the meager information for the central site in winter suggests the possibility of a shoreward directed flow.

An observational programme involving direct current measurements by free drifting drogues and radio current meters is therefore set up for a one- month period during the heart of the winter season. These observations show that the flow which passes through the proposed central site does indeed have a shoreward component south of the site. Figure 2 represents the flow pattern, as deduced from the older measurements, plus the new measurements obtained in the vicinity of the central site. It is seen that

1 4 9


150

Fig. 2Sample of flow pattern for evaluation of disposal site


Appendix VIII

the flow, after leaving the proposed central site, proceeds toward shore in the vicinity of the location of the commercial salt basins south of Port A. The central site therefore definitely appears less suitable than either the northern or southern locations. However, consideration will be given to the probable effect of turbulent diffusion on the concentration of activity downstream from the site before making any final decision regarding the retention or elimination of this site.

The magnitude of the current in meters per second is also shown at representative locations on Fig. 2.

E v a l u a t io n o f d is p e r s io n by t u r b u l e n t d if f u s io n

Available information indicates that properly-designed packages will contain the radioactive waste materials for at least 10 years, allowing for considerable decay of the isotopes with a short half-life, and some decay of even such long-lived isotopes as strontium-90. However, in making this type of evaluation, it is recommended that the assumption be made of complete failure of packages without decay. Thus, a considerable safety factor is included in the results.

There are various theoretical or semi-empirical semi-theoretical relationships which have been developed depicting the phenomena of horizontal turbulent diffusion in the sea. Recent improvements in techniques for the measurement of very low concentrations of certain non-toxic fluorescent dyes make direct measurement of dispersion locally around the proposed site economically feasible. Here, assume that such direct observations have established that the characteristics of turbulent dispersion are about the same for all three sites. Assume also that the available data on dispersion indicate that the integral diffusion concept discussed in Appendix VI is applicable to this coastal region. It is extremely difficult to include the effects of both micro-scale and macro-scale diffusion in the computations; however, if the criteria for the safe rate of discharge are based on macro-scale considerations only, then a further safety factor is introduced. Close to the point of release the concentrations of contaminant will be less, as a result of micro-scale diffusion, than the computed concentrations based on macro-scale considerations only.

Observational evidence over a rather wide range of oceanographic phenomena indicates that in the open sea the weighted turbulent velocity, or diffusion velocity, W, which appears as a parameter in the integral diffusion equations given in Appendix VI, is of the order of 2 cm/sec. However, in restricted coastal areas there is some evidence that the value of W

151


may be of the order of 0.1 cm/sec or smaller. In the present example, consider that observational data indicate that the value of this parameter for the open coastal region under consideration is 1 cm/sec.• In this example evaluation, two extreme types of releases of material from the disposal site will be considered. The two problems can be stated in terms of the following questions:(1) Assuming a steady, continuous discharge of activity at a rate equal

to the mean rate of introduction, what is the maximum amount of activity which may be disposed of during the year without exceeding safe concentrations of activity in the water?

(2) Assuming that all containers disposed of over a one-year period were by some means broken at the same time, and released all their activity to the sea, would the rate of disposal determined from conditions (1) above still be a safe rate of disposal?

Before proceeding with the computation it is necessary to establish the maximum permissible concentrations of the various isotopes involved in the sea-food and in the sea-water.

Partial maximum permissible concentrations in food originating from the subject continental shelf areas• While a number of isotopes will be involved in any actual low-level packaged disposal operation, the principles involved can be elucidated by considering that the disposal involves only four isotopes. Table I lists the four isotopes used in this example computation. Also shown in this Table are the m pc values for drinking water for occupational workers, as well as other data to be discussed below.

Appendix VIII

T a b le IDATA ON SELECTED ISOTOPES

Isotope MPC(fi.c/ml)

(PPC)f(ac/m l)

Concentrationratio

(PPc)w([/.c/ml)

£131 2 X 10“ 5 4 x 10-“ 102 4 x 10-8S a !< 3 x t o - 1 6 x 1 0 - 5 0.5 1 X 10-*

6 x lO -3 60 1 X 10~4*Sr9u 1 X 10-“ 2 x 1 0 ~ 7 10 2 x 1 0 - 8P 32 2 X 10~4 4 x 10-5 4 x 104 1 X 10-9

* These dual values represent the two possible routes for Na84 to return to man; that is,• through sea-food and throug’h salt harvested from the sea. Since these routes may be

additive, Ihe value 5 X 10—5 [Ac/ml should be used in determining permissible rates of disposal.

152


Appendix VIII

Since this treatment deals only with the contribution to the maximum permissible dose which may originate from packaged-waste disposal, and since there are other sources of activity released to the environment, the allowable concentrations which are computed here are partial maximum permissible concentrations. For sea-food this concentration is denoted by ( p p c ) f . The relationship between m p c and ( p p c ) f is obtained by considering:(1) The maximum permissible dose-rate to the special group utilizing

locally harvested sea-food, and to the general population.(2) The further apportionment of this dose to sea disposal.(3) The ratio between the average daily intake of sea-food and the aver

age daily intake of drinking water.For the special population group, and for the ( p p c ) f which applies to

local fisheries, these factors give the relationship:(ppc)f = 0.01 X 0.2 X 100 X (m p c ) = 0.2 (m p c )

For the population at large, the mean concentration in the sea-food harvested over the entire segment of the continental shelf should not exceed the ( p p c ) f value given by:

(ppc)t = 0.01 X 0.2 X 100 X (m p c ) = 0.2 (m p c ) .

It is evident, then, that if the disposal operation is safe from the standpoint of the special groups, it will also be safe for the general population. The ( p p c ) f values thus determined are listed in the third column of Table I.

Two values are given for Na24. The upper value is based on the above relationship for sea-food, while the lower value applies to the salt evaporated from the sea and eaten by man. The ratio of water intake per day to salt requirement per day is about 108. Hence the partial maximum permissible concentration in the salt harvested from the sea would be, for the whole population, about twice the corresponding m p c value for industrial workers.

Partial maximum permissible concentrations in the sea-waters of the shelf areas

The partial maximum permissible concentrations in the sea-water, (ppc)w, can be obtained from the ( p p c ) f values if the ratio of the amount of the particular element in sea-food to the amount in sea-water is known. In the fourth column of Table I are listed the ratios by which edible marine organisms concentrate the various elements from sea-water. The values

153


given are generally conservative values, since fish flesh, which would ordinarily constitute the largest portion of the sea-food eaten by man, has lower concentration ratios than the total organism. Invertebrates, and certain organs and bones of the fish, concentrate many elements more highly than does fish flesh.

For Na24 two values are again given. The upper value is for marine organisms, while the lower value of 60 represents a conservative estimate of the concentration ratio in the production of edible salt from sea-water.

The (ppc)w value is obtained by dividing the (ppc)f value by the concentration ratio. The resulting values are given in the fifth column of Table I. Note that the (ppc)w values for Na24, based on intake through sea-food or salt, are very nearly the same. Since both routes would possibly provide a return of activity to man, their effects are additive. In order to take this additive effect into account, a (ppc)w value lower than either must be taken, such that the combination of these two routes would provide no more activity than would be provided by either route alone at the listed values of (ppc)w. The appropriate value of (ppc)„- for Na24 to be used in further computations is then 5 X 10 r’ jxc/ml.

In general, the relative amounts of the various isotopes requiring disposal will not be known at the time of site evaluation. The further computations must then be carried out in terms of a representative isotope, and the additive effects of a number of isotopes treated in the manner outlined in Appendix II. For the case at hand it is convenient to take care of the additive principle in the following manner.

The computations of allowable discharge rates are made on the basis of Sr90. Since this isotope has the longest half-life of those listed in Table I and, in general, will have the longest life of the isotopes to be disposed of in package form in the ocean, a very conservative method of determining the number of curies of any given isotope which would be equivalent to one curie of Sr00, from the standpoint of sea disposal, would simply be to take the ratio of the (ppc)w for the subject isotope to the (ppc)w for Sr90. The sum of these equivalent activities for the several isotopes which might be disposed of into a given site in a given time period must then not exceed the allowable rate of discharge of Sr90 alone to the site.

Computations of allowable rate of disposal at each siteThe conditions which are used in this example computation to establish

the safe rate of disposal of packaged wastes to the site in question are based on the following considerations.

Appendix VIII

154


Appendix VIII

The proposed disposal sites are square-shaped areas about 10 km on a side, located within regions which are not suitable for commercial fishing. However, fishing may occur just outside the non-fished region, and migratory fish will undoubtedly pass through the disposal areas from time to time. Appropriate inspection of disposal operations could ensure a reasonably uniform distribution of disposed containers over the designated site, and such a distribution would provide the most desirable conditions for dilution. However, for the purposes of computation the conservative condition is taken that all packages are discharged at a single point within the site. Containment time in the packages is neglected; that is, the conservative assumption is made that all packages break immediately on impact with the bottom. If it is required that concentrations exceeding the (ppc)w values occur over no more than one-tenth of the area of the site about the point source, then it is reasonable to assume that fish harvested outside the site area will have concentrations of activity less than the partial maximum permissible concentrations in sea-food. Since the nearest site locale is some 50 km from the salt basins at the coast, the above criteria would also more than satisfy the requirements for the safe harvesting of salt. It is also evident that the mean concentration over this entire segment of the shelf would be several orders of magnitude below the (ppc)K values if the above locale criteria were satisfied.

The appropriate equation from Appendix VI applicable to a continuous point source release is

M WV {X,y) ~ 2 Tza (W* + U*)'A [(TP + U 2)'A r - ux]

where p is the concentration of activity in c/m3 (or uc/ml) at the position x, y measured from an origin at the source; M is the rate of release of activity in c/sec; a is the depth over which vertical mixing takes place; W is the diffusion velocity, here taken as 10-2 m/sec; u is the velocity in m/sec; x is the co-ordinate axis directed parallel to the velocity u; r is the horizontal distance from the point of discharge, and given by (x2 + {/-)1 where y is the horizontal co-ordinate perpendicular to thedirection of the water movement.

This relationship involves macro-scale turbulence only. Near the source the concentrations will be appreciably less than given by this relationship as a result of micro-scale turbulence.

On the basis of observations of the vertical density distribution in the shelf waters, the conclusion is reached that rapid vertical mixing will occur in the lower 15 m of the water column, that is, the value of a in

155


the above equation is set at 15 m. The velocity u is taken at 5 X 10 2 m/sec, and the constant W at 10 ' 2 m/sec, values representative of the sites being evaluated.

The ratio of concentration, p (x, y), to rate of introduction, M, can then be computed for various positions x and j . If these values are plotted and contoured, the shape of the lines of equal concentration will be approximately elliptical. The closed equal concentration iso-lines, within which the area is equal to one-tenth of the area of the proposed site, can readily be found by trial and error. From this value of the ratio p/M the maximum permissible rate of discharge can be found by setting p equal to the (ppc)w value.

For this example computation, the value of the maximum permissible rate of discharge for Sr90, using a (ppc)w value of 2 X 10-8 , for each site, computed as described above, comes to approximately 1400 c/yr.

Consideration should be given, however, to the effect of one disposal site on another. The sites are approximately 50 km apart and strung along the general southerly flow of the area. The discharge of 1400 c/yr at a fairly steady rate would produce a concentration of about 2 X 10 _9 jxc/ml at a distance of 50 km downstream of these sites. This would have the effect of decreasing the allowable rate of discharge at the next most southerly site by about 10%. To take into account this additive effect of one disposal site on another, the computed allowable rate of discharge in this particular case is set at the value of 1000 c Sr90 equivalent per year.

This estimate is based on steady discharge without containment. Actually the packages will not be disposed of at a uniform rate, though sufficient containment can be expected so that the computed maximum rate of discharge given above would be conservative. However, some consideration should be given to a catastrophic release of activity which has accumulated in one of the sites. Thus, suppose that some unforeseen natural phenomenon results in the instantaneous discharge of the activity from packages which have accumulated for one full year. It is assumed that the full 1000 c of SrIJ0 equivalent are released at a given instant of time. The radioactive decay prior to and after discharge is neglected.

The contamination would move downstream as a cloud of ever-increasing dimensions and decreasing peak concentration. After one day an area of about 1 km radius would have concentrations exceeding 10-5 uc/ml; after 10 days the peak concentration would be about 2 X 10 " uc/ml; and after 40 days about 10 * |xc/ml. At this time the cloud would have moved downstream some 200 km. The area within which concentrations exceed (ppc)w values for Sr90 would have a maximum radius of about 25 km and

Appendix VIII

156


Appendix VIII

would occur 20 days after discharge, after which the area having such concentrations would decrease in size.

The northernmost and southernmost sites have flows parallel to the coast, and only the edges of the contaminated cloud from these sites would touch shore where the concentrations would not exceed3 X 10-9 |xc/ml. However, the flow through the central site has a shoreward component which would carry the contaminated cloud to the vicinity of the salt basins south of Port A (see Fig. 2) in about seven days. At this time the concentration near the centre of the contaminated volume would be about 4 X 10 ~7 uc/ml for a 1000-c release. While this value is about 20 times the (ppc)w value for Sr90, based on an apportionment of the long time exposure for the population as a whole, it is well below the concentration which would provide undue risks to man for short-time exposure. However, in view of the possible public concern, and hence reluctance to use the salt should such a release of activity occur, it would appear to be advisable to eliminate the central site from consideration and to limit disposal to the northern and southern sites.

From Fig. 1 it is clear that the distance from Port A to the southern disposal site is not significantly less than the distance to the 1000-m depth contour. Since disposal of a given amount of waste materials in depths of over 1000 m would involve even less risk than on the designated disposal sites, and since travel time from Port A to the disposal site would not be appreciably greater, it would appear reasonable to limit disposal operations from Port A to a designated site in waters of over 1000 m.

Having established the probable safe rate of discharge for the selected disposal sites, that is, the northernmost site at 30 m in depth and a site seaward from Port A in water of 1000 m in depth, actual discharge to the sites should be limited initially to a much lower rate for a sufficient time period so that direct observations of the resulting contamination could establish the validity of the computations. It is suggested here that discharges be limited initially to one-tenth of the computed safe rate.

Thus, the initial authorization for disposal at each site should be limited to the equivalent of 100 c of Sr90. The corresponding limits for other isotopes would be obtained by using the ratio of the (ppc)w for each isotope to the (ppc)w for Sr90, taking into account the additive effect if more than one isotope were involved, as already discussed. Thus, if the authorized disposal rate were to be divided equally among the four isotopes listed in Table I, then 25 c of Sr90, 50 c of I131 about 1 c of P32, and 62.5 X 103 c of Na24 could all be disposed of at each site without exceeding the authorized limit of 100 c of equivalent Sr90.

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RA DI OA C T I V E WA S T E S FROM R E A C T OR - P O WE R E DSHIPS

(Example computation)

The following computation to determine the safe limits of radioactive waste disposal from a nuclear-powered ship is carried through in considerable detail. There is no suggestion that this is the only possible approach, and differences might be noted between this method and those used in other examples of sea waste disposal. However, it is believed that the major conclusions reached in this computation are not materially different from those that would be reached from any reasonable analysis.

ScopeThis evaluation is limited to considerations of the marine environment,

particularly the open sea, continental shelf regions directly adjacent to open sea areas, and tidal estuaries and embayments. Locked harbours and semi-enclosed seas having small tidal range would require special treatment not given here.

The presently operating or planned nuclear-powered ships utilize light water-moderated reactors. Undoubtedly other types of marine reactors will be utilized in the future, but the character and amount of wastes which might be introduced into the marine environment from such future types of marine reactors cannot be predicted with any accuracy. In this Appendix consideration is limited to available information on waste from pressurized water-moderated marine reactors.

On the basis of available information on actual and planned construction, and forecasts of probable utilization of nuclear energy to power merchant ships, it is here concluded that, by the end of the next decade, there could be about 300 nuclear-powered ships either operating, under construction, or definitely planned throughout the world. Therefore, in this evaluation the effect of waste materials from 300 nuclear-powered ships is considered.

Modification of the “general approach” required for evaluation of nuclear- ship waste-disposal problem

In Chapter III a schematic description is given of the general approach to an evaluation of the suitability of any segment of the marine environment as a receiver of radioactive wastes. Modification of this approach

Appendix IX

158


Appendix IX

must be made for the case of waste disposal from nuclear-powered ships. These required modifications involve the following considerations:

(1) The source of wastes is not stationary but moves through all types of marine environments. This has the disadvantage that the most restrictive segment of the marine environment from the standpoint of suitability as a waste receiver must control certain features of the operation of nuclear-powered ships. It has the advantage that certain wastes, which are unsuitable for discharge in some segments of the sea, may be stored on shipboard and discharged when the ship is passing through areas which do have the safe capacity to receive them.

(2) The significant wastes are not discharged as a continuous effluent, but are released as discrete amounts of activity at essentially a point source in time and space. The end result of this evaluation of the marine environment is, then, not expressed as an allowable rate of continuous discharge of radioactive wastes, but as the allowable amount of activity which may be contained in any single release of waste material from a nuclear-powered ship, and the number of such releases which may be made in a given segment of the sea in a given time period.

Because nuclear-powered ships may traverse all types of marine environments, regulations controlling general operating doctrine must be based on the most restrictive consideration regarding the return of radioactive materials to man. The primary consideration made is that utilization of the marine environment by man will be in no way restricted, either on the basis of the present harvest rate or of possible future harvest rates. Therefore, it is here assumed that a population exists which receives all its protein needs from the sea and the computations are based on the requirement that no undue risk to such a population should result from the operation of nuclear-powered ships. On the other hand, any specific evaluation of the suitability of a given harbour, for example, to serve as a base or major port of call for nuclear-powered ships should include a study of man’s actual utilization of that particular area.

Subdivisions of the marine environment

In describing the properties of the ocean (Chapter V), a division was made on physical grounds into nearshore areas, the continental shelf, and the deep sea. While from some points of view a further subdivision is

159


possible [1], the above division of the marine environment will be retained in this example computation, with the following defining criteria:

Z o n e A (nearshore area): harbours, estuaries, and inshore waters within two miles of the coastline.

Z o n e B (the continental shelf and coastal area): the area seaward from two miles offshore to the 400-m depth contour, or to 10 miles offshore, whichever is more seaward.

Z o n e C ( t h e d e e p s e a ) : t h o s e a re a s o f t h e o p e n s e a m o r e t h a n 1 0 m ile s f r o m t h e c o a s t a n d h a v in g d e p t h s g r e a t e r t h a n 4 0 0 m .

Maximum permissible dose which may arise from the operation of nuclear- powered ships

In Chapter IV it was pointed out that, for the foreseeable future, waste disposal will, in general, affect special population groups rather than the population at large, and the critical dose-rate will usually be 0.5 rem/yr to the individual. This criterion will apply to the nuclear-powered ship problem only in the case of Zone A (nearshore area), where waste disposal will directly expose only a relatively small fraction of the whole population. In the case of Zone B (continental shelf and coastal area) and Zone C (the deep sea) it is more likely that international utilization of marine products will require the use of the genetic apportionment of 0.2 rem recommended in Chapter IV for a population as a whole.

In the case of Zone A, if the size of all the special groups in the nation involved should exceed some critical value, which is dependent upon the apportionment of the whole population genetic dose to the special groups, then the annual dose-rate averaged over individuals of the special group will need to be less than 0.5 rem. This dose-rate can be calculated from the apportionment and from the size of the special groups as shown in Chapter IV (see p. 32).

In this example computation the following quite conservative assumptions are made:(1) The special population group which is of concern in regard to possible

waste disposal from nuclear-powered ships into Zone A is assumed to comprise a significant fraction of the special groups B (c) which, in turn, is assumed to comprise 5°/o of the whole population. It is further assumed that the members of this fraction of the special group receive all their protein requirements from the sea.

(2) In considering Zones B and C, it is assumed that the population at large in a nation receives all its protein requirement from the sea.

Appendix IX

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Appendix IX

Partial maximum permissible concentrations in sea-foodThe only significant route whereby activity associated with waste

disposal from nuclear-powered ships could return to man is through the ingestion of sea-food. The determination of the partial maximum permissible concentration in sea-food which may result from nuclear-powered shipping may be made in the following manner:

The basic data employed are the maximum permissible concentrations in drinking water for the various radioisotopes recommended by ICRP. Table I contains a list of pertinent data on a number of isotopes, including the more important corrosion products and fission products which may occur in wastes from ship-borne reactors. In the third column of this Table the m pc values in water for the industrial worker, as recommended by the ICRP, are given.

These m pc values are based upon an intake of water per individual of 2200 ml per day. Individuals who obtain their full protein requirement from sea-food would ingest approximately 1500 g per week. Thus, one step in obtaining the partial maximum permissible concentrations in seafood from the given m pc values is to obtain the ratio of drinking water ingested per week to sea-food ingested per week. That is:

7 x 2 2001 500 — '

Hence,(MPC)food = 10 (m p c ) water-

The next step in the procedure is to obtain a factor representing the ratio of the permissible annual dose for the special population groups which might be exposed to the effects of sea disposal from nuclear-powered ships to the permissible annual dose for occupational workers.

Z o n e AHere it is first necessary to compute the allowable annual dose for this

special group of the population. The procedure described in Chapter IV (p. 35) is followed. The special group B (c) affected by peaceful uses of nuclear energy, other than those directly occupied in the nuclear industry, is assumed here to constitute 5°/o of the whole population. The allotment to this special group from the whole population genetic dose is taken to be 0.5 rem. The maximum permissible annual dose averaged over individuals of the special group is then

3 0 ^ = 3 0 ^ 0 5 = ° -33rem/yr-

11 16J


Appendix IX

This is less than the maximum permissible dose to any individual of 0.5 rem/yr, and thus, in this case, the genetic control can also be limiting.

The m p c values listed in Table I a r e based on a maximum allowable occupational exposure of 5 rem/yr. Hence, the ratio of the maximum allowable average dose for the special group to the maximum allowable dose for the occupational worker is given by

0.335.0 0.067.

There are other potential sources of radiation exposure for the special group than nuclear ship operation in Zone A, and the full allotment of 0.33 rem/yr for this group cannot be utilized by this one source. However, this portion of the population is designated as a special group because of possible exposure to the effects of nuclear shipping, and hence it would be reasonable to assign 50% of the maximum permissible dose for this group to these effects. Thus, the partial maximum permissible concentration of the several isotopes in sea-food for Zone A is related to the m pc values for water by the relationship:

( p p c ) f , a = 10 X 0.067 X 0.5 (m p c ) = 0.34 (m p c ).Z o n e B

Here the recommended apportionment from the whole population genetic dose for sea-disposal problems of an international character applies. In Chapter IV it is recommended that l/25th of the genetic dose, or 0.2 rem over the average reproductive life, be allotted to problems of sea disposal having an international character. The ratio of the partial maximum permissible annual dose which might arise from sea disposal to the maximum permissible annual dose to occupational workers is, then, for Zone B:

T,,,- 2 g = 1.33 x 10 -3.30 x 5

Nuclear-powered shipping appears to be one of the primary likely sources of waste problems having international implications, though in Zone B other possible sources, such as packaged-waste disposal must also be considered. It seems reasonable to assign 25°/o of the apportionment of 0.2 rem to nuclear-powered shipping in this zone. Hence, the partial maximum permissible concentration of the various isotopes in sea-food which may result from nuclear-ship operation in Zone B is related to the m pc values for water by the relationship:

( p p c ) f , b = 0.25 X 10 X 1.33 X 10~3 X ( m p c ) = 0.33 X 1 0 -2 (m p c ) .

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T a b l e I

DATA ON CERTAIN RADIOISOTOPES WHICH MAY BE PRESENT IN WASTE FROM NUCLEAR-POWERED SHIP REACTORS

Isotope Half-life

JL'L’C in potable water

((ic/m l)

Partial m aximum permissible concentrations in marine foods

(n c /g)

W eighted mean con centration ratios from sea-water

to sea-food

Partial maximum permissible concentration in sea-water

([xc/ml)

Zone A Zone B Zone C Zone A Zone B Zone C

Cobalt-60 5.2 yr 3 X 10-" 1 X 1 0 '4 1 X i o - 6 3 X 10-° 3 X 103 3 X 10-8 3 X 1 0 '10 1 X 10-9Iron-55 2.9 yr 8 x 10“ 3 3 X 10 -3 3 X 10 -5 8 X 10~5 3 X 103 1 X 10 -6 1 X 1 0 '8 , 3 x 10“ 8Iron-59 45 days 5 X 10-4 2 x 10“ 4 2 x 10-« 5 X lO-6 3 X 103 7 X 10_s 7 X 10-10 .2 x 10-9Chromium-51 27 days 2 X 10~2 7 X 10-3 7 X lO -5 2 X 10 -4 3 x 102 2 x 10-5 2 X 10~7 7 x 10~7C opper-64 12.8 yr 2 X 10~3 7 X lO^4 ■ 7 X 10“ B 2 X 10 -3 2 X 103 3 X 10 -7 3 x 10~9 1 x 10~ sTantalum -182 112 days 4 X 10~4 1 X 10~4 1 x 1 0 " 6 4 X 10-« 3 x 10- 3 X 10 -7 3 x 10~» 1 x 1 0 - 8Zinc-65 250 days 1 x 10“ 3 3 x 10-4 3 x 10-6 1 X 10“ 5 3 X 103 1 X 10 -7 1 x 10 '° 3 x 10"9Sodium-24 15 hr. 3 x 10-4 1 X 1 0 '4 1 x 10-* 3 X lO '8 0.5 2 X 10~4 2 x 10~« 6 x 1 0~ 6Cobalt-58 7 2 days 9 X 10-4 3 X 10"4 3 X 10~6 9 X lO "6 3 X 103 1 X 1 0 -7 1 x 10'° 3 X 10~9


Z o n e CAs with Zone B, waste-disposal operations of nuclear-powered ships

in Zone C involve international populations, and the ratio of the partial maximum permissible annual dose which might arise from sea disposal to the maximum permissible annual dose to occupation workers is, then, for Zone C, 1.33 X 10“ 3. However, nuclear-powered shipping is likely to be the primary source of waste problems having international character in Zone C and it is therefore reasonable to assign 75°/o of the apportionment of 0.2 rem to nuclear-powered shipping in this zone. The partial maximum permissible concentration of the various isotopes in sea-food which may result from nuclear-ship operation in Zone C is then related to the m p c values for water by the relationship:

( p p c ) f , c = 0.75 X 10 X 1.33 X 10~3 = 10~2 (m p c ).

The partial maximum permissible concentrations in sea-food for the various isotopes given in Table I are listed in the fourth, fifth, and sixth columns of that Table for Zones A, B, and C, respectively.

Partial maximum permissible concentrations in sea-waterHaving estimated ppc’s in marine food organisms, ppc’s in sea-water

can be obtained if the factor by which food organisms concentrate the isotopes in question in their bodies from the water is known. In the seventh column of Table I are listed the concentration factors for the various isotopes which are utilized in this computation. They are based on values given in various published papers [1, 2, 3, 4] and represent weighted mean values assuming a reasonable distribution of invertebrates, fish flesh, and fish skeleton in the diet. Thus, for this population which receives all its protein requirement from sea-food, it is here assumed that 20% of the diet is from invertebrates, 75% from fish flesh, and 5°/o from fish skeleton.

The partial maximum permissible concentration in sea-water, for each of the zones, is then obtained by dividing the ppc values for sea-food for each of the zones, for each isotope, by the corresponding concentration factor. The ppc values for sea-water for Zones A, B, and C are given in Table I in columns 8, 9, and 10 respectively.

Waste from a typical nuclear-powered shipAvailable published material has been utilized to establish the probable

character and amount of potential wastes from nuclear-powered merchant ships [1, 5, 6]. The major components of the waste will be corrosion products; the kind and amount of the isotopes which will be of importance

Appendix IX

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Appendix IX

in the wastes will depend on the metallurgy o f the primary coolant system and the fuel element cladding. The data used in this evaluation are representative of one particular reactor system [6] ; however, the conclusions based on these data are probably on the safe side since actual observed activities in wastes from existing nuclear-powered vessels [5] are significantly lower than those used in this evaluation.

The expected quantities of various nuclides in the primary coolant water and in the ion exchangers are tabulated in Tables II and III for those isotopes that present the greatest potential hazard through ingestion in marine food organisms.

T a b le IIIMPORTANT ISOTOPES IN REACTOR COOLANT WATER OF A TYPICAL

NUCLEAR-POWERED SHIP

IsotopeConcentration

in primary coolant ([ic/m l)

Am ount discharged per start-up*

(o)1.1 X 10“ 2 9.0 X 10-2

Cr51 2.2 X 10-2 1.8 X lO '1F e55 1.5 X 10 -2 1.2 X 10-1F e59 3.1 X 10~4 2.5 X 10^3

. Co58 1.3 X 10-“ 1 . 1 x i o - 2Co60 3.7 X 10-" 3.0 X 10-3

Gross activity for isotopes listed above 5.0 X 10-2 4.1 X 10 -1

Weighted ppc value for above-listed isotope mixture: Zone A = 1 X 10_e[ic/ml; Zone B = 1 X 10- 9 jxc/ml; Zone C = 3 X 10 -8 jxc/ml.* From assumed expansion volume of • 8.2 X 10° ml.

T a b le IIIIMPORTANT ISOTOPES IN SPENT DEMINERALIZER OF A TYPICAL

NUCLEAR-POWERED SHIP

IsotopeTotal activity

in demineralizer (<=)

N a84 1Cr51 70Fe55 80Fe«* 1Co58 5Cof,° 2

Gross activity forisotopes listed above 100

Weighted ppc value for above-listed isotope mixture: Zone A = 7X 10 -7 M-c/ml; Zone B = 7 X IQ-9 [Xc/ml; Zone C = 2 x 10 -8 jAc/ml.

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The evaluation o f permissible rates of discharge of nuclear wastes is com plicated by the fact that the potential effluents from nuclear-powered ships are com posed o f a mixture o f isotopes which may have additive effects on man. In order to include this feature in later computations, it is convenient to determine a weighted mean ppc value for the isotope mixture in the primary coolant. This w eighted mean p pc value can then be com pared with the gross activity resulting from the mix o f the significant isotopes listed. In com puting the weighted mean ppc value and the gross activity, w hich are included in Table II, only the isotopes listed in the Table have been considered. Very short-lived isotopes are not included in the calculation.

Basis for evaluation of safe discharge ratesAs shown in Table II, the amount o f activity likely to be involved in

the discharge o f a single warm-up volum e w ould be about 4 X 1 0 c. Recent experiments with point source releases of tracer dye volumes, o f about the same order o f magnitude as the volum e discharged on warm-up, show that even in harbour areas o f rather low tidal currents, the ratio of concentration to total contaminant released is reduced to 10- 5/m 3 or less in the first hour after release. Such initial dilution w ould provide a concentration one hour after release o f no more than4 X 10-G uc/ml for warm-up volumes discharged from the vessel. A dilution o f at least another factor o f ten takes place within two hours. Thus, within two to three hours after discharge o f a single warm-up volume, the concentrations w ould be less than the weighted mean pp c values for Zone A, and w ould be approaching those for Zones B and C (see Table II), providing that the dilution ivater is “ new” ivater unaffected by previous discharges. The allowable number o f discharges o f warm-up volumes which may be made in a given time period is a problem involving the rate at which “ new ” , essentially uncontaminated water is made available to the segment o f the harbour in which docking o f nuclear-powered ships takes place, and also the rate o f renewal of the harbour waters on the whole, rather than the details o f diffusion and advection within the area.

In some harbour and inshore areas the rate o f renewal o f the water may be so low as to preclude the discharge o f even these low-level liquid wastes, in which case the material w ould require to be stored in tanks aboard the vessel for discharge in offshore areas (Zones B and C). In these areas the early stages o f mixing would provide at least as high a dilution as indicated above, so that the problem again involves the gross rate of

Appendix IX

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Appendix IX

exchange of the waters in the area o f discharge with adjacent uncontaminated waters, rather than the details o f the dispersion o f a single release.

The amount of activity associated with the discharge o f a spent ion- exchange bed is about 160 c. As will be shown later, the discharge o f these amounts o f activity cannot be tolerated in the harbours, estuaries or other inshore areas. Experience with the resins from existing nuclear- pow ered vessels indicates that the activity is released from the resin to the sea-water in a few minutes after discharge. Initial mechanical dilution o f this activity is necessary, and it is recom m ended that the discharge o f spent ion-exchange resins be made into the turbulent propeller wake while the ship is under way at near maximum speed.

Ships o f the size likely to be pow ered by a nuclear reactor travelling at, say, 15 knots for a period o f 10 min w ould sweep out a turbulent wake, having a volum e o f about 106 m3. If the spent resin were discharged at a uniform rate during this 10-min period, the activity w ould be uniformly distributed within this volume. The initial concentration o f activity would then be 1.6 X 10^ 4 [xc/ml for a discharge o f 160 c. The weighted mean m p c value for occupational workers is 8 X 10 ~ 4 uc/rnl for an isotope mix such as has been indicated will be associated with spent ion exchangers. Thus, the initial concentrations w ould be below levels which would give any concern from the standpoint o f direct individual exposure, but well above the partial maximum permissible concentrations for Zones B and C of the ocean.

The partial maximum permissible concentrations are, however, based on the apportionment o f the genetic dose for a whole population and are com puted on the basis o f continual exposure o f the entire protein food supply of the population. Concentrations exceeding p p c values originating from a single discharge o f a spent ion-exchange bed w ould occur over a limited area com pared to the area from which the population considered could harvest its entire protein food supply, and w ould occur for a limited time. After one day the material w ould be mixed vertically dow n to the depth o f the thermocline (50 to 100 m in the open sea) and w ould have been dispersed horizontally. On the basis o f available data on diffusion in the ocean, the peak concentration in the centre o f the dispersing volum e of waste materials would, after one day, be reduced to about 1 X 10 “ 7 lie/ml for the 160-c release. After 10 days the corresponding concentration w ould be about 1 X 10“ 9 |xc/ml.

The concentrations given above are based on the condition that the mixing is taking place with water which is not contaminated by previous discharges. The question as to whether disposal o f spent ion-exchange

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resins from nuclear-powered ships can be made safely into a given ocean area then involves the rate of exchange of the waters in that area with waters from adjacent areas.

Consider, for example, a given region of the ocean which is presumed to supply the entire protein requirement of a whole population, and into w hich a given number of discharges of waste materials is made in a given time period. The rate at w hich “ new ” water is added to this region must be such that the_mean concentration of activity within the region is less than the pp c values for the isotope mix which is discharged. Since it cannot be presumed that the dischargers will be completely random in time and space, some sort of weighted mean concentration, higher than the arithmetic mean concentration over the area, is proposed. Present information is sufficient to provide for any accurate method o f obtaining the correct weighted mean concentration. H owever, to be on the safe side the weighted mean concentration is taken as twice the arithmetic mean over the area.

Thus the criterion which will be utilized in determining the rate at w hich waste materials from nuclear-powered ships may be introduced during a given time period into a given segment of the ocean, is that the mean concentration over the area in question should not exceed one-half o f the pp c values for the isotope mixture. The mean concentration is com puted on the basis o f the fractional rate of exchange of the waters o f the subject area with adjacent areas, rather than on the basis of the total volum e o f water present in the upper mixed layer of the subject area at a given time.

The ultimate capacity of the surface layer of the whole oceanThe arguments leading to the above criteria require that there is avail

able to the segments o f the ocean considered a supply of relatively uncontaminated “ new ” water for dilution. The surface layers of the ocean do exchange with deep waters, and activity w ill be slowly removed from the surface layers as a result o f uptake on particulate matter and ultimate sedimentation. Radioactive decay would, o f course, represent an effective^ rate of removal o f activity.

At steady-state, the rate of introduction of activity to the surface layers o f the ocean w ill equal the rate o f removal b y the three processes given above. The present best estimate o f the average retention time for the waters in the upper 75 m (the mean depth of the upper mixed layer) is seven years. G o l d b e r g and A r r h e n iu s [7] have com puted the mean residence time o f various elements in the ocean, including iron and cobalt,

Appendix IX

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Appendix IX

two major contributors to the activity on spention-exchange beds. These values, together with the known decay rates for the various isotopes, can be utilized in com puting the mean steady-state concentration o f activity in the surface layers of the ocean for a given rate o f introduction of radioactive materials.

The North Atlantic Ocean is used here as an example. If each of 300 nuclear-powered ships o f the type considered here were to discharge spent ion-exchangers, each discharge containing about 160 c o f the isotope mixture given in Table II, six times a year, into the North Atlantic Ocean, the steady-state mean concentration o f activity in the upper 75 m w ould be 7 X 10- n [j,c/ml, o f w hich about 6 X 10~u (xc/ml w ould be iron-55. It should be pointed out that some existing nuclear-powered vessels have reactor systems with different metallurgy, and cobalt-60 is of more importance as a corrosion product in the wastes than iron-55 [5 ], H ow ever, the observed amounts o f radionuclides in the spent ion-exchangers of such vessels are considerably less than those assumed in the evaluation; the steady-state cobalt-60 concentration in the North Atlantic Ocean resulting from 300 such vessels w ould be o f the order of 1 X 10- u [xc/ml. In any case, the above concentrations are sufficiently below the maximum partial permissible concentrations for the isotopes involved so that, in the com putations for a given segment o f the oceans, the diluting water can be considered as uncontaminated.

Evaluation of the suitability of the different zones to receive wastes from nuclear-powered ships

On the basis o f the preceding discussion it is possible to evaluate the suitability o f given segments of each o f the three zones o f the ocean, as defined in Section C o f this Appendix, as receivers o f wastes from nuclear- pow ered ships. In the follow ing example, computations are made for specific segments of each zone in order to provide numerical support for the conclusions w hich appear in the last section o f this Appendix.

Z o n e A

The rates o f renewal o f the waters o f embayments and estuaries differ markedly, and two examples are treated here. The hypothetical harbours discussed are m odelled on known waterways and are each typical o f a class o f real harbour.

First, consider a moderate-sized harbour in which the combination of fresh water inflow and tidal-induced mixing produce a strong estuarine

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circulation pattern characteristic o f a partially-mixed estuary. The volume of the harbour is taken to be 108 m3. The time required to replace half the waters o f the harbour with new water from the adjacent coastal area and from river inflow is assumed to be ten days, which represents a fairly typical flushing rate for systems o f this size and type.

The question to be answered is as follow s: H ow many discharges of reactor warm-up volumes may be made into this harbour over a given time period of, say, one month, without having the volum e mean concentration of activity exceed one-half the weighted mean ppc values for the isotope mixture involved. I f w e designate the half-life o f the harbour water (i. e. the time required to renew one-half o f the water volum e of the harbour) as <1/2; the volum e o f the harbour as V ; the amount o f activity realeased per discharge as M (curies); the allowable number of releases over the designated period o f averaging as N; the length of this period as T ; and the weighted mean partial maximum permissible concentration for the isotope mixture involved as ppc; then the relation:

2 N M til^ _ 1V T 2

satisfies the criteria of safety discussed above. Therefore, the maximum allowable number o f discharges per month w ould be given by

30 V pp(7

Here a 30-day month has been taken, and 11/2 w ould be expressed in days.

Data on the predicted concentration of activity in the primary coolant, as given in Table II, show that the probable maximum amount o f activity per discharge w ould be about 4.1 X 10-1 c. Using this value, together with the volum e and half-life of the harbour and the w eighted mean ppc value of 1 X 10~° j.ic/ml, gives:

30 x 108x 1 x 10~6 1A2 ,,A' = —— —— ——— —— = 2 x 10! per month.4 x 4.1 X 10 X 10 1

Thus, this example harbour w ould have ample capacity for the safe discharge o f warm-up volum e wastes from nuclear-powered vessels.

For the second example, consider a harbour in a bar-built lagoon having a relatively restricted inlet from the sea. Tidal currents in such systems are frequently restricted to the inlet channel, and dispersion within the embayment is primarily dependent on w ind-induced mixing. For this

] 70


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example computation, consider such an embayment having a volum e of 108 m 3 and a half-life o f 10 months. Equation (2) then gives:

_ 30 x 10* x 1 x 10-« _ '” 4 x 4.1 x 10' 1 X 3 X 10! “

Thus, only seven ships per month could release warm-up volumes into this embayment. Since, in addition, the dispersion characteristics within such systems are poor, this example embayment w ould be unsuited for release o f warm-up expansion volumes from nuclear-powered ships.

M any harbours which serve as bases or ports o f call for nuclear-powered shipping could safely receive discharges o f liquid low -level waste associated with warm-up expansion o f the primary coolant. Other harbours w ould be unsuitable for the discharge o f such an effluent. Since nuclear- pow ered vessels w ill probably enter ports of varying flushing characteristics, it appears desirable to have facilities for storage o f such wastes on tanks aboard ship for later release in regions o f ample waste-receiving capacity. Activities associated with spent ion-exchange resins w ould be far in excess o f the capacity o f most harbours to receive release of this type.

Z o n e B

The continental shelf off most coasts extends into international waters,and serves as the major fishing area throughout the w orld ’s oceans. Forpurposes of illustrative computation consider the Grand Banks region ofthe North Atlantic Ocean off Newfoundland. The area o f the shelf usedfor this evaluation, having depths less than 400 m, is about 2.5 X 1011 n r,with linear dimensions o f about 400 by 600 km. The volum e o f the mixedlayer, with a depth of about 40 m, is then 1013 m 3. A conservative estimateo f the median residence time (half-life) o f the water over the Banks is100 days. For these international waters the weighted mean partialmaximum permissible concentration as given in Table II for the isotopemixture in the liquid wastes, while operating in ports and nearshoreregions, w ould result in an accumulation o f such wastes having a totalactivity about three times the activity due to a single warm-up expansionvolume, or about 1.2 c, then the number o f such releases w hich couldtake place over a one-month period in this region is, from Equation (2):

A7 30 x 2.5 x 1011 x 10-8 N = -------- — — — ------- = 1 6 0 per month.4 x 1 . 2 x 1 0 *

The probable amount of activity w hich w ould be accum ulated with the stored liquid wastes over a one-m onth period w ould not exceed one curie,

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and hence this area could safely receive the liquid wastes from 160 ships o f the type considered here, month after month. It thus appears that continental shelf waters adjacent to the open sea, from two miles offshore out to the 400-m depth, or to a distance 10 miles offshore, whichever is further from the coastline, could safely receive the normal operating liquid wastes from nuclear-powered ships.

For discharges o f spent ion-exchangers with a gross activity o f 160 c and a value of ppc of 7 X 10 -9 (see Table III), Equation (2) gives:

AT 30 x 2.5 x 1011x 7 x 1 0 "9 . AOA/ = ----------- — - - - — — ----------= 0.8 per month.4 x 1 6 0 x 1 0 s r

As the number of nuclear-powered ships increases, the probability of more than one traversing such a segment of the continental shelf at a time w hen the discharge of a spent ion-exchange bed m ight be desirable, is sufficiently large so that such areas w ould appear to be generally unsuited to receive such waste materials. Thus, the discharge of spent ion-exchange resins should not be made in continental shelf waters, defined as the area having depths less than 400 m, or occurring within 10 miles o f the coast, whichever criterion extends more seaward.

Z o n e CThe open sea, that is those areas o f the ocean more than 10 miles from

shore, and with depths greater than 400 m, has greater capacity to receive radioactive wastes safely than either Zone A or Zone B. Since the waters o f the continental shelf are suitable receivers of the low-level liquid effluent from nuclear-powered ships, it is evident that the introduction of such wastes into the open sea can be made without undue risk to man.

In evaluating the capacity o f the open sea to receive spent ion-exchange resins, consider a trade route in the North Atlantic between North America and Europe. The total area o f the trade route is taken at 6 X 105 km2 (6000 by 100 km), and the volum e o f the upper mixed layer (here taken as 100 m in depth) is then 6 X 1013 m3. The median retention time for water in this region is taken conservatively as 100 days though current charts indicate a more probable value is about 20 days. Equation (2) then gives for the maximum allowable number o f discharges o f spent ion- exchange resins (each containing 160 c) into this area each month,

30 x 6 x 1013 x 2 x 10~8 _4 x 1 6 0 x lO 2

Thus, if 300 nuclear-powered ships operated regularly on this trade route, and each ship discharged a spent ion-exchange bed having 160 c

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once every two months, only about one-sixth o f the capacity o f the area to receive such wastes w ould be utilized.

SummaryThe waste to be disposed o f at sea in connection with nuclear shipping

will depend upon the design o f the reactor and ancillary equipm ent used. It is only possible to deal with presently proposed ship propulsion units, but it can be assumed that such wastes w ill be of low or intermediate activity for the present. Radioactive waste materials w hich m ight be introduced into the marine environment from presently designed pressurized water-moderated reactor-powered ships include low -level liquid effluents originating from warm-up expansion volumes and leakage o f the primary coolant, plus intermediate level wastes contained in spent ion-exchange resins.

Nuclear-powered ships will traverse regions o f the sea which are unsuited as safe receivers of nuclear wastes. H owever, over much of the open sea region traversed by trade routes, conditions are suitable for the discharge, without undue risk to man, o f amounts o f activity associated with the normal operating wastes from nuclear ships. In order to obtain maximum initial mechanical dilution of the radioactive waste discharged from nuclear-powered ships, such wastes can be introduced into the turbulent propeller wake while the ship is under way.

Harbours, estuaries, and other inshore areas, appear unsuited for the discharge of spent ion-exchange resins from nuclear-powered ships. M any harbours could, without undue risk to man, receive the low -level liquid effluent associated with the warm-up expansion volum e and normal leakage. H owever, some harbours o f poor flushing character, from w hich man harvests a significant amount o f food , would be unsuited for such release o f activity. The degree to w hich a particular inshore area can be utilized as a receiver of low -level liquid wastes from nuclear-powered ships can only be judged on the basis of a specific study o f the area in question. All discharge o f radioactive wastes from ships in harbours and other nearshore areas should be in conform ance with conditions laid dow n by the local authority.

The continental shelf and coastal area from a few miles offshore out to the 400-m depth contour, or 10 miles from shore, whichever is further seaward, has adequate safe capacity to receive the low -level liquid wastes arising from normal operations of nuclear-powered ships. This area o f the sea is not recom m ended for the release o f spent ion-exchange resins from nuclear-powered ships.

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R E F E R E N C E S

[1] N ATION AL ACAD EM Y OF SCIENCES — N ATION AL RESEARCH CO U N CIL, Publication No. 658: “ Radioactive Waste Disposal From Nuclear- Powered Ships” , W ashington, D . C., United States (1959).

[2] N ATIO N AL ACAD EM Y O F SCIENCES — N ATION AL RESEARCH CO U N CIL, Publication No. 655: “ Radioactive Waste Disposal into Atlantic and Gulf Coast Waters” , Washington, D . C., United States (1959).

[3] REVELLE, R., et ml., “ The Effects o f Atomic Radiation on Oceanography and Fisheries” , National Academ y o f Sciences, National Research Council, Publ. No. 551, Washington, D . C., United States (1957).

[4] D E COURCEY, M., Jr., “ The Uptake of Radioactive Wastes by Benthic Organisms” , Ninth Pacific Science Congress (1957).

[5] JOINT CO M M ITTE E ON A TO M IC ENERGY, CONGRESS O F THE U N ITED STATES (Hearings before the Special Subcommittee on Radiation): “ Industrial Radioactive Waste Disposal” , Eighty-Sixth Congress, First Session, January-February (1959).

[6] OAK RIDGE N ATION AL LABORATORY, Annual Report for Period Ending Novem ber 30, 1958: “ Maritime Reactor Project” , ORNL-2657, TID-4500 (14th Ed.).

[7] G O LD BERG , E. D . and ARRHENIUS, G. O. S., “ Chemistry o f Pacific Pelagic Sediments” , Geoch. et cosmoch. Acta, 13 (1958) 153— 212, Pergamon Press, London.

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Radioactive Waste Disposal into the Sea

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