Brit. J. industr. Med., 1955, 12, 147

RADIATION SAFETY AT AN ATOMIC ENERGY FACTORYBY

D. R. R. FAIRFrom the Department ofAtomic Fnergy, Windscale Works, Sellafield

Many people still think of atomic energy as amatter of scientists with scientific assistants andlaboratories with laboratory-type equipment. Thefactories of the Industrial Group of the U.K. AtomicEnergy Authority are controlled and directed byengineers and industrial chemists as well as byphysicists, most of whom must be as skilled inmanagement as they are in the technical complexitiesof their work. The employees are process workersof various grades and skilled tradesmen such asfitters, electricians, and instrument mechanics.When we are thinking of radiation protection we

are thinking mainly of workpeople in factories andnot of scientists in laboratories.

External RadiationTo achieve safe working conditions in a factory

operating nuclear piles or chemical plants whichseparate the plutonium, uranium, and fissionproducts formed in the piles, certain data arenecessary. First, the magnitude and spatial distribu-tion of the sources of radiation; second, the typeand energy of the radiations emitted by the sources;third, the variation of both of these with time, forexample, with the age and operational state of apile or with the stage reached in a chemical flowsheet; fourth, technical information regarding thetypes of shielding available, their effectiveness andcost, and the so-called " maximum permissiblelevels " for the various radiations concerned.With this data the design staff select the best and

most economical material to build the shield aroundthe plant. Gamma rays are stopped most easily byheavy metals like lead, but lead is expensive and it isoften cheaper to put up a thick shield of concretethan a thinner shield of lead. To screen a neutronsource it is necessary to surround it by a materialwhich will slow neutrons down. (The mechanism ofthe absorption process is different from that applyingto gamma rays.) A good slowing-down medium forneutrons must be made up of light atoms. Concrete,containing as it does a great deal of hydrogen, is abetter shielding material for neutrons than lead oriron. Concrete is in fact very useful for shielding

purposes because, provided the composition andthickness are properly chosen, it is efficient, cheap,and an excellent building material.The determination of shield thickness often

requires very elaborate calculations but practicalexperience of shielding large radiation sources is, ofcourse, now available to the industry. Not allshielding is concrete. Water is often an excellentshield since it also permits underwater manipulationof the active material.

It is not always necessary or desirable to shieldparts of plant or equipment. The early assessmentof the external radiation hazard associated withchemical plant which has carried highly or mediumactive liquors was such that it was thought either tobe impossible or at best extremely difficult and costlyto carry out maintenance operations on such plantat all. This had a profound influence on the designof the plant. Considerable ingenuity and inventive-ness were exercised to avoid putting items whichrequired maintenance behind biological shields.Also the method of access to the plant and equip-ment behind the shields was not considered in detailsince it was thought that no one would be able to gobehind the shields once the plant had become active.In fact the early estimates of radiation levels werenot substantially incorrect but the extent to which itwould be possible to control work in high-radiationfields so that the worker was not exposed to aradiation dose greater than the permissible wasunderestimated. It has now been found possibleto undertake maintenance and modification work onactive plant, and it is important that such workshould not be made more difficult and dangerous tothe maintenance man because of shielding placed tosafeguard the plant operator. The design shouldnot be distorted to accommodate a shield if safetymay be achieved for the plant operators by distance.In many cases, the hazards from radiation decreaseroughly as the square of the distance. For safetyby distance to be effective with the high-radiationfields met with in the atomic energy industry themethod of entry to the dangerous areas must becontrolled as strictly as the entry to high-voltageareas in an electrical distribution system.

147

on Novem

ber 1, 2021 by guest. Protected by copyright.

http://oem.bm

j.com/

Br J Ind M

ed: first published as 10.1136/oem.12.2.147 on 1 A

pril 1955. Dow

nloaded from

BRITISH JOURNAL OF INDUSTRIAL MEDICINE

Safety by shielding and safety by distance arecontributions to the workers' safety from externalradiation which are made by the design officers.

Plant and equipment designed for radioactivematerials do not differ from other plant in that theydo from time to time require either maintenance ormodification and it is during such work that thefactory management is faced with its greatestproblems of control. The questions to be answeredbefore beginning work in a very high radiation fieldof, say, 10 to 10,000 times the maximum permissiblelevel are:

(1) Is anything to be gained by waiting ? This isalways an unpopular thing to do in a factory. Incertain cases where the radioactivity is due to freshfission products a safety factor of 10 or more isgained in 24 hours by allowing the short-lived of thefission products to decay completely before begin-ning work.

(2) Is it possible to reduce the radiation field ?For example, if it is due to fission products insidevessels or pipework, decontamination may be bothpossible and worthwhile.

(3) What is the radiation dose-rate in and aroundthe area where work is to be done ? A survey of bothbeta and gamma radiations is carried out to give thisdata.

(4) Is it possible to erect temporary radiationshields around high centres of activity or around theimmediate working location ? The answer to thisquestion is generally delicately balanced and dependsupon the probable length of the work to be done,the intensity of the field, the ease with which ashield may be provided, since it must not be for-gotten that men will have to erect the shield, andthe influence of a shield on the work to be done.In certain locations where space is very limited ashield might so impede the maintenance man thathis radiation exposure is actually increased becauseof the extra time needed to do the job.

(5) Are special tools necessary for remote hand-ling of the plant or equipment ? Again the answerto this question is often delicately balanced anddepends upon the beta radiation present as well asthe gamma, since if the beta level is high this willconstitute an additional hazard to the hands. It isoften thought that thick gloves give complete betaprotection, but this is not necessarily true and inany case many tasks demand manual dexterity anda good sense of feel, so that, although gloves areworn, they are often thin and well fitting-ratherlike surgeons' gloves.When the method of working and permissible

working time per man have been determined, thenthe man himself is briefed, radiation monitoring

films are placed on his body, wrist, and cap, and hewill carry also a pocket dosimeter, which gives adirect reading of the dose received. The man'sentrance to the radiation area will be timed and hewill be recalled from the job by a man speciallydetailed to control working times.The men have been trained in simple procedures

to reduce radiation exposure; discussion of the.next step to be taken should not take place righton the job but away from it in a low-radiationfield; a mate should not stand at the craftman'sshoulder unless there is a task to do.By these commonsense methods, work in high-

radiation fields has been carried out successfullywithout over-exposing the workers.

Internal RadiationThe problems associated with the protection of

the workers in the atomic energy industry from theinhalation or ingestion of radioactive materials havebeen amongst the most difficult the industry has hadto tackle.The problem itself is not new in principle; it is

new only in degree. The maximum permissibleconcentration (m.p.c.) or maximum allowableconcentration (m.a.c.), or "design concentration",to use the terminology suggested by Dr. Goldblattat our last conference, of plutonium in air is 32micro-micrograms per cubic metre of air, and it is thistiny quantity of the industry's product that must notbe exceeded in theworking space. As well as this levelfor plutonium there are similar or lower levels forfission products such as strontium and iodine, whichare waste-products of the industry. As for externalradiation the solution is a combination of gooddesign and good management. Radioactive materialcan escape into the air only when pipework orvessels are vented to air or leak or when it isnecessary to transfer material from one vessel toanother. The design officers provided the mainchemical plant buildings with a high stack so thatany radioactive material arising from vented vesselsand not removed by a scrubbing system would be sodiluted before it diffused to ground level that itwould be quite harmless. Also in the main chemicalseparation plant the columns, tanks, feed pipes, andso on were fabricated from stainless steel and weldedtogether. A special corrosion-resistant stainlesssteel was developed to meet this requirement, andthe technique of welding stainless steel had to befurther developed to deal with the type of steel usedand the very high standard of welding demanded.It was not possible, however, for the designers toprovide an all-welded construction in plants fedfrom the main chemical separation plant and neither

148

on Novem

ber 1, 2021 by guest. Protected by copyright.

http://oem.bm

j.com/

Br J Ind M

ed: first published as 10.1136/oem.12.2.147 on 1 A

pril 1955. Dow

nloaded from

RADIATION HAZARDS IN INDUSTRY

was it possible to avoid taking liquor out of plantfor transfer or temporary storage at certain stages.Liquor transfer becomes progressively more difficultas the transfer takes place later and later in theplutonium production process; that is, withstronger and stronger plutonium solutions. Onemethod of transfer is to use a hypodermic needletechnique for filling and emptying containers coveredwith specially well fitting rubber caps. However,the small quantity of plutonium needed to give riseto an m.p.c. in air is such that even the hypodermictechnique cannot be carried out in the open but mustbe done in a specially ventilated enclosure. The vesselsare therefore normally raised on to the needle ratherthan the needle inserted into the cap of the vessel,and this operation is done remotely. It is by suchmethods as these that air contamination duringnormal process operations has been kept undercontrol. However, plant needs modification ormaintenance, and if work is to be carried out onactive plant air contamination is generally boundto arise. The exception is when the plant or itemsconcerned can be completely decontaminated beforeremedial work starts, but even then air contamina-tion is caused more often than not when the item isremoved for decontamination.The air contamination is reduced by carefully

cleaning out the vessels and pipes before openingthem and by arranging the work in a precise sequenceso that messy or dusty actions or movements areavoided. Careful briefing of the craftsmen inprocedure is necessary. Also the point where thebreak into the active system is made is sprayed witha solution of glycerine in water to lay any dust assoon as it becomes airborne. The glycerine ishygroscopic and prevents the water evaporating tooquickly. Considerable use is made of absorbentpaper shrouds placed around the necks of vesselsand under pipes to facilitate the subsequent cleaningup. The volume of air which is contaminated iscarefully defined by building around the work to becarried out a tent-like enclosure made of tubularsteel framework and polyvinyl chloride sheet, thejoins of which are sealed by a cocooning processsimilar to that used by the Services to encasemilitary equipment. The contaminated air isexhausted from the tent enclosure through a high-efficiency vacuum cleaner and is then fed into oneof the air-trunking systems connected to the stacks.It is fortunate that as the plutonium concentrationincreases and the careful enclosure of active workbecomes more and more necessary, so the beta-gamma content of the solution becomes less and lessand the external radiation hazard decreases, therebymaking the erection of the enclosures possible.

To provide the worker with clean air one of threemethods is followed. A dust respirator fitted with aPorton dust filter type D8/42 is worn. The filter isdesigned to permit no more than 0-00001% pene-tration for i micron size particles, but the reallimitation is the fit of the respirator to the man'sface. When the air contamination is very high ortoxic gases may be present in quantity-many of theplants have an installed carbon-dioxide fire-fightingsystem-then clean air must be provided for theworker rather than reliance placed upon filtered air.If the job is of short duration of up to 20 min. orgreat mobility is needed, then the worker carries anair bottle on his back. The fireman's " self-air "apparatus is the one in use. If the job is a largerone the worker has an airline mask fed from afiltered off-take from the factory's compressed airmain or is dressed in a pressurized suit whichhas been developed for this type of work. Thepressurized suit is made of all-welded polyvinylchloride sheet and totally encloses its wearer. Thehead is in a transparent polyvinyl chloride helmetand the air supply is fed in near the neck of thehelmet. The air is exhausted from the suit via afilter which both prevents back diffusion of activityinto the suit and provides a pressure drop tokeep the suit inflated and held just comfortablyoff the wearer's body.Not only is it necessary to take these precautions

during maintenance or modification work, but alsoit is most important to clean up completely after theoperation so that any contamination left is below alevel which could give rise to an ingestion orinhalation hazard. Permissible surface contamina-tion has been set at such levels that it is believed thatworking for a full working lifetime with such levelson floors, benches, walls, plant, equipment, and soon, will not be injurious to the individual exposed.Detailed surface contamination surveys follow workon active plant and are part of normal routine. Theworker is dressed according to the task he has totackle. He will wear a simple coverall over his ownclothes for most normal process work in the chemicalplant, and will be progressively clothed as thehazard increases until he is dressed from the skinup in factory clothing and enveloped in a P.V.C.suit for the most difficult job. Undressing aman who has been in contact with active materialsis a potent source of air and surface contamination,and undressers with dust respirators have beentrained to do this. The wearer of a pressurized suitoften has to pass through a water shower followedby a shower containing both wetting and complex-ing agents before removing his suit.

Just as detailed, surface-contamination surveys

149

on Novem

ber 1, 2021 by guest. Protected by copyright.

http://oem.bm

j.com/

Br J Ind M

ed: first published as 10.1136/oem.12.2.147 on 1 A

pril 1955. Dow

nloaded from

0BRITISH JOURNAL OF INDUSTRIAL MEDICINE

are part of every day's work, so are carefulsurveys of contamination of the workers. There arethree stages by which workers are examined forcontamination: (1) Monitoring of the individualwith portable equipment on the job: this is tolocate contamination as soon as it arises. As withany other form of dirt, contamination is most easilyremoved if cleaning is undertaken quickly; also,monitoring on the job, as well as protecting theworker concerned, protects also his workmates andthe rest of the plant, since it is very easy to transfercontamination from one place to another. (2)Monitoring of the individual with installed equip-ment before he leaves a building: this, again, is toprotect the worker and also the plant. Cross-con-tamination of two plants dealing with uranium andplutonium, for example, would lead to the adoptionof the plutonium design concentration in the uraniumplant, since it is not possible to say quickly whetheralpha air contamination is due to alpha particlesfrom uranium or alpha particles from plutonium.Cross-contamination must therefore be avoided.(3) Monitoring of the individual with installedequipment before he leaves the factory: the workerhas to wash at least his hands and may have toshower if he has undertaken certain tasks. Afterwashing he presents his hands to a machine and abell rings if they are contaminated.

Before leaving the subject of ingestion andinhalation control, mention must be made of certainareas of the plant where small laboratory-type opera-tions are carried out and also of the control labora-tories where process-line samples are analysed andassessed. In each of these areas a new factor otherthan the health of the worker exerts a controllinginfluence: in the plant it is the purity of the product,and in the laboratory it is the necessity to maintaina low radioactivity background to enable accuratemeasurements on low-activity samples to be made.Operations are carried out in perspex-fronted boxeswhich are sealed from the working space and main-tained at a negative pressure to it. Materials andsamples are posted into the box through an air lockand manipulation of the equipment is carried outthrough long gloves which are sealed to holes cutin the perspex front.

Detection and Measurement of HazardsBefore it can be hoped fully to control a hazard

quantitative determination ofthe hazardous materialsmust be made. The measurement of radioactivehazards with certain exceptions are not undulydifficult.The simplest monitor makes use of the effect by

which radioactivity was discovered in 1896, namely

the blackening of a photographic film. Beta-gammaradiation survey instruments and beta-gamma sur-face contamination instruments both use theionization of a gas in a closed space. In the formerthe net electrical charge resulting from the ionizationis collected by a metal electrode in the ionizationchamber and the current is measured directly by asensitive electrometer or more usually after amplifi-cation. In the latter, that is, in most contamination-monitoring instruments, the ionization is used totrigger off bigger electrical discharges which arethen counted electronically. This is the Geiger-Muller effect. In the ionization chamber theionization current will depend upon the energy ofthe radiation whereas in the contamination monitor,dependent upon the Geiger-Muller effect, themethod is independent of the energy of the radiationprovided it exceeds the minimum necessary to triggeroff the discharge. Alpha surface contamination ismeasured by the same method, in principle, as thatused originally by Rutherford and his co-workers.The scintillations caused by alpha particles fallingon a zinc sulphide screen are viewed electronically,that is, with a photomultiplier tube, and the resultingelectric impulses from the tube are counted byelectronic counters. The zinc sulphide screen mustbe protected from light and is therefore enclosed in alight-tight box, one side of which is closed by analuminized nylon foil. It is this foil which makesthis instrument difficult to keep serviceable since thefoil must be so thin that it will not stop an alphaparticle and yet sufficiently robust to remain light-tight even when used in a factory. Air contaminationis measured by taking large-volume air samples ofthe order of five to 25 cubic metres per hour. The airis drawn through a Whatman filter paper by amodified vacuum cleaner unit and the volume ismeasured by an anemometer. The filter paper,with the airborne radioactivity now deposited uponit, is presented to beta-gamma and alpha countingequipments working on the same principles as thosedescribed earlier. The activity measured is cor-rected for the counter efficiency, the self-absorptionof the activity in the filter paper, and the filter paperefficiency, when this is necessary.The development of laboratory tools into factory

survey instruments has been the responsibility of theAtomic Energy Research Establishment at Harwell.

SurveysA very large number of radiation, surface con-

tamination, and air contamination surveys have tobe made every day. It was decided to select andtrain a group of process workers to set up, calibrate,and operate radiation-monitoring instruments. The

150

on Novem

ber 1, 2021 by guest. Protected by copyright.

http://oem.bm

j.com/

Br J Ind M

ed: first published as 10.1136/oem.12.2.147 on 1 A

pril 1955. Dow

nloaded from

RADIATION HAZARDS IN INDUSTRY

process workers, called health physics monitors,have carried out most successfully a very heavyprogramme of surveys over the last few years. Theyalso interpret to the engineering and productionsides the results of their surveys as long as " rule-of-thumb" interpretation is possible. The factory haslaid down a series of contamination levels both airand surface and has specified what action is to betaken at each level. The work of the surveyors iscontrolled by a physicist and interpretation of asurvey which is beyond the " rule-of-thumb"category is made by him.

Plutonium Air ContaminationThe detection of plutonium contamination is a par-

ticularly difficult matter. The design concentrationmay be expressed as a quantity of plutonium whichwill give about 10 d.p.m./m.3 of air. Unfortunatelythe air contains naturally the daughter-products ofboth radon and thoron and amongst the isotopesin the Ra A, B, C, C', C", and D chain and thesimilar thorium chain are alpha emitters. Theconcentration of radon and thoron decay productsvaries widely from day to day but is in the range of5 to 500 d.p.m./m.3 of air. Therein lies the problem;when an air sample is taken, and the alpha activitycounted, the plant man requires to know at once ifthere is any plutonium present. The physicist isunable to do an immediate identification of thealpha activity. Two ways are open to him: first,to measure the alpha energy by an alpha energydiscrimination of some sort, but this is a laboratorytool and not a factory survey instrument. In anycase it is time consuming. Second, to measure thevariation of activity on the filter paper with time.If it is plutonium no decay will occur since plutoniumhas a half-life of 25,000 years. If it is the decayproducts of radon and thoron then within one hourmeasurable decay will have occurred. But theplant man has had to wait for an hour and eventhen the sample tells him only of conditions an hourago. Out of this unpromising position an opera-tional procedure has been devised which has workedmost satisfactorily.Although the natural background varies both

with time and with place, it is unusual to find itwidely different at different places on the same fac-tory site at the same time. So the evidence from onepart of the plant is used to help to judge conditionsin other parts. If the level is less than 10 d.p.m./m.3then no action is required to identify the alphaactivity since it is below a design concentrationeven if it is plutonium. If the level exceeds what isgenerally judged to be the area background activityat the time by 100 d.p.m./m.3 or more, that is, by

more than 10 times the design concentration, thensafety precautions are immediately instituted. Dustrespirators are worn and active measures institutedto locate the contamination source if this is notknown or already suspected. If the level exceedswhat is generally judged to be the area backgroundactivity at the time by more than 10 d.p.m./m.3 butless than 100 d.p.m. Im.3. that is, by more than onedesign concentration but less than 10 design con-centrations, then safety precautions are brought toreadiness, all possible sources of air contaminationare checked and a second determination of theactivity of the sample is made 30 min. after the firstdetermination. The extent of the decay enables ajudgment to be made whether the sample does ordoes not contain plutonium. In any case a secondsample is started immediately the first one is takenoff, so during the 30 minutes' decay of the firstsample the second sample is taken and assessed andthat too helps in assessing the position.At the present time the Atomic Energy Research

Establishment at Harwell are working on new alpha-measuring instruments which, it is hoped, willimprove the position still further. One suchinstrument prints the alpha activity in the workingspace on a recorder and side by side with this printsthe alpha activity in air drawn from outside thebuilding. A direct comparison between the two isthus possible.

Safety Control in the FactoriesA department independent of both the production

and engineering sides of the factory has been setup with its head answerable to the works generalmanager. This department, the Health PhysicsDepartment, is responsible for carrying out all theradiation, surface contamination, and air con-tamination surveys in the factory. As each surveyis completed a copy is handed direct to the plantsupervisor with recommendations for action whereappropriate. The surveyors or health physicsmonitors are encouraged to work as additionalmembers of the production and engineering team.Safety is not achieved by policemen but by thewilling and full cooperation of those whom oneseeks to make safe.The head of the Health Physics Department has

also been made responsible for the normal factorysafety under the Factories Act and the works safetyofficer answers to him. This has provided anexcellent and most salutary lesson to the physicistsin charge of the department. They have foundthat accident prevention follows four well-triedpaths: (1) to remove the hazard; (2) to shield thehazard; (3) to shield the worker; (4) to warn the

l5I

on Novem

ber 1, 2021 by guest. Protected by copyright.

http://oem.bm

j.com/

Br J Ind M

ed: first published as 10.1136/oem.12.2.147 on 1 A

pril 1955. Dow

nloaded from

BRITISH JOURNAL OF INDUSTRIAL MEDICINE

worker. The principles necessary to achieve radia-tion safety are no different. It is very easy whentackling a new problem, such as radiation safety inindustry, to think that it is new in principle, butresponsibility for industrial safety has taught thatit is not so. Safety in the atomic energy field isachieved, as safety is achieved in other industries,by a combination of "design for safety" by thedesign offices and "manage for safety" by theworks management.

DiscussionDr. A. NEMET (Philips Balham Works Ltd.) said that

medical and industrial x-ray workers had learned toprotect themselves from external radiation and, inindustrial work at least, this could be done without anydetriment to the quality of the work. The medical man,however, lived in a constant struggle between his naturalwish to see more of the x-ray screen and his prudencein protecting himself with clumsy lead-rubber apronsand gloves, which hampered him. Without that pro-tection the radiologist would suffer the maximumpermissible dose, due to scatter from his own patient, in asingle morning in an average hospital doing bariummeals only. There seemed to be no doubt that atomicfactory workers were safer from that kind of hazard thanthe average hospital radiologist or radiographer.The two other hazards, airborne dust and ingestion,

were of quite a different order, partly because thetolerance levels were so very low and were still gettingsteadily lower due to advances in biological research,but also because it appeared to be so difficult to protectthe worker against carelessness.The most serious risk was inhaled radioactive dust,

because in measuring this type of contamination it wasnecessary to compensate for the harmless backgroundradiation which, as Mr. Fair had said, might be onehundred times higher than the maximum permissiblelevel of plutonium.Something which Mr. Fair had not pointed out, but

which was really the limiting factor, was the statisticalfluctuation of both the background and the contamina-tion. As, in addition, the background varied by asmuch as 30-1, it became clear that it was impossible to

record airborne activity instantaneously; the collectionof dust and the counting must take a long time in orderto gather sufficient counts so that the desired accuracyof, say, 10% was obtained.Another practical difficulty with particle-borne

radiation was to make reasonably certain that thesampled air was really representative of the backgroundand the suspect channels of the air breathed.

Mr. D. R. R. FAIR, in reply, said that the position wasvery different from that which existed in hospitals andlaboratories, where it was necessary to depend on theindividual himself; in factories there was factorydiscipline.The alpha air contamination problem was the most

difficult. In any one area or factory site there was alarge number of air samplers operating at the same time,which made it possible to judge one particular locationin the light of others. Moreover, in a process plant onehoped to be doing tomorrow the same as one was doingtoday. Many members of the audience were researchworkers, development workers, or associated with thatkind of activity, and they were always hoping to be doingsomething new, but they should remember that the aimof the man responsible for production was to operatehis plant on a steady basis. That fact helped con-siderably in locating trouble, because the plant wasinstrumented throughout and, if there was any likelihoodof air contamination, it was very seldom necessary tolook for it; the man in charge of the plant almost alwaysknew of any minor change in operating conditions likelyto give rise to air contamination.

In reply to other questions, Mr. FAIR said that perspexwas used for equipment and appliances becauise it wasunbreakable. Neither perspex nor polyvinyl chloridewas damaged at the ordinary radiation levels to whichman might be exposed.As their knowledge grew, it was possible to relax

safety precautions. This had been done without causingany alarm to the workers by explanation and by dis-cussion of the Joint Factory Council.

Mr. FAIR thought Dr. EDSON'S comment was reason-able in that it was too early to say that all occupationalhazards had been confronted since incubation of diseasesinduced by radiation ranged from three to 40 years.

152

on Novem

ber 1, 2021 by guest. Protected by copyright.

http://oem.bm

j.com/

Br J Ind M

ed: first published as 10.1136/oem.12.2.147 on 1 A

pril 1955. Dow

nloaded from