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Topics:Low-level radioactive wastesRadioactive waste disposalHydrogen productionLiterature reviews

EPRI NP-5977Project 2724-1Final ReportSeptember 1988

EPRI LM

Radwaste Radiolytic GasGeneration Literature Review

E.RI U.R..

Prepared bySargent & Lundy EngineersChicago, Illinois

RET E P 0 R SUMMARYSUBJECT Low-level radioactive waste management

TOPICS

AUDIENCE

Low-level radioactive wastes Hydrogen production

Radioactive waste disposal Literature reviews

Generation engineers and designers

Radwaste Radiolytic Gas GenerationLiterature Review

This literature review provides information on the mechanismsand quantities of hydrogen gas generation in low-level radioactivewaste transportation packages. Some waste forms generate muchless hydrogen gas than originally thought, reducing concernabout possible combustion within sealed packages.

BACKGROUND Industry concern about requ'rements for testing to determine combustiblegas generation in low-level radioactive waste (LLRW) transportation pack-ages prompted NRC to revise certificates of compliance for radwaste trans-portation casks. The regulatory revision led to the subsequent issuing ofNRC IE Information Notice 84-72. This notice describes NRC concern aboutthe potential generation of combustible quantities of hydrogen, which might

-result in combustion and cask damage in the event of a transportation acci-dent. The revised NRC regulations require testing and measurement todetermine whether, in twice the expected shipment time, the package couldgenerate hydrogen equaling or exceeding 5% of the volume of the trans-portation cask secondary container. NRC regulations permit calculationalanalysis to determine gas generation quantities. In lieu of testing or analysis,or if results show excess gas, oxygen in the secondary container-thedrum, cask liner, or high-integrity container-may be diluted with an inertgas to less than 5% volume. Low specific activity packages shipped within10 days of sealing or venting are exempted from this requirement.

OBJECTIVES

APPROACH

To examine and summarize the literature on radiation damage for informa-tion on the generation of combustible gases from LLRW.

Investigators reviewed chemical literature for information on chemicalreactions in irradiated materials. The review identified the primary mecha-nisms for generation of hydrogen and other combustible gases and identi-fied nonradiolytic chemical reactions leading to hydrogen production. Theysummarized their findings and compiled an annotated bibliography.

RESULTS • Water accounts for most LLRW radiolytic hydrogen generation.

• Hydrogen reaction yields reported in the literature probably lead to con-servatively high predictions of the amounts of hydrogen generated by

EPRI NP-5977S

radiolysis in LLRW because of high radionuclide concentrations used inthe studies. Concerns about combustion within a sealed package ofLLRW are then unfounded.

* Of the LLRW solidification binders, vinyl ester styrene generates theleast radiolytic hydrogen.

* Dried organic ion-exchange resins produce 10 times less radiolytichydrogen than do fully swollen or dewatered resins.

- Cement solidification of waste does not appreciably reduce hydrogenyield, but it does fill the voids in dewatered resins.

- Chemical production of hydrogen in a corrosion process can over-whelm radiolytic production.

- Asphalted, cemented, and dewatered waste that is an appreciablefraction of the Class C limit and is stored for one to five years mayrequire special considerations for hydrogen generation.

EPRI Results of this literature review provide realistic estimates of hydrogenPERSPECTIVE gas generation in LLRW transportation packages. This information may

also significantly affect combustible gas testing requirements for LLRWtransportation packages if the Department of Transportation incor-porates International Atomic Energy Agency requirements.

PROJECT RP2724-1EPRI Project Managers: Michael D. Naughton; Patricia J. RobinsonNuclear Power DivisionContractor: Sargent & Lundy Engineers

For further information on EPRI research programs, callEPRI Technical Information Specialists (415) 855-2411.

Radwaste Radiolytic Gas Generation LiteratureReview

NP-5977Research Project 2724-1

Final Report, September 1988

Prepared by

SARGENT & LUNDY ENGINEERS55 East Monroe StreetChicago, Illinois 60603

Principal InvestigatorC. R. Palmer

Program ManagerL. C. Oyen

Prepared for

Electric Power Research Institute3412 Hillview Avenue

Palo Alto, California 94304

EPRI Project ManagersM. D. NaughtonP J. Robinson

Radioactive Waste Management ProgramNuclear Power Division

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Copyright @ 1988 Electric Power Research Institute, Inc. All rights reserved.

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THIS REPORT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORK SPONSOREDOR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBEROF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) NAMED BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANYOF THEM:

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ORGANIZATION(S) THAT PREPARED THIS REPORT.Sargent & Lundy EngineersChicago, Illinois

ABSTRACT

This report presents the results of a literature review on radiolytic gas generation from Low-Level RadioactiveWaste (LLRW) and includes an annotated bibliography of 37 references on the subject. The review shows thathydrogen is the only combustible radiolytic gas that is generated in sufficient quantities to be of concern. WaterIs consistently the major constituent of LLRW that produces radiolytic hydrogen. Examination of typical PWRand BWR waste streams indicates that most of the waste generated by utilities can be categorically excludedfrom concern with respect to hydrogen generation.

III

TABLE OF CONTENTS

CHAPTER PAGE

Abstract .................................................. ............. iii

Sum m ary ................................................. .............. ix

1. Introduction ............................................... .............. 1

2. Principles of Radiation Damage .............................. .............. 3

3. Combustible Gas Production Mechanisms .................................... 5

4. LLRW Waste Forms and Types ............................... .............. 9

5. Summary and Review of Data .............................................. 11

6. Conclusion .............................................................. 19

7. Annotated Bibliography ................................................... 23

A ppendix ............................................................... 31

V

LIST OF TABLES AND FIGURES

TABLE PAGE

5-1 Base M aterials ......................................................... 15

5-2 Solidification Binders ................................................... 15

5-3 Ion Exchange Resins .................................................... 16

5-4 Solidified W aste ........................................................ 17

FIGURE PAGE

2-1 Cumulative radiation dose for BWR waste forms as a functionof activity concentration ......................... I ......................... 4

2-2 Cumulative radiation dose for PWR waste forms as a functionof activity concentration ................................................... 4

vii

SUMMARY

This report presents the results of a literature surveyon radiolytic gas generation from the group ofmaterials that constitutes low level radioactive waste(LLRW). This report includes an annotatedbibliography of 37 references on the subject. It isintended that this report be used in conjunction withthe development of calculational methods for thedetermination of the quantity of combustible gasgenerated by radiolysis of LLRW. This combustiblegas determination is required of users of NRCapproved transportation casks for Type B quantitiesof LLRW.

The basic process of radiation damage in the materialsthat constitute LLRW is the breaking of covalentchemical bonds by high energy gamma photons andbeta particles. This results in the creation of highly reac-tive free radicals within the irradiated material. Inorganic materials, the hydrogen atom is produced. Itthen reacts with another nearby hydrogen atom to formmolecular hydrogen gas. In water, another mechanismis available in addition to this. In water, free electronscan be produced that react with the water moleculesto form hydrogen gas. Hydrogen can also be producedin a corrosion process in a sealed steel container ofirradiated ion exchange resins.

A review of the available data shows that hydrogenis the only combustible radiolysis gas that is generatedin sufficient quantities to be of concern. Data wasobtained on hydrogen generation in the basic materialconstituents of LLRW, the binders used to solidifyLLRW, organic and inorganic ion exchange resins andsolidified LLRW. Water is the major source of radiolytichydrogen gas and cement, organic ion exchangeresins, and asphalt are all in the same order ofmagnitude as water. The radiolytic hydrogen yield,G-value, (molecules H2/100eV absorbed) for pure

water is reported as 0.45. For the radwaste solidfica-tion binders cement, asphalt and vinyl ester styreneG-values are reported as 0.11 to 0.35, 0.3 to 0.6, and0.03, respectively. Organic ion exchange resins haveG-values reported in the 0.1 to 0.6 range when fullyswollen with water (dewatered). This yield is reducedby a factor of ten for dried resins.

Several conclusions can be reached from the datareviewed here. Water is consistently the major con-stitutent of LLRW that produces radiolytic hydrogen.When water is removed from the waste form thehydrogen yield drops by a factor of ten. Another majormaterial constituent of LLRW, styrene, is notably stabletoward radiolytic gas genertion, having hydrogenyields a factor of ten to one hundred less than otherorganic compounds.

When studying the radiolysis of cement and cement/waste mixtures, all researchers report a reduction inhydrogen yield at high container pressure. Oneresearcher found this pressure to be consistently doserate dependent, indicating a significant reduction inhydrogen yield at low dose rates. This is significantin that all of the work reviewed took place at high doserates, many orders of magnitude greater than evenhigh activity LLRW. It is probable that the hydrogenyields (G-values) reported in the literature for cementand other water containing waste forms are conser-vatively high for the purpose of combustible gas deter-mination. Future research on hydrogen generation inLLRW should consider this dose rate dependence andbe performed in part at dose rates approximatingactual waste rather than the high dose rates used foraccelerated studies.

Examination of typical PWR and BWR waste streamsindicates that most of the waste generated by utilitiescan be categorically excluded from concern with

ix

X Summary

respect to hydrogen generation. The waste that maybe of concern is at most the upper portion of ClassB and Class C waste that is stored on site for one tofive years prior to shipment. This concern can bemitigated by removing water and non-aromatichydrocarbons from the waste from.

To assess the combustible gas hazard by calculation,it is necessary that a reasonable and accurate method

for calculating absorbed dose be established. Manymethods currently exist and computer codes usingthem have been written. These methods forcalculating absorbed dose should be tested exper-imentally and evaluated carefully for their applicabilityto hydrogen generation. Possibly a standardizedmethod could be chosen.

1

INTRODUCTION

During the past four decades, the study of the effectsof ionizing radiation on all manner of materials hasreceived great attention in the scientific community. Alarge part of this attention has been directed specificallyat the materials which are used in the nuclear powerindustry. The purpose of this study was to examine theliterature on radiation damage for information relatingto the generation of hydrogen and other combustiblegases from the broad group of materials which con-stitute low-level radioactive waste (LLRW).

IE Information Notice 84-72This literature study was prompted by industry con-cerns over the-testing requirements for determinationof the generation of combustible gases in the pack-ages used to transport LLRW. These concerns wereincorporated into by regulatory requirements by theU.S. Nuclear Regulatory Commission (NRC) with therevision of the certificates of compliance for radwastetransport casks and the subsequent issuance of NRCIE Information Notice 84-72, entitled "Clarification ofConditions for Waste Shipments subject to HydrogenGas Generation:'

IE Information Notice 84-72 describes the NRC con-cern that the potential exists for the generation of com-bustible quantities of hydrogen from LLRW. This couldpossibly result in combustion during a transportationaccident causing damage to the transportation cask.

The NRC has defined the packaging requirements forthe transportation of "Type B" quantities of radioac-tive waste in 10 CFR 71. This regulation states thatpackages used to transport moderately large quan-tities of radioactive material must be designed to with-stand hypothetical accident conditions. The limits forthe quantity of radioactivity which requires this special

packaging and the design requirements for thepackage are given in detail in 10CFR71. An exemptionis given to wastes which contain low concentrationsof radioactivity. These low specific activity (LSA)materials require packages designed only to meet thenormal conditions of transport that are identical tothose for Type A packages. However, both the TypeB package and the LSA greater than Type A packagemust be NRC licensed. This licensing process isaccomplished through the transport package (cask)certificate of compliance, and this certiificate has beenmodified to incorporate the NRC's concern overhydrogen generation.

The waste forms identified as pertinent by the Infor-mation Notice are ion exchange resins, waste filtersludge, wet cartridge filters and radwaste solidifiedwith binders. Dry compacted and uncompacted wasteand irradiated hardware are specifically excluded. Therequirement for users of NRC approved packages is:for any package containing water and/or organicsubstances that could radiolytically generate com-bustible gases, it must be determined by tests andmeasurements of a representative package whetheror not, for twice the expected shipment time, a quan-tity of hydrogen is generated which is equal 5% ofthe volume of the secondary container void (orequivalent limit for other inflammable gases). Thesecondary container is the drum or cask liner insideof the transportation cask. As of May 22, 1985 analternative to testing and measurement was permittedby an NRC revision to the transportation cask cer-tificate of compliance. The alternative is determina-tion of gas quantities by analysis (calculation).

In lieu of the above test or analysis, or in case theresults show excess gas, the secondary container(drum, cask liner or HIC) and cask cavity may be

I

2 Introduction

inerted by diluting to less than 5% oxygen by volumewith an inert gas. An exemption is included for LSAmaterials, whereby packages shipped within ten days

of sealing or venting need not have the gas determina-tion performed.

2

PRINCIPLES OF RADIATION DAMAGE

Nuclear radiation, such as, alpha, beta, gamma, radia-tion, produces excited and ionized atoms andmolecules as it passes through materials. Theseexcited and ionized species can then undergo avariety of chemical reactions which manifestthemselves as physical changes in the irradiatedmaterial. Some typical physical changes are embrit-tlement, volume change, and gassing in organicpolymers; discoloration, dielectric constant change,embrittlement and gassing in inorganic crystals; andgassing, oxidation/reduction, and pH changes in wateror aqueous systems.

Of particular interest in this survey are radiationinduced changes which either directly or indirectlyresult in the production of combustible gases from theconstitutents of low-level radioactive waste (LLRW).

Quantitative data on the effects of ionizing radiationis often reported in terms of a "G-value' This valueis defined as the number of molecules of a materialwhich are consumed or produced for each 100 elec-tron volts of energy absorbed (9, 25). It is a measureof the reaction yield.

The amount of energy absorbed by irradiatedmaterials depends on the type of radiation (alpha,beta, or gamma), the absorption coefficient of thematerial and the system geometry. Energy isdeposited over a very short distance when alpha andbeta radiation passes through a material. For thisreason, it can be assumed that all of the energy fromalpha and beta radiation is deposited in the material.

The amount of energy deposited in a material as aresult of gamma radiation depends on both the degreeof interaction between the material and the gammaray and the length of material through which thegamma ray must pass.

The degree of interaction is described numerically bythe gamma ray mass absorption coefficient. Thiscoefficient is a function of the electron density of theabsorbing material and the energy of the gamma ray.The Radiological Health Handbook (6) graphs thiscoefficient for all of the elements. Fortunately, materialswhich have lower atomic numbers than iron (Fe) haveelectron densities which are very similar. This resultsin a group of elements which have similar absorptioncoefficient vs. energy curves. Most of the materialswhich compose LLRW fall into this group. For thisreason, it can be to assumed (±10%) that the massabsorption coefficient of irradiated LLRW materials isequivalent to that of the element carbon (C).

The other important factor in assessing the amountof gamma energy that is deposited in a material isthe length of material through which the gamma raypasses. For LLRW, this is a complex matter, becausemany point sources of gamma rays are distributedrelatively homogeneously throughout the material. Theimpact of each of these point sources on the entirewaste form must be assessed. Many sophisticatedcomputer codes exist to calculate this geometric effectover many different shapes. An example of a popularcode is ISOSHIELD.

Hine and Brownell (21) have formulated a quantitativemethod to perform this assessment which is conve-nient for hand calculations. The pivotal parameter intheir analysis is the calculation of an "averagegeometrical factor," which normalizes the dose ofthese spatially distributed sources over the geometryof the incorporating material. Hine and Brownell havetabulated average geometrical factors for cylinders upto 35 cm in radius and 100 cm in height.

This method for absorbed dose calculation waspresented by Swyler, et. al. (32) in a calculation for

3

4 Principles of Radiation Damage

the dose absorbed by dewatered resins from theabsorbed radionuclides as a function of time.

Colombo and Nielson (10) calculated the self dose fortypical PWR and BWR wastes. Their calculationassumed uniform activity distributed through a wasteform with a density of 2.0 g/cm 3. This is representativeof LLRW solidified with cement. The waste radio-nuclide compositions they used were taken from

WASH-1258 as being representative of a typical BWRand PWR. The results of their calculation arereproduced in Figures 2-1 and 2-2. Using a differentspectrum of radionuclides would result in a differentabsorbed dose because the half life and decay energyare important parameters. It is therefore, necessaryto perform this calculation on a case by case basis.

-QI Q

10,

le

U,C4wC,,

g

BWR WASTES (AFTER WASH-1258"

i00 Ci/t3

1.0 Ci/ft3

0,1Ci/fl3

0.1 Ci/ft3

0.O1ia/tt 3

U,C4

U,00

IU

dIo

o6

I0

410

:PWR'W4ASTE'S' ,ooc'/,•(AFTER WASH-12518)

lOCi/ft3

1.0 Ci/ft3

0.1 Ci/ft3

0.01 Ci/. . .

410

3I0

I0 too 1000 to 100 1000TIME, YEAR

Figure 2-1. Cumulative radiation dose for BWR wasteforms as a function of activity concentration. (10)

TIME, YEAR

Figure 2-2. Cumulative radiation dose for PWR wasteforms as a function of activity concentration. (10)

3

COMBUSTIBLE GAS PRODUCTION MECHANISMS

A great number of chemical reactions occur in irra-diated materials and a large amount of information hasbeen reported in the chemical literature concerningthem. This survey identified the primary mechanismsby which hydrogen and other combustible gases aregenerated. Also, non-radiolytic chemical reactionswhich lead to hydrogen production were also identified.

Radlolysis of HydrocarbonsThe primary gaseous radiolysis product from the irra-diation of organic liquids and polymers has been con-sistently found to be hydrogen. In organic materialswhich contain little oxygen, such as ion exchangeresin, hydrogen accounts for over 90% of the totalradiolysis gas formed. Unsaturated hydrocarbons suchas the paraffins octane, butane, etc, generate the mosthydrogen, having G-values from 2 to 6. Aromatichydrocarbons such as benzene, styrene, etc. are themost stable, having hydrogen G-values from 0.04-0.4(25).

When irradiating typical organic radwaste such asbead resins and vinyl ester styrene, carbon monox-ide and dioxide are the next most abundant radiolysisgases produced, especially in systems open to theatmosphere. This is because of an efficient radiolyticreaction in which the carbon structure of the organicmolecules is oxidized. In fact, in closed systems,oxygen present at the beginning of irradiation isquickly removed by this reaction (7). Swyler, et. al. (33)examined the kinetics of this reaction and found ina sealed dewatered bead resin system, oxygen isremoved fast enough so that an explosive mixture ofoxygen and radiolytic hydrogen does not exist.

Methane, ethane, etc. are also produced by hydrocar-bon radiolysis; however, they usually account for less

than 1% of the total radiolysis gas produced by typicalorganic radwastes.

The mechanism by which hydrogen is formed in irra-diated organic radwastes is by breaking the C-H bondand formation of a free radical hydrogen atom thatreacts with a hydrogen atoms attached to a nearbycarbon skeleton to form hydrogen gas. The remain-ing carbon frame-work then crosslinks, forms a doublebond, or undergoes chain scission (degredation) tobalance charge. Of the common commercial organicpolymers, polystyrene was found by Bopp and Sisman(5) to be the most stable to this attack, having ahydrogen G-value of 0.008. This is important to rad-waste in that polystyrene is the backbone of bothorganic ion exchange resins and VES, the Dowsolidification agent.

Radiolysls of Water

Water is the primary constituent of dewatered ionexchange resin (66%) and constitutes a fair propor-tion of hydrated cement (25-50%). The role of waterin gas production over resins has been studied. Swyler(33) found the hydrogen yield to decrease by a factorof 10 when irradiating dry cation resin. Tulupov andButaev (35) found the composition of the radiolysisgas over resins to change from 92% H2 to less than50% H2 after drying the resins. They did not reporttotal yields for this experiment but noted that theradiolysis of water was the primary source of gaseoushydrogen in bead resin. For these reasons the interac-tion of water and ionizing radiation is crucial to thissurvey.

As high energy radiation passes though water, it inter-acts with the water molecule in several ways. One typeof interaction is for the radiation to increase the

5

6 Combustible Gas Production Mechanisms

vibrational or rotational energy of the water molecule.The resulting excited water molecule might then simp-ly lose this energy to the liquid, resulting in an increasein liquid temperature. Or, if sufficient vibrational energywas given to the water molecule, it may break in Hand OH fragments. These fragments are highly reac-tive and their fate can lie along many reactionpathways. However, a more likely interaction is for thehigh energy radiation to ionize the water molecule bydislodging an electron. The result of this energytransfer is an ionized water molecule, H20+, and afree electron. Because of the polar nature of water,the free electron can cause the dipole moments ofthe water molecules to line up in a pattern. This pat-tern generates an electro-magnetic field that willstabilize the free electron. An electron stabilized bynon-randomly oriented water molecules such as this,is called a hydrated electron. Of course, this electroncould simply recombine with the ionized watermolecule, H20+, to form stable water. However, thehydration process occurs faster than the recombina-tion process, resulting in a fair number of hydratedelectrons which are free to interact with other watermolecules, or molecules in solution, or materials incontact with the water. Free electrons can also be pro-duced in cement or other solid radwaste.

The yield of these three highly reactive species, theH and OH fragments and the free hydrated electron,can be described In terms of G-values. Averagingseveral sources, these yields are: GOH = 2.7, GH =0.6 and Ge = 2.7 (14). These reactive species canundergo many reactions after they are formed. Theirreaction pathway will depend on the concentration ofthe molecules around them. There are three reactionswhich result In the formation of gaseous molecularhydrogen, H2.

These reactions are, in order of importance:

eaq + ead - H2 + 20Hea• + H - H2 + OHH + H - H2

It is therefore understandable why many researchershave found that the existence of multivaelent metalions such as iron (Fe3 +) in irradiated hydratedmaterials has resulted in an appreciable decrease ingaseous hydrogen production. These metal ions areacting as electron scavengers and removing the

primary source of gaseous hydrogen, the hydratedelectron. This effect has been noted in aquaeous solu-tions (25), Irradiated swollen resins (33) and cementsolidified waste (4).

The other molecular product of the radiolysis of wateris hydrogen perdoxide, H20 2. This molecule isformed by the reaction: OH + OH - H20 2. TheG-values for H2 and H20 2 , the primary molecularradiolysis products of water, have been reported to beIndependant of solution pH. They are GH2 = 0.45and GH202 = 0.7 (14). These yields are, however, sen-sitive to, among other things, LET values, temperature,and concentration of electron scavengers.

A reaction also operates during the radiolysis of waterthat consumes gaseous hydrogen. This reaction is:H2 + OH - H20 + H. However, this reaction pro-ceeds at a rate that is 100 to 1000 times slower thanthe reactions which produce gaseous hydrogen. Forthis reason its effect on the gaseous hydrogen yieldhas been masked in most irradiation studies becausethey take place at extremely high dose rates, generallyon the order of 104 to 107 rads per hour. However, threestudies of the Irradiation of cement have identified areduced hydrogen yield at high pressures (4,10,2).Thisis the result of a backreaction that is pressure depen-dent and consumes hydrogen. The reaction at the rootof this effect is probably the one described above.

Chemical Production of HydrogenIt is a well known phenomenon for metals submergedin mineral acids to bubble, signalling the oxida-tion/reduction reaction which results in oxidation ofthe metal and the formation of gaseous hydrogen.Since many LLRW containers are constructed fromcarbon steel, the existance of acidic conditions andthe contact of this acid with the metal container couldresult in the production of hydrogen gas. The hydrogenforming oxidation and reduction reactions are:

Fe - Fe2 + + 2e-2H+ 2e- - H2

This is important because during the irradiation ofhydrogen form cation ion exchange resins the primaryradiolysis product has been identified by severalinvestigators to be sulfuric and sulfurous acid(30,33,35). Furthermore, Swyler (34) has shown that

Combustible Gas Production Mechanisms 7

irradiating hydrogen form cation resins in the presenceof mild steel coupons in a sealed system results inhydrogen gas formation at a rate which greatlyexceeds that of radiolysis of the resins alone (34). Thiseffect was greatly reduced by expending the cationresins with sodium prior to irradiation.

Gangwer and Pillay performed similar irradiations invented systems and found accelerated corrosion of

the metal coupon (17). Since the system was vented,the primary reaction was most likely one involvingoxygen consumption with no hydrogen gas formation.Nevertheless, the pH change and corrosive nature ofirradiated ion exchange resins were well documented.

4

LLRW WASTE FORMS AND TYPES

Waste Types AffectedAs stated earlier, IE Information Notice 84-72 appliesto LLRW packages which contain water and/or organicsubstances (ion exchange resins, waste filter sludge,cartridge filters and radwaste solidified with binders)that could radiolytically generate combustible gases.In performing the literature review, information wasgathered on both hydrogen generation from the wastetypes themselves, the binders used for solidification,and the composite waste form.

Ion Exchange ResinsIon exchange resins used in radioactive service fallinto two categories; organic and inorganic. Within theorganic category, resins are further segregated byphysical form into powdered or bead, and finallydivided by chemical affinity into cation or anion form.However, all organic ion exchange resins can bedescribed as a high polymer structure, such aspolystyrene, onto which are placed ion exchange sitesor functional groups, such as sulfonic acid.

Organic ion exchange resins which have beensaturated with water can contain as much as 66%water by weight even though no water is visible. Thiswater is adsorbed on the surface of the resin,absorbed within the resin's polymer structure, andchemically bound to the resins ion exchange sites.

Organic ion exchange resins that are commonly usedin radioactive waste treatment are termed strong acidcation and strong base anion. These consist of apolystyrene-divinyl benzene copolymer backbonewhich has either sulfonic acid groups or a trimethylamine groups attached to form the ion exchangesites. The polymer backbone, in chemical termi-nology, is largely aromatic in nature. Possible sources

of radiolytic hydrogen gas from organic resins are thewater which is contained within the resin and theorganic polymer backbone.

The other category of ion exchange resins used inradioactive service are the inorganic type. Zeolites andglass beads are members of this category. They areporous metal oxides and glasses whose pore size andsurface characteristics are chosen to selectively removeradionuclides from liquid radwaste streams. Theprimary source for radiolytic hydrogen gas frominorganic ion exchangers is the water which adsorbsonto the exchanger particles or beads or is containedin the pores. This can be as much as 33% (wt).

Other Waste TypesThe operation of large precoat filters at BWR's resultsin the generation of large amounts of filter sludge. Thissludge consists of a mixture of the particle which werefiltered out of a liquid stream and the precoat materialwhich was placed on the filter to collect the particles.Precoat materials commonly used are diatomaceousearth, cellulose fibers, activated charcoal and powderedorganic ion exchange resin. Other than the powderedorganic ion exchange resin, the only source of radiolytichydrogen gas from filter sludge is the water whichremains in the waste after it is processed for disposal.Powdered resins behave as do the organic bead resinsdiscussed previously.

In addition to the largely solid waste discussed above,Ught Water Reactors (LWR) also produce concentratedliquid wastes. These wastes are aquaeous solutionsand slurries produced by evaporation and consistprimarily of inorganic salts. Ultimate disposal of thesewastes requires solidification with an appropriate bindersuch as cement or asphalt. The primary source of

9

10 LLRW Waste Forms and Types

radiolytic hydrogen gas from concentrated wastes isthe water which is bound up in the solid matrix andany organic material used as the binder.

A waste stream which is primarily a characteristic ofPWR's is spent cartridge filters. These filters are con-structed from cloth, cellulose, metal and sometimesplastics. They are used to filter water that is relativelyclean with respect to suspended particulates , but itcan contain a high concentration of radionuclides. Theprimary source of radiolytic hydrogen from spent car-tridge filters is any water remaining on the filter andthe binder used to encapsulate the filter.

Waste Forms and Packages AffectedThe waste types described above can be processedfor disposal and packaged in a variety of ways. Pro-cessing the waste into a form acceptable for disposalis primarily governed by burial site requirements.Packaging is usually governed by transportationrequirements. However, both processing and packag-ing requirements can be affected by either one. Onlythe most common processing and packaging com-binations are described here. For the purpose of satis-fying IE Notice 84-72 examination of the packagecharacteristics is necessary on a case by case basis.

Dewatered Resin and SludgeIn addition to solidifying ion exchange resins andwaste filter sludge, it is also an accepted practice todewater this waste by either pumping or vacuumingessentially all of the free water out of the package.Depending on the concentration of radionuclides inthe remaining sludge, the package commonly usedfor this process is either a 170-200 ft3 carbon steelcylinder called a cask liner or a similar sized highmolecular weight polyethylene cylinder called a highintegrity container (HIC). The sludge or resins whichremains in the processed package may contain notmore than a maximum of 1% by volume free water,plus all of the water that is absorbed, adsorbed andchemically bound to the resin or sludge.

Therefore, the available material inventory for theradiolytic generation of hydrogen gas is the remainingwater in the package plus the organic material con-tained in the ion exchange resin. Hydrogen production

by chemical interaction with the container is a possi-bility for the carbon steel package, but because of thechemical inertness of polyethylene a reaction of thisnature can be discounted for the polyethlene HIC.

Solidified Resin, Sludge, Concentrates andFiltersLLRW can also be bound together or encapsulated bya binder in a process called solidification. There arethree binders which are used in nearly all LLRWsolidification. These are Portland cement, vinyl esterstyrene (Dow binder) and bitumen (asphalt). Solidifica-tion processes exist which utilize other plastic binderssuch as epoxy, polyethylene, and polyester.

Sources for hydrogen gas in a solidified waste formare the incorporated waste and the binder. The wastetypes and their source of hydrogen have beendescribed above. Portland cement contains from 25%to 50% (wt) water. This water is primarily present asthe water of hydration of the oxides which form thecementitious matrix, however some water is alsotrapped within the capillaries and inerstices of thecement matrix.

VES can be used to solidify either wet wastes or driedwastes. With wet wastes, the waste and associatedwater, plus the VES are sources of hydrogen. VES isa largely aromatic polymer with some alkyl chainsbetween the aromatic groups. Dried wastes such asthe product from a dryer or incinerator when incor-porated in VES will have as sources of hydrogen theVES and any residual organic matter as may resultfrom the drying of ion exchange resins.

Asphalt is used as a binder in an evaporative solidifica-tion process which drives of nearly all water, leavingonly the dried resin bead, sludge or inorganic salt andthe asphalt binder. Sources of hydrogen here are anyresidual organic matter plus the asphalt binder. Asphaltcan be purchased as distilled or air blown. Both formscontain primarily aromatic compounds along with longchain unsaturated hydrocarbons. Air blown is anoxidized form of asphalt. Both forms should behavesimilarly with respect to hydrogen gassing.

Spent cartridge filters may also be placed in HIC's fordisposal; however, there is a relatively small amountof material available in this waste form for the genera-tion of hydrogen.

5

SUMMARY AND REVIEW OF DATA

Data on the composition and yield of radiolysis gas wasobtained for materials ranging from the individual con-stituents of LLRW to the binders used for solidifica-tion to actual waste forms. These data were not alwaystaken under conditions that correspond completely totypical LLRW, however some general and specific con-clusions can be reached from them as well as identi-fying some areas requiring further study.

Base Materials

Data was identified on the radiolytic gassing of thebasic material constituents of LLRW which have apotential to generate combustible gases. The data aresummarized in Table 5-1. Most of these data have beendiscussed in Section 2 and 3 of this report along withthe development of the principles of radiation damageand hydrogen production mechanisms.

Of the materials that constitute LLRW, saturated andunsaturated hydrocarbons generate the mosthydrogen, having hydrogen G-values in the 1-6 range.These organic materials do not account for very muchof LLRW and are seldom present in waste forms thatalso contain sufficient radioactivity to generatehydrogen. Polyethylene is the most common of thesematerials in LLRW as it is used to fabricate High Integ-rity Containers (HIC) for the disposal of dewateredsludges and resins. Polyethylene has also been con-sidered for use as a solidification binder.

A relatively narrow thickness (0.625 in) and smallamount of polyethylene is exposed to radiation in a HIC,thus a small radiation dose will be absorbed and onlya small amount of hydrogen could be transferred tothe package interior. For these reasons, hydrogen gass-ing from a HIC should not be a transportation concern.

Contaminated oils also contain saturated and unsat-urated hydrocarbons, however they rarely contain suf-ficient radioactivity to provide an absorbed dose largeenough to produce any hydrogen of concern.

The next largest generator of hydrogen from the basematerial constituents of LLRW is water. Dragnic andDragnic (14) have reported a G-value for pure waterof 0.45. This value is independent of pH, however, itis dependent on the concentration of electronscavengers such a multivalent metals. Since water isfound in most all LLRW waste forms, its effect onhydrogen generation is profound.

Finally, the class of materials found in LLRW that ismost stable toward radiolytic hydrogen generation arethe aromatic hydrocarbons. These materials arecharacterized by the presence of the benzene ring andhave hydrogen G-values from 0.008 to 0.4. In LLRWthey are found in the solidification binders asphalt andVES and in organic ion exchange resins. Polystyreneis among this class and is reported to be one of themost radiaiton stable polymers, having a hydrogenG-value of 0.008 to 0.04 (5,37). This is important, aspolystyrene is the backbone of both VES and mostorganic ion exchange resins.

LLRW Solidification Binders

A fair number of studies have been performed onradiation effects in the group of materials which areused to solidify LLRW. The most frequently used ofthese solidification binders are cement, asphalt andVES. Hydrogen gassing data for these and otherbinders is summarized in Table 5-2.

Of the commonly used solidification binders, asphaltgenerates the most hydrogen. Radiolytic hydrogen

11

12 Summary and Review of Data

G-values for asphalt are reported to range from 0.3to 0.6 (8•1610,15). Colombo and Nielson (10) found theG-value to increase as the irradiation time increased,rising from an initial value of 0.07 to a value of OA1at the end of the irradiation period. This may bebecause hydrogen formed at the interior of the sam-ple took some time to diffuse out to the monitor. Gasesformed in asphalt tend to produce bubbles in thebinder which have difficulty reaching the surface ofthe sample. Most other researchers heated the asphaltafter irradiation to ensure, that all hydrogen formedescaped from the sample. However, when the rate atwhich hydrogen will diffuse through asphalt is com-pared to the rate at which hydrogen is generated ina typical LLRW waste form, It becomes apparent thatvery little of the hydrogen formed will not escape fromthe binder (15). The hydrogen simply diffuses out ofthe binder faster than it is generated, making thephenomenon observed by Colombo and Nielson onethat will probably not occur at the dose rates of typicalLLRW. Colombo and Nielsons' work took place at 4.6x 106 R/hr, many orders of magnitude greater than

will be seen for most LLRW.

There is no apparent difference in the hydrogen yieldbetween air-blown and distilled asphalt. The differencein all of the reported values is within the experimen-tal uncertainty.

The next largest producer of radiolytic hydrogen gasis hydraulic cement. Hydrogen gas G-values rangingfrom 0.11 to 0.35 have been reported (10). However, aninteresting phenomenon has been observed in threeindependent studies on radiolytic gas generation fromcement (2,4,10). Both the rate of gas evolution andhydrogen yield decreased in all cases as the pressurebuilt up in the sealed container. This is evidence of abackreaction which consumes hydrogen that ispressure dependent. Bibler (4) also found that thisphenomenon is dose rate dependent, with thebackreaction having a greater effect at lower dose rates.For this reason, the G-values reported for cement willmost likely be high when compared to LLRW, as thedose rates in these studies were several orders ofmagnitude greater than those in LLRW.

The commonly used binder that is most stable towardradiolytic gas production is VES. A hydrogen G-valueof only 0.03 is reported for this binder (19). This lowhydrogen yield is the result of the radiation stability

of the styrene functional group along with the com-plete lack of water in the binder.

Ion Exchange Resins

More work has been performed on the radiationbehavior of ion exchange resins for any other singletype of LLRW. This is because these resins have beenused extensively on the extraction of radionuclidesfrom high level wastes as well as in the decontamina-tion of the damaged reactor at Three Mile Island. Thedata obtained for ion exchange resins is summarizedin Table 5-3.

The inorganic zeolites have shown themselves to beuniquely stable toward radiation damage. The onlyhydrogen that is evolved from zeolites comes from thewater that is adsorbed onto the beads. Pillay reportshydrogen G-values of 0.005 to 0.05 (30) for zeolitessaturated with water. Capolupo reports higher G-values,ranging from 0.075 to 0.18 (7). Pillay observed a gradualincrease in the hydrogen yield as the irradiation pro-ceeded. This is probably because of hydrogen adsorp-tion on the zeolite surface. Once the zeolite surfacehad become saturated with hydrogen, more could enterthe gas phase and escape to the container. Capoluporeported the same trend.

Although they are apparently dry, organic ionexchange resins contain from 1/½ to 2/3 water as theyare delivered from the manufacturer. This is essen-tially the same condition of the resin as when it isdisposed of in its "dewatered" form.

The hydrogen gas G-value for fully swollen organicion exchange resins is generally reported to be from0.1 to 0.6 (4,28,3327,2) with several special cases fall-ing outside of this range.

Anion resin generates more hydrogen than cationresin (33). This is probably a result of radiolysis of thetrimethyl amine functional group on the anion resin.No decrease in hydrogen yield has been observed athigh container pressure in swollen ion exchangeresins. This indicates that the hydrogen consumingreaction identified in cement either does not operatein ion exchange resins or operates at a slower rate.The latter is more likely as water is the primaryhydrogen source in both cases. Dried resins have alsobeen irradiated and their hydrogen gas G-value found

Summary and Review of Data 13

to be a factor of 10 less than swollen resins. Swyler,et. al. (33) found the G-value for resin dried to 7%water to be about 0.01. Capolupo (7) found it to be0.067, and Mohorcic and Kramer (28) found it to befrom 0.001 to 0.026. These values are near thosereported for polystyrene alone, 0.008 to 0.0446 (5,37).It Is, therefore, apparent that the water associated withion exchange resins is the major contributor tohydrogen gassing and that with it removed by drying,a factor of 10 less hydrogen is generated.

This phenomenon was verified by the Russians,Tulupov and Butaev (35), however, the only effect theyreported in numeric terms was the effect on gas com-position. They went on to state in their analysis thatthe net hydrogen production was much less for thedried resin.

Solidified Waste FormsSeveral studies have examined radiolytic gas forma-tion from simulated solidified radioactive waste, andone reported on this phenomenon in actual solidifiedwaste. The data reported in these studies is summar-ized in Table 5-4.

The data reported for asphalt indicate that incorpora-tion of LLRW into this binder results in a waste formwhich generates less hydrogen than the binder alone.This is because the asphalt solidification process isevaporative, thereby removing almost all of the waterpresent in the unsolidified LLRW. The remaining saltor dried resin beads account for 50% of the wasteform and generate little or no hydrogen themselves.Solidified asphalt waste forms have hydrogen G-valuesreported in the 0.15 to 0.25 range (15,19). There is nodiscernable difference between air-blown and distilledasphalt with respect to hydrogen generation fromsimulated asphalt waste forms.

Barletta, et. al. (2) have studied a cement/ion exchangeresin waste form for its radiolytic gas generation rate.The resin mixture was a proprietary formulation oforganic and inorganic ion exchange resins that wereused in the TMI-2 cleanup. Barletta, et. al. reportedhydrogen G-values ranging from 0.19 to 0.24.

Bibler (4) studied cement waste forms containingoxides of Iron, manganese, and nitrogen. Bibler doesnot report hydrogen yield in terms of a G-value for

cement because the gas production varied with timefor gamma radiolysis. Bibler was able to identify areaction which consumes hydrogen that is dependentupon both pressure and does rate. As the pressurebuilt up in the sealed containers, the rate of hydrogenproduction decreased until a steady state pressuredeveloped, at which no further radiation dose wouldproduce any increase in pressure indicating that thehydrogen production and consumption reactions hadequilibrated. A G-value has no meaning In this con-dition. This steady state pressure was dose ratedependent, increasing with dose rate. Similarphenomena have been observed by Barletta, et. al.(2) and Colombo and Nielson (10). Bibler found thesteady state presure to be dependent on the incor-porated metal oxide, indicating that the metal oxidewas participating in a reaction that affects thehydrogen yield, possibly by electron scavenging.

It should be noted that Bibler could not develop asteady state pressure less than 200 psig for alpharadiolysis and for extremely high gamma dose rates.Therefore, the balance of reactions must be a functionof both LET and dose rate. Bibler's work, as well asthe work of Barletta, et. al. and Colombo and Nielsonall took place at dose rates for exceeding that of mostLLRW. This makes direct comparison difficult.However, it seems certain that the G-values reportedfor cement will be high, because the hydrogen con-suming reaction identified by Bibler plays a larger roleat the low dose rates typical of LLRW.

Effect of Irradiation Conditions

It has been shown that the chemical, physical andradiological conditions during irradiation all play a rolein determining the composition and yield of theradiolysis gas produced.

Almost all experimenters report an initial drop inpressure when irradiating sealed containers. This isirrespective of the binder or waste type, organic orinorganic. This pressure drop has been shown (7, 33)to be the result of a radiolytic reaction that consumesoxygen. Conversely, when Irradiating unsealedsamples the yield of carbon dioxide and carbonmonoxide increases, presumably as a result of thesame reaction. However, in most cases hydrogen con-tinues to be the dominant radiolysis gas produced and


certainly the dominant combustible gas produced. Theoxygen consuming reaction will mitigate concerns overcombustible mixtures forming within the secondarypackage (drum or liner). This reaction occurs manytimes faster than the hydrogen producing reactions,removing most of the oxygen before appreciablehydrogen can form. However, this reaction does nothingto remove oxygen from the transportation cask interior,thereby leaving open the possibility of a combustiblemixture there should the secondary packages leak.

Through the work of Bibler (4) it has been shown thatthe dose rate can have a determining effect on theyield of hydrogen from irradiated cement waste forms,and possibly all wastes that contain water. By examin-Ing the three radiolytic reactions in water that resultin hydrogen formation (see Section 3) it can be seenthat all are second order in dose rate. That is, bothreactive species are generated by radiation. Thisresults In a squared dependence of hydrogen forma-tion on dose rate. However, the reaction which con-

sumes hydrogen is only first order in dose rate. Thisresults in a linear dependence of hydrogen consump-tion on dose rate. Furthermore, the hydrogen produc-tion reactions in water all operate 100 to 1000 timesfaster than the hydrogen consumption reaction (14).

The net hydrogen yield from water containing wasteforms will depend on how these two sets of competingreactions balance out. Since the second order produc-tion reactions are more sensitive to dose rate than thefirst order consumption reactions, it is reasonable thatthe hydrogen yield will be lower at lower dose rates.This was verified by Bibler when he observed a lowersteady state hydrogen pressure for lower dose rates.Increasing the hydrogen pressure increases the rateof the hydrogen consumption reaction. At lower doserates, a significantly lower hydrogen pressure wasrequired to establish steady state, indicating that thehydrogen production reactions had slowed significantlymore than the hydrogen consumption reaction.


Table 5-1. Base Materials

GH2 Dose Rate Total Dose RadiationIrradidated Material (RPhr) (red) Source Remark Ref.

Polystyrene 0.008 Test Reactor Sealed Samples 5Neutron, Gamma

Polyethylene 2.0 Test Reactor Sealed Samples 5Neutron, Gamma

Styrene/Butadiene 0.01 Test Reactor Sealed Samples 5Copolymer Neutron, Gamma

Aromatic Liquids 0.05-0.1 11

Pure Water 0.45 Unaffected by pH 14

Saturated Hydrocarbon 2-6 25(Paraffins)

Unsaturated

Hydrocarbons (Olefins) 1 25

Aromatic Hydrocarbons 0.04-0.4. 25

Polystyrene 0.0262-0.0446 Co-60 37

Table 5-2. Solidification Binders

GH2 Dose Rate Total Dose RadiationIrradiated Material (R/hr) (red) Source Remark Ref.

Vinyl Ester Styrene 0.03 Mostly CO & C02, only 17% H2 19(Dow Binder)

Epoxys 0.10-0.23 6 x 10a 3 x 10 Spent Fuel Varied depending on resinlhardner 29Gamma combination

Cement - 2.8 x 107 Co-60 GH2 was time dependent, steady state 4pressure of 100 psIg developed

Cement (Q'ype II) 0.35-0.11 4.6 x 108 10s -109 Co-60 33% H20; GH2 decreased with total dose 10as pressure built up In sealed container

Asphalt 0.3-0.6 Survey of four references, details not given 8

Asphalt-Distilled 0.41 16

Asphalt-Air Blown 0.46 16

Asphalt-Pioneer 221 0.07-0.41 4.6 x 106 103 -109 Co-60 Increased with total dose (time) 10

Asphalt-Air Blown 0.43 105 100 Fuel Element 15Gamma

Asphalt-Distilled 0.32 103 108 Fuel Element 15Gamma


Table 5-3. Ion Exchange Resins

Irradidated GH2 Dose Rate Total Dose RadiationMaterial (RPhr) (rad) Source Remark Ref.

Cation Resins

Dowex MSC-1 0.46 3.5 x 10' 1.4 x 109 Co-60 Covered In 0.5 N HCI 24Amberlite 252 0.53 3,5 x 10' 1.4 x 109 Co-60 Covered In 0.5 N HCI 24Duollte C-264 0.38 a5 x 105 1.4 x 10' Co-60 Covered In 0.5 N HCI 24Dowex 50W 0.10 1.25 x 106 5 x 108 Co-60 Air dried (66% H20) 22Dowex HCR-S 0.05 5 x 108 2.5 x 10' Co-60 Fully swollen, dewatered, 27

sodium formDowex 50 1.06 2.5 x 10' 5 x 107 - 2 x 10' Co-60 H+ form, covered In water 28Dowex 50 0.81 2.5 x 10a 5 x 107 - 2 x 10' Co-60 Lithium form, covered In water 28Zeo Karb 215 1.06 2.5 x 10' 5 x 107 - 2 x 108 Co-50 H+ form, covered In water 28Dowex 50 0.06 25 x 10' 5 x 107 - 2 x 108 Co-60 H+ from, fully swollen 28Dowex 50 0.07 2.5 x 105 5 x 107 - 2 x 108 Co-60 Lithium form, fully swollen 28Zoo Karb 215 0.08 2.5 x 105 5 x 107 - 2 x 108 Co-60 H+ form, fully swollen 28IRN-77 0.13 4 x 104 - 109 Co-60 H+ form, fully swollen 33

1.6 x 108IRN-77 0.16 4 x 104 - 109 Co-60 Sodium form, fully swollen 33

1.6 x 10'

Anion Resins

Dowex 1 0.09 1.2 x 10' 6 x 108 Co-60 Air dried (48% H20) 23IRN-78 0.62 1.6 x 108 109 Co-60 Hydroxide from, fully swollen 33IRN-78 0.34 1.6 x 108 10' 00-60 Chloride from, fully swollen 33Dowex SBR-OH 0.38 5 x 108 7.9 x 108 Co-60 Borate form, fully swollen, 27

dewatered

Mixed Resin

IRN-150 0.3 - 4 x 10'4- 109 Co-60 Varied with chemical from 330.5 1.6 x 108 (degree of resin depletion)

D-Mix 0.19- 4.5 x 106 9 x 10' Co-60 Proprietary formulation of TMI-2 20.24 cleanup resins, sodium borate

form, fully swollen, dewateredDowex HGR-H 0.07 1.2 x 10' 5 x 107 Co-60 Dried resin 7Cation ResinIRN-77Cation Resin 0.01 109 Co-60 Dried to 7% water content 33Dawex 50 0.03 2.5 x 105 5 x 107 - 2 x 109 Co-60 H+ form, dried resin 18Cation ResinDowex 50 0.001 25 x 105 5 x 107 - 2 x 10' Co-60 Lithium form, dried resin 18Cation ResinZeo Karb 215 0.05 2.5 x 10' 5 x 10 - 2 x 10' Co-SO H+ form, dried resin 18Cation ResinIonsiv IE-95 0.05- 3.9 x 10' 1.4 x 10' Co-60 21-33%/ water content 30Zeolite 0.005Linde IE-95 0.75- 1.2 x 10' 5 x 107 Co-60 Saturated with cater 7Zeolite 0.18Miscellaneous 1-3.1 Work of the Russian Egorov, 18Resins conditions not given, ca. 1965


Table 5-4. Solidified Waste

Irradidated GH2 Dose Rate Total Dose RadiationMaterial (R/hr) (rad) Source Remark Ref.

Cement/D.mlx

Cement/Fe2 03

Cement/Fe2 03

Cement/Fe203

Cement/Fe20 3

Cement/Mn0 2

Cement/Mn0 2

Cement/MnO2

Cement/Mn0 2

Cement/NOi- ,N0g

Airblown Asphalt/NaN03

Distilled Asphalt/NaN03

Distilled Asphalt/Mixed Resin

Asphalt/Resin

0.19-0.24 4.5 x 106

- 8.9 x 104

- 3,9 x 105

- 1.4 x 107

- 2.8 x 107

- 8.9 x 104

- 3,9 x 10O

- 1.4 x 107

- 2.8 x 107

- 8.9 x 104

0.25 105

0.18-0.26 10'

9 x 100 Co-60

Co-60

Co-60

Co-60

Co-60

Co-60

Co-60

Co-60

Co-60

Co-60

108 Fuel ElementGamma

107 -108 Fuel ElementGamma

107 -10J Fuel ElementGamma

8 x 107

Proprietary resin formulation of TMI-2cleanup resins solidified in ametasilicate modified cement

30 psig steady state pressure developed


100 psIg steady state pressure developed







50:50 mixture of asphalt and salt

50:50 mixture of asphalt and salt

50:50 mixture of asphalt and mixedrexln In the lithium borate form

Resin expended with lithium borate,10% residual water

2:1 resin to binder ratio

2

4

4

4

4

4

4

4

4

4

15

15

15

16

19

0.19-0.240.24

0.15

10'

Dow/Resin 0.57

6

CONCLUSION

Example Calculation

A good way to bring home some of the aspects ofradiolytic hydrogen generation is to perform a samplecalculation evaluating a common LLRW waste form.Such a calculation was performed and is included asthe Appendix to this report. In this calculation the doserequired to generate a combustible quantity of hydro-gen in the void over a cement solidified drum of ionexchange resins was determined.

The first step of the analysis is to determine the volumein the package available for the gas to occupy. Burialsite criteria require all packages to be at least 85%full. In addition to the free void, dewatered bead resinshave approximately 35% void space between thebeads. Because the particle size is smaller, dewateredsludges are only about 25% void. Therefore, the totalvoid space into which hydrogen gas can expand isabout 45% of the internal package volume fordewatered bead resin and 36% for dewatered sludges.Based on the 5% limit given in Information Notice84-72, a maximum of 2.5% of the total internalpackage volume is available for hydrogen gas at roomtemperature and pressure dewatered bead resin. Thecorresponding volume is 1.8% for dewatered sludges.These limits apply to a package which is sealed andgiven no consideration for venting from the time ofclosure to the time of disposal. The volume availablefor hydrogen gas in a solidified waste form is limitedto the unused space in the package above the waste.This is because the binder fills the voids that arepresent in dewatered resin and sludge. The freevolume for hydrogen gas is dictated by the packag-ing process, but in all cases must be at most 15%(vol) of the internal package volume based on burialsite criteria. Applying the 5% limit to this, a maximum

of 0.75% of the internal package volume is availablefor hydrogen gas at room temperature and pressure.

The next step is to determine the amount of hydrogenthat will have to be formed to achieve a 5% concen-tration in this void. Finally, the energy and absorbeddose is determined that will generate this muchhydrogen from the waste being considered. Thisenergy depends on the hydrogen G-value of thematerial being studied. When evaluating data or mak-ing predictions of gas generation rates using aG-value, it is important to remember that this numberis a ratio and its accuracy is dependent upon theaccuracy of measuring both the reaction yield and theabsorbed energy.

Now that the limiting absorbed dose is known whichwill generate a combustible quantity of hydrogen, thismust be translated to an activity loading in the drum.This activity loading will be a characteristic of thewaste stream, reactor type and hold up time beforepackaging. Using the results of Colombo and Nielson(10) for "typical" PWR and BWR wastes (Figures 2-1and 2-2), an activity loading of about 1 Ci/ft3 will resultin an absorbed dose on the order of 106 rads after5 years at either a PWR or BWR. This limiting activityloading increases by a factor of 3 to 5 if the drum isshipped prior to 1 year after being sealed. As a pointof comparison, a 1 Ci/ft3 waste form having the sameradionuclide composition as Colombo and Nielson'sPWR waste would be classified as Class B accordingto the current Barnwell Waste Management FacilityLicense. This waste would also be 35% of the ClassC limit.

It would therefore appear that the primary impact ofhydrogen generation on transportation will be fromLLRW that is relatively highly loaded with radionu-clides and also stored for a period of one to five years.

19

20 Concluslon

Waste stored less than one year will have to be nearClass C to generate a combustible quantity of hydro-gen prior to shipment.

Main Conclusions

The main conclusions of this investigation can belisted as:

* Water accounts for most of the radiolytic hydrogengenerated by LLRW.

" Hydrogen G-Values reported in the literature forwater containing species will probably result in con-servatively high predictions of the amount ofhydrogen generated by radiolysis in LLRW becausethese data were all taken at dose rates that areseveral orders of magnitude larger than exist inmost LLRW. It has been shown that the hydrogenyield for cement will decrease at lower dose rates,and this may hold true for other water containingwaste forms.

* Concerns over combustion within a sealed packageof LLRW are unfounded. This is because an effi-cient radiolytic oxidation reaction removes oxygenfrom the atmosphere in a sealed package. The con-cern for combustion surfaces during a packagefailure situation, such as a transportation accident.This is the source of the requirement for limitinghydrogen or inerting the transportation cask interior.Another area of concern is extended storage of ClassB and C waste in confined spaces where local con-centrations of hydrogen can accumulate.

" Vinyl ester styrene generates the least radiolytichydrogen of the LLRW solidification binders. Thisis because it contains no water and is a largelyaromatic polymer. Asphalt and cement generateas much as a ten times more hydrogen.

" Dried organic ion exchange resins produce a fac-tor of ten less radiolytic hydrogen than fully swollen(dewatered) resins.

* Cement solidification of waste does not appreciablyreduce the hydrogen yield, but it does fill the voidsin dewatered resin. This results in less void volumefor the gas to fill, producing a combustible quantityof hydrogen at a lower absorbed dose. This effectcan be significant because dewatered bead resin

can contain as much as 35% void volume betweenthe beads.

Chemical production of hydrogen in a corrosion pro-cess can overwhelm radiolytic production. Theimportance of this reaction pathway is somewhatmore elusive than that of hydrogen formation bydirect irradiation of water or organics. Most LLRWtransportion packages contain insufficient free waterto support such a chemical reaction. However, rad-waste spent resin storage tanks do. It is possiblethat measurements may be taken in the field at thespent resin tank to verify the presence of hydrogenprior to packaging for disposal. For this reason, itis just as improtant to characterize the chemicalnature of the spent resins as it is their radiologicalnature when performing field measurements of thehydrogen gas yields pursuant to IE-Notice 84-72.Furthermore, Swyler (33) identified that the irradia-tion of anion exchange resins results in a releasefrom the resin bead of some of the bound waterat absorbed doses on the order of 5 x 108 rads.Although, this radiation dose is quite large fortypical LLRW, this release of water could provideenough acid contact with a metal surface to resultin sufficient corrosion to produce hydrogen. Again,it is important to remember here that both thechemical and radiological conditions, as well as thenature of the package, must be considered jointlywhen examining a hydrogen production mechanismof this kind.

Asphalted, cemented and dewatered waste that isan appreciable fraction of the Class C limit and isstored for one to five years may require special con-siderations for hydrogen generation.

Recommendations for Future Work

Several workers have identified a trend in cementsolidified waste that the radiolytic hydrogen yielddecreases with dose rate. This is not surprising in thatdose rate dependence is common in the study ofradiation effects in solids. There is also reason tobelieve that the reactions that operate in cement alsooperate in other water containing waste, such asdewatered ion exchange resins. Since all of theresearch to date has taken place in the 105 to 107 radper hour range, and even Class C utility waste is

Conclusion 21

significantly below this, it would be beneficial to deter-mine the hydrogen yield at dose rates which closerapproximate LLRW. This will fill a large gap in theexisting hydrogen generation data base.

Since measurements at low dose rates will producehydrogen at correspondingly low rates, the accuracyof measuring the quantity of hydrogen produced willhave to be carefully evaluated. Very sensitive analyticalmethods will be required to monitor this small quan-tity of hydrogen.

Since the calculation of the absorbed dose is so criticalto the analytical determination of hydrogen generation,

methods for this calculation should be examined anda standardized calculation developed. Based on varia-tions in the modelling technique, it is concievable that50-100% error can be made in the calcualtion ofabsorbed dose, leading to either gross underestima-tion or overestimation of the hydrogen producedbetween packaging and transportation. This isespecially significant with the advent of the storage oflarge quantities of LLRW at reactor sites for periodsof up to five years.

7

ANNOTATED BIBLIOGRAPHY

1. Ballantine, D.S., 'The Significance to ASTM ofPost-irradiation Effects in Irradiated Materials,"Materials In Nuclear Applications, ASTM SpecialTechnical Publication No. 276, 1960.

Identifies the basic radiolytic reactions which resultin polymer degradation. Radiolytic ionization orexcitation causes C-C or C-H bond rupture. Thisis followed by oxidation in the presence of oxygen,hydrogen gas formation, recombination, depoly-merization or crosslinking. The reaction pathwaydepends on the size of the radical or ion and theviscosity or rigidity of the parent compound.

Evidence of the existence of trapped free radicalsis sited. These trapped free radicals lead to postirradiation reactions. These radicals have beendetected in polyethylene 3000 hours after irradia-tion at room temperature. The author stressedthe importance of considering post irradiationreactions in the results of any materials testing.

2. Barletta, R. E., Swyler, K. J., Chan, S. F. andDavis, R. E., Solidification of Irradiated Epicor-IIWaste Products, NUREG/CR-2969, BNL-NUREG-51590, May 1983.

Ion exchange resins similar to those used todecontaminate TMI-2 were irradiated in bothdewatered and solidified form. These resins area combination of organic and inorganic ionexchangers. The resins studied, termed "D-mix:'were representative of those used in a deep bedprefilter. The resins were expended using sodiumborate and irradiated with a cobalt-60 source at4.5 x 106 rad/hr to a total dose of 9 x 108 rad.For dewatered D-mix, a hydrogen G-value of 0.19to 0.24 is reported, with a total gas G-value of0.25 to 0.3a Carbon dioxide was the other prin-cipal gas involved.

For cement solidfied D-mix (composition: 350:153: 514: 51, D-mix: water: Type I cement:sodium metasilicate, by weight) a total gasG-value of 0.19 to 0.24 is reported with hydrogenbeing the only significant gas produced (> 98%).Specific gravity for the solidified D-mix was about1.4, with 1.1 for D-mix alone.

3. Bibler, N. E., "Radiolytic Gas Production Dur-ing Long-Term Storage of Nuclear Wastes,"Savannah River Laboratory Technical Paper. No.DP-MS-76-51, 1976.

Presents the results of work which was laterreported on in DP-1484. This work consistedof irradiating cement and simulated cementwaste forms and monitoring the radiolysis gas.In addition to work discussed in DP-1484, gasgeneration results of irradiation of vermiculitecontaining absorbed organic liquids and cellu-losics (paper towels) containing alpha-emittingisotopes are presented.

4. Bibler, N. E., Radlolytic Gas Generation FromConcrete Containing Savannah River PlantWaste, Savannah River Laboratory Report No.DP-1464, 1978.

Samples of cement and simulated cement wasteforms containing Fe 20 3, MnO2, NO and NOýwere irradiated with both gamma and alpharadiation and radiolytic gas production wasmonitored. The effect of gamma dose rate wasstudied over the range of 8.9 x 104 to 2.8 x 107rad per hour. Hydrogen was the only significantproduct for gamma radiolysis. A steady statehydrogen pressure was attained with gammaradiolysis that was dose rate dependent. This isevidence of a back reaction which consumes

23

24 Annotated Bibliography

hydrogen. No steady state pressure could beattained with alpha radiolysis.

5. Bopp, C. D. and Sisman, 0., Radiation Stabilityof Plastics and Elastomers, ORNL-1373, July 23,1953.

Plastics and elastomers were irradiated on themaximum flux region of the ORNL GraphiteReactor. To increase the gamma dose, somesamples were rapped in cadmium during irradia-tion. Energy absorbed was calculated from theelemental composition of the materials by usingcalorimetrically determined values for theelements. Energy absorbed was highly depen-dent on hydrogen atom content, since a hydrogenatom has "high stopping power for fast neutrons."

0.2 to 0.5 gram samples were irradiated in sealedglass capsules. In the range of 1 to 50 ml (STP)of gas evolved, gas evolution was proportionalto exposure (in nvt).

Total gas G-values are are reported as:

Polystyrene - 0.008Polyethylene - 2.0Styrene/Butadiene Copolymer - .01

6. Bureau of Radiological Health and the TrainingInstitute, Environmental Control Administration,Radiological Health Handbook, U.S. GovernmentPrint Office, Washington, D.C., 1970.

A general handbook containing data on theradioactive decay properties of the radioisotopes.Of particular interest are the energy and half-lifedata that is given for essentially all known radio-nuclides. Also given are mass absorption coef-ficients for many materials, along with otherinformation pertaining to radiation dose calcula-tions. These data are required for calculating theabsorbed dose to a waste form from incorporatedradionuclides.

7. Capolupo, W. R, Sheff, J. R., "Radiolytic GasGeneration and Oxygen Depletion in IonExchange Materials:' Scientific Basis for NuclearWaste Management Vi, Materials ResearchSociety Symposia Proceedings Vol. 15, 1983.

Both organic and inorganic ion exchangers wereirradiated at 1.2 x 105 R/hr using a cobalt-60

source up to an absorbed dose of 5 x 107 rad.Particular emphasis was placed on the earlystage of radiolysis. Rapid depletion of oxygenover the organic resin was observed, with 99.8%of the oxygen being consumed at 2.5 x 106 rad.No oxygen consumption was observed over theZeolite. The Zeolite, Linde IE-95, was irradiatedfully hydrated and yielded a total gas G-value of0.075-0.18. The gas yield was low at low dose butincreased at high dose, indicating some gasinteraction with the Zeolite surface. The organicresin, Dowex HGR-H+, was irradiated bothhydrated (50% water) and dried. Dried resinexhibited a total gas G-value of 0f067. No G-valuewas reported for wet resin as the pressure in thesealed container varied nonlinearly over therange of dose.

8. Carleson, G., Radiation Stability of Solidified Ion-Exchange Resin (In Swedish), Studsvik TechnicalReport NW-83/490, 1983.

A literature review of the period 1965-1982 ispresented concerning the radiation stability ofion-exchange resins solidified with cement orbitumen. Sites 67 references from both the U.S.and world at large. Pays particular attention toradiolytic gas generation in binders. For cement,reports that in sealed systems, hydrogen produc-tion increases with dose to an equilibriumpressure of 5-20 bar, with the pressure being afunction of dose rate. Reports total gas G-valuefor cement of 0.4 ± 0.2. Reports hydrogen yieldsfrom bitumen of 7 ± 3 1/g Mrad, which translatesto a G-value of 0.3-0.6. Reports decrease in gasgeneration with higher resin loading in bitumenwaste forms.

9. Carswell, D.J., Introduction to Nuclear Chemistry,Elsevier Publishing Co., New York, N.Y., 1967.

A general textbook on Nuclear Chemistry. Pro-vides a good description of the basicmechanisms of the chemical reactions occurringin irradiated materials. Also, defines G-value.

10. Colombo, P, Nielson, R.M., Jr., Properties ofRadioactive Wastes and Waste Containers - FirstTopical Report, NUREG/CR-0619, BNL-NUREG-50957, August 1979.

Annotated Bibliography 25

A topical report on the results of research con-ducted by BNL on the properties of solidifiedradioactive wastes and their containers.Radiolytic gas formation from three radwastebinders during irradiation from a cobalt-60source was studied. The binders that werestudied were Portland Type II cement (33% W/WH20), urea-formoldehyde, and Pioneer 221asphalt. Also presented, is a calculation ofabsorbed dose as a function of specific activityand time for "typical" PWR and BWR wastessolidified in a waste form having a specific gravityof 2.0 g/cc.

11. Cosgrove, S.L., and Dueltgen, R.L., The Effectof Nuclear Radiation on Lubricants and HydraulicFluids, Radiation Effects Information Center(REIC) Report No. 19, Battelle Memorial Institute,May 31, 1961.

Gives quantitative data on radiation effects in allmanner of organic fluids and polymers. Fororganic compounds similar to polystrene,G-values for total gas production are given in the0.05-0.1 range. Straight chain alkanes (paraffins)are reported as having the highest G-valves fortotal gas production, being in the 4-6 range.

12. Collins, C.G., and Calkins, V.P, RadiationDamage to Elastomers, Plastics and OrganicLiquids, General Electric Aircraft Nuclear Propul-sion Department, APEX-261, Sept. 1956.

Presents a collection of data on radiationdamage to organic materials, including physicalproperties, mechanical strength and gas genera-tion. The Primary source for gas generation datais the work of 0. Sisman and C.D. Bopp.

13. Dole, M., Keeling, C.D. and Rose, D.G., "The PileIrradiation of Polyethylene," J. Amer Chem. Soc.,76, pp. 4304-4311 (1954).

Polyethylene in films and granules was irradiatedin a heavy water reactor in vacuum and in air.Amount and composition of the radiolysis gaseswere determined. Exposure is reported in termsof hours and total dose is not reported, therefore,a G-value is not calculable. However, gas genera-tion is plotted vs. time and is apparently linearfor the three points shown.

The composition of the radiolysis gas in theevacuated container was 98.6% H2, 0.2% OH 4and the balance was higher degree saturatedparaffins (CnH 2n + 2).

14. Dragnic, I.G. and Dragnic, Z.D., The RadiationChemistry of Water, Academic Press, New York,N.Y., 1971.

A thorough textbook on the radiation chemistryof water and aquaeous systems. Gives theprimary radiolysis products of water as H, OH,H20 2 and H2 . Reports that the hydrogenG-value of pure water Is 0.45 regardless of pH.The primary radiolytic pathway for the produc-tion of molecular gaseous hydrogen is throughthe recombination reaction of two hydrated elec-trons. It has been documented that the presenceof electron scavengers such as metal ions cangreatly reduce the production rate of hydrogengas in aquaeous solutions.

15. Duschner, H., Schorr, W. and Starke, K.,"Generation and Diffusion of Radiolysis Gasesin Bituminized Radioactive Waste," Radio-chemica Acta, 24, 133 (1977).

Simulated bituminized radioactive wastes wereirradiated by a 10- R/hr fuel element source to108 rads and the radiolysis gases studied. Bothair blown and distilled bitumen binders wereused. Wastes studied were sodium nitrate andmixed anion-cation organic ion exchange resinin the lithium borate form. Gas analysis was per-formed by mass spectrometry. Hydrogenaccounted for about 95% of the radiolysis gasin all cases. Irradiations were performed insealed containers with both air and argon atmos-pheres. Hydrogen diffusion experiments werealso performed on asphalt discs, and the rateof permeation and absorption coefficient arereported. Hydrogen generation rates of 0.48 - 1.1x 102 cm3/MR per gram of simulated waste arereported. Results were linear with absorbed doseand dose rate effects were discounted based onwork by others.

16. Eschrich, H., Properties and Long.Termi Behavior ofBitumen and Radioac& Waste-Bitumen Mixtures,SKBK-KBS Technical Report 80-14, Oct. 1980.


Presents the results of a review of over 300references on the properties of bitumen for rad-waste solidification. With respect to gas genera-tion, hydrogen and methane are the primaryradiolysis gases reported (75-95%). States thatinternal radiation sources yield approximatelytwice the hydrogen as external sources.Hydrogen generation in bituminized ionexchange resin is reported as 0.11 to 0.30 cc/gat 760 torr and 250C when exposed to 8 x 107rad. For pure asphalt, hydrogen G-values of 0.41for distilled and 0.46 for air-blown are reported.

17. Gangwer, T.E., and Pillay, K. K. S., "Radiation-Induced Corrosion of Mild Steel In Contact withIon-Exchange Materials," Nuclear Technology 58(3), Sept. 1982.

Mild Steel coupons were irradiated whileembedded in cation, anion and zeolite ionexchange materials. Steel weight loss from cor-rosion in the organic media was 13-32 mg lossper square centimeter after exposure to 2 x 109rad from a COBO source. Weight losses of 5.2-27mg/cm 2 were also observed after exposure to 4.4x 108 rad from reactor fuel rads. Rust and pittingwas visible on each of the metal coupons follow-ing exposure. It was not reported whether theirradiation took place in a sealed or open system.

18% Gangwer, T. E., Goldstein, M. and Pillay, K. K. S.,Radiation Effects on Ion Exchange Materials,BNL-50781, Nov. 1977.

An extensive literature review and data compila-tion on the radiation damage of ion exchangeresins. States that in the majority of the literature,experimenters have assumed that mass absorp-tion coefficients for resin and water are approx-imately equal.

With respect to gas generation, the review is ofthe work of Kazanjian, et. al., and Mohorcic, et.al., as well as a 1965 review by the Russian,Egorov. Gaseous radiolysis products aredominated by H2 with C02, CO, SO2 CH4, N2,NO2 and NO also being reported. HydrogenG-values reported by Egorov are around 1.0 to al,or an order of magnitude greater then those com-monly reported in the U. S.

19. Haighton, A.R, The Solidification of Ion ExchangeWaste Part 6 - Characterization of a Vinyl EsterBinder, NW/SSO/RR/75/80, Central ElectricGenerating Board, Manchester, United Kingdom,1980.

Vinyl ester styrene (VES), also known as the DowBinder, was irradiated both with and withoutsimulated waste (containing water and ionexchange resins). For the pure binder, 0.41cc/g-100 mR of total gas was evolved when irradi-ating to 1420 MRad. The gas composition was35% 10 CO, 43% CO2, 17% H2 and CH4 . Forthe binder encapsulating water, 0.61 MRad. Thegas composition was 40% H2, 22% CO, 34.5%C02 and 3.5% CH4. Finally, for the binder con-taining organic ion exchange resin in a 2:1 resinto binder ratio, 1.34 cc/g-100 mR total gas wasevolved at 1030 MRad, with the gas being com-posed of 98% H2.

20. Harrington, R., and Giberson, R., "Chemical andPhysical Changes in Gamma-Irradiated Plastics,"Modem Plastics, 36, p. 199 (Nov. 1958).

Films of plastic ranging from 3 to 20 mils wereirradiated in a vacuum to lx108 roentgensexposed dose. A 1.3x106 roentgen per hr.cobalt-60 source was used. Marlex polyethleneand polystyrene were among the plastics studied.Within the sensitivity of the instrumentation, nogassing was observed for the polystyrene at atotal exposure dose of 1 x10 8 roentgen. For theMarlex high density polyethlene the gas composi-tion as 97.8% H2, 0.100/o CH4, 1.10/o C2Hx witha mixture of light hydrocarbons comprising thebalance. Total gas yield was not reported.

21. Hine, G.J., and Brownell, G.L., Radioactive Dosi-metby, Academic Press, Inc. New York, N. Y., 1956.

A general textbook on radiation dosimetry.Describes a method for calculating the radiationdose absorbed by a cylinder of uniformlydistributed gamma emitters. Relies on an "averagegeometrical factor," §, to approximate the attenu-ation provided by a given shape of material.

22. Kazanjian, A.R. and Horrell, D.R., Radiation Effectson Ion Exchange Resins, Part I. Gamma Irradia-tion of Dowex 50W, Dow Chemical Rocky FlatsDivision Report No. RFP-2140, May 10, 1974.


Dowex 50W, a sulfonic acid cation exchangeresin was irradiated to 5x108 rads using a1.25x106 rad per hour cobalt-60 source. Gasyields were measured for hydrogen form air-dried resin (66%/o H20), resin in 0.1 N HC1, and,0.1 N HC1. Hydrogen G-values are reported as0.10 for each.

23. Kazanjian, A.R., and Horrell, D.R., RadiationEffects on Ion-Exchange Resins, Part i1:Gamma Irradiation of Dowex 1, Dow ChemicalRocky Flats Division Report No. RFP-2354,Feb. 27, 1975.

Dowex-1, a trimethylamine anion exchange resin,was irradiated to 6x108 rads using a 1.2x10 6 radper hour cobalt-60 source. Gas yields weremeasured for nitrate form air dried resin (48%/oH20), resin in 7 N nitric acid, and 7 N nitric acid.The hydrogen G-value is reported as 0.09, 0.02and 0.02, respectively. Carbon monoxide, andnitrous oxide are the only other gases reportedfor the dried resin. No methane is reported.

24. Kazanjian, A.R., and Stevens, J.R., RadiationEffects on Dowex MSC.1, Amberlite 252, andDuolite C-264 Ion Exchange Resins, RockwellInternational Energy Systems Group Rocky FlatsPlant Report No. RFP-3541, Sept. 12, 1983.

Three sulfonic cation exchange resins wereirradiated to 1.38x10 9 rad using a 3.48x105 radper hour cobalt-60 source, The samples wereirradiated in sealed vials and were barelycovered with 0.5 N hydrochloric acid. Hydrogenwas the only combustible species detected,having a G-value of 0.46, 0.53 and 0.38 for theDowex, Amberlite and Duolite resins, respectively.

25. Kircher, J.F., and Bowman, R.E., (ed.), Effectsof Radiation on Materials and Components,Reinhold Publishing Corp., New York, NY, 1964.

A basic text on radiation damage which also con-tains a large amount of data. Gives the defini-tion of "G-value" as "the number of productmolecules formed or reactant molecules con-sumed per 100 ev of energy absorbed:' Forparaffins, hydrogen is always the major radiolysisproduct. Unsaturated aliphatics (eg. ethylene)react by chain mechanisms which lead topolymers and a low yield of gas, particularly

hydrogen. Aromatics (eg. benzene) are notablystable under irradiation because of the ability ofthe ring to absorb large amounts of energywithout cleaveage. Decomposition and gas for-mation rates in aromatics are an order ofmagnitude lower than for aliphatic compounds.

With respect to polymer radiolysis, says: "Fromthe standpoint of change in physical propertiesand hydrogen evolution during irradiation,polystyrene is one of the most stable of all highpolymers:'

General hydrogen G-values are:

Saturated HydrocarbonsUnsaturated HydrocarbonsAromatic Hydrocarbons

2-610.04-0.4

Radiation induced gas release from concreteis reported as 4-6 cc/g-day in pile reactorshields. Gas composition is 75% H2 with someCO and C02.

26. MacKenzie, D. R., Lin, M., and Barletta, R. E.,Permissible Radlonuclide Loading for OrganicIon Exchange Resins from Nuclear PowerPlants, NUREG/CR-2830, BNL-NUREG-51565,October 1983.

Reports on the results of a literature review andpower plant survey on the radiation effects in ionexchange resins and the radionuclide loadingsseen in the industry. Review of radiation effectsconsiders gas generation. Primary referencesare the research of Mohorcic and Kramer,Kazanjian and Horrell, and McFarland, as wellas the reviews of Gangwer, Goldstein and Pillay(BNL-50781), Swyler, Barletta and Davis (BNL-NUREG-28682), and Pillay (NUREGICR-1863).

Proposes a permissible resin loading in termsof a delivered dose of 108 rad. A computer codeis presented to calculate delivered dose basedon Curie inventory, container size and length ofdecay. This code Is developed using the methodof Swyler, et al (BNL-NUREG-28682).

27. McFarland, R. C., Analysis of Irradiated IonExchange Materials, Final Research Report, Pro-ject A60-11. Published as Appendix C to Morcos,N. et. al, Properties of Radioactive Wastes and


Waste Containers, NUREG/CR-2617, BNL-NUREG-51515, April 1982.

Sodium form Dow HCR-5 cation and borate formDow SBR-OH anion exchange resins were irradi-ated in sealed containers and gas pressurebuildup and composition were monitored. A 5x 106 rad per hour cobalt-60 source was usedwith absorbed dose totalling 7.9 x 108 rads forthe anion resin and 2.5 x 109 rads for the cationresin. Resins were fully swollen and dewateredfor the irradiation. For the anion resin, G-valueswere as follows: total gas = 0.68, hydrogen gas0.38, methane = 0.04. For the cation resin,G-values were: total gas = 0.11, hydrogen gas= 0.05, and methane = 0.002.

28. Mohorcic, G, and Kramer, V., "Gases evolved bycobalt-60 Radiation Degradation of StronglyAcidic Ion Exchange Resins," J. Polymer Science:Part C, 16, pp 4185-4195 (1968).

Sealed sulfonic acid cation exchange resinswere subjected to a 2.5 x 105 rad per hrcobalt-60 source to absorbed doses of 5 to 20x 107 rads. Experimental conditions werehydrogen and lithium forms in excess water,swollen and dry states. Gas analysis showedlinear dependence on absorbed dose over therange studied. Dowex-50, a polystyrene-divinylbenzene based resin, had hydrogen gasG-values of 0.026, 0.059 and 1.06 in dry, swollenand excess water conditions in hydrogen form.In lithium form, Dowex-50 had hydrogen gasG-values of 0.001, 0.069 and 0.812 in the sameorder of conditions. Zeo Karb 215, a phenol-formaldehyde based resin, had hydrogenG-values of 0.051, 0.075 and 1.06 under the sameconditions combustible gases are reported,however, a large sulfur dioxide yield wasreported for dry Dowex-50 (G=0.87). It should benoted that Mohorcic reported resin G-values interms of dry resin only and these values havebeen converted to account for the additionalweight of water in the swollen and excess waterstates.

29. Morgan, J.T., et al., Gas Evolution from EpoxyResins by High Energy Radiation, Rutherfod HighEnergy Lab Report No. RHEL/R-196, Aug. 1970.

Cast epoxy resins were exposed to gamma radia-tion from spent fuel in sealed tubes and the gasevolution rate and composition were monitored.The gas evolution rate was found to be constantup to 3x109 rad absorbed dose. HydrogenG-values ranged from 0.10 to 0.23, depending onthe epoxy resin/hardner combination and theresin curing temperature. Hydrogen accounted for80-90% of the gas evolved in most cases exceptthree, where carbon dioxide and monoxideprevailed. Trace quantities of the lower hydrocar-bons, (methane, ethane, etc.,) were also detected.The predominance of small molecules agreeswith the "cage effect" in which large moleculesare restricted from leaving the cage of the sur-rounding molecules and subsequently recombine,cross-link or cause chain scission. Smallmolecules can more readily diffuse away to reactand form gases.

30. Pillay, K.K.S., Radiation Effects on Ion ExchangersUsed in Radioactive Waste Management, Penn-sylvania State University, NEIRWM-80-3, October1980. Published as Appendix A of Morcos, N. andWeiss, A. J., Properties of Radioactive Wastes andWaste Containers-Quarterly Progress Report July-Sept 1980, NUREG-CR-1868, BNL-NUREG-51316,Jan 1981.

Report is an extension of Pillay's work onBNL-50781 (1977). The literature search donethere is updated and augmented. Also, experi-ments are reported on the irradiation of sulfonicacid cation resins (Amberlite IR-120), amine anionresins (Amberlite IRA-400) and an inorganicZeolite (IONSIV-IE-95). A pH change from U4 to1.5 is reported for cation resin in both hydrogenand ammonium form after irradiating to 7 x 107rads. The Zeolite (21-33% H20) was irradiated to1A x 108 rads with gas evolution being monitoredin a sealed, atmospheric container. From thesedata, a G-value for hydrogen of about 0.05 to 0.005can be calculated. The low H2 yield washypothesized to be a result of a hydrogen adsorp-tion on the Zeolite surface. Significant corrosionof up to 32.4 mg/cm 2 of mild steel coupons wasalso reported when irradiating them with theabove ion exchangers.


31. Sun, K.H., "Effects of Atomic Radiation on HighPolymers," Modem Plastics, 32, p.141 (Sept. 1954).

A review of the basics of radiation damage topolymers. The nature of radiation, units ofdosmetry, principal chemical reactions andphysical property changes are all discussed. Withrespect to gas formation it is stated that indepen-dent of the radiation type or polymer type,over 94% of the gas liberated is hydrogen, therest being the light hydrocarbons (ie. methane,ethane, etc.). This is based on a review of theliterature to date.

32. Swyler, K.J., Barletta, R.E. and Davis, R.E.,Review of Recent Studies of the Radiation InducedBehavior of Ion Exchange Media, BNL-NUREG-28682, Nov. 1980.

Reviews the published work of R.C. McFarlandand K.K.S. Pillay on radiation effects in ionexchangers. Also reviews them unpublished workperformed at BNL which was later published asNUREG/CR-3383 and NUREG/CR-3812.Presents a method for calculating the doseabsorbed by a cylindrical bed of organic ionexchange resin from absorbed radionuclides.

33. Swyler, K.J., Dodge, C.J., and Dayal, R. Irradia-tion Effects on the Storage and Disposal of Rad-waste Containing Organic Ion-Exchange Media,NUREG/CR-3383, BNL-NUREG-51691, Oct. 1983.

This study consisted of irradiating cation, anionand mixed resins at dose rates from 104 to 106Rad/hr until the absorbed dose totaled about 109rad. Gaseous and aqueous radiolysis productswere monitored both qualitatively and quantitavely.Two to six gram resins samples were irradiatedin both sealed and open systems. Dried, saturatedand submerged resins were studied.

The primary effect of radiolysis on the resin struc-ture was observed to be the formation of sulfuricacid and sulfate salts resulting from radiolytic scis-sion of the cation resins functional group. Anionresin exhibited a release of absorbed water at anabsorded dose of about 5x10 8 rad. This wateramounted to 60% of the water absorbed in theresin. Measurements of the pH of this free wateron mixed resin were in the 1 to 4 range, depen-ding on the dose and degree of resin depletion.

Acidity was reduced by expending the cationresin as H + formed by radiolysis is exchangedwith the cations on the undamaged resin.

Gas generation from both sealed and opensystems was dominated by hydrogen, with car-bon dioxide being second. Radiolysis of absorbedwater was identified as the most likely source ofhydrogen, as dried resin generated a factor of tenless hydrogen. In sealed systems, oxygen wasrapidly depleted from the atmosphere by an effi-cient radiolytic oxidation reaction.

Hydrogen G-values of 0.13 and 0.16 are reportedfor cation resin in the hydrogen and sodiumform, respectively. For anion resin, 0.62 and 0.34are reported for hydroxide and chloride form,respectively.

The hydrogen gas G-value for mixed resins wasmeasured at 0.3 to 0.5 depending on the degreeof resin depletion. This is comparable to thevalue for pure water (0.45) and is relatively insen-sitive to dose rate over the range studied.

34. Swyler, K.J., Dodge, C.J., and Dayal, R., Assess-ment of Irradiation Effects in Radwaste Contain-Ing Organic Ion Exchange Media. NUREG/CR-3812, BNL-NUREG-51774, May 1984.

This study investigated the practical conse-quences of radiation on ion exchange resins andtheir impact on resin storage and disposal. Theprimary effect investigated was the corrosion ofmild steel in irradiated resins. Radiolytic acidgeneration was found to be in competition withacid uptake in the corrosion process. Corrosionwas found to be most extensive in H + formcation resins and decreased notably for depletedcation resins.

For H+ form cation resins, hydrogen gas genera-tion from the corrosion process far exceededradiolytic hydrogen formation alone. For otherresin forms, since corrosion was not extensive,no apparent effect could be determined.

Study also examined prevously reported datafrom the TMI EPICOR resins. This data and BNLcalculations show that a dose of 1.2x108 kg-radbeing sufficient to remove 7 liters of oxygen fromthe atmosphere over liner PF-16. Estimated


hydrogen generation rates in liner PF-3 were 9.9cm3/hr in which the pH was 2.6 to 4.9.

35. Tulupov, RE., Butaev, A.M., and Greben, V.R,"Effect of Content of Divinylbenzene in KU-2Cation-Exchange Resin on its Resistance toIrradiation to Water," Russ. J. Phys. Chem, 47 (4),551 (1973).

Sulphonated polystyrene cation-exchange resinswith varying divinylbenzene content were irradi-ated in swollen form with a small excess of water.The primary aqueous radiolysis product was iden-tified as H2 SO4 for the hydrogen form resins.Gaseous radiolysis products were not determined.

36. Tulupov, RE., Butaev, A.M., "Role of Water in theRadiolysis of the Sulphonic Acid Groups in theKU-2 Cation Exchanger," Russ J. Phys. Chem,54(12), 1765(1980).

The water content In a sulphonated cation ionexchange resin was varied from fully swollen todried and the radiolysis products weredetermined. In the gas phase over dried resin,

hydrogen comprised 49.0% at 1.3x10 7 rad andonly 29% at 3.5x108 rad, with carbon dioxideand monoxide accounting for most of thebalance. Similar work by Russian scientists withcation resin in water is reported to have yielded92.5% hydrogen in the gas phase. Total yield isnot reported, however, it is stated that the primarysource of hydrogen in swollen resins is throughthe radiolysis of the absorbed water.

37. Wall, L.A. and Brown, P.W., "Gamma-Irradiationof Polymethly Methacrylate and Polystyrene," J.Phys. Chem. 61(2) p.129 (Feb. 21, 1957).

Disks of polystyrene were irradiated inevacuated sealed tubes and hydrogen gadsyields were determined by mass spectroscopy.The source was cobalt-60. Deuterated poly-styrene was studied for the effect of isotopesubstitution. Hydrogen G-values were found torange from 0.0262 to 0.0446, decreasing withdeuterium content.

APPENDIX

Example Calculation of the dose required to generate 5% Hydrogen in a cemented drum of organic ionexchange resins.

Assumptions and Data:

Drum Internal Volume = 7.7 ft3

Drum Fill Factor = 85%Density of Waste Form = 87.4 Ib/ft3 .. (2)GH2 = 0.24 ..................... (2)Ideal Gas Law: PV = nRT

Volume Available for Hydrogen Gas = (7.7 ft3)x(0.15)x(0.05)= 5.8x10-3 ft3

Molecules of Hydrogen Gas = NH2 _ PV NA

RT

NH2 --- (latm) x (5.8x10- 3 ft3) x 6.02x10 23 molecules

(0.0029 atm-ft3 x 2980K) molemole-OK

NH2 = 4.02 x 1022 molecules H2

Absorbed Energy Required to from NH2 Molecules = E

E =N-H-2GH24.02x10 22 molecules H2 = 1.68xJ025 eV

0.24 molecules H2100 ev

Absorbed Dose Required to Deliver Energy E = D

D = (1.68 x 1025 eV) x 1 erg X 1 X6.241x1011 eV 2.6x10 5 g/drum

D = 1.03 x 106 rads

1 rad100 erg/g

31

32 Appendix

10 9 . . . .I .M 1 11•...,8WR 'WASTES (AFTER W'ASý-;2iý)' ...

/ "•--" 00Ci/f t 3

,08

o o

0.Ci/ft 3

o 0.0Ci/ft3

w IcP

0 0

IO IO0I01 10 100 1000

TIME,* YEAR TIME, YE AR

Note: Figures taken from Colombo and Nielson (10)

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