AECL-7757

ATOMIC ENERGY C S B L'ENERGIE ATOMIQUEOF CANADA LIMITED X^JJ DU CANADA LI MITE E

IMMOBILIZATION AND PACKAGING OFRECOVERED TRITIUM

Immobilisation et empaquetage du tritium recupere

W.J. HOLTSLANDER and J.M. MILLER

Chalk River Nuclear Laboratories Laboratoires nucleaires de Chalk River

Chalk River, Ontario

September 1982 septembre

ATOMIC ENERGY OF CANADA LIMITED

Immobilization and Packaging of Recovered Tritium

by

W.J. Holtslander and J.M. Mi l ler

Chalk River Nuclear LaboratoriesChalk River, Ontario KOJ 1J0

1982 SeptemberAECL-7757

L'ENERGIE ATOMIQUE DU CANADA, LIMITEE

Immobilisation et empaquetage du tritium rëcupëré

par

W.J. Holtslander et J.M. Miller

Sommaire des travaux effectués dans le cadre d'un programme derecherche coordonnée d'une durée de trois ans ayant été organisépar l'Agence internationale de l'énergie atomique. Ce sommaire aété présenté 8 la troisième réunion des principaux chercheurs tenueau Centre de recherche nucléaire Bhabha 8 Trombay en banlieue deBombay, Inde, du 22 au 26 février 1982.

Résumé

L'évaluation dss hydrures de métaux comme gangues pour l'im-mobilisation du tritium est examinée. Les travaux effectués ontpermis de mettre su point des méthodes de préparation et d'évaluerles propriétés des hydrures de zirconium et de titane pour cetteapplication. Ils ont également permis d'étudier diverses méthodesd'empaquetage des hydrures de métaux pour le transport et lestockage du tritium dans des conditions permettant de le récupérer.

Laboratoires nucléaires de Chalk RiverChalk River, Ontario KOJ 1J0

Septembre 1982

AECL-7757

ATOMIC ENERGY OF CANADA LIMITED

Immobilization and Packaging of Recovered Tritium

by

W.J. Holtslander and J.M. M i l l e r

Summary of work performed as part y f a three-year coordinatedresearch program organized by the In te rna t i ona l Atomic Energy Agency -presented to the t h i r d meeting of p r i nc ipa l i n v e s t i g a t o r s , Bhabha AtomicResearch Centre, Trombay, Bombay, I nd i a , 1982 February 22-26.

ABSTRACT

The eva luat ion of metal hydrides as a medium fo r immobi l izat ion oft r i t i u m is reviewed. The work demonstrated methods of preparat ion andexamined the proper t ies of t i t an ium and zirconium hydride fo r t h i s a p p l i -c a t i o n . Methods of packaging the metal hydrides fo r t r anspo r ta t i on andrecoverable storage of t r i t i u m were also examined.

Chalk River Nuclear Laborator iesChalk River , Ontario KOJ 1J0

1982 September

AECL-7757

TABLE OF CONTENTS

Page

1. Introduction 1

2. Options for Packaging Recovered Tritium 1

3. Immobilization of Tritium as Metal Tritides 2

4. Isotopic Analysis of Hydrogen 11

5. Packaging Metal Tritides 11

6. Tritium Laboratory 14

7. Acknowledgements . 14

8. References 15

Immobilization and Packaging of Recovered Tritium

1. INTRODUCTION

Tritium is a radioactive isotope of hydrogen that decaysto He with a 12.3-year ha l f - l i f e by emitting a low-energy betapart icle (average energy 5.7 keV). Tritium is formed in CANDUreactors primarily by neutron capture by the deuterium atoms ofheavy water. The concentration of t r i t ium as DTO builds upslowly with operating time to an equilibrium value. Thepresence of t r i t ium in the heavy water systems of the reactorsis a source of radiation for the operating personnel. Tominimize this radiation exposure, plans are under way to extractand recover the t r i t ium. Ontario Hydro has committed a t r i t iumextraction system for the Pickering Generating Station [1 ] thatw i l l recover t r i t ium from the eight reactors. A small plant torecover t r i t ium from AECL's research reactors, and todemonstrate l iquid phase catalytic exchange for the t r i t iumtransfer step, has been committed at Chalk River NuclearLaboratories.

2 . OPTIONS FOR PACKAGING RECOVERED TRITIUM

The radiological hazard of t r i t ium in the form of Tg isseveral orders of magnitude smaller than in the water form [2 ,3 ] .For this reason, i t is desirable to keep the t r i t ium in the lesshazardous chemical form for packaging and storage. Storage ofthe Tg as a gas in a steel cylinder is a simple, well-establishedtechnology, and is currently practised in both the U.S. andEurope. The gas is easily recoverable. However, because i t ishydrogen gas, i t is prone to leakage. This is a disadvantagefor long-term storage or disposal, and for this reason i t isdesirable to immobilize the t r i t ium in solid form.

The immobilization of t r i t ium gas can be achieved byreacting i t with a suitable metal to form a solid metal hydride( t r i t i d e ) . With the proper choice of metal, a solid metalt r i t i d e can be formed that t ight ly binds the t r i t ium into astable chemical compound suitable for long-term storage ordisposal, but s t i l l allows t r i t ium to be recovered by heatingthe t r i t i d e . The metal t r i t i de would be placed in a suitablesteel container for storage or disposal.

This paper describes the work that has been done at ChalkRiver Nuclear Laboratories to identify suitable metals fort r i t i d e formation, to determine procedures for preparation ofthe t r i t i des , to evaluate their properties, to design a packagein which to store them and to evaluate various steels forfabrication of the package.

. 2 -

3. IMMOBILIZATION OF TRITIUM AS METAL TRITIDES

Many metals react with hydrogen to form solid hydridesbut only transit ion metals have the required properties for thet r i t ium storage application. The properties of these metalhydrides that make them suitable are very low dissociationpressures at normal temperatures, high capacity for t r i t i um,ease of preparation, and s tab i l i ty in air and water at storagetemperatures. The hydrides of zirconium, titanium, hafnium, andyttr ium [ 4 ] , as well as erbium, have been suggested as usefulfor t r i t ium storage. The dissociation pressure of titanium andzirconium hydrides i s less than lO"1^ pa at 25°C and less than5 kPa at 500°C, but at 1000°C these hydrides are completelydissociated, whereas hydrides of yttr ium and erbium areextremely stable with dissociation pressures less than 100 Paeven at 1000°C. Titanium and zirconium hydrides would besuitable for recoverable storage, whereas the hydrides of erbiumand yttr ium would be more suited for non-recovery of the t r i t ium.

For al l practical purposes there is no t r i t ium partialpressure above these compounds at temperatures expected forstorage, <100°C. This means rupture of the storage containerw i l l not result in t r i t ium release. Another advantage of metalt r i t i des is their large capacity for t r i t i um. The density ofhydrogen in some metal hydrides is similar to or greater thanthat of l iquid hydrogen [ 5 ] .

The recovery of t r i t ium from t r i t i des by heating (450 -600°C for Ti and Zr) is not as convenient as simply opening avalve on a gas cylinder, but i t does provide a simple method forseparating the decay product (^He) from the t r i t i um. Helium-3has a signif icant commercial value.

Metal hydrides are formed by the direct combination ofthe metal and hydrogen

(1)

where M represents the metal and x the appropriate stoichiometryfor the reaction of that metal.

For this reaction to proceed quickly the metal surfacemust be clean and the hydrogen must be pure. The work has beendone with titanium and zirconium in the form of metal sponge,turnings and rod or plate. The metal surface is cleaned bybeing heated in vacuum (vacuum annealing) for a period of time

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to dissolve the surface oxide, then being cooled to the desiredreaction temperature. The hydrogen is purified by either beingpassed through a hjt palladium-silver alloy membrane orabsorption/desorption on a uranium metal bed.

Zirconium and titanium have been hydrided to differenthydrogen-metal ratios under various reaction conditions. Therate of formation of titanium hydride from the titanium sponge,chips and plate is i l lustrated in Figure 1. For each of themetal forms the metal was vacuum-annealed at 1000°C for a periodof one-half to two hours. The choice of 1000°C was arbitrary inthese i n i t i a l experiments. Figure 1A shows the effect of thei n i t i a l reaction temperature on the formation of titaniumhydride from 1-2 g samples of titanium sponge (-4 + 40 mesh).The reaction rate is fast with the reactions complete in lessthan f ive minutes, even with an i n i t i a l reaction temperature aslow as 25°C. The reaction temperatures quoted are i n i t i a l onesbecause the reaction is exothermic and the temperature increasesas the reaction proceeds. The reaction at 600°C is limited to ahydrogen-metal rat io of 0.9 because of the pressure-temperature-composition relationship for the titanium-hydrogen system. Allreactions were done using i n i t i a l hydrogen pressures of ^100 kPa,for two reasons: the f i r s t was that the apparatus was glass, andthe second was that this pressure was adequate to process theexpected quantity of t r i t ium from a recovery plant.

The reaction rate of titanium chips or plate is slowcompared with that of the sponge. At an i n i t i a l reactiontemperature of 25°C the chips did not react, but, on heating,the reaction started at MOCC and proceeded quickly above 130°Cas shown in Figure IB. When a sample was i n i t i a l l y heated to100°C before the hydrogen was admitted, a five-minute inductionperiod was noted before any reaction was observed. A previouslyhydrided sample reacts much faster on the second hydriding dueto the increased surface area resulting from the hydriding-dehydriding procedure. For a fast reaction of titanium chips orturnings an i n i t i a l reaction temperature of ^300°C is requiredfor the f i r s t hydriding. Temperatures of 500-600°C are requiredfor titanium plate or bars. An increase in the i n i t i a l reactiontemperature of the blocks results in shorter induction periodsand a faster i n i t i a l reactiosi, but the higher temperatures l im i tthe reaction to a hydrogen-metal rat io less than 2 because ofthe pressure-temperature-composition relationship for the system.

The rate of the hydride formation reaction at variousreaction temperatures is dependent on the surface area of thesample, as might be expected. Sponge samples have a much highersurface area to volume ratio temperature than bulk samples suchas turnings and bars. The sponge samples react more quickly atlower temperature than the bulk samples. Because of the bulk

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FIGURE 1A: FORMflTiON OF TITflNIUM HYDRIDE FROM TITANIUM SPONGE

-o-

IN IT IAL

0

a

25

200

300

600

REACTION TEMP

°C

°C

°C

°C

F I G U R E I B : F O R M A T I O N O F T I T A N I U M H Y D R I D E F R O M T I T A N I U M C H I P S(VACUUM ANNEALED AT 1000°C)

104° — 130

FIGURE 1C: FORMATION OF TITANIUM HYDRIDE FROM TITANIUM PLATE

VACUUM ANNEALED AT !000cC , 500 - 5 1 5 ° C

- 5 -

form of the turnings and bars, diffusion of the hydrogen intothe metal is believed to be the rate-controlling step [6] in thereaction and hence higher temperatures are required. Thedistance that the hydrogen has to diffuse in the sponge is muchsmaller than that for the bulk samples because of the largerspecific surface area and porous nature of the sponge. Theamount of hydrogen diffusing into a metal cylinder dependsinversely on the square of the distance [7] and hence a morecomplete penetration of hydrogen at a particular time andtemperature ( i . e . , a faster hydriding rate) is noted for spongecompared with that for the bulk samples.

Similar results were observed with various zirconiumsamples as shown in Figure 2.

2.0

1.6

1.2

0.8

0.4

o.o c

FIGURE Z- FORMATION OF ZIRCONIUM

(VACUUM ANNEALED AT ~

0 STr

— T1

-J I-+— Zr SPONGE AT 25*C

HYDRIDES

1000*0

yT ^ RODS <s

1 1 1

PREHYDRIDED ROD324 - 326*C

o TURNINGS300 - 3 1 3*C

S 6 10 - 6 1 5*C

1 1 15 6 7

TIME (minutes!

10 I I 12 25 30

The minimum annealing temperature required for rapidhydriding of titanium sponge at room temperature was determinedto be ~400°C. Annealing at 300°C resulted in a negligiblehydriding rate at 25°C, whereas annealing at temperatures of400-1000°C a l l resulted in fast reactions at 25°C. Thesetemperatures are constant with the 400°-500°C temperature

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required to dissolve the surface oxides into the bulkmetal [8],

Hydriding reactions using deuterium with and withouttrace quantities of tritium showed rates of reaction equal,within experimental scatter, to those observed with hydrogen,implying there is not a large kinetic isotopic effect.

The major difference in the chemistry with tritiumcompared with hydrogen or deuterium is the effect of ^He fromtritium decay. This helium is known to inhibit the hydridingreaction [9]. To simulate this effect, samples of titaniumsponge were hydrided with hydrogen-containing helium, using thestandard hydriding procedure. The results are shown in Figure 3.In the presence of helium there is an initial rapid absorptionof hydrogen followed by a very much slower rate of reaction.With as little as 0.5% He, only half of the hydrogen is reactedquickly while the remainder reacts at a very slow rate. Thiseffect is thought to be due to a blanketing effect of the metalsurface by the helium preventing access to the surface by thehydrogen. To reduce this blanketing effect the procedure andapparatus were modified to allow circulation of the gas over themetal surface. This greatly improved the rate of reaction asshown so that complete reaction of the hydrogen in a mixturecontaining initially 6% He occurred in about 10 minutes.

The possibility of the observed effect being due tooxygen as an impurity in the helium had been suggested [10].The effect of oxygen and helium impurities in the hydrogen wasstudied in both static and dynamic (circulation of the gas overthe metal) experiments. The results are summarized in Figure 4.These results clearly show the reduction in the hydriding rateobserved in static reactions is due to helium and that oxygenconcentrations up to 910 uL/L have little effect.

The hydride property of most interest for tritium storageis stability at expected storage and accident conditions. Thecompounds should be unreactive in air and resistant to leachingof the tritium out of the sample in water.

None of the hydrides prepared are pyrophoric in air atroom temperature. The reactivity of these hydrides at elevatedtemperatures has been investigated qualitatively by heating themon a hot stainless steel plate in air and observing when theystart to spark and/or burn. These observations showed thesamples do not burn in air, even at elevated temperatiires,unless they are finely divided. Of the various zirconiumhydride samples, the lowest ignition temperature noted was 450°Cfor a fine powder of ZrH2« Sponge samples of zirconium metal

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•a

FIGURE 3A: EFFECT OF HELIUM ON FORMATION OF TITANIUM HYDRIDEFROM TITANIUM SPONGE

o. i

0.0

0.7

0.6

0.5

0. 4

0 . 3

0. 2

0. 1

o.o1

t> NO H E L I U M

S T A T I C H e - H 2 M I X T U R E S

I N I T I A L R E A C T I O N T E M P C f l A T U R E 2 5 °

0.5'. He

He

FIGURE 3B: EFFECT OF RECIRCULATION OF GAS

T l T A N I U M S P O N G E , I N I T I A L R E A C T I O N T E M P E R A T U R E 2 5 ° C

W I T H G A S C I R C U L U T I O N

C l P C U L A T I O N ON\S T A T I C G A S

I i I I

1 0 1 2 1 4 1 6

TIME ( m i n )

18 20 22 24 26

HYDROGEN-TITANIUM RATIO

o — _ _ _

m

mTl* 1

-nmoHO

-noXam2>2O

XELI

c

a:o

o2O

m

o

o

o

2

05TJO2CDm

- 9 -

and hydride did not react unti l dropped on a hot surface of560°C; when heated from 25°C to 800°C this material did not burnbut rather showed a gradual colour change as i t oxidized.Samples of titanium hydride prepared from sponge did not burn atany temperature up to 800°C. Slow changes in colour indicated atransformation of the hydride to the various oxides of titanium.

These observations are consistent with those summarizedin the l i terature by Blackledge [11] , which include an ignit iontemperature of 430°C for a finely divided powder of ZrH2suspended in a i r . Our conclusion from these qualitative testsis that metal t r i t ides prepared as described previously fromsponge metals w i l l not burn in air at expected storageconditions.

The leaching of t r i t ium from samples of zirconium andtitanium deuterides containing trace quantities of t r i t ium hasbeen observed in deionized water and various salt solutions forapproximately 600 days. In the leach test procedure, theInternational Atomic Energy Agency standard leach testmethod [12] was followed as closely as possible.

The i n i t i a l incremental leach rate (Rn)» calculated usinggeometric surface area, ranged between 10"° and 10-9 cm/day forthe various zirconium and titanium sponge samples. These rateshave stabilized to 10"° - 10~*0 cm/day over the duration of thetest period. The leach rate (cm/day) for the static testing oftitanium sponge samples is shown in Figure 5. Although thehydrogen-metal ratio varied from 0.5 to 1.9, the leach rates arevery similar. The scatter shown is typical of that observed inal l the data.

Samples of hydrided metal rods (approximately 0.6 cmdiameter) had a leach rate that ranged from 10"10 to 10"11 cm/dayat the end of the test period.

Cumulative fractional releases have also been calculatedfor the various t r i t i a ted samples. The fractional release(total amount of act iv i ty leached/total i n i t i a l amount ofac t iv i ty ) is less than 0.05% over 600 days.

The leach test data obtained from t r i t i a ted zirconium-and titanium-hydride sponge samples indicates that these metalhydrides are stable compounds and suitable for theimmobilization of recovered t r i t i um.

INCREMENTAL LEACH RATE Rn (cm/day)

HHA

NIU

I

COTJO

CDmCO

c;om\Jl

zoRE

ME

z- I

LEA

o

mCO

>

m<CO

m-no70

- ox -

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4. ISOTOPIC ANALYSIS OF HYDROGEN

When packaging t r i t ium i t is necessary to know the amountof t r i t i um put in each container. To do th i s , the quantity ofgas is measured by conventional pressure-voiume-temperaturemeasurements and the gas analysed for the fraction of t r i t i umpresent. Three methods are being considered: gas chromato-graphy, mass spectrometry and ion chambers. Preliminary evalua-t ion of gas chromatography using the method of Genty andSchott [13] has shown this method is feasible and the separationof hydrogen and deuterium isotopes on a 3 m ferr ic hydroxide-treated alumina column at 77 K was achieved. This is shown inFigure 6. However, there has been a problem with s tab i l i t y ofthe column and deterioration of the resolution with time. Asmall quadrupole residual gas analyser has been installed andshown to provide adequate resolution for tip, HD and D2S and onthe basis of work reported in the l i terature [14] is expected tobe adequate for DT and T£. An ion chamber has been bui l t butnot yet evaluated, but similar ones have been used successfullyelsewhere [15] .

5. PACKAGING METAL TRITIDES

A conceptual design of a primary container and a shippingpackage has been made to contain 0.5 MCi (19 PBq) of t r i t ium asthe metal t r i t i d e [16]. The schematic diagrams of the primaryvessel and the transportation package are shown in Figure 7.

The primary vessel is a 6 L stainless steel containerdesigned to contain the helium generated by the complete decayof the t r i t i um. This vessel has been designed to double as thereactor vessel in which the metal t r i t i d e is prepared. For thisreason i t is equipped with two valves to permit circulation ofthe gas during the hydriding procedure. The inlet end exit ofthe vessel are protected by sintered steel f i l t e rs to preventloss of any metal t r i t i d e particles that may be present. Testswith a prototype primary vessel of this design have shown thehydriding reaction can conveniently be carried out in thisvessel.

For transportation i t is expected the primary containerw i l l be placed in a second stainless steel container with aflange closure and this two-container assembly wi l l be placed ina suitable-sized drum packed with insulation to provideprotection from heat in the event of a f i re [16]. A prototypetransportation package has been fabricated but not yet tested.

An extensive evaluation of applicabil i ty of austeniticstainless steel for the containment of t r i t ium has been carried

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H2

ft

10 12 14

TIMf (min)

FIGURE 6: SEPARATION OF H2, HD, D? ON AN ALUMINA COLUMN COATED WITH FERRIC HYDROXIDE

(80 -100 MESH, 3m x 1mm); 77 K; HELIUM FLOW, 98 mL/min

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CONCEPTUAL DESIGN FOR METAL TRITIQE CONTAINER

VALVE

SINTERED STAINLESS STEEL FILTER

STAINLESS STEEL PIPE

STAINLESS STEEL PIPE CAP

METAL TRITIDE PENCILS

CONCEPTUAL DESIGN OF A TRITIDE TRANSPORTATION PACKAGE

CARBON STEF.L DRUM

PACKING

VALVE PROTECTOR

INSULATION

SECONDARY CONTAINER

PRIMARY CONTAINER

METAL TRITIDE

Figure 7

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out by Ells [17,18,19]. He has shown for type 316L stainlesssteel at ambient storage conditions that the permeation oft r i t ium into the vessel wall and subsequent decay of the heliumwi l l not jeopardize the integrity of the vessel. I t wasconcluded there would be negligible permeation of t r i t ium(whether stored as a gas or a metal t r i t i de ) through the wallsof a 6 mm, 316L stainless steel wall at <348 Y.. Even in thecase of t r i t ium gas at 1 MPa and 573 K for 12 h, the release of<10"12 Ci (0.4 Bq) was predicted.

6. TRITIUM LABORATORY

The work described here, with the exception of the leachtests, has been done with hydrogen and deuterium. To do thesame work with high specific act iv i ty t r i t ium as T2 requiresspecial f ac i l i t i es for handling the radioactive materials. AtCRNL a t r i t ium laboratory has been bui l t to package highspecific act iv i ty metal t r i t i des . The main components of thelaboratory are a high integrity inert atmosphere glove boxcontaining a hydriding apparatus and associated analyticalequipment to accurately measure the quantity of t r i t ium in eachpackage, a t r i t ium monitoring system, and a special glove boxfor maintenance of tritium-contaminated equipment.

7. ACKNOWLEDGEMENTS

The contributions of R.E. Johnson, S.R. Bokwa,C.T. Grahl, F.B. Gravelle, and H.M. Philippi of CRNL andstudents J.M. Berlie, M.D. Small, K.I. Skorey, K.M. Kimberley,C.L. Cantlon, E.H. Bromley, and T.S. Lauder to various aspectsof this work are gratefully acknowledged.

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8. REFERENCES

[1 ] Si lver, R., "Ontario Hydro's Pickering Station to GetTritium Extraction System", Nucleonics Week, 21 36 (1980)12. ~

[ 2 ] "International Commission on Radiological Protection.Limits for Intake of Radionuclides by Workers (Adopted1978 July)" , ICRP Publication 30, Supplement to Part 1 ,Pergamon Press, New York (1978).

[ 3 ] Evans, E.A., "Trit ium and I ts Compounds", John Wiley andSons, Inc., New York (1974).

[ 4 ] Burger, L.L., Trevorrow, L.E., "Release of Tritium fromFuel and Collection for Storage", Controlling Air-BorneEffluents from Fuel Cycle Plants (ANS-AIChE Meeting, 1976).

[5 ] Cox, K.E., Williamson, K.D., "Hydrogen and I ts Technology,Volume I I " , CRC Press, Cleveland (1977).

[6 ] Libowitz, G.C., "Solid State Chemistry of Binary MetalHydrides", W.A. Benjamin, Inc., New York (1965).

[7 ] Crank, J . , "The Mathematics of Dif fusion", Clarendon Press,Oxford (1956).

[8 ] Dushman, S., "Vacuum Technique", John Wiley and Sons,Inc. , New York (1949).

[ 9 ] Carlson, R.S., "The Uranium-Tritium System - The Storageof Tr i t ium". Proc. In t . Conf. on Radiation Effects andTritium Technology for Fusion Reactors, Gatlinburg,Tennessee, 1976.

[10] Cox, B., Ling, V.C., in "Chemistry and Materials DivisionProgress Report PR-CMa-55, 1980 October - December",Atomic Energy of Canada Limited, Report AECL-7242 (1981).

[11] Blackledge, J.P. , "Chemistry of Metal Hydrides as Relatedto their Application in Nuclear Technology", MetalHydrides (Mueller, W.M., Blackledge, J.P., Libowitz, G.G.,Eds.) Academic Press, New York (1968) 119-135.

[12] Hespe, E.D., "Leach Testing of Immobilized RadioactiveWaste Solids", Atomic Energy Review (Hespe, E.D., Ed.) £(1971) 195.

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[13] Genty, C , Schott, R., "Quantitative Analysis for theIsotopes of Hydrogen - H2, HD, HT, Dj, DT, and T2 byChromatography", Anal. Chem. 42 (1970) 7.

[14] Eliefson, R.E., Meddeman, W.E., Dylla, H.F., "HydrogenIsotope Analysis by Quadrupole Mass Spectrometry", J . Vac.Sci. Techno!. JL8 (1981) 1062.

[15] Carstens, D.H.W., David, W.R., "An Ionization Chamber forMeasurements of High-Level Tritium Gas". Proc. TritiumTechnol. in Fission, Fusion and Isotopic Applications,Dayton, Ohio, 1980, CONF. 800427.

[16] Taylor, W.R., Atomic Energy of Canada Limited, privatecommunication.

[17] E l ls , C.E., Kushneriuk, S.A., "Helium in the AusteniticStainless Steel of Tritium-Handling Fac i l i t ies" , AtomicEnergy of Canada Limited, Report AECL-6844 (1980).

[18] E l ls , C.E., "Tritium in Austenitic Stain*ass Steel Vessels:The Integri ty of the Vessel", Atomic Energy of CanadaLimited, Report AECL-6972 (1980).

[19] El ls , C.E., Kushneriuk, S.A., Van der Kuur, J.H., "TheContainment of Tritium in Austenitic Stainless SteelVessels", Atomic Energy of Canada Limited, ReportAECL-7159 (1981).