Journal of Nuclear Materials 191-194 (1992) 23-29North-Holland

journal ofnuclear

materials

BEATRIX-II: A multinational solid breeder materials experiment

G.W. HollenbergPacific Northwest LaboratOlY, Richland, WA, U.sA

H. WatanabeJapan Atomic Energy Research Institute, Tokai-mura, Ibaraki-ken, Japan

1.1. HastingsAtomic Energy of Canada, Ltd., Ottawa, Ontario, Canada

S.E. BerkU.S. Department of Energy, Washington, D.C., USA

BEATRIX-II is an in situ tritium recovery experiment in the fast flux test facility (FFTF) reactor designed to characterizethe feasibility of utilizing solid breeder materials at extended burnups in a fast neutron flux. Although not yet complete, theBEATRIX-II experiments have already substantiated that the solid breeder selected for ITER, LizO, has good irradiationstability and tritium recovery. Temperature stability, lithium transport, dimensional stability and tritium recovery issues ofLi 20 up to 5% Li burn up were addressed in this experiment. Temperature gradients far more severe than in the ITERdesign, 400 to lOOODC, were found to be essentially unchanged by burnup and produced no observable instability, either fromswelling or lithium vapor transport. Temperature change experiments illustrated that lithium inventories do not appear toincrease as a result of irradiation to burnups of 5%.

1. Introduction

BEATRIX-ll is an International Energy Agency(lEA) program focused on tritium recovery experi­ments on lithium ceramic materials in a fast neutronreactor (FFTF) which simulates the environment of afusion blanket. In addition to providing data on theperformance of LizO and LizZrO" the BEATRIX-IIprogram also provides information on innovative tech­nologies associated with tritium recovery. The success­ful execution of the BEATRIX-II program also offersa model for the organization and interfaces that otherinternational programs should consider. Japan, Canada,and the USA are participants in the BEATRIX-IIprogram with primary responsibilities being assigned toJapan Atomic Research Institute, Atomic Energy ofCanada Ltd., Battelle Pacific Northwest Laboratory,and Westinghouse Hanford Company.

The objective of the BEATRIX-II experiment is tostudy in situ tritium recovery from ceramic solid breedermaterials under irradiation conditions which span theburnup, irradiation damage, tritium production, andtemperature regimes previously investigated. A liquidmetal, fast neutron reactor was selected because spa-

tial vanatlOns in tritium and heat production (i.c.,self-shielding and flux depression) are minimized andtemporal variations in the lithium burnup at heat gcn­eration rates (i.e., burnout) are also minimal. Thesestable homogeneous conditions provide the best condi­tions for high burnup irradiation of solid breeder mate­rials to permit simplest data interpretation. The FFTFwas selected because it possessed a high level of fastneutron flux, excellent control and monitoring capabili­ties and ready access for a tritium recovery experiment[1-31. The BEATRIX-II program is comprised of twoseparate irradiations: Phase I in Cycle 11 of FFTF wasstarted in January 1990 and Phase II started in May1991.

The BEATRIX-II program evolved through severalstages over a long period of time, even though itpossesses a relatively straightforward objective. Initialconcept definition started in 1983 with an internationalworkshop in Albuquerque, NM, USA to discuss theconcept of international collaboration in the solidbreeder materials area. The BEATRIX-I program un­der the lEA conducted a very successful set of world­wide collaborative irradiations that consisted of a ma­trix of fabrication of lithium ceramics at numerous sites

0022-3115/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved

24 G. W Hollenberg et al. / A solid breeder materials experiment

and irradiations in a variety of reactors. With thesuccess of the BEATRIX-I program, the BEATRIX-IIconccpt continued to mature with workshops in Tokyo(1984), Ispra (1985), and Hanford (1986) further refin­ing the definition of scope, funding, and organizationalresponsibilities. The formal agreement for BEATRIX­II was executed by the signing of Annex-III of thc IEAimplementing agreement of a Programme of Researchand Development of Radiation Damage in Fusion Ma­terials in January 1988. Concurrently, informal designactivities between the participants proceeded in orderto establish the technical requirements for the experi­ment and establish design options to address feasibilityissues. By March 1988, a design analysis was completedand a formal design review by the participants estab­lished acceptance of the design prepared by Westing­house Hanford Company in coordination with otherparticipants. Fabrication activities were subsequentlyinitiated in the participant organizations. Scrupulousattention to detail is necessary when diverse organiza­tions cooperate in the construction of such a complexexperiment. For example, thermocouple wire charac­teristics were found to be inverse in Japan and the USand this led to confusion during assembly. Componentswere received from a variety of sources and integratedinto a functioning instrumentation and control system(I & C), a tritium handling system (THS), and the actualin-reactor hardware within the materials open testassembly (MOTA). But even after installation at thereactor site, an entire year of component and systemacceptance testing was necessary before operation wasachieved in January 1990. Irradiation operations anddata collection continue in a very satisfactory mannerup to the present time (November 1991). Postirradia­tion examination and data dissemination and analysiswill continue into 1993.

In reviewing the activities for BEATRIX-II, severalimportant aspects should be highlighted:

(1) An international cooperative experiment withthe complexity of BEATRIX-II required almost adecade from conceptualization to completion. Only byincluding many parallel activities and maintaining ahigh level of motivation among the individuals involvedat all levels could this schedule be maintained. It wasrecognized that changes in scope had to be minimizedafter the concept of the test became formalized inorder to maintain the schedule.

(2) The establishment of working relationships dur­ing the previous and far simpler BEATRIX-I programprovided researchers with interfaces and insights thatpermitted BEATRIX-II to operate more effectively.

(3) The execution of informal activities with allparticipants prior to formal documentation and or ap­proval by specified individuals was an efficient methodof expediting progress.

Collaborative research programs can be establishedwith or without the following characteristics: joint

funding, task sharing, facility sharing, equipment shar­ing, technology sharing, and duplication of tasks. ForBEATRIX-II, the program consisted of substantialjoint funding, in addition to task sharing, equipmentcontributions, and tcchnology contributions by all ofthe participants during the fabrication phase. Duplica­tion of tasks occurred only in the data analysis part ofthe program.

The lEA executive committee has continued toprovide the leadership that set the pace for the entireactivity. The BEATRIX-II Working Group, made upof a representative from each participating country,has monitored the technical progress, scope and bud­get of the program. Programs of this nature requirethat compromises and decisions be constantly made onthe basis of scope, schedule, and budget. For BEA­TRIX-II, budget dominated these decisions becausethe original budget, established in 1987, was main­tained throughout. A clear understanding of this at alllevels of the program provided for less confusion dur­ing critical decisions. Other programs may, by neces­sity, choose schedule or scope to be dominant in deci­sions. To say that all three are equal would have madedecision-making far more difficult.

It is important that a local entity, in this case thetask manager/ experimentcr, provide a continuingpresence as an advocate of the collaboration's require­ments and policies to assure timely guidance. Selecteddata are then forwarded to the modelers and codedevelopers group which can transform the data intopredictions and extrapolations for fusion blanket de­signs.

In essence BEATRIX-II has functioned by a paral­lel structure. On one side are a set of lEA committeeswhich periodically review, reassess, redirect, and, fi­nally, utilizc the data of BEATRIX-II. On the otherside, individuals were givcn specific responsibilities inorder to assure the execution of the directed tasks. Thetask manager was separately funded specifically toassure autonomy.

2. Experimental description / operation

The BEATRIX-II, Phase I irradiation has beencompleted and postirradiation examination is inprogress. Detailed description of the design and con­struction parameters of BEATR1X-1I irradiation vehi­de-has been previously described, and is summarizedin table 1 [1-3]. Tritium releascd from the LizO in theFFTF core (300 MW) is measured by using purge gaslines connected to handling systems. Tritium generatedby neutron reactions with the lithium atoms is releasedto the purge gas which then carries the tritium to theexternal tritium handling system. Til the tritium han­dling system, the tritium in the purge gas is chemicallyreduced, measured and trapped in a specially designed

G. W Hollenberg et al. I A solid breeder materials experiment 25

Table 1Comparison of BEATRIX-ll operating conditions to ITERtesting needs

Parameters Phase I BEATRIX-JI

ITER Ring Solid

Material LizO LizO LizOGrain size 20 5.5 46Porosity 20% 20% 7-15%Surface Area

[cmZlgm] 500 600Enrichment 95% 6Li 61% 6Li 61% 6LiConfiguration 1 cm 1.5 mm 1.7cm

layered thick ring dia. pelletplates

Temperature rOC] pulsed adjustable constantMin. temp. 442 500 450Max. temp. 609 640 1000Peak temp.

difference 101 40 550Tritium generation

rate [mCijgm-day]average 85.5 420 360

Lithium burnup [at%]Average 5.2 6.2 5.4Exposure (EFPD) 1100 300 300

Purge chemistryHz Pressure [Pal 200 150 150

« 1-150) «1-150)HIT (reference) 30 75 30

that of the ITER design but the ultimate bumup isconsistent with the ITER design because of the shorterexposure time. The purge gas chemistry of BEATRIX­II under reference conditions is very similar to thcITER design. The agreement betwecn the ITER de­sign and BEATRIX-II experimental parameters shouldbe considered fortuitous since the BEATRIX-II designwas originated long before the ITER design was com­pleted.

Smith [5] has identified the current issues for theseleetion and adoption of LizO as the solid breedermaterial for ITER:(l) LizO compatibility with beryllium metal.(2) Lithium mass transport for LizO under prototypi­

cal temperature gradients.(3) Irradiation performance for lithium bumups up to

5 at%. Jrradiation performance is manifested inparameters such as: (a) low tritium inventory, (b)dimensional stability, and (e) temperature stability.

Although PIE of BEATRIX-II is not yet completed,operational data have been obtained that support theacceptable performance of Li zO with respect to thelast two issues.

In fig. 1, the centerline temperature history duringPhase I irradiation of the solid LizO pellet is pre­sented. The irradiation was divided into three cycles,1l-B.1, ll-B.2 and 11-C each of approximately 100

Phase 1

_UppetTC

·OW", '~"" \ A' 4 Jan 90Cyclel1B1 yr 10 Jan 90

jj "'. '12 feb 90

7 Mar 90~...'"23 Mar 908 Apr 90

Cycle 11B2,.-~Startup 29 May 90~"-.- .. Reactor F'eedback

1" Test 5 Jun 90, '''Scram 12 Jun 9(1

"- \power Shift 28 Jun 90"".~~ Power ShUt 31 Jut 90~'Scram 7 Sap 90

~. _~Scram 14 Sep 90

V/£hd.ot~CYCle 28 Oct 90

-

Cycle ,ie ~::::St.rtup 20 Dec 901 """,-Power Coof. Test 29 Dec 90

1"'''-. Power Test 4 Jan 91~ 'Power Sl1ift 22 Jan 91

""--Seram 11 Feb 91.1-------power Shift 5 Mar 91

, '-'~End--of~Cycle 19 Mar 91299.7 EFPD

I

360

180

540~ q ~ Q 1~ 1~ 1~ 1b

Temperature ("C)

Fig. 1. The centerline temperature of the solid Li zO specimenduring the BEATRIX-JI (Phase 1) experiment demonstratedthe temperature stability to be expected in LizO fusion blan-

kets.

getter bed prior to exhausting the purge gas. A com­puterized control system monitors many of the experi­mental parameters and provides for data acquisitionevery 10 seconds or when the parameters change forthe entire 300 days of irradiation.

The operating and specimen conditions for BEAT­RIX-II canisters for Phase I are compared to an inter­national thermonuclear experimental reactor (ITER)blanket design concept [4]. The LizO ring specimenoperated near the temperature range of the pulsedITER blanket but its temperature was changed period­ically to evaluate tritium inventory changes. Tritiumrecovery experiments commonly presume that when anincrease in temperature occurs the change in tritiuminventory is dominated by a classical activation processwhich predicts that further heating would result in asmaller reduction in the tritium inventory. In contrastto the ring specimen, the temperature of solid LizOspecimen ranged from Icss than 450°C on the surfaceto 1000°C at the center but was not changed by exter­nal controls. This temperature profile was essentiallyconstant throughout the life of the experiment. Thedimensions of the cylindrical pellet in the solid BEA­TRIX-II canister (1.7 em) are approximately the sameas the ITER plate (l em).

BEATRIX-II could be considered an acceleratedtest, because tritium production rates are higher than

26 G. W Hollenberg et al. / A solid breeder materials experiment

Bottom

fPurgeGasFlow

Fig. 2. A neutron radiograph of the solid LizO specimen afterirradiation indicated that lithium transport and dimensional

stability should be expected from LizO fusion blankets.

No ObservableDownstreamTransport ot lithIum(Specimen Tempel1llure450 to 1000 ·C)

No Closure otPorous NickelFlow Path

Top

swelling of LizO. The porous, pure nickel that sur­rounds the solid pellet is very malleable and it was amajor experimental design consideration. The fact thatthere was no increase in the purge gas pressure re­quired to maintain purge gas flow during the irradia­tion is further evidence that the porous nickel flowpath was not disturbed by swelling. Hence, Issue 3b didnot appear to be significant for the BEATRIX-II irra­diation condition.

In fig. 3, tritium recovery data from the ring speci­men during temperature changes between 650°C and550°C are presented. These data are qualitatively inagreement with previous thermal reactor tritium recov­ery experiments (i.e., YOM, CRITIC, ... ) [I 0, 11] wheretemperature changes in this temperature range resultin transients with small peak heights which may beassociated with the minimum temperature in the speci­men being greater than 500°e. In fig. 4, the effect ofexposures between 80 and 290 effective full power days(EFPD) on the transient tritium recovery response isshown for temperature changes between 550°C and650°C. It does not appear that irradiation produces asignificant effect on the tritium inventory (1) changebetween these two temperatures. Note that the shapeof the peaks changes as the exposure increases, with a

No ObservableDeformation ofStructuralMaterial ___

effective full power days. Even though FFTF operatedat relatively constant power, the reactor scrammed fora variety of operational and regulatOlY situations. Notethat the temperature at the centerline of the LizOpellet, as measured by two thermocouples, remainedrelatively constant at approximately 1000°C when thereactor was at 300 MW. The slow decrease in thetemperature is attributed to the withdrawal of controlrods from the reactor which caused flux tilting withinthe core. Self-powered neutron detectors next to thesolid pellet canister also indicated flux changes whichmatch most of the temperature changes. Only duringthe initial startup and after the September 14 scramdid there appear to be temperature changes that couldnot be attributed to flux changes. In these periods theaccentuated temperature decline may be attributed torestructuring of the LizO.

Instability of temperatures has been a design issuewith LizO because of the uncertainty associated withthe effect of irradiation on the thermal conductivity.Thermal diffusivity data on irradiated LizO [6] taken attemperatures above the irradiation temperature indi­cate very little change (or possibly even an increase) inconductivity of LizO at comparable fluences. Graingrowth was thought to be the mechanism for increasedconductivity which would explain thc two periods ofaccentuated temperature decline. Hence issue (3c)temperature stability, above does not appear to besignificant under the BEATRIX-II conditions.

Postirradiation examination has not been completedas of this writing. However, the postirradiation neutronradiograph of the solid specimen canister in fig. 2 isvery revealing. No observable downstream transport oflithium can be observed in this neutron radiograph.Since the neutron cross section for 6Li is very high,neutron radiography is a very sensitive means of de­tecting its location. There do not appear to be any 6Lideposits in the top, i.e., downstream, of the BEAT­RIX-II solid pellet canister even though the LizOoperated at temperatures between 450 and 1000°C. Itshould be noted however that the primary gas flowpath was not through the lOOO°C pellet center, butrather it was channel led along the lower-temperaturecircumference of the pellet. This flow configuration isconsistent with that of the ITER design [4]. If, how­ever, an open pebble bed design is adopted where theLizO and gas flow are present at lOOO°C, then lithiumtransport could become important. Hence, lithium masstransport above does not appear to be significant if aBEATRIX-II-type configuration is adopted.

Also from fig. 2, no deformation of either the outerstainless steel canister or the nickel flow path of thesolid specimen was observed. Previous indications ofsignificant LizO swelling [7] were observed in irradia­tions where no restraint was present. Because of thehigh creep rate of LizO [8,9], it has long been antici­pated that very little constraint is required to limit the

G. W Hollenberg et al. / A solid breeder materials experiment 27

4020 30Relative TIme (h)

10

34 r-------------R.mg SpecimenTemperaWre Change (550·650 "C)

c.Q

!!1i 30g"~:§I- 28

Fig. 4. Tritium recovery from the LizO ring specimen duringthermal transients between 550 to 650°C at 80 to 290 EFPDindicates no significant effect of burn up to 5% lithium on this

inventory change.

2010

_.-;;;;::--------------..,70013"'­I!!~

-' 600 1i

l. 500 I-

t 20 --

~ 0

Fig. 3. Tritium recovery from the LizO ring specimen duringthermal transients between 550°C and 650°C (peak tempera­ture) provided very small changes in tritium concentration in

the purge gas.

pronounced double peak at low exposure transitioningto a single peak at high exposure. The second peakobserved at low exposures, has been associated withthe moisture content in the purge gas. It is conjecturedthat oxidized tritium (HTO) in the second peak iseither desorbed slower from the specimen or is sloweddown by adsorption/ desorption along the surface ofthe tubing that connects the capsule to the ion cham­ber: much like open tube gas chromatography. If thelatter is the case, then the observed changes in tran­sient tritium recovery kinetics (not inventOlY) may beassociated with changes in the surface of the tubing,etc., rather that irradiation damage in the specimen.Hence, there docs not appear to be a significant in­crease in tritium inventory in LizO at burnups andtemperatures near those of ITER.

During the BEATRIX-II experiment, the composi­tion of the purge gas was selectively changed from thereference condition of helium with 0.1% Hz to purehelium, helium with 0.01% Hz and 1% Hz. As inprevious in situ tritium recovery experiments, the pres­ence of 0.1 % H 2 enhanced the release of tritium from

Li 20; however, detailed evaluation of ion chambercalibration response indicates decalibration with theintroduction of Hz into pure helium, i.e., the Jessieeffect. This complicates the analysis of data from onegas to another. In the casc of shutdowns from irradia­tion, however, the difference between 0.1% H 2 and"pure" helium is clear (see fig. 5) for the solid speci­men. In 0.1% H 2 , during a scram the reduction intritium concentration in the purge gas is rapid, like thereduction in tritium production in the specimen that isproportional to the relative neutron flux. However,when a controlled shutdown is conducted in "pure"helium, the tritium concentration in the purge gasincreases even though the tritium production is beingreduced. It should be noted that the radial tempera­ture distribution is approximately 450°C to lODDoC cen­terline but is reduced to 450°C to 450°C at zero power.Clearly, the response to temperature cycling will be fardifferent when LizO is in a helium atmosphere ratherthan a D.l % Hz purge gas.

Table 2Innovative technologies in BEATRIX-II

Purpose Description

Canada1. Getter bed2. Ion chambers3. Li zZr03 spheres

Japan4. Ceramic electrolysis cell5. Thin-walled LizO

USA6. Tritium barrier7. Channeled nickel liner8. Nb/Zr termocouple

Detritiation of purge gasTritium measurement with low backgroundTest specimen

Reduction of tritium to HT or TzReduction of temperature gradients

Reduction of tritium losses inreactorControlJed gas flow with high heat transferHigh temperature/irradiation resistant TC

Based upon SAES 707 getterLow volume IC with mesh electrodes1.0 mm diameter spheres

Oxygen ion conductor under reverse polarity1 nUll wall ceramic

Aluminized stainless steelSintered porous nickelRefractory metal thermocouple

G. W Hollenberg et al. / A solid breeder materials experiment

,..---,----,----,..------,10O.1%H,I!

!:u::L-__L-.-J.._l-.__l-._--' 0 "

10 15 20 E'5

HE 10 ~

S ~Gi0:

10 15

TUn. (h)

Fig. 5. Tritium concentration in the purge gas of the solidspecimen during reactor shutdowns in helium with 0.1 % Hzand "pure" helium demonstrate the significant difference inbehavior between the two environments during power pulsing.

3. Technological innovations

As summarized in table 2 several technological in­novations are listed which were successfully incorpo­rated into the BEATRIX-Il program. In fig. 6, a plotof the moisture in the sweep gas entering and exitingthe ceramic electrolysis cell (CEC) is presented for aseries of temperature transients on the ring specimen.

Moisture (HTO) is the thermodynamically predictedrelease specie from Li 20 if stoichiometry is to bemaintained. Moisture in the purge gas is a problem forthe tritium handling systcm in that it causes rapidbackground buildup in ion chambers and can reducethe efficiency of the downstream getter beds. Althoughit is possible to use oxygen getters to remove theoxygen, the BEATRIX-II experiment employed a solidceramic electrolyte to remove oxygen. The electrolyteis an ionic conductor of oxygen and when a voltage isapplied through the wall of the electrolyte, oxygen istransferred from the purge gas into an outer chamber.In fig. 6, it should be noted that the CEC cell wasapproximately 99% efficient in reducing the moisturelevel in the sweep gas. Although there is room forimprovement in efficiency, the relatively stable andtrouble-free operation of this unit for more than 300EFPD makes it worth considering for future tritiumsystems like ITER.

In fig. 7 the tritium concentration of the sweep gasbefore entering the tritium removal system is com­pared with that at the outlet of the tritium removalsystem. Because FFTF is not designed to dischargeradioactive gases, stringent controls were placed on thegas exiting the BEATRIX-II tritium handling system.It was necessary at times to achieve tritium reductionfactors over 25000 in the tritium removal system. ASAES 707 getter was selected and used to fabricategetter beds that were heated to a temperature of 375°Cfor optimum tritium rcmoval. Notc in fig. 7, that al­though a sizeable tritium recovery transient occurred,essentially all of the tritium was recovered by thegetter, The outlet tritium concentration is so low that

20 -'-r

15,.....,ECl.. 10Cl..

"-/ Before CEeQ)

5...:J(/)

0~

(/)

0 0.10C-'Cl..Q)Q)

~ 0.05(f)

0.000 20 40 60 80 100

Time (h)

Fig. 6. Moisture concentration in the purge gas before and after the ceramic electrolysis cell during transients demonstrates theefficiency of the CEC cell in reducing HTO to HT.

G. W. Hollenberg el al. / A solid breeder malcrials experiment 29

Outlet

organization, and methods employed in this interna­tional collaboration may be useful to those pursuingother col1aborations. The data already obtained fromBEATRIX-II support the viability of solid breederblankets. Major issues for Li 20 blankets, such aslithium transport, swel1ing, tritium release at high bur­nups, and temperature stability no longer appearthreatening, even before the availability of detailedPIE results. Finally, the successful BEATRIX-II pro­vided an operational test bed for demonstrating severaltechnical innovations that could be used on fusionblanket systems.

Inlet to TrllJumRemoval System

500 r--------------------,

0.010 ~----___;==::::;-;:=:::::_;==:_==~_4Background Reading Previous Shutdown

0.005 Ll..LJL.U.l..LJ.J..LLl.LLLLl..LJLLl..l..LJ.J..ll.LllLLLl..lLLl..l..LJ.J..ll.LLUJo 12 24

TlmO(h)

Fig. 7. Tritium concentration in exiting purge gas before andafter the getter beds indicate tritium reduction factors ofgreater than 25000 during a transient, indicating the effective-

ness of the system for tritium removal.

the deviation from background, may not be resolvable.It was necessary to change out the getter beds six

times during Phase I of BEATRIX-II, primarily toremain below normal shipping limits (1000 cn. Thegetter beds are being transferred to the TSTA (tritiumsystem test assembly) at Los Alamos National Labora­tory, USA, where the tritium in the getters can beextracted and converted to a DT fuel. The successfuloperation of these getters offers some verification of aviable fuel cycle for solid breeder blankets.

Measurement of in situ tritium recovery from solidbreeder materials is useful in establishing kinetics,especially for conditions in which significant inventorychanges are encountered. In addition, ion chamberstability, especially during purge gas compositionalchanges, does not permit resolution of small changes ininventory. It should be realized that tritium inventorywithin the solid breeder is the fundamental safetycriterion for acceptance of a solid breeder and thattritium release rates (> 95%) for Li 20 are obviouslyadequate for economic purposes. Hence, future testingis proposed for multiple capsules much like the solidpellet in this paper under stable conditions in whichthe emphasis is on PIE inventory measurements ratherthan the in situ data.

4. Conclusions

This paper provides an overview of the extensivedata produced during the BEATRIX-I1 experiment.Three main areas have been addressed. The structure.,

Acknowledgements

The continued support of DOE and the lEA Execu­tive Committee, cspecial1y Drs. T.C. Reuther, R.E.Price, T. Kondo, and G. Phillips, has made this collab­oration possible. The list of individual contributorswho made BEATRIX-II a success is large, but theobvious work of O.D. Slagle, D.E. Baker, R.J. Puigh,R.A. Verrall, J.M. Miller and T. Kurasawa deservesspecial recognition.

References

[1] U.W. Hollenberg, T. Kondo, H. Watanahe, T. Kurasawa,RJ. Puigh and T.e. Reuther, J. Nuel. Mater. 155-157(1988) 202.

[2J G.W. Hollenberg, T. Kurasawa, S.E. Berk, 1.1. Hastingset aI., Fusion Tech. 15 (1989) 1349.

[3] R.J. Puigh, G.W. Hollenberg, T. Kurasawa, H. Watanabeet aI., Proc. 15th Symp. on Fusion Technology (Elsevier,Amsterdam, 1989) p. 1282.

[4] Y. Gohar, H. Attaya, M. Billone et aI., Fusion Tech. 19(1991) 1538.

[5] D.L. Smith et aI., ITER blanket, shield and materialsdata base, ITER Documentation Series no. 29 (Vienna,1991).

[6] J.L. Ethridge, D.E. Baker and A.D. Miller, in: Advancesin Ceramics 25, eds. 1.1. Hastings and G.W. Hollenberg(American Ceramic Society, 1989) p. 165.

[7) G.W. Hollenberg and D.L. Baldwin, J. Nucl. Mater.133&134 (1985) 242.

[8] G.W. Hollenberg, Y.Y. Lui and B. Arthur, J. Nucl.Mater. 133&134 (1985) 216.

[9] Ke. Goretta, D.S. Applegate, R.B. Poeppel, M.e. Bil­lone and J.L. Routbort, J. Nucl. Mater. 148 (1987) 166.

[10] R.A. Verrall, J.M. Miller, I.J. Hastings et aI., in: Ad­vances in Ceramics 27, eds. G.W. Hollenberg and I.J.Hastings (American Ceramic Society, 1990) p. 299.

[11] T. Kurasawa, H. Watanabe, G.W. Hollenberg et al., J.Nuel. Mater. 141-143 (1986) 265.