Karsten, G.

Muehling, G.

Plitz, H.

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Oktober 1974Projekt Schneller BrüterKFK 2111Motivations and Performances of Carbide Fuel DevelopmentG. Karsten, G. Mühling, H. PlitzAls Manuskript vervielfältigtFür diesen Bericht behalten wir uns alle Rechte vorGESELLSCHAFT FüR KERNFORSCHUNG M. B. H.KARLSRUHEKERNFO~SCRUNGSZENTRUM KARLSRUHEKFK2111Projekt Schneller BrüterMotivations and Performances of Carbide Fuel Developmentvon• • +)G.Karsten, G.Mühl1ng, R.Pl1tzGesellschaft für Kernforschung mbR, Karlsruhe+) KWU ErlangenABSTRACTDifferent strategies have been elaborated for the future development of nuclearenergy. One of them has been described in the UNIPEDE study, which was edited bythe European Community in March 1974. This study underlines the necessity of breederreactors under the aspect of saving uranium resources. Especially the carbide reactorwill be very effective by its small Plutonium inventory and high breeding gain. There-fore a research and development program, performed by GfK, CEN, RCN, TUI, EIR, Alkemand Nukem within the Coordinated Carbide Program, will develop a fuel element for acarbide fuelled power reactor until 1985. The fuel element concept foresees a linearrating of 800 W/cm, a pin diameter of approximately 8rom with helium bonded pins. Be-cause of restrictions by clad material swelling the maximum neutron dose of about1.5xI023n/cm2 > 0,1 MeV will limit the maximum nominal target burnup in the range of60-90.000 MWd/tm. Up to now these burnups have been reached within this program withoutindication of principal difficulties, even under conditions of higher fuel swellingand mechanical interactions with the cladding. Therefore the present design seems tobe capable to meet the target conditions.KURZFASSUNGBegründung und Durchführung der Entwicklung eines karbidischen BrennelementesFür die zukünftige Einführung nuklearer Energieerzeugung sind verschiedene Strategienentwickelt worden. Eine davon wird durch die Unipedestudie beschrieben, welche vonder Europäischen Gemeinschaft im März 1974 veröffentlicht wurde. Diese Studie unter-streicht die Notwendigkeit von Brutreaktoren unter dem Aspekt der Schonung der Uran-reserven. Der Karbidreaktor mit seinem kkmen Plutoniuminventar und hohemBrutgewinn wird in dieser Hinsicht besonders wirksam sein. Daher wird durch ein koor-diniertes Karbidprogramm die Forschungs- und Entwicklungsarbeit bis 1985 durchgeführt.Die Partner, welche das karbidische Brennelement entwickeln werden, sind GfK, CEN,RCN, TUI, EIR, Alkem und Nukem.Das Brennelementkonzept sieht eine lineare Stableistung von 800 W/cm, einen Stabdurch-messer von annähernd 8mm und Heliumbindung vor. Wegen der Beschränkung durch das Hüll-materialschwellen wird die maximale Neutronendosis von 1,5xI023n/cm2 > 0,1 MeV denmaximalen nominellen Abbrand im Bereich zwischen 60 und 90.000 MWd/t fixieren. Bishermsind solche Abbrände in diesem Programm ohne Hinweis auf grundsätZliche Schwierigkei-ten erreicht worden. Dabei sind auch aus den Bedingungen des höheren Brennstoff-schwellens und mechanische Wechselwirkung mit der Hülle keine neuen Probleme entstan-den. Daher scheint das gegenwärtige Konzept geeignet zu sein, die gestellten Anfor-derungen zu erfüllen.Motivations and Performances of Carbide Fuel Development +)(G.Karsten, G.Mühling, H.Plitz)A. IntroductionDifferent strategies have been elaborated for the future development of nuclearenergy. One of these many examples can be given by fig I, taken from the UNIPEDEstudy of the European Community. It can be seen that oxide breeder reactors reducethe consumption of U308 remarkably, even more effectively, if they are combinedwith HTGR's or HWR's. Because of its small inventory of fissile Pu and higherbreeding gain the carbide reactor is even more effective. Therefore this reactortype has the potential to give economic relief in the decades to come. The savingswould be about 2 million tons of U30S in the European Community. The incentivetherefore to develop the carbide reactor as a profitable alternative even to anadvanced oxide breeder is understandable. The decision which way finally will bechosen, can be made between 19S0 and 1985. If carbide will be technically feasible,carbide will be introduced into the breeder system. Enough knowledge about oxidehas been gained to build and operate an advanced oxide core of the SNR Mk I concept.The carbide development will be performed up to that point of decision as the onlyadvanced materials alternative.+) Reported during ANS winter meeting 1974, Washington Oct 28 - 31.- 2 -- 2 -B. ProgramCharacteristicsOne of the characterisitics is that this program is performed in a comp~mentaryway by contributions of seven partners, fig 2, since 1969.After careful analyses, a reference design has been evaluated, which is charac-terized by modest design criteria in order to reduce pin failures to aminimum,fig 3. Therefore linear ratings are below 1000 W/cm; fTöm reasons of high msssratings the pin diameter will remsin below 8 mm. It is important to notify, thatHe bonding is preferred, because it offers the smallest chance of failures due tomechanical interactions or bonding losses. In addition:it is cheaper to make. Bygas bonding the potential of carbide in terms of doubling time or burnupalready will be exploited to a fairly large extent, fig 4. Burnup increases beyond10 %, as could be reached by sodium bonding, probably would mied a new claddingtype because of the swelling problem. As is shown in fig 5 it is confirmed forsolution annealed stainless steils that there will be a quic~ swelling increasefrom 4 to more than 10 % after about 6 x 1022n / cm2 dosis >0,1 MeV within only.:2) 3)one month of operation of a great power reactor.From evaluations of representative simulation experiments, and also indicated bypin experiments, with cold worked stainless steels, it appears that the dislocationdensity after about 1 x 1023 m /cm2 comes down to the same values of non coldworked specimena. This indicates a destruction of the cold worked effect by ir-radiation energy. Therefore it may be expected that the use of stainless steelsof the non stabilized type will be limited to about 1 x 1023 n/cm2 or a bit higher,if values of no more than 10 % or 15 % volume increase by swelling would be to-lerated. Of course, the full potential to be reached by stabilization of stainlesssteels still is unknown. From Hg 4 then it can be deduced that very advancedsystems still could reach about 8 - 10--% ; peak burnup; this means average dis-charge of less than 7 %,burnup.The conclusion therefore can be drawn, that the moderate He bonded carbide or theadvanced oxide concept could possibly still be operated with stabilized stainlesssteels in more advanced modifications. Carbide, however, which was demonstratedin fig already, finally would have its maximum effect with highest ratingspossible with the sodium bonded concept plus advanced cladding materials.- 3 -- 3 -The time schedule foreseen for different irradiation experiments can also beseen from fig 2: As soon as the smaller screening tests will have been finished,bundle tests in PFR and KNK 11 will follow.C. Program performanceUp to now about 30 specimens have been tested, fig 6, both with gas and sodiumbonding, to burnups of 80 000 and 90 000 MWd/t burnup. The first evaluation re-sults indicate a modest diametral increase of the pins. From US results, fig 7and 8, it appears that carbide fuel, swelling at about 2 %per % burnup couldstrain the pin diameter about 2 % per % also, if claddings with low creepresistance are applied~)With data, corresponding to 1.4970 stabilized stainlesssteel, cold worked, the following explanationtof our low diametral changes aregiven:Fig 9 represents fuel pressures, when fuel and clad creep as weIl as fuel andclad swel1ing are taken into account. The dotted lines especially include cladswelling, which is excluded in the rest of the lines. With such steady statepressures appli'ed, only very small diametral changes can be expected, fig 10.On1y the application of a model for short time fiel clad mechanical interactions,due to power cycling, resalts in greater strains as were found in the experiments,fig 11. Therefore it can be assumed, that claddings, such as 1.4970 with a highyield strength and slow creep properties, represent a strong restraint to carbidefuel.Finally, some safety considerations have been made. Calculations, comparingtemperature profile shifts due to 2-3 $ Isec power excursions, indicate thatthere will be no principle differences between oxide and carbide, fig 12, 13.C. Fabrication of U-PuC CarbideFor fabrication of mixed carbide fue1 various procedures~exist, but arealfabrication route on an industrial scale is not yet developed. Therefore acomparison of the fabrication costs between mixed oxide and mixed carbide isnot possible to-day taking especially into account that the state of technologyreached in mixed oxide fabrication is much more advanced in any case.- 4 -- 4 -The basis of all used procedures for mixed carbide preparation i8 the carbother-mic reduction of the pure oxides. This process has proven to be the most economicone and it is believed that the technological problems which still exist can besolved.To prepare the mixed carbide fuels for our irradiation program a modified proce-dure was developed (reactionsintering) where pure Uraniumcarbide is mixed with anintermediate reduction product coming out from the non-quantitative reduction ofPUOz with carbon (Pu-O-C). The advantage of this method is based, as we believe,at first on the fact that the primary reduction leading to the interrnediate pro-duct, which contains still a remarkable amount of Oxygen, can be performed atlower temperature and therefore the Pu-losses are less; and secondly the UC can beproduced by aseparate process without hazard penalties and is introduced to thePu-line at a very late stage. A disadvantage of the described process is,thatduring the final sintering areaction takes place leading to a CO-formation inform of larger pores. However fairly high fuel densities (above 93 % theor. dens.)can be gained by this method.With this described process about 30 kg of mixed U-Pu-carbide fuel were producedduring the last year for irradiation experiments with a good reproducebility.A capacity increase for KNK-!! with approx. 400 kg/year is under preparation.- 5 -- 5 -D. Conclusions1. Carbide fuel is an alternative to oxide.2. The incentive to develop a carbide core is that a small Pu-inventory andhigh breeding gain will be very effective in saving uranium resources.This gain can be increased the more the earlier the carbide breeder willbe introduced into the breeder system.3. The gas bonded concept will exploit as well the carbide potential a~ thepresent materials' properties to a great extent.4. The experience gained in the world up to now and the characteristics ofthe materials used will allow a sufficient burnup even with stainlesssteel, without danger for unacceptable amounts of clad deformation orfailures.5. The present target is to develop carbide fuel elements until, after success-ful development, the decision can be taken between 1980 and 1985 to constructcarbide fuelled fast breeder reactors as power plants.- 6 -L i t e rat ure1) Prospects of the long-term development of fast breeder reactors ~n theEuropean Community of the Nine, March 1974~) W.Dienst, K.EhrlichMaterial problems in oxide fuel pins for fast breeder reactorsTo be published during the European Nuclear ConferenceApril 21 - 25, 1975, Paris3) H.J.Busboom, G.C.McClellan, W.L.BellSwelling in types 304 and 316 S.S. irradiated to high neutron fluencesTrans. ANS, winter meeting, Washington D.C., Oct 1974Vol. 19, p. 148-1494) J.D.B.Lambert, D.L.Johnson, J.R.Honekamp, L.A.NeimarkAn overview of advanced fuels' behaviour in EBR 11Trans. ANS, winter meeting, Washington D.C., Oct 1974Vol. ·19, p. 90-91- 7 -2(0) 2020 2040FBRO = Na-cooledoxide breederPSBUNIPEDE MIXED BREEDERMIN. STRATEGY 10 yrs delay103 tons LWRU30a / yr I LWR+I90 /FBRo...""80 ,,"70700 GWe ~8~60 30%FBRS) (2020 )40 BRo+HWR302fig.1Contributor Topic 1970 1975 1980 1985GFK CEN swelling MollS, I 30 specimens ,TUI POMGFK TU I heat transfer ,30 specimens ILoop4 TRESON,MINUPGFK mechanical I 25 specimensproperties ILoop5MollO,12GFK CEN pin performance ,30 pins, IMollI, CIRCEG~K TUI minisubassembly I 40 pins ,EIR DFRGFK minisubassembly ,24pin~PFRGFK CEN KNK 11 I 350 pins rbundle testsAlkern, Nukem, ReN for fuel fabrication, onlyCoordinated Carbide Program PSBfig.21. FuelTypeSmear densityBonding2.CladdingTypeDiameterWall thickness- 8 -(U Pu)C75- 80% th. DHeliumColdworked,stabilizedaustenitic stainless steel7.5-8S mm0.5-0.55mmlOperational conditionLinear rating 1100-800 W/cmSpecific power 300 t 50 W/gAverage discharge 50-70000 MWd/tburnupIReterence Data. tor the SNR Carbide IFuel Element PS BHg.3Rating Pin Breeding Syst. Neutron Dosis >0.1 MeVW/g Diarn. Ratio Doubl. t Discharge burnup, averagern years+)+ 50 mm tO% 7% 5%-23 2xlO u/crnOxide 170 7.5 1. 15 40 3.0 2.0 1.5Adv. Oxide 300+) 6 1. 25 20 2.0 1.5 1.1Carbide 300+) 7.5 J. 35 15 2.0 1.5 1.1LMFBR CHARACTERISTICS, approx. values PSBfig.4- 9 -~ 203M Ä~ TEM I0~ dGI DFR 304 I 6.VI DFR 350 • 0Cl 10GI... DFR 397u 8.56 DFR 435 • 0GIE Raps.M.;:) vö4 Raps.P. Ä 6. ~>1500 !25°CI Ä•Ä B2 ~~....-~8 10Neutron dose l10 22 n/cm2;E>0.1 MeV]ib.Sfig 6GfK-Carbide Fue1 I rradiati on ResultsExperiment Number Bon- Pellet Gap Heat ra- Max.burn- liD Fi ss ion Remarksof ptns ding densi ty size ting up (MWd/kgM) 0 gas rele-(% th.d.) (mrn) (kW/ft) (%) ase (%)Mo1- 1.1. K. 1. 1 1 He 94 0.10 39.5 35 1.3 21. 4 UC-defect atMol-11.K.2.1 1 He 83 0.14 36.5 41 0.19 - 17 MWd/kg M(capsule failure)Mol-11.K.2.2 1 He 83 0.18 38 77 0.77Mol-15 3 Na 90 0.50 32 89 - - Neutrographs o.k.1 Na 90 0.50 32 67-0IFR-2 Vg.6A 3 He 86 0.05 30.5 45 - - 1 Defect (capsuleFR-2 Vg.6A 2 He 86 0.05 30.5 22.5 - - failure) all otherintactFR-2 Vg.6C 3 Ar 86 0.08 30.5 45FR-2 Vg.6C 2 Ar 86 0.08 30.5 22.5FR-2 Vg.6D 3 He 86 0.50 30.5 45FR-2 Vg.6E 3 Na 93 0.50 30.5 45DFR-330/1 7 Na 95 0.84 36 46 0.3-0.4 15.3/17.6 1 Defect (liD/D = 1. 4%)- 11 -SWELLI NG OF CARB IOE FUELSWITH BURNUP & TEMPERATUREo Profilometry" Fuel densi tvoo 00oo 000 0,-o 0 /> ..oS......o 0...... 0,-~e. .eg....~ _.... .~-246-;----------"--------,"Io/:::.VI Vper OJoBUO~-.---------,r-----____r-l1000 1500 2000Maximum Fuel Temp. (oC)Hg.70 Profilometry . 9 0II20- 6) Fuel density 9IOJobV II•15- ~ 00I9 1 00 ~ Io~ •10- ~o 'I0 ~\, 105- I IGD CD8oo-+-r-'-'-,-'-,-.--,--rl-'I-'I-.---12 4 6Average At. 0J0 Burn upHg.8100 200 300 400 500 600 700 800 900 1000- Heat ratin (W.t:m)- 12 ;...NE~ 150a.~] 50couI 0L....----.---+-----1--t---t-----t--+--+----t---+oSweUing pressure / heat rating, parameter PSBclad temperature10-'I.c.c 10-8.2Ö~o.."'0] 10-8u;:;:;;cClClC~t 10:10 L----.----.---r--.----.---,--..---'-r--..----,o 100 200 300 400 500 600 700 sOO 000 1000-Hoat ratin lW/tm)Tangential c1ad deformation rate versus hea PSBrating parameter clad temperatureHg,10- 13 -10-1OOW/cm +---'::---\1---"r---::I-----,- --'\-__TC~700 °C \----Tc=600 °C \I~l----+-----jl---"'---lo 0.2 Q4 0.6__Crack length/pellet radiusResidual clad creep defor-mation due to apower PSBincrease of 40% os functionof pellets crack lengthfi~. 11- 14 -2 3----jli"'__ radius [mm)20001000 l..--~__--' --'- -U__-Jou---r------iII"CoPF==2=7=m=s,,*~=c====:l::1:::::---.-J~ nm~c I3 (0) -------- -+------- i -~---- -119msec i\...iJ-1---;:~::::::::::+I-~Oxid response to power transient Hg. 121(0) l- -'.- -'- .l-_--I23_____ radius [mm J fig.13Carbid response to power tran .

Motivations and Performances of Carbide Fuel Development

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Motivations and Performances of Carbide Fuel Development

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