RG1.126 燃料密实度分析的一种可接受模型和相关的统计方法 1978

U.S.NUCLEARREGULATORYCOMMISSIONRevision1March1978REGULATORYGUIDEIsOFFICEOFSTANDARDSDEVELOPMENTREGULATORYGUIDE1.126ANACCEPTABLEMODELANDRELATEDSTATISTICALMETHODSFORTHEANALYSISOFFUELDENSIFICATIONA.INTRODUCTIONAppendixK,ECCSEvaluationModels,to10CFRPart50,LicensingofProductionandUtilizationFacilities,requiresthatthesteady-statetemperaturedistributionandstoredenergyinthefuelbeforeahypotheticalloss-of-coolantaccident(LOCA)becalculated,takingfueldensificationintoconsideration.ThisguideprovidesananalyticalmodelandrelatedassumptionsandproceduresthatareacceptabletotheNRCstaffforpredictingtheeffectsoffueldensificationinlight-water-coolednuclearpowerreactors.Theguidealsodescribesstatisticalmethodsrelatedtoproductsamplingthatwillprovideassurancethatthisandotherapprovedanalyticalmodelswilladequatelydescribetheeffectsofdensificationforeachinitialcoreandreloadfuelquantityproduced.TheAdvisoryCommitteeonReactorSafeguardshasbeenconsultedconcerningthisguideandhasconcurredintheregulatoryposition.B.DISCUSSIONIn-reactordensification(shrinkage)ofoxidefuelpelletsaffectsfueltemperaturesinseveralways:(1)gapconductancemaybereducedbecauseofthedecreaseinpelletdiameter;(2)thelinearheatgenerationrateisincreasedbecauseofthedecreaseinpelletlength;and(3)thepellet-lengthdecreasesmaycausegapsinthefuelcolumnandmayproducelocalpowerspikesandthepotentialforcladdingcollapse.Dimensionalchangesinpelletsinthereactordonotappeartobeisotropic,soaxialandradialpelletdimensionchangeswillbetreateddifferently.Furthermore,items(1)and(2)abovearesingle-pelleteffects,whereasitem(3)istheresultofsimultaneouschangesinalargenumberofpellets.Thesedistinc*Linesindicatesubstantivechangesfrompreviousissue.tionsmustbetakenintoaccountinapplyinganalyticalmodels.TheNRCstaffhasreviewedtheavailableinformationconcerningfueldensification,andthetechnicalbasisfortheregulatorypositionofthisguideisgiveninReference1.ThemodelpresentedinSectionsC.AandC.2ofthisguideisnotintendedtosupersedeNRC-approvedvendormodels.Thestatisticalmethods(SectionC.3),measurementmethods(SectionC.4),andisotropyassumptions(SectionC.5)arecompatiblewithmostvendormodels.ThereforeSectionsC.3,C.4,andC.5couldbeappliedtodensificationmodelsthatdifferfromtheonepresentedinSectionsC.1andC.2.C.REGULATORYPOSITION1.MaximumDensificationThedensityofafuelpellettinthereactorincreaseswithburnupandachievesamaximumvalueatarelativelylowburnup(generally10,000MWd/t).Foranalyticalpurposes,thismaximumdensityminustheinitialdensity,i.e.,themaximumdensitychange,isassumedtobethesameasthedensitychangeAPsntrthatwouldoccuroutsidethereactorinthesamepelletduringresinteringat1700'Cfor24hours.Wheretheex-reactorresinteringresultsinanegativedensity-change(i.e.,swelling),zeroin-reactordensificationshouldbeassumed.tThemodelpresentedinthisguideisapplicabletoU02,UOPuO2,andU02-Gd2O3fuelpellets.USNRCREGULATORYGUIDESCommentsshouldbesenttotheSecretaryoftheCommission.US.NuclearRegulatoryCommission.Washington,D.C.20555,Attention:DocketingandServiceRegulatoryGuidesareissuedtodescribeandmakeavailabletothepublicmethodsBranch.acceptabletotheNRCstaffofimplementingspecificpartsoftheCommission'sregulations,todelineatetechniquesusedbythestaffinevaluatingspecificproblemsTheguidesareissuedinthefollowingtenbroaddivisionsorpostulatedaccidents,ortoprovideguidancetoapplicants.RegulatoryGuidesarenotsubstitutesforregulations,andcompliancewiththemisnotrequired.1.PowerReactors6.ProductsMethodsandsolutionsdifferentfromthosesetoutintheguideswillbeaccept-2.ResearchandTestReactors7.Transportationableiftheyprovideabasisforthefindingsrequisitetotheissuanceorcontinuance3.FuelsandMaterialsFacilities8.OccupationalHealthofapermitorlicensebytheCommi~sion.4.EnvironmentalandSiting9.AntitrustReview5.MaterialsandPlantProtection10tGeneralCommentsandsuggestionsforimprovementsintheseguidesareencouragedatallRequestsforsinglecopiesofissuedguideslwhichmaybereproduced)orforplace.times,andguideswill*berevised,asappropriate,toaccommodatecommentsandmentonanautomaticdistributionlistforsinglecopiesoffutureguidesinspecifictoreflectnewinformationorexperience.ThisguidewasrevisedasaresultofdivisionsshouldbemadeinwritingtotheU.S-NuclearRegulatoryCommission,substantivecommentsreceivedfromthepublicandadditionalstaffreview.Washington,D.C.20555,Attention:Director,DivisionofDocumentConitrol.2.DensificationKineticsForpelletsthathavearesinteringdensitychangeAPsntroflessthan4%oftheoreticaldensity(TD),thein-reactordensitychangeApasafunctionofburnupBUmaybetakenastAp=0(la)(forBU20MWd/t);Ap=mlog(BU)+b(lb)(for20BU2000MWd/t);andAp=APsntr(forBU2000MWd/t),wherethecoefficientsmandbaregivenby0=mlog(20)+bandAPsntr=mlog(2000)+b.Forpelletsexhibitingaresinteringdensitychangeinexcessof4%TD,thein-reactordensitychangeasafunctionburnupmaybetakenasAp=0(2a)(forBU5MWd/t);Ap=mlog(BU)+b-(2b)(for5BU500MWd/t);andAp=APsntr(2c)(forBU500MWd/t),wherethecoefficientsmandbaregivenby0=mlog(5)+bandApsntr=mlog(500)+b.InapplicationsofEquations1and2,ApsntrwillhavethevalueAp*s*torAPs'ntr,whichwillbedescribedinSectionC.3.TheburnupunitMWd/tintheabo