Analysisofmechanicalloadoncladdinginducedbyfuelswellingduringpowerrampinhighburn-uprodbyfuelperformancecodeFEMAXI-6OriginalResearchArticle

Mechanicalloadoncladdinginducedbyfuelswellinginahighburn-upBWRtyperodwasanalyzedbyafuelperformancecodeFEMAXI-6.ThecodewasdevelopedfortheanalysisofLWRfuelrodbehaviorsinnormaloperationandtransientconditionsusingfiniteelementmethod(FEM). Duringapowerrampforthehighburn-uprod,instantaneouspelletswellingcansignificantlyexceedthelevelthatispredictedbya“steady-rate”swellingmodel,causingalargecircumferentialstrainincladding.Thisphenomenonwassimulatedbyanewswellingmodeltotakeintoaccountthefissiongasbubblegrowth.AsaresultitwasfoundthatthenewmodelcangivereasonablepredictionsoncladdingdiameterexpansionincomparisonwithPIEdata.Thebubblegrowthmodelassumesthattheequilibriumstateequationholdsforabubbleunderexternalpressure,andsimultaneoussolutionisobtainedwithbothbubblesizedeterminationequationanddiffusionequationoffissiongasatoms.Inaddition,apellet-cladbondingmodelwhichhasbeenincorporatedinthecodetoassumesolidmechanicalcouplingbetweenpelletoutersurfaceandcladdinginnersurfacepredictedthegenerationofbi-axialstressstateinthecladdingduringramp.