ThermalresponseofamodularhightemperaturereactorduringpassivecooldownunderpressurizedanddepressurizedconditionsOriginalResearchArticle

TheconceptofinherentsafetyfeaturesofthemodularHTRdesignwithrespecttopassivedecayheatremovalthroughconduction,radiationandnaturalconvectionwasfirstintroducedintheGermanHTR-module(pebblefuel)designandsubsequentlyextendedtoothermodularHTRdesigninrecentyears,e.g.PBMR(pebblefuel),GT-MHR(prismaticfuel)andthenewgenerationreactorV/HTR(prismaticfuel). ThispaperpresentsthenumericalsimulationsoftheV/HTRusingthethermal-hydrauliccodeTHERMIXwhichwasinitiallydevelopedfortheanalysisofHTRswithpebblefuels,verifiedbyexperiments,subsequentlyadoptedforapplicationsintheHTRswithprismaticfuelsandcheckedagainsttheresultsofCRP-3benchmarkproblemanalyzedbyvariouscountrieswithdiversecodes. Inthispaper,thethermalresponseoftheV/HTR(operatinginlet/outlettemperatures490/1000°C)duringpostshutdownpassivecoolingunderpressurizedanddepressurizedprimarysystemconditionshasbeeninvestigated.Additionalinvestigationshavealsobeencarriedouttodeterminetheinfluenceofotherinlet/outletoperatingtemperatures(e.g.490/850,350/850or350/1000°C)onthemaximumfuelandpressurevesseltemperatureduringdepressurizedcooldowncondition.Inaddition,somesensitivityanalyseshavealsobeenperformedtoevaluatetheeffectofvaryingtheparameters,i.e.decayheat,graphiteconductivity,surfaceemissivity,etc.,onthemaximumfuelandpressurevesseltemperature.Theresultsshowthatthenominalpeakfueltemperaturesremainbelow1600°Cforallthesecases,whichisthelimitingtemperaturerelatingtoradioactivityreleasefromthefuel.TheanalysespresentedinthispaperdemonstratethatthecodeTHERMIXcanbesuccessfullyappliedforthethermalcalculationofHTRswithprismaticfuel.TheresultsalsoprovidesomefundamentalinformationforthedesignoptimizationofV/HTRwithrespecttoitsmaximumthermalpower,operatingtemperatures,etc.