AnalysisofthehotgasflowintheoutletplenumoftheveryhightemperaturereactorusingcoupledRELAP5-3DsystemcodeandaCFDcodeOriginalResearchArticle

Theveryhightemperaturereactor(VHTR)systembehaviorshouldbepredictedduringnormaloperatingconditionsandpostulatedaccidentconditions.Theplantaccidentscenarioandthepassivesafetybehaviorshouldbeaccuratelypredicted.Uncertaintiesinpassivesafetybehaviorcouldhavelargeeffectsontheresultingsystemcharacteristics.DuetotheseperformanceissuesintheVHTR,thereisaneedfordevelopment,testingandvalidationofdesigntoolstodemonstratethefeasibilityofthedesignconceptsandguidetheimprovementoftheplantcomponents.Oneoftheidentifieddesignissuesforthegas-cooledreactoristhethermalmixingofthecoolantexitingthecoreintotheoutletplenum.Incompletethermalmixingmaygiverisetothermalstressesinthedownstreamcomponents.Toprovideflowdetails,theanalysispresentedinthispaperwasperformedbycouplingaVHTRmodelgeneratedinathermalhydraulicsystemscodetoacomputationalfluiddynamics(CFD)outletplenummodel.TheoutletconditionsobtainedfromthesystemscodeVHTRmodelprovidetheinletboundaryconditionstotheCFDoutletplenummodel.Bycouplingthetwocodesinthismanner,theimportantthree-dimensionalfloweffectsintheoutletplenumarewellmodeledwhileavoidingmodelingtheentirereactorwithacomputationallyexpensiveCFDcode.Thevaluesofpressure,massflowrateandtemperatureacrossthecoupledboundaryshoweddifferencesoflessthan5%ineverylocationexceptforonechannel.Thecouplingauxiliaryprogramusedinthisanalysiscanbeappliedtomanydifferentcasesrequiringdetailedthree-dimensionalmodelinginasmallportionofthedomain.