Three-dimensionalsimulationofthecoupledconvective,conductive,andradiativeheattransferduringdecayheatremovalinanHTROriginalResearchArticle

Athree-dimensionalmodelhasbeenconstructedtosimulatethepassiveheatremovalinamodularprismatic-blockhightemperaturereactorduringalossofactivecoolingaccident.Thismodel,developedusingtheSTAR-CDgeneralcomputationalfluiddynamicscode,solvesthecombinedconductive,convective,andradiativeheattransferwithina30°sectionofthecoreandreactorvessel.Toaccommodatethedifferentspatialscales,ituseshomogeneousequivalentmediatorepresentthecoolantflowandtheprismaticfuelblocks.Acustomizedprocedurethatmanagessolvingalternativelythedynamicandthermalfieldspermitsthecomputationofverylongtransients,whichtypicallyareperformedfor100ormorehoursofsimulatedtime. Theglobalmethodologyandspecificmodelingproceduresareexplained,andkeypointsoftheCFDanalysisarehighlighted.Next,theresultsofseveralcalculationsarepresented,andthephysicalphenomenarepresentedaredescribed.Twocommonlyinvestigatedlossofactivecoolingscenariosareconsidered:depressurizedconductioncooldownandpressurizedconductioncooldown.Theresultsforthesetwoscenariosarecomparedtoassesstheeffectofheattransferviainternalnaturalconvection–whichisnegligibleduringthedepressurizedevent–onthethermalbehaviorofthesystem.Inaddition,theevolutionofthenaturalconvectionflowthroughthecoreandintheannularspacesisexaminedanddiscussed.