ValidationandapplicationoftheWABEcode:Investigationsofconstitutivelawsand2DeffectsondebriscoolabilityOriginalResearchArticle

TheWABE-2Dmodelaimsattheproblemofcoolabilityofdegradedcorematerialduringasevereaccidentinalightwaterreactor(LWR)anddescribesthetransientboil-offandquenchingbehaviorofdebrisbeds.ItisbeingdevelopedintheframeoftheKESScodesystem,whichisconsideredtodescribetheprocessesofcoreheatup,melting,degradationandrelocationtothelowerplenumaswellasthesubsequentbehavior.ThemodelsdevelopedinthisframearebeingintegratedintheGermansystemcodeATHLET-CD. Anemphasisofthepresentcontributionliesonmultidimensionalaspectsofthecoolingbehavior.Frommultidimensionalfeaturesasignificantimprovementofoverallcoolabilityisexpectedcomparedtowhatisconcludedbasedonclassicalone-dimensionalanalyses.Suchanalyses–alsomainlyorientedattopcoolingconditions–additionallymisstheexpectedimportanceofinterfacialdragwhichshouldsupportcoolabilityinco-currentflowsituationsduetobottomflooding.Thelattersituationplaysaroleinthemultidimensionalbehaviorexpectedunderrealisticconditions.Thus,afurtheremphasisinthepresentcontributionliesontheconstitutivedraglawsandtheireffectsinsuchconfigurations. Calculationscomparingtopandbottomfloodingandtheinfluenceofinterfacialfrictionarepresented.AnexplanationforeffectsobservedinrelatedexperimentsatForschungszentrumKarlsruheisprovidedbasedonthisinfluence.Thesignificantincreaseofdryoutheatfluxwithwaterinflowfrombelow,drivenbyalateralwatercolumn,isreproducedandunderstood.Enhancedcoolingduetothisandingeneralbylateralinflowisalsodemonstratedforreactorscenarios,consideringparticulatedebrisinthelowerheadofthereactorpressurevessel(RPV)ofaLWRorinadeepwaterpoolinthereactorcavityofaboilingwaterreactor(BWR).Coolingbysteamflowthroughlocaldryzonescanestablishunderlateralwatersupplytoregionsbelowandyieldafurtherextensionofcoolability.Quenchingofhotmaterialisalsoanalyzed.Finally,caseswithlossofcoolability,dryzoneformationandmeltingareconsidered,especiallyintheperspectivetoanalyzemeltpoolformationinthelowerheadoftheRPVandthehistoryofthermalinteractionwiththelowerheadwall.ThelatterwilldeterminefailurepossibilitiesandmodesoftheRPV.