SweepoutmodelimplementationinRELAP5/MOD3.3toimproveRCScoolantinventorycalculationduringaLBLOCAOriginalResearchArticle

AccordingtotheexperimentsoftheUpperPlenumTestFacility(UPTF)andadvancedpowerreactor1400MWe(APR1400),thesweepoutinthedowncomerhasbeenidentifiedtoplayanimportantroleindepletingthecorecoolantinventoryduringaLarge-BreakLoss-of-CoolantAccident(LBLOCA).Inordertoidentifythesweepoutmechanismandtoestimatetheamountofcoolantdischargedbysweepout,theseparate-effecttestwascarriedoutintheplatetypetestapparatus,whichwasscaleddownto1/5ofthesizeoftheAPR1400downcomer.Inaddition,thesweepoutmodelwasdevelopedbycorrelatingtheexperimentaldataonthecriticalvoidheightandthedischargeflowrateatthebreaktothevaluesofanalyticallyderivednon-dimensionalparameters.ThismodelwasimplementedinRELAP5/MOD3.3toimproveitscalculationofcoolantinventorylossduringaLBLOCA.TovalidatethemodifiedRELAP5/MOD3.3byimplementingthesweepoutmodel,thesweepoutseparate-effecttestwassimulatedbyboththeoriginalandthemodifiedRELAP5/MOD3.3.Theoriginalonepredictedthedifferentdischargeflowratesaccordingtothenodesizeofthedonorvolume,andtheseflowrateswerelargerthanthoseoftheexperiment.Ontheotherhand,themodifiedonecalculatedthedischargeflowrateandthecriticalvoidheightmuchmoresimilartothoseoftheexperimentthantheoriginalmodeldid.Inthefuture,theimprovedRELAP5/MOD3.3adoptedinanintegratedanalysissystemwillsupportamorerealisticthermalhydraulicanalysis.