ExperimentalvalidationofthemodifiedlinearscalingmethodologyforscalingECCbypassphenomenainDVIdowncomerOriginalResearchArticle

Inthedirectvesselinjection(DVI)systemdowncomer,thedirectemergencycorecoolant(ECC)bypassisactivatedduringtherefloodphaseofalarge-breakloss-of-coolantaccident(LBLOCA)bytheinteractionbetweenthedownward-flowingliquid-filmandthetransversegasflow.DirectECCbypassisreportedlythemajorbypassmechanismofECC,andvariousexperimentshavebeenperformedtoobtaindetailedinformationabouttheECCbypassinaDVIdowncomer.Theseleadtoaproposednewscalingmethodology,named‘modifiedlinearscaling’,whichisexpectedtopreservethephasedistributioninthedowncomerandtheECCbypassphenomena.Inthepresentstudy,modifiedlinearscalingwasexperimentallyvalidatedinair–watertestscomprisingTest21-Doftheupperplenumtestfacility(UPTF).ThecounterparttestsofUPTFTest21-Dwereperformedin1/7.3and1/4.0scalemodelsofaUPTFdowncomer,andthetestresultswerecomparedwiththeexperimentaldataofUPTFTest21-D.TwoimportantparametersofdirectECCbypass–thenormalizedliquid-spreadingwidthonthedowncomerwallandthedirectECCbypassfraction,whichisthefractionofinputwaterbypassedoutthebrokencold-leg–wereconsideredinthevalidation.ThecomparisonrevealedthatthescalingparametersofdirectECCbypassarewellpreservedintheprototypeandreducedmodels,fromwhichweconcludethatthemodifiedlinearscalingmethodologyisappropriatefordesigningareducedtestfacilityandforascalinganalysisofdirectECCbypassintherefloodphaseofanLBLOCA.