DemonstrationoftheheatremovingcapabilitiesoftheEPRcorecatcherOriginalResearchArticle

TheEPRimplementsanadditional,fourthlevelofdefense-in-depththataimsatlimitingandrestrictingtheconsequencesofapostulatedsevereaccidentwithcoremeltingtotheimmediatevicinityoftheplant.Asthisrequiresanintactconfinement,itisnecessary,amongothers,toavoidanattackofthemoltencoreonthebasemat.Forthatpurpose,theEPRincludesalargeex-vesselcorecatcher.Itincreasesthesurface-to-volumeratioofthemeltafteritsreleasefromthereactorpressurevessel(RPV)andallowstheeffectivequenchingandstabilizationofthemeltbeforeitcanattackthestructuralconcrete. Thebottomandsidesofthecorecatcherarecooledbyasystemofhorizontalwater-filledchannels.Thewaterisprovidedeitherpassively,byoverflowfromaninternalreservoir,oractivelybythecontainmentheatremovalsystem(CHRS). Toquantifytheheatremovingcapabilityofthehorizontalpartoftheproposedcoolingstructure,asetofexperimentsinafull-scale,horizontal,5mlongcoolingchannelhavebeenperformed.Tosimulatedecayheat,thechannelwaselectricallyheatedfromthetop.TheexperimentwasintegratedintheBENSONtestrig,ahighlyflexible,separate-effecttestfacilityoperatedbyFramatomeANP.Inaccordancewiththepotentiallatermodesofoperation,bothco-currentandcounter-currentflowofthewater/steammixturehavebeeninvestigated. Thetestsdemonstratedthegood-naturedbehaviorofthesystem,evenforinducedheatfluxesthatsignificantlyexceedrealisticallyexpectablemaximumvalues.Although,athighheatfluxes,alocaldry-outoccurredatthetopofthechannel,structuraltemperaturesremainedinasaferange.Thisexcellentperformanceisattributedtothefactthatheatcanenterthewaterthroughboththehorizontalandverticalsurfacesofthecoolingchannel.Asaresultahigh,effectivecriticalheatflux(CHF)levelisachieved.TheperformedtestsyieldavaluablecontributiontothevalidationofthefunctionoftheEPRcorecatcherconcept.