DryoutheatfluxexperimentswithdeepheterogeneousparticlebedOriginalResearchArticle

AtestfacilityhasbeenconstructedatTechnicalResearchCentreofFinland(VTT)tosimulateasaccuratelyaspossibletheex-vesselcoreparticlebedintheconditionsofOlkiluotonuclearpowerplant.TheSTYXparticlebedreproducestheanticipateddepthofthebedandthesizerangeofparticleshavingirregularshape.Thebedisimmersedinwater,creatingtopfloodingconditions,andinternallyheatedbyanarrayofelectricalresistanceheatingelements.Dryouttestshavebeensuccessfullyconductedat0.1–0.7MPapressureforbothuniformlymixedandstratifiedbedgeometries.Inalltests,includingthestratifiedones,thedryzonefirstformednearthebottomofthebed.Themeasureddryoutheatfluxesincreasedwithincreasingpressure,from232kW/m2atnearatmosphericpressureto451kW/m2at0.7MPapressure.Thedatashowsomescatterevenfortheuniformbed.Thetestswiththestratifiedbedindicateaclearreductionofcriticalpowerduetothepresenceofalayerofsmallparticlesontopoftheuniformbed.Comparisonofdatawithvariouscriticalpower(dryoutheatflux)correlationsforporousmediashowsthatthemostimportantparameterinthemodelsistheeffectiveparticlediameter.Adiabaticdebrisbedflowresistancemeasurementswereconductedtodeterminethemostrepresentativeparticlediameter.Thisdiameterisclose,butnotequal,totheparticlenumber-weightedaveragediameterofthebedmaterial.Withit,uniformbeddatacanbecalculatedtowithinanaccuracyof3–28%usingLipinskiʹs0-Dmodel.Inthestratifiedbedexperiments,itappearsthatthetoplayerwaspartiallyfluidized,hencethemeasuredcriticalpowerwassignificantlyhigherthancalculated.Futureexperimentsarebeingplannedwithdensertoplayermaterialtoeliminatenon-prototypicfluidization.