Abstract :
ThisstudydealswithCHFinnarrowgapsandthepurposeistoproposeapredictivemodelfortheCHF,takingintoaccounttheeffectofgeometryandpressure.Themodellingisbasedonalimitationbyfloodingoftheflowenteringthegap(CCFLforcounter-currentflowlimitation).Amodelhasbeenderivedforbothverticalplateandhemisphericalgeometry.TheformulationproposedbyKutateladze(Eqs.andwitha=1andb∼1.7)providesbest-fitresultsforbothverticalchannelsandhemisphericalgeometry.ThecomparisonwiththeresultsobtainedbyKöhleretal.[Köhler,W.,Schmidt,H.,Herbst,O.,Krätzer,W.,1998.ThermohydraulischeUntersuchungenzurDebris/Wand-Wechselwirkung(DEBRIS),AbschlussberichtProjectNo.1501017,November;Köhler,W.,Schmidt,H.,Herbst,O.,Krätzer,W.,1998.ExperimentsonheatremovalinagapbetweendebriscrustandRPVwall.In:OECD/CSNIWorkshoponIn-VesselCoreDebrisRetentionandCoolability,Garching,Germany,March3–6,alsoinFirstEuropean-JapaneseTwo-PhaseFlowGroupMeeting,36thEuropeanTwo-PhaseFlowGroupMeeting,Portoroz1–5June,andSeventhConferenceonNuclearEngineeringTokyo,Japan,April19–23,2000ICONE7012.]seemstoindicatethatthevalidityofmodelsbasedonCCFLcontrolledCHFislimitedtogapsoflessthan3–5mm.Beyondthisgapsize,mechanismsotherthanCCFLmightcontroltheCHF.However,theexperimentalresultsaretooscarceandaffectedbytoolargeuncertaintiestovalidateatheoreticalmodel.Experimentaluncertaintiesaremainlylinkedtothepositioningofthestructure(evolutionofthegapwiththetemperature)andtothecriteriathatareappliedtodetecttheCHF.TheconclusionofapplicationstoreactorsituationsatreducedpressureisthatthecoriummassthatmightbecoolablethroughagapiscertainlymuchnearertothemassobservedinTMI2(∼10–20tonnes)thantothewholemasscontainedinacore(100tonnes).Themainuncertaintyforreactorapplicationsstillremainstheknowledgeofthedistributionandconfigurationoftherelocatedcorium.
