Amodifiedequilibriumvoiddistributionmodelapplicabletosubchannel-scalevapor–liquidcrossflowmodelforconventionalsquareandtightlatticeBWRfuelbundlesOriginalResearchArticle

AsapartoftheadvancedsubchannelcodedevelopmentprojectsponsoredbyMinistryofEconomy,TradeandIndustry,Japan,thispaperdescribesimprovementoftheequilibriumvoiddistributionmodelthatisamainpartofthevapor–liquidcrossflowmodel. Thethree-componentcrossflow(TCCF)modelisdefinedasthepresentframeworkthatseparatescontributionsofdiversion,turbulentmixingandvoiddrift.TheLaheyʹsvoidsettlingmodelisintroducedtoexpressthelattertwocomponents.Basedonthehigh-resolutionair–waterdatabaseandotherpublisheddataofsteam-watertests,generaltrendsofvapor–liquidcrossflowprocessesareexamined.Itcanbeassumedthatsubchannelvoiddistributionsaredominatedbythethreemajoreffects,i.e.thefluiddynamiceffect,thegeometricaleffectandthenarrowgapeffect. Theequilibriumvoiddistributionmodelismodifiedtoincludetheabove-mentionedthreeeffects.Threecharacteristicparametersareassignedforeachofthethreeeffectsandtheyareidentifiedexperimentallyasfunctionsofthevoidfraction.Multi-dimensionallatticegeometriesareincorporatedbasedonthetwo-dimensionalflownetworkmodel.Thenetworkequationisconstructedbymappingtheequilibriumvoidbalanceproblemintotheforce-deflectionproblem.TheresultantmodelsareverifiedbasedonequilibriumvoiddistributiondataobtainedbySadatomiandKawahara.