ValidationoftheCFDcodefluentbypost-testcalculationofadensity-drivenROCOMexperimentOriginalResearchArticle

Duringthelastyears,borondilutioneventswiththepotentialofreactivitytransientswereanimportantissueofGermanPWRsafetyanalyses.Acoolantwithalow-boronconcentrationcouldbecollectedinlocalizedareasofthereactorcoolantsystem,e.g.,byseparationofaboratedreactorcoolantintohighlyconcentratedanddilutedfractions(inherentdilution)whichcanoccurduringreflux-condenserheattransferafterasmallbreaklossofcoolantaccidentwithalimitedavailabilityoftheemergencycorecoolingsystems. Duringthecourseoffollowercoreassessments,TÜVNORDSysTecappraisessafetyanalysesofborondilutioneventspresentedbytheutilities.Theseanalysesarebasedonthesimulationofborondilutionandtransportprocessesinconjunctionwithanumberofdedicatedexperiments.Theanalysesdemonstratethatborondilutioneventscannotleadtorecriticalityofthecore.Hence,theboronconcentrationatthecoreinlethastobedetermined. TÜVNORDSysTecappliestheCFDcodeFLUENTfortheinvestigationofborondilutioneventsinpressurizedwaterreactors.ToaffirmtheFLUENTabilitiesforthesimulationofborondilutionevents,avalidationagainsttheROCOMexperimentT6655_21withadensity-drivencoolantmixingwasperformed.ThisvalidationprovesthatFLUENTisabletoappropriatelysimulatetheeffectsofborontransportanddilutionsuchasstreaksofcoolantwithlowerdensityinthedowncomer.Deficitswereidentifiedinthesimulationoffluidlayeringinthecoldleg,whichfortunatelyhavearathersmallinfluenceonthepredictedcoreinletconcentration.Therefore,theboronconcentrationinthereactorcorecanbedeterminedwithsufficientaccuracytosolvethesafetyissue,regardlessofthecorebecomingcriticalornot.