Modelingofabuoyancy-drivenflowexperimentattheROCOMtestfacilityusingtheCFDcodesCFX-5andTrio_UOriginalResearchArticle

Theinfluenceofdensitydifferencesonthemixingoftheprimaryloopinventoryandtheemergencycorecooling(ECC)waterinthedowncomerofapressurizedwaterreactor(PWR)wasanalyzedattheROssendorfCOolantMixing(ROCOM)testfacility.ROCOMisa1:5scaledmodelofaGermanPWR,andhasbeendesignedforcoolantmixingstudies.Itisequippedwithadvancedinstrumentation,whichdelivershigh-resolutioninformationfortemperatureorboronconcentrationfields. Anexperimentwith5%ofthedesignflowrateinoneloopand10%densitydifferencebetweentheECCandloopwaterwasselectedforvalidationoftheCFDsoftwarepackagesCFX-5andTrio_U.Twosimilarmesheswithapproximately2millioncontrolvolumeswereusedforthecalculations.TheeffectsofturbulenceonthemeanflowweremodeledwithaReynoldsstressturbulencemodelinCFX-5andaLESapproachinTrio_U.CFX-5isacommercialcodepackageofferedfromANSYSInc.andTrio_UisaCFDtoolwhichisdevelopedbytheCEA-Grenoble,France. Theresultsoftheexperimentandofthenumericalcalculationsshowthatmixingisdominatedbybuoyancyeffects:athighermassflowrates(closetonominalconditions)theinjectedslugpropagatesinthecircumferentialdirectionaroundthecorebarrel.Buoyancyeffectsreducethispropagation.TheECCwaterfallsinanalmostverticalpathandreachesthelowerdowncomersensordirectlybelowtheinletnozzle.Therefore,densityeffectsplayanimportantroleduringnaturalconvectionwithECCinjectioninPWRs.BothCFDcodeswereabletopredictwelltheobservedflowpatternsandmixingphenomena.