Author/Authors :
DirkWilhelm، نويسنده , , GuillaumeBiaut، نويسنده , , YoshiharuTobita، نويسنده ,
Abstract :
IRSNhasstartedusingthecoupledneutronics–fluiddynamicscodeSIMMER[]tostudycore-disruptiveaccidentsinducedbyinsertionsoflargereactivitiestoproduceveryshortperiodpowerexcursionsinfuelplate-typeandwater-moderatedexperimentalresearchreactors.Untilnow,Frenchsafetyanalysesretainaboundingthermalenergyreleasedandmechanicalyields,deducedfromanalysisofdestructivein-piletestprograms,tostudythebehaviorofsuchreactorsanddesigntheirstructuresandcontainment.
Contrarytothisapproach,thepresentresearchprogramaimsatmodelingthedesignbasisaccidentofresearchreactorswithalow-enrichedfuelusingaCFDcode.Theobjectiveistoanalyzetheeffectsofreactivityfeedbacksandhowtheywouldlimitthegeneratedthermalenergyreleasedinthefuel.Theseaspectsrequireaclosecouplingoftheneutronicstothefluiddynamicsanalysis.Theconsequencesofthenuclearpowerexcursion,thechangesofstateofthefuelandthecoolant,andultimatelythemechanicalenergyreleasedarecalculatedbySIMMER.Forlargestep-wisereactivityintroductions,theDopplereffectand,atalowerextent,thefuelelementthermaldilatation,whichgenerateslocallyadecreaseofthemoderatortofuelratio,limitthepowerexcursionbeforetheenergyreleasedishighenoughtomeltalargepartofthefuel.Moreover,ithasbeenshownthatimposinganexternalreactivityasastep-wiseortime-dependentreactivityintroductionyieldsresultsquitedifferentfromthoseofthephysicalmovementofcontrolrods.
