Author/Authors :
S.Kliem، نويسنده , , U.Rohde، نويسنده , , F.-P.Wei?، نويسنده ,
Abstract :
Aparameterstudy,incorporatingstationaryandtransientcorecalculations,wascarriedoutforahypotheticalborondilutioneventinapressurizedwaterreactor,usingthethree-dimensional(3D)neutronkineticscoremodelDYN3Dincombinationwithafastrunningsemi-analyticalcoolantmixingmodel.Itwasassumedthataslugofdeboratedwaterwasformedinoneoftheloops,duetoasecondary-to-primarysteamgeneratorleakageduringoutage.Itwasfurtherassumedthatthisslugisnotrecognisedandthatthefirstmaincoolantpumpisstarted,inpreparationtoreturningtopower.Attheinitiationofpumpstart-up,thereactorisstillinthecoldanddeeplysub-criticalstate.Byvaryingtheinitialslugvolume,itwasfoundinstationarycalculationsthat,forthegivencoreconfiguration,slugsoflessthan14m3donotleadtore-criticality.Transientcorecalculationswithlargerslugvolumesshowasignificantreactivityinsertionandover-criticality.However,accordingtothecalculations,evenanover-criticalityofabout2$didnotleadtosafety-relevantconsequences.ThepowerexcursionismitigatedandstoppedbyDopplerfeedback.Theinfluenceofthecross-sectionlibraryonthecourseofthetransientwasinvestigated,applyinganalternativelibrary.Differencesintheglobalcoreparametersleadtoquantitativedifferencesinthetimeandheightofthepowerexcursion.Inaddition,itisshownthatnumericaldiffusionhastobesuppressedinordertodescribetheborontransportcorrectly,especiallyatlowflowvelocities.Otherwisetheneutronkineticcorebehaviourcannotbecorrectlymodelled.
