LWRsevereaccidentsimulation:synthesisoftheresultsandinterpretationofthefirstPhebusFPexperimentFPT0OriginalResearchArticle

TheinternationalPhebusFissionProduct(FP)programme,initiatedin1988andperformedbytheFrenchInstitutdeRadioprotectionetdeSûretéNucléaire(IRSN),investigateskeyphenomenaofseverewaterreactoraccidents.Sixin-pileexperimentswereplanned.Fourhavebeensuccessfullyperformedin1993,1996,1999and2000. Thefirstexperiment,calledFPT0,useduraniumdioxidefuelof4.5%enrichmentin-situirradiatedfor9daystoaburn-upof230MWdt−1.Itwasdesignedtoreachsignificantfuelmeltingandtostudylowpressurefissionproductsreleaseandtransportthroughtheprimarycoolingsystemincludinganon-condensingsteamgeneratorandintothecontainmentvessel.Asthefirsttestoftheprogramme,FPT0wasintendedtodemonstratetheadequacyofthenew,complexPhebusfacilitytosimulatetheanticipatedphenomenaandwasthefirstattemptinusingthenewexperimentalresultsforverifyingcodes. ThescientificresultsfromFPT0weresufficientlychallengingthattheydeservetobedocumentedandinterpreted.Sincesomeofthemdidnotcorrespondtothepredictedandpre-calculatedbehaviour,thepost-testanalysisandinterpretationperiodwasratherlong.Threeyearslater,thesecondexperimentFPT1,rathersimilarinitsboundaryconditionsbutusingafuelburnedinareactor(23GWdt−1),confirmedcertainFPT0results,helpingintheirfinalinterpretationandremovingdoubtsaboutpossiblefundamentalshortcomingsofthePhebusfacility.MoredetailedexperimentalresultsofthetestareavailableinthefinaltestreportdeliverableonCD-ROMsupport.ItcanbeobtaineduponrequestfromIRSN. ThisreportretracesthehistoryofFPT0anditsgeneralprogrammecontext,andbrieflydescribesthelayoutofthefacility,supportingseparateeffecttestsandcomputationaltools.Itthenpresentsthesynthesisoftheresultsandoftheinternationalunderstandingreachedconcerningtheirinterpretation,withemphasisonfuelandfissionproductbehaviour. Finally,conclusionsarepresentedabouttheimpactofFPT0onsevereaccidentmodellingwithimplicationsonsourcetermevaluationandonaccidentpreventionandmitigationstudies.