StrengthevaluationofasteamdistributiondeviceintheIgnalinaNPPaccidentlocalisationsystemOriginalResearchArticle

TheIgnalinaNPPhasapressuresuppressiontypeofconfinement,whichisreferredtoastheaccidentlocalizationsystem(ALS).TheALSpreventsthereleaseoftheradioactivematerialfromtheNPPtotheenvironmentduringaloss-of-coolantaccident(LOCA).TenwaterpoolsarelocatedinthetwoALStowers(fivepoolsineachtower),whichseparatethedrywellfromthewetwell.Thesewaterpoolscondensetheaccident-generatedsteamandpreventhighoverpressuresinthecompartments. Thesteamdistributiondevice(SDD),withtheverticalventpipes(nozzles)thatareinsertedunderthewaterofthecondensingpools,connectsthedrywellandthewetwell.Incaseofanaccident,thesecomponentsmustbecapableofwithstandingthedynamicloadsgeneratedbyaLOCAforsuccessfulpressuresuppressionfunction. ThispaperpresentsthetransientanalysisoftheSDDandtheirconnectionstotheverticalsteamcorridorsfollowingaLOCA.Athermo-hydraulicanalysisoftheSDDwasperformedusingthestate-of-the-artCOCOSYScodetodeterminepressureandtemperaturehistoriesresultingfromaLOCA.ThefiniteelementcodeNEPTUNEwasusedtoevaluatethestructuralintegrityoftheSDDanditssupportingreinforcedconcretewall.Resultsshowthat,althoughportionsoftheSDDundergoplasticresponseandtheoutsidesurfaceoftheverticalsteamcorridorreinforcedconcretewallcracks,thestructuralintegrityoftheSDDandwallaremaintainedduringaLOCA.