SeismiccapacityevaluationofagroupofverticalU-tubeheatexchangerwithsupportframesforseismicPSAOriginalResearchArticle

ThispaperpresentsanevaluationofseismiccapacityofagroupofverticalU-tubetypeheatexchangers(HXs)withsupportframestocontributetorefinementofseismiccapacitydataforseismicProbabilisticSafetyAssessment(PSA)inJapan.AccordingtousualpracticeofseismicPSAs,capacityofcomponentisrepresentedasalog-normallydistributedrandomvariabledefinedbyamedianandlogarithmicstandarddeviations(LSDs),whichrepresentinherentrandomnessaboutthemedian,βr,anduncertaintyinthemedianduetolackofknowledge,βu.UsingdesignspecificationsoffourHXsforresidualheatremovalsystemsof1100MWeBWRs,theauthorsevaluatedagenericcapacityofHXswithaLSDforuncertaintyduetolackofknowledgetotakeintoaccountdesignvariability.ThemediancapacitywasevaluatedbytheuseofatimehistoryresponseanalysiswithadetailedmodelforaselectedrepresentativeHX,whichwasextendedfromamodelusedinseismicdesign.TheLSDforuncertaintyduetolackofknowledgewasevaluatedwithconsiderationofthevariabilitiesinthreeinfluentialdesignparameters,i.e.,diameterofanchorbolt,weightofHXandpositionofcenterofgravityofHXwiththedetailedmodelandasimplifiedstaticmodel.TheLSDforuncertaintyduetorandomnesswasdeterminedfromthevariabilityinmaterialproperty.ThedominantfailuremodeofHXswasidentifiedasthefailureofanchorboltsoflugsmainlyduetoshearingstress.ThecapacityexpressedintermsofzeroperiodaccelerationonthefoundationofHXwasevaluatedtobe4180Gal(4.3g)formedian,LSDforuncertaintyduetorandomnesswas0.11andLSDduetolackofknowledgewas0.21–0.53dependingoncombinationofthevariabilitiesindesignparameterstobeconsidered.