Safetyanalysisofmultiple-failureofpassivesafetysystemsinSBWR-1200SBLOCAOriginalResearchArticle

Thedesignofthesimplifiedboilingwaterreactor(SBWR-1200)ischaracterizedbyutilizingfullypassivesafetysystems.Theemergencycorecoolingisrealizedbythegravitydrivencorecoolingsystem,andthedecayheatremovalisdonebythepassivecontainmentcoolingsystemandisolationcondensersystem.Allofthesystemshavemultipleunitsandcouldbepartiallyfailed.TheobjectiveofthispaperistoanalyzethesystemresponseunderthemultiplemalfunctionsofpassivesafetysystemsintheSBWR-1200. Thechosenaccidentscenarioisasmallbreaklossofcoolantaccidentwithoneofthreegravitydrivencorecoolingsystemdrainlinesblockedandoneofthreepassivecontainmentcoolingsystemcondensersdisabled.AnintegraltesthasbeencarriedoutinthePUMAfacilityfor16h.Thefacilityisdesignedforlowpressure,longtermcoolingoperationwiththemultiplesafetyrelatedcomponents;therefore,ithastheflexibilitytodemonstratetheasymmetricormultiple-failureeffectswiththecombinationofdisabilityofsafetysystems.Thetestinitialconditionsat1MPa(150psi)areobtainedfromRELAP5/MOD3.2codesimulationfortheSBWR-1200withappropriatescalingconsiderations. Comparisonshavebeenfirstmadebetweenthemultiple-failuretestandasingle-failuretestpreformedpreviously.Itshowsthatthecorehasbeencoveredwithliquidcoolantduringallofaccidenttransienteventhoughthereisanapparentcoolantinventoryreductioninthemultiple-failuretest.Thedecayheatremovalhasnosignificantdifferencebecausetheremainingtwopassivecontainmentcoolingcondensersincreasetheircoolingcapacities,andeventhedrywellpressureisslightlylowerduetothecoldwaterinjectionfromthesuppressionpool.Comparisonshavealsobeenmadebetweenthescaled-uptestdataandthecodesimulationattheprototypiclevel.TheprototypicsimulationisdonebyRELAP5/MOD3.2.Agreementsbetweenthecodesimulationandthescaled-uptestdataconfirmthecodeapplicabilityandthefacilityscalabilityforthisaccidentscenario.