Assessment of two BWR accident management strategies

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1、ASSESSMENTOFTWOBWRACCIDENTMANAGEMENTSTRATEGIES*S.A.Hodge,M.PetekOakRidgeNationalLaboratoryCONF-9U079--2OakRidge,Tennessee37831DE92002318ABSTRACTCandidatemitigativestrategiesformanagementofin-vesseleventsduringthelatephase(aftercoredegradationhasoccurred)ofpostulatedBWRsevereaccident

2、swereconsideredatOakRidgeNationalLaboratory(ORNL)during1990.Theidentificationofnewstrategieswassubjecttotheconstraintthattheyshould,tothemaximumextentpossible,makeuseoftheexistingequipmentandwaterresourcesoftheBWRfacilitiesandnotrequiremajorequipmentmodificationsoradditions.Asaresul

3、tofthiseffort,twoofthesecandidatestrategieswererecommendedforadditionalassessment.Thefirstisastrategyforcontainmentfloodingtomaintainthecoreandstructuraldebriswithinthereactorvesselintheeventthatvesselinjectioncannotberestoredtoterminateasevereaccidentsequence.Thesecondstrategyperta

4、instotheoppositecase,forwhichvesseiinjectionwouldberestoredaftercontrolblademeltinghadbegun;itspurposeistoprovideaninjectionsourceofboratedwaterattheconcentrationnecessarytoprecludecriticalityuponrecoveringadamagedBWRcore.Assessmentsofthesetwostrategieshavebeenperformedduring1991und

5、ertheauspicesoftheDetailedAssessmentofBWRIn-VesselStrategiesProgram.Thispaperprovidesadiscussionofthemotivationforandpurposeofthesestrategiesandthepotentialfortheirsuccess.1.INTRODUCTIONBoilingWaterReactors(BWRs)haveuniquefeaturesthatwouldcausetheirbehaviorundersevereaccidentconditi

6、onstodiffersignificantlyfromthatexpectedforthepressurizedwaterreactordesign1'5.Consequently,ithasbeennecessarytoanalyzeBWRaccidentsequencesseparately,andtheNRChassponsoredprogramsatORNLforthispurposesince19806.TheobjectiveoftheseBWRsevereaccidentprogramshasbeentoperformanalysesofasp

7、ectrumofaccidentsequencesbeyondthedesignbasisfortypicalspecificU.S.BWRreactordesigns.TheaccidentsequencesselectedforanalysishavebeeningeneralthoseidentifiedasdominantinleadingtocoremeltforBWRsbythemethodsofprobabilisticriskassessment(PRA)ascarriedoutbyotherprograms.Thespecificplants

8、modeledandtheaccide