ML18026A448
| ML18026A448 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 11/21/1994 |
| From: | BYRAM R G PENNSYLVANIA POWER & LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML17164A434 | List: |
| References | |
| PLA-4228, NUDOCS 9411290136 | |
| Download: ML18026A448 (13) | |
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tgATTACHMENTTOPLA-4228SAFETYASSESSMENThINCREASEOFMSIVLE<AKAGERATE<ANDDELETIONOFLEAKAGECONTROLSYSTEMTheMainSteamLines(MSL)installedoncurrentBoilingWaterReactor(BWR)plantsareprovidedwithdualquick-closingisolationvalves.Thesevalvesfunctiontoisolatethereactorsystemintheeventofabreakinasteamlineoutsidetheprimarycontainment,adesignbasisLoss-ofCoolantAccident(LOCA),orothereventsrequiringcontainmentisolation.Forasteamlinebreak,theisolationvalveswouldterminatetheblowdownofreactorcoolantinsufficienttimetopreventanuncontrolledreleaseofradioactivityfromthereactorvesseltotheenvironment.FortheLOCA,thevalveswouldisolatethereactor&omtheenvironmentandpreventthedirectreleaseoffissionproductsfromthecontainment.AlthoughtheMainSteamIsolationValves(MSIVs)aredesignedtoprovidealeak-tightbarrier,industryoperatingexperiencehasindicatedthatdegradationhasoccurredintheleak-tightnessofthesevalves.Asaresult,RegulatoryGuide1.96,"DesignofMainSteamIsolationValveLeakageControlSystemsforBoilingWaterReactorNuclearPowerPlants,"Revision0,May1975wasissuedandrecommendedtheinstallationofasupplementalleakagecontrolsystem(LCS)toensurethattheisolationfunctionoftheMSIVscompliedwiththespecifiedTechnicalSpecification(TS)leakagelimits.Tolimitdoses,aLCShasbeeninstalledonmanyBWR'stodirectanyleakagepasttheMSIV'sduringtheLOCAtoanareaservedbytheStandbyGasTreatmentSystem(SGTS).However,iftheleakageratethroughtheMSIV'sisgreatlyinexcessofthetechnicalspecificationvalue,theLCSmaynotbeeffectivebecauseoflimitationsinitsdesign.TheBWROwners'roup(BWROG)initiallyformedtheMSIVLeakageCommitteetodeterminethecauseofandsolutiontoMSIVfailuresoflocalleakratetestingbylargemargins.ThisCommitteewassubsequentlyre-formedintotheMSIVLeakageClosureCommitteetoprovideadditionalactionstoresolveon-going,butlesssevereMSIVleakageproblemsandtoaddressthelimitedcapabilityoftheLCS..InaccordancewiththesuggestionsofMJREG-1169,"TechnicalFindingsRelatedtoGenericIssueC-8;BoilingWaterReactorMainSteamIsolationValveLeakageandLeakageTreatmentMethod."thisBWROGCommitteegeneratedtypicalgenericlicensingsubmittalswhichwouldsignificantlyincreaseallowableMSIVleakageratesand,whereapplicable,eliminatetherequirementsforLeakageControlSystems.ThesesubmittalsweredocumentedinBWROGReportNEDC-31858P,Revision2entitled,"BWROGReportforIncreasingMSIVLeakageRateLimitsandEliminationofLeakageControlSystem."ThisreportconcludedthattheproposedincreaseoftheMSIVleakagelimitwillreduceradiationexposuretomaintenancepersonnel,reduceoutagedurationsandextendtheeffectiveservicelifeoftheMSIV's.ThisreportalsoconcludesthattheproposedeliminationoftheLCSwillsimilarlyreducepersonnelexposureandoutagedurations,andthatthe.9411290136PaSe10f]p k-ATTACHMENTTOPLA-4228LCScanbereplacedwithanalternatemethodfor'MSIVleakagetreatmentusingthemainstemlineandcondenser.ThisproposedalternatetreatmentmethodtakesadvantageofthelargevolumeinthemainsteamlinesandthemaincondensertoprovideholdupandplateoutoffissionproductsthatmayleakthroughtheclosedMSIV's.Thismethodusesthemainsteamdrainlinestodirectleakagetothemaincondenser.~~iTheproposedchangewould(Enclosure1):1.increasetheallowableleakageratespecifiedinTS3.6.1.2fromthecurrent11.5standardcubicfeetperhour(scfli)foranyoneMSIV,to100scfliforanyoneMSIVwithatotalmaximumpathwayleakageof300scfhthroughallfourmainsteamlines;2.addanewrequirementtoTS3.6.1.2relatedtotherestorationofacceptableleakratesifanyoftheproposedlimitsareexceeded,suchthatifanyMSIVexceeds100scfli,itwillberepairedandretestedtomeetaleakratelimitof11.5scflipervalve;3.modifyTS3.6.1.4,Tables3.6.3-1and3.8.4.2.1-1,andBases3/4.6.1.4todeletetheMSIVLeakageControlSystemfromTS;and,4.administrativelymodifytheIndex,TS3/4.6.1.4andBases3/4.6.1.4toreflectaboverequestedchanges.fnIiAnalysisTheBoilingWaterReactorOwners'rouphasevaluatedtheavailabilityofmainsteamsystempipingandmaincondenseralternatepathwaysforprocessingMainSteamIsolationValveleakage,andhasdeterminedthattheprobabilityofanearcoincidentLossofCoolantAccidentandaseismiceventismuchsmallerthanforotherplantsafetyrisks.Accordingly,thisalternateMSIVleakagetreatmentpathwaywillbeavailableduringandafteraLOCA.Nevertheless,theBWROGhasalsodeterminedthatmainsteampipingandmaincondenserdesignsareextremelyrugged,andthatthedesignrequirementsappliedtotheSusquehannaSteamElectricStation(SSES),Unit1andUnit2mainsteamsystempipingandmaincondensercontainsubstantialmargin,basedontheoriginaldesignrequirements.Inordertofurtherjustifythecapabilityofthemainsteampipingandmaincondenseralternatetreatmentpathway,theBWROGhasreviewedlimitedearthquakeexperiencedataontheperformanceofnon-seismicallydesignedpipingandcondensersduringpastearthquakes.AssummarizedinGeneralElectric(GE)Report,"BWROGReportforIncreasingMSIVLeakageRateLimitsandEliminationofLeakageControlSystem,"NEDC31858P,Revision2,submittedPage2of10 Cj~aC.~4'I1>>4 ATTACHMENTTOPLA-4228totheNRCbyBWROGletterdatedOctober4,1993,thisstudyconcludedthatthepossibilityofafailurewhichwouldcausealossofsteamorcondensateinBWRmainsteampipingorcondensersintheeventofadesignbasis(i.e.,safeshutdown)earthquakeishighlyunlikely,andthatsuchafailurewouldalsobecontrarytoalargebodyofhistoricalearthquakeexperiencedata,andthusunprecedented.WehaveevaluatedtheseismicadequacyoftheUnit1andUnit2mainsteampipingandmaincondenserwiththeguidelinesdiscussedinSection6.7ofNEDC-31858P,Revision2toprovidereasonableassuranceofthestructuralintegrityofthesecomponents.Thisevaluation,"MSIVLeakageAlternateTreatmentMethodSeismicEvaluation,forSSESUnit1andUnit2,"datedOctober19,1994isattached(Enclosure2).TheresultsoftheevaluationclearlydemonstratethattheMSIVLeakageAlternateTreatmentMethodmeetstheintentof10CFR100AppendixA,withregardtoseismicqualification.ExceptfortherequirementtoestablishaproperflowpathfromtheMSIVstothecondenser,theproposedmethodispassiveanddoesnotrequireanyadditionallogiccontrolandinterlocks.ThemethodproposedforMSIVleakagetreatmentisconsistentwiththephilosophyofprotectionbymultiplebarriersusedincontainmentdesignforlimitingfissionproductreleasetotheenvironment.Aplant-specificradiologicalanalysishasbeenperformedinaccordancewithNEDC-31858P,Revision2toassesstheeffectsoftheproposedincreasetotheallowableMSIVleakagerateintermsofControlRoomandoff-sitedosesfollowingapostulateddesignbasisLOCA.Thisanalysisutilizesthehold-upvolumesofthemainsteampipingandcondenserasanalternatemethodfortreatingtheMSIVleakage.Asdiscussedearlier,thereisreasonableassurancethatthemainsteampipingandcondenserwillremainintactfollowingadesignbasisearthquake.TheradiologicalanalysisusesstandardconservativeassumptionsfortheradiologicalsourcetermconsistentwithRegulatoryGuide(RG)1.3,"AssumptionsUsedforEvaluatingthePotentialRadiologicalConsequencesofaLoss-Of-CoolantAccidentforBoilingWaterReactor."Revision2datedApril1974.TheanalysisresultsdemonstratethatdosecontributorsfromtheproposedMSIVleakageratelimitof100scflipersteamline,nottoexceedatotalof300scfliforallfourmainsteamlines,alongwiththeproposeddeletionoftheLeakageControlSystem(LCS),resultinaninsignificantincreasetotheLOCAdosespreviouslyevaluatedagainsttheregulatorylimitsfortheoff-sitedosesandcontrolroomdosescontainedin10CFR100and10CFR50,AppendixA,GeneralDesignCriterion(GDC)19,respectively.Theoff-siteandcontrolroomdosesresultingfromaLOCAarediscussedinSection15.6.5oftheFSAR..Theoff-siteandcontrolroomdosesresultingfromaLOCAassociatedwiththeproposedchangesarethesumoftheLOCAdosesevaluatedinthepowerupraterevisiontothedesignbasisDBA-LOCAcalculation(EC-RADN-1009)andtheadditionaldosescalculatedusingthealternateMSIVleakagetreatmentmethod.Enclosure3summarizestheoff-siteandcontrolroomdosesandcomparesthealternatetreatmentmethoddosestotheoriginalMSIV-LCStreatmentmethoddoses.Page3of10 ATTACHMENTTOPLA-422SConclusionInsummary,theproposedchangesdonotresultinasignificantincreaseintheradiologicalconsequencesofaLOCAwhenthesameassumptionsandmethodsspecifiedintheFSARareused,recognizingthatradiologicalconsequencescalculatedintheFSARandfortheseproposedchangesaresignificantlyhigherthanthoseusingmorerealisticassumptionsandmethods.Thecalculatedoff-siteandcontrolroomdosesresultingfromaLOCAremainwellbelowtheregulatorylimits.7DTheproposedchangesdonot:I.Involveasignificantincreaseintheprobabilityorconsequencesofanaccidentpreviouslyevaluated.TheproposedchangestoTSSection3.6.1.2donotinvolveachangetostructures,components,orsystemsthatwouldaffecttheprobabilityofanaccidentpreviouslyevaluated.TheTSlimitsforMSIVsareincreasedfrom46scfperhourforallfourmainsteamlinesto<100scfperhourforanyoneMSIVandacombinedmaximumpathwayleakagerateof<300scfperhourforallfourmainsteamlines.Theconsequencesofanaccidentareaffectedasdiscussedinthissection.TheproposedchangestoTSSection3.6.1.4eliminatetheMainSteamIsolationValves(MSIVs)LeakageControlSystem(LCS)requirementsfromtheTS.AsdescribedinSection6.7oftheFSAR,theLCSismanuallyinitiatedinabout20minutesfollowingadesignbasisLossofCoolantAccident(LOCA).SincetheLCSisoperatedonlyafteranaccidenthasoccurred,theseproposedchangeshavenoeffectontheprobabilityofanaccident.SinceMSIVleakageandoperationoftheLCSareincludedintheradiologicalanalysisforthedesignbasisLOCAasdescribedinSection15.6.5oftheFSAR,theproposedchangesdonotaffecttheprecursorsofotheranalyzedaccidents.Analysisoftheeffectsoftheproposedchangesdo,however,resultinacceptableradiologicalconsequencesforthedesignbasisLOCApreviouslyevaluatedinSection15.6.5oftheFSAR.SSES,Units1and2haveaninherentMSIVleakagetreatmentcapabilityasdiscussedbelow.WeproposetousethedrainlinesassociatedwiththemainsteamlinesandmainturbinecondenserasanalternativetotheguidanceinRegulatoryGuide1.96,"DesignofMainSteamIsolationValveLeakageControlSystemForBoilingWaterNuclearPowerPlants",Revision0,May1975,forMSIVleakagetreatment.Ifapproved,wewillincorporatethisalternatemethodintheappropriateoperationalproceduresandEmergencyOperatingProcedures.Page4of10 ATTACHMENTTOPLA-4228TheBoilingWaterReactorOwners'roup(BWROG)hasevaluatedtheavailabilityofmainsteamsystempipingandmaincondenseralternatepathwaysforprocessingMSIVleakage,andhasdeterminedthattheprobabilityofanearcoincidentLOCAandaseismiceventismuchsmallerthanforotherplantsafetyrisks.Accordingly,thisalternateMSIVleakagetreatmentpathwayisavailableduringandaAeraLOCA.Nevertheless,theBWROGhasalsodeterminedthatmainsteampipingandmaincondenserdesignareextremelyrugged,andthedesignrequirementsappliedtoSSESUnit1andUnit2mainsteamsystempipingandmaincondensercontainsubstantialmargin,basedon'heoriginaldesignrequirements.Therefore,thealternatetreatmentmethodhasbeenevaluatedforitscapabilitytomitigatetheconsequencesofaLOCA,andhasbeenevaluatedtoassureitsavailabilityconsideringaseismicevent.Inordertodeterminethecapabilityofthemainsteampipingandmaincondenseralternatetreatmentpathway,theBWROGhasreviewedearthquakeexperiencedataontheperformanceofnon-seismicallydesignedpipingandcondensersduringpastearthquakes.ThedataissummarizedinGeneralElectric(GE)Report,"BWROGReportforIncreasingMSIVLeakageRateLimitsandEliminationofLeakageControlSystems,"NEDC31858P,Revision2,submittedtotheNRCbyBWROGletterdatedOctober4,1993.ThisstudyconcludedthatthepossibilityofafailurethatcouldcausealossofsteamorcondensateinBoilingWaterReactor(BWR)mainsteampipingorcondensersintheeventofadesignbasis(i.e.,safeshutdown)earthquakeishighlyunlikely,andthatsuchafailurewouldalsobecontrarytoalargebodyofhistoricalearthquakeexperiencedata,andthusunprecedented.AverificationhasbeenperformedoftheseismicadequacyoftheUnit1andUnit2mainsteampipingandmaincondenserconsistentwiththeguidelinesdiscussedinSection6.7ofNEDC-31858P,Revision2,toprovidereasonableassuranceofthestructuralintegrityofthesecomponents.Anevaluation,includingthewalkdownreportoutliers,"MSIVLeakageAlternateTreatmentMethodSeismicEvaluation,"forUnit1andUnit2,isattached.TheresultsoftheevaluationclearlydemonstratethattheMSIVLeakageAlternateTreatmentMethodmeetstheintentof10CFR100AppendixA,withregardstoseismicqualification.ExceptfortherequirementtoestablishaproperflowpathfromtheMSIVstothecondenser,theproposedmethodispassiveanddoesnotrequireanyadditionallogiccontrolandinterlocks.ThemethodproposedforMSIVleakagetreatmentisconsistentwiththephilosophyofprotectionbymultiplebarriersusedincontainmentdesignforlimitingfissionproductreleasetotheenvironment.Aplant-specificradiologicalanalysishasbeenperformedinaccordancewithNEDC-31858P,Revision2,toassesstheeffectsoftheproposedincreasetotheallowableMSIVleakagerateintermsofcontrolroomandoff-sitedosesfollowingapostulateddesignbasisLOCA.Thisanalysisutilizesthehold-upvolumesofthemainsteampipingandcondenserasanalternatemethodfortreatingtheMSIVleakage.Asdiscussedearlier,thereisreasonableassurancethatthemainsteampipingandcondenserremainintactfollowingadesignbasisearthquake.TheradiologicalanalysisusesstandardconservativeassumptionsfortheradiologicalsourcetermconsistentwithRegulatoryPage5of10 ATTACHMENTTOPLA-4228Guide(RG)1.3,AssumptionsUsedforEvaluatingthePotentialRadiologicalConsequencesofaLoss-Of-CoolantAccidentforBoilingWaterReactor,Revision2,datedApril1974.TheanalysisresultsdemonstratethatdosecontributionsfromtheproposedMSIVleakageratelimitof100scfhpersteamline,nottoexceedatotalof300scfhforallfourmainsteamlines,andfromtheproposeddeletionoftheLCS,resultinaninsignificantincreasetotheLOCAdosespreviouslyevaluatedagainsttheregulatorylimitsfortheoff-sitedosesandcontrolroomdosescontainedin10CFR100and10CFR50,AppendixA,GeneralDesignCriterion.(GDC)19,respectively.Theoff-siteandcontrolroomdosesresultingfromaLOCAarediscussedinSection15.6.5oftheFSAR.Theoff-siteandcontrolroomdosesresultingfromaLOCAassociatedwiththeproposedchangesarethesumofLOCAdosesevaluatedinthepowerupraterevisiontothedesignbasisDBA-LOCAcalculation(EC-RADN-1009)andtheadditionaldosescalculatedusingthealternateMSIVleakagetreatmentmethod.Enclosure3summarizestheoff-siteandcontrolroomdosesandcomparesthealternatetreatmentmethoddosestotheoriginalMSIV-LCStreatmentmethoddoses.The30-daywholebodydosesattheLowPopulationZone(LPZ)didnotchangeandremainedat.37remforthealternatetreatmentmethod.The30-daycontrolroomwholebodydosesincreasedslightlyfrom.38remto.76remforthealternatetreatmentmethod.Theincreaseincontrolroomdoseisnotsignificantsincethereviseddosesarewellbelowtheregulatorylimits,i.e,76remcalculatedversusthelimitof5reminthecontrolroom.Thetwo-hourwholebodydoseattheExclusionAreaBoundary(EAB)decreasedslightlyfrom2.47remto2.217rem.The30-daythyroiddoseattheLPZincreasedfrom30.4remfortheMSIV-LCStreatmentmethodto41.74remforthealternatetreatmentmethod.Thisincreaseisnotsignificantsincethereviseddoseof41.74remiswellwithintheregulatorylimitof300rem.Thetwo-hourthyroiddoseattheEABdecreasedslightlyfrom127.8remto125.61rem.The30-daycontrolroomthyroiddoseincreasedfrom14.19remfortheMSIV-LCStreatmentmethodto18.55remforthealternatetreatmentmethod.Theincreasedcontrolroomthyroiddoseisnotsignificantsincethereviseddoseremainswellbelowtheregulatorylimitof30rem.The30-daycontrolroombetadoseincreasedinsignificantlyfrom12remfortheMSIV-LCStreatmentmethodto12.17remforthealternatetreatmentmethod,remainingasmallfractionrelativetothelimitof75rem.Insummary,theproposedchangesdiscussedabovedonotresultinasignificantincreaseintheradiologicalconsequencesofaLOCAwhenthesameassumptionsandmethodsspecifiedintheFSARareused,recognizingthatradiologicalconsequencescalculatedintheFSARandfortheseproposedchangesaresignificantlyhigherthanthoseusingmore=realisticassumptionsandmethods.Nevertheless,thecalculatedoff-siteandcontrolroomdosesresultingfromaLOCAremainwellbelowtheregulatorylimits.Page6of10 ATTACHMENTTOPLA-4228Theproposedchangeto.TSTable3.6.3-1deletestheLCSvalvesfromthelistofprimarycontainmentisolationvalves.ThisproposedchangeisconsistentwiththeproposeddeletionoftheLCS.TheLCSlinesthatareconnectedtothemainsteampipingareweldedand/orcappedclosedtoassureprimarycontainmentintegrityismaintained.TheweldingandpostweldexaminationprocedureswillbeinaccordancewithAmericanSocietyofMechanicalEngineers(ASME)Code,SectionIIIrequirements.Theseweldsand/orcapswillbeperiodicallytestedaspartoftheContainmentIntegratedLeakRateTest(CILRT).ThisproposedchangedoesnotinvolveanincreaseintheprobabilityofequipmentmalfunctionpreviouslyevaluatedintheFSAR.Infact,thisproposedchangereducestheprobabilityofequipmentmalfunctionsince,uponimplementationoftheseproposedchanges,theplantwillbeoperatedwithlessprimarycontainmentisolationvalvessubjectedtopostulatedfailure.ThisproposedchangehasnoeffectontheconsequencesofanaccidentsincetheLCSlineswillbeweldedand/orcapclosed,thusassuringthatthecontainmentintegrity,isolationandleaktestcapabilityarenotcompromised.TheproposedchangetoTSTable3.8.4.2.1-1deletestheLCSmotoroperatedvalvesfromthelistof"MotorOperatedValvesThermalOverloadProtection-Continuous."Theproposedchangehasnoeffectontheprobabilityorconsequencesofanaccidentsincethevalvesareeliminatedand.notperformingasafetyfunction.Therefore,asdiscussedabove,theproposedchangesdonotinvolveasignificantincreaseintheprobabilityorconsequencesfromanyaccidentpreviouslyevaluated.Createthepossibilityofanewordifferentkindofaccidentfromanyaccidentpreviouslyevaluated.AsstatedinSectionI,theproposedchangesdonotinvolveachangetostructures,components,orsystemsthatwouldaffecttheprobabilityofanaccidentpreviouslyevaluated,norwouldthesechangescreateanynewordifferentkindofaccidentfromanypreviouslyevaluated.Theproposedchangeswillintroduceandtakecreditforanewlevelofoperationalperformanceforexistingplantsystemsandcomponentstomitigatetheconsequencesoftheaccident.Theeffectonthisequipmenthasbeenevaluatedandfoundtoprovideanacceptablelevelofreliabilityresultingintherequiredlevelofprotection.ThisconclusionisbasedontheevaluationperformedinNEDC31858P,Revision2,andtheplantspecificseismicevaluationprovidedintheEnclosure2,"MSIVLeakageAlternateTreatmentMethodSeismicEvaluation."TheLeakageControlSystemhasbeeninstalledtodirectanyleakagepasttheMSIVsduringtheLOCA;actingaftertheaccidenthasoccurred.TheresultingconsequencesoftheevaluatedaccidentshavebeenaffectedasdiscussedinSectionIresultinginnosignificantincreaseintheprobabilityorconsequencesofsaidaccident.Therefore,relianceondifferentequipmentthanpreviouslyassumedtomitigatetheconsequencesofanaccidentdoesnotcreatethepossibilityofanewordifferentkindofaccidentfromanyaccidentpreviouslyevaluated.Page7of10
,\
ATTACHMENTTOPLA-4228TheBWROGevaluatedMSIVperformanceandconcludedthatMSIVleakageratesupto200scfhpervalvewillnotinhibitthecapabilityandisolationperformanceoftheMSIVstoeffectivelyisolatetheprimarycontainment.ImplementationoftheproposedchangesdoesnotresultinmodificationswhichcouldadverselyimpacttheoperabilityoftheMSIVs.TheLOCAhasbeenanalyzedusingthemainsteampipingandmaincondenserasatreatmentmethodtoprocessMSIVleakageattheproposedmaximumrateof100scfhpermainsteamline,nottoexceed300scfhtotalforallfourmainsteamlines.Therefore,theproposedTSSection3.6.1.2changetoincreasetheallowedMSIVleakageratedoesnotcreateanynewordifferentkindofaccidentfromanyaccidentpreviouslyevaluated.TheproposedTSSection3.6.1.4changetoeliminatetheLCSdoesnotcreatethepossibilityofanewordifferentkindofaccidentfromanyaccidentpreviouslyevaluatedbecausetheremovaloftheLCSdoesnotaffectanyoftheremainingSSESUnit1andUnit2systems,andtheLOCAhasbeenre-analyzedusingtheproposedalternatemethodtoprocessMSIVleakage.TheassociatedproposedchangetodeletetheLCSisolationvalvesfromTSTable3.6.3-1andTable3.8.4.2.1-1doesnotcreatethepossibilityofanewordifferentkindofaccident.Theaffectedmainsteampipingwillbeweldedand/orcappedclosedtoassurethattheprimarycontainmentintegrity,isolation,andleaktestingcapabilityarenotcompromised.TheaffectedLCSmotoroperatedvalveswillbeeliminatedsotheirthermaloverloadswillnotneedtobebypassed.Therefore,asdiscussedabove,theproposedchangesdonotcreatethepossibilityforanynewordifferentkindofaccidentfromanyaccidentpreviouslyevaluated.Involveasignificantreductioninamarginofsafety.TheproposedchangetoTSSection3.6.1.2toincreasetheMSIVallowableleakagedoesnotinvolveasignificantreductioninthemarginofsafety.AsdiscussedinthecurrentBasesforTSSection3/4.6.1.2,theallowableleakratelimitspecifiedfortheMSIVsisusedtoquantifyamaximumamountofleakageassumedtobypassprimarycontainmentintheLOCAradiologicalanalysis.Accordingly,resultsofthere-analysissupportingtheseproposedchangesareevaluatedagainstthedoselimitscontainedin10CFR100fortheoff-sitedoses,and10CFR50,AppendixA,GDC19,forthecontrolroomdoses.Asdiscussedabove,sufficientmarginrelativetotheregulatorylimitsismaintainedevenwhenassumptionsandmethods(e.g.,RG1.3)thatareconsideredhighlyconservativerelativetomorerealisticassumptionsandmethodsareusedintheanalysis.Resultsoftheradiologicalanalysisdemonstratethattheproposedchangesdonotinvolveasignificantreductioninthemarginofsafety.Wholebodydoses,intermsofmargin'ofsafety,areinsignificantlyreducedby.38reminthecontrolroom.ThemarginofsafetyremainsconstantfortheLPZwholebodydoseoractuallyincreasesby.253remfortheEABwholebodydose.Themarginofsafetyforthyroiddosecategoryisreducedby11.34remattheLPZand4.36reminthecontrolroom.ThemarginofsafetyisfoundtoPage8of10 ATTACHMENTTOPLA-4228increasefortheEABthyroiddoseby2.19rem.Themarginofsafetyforbetadoseisinsignificantlyreducedby.17reminthecontrolroom.Thereductionsinthemarginofsafetyarenotsignificantsincetherevisedcalculateddosesarehighlyconservativeyetremainwellbelowtheregulatorylimits,andtherefore,asubstantialmargintotheregulatorylimitsismaintained.TheproposedchangetoeliminatetheLCSfromTSSection3.6.1.4doesnotreducethemarginofsafety,infact,theoverallmarginofsafetyisincreased.ThefunctionoftheLCSforMSIVleakagetreatmentwillbereplacedbyalternatemainsteamdrainlinesandcondenserequipment.ThistreatmentmethodiseffectiveinreducingthedoseconsequencesofMSIVleakageoveranexpandedoperatingrangecomparedtothecapabilityoftheLCSandwill,thereby,resolvethesafetyconcernthattheLCSwillnotfunctionatMSIVleakagerateshigherthantheLCSdesigncapacity.ExceptfortherequirementtoestablishaproperflowpathfromtheMSIVstothecondenser,theproposedmethodispassiveanddoesnotrequireanynewlogiccontrolandinterlocks.Thisproposedmethodisconsistentwiththephilosophyofprotectionbymultiplebarriersusedincontainmentdesignforlimitingfissionproductreleasetotheenvironment.Furthermore,aspreviouslyidentified,basedontheevaluationsdiscussedinNEDC-31858P,Revision2,andtheseismicevaluationprovidedintheEnclosure2report,"MSIVLeakageAlternateTreatmentMethodSeismicEvaluation,"thedesignoftheMSIVleakagealternatedrainpathway,meetstheintentofthe10CFR100,AppendixArequirementforseismicqualification.Therefore,theproposedmethodishighlyreliableandeffectiveforMSIVleakagetreatment.TherevisedcalculatedLGCAdosesremainwithintheregulatorylimitsfortheoff-siteandthecontrolroom.Therefore,theproposedmethodmaintainsamarginofsafetyformitigatingtheradiologicalconsequencesofMSIVleakagefortheproposedTSleakageratelimitof100scflipermainsteamline,nottoexceedatotalof300scfliforallfourmainsteamlines.TheproposedchangetodeleteLCSisolationvalvesfromTSTable3.6.3-1andTable3.8.4.2.1-1doesnotreducethemarginofsafety.Weldedand/orcappedclosureoftheLCSlinesassuresthattheprimarycontainmentintegrityandleaktestingcapabilityarenotcompromised.Theseweldsand/orcapswillbeperiodicallyleaktestedaspartoftheCILRT.TheLCSmotoroperatedvalveswillbeeliminatedsotheirthermaloverloadswillnotneedtobebypassed.Therefore,theproposeddeletionoftheLCSisolationvalvesdoesnotinvolveareductioninthemarginofsafety.ThisrequestisconsistentwiththeSusquehannadesignbasis,inthattheproposedchangesofincreasingallowableMSIVleakagerateandreplacingtheMSIV/LCSwithanalternatetreatmentmethodwillresultinnosignificantchangestotheLOCAradiologicalanalysiswhilecontinuingtoreducedoseconsequencesassociatedwithMSIVleakageoveranexpandedoperatingrange.Page9of10 ATTACHMENTTOPLA-4228Therefore,noenvironmentalconsequencesthathavenotbeenpreviouslyconsideredareanticipated.ThemodificationsassociatedwiththisproposedchangearecurrentlyscheduledtobeperformedduringtheUnit27th,andtheUnit19thRefuelingandInspectionOutages.Asaresult,werequestNRCtocompleteitsreviewnolaterthanMay26,1995,withtheconditionthattheamendmentbecomeeffectiveuponunitrestart.Page10of10