ML18040A227

Nuclear Engineering Rept, Nine Mile Point Unit 1 Shroud Cracking Safety Assessment for GL 94-03.

ML18040A227
Person / Time
Site:	Nine Mile Point
Issue date:	08/19/1994
From:	INCH G B, KIRCHNER R F, YAEGER W NIAGARA MOHAWK POWER CORP.
To:
Shared Package
ML17059A420	List: ML17059A419 ML18040A227
References
GL-94-03, GL-94-3, NER-1M-014, NER-1M-14, NUDOCS 9409010263
Download: ML18040A227 (74)

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NIAG2GMMOHAWKPONERCORPORATIONNUCLEARENGINEERINGREPORTNINEMILEPOINT1SHROUDCRACKINGSAFETYASSESSMENTFORGENERICLETTER94-03REPORTNO.NER-1M-014PrincipalContributors:Reviewedby:G.B.InchR.F.KirchnerM.S.LeonardR.CorieriD.L.PikeT.D.LeeA.G.VierlingApprovedby:aerManager,Unit1Engineeringate9409010263940823PDRADOCK050002201P,PDRL 0rI TableofContentsSectionExecutiveSummary1.0Introduction2.0SusceptibilityAssessment3.0StructuralMarginAssessment4.0ShroudDisplacementLikelihood5.0IntegratedShroudAssessment6.0Conclusions7.0ReferencesFigures1-1ShroudWelds1-2DetailTopGuideFlange1-3DetailCorePlateFlange1-4DetailShroudtoShroudSupportJoint2-1ReactorWaterConductivityMeanValuesTables2-1ShroudMaterialTypes2-2NineMilePoint1WaterChemistryHistory2-3NineMilePoint1ShroudWeldsEstimatedFluence2-4NineMilePoint1ShroudVisualInspectionsAppendicesPage121314151623341189910A)AnalysisoftheHSweldshroudringtoinconelsupportconeB)ProbabilisticSafetyAssessmentofPotentialIGSCCshroudweldfailure

~r ExecutiveSummaryTheNineMilePoint1safetyassessmentutilizestheBWRVesselInternalsProject(BWRVIP)genericassessmentandreviewsanydiffezencesinshroudcrackingsusceptibilityincluding:availableNineMilePoint1shroudinspections,shroudfabrication,waterchemistry,shroudmaterialcarboncontent,neutronfluenceandon-lineyearsspecifictoNineMilePoint1.ThegenericBWRVIPassessmentestablishesthatthelikelihoodofupto360degreecrackingatsomedepthisfairlyhighfortheH1throughH7shroudwelds.Thestructuralmarginassessment,assuming360degreecracking,determinesthatitisunlikelythatanycracksexceed90%depthattheH1throughH7locations.ThevisualinspectionsavailableforH1,H2,H3,H4andH7supportthisconclusion.TheoverallstructuralmarginassessmentconsiderstheuncertaintiesinthedegreeofcrackingandrecommendsthattheOysterCreekshroudinspectionresults,scheduledtobecompletedOctober1994,beusedtoassesstheuncertaintyinestimatingthepotentialshzoudcrackingdepthfortheHlthroughH7welds.TheNineMilePoint1specificsafetyassessmentreviewsindetailtheshroudringtoinconelconeweld(H8)forNineMilePoint1sincefailureofthisweldhadbeenpostulatedtopotentiallydegradethecorespraysystemduringthedesignbasisrecirculationlineLOCA.ThisanalysisdemonstratesthatintezgranularstresscorrosionCracking(IGSCC)crackingalongtheH8weldisextremelyunlikely.TheASMEXIinspectionsoftheH8weldperformedduringthe1993refueloutage,wereconductedintheareaswherethiscrackingispredictedtoinitiate.Surfacecrackingwasnotobserved.Therefore,failureoftheH8weldpriortoFebruary1995(i.e.,360degreethrough-wallcracks)isnotconsideredcredible.Theabilityoftheplantsafetyfeaturestoperformtheirdesignbasisfunctions,assuming360degreethrough-wallcracks,isreviewedwiththeconclusionthatforthelimitingmainsteamlinebreakandrecirculationlinebreak,controlrodinsertionisnotexpectedtobeimpactedandcorespraywouldperformitsdesignbasisfunction.TheseconclusionsazebasedonpreliminaryanalysesregardingtherecirculationasymmetricloadsandpreliminarydetailedmainsteamlinebreakanalysesforwhichBWRVIPassessmentcommitteedetailedanalysesareinprogress.Inaddition,apzobabilisticsafetyassessmentconsideringtheprobabilityofadesignbasiseventcoupledwithshroudweldfailureisperformed.Thisassessmentdeterminesthattheoverallinczementalcozedamageandlarge/earlyreleasefrequencyislessthan8.3E-8peryearorapproximately4E-8foraperiodbetweennowandthescheduledFebruary1995refuelingoutage.TheNineMilePoint1safetyassessmentsupportscontinuedoperationuntilthescheduledFebruary1995refueloutagebasedontheextremelylowprobabilitythatthecoreshroudwouldfailtomeetitsdesignbasisstructuzalintegritymarginduringthistimeperiod.This,coupledwiththeextzemelylowoverallprobabilisticriskestimate,supportscontinuedoperationuntilthescheduledFebruaryrefueloutage.

C 1.0Introduction1.1PurposeThepurposeofthissafetyassessmentistorespondtoGenericLetter(GL)94-03,whichrequestedasafetyanalysissupportingcontinuedoperationofNineMilePoint1untilthescheduledFebruary1995refueloutage.1.2ScopeThisNineMilePoint1specificshroudcrackingsafetyassessmentusestheBWRShroudCrackingGenericSafetyAssessment'ubmittedtotheNRCthroughtheBWRownersgroup.As,requestedinGL94-03,thissafetyassessmentincludesdetailsoftheconditionsthatinfluencetheprobabilityofoccurrenceofcrackingandtherateofcrackgrowthatNineMilePoint1.Basedonthisinformation,thelikelihoodofshroudcrackinginexcessoftherequiredstructuralmarginsisassessedandtheuncertaintyintheextentofcrackingisreviewedandifappropriate,correctiveactionsidentified.ThesafetyassessmentincludesapzobabilisticsafetyassessmenttodefinetheNineMilePoint1overallriskassumingshroudweldfailure.Inaddition,theshroudresponsetodesignbasisloadsassuming360degreethrough-wallcrackingandtheabilityoftheplantsafetyfeaturestoperformtheirdesignbasisfunctionsarereviewed.ThissafetyassessmentprovidesthebasisforcontinuedoperationofNineMilePoint1consideringtheuncertaintyintheextentofcrackingoftheshroudweldsidentifiedinFigure1-1.1.3ShroudFunctionandWeldDesignationsTheshroudisastainlesssteelcylindricalassemblythatprovidesapartitionbetweenthecozeregionandthedowncomerannulus,toseparatetheupwardflowofcoolantthzoughthecorefromthedownwardrecirculationflow.Theshroudalsoprovides,inconjunctionwithothercomponents,aeoolablecoregeometry.NineMilePoint1reliesoncorespraycoolingfoztherecirculationlineLOCAanddoesnotrequiretheshroudtomaintainafloodablegeometryfollowingapostulatedrecirculationlinebreak(i.e.bottomentryrecirculationlinesprecludeafloodableregion).Theshroudisnotaprimarypressureboundarycomponent.ThefollowingaretheNineMilePoint1shroudwelddesignations,alsoshowninFigures1-1,1-2,1-3and1-4.H1,H2:H3:H4,H5:H6A,H6B:H7:H8:H9:Upperwelds,withH1aboveandH2belowtheemergencycorecoolingsystem(ECCS)injection.UpperweldlocatedbelowthebottomofthetopguidesupportringMid-planeweldslocatedabovethecoreplateTheweldslocatedjustaboveandbelowthecozeplateLowershroudtoshroudsupportringweldInconel182weldbetween304SSshroudsupportringtoinconelshroudsupportconeShroudSupportConetoVesselWeld 1

UPPERRINGUPPERCYLINOERCENTRALRINGCENTRALUPPERCYLINOERCENTRALHIDCYLINOERSEEFIGURE1-2H3H4CENTRALLOWERCYLINOERH5LOWERRINGLOWERCYLINOERH7SEEFIGURE1-4HSAHGBSEEFIGURE1-3SHROUOSUPPORTRINGINCONELSHROUDSUPPORTSKIRTFIGUREI-ININEMILEPOINTISHROUDWELDS

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H2CENTRALRING(TOPGUIDEFLANGE)H3FIGURE1-2DETAILTOPGUIDEFLANGELOWERRING(COREPLATEFLANGE)HBBFIGURE1-3DETAILCOREPLATEFLANGE J'I LOSERSHROUDCYLINDERSEEDETAILGH7WELDSHIM(IFNECESSARY)TOOBTAINALIGNMENT179'HROUDO.D.5/16MIN.RI/217NNULUS213'ESSEL1.0.FIELDWELDSEEDETAILGB8GC3/16FLOWBAFFLEI/4FIELDWELDSFENOTESBELOW3/8MAXGAPALLOWEOH8WELDCONESKIRTSB168RI/2I'/2REF.SUPPORTRINGFORGING(SA336F8)DETAILGANOTES:I.JWELDINTOLEDGEJOINEDWITH3/16FILLETWHERELEDGESIZEPERMITTED.OTHERWISEBLENDOFWELDINTOLEDGEWASREOUIRED.2.FLOWBAFFLEFABRICATIONBYP.F.AVERY.SUPPORTRING/INCONELCONESKIRTFABRICATEDBYCOMBUSTIONENGINEERING3.ALLFIELDWELDSHOWNHEREREQUIREDWELDINGELECTRODESPERASTMA298E308ORASTMA37IER308,EXCEPTFORH8SHOPWFLD.HBWELDISINCONEL182,37I/2'EF.MIN.RPVSHELL(SA302GRB)INSIDE-1.50S(74.50S)74.00I.oo-l3II/I6lo755002XR.3I~25ISI80.62BACKOROOVETOSOUNDMETAL5WELD-II-09R.37S(69,00S(70.00~252X,15'ETAILGSI80.62DETAILGBDETAILGCFlGUREI-4DETAILSHROUDTQSHROUDSUPPORTJOINT

2.0SusceptibilityAssessment2.1OverviewTheBWRShroudCrackingGenericSafetyAssessment'rovidedadiscussionofthefactorswhichcontributetothesusceptibilityofashzoudtostresscorrosioncracking(IGSCC).Thesusceptibilitycriteriaappliedinrefezence1,SIL0572,Rl'ndtheBWROwnersGroup(BWROG)BWRCozeShroudEvaluation'rewaterchemistry,materialcarboncontent,fabricationhistory,neutronfluenceandhotoperatingtimeThegenericassessmentrecognizedthatfactorssuchasdegreeofcoldworkandweldresidualstressaresignificantfactorsaffectingsusceptibility;however,sincequantitativeinformationwasnotavailablethesefactorswerenotincluded.TheNineMilePoint1plantspecificreviewofsusceptibilitydiscussestheabovefactorsincludingresidualstress,andavailablevisualinspectioninformation.2.2NineMilePoint1ShroudInspectionsThegenericassessment'iscussedtheinspectionrecommendationsofSIL0572,Rl'ndtheBWROGBWRCoreShroudEvaluation'ndprovidedbothaqualitativesummaryoftheinspectionresultsandaquantitativesummaryofdegreeofcrackingversusinitialfivecyclemeanconductivityandcrackingversusnumberofon-lineyears(hotoperatingtime).Thisinformation,coupledwiththesusceptibilitygroupingfactors,wasusedtoestablishthepotentialshroudweldsfor360degreecracking.NineMilePoint1wasclassifiedinthegenericassessmentinthelastgrouping,304SSshroudswithweldedplateringsandhighestconductivity.Thelikelihoodof360degreecrackingforthisgroupingwasconsideredfairlyhigh,however,crackinggreatezthan90%through-wallwasconsideredunlikelyintheshortterm.WhileNineMilePoint1hasnotcompletedinspectionsinaccordancewithSIL0572,Rl,visualinspectionsofweldsH7andHShavebeenperformedasrequiredbyASMECodeSectionXIvisualinspectionexaminationcategoryB-N-1,ItemB13.40,"CoreSupportStructure."TheseinspectionssatisfytherequirementsofSIL0572,Rlwiththeexceptionthatnopriorcleaningoftheweldswasperformed.Inaddition,visualsofshroudweldsH1,H2,H3andH4doexistasaresultofaccessstudiesperformedin1989.ThelightingprovidedwastothelevelneededfozverificationofaccessanddidnotmeettherequirementsofSIL0572R1;however,theweldswereclearlyvisible.Thecameraresolutionlevelwasasneededtogageaccessibility.Nopriorcleaningwasperformed.TheshroudvisualinspectionsaresummarizedinTable2-4.NiagaraMohawkisactivelyparticipatingintheeffortsoftheBWRVIPinspectionsubcommitteetodevelopstandardizedvisualinspectioncriteria.Thesestandardizedinspectioncriteriawillincludequalificationofexaminationpersonnelthroughshroudspecificexperienceandon-the-jobtraining.Inthisregard,theinspectiontapessummarizedinTable2-4havebeenreviewedbyanNMPCLevelIIIqualifiedexaminezconcurrentlywithaGElevelIIIqualifiedexaminer,whoparticipatedintheexaminationactivitiesatbothQuad 4I CitiesandDresdenandwhoisqualifiedtotheenhancedlevelproposedbythenewstandards.Bothexaminersconcludedthattherewasnoevidenceofcrackingatthelocationsinspected.2.3BasisForRankingNineMilePoint1ShroudfieldsANineMilePoint1specificreviewofthefabricationhistory,waterchemistry,materialcarboncontent,neutronfluence,andonlineyearshasbeencompletedandisprovidedbelow.2.3.1FabricationHistoryThegenericassessment'dentifiestheshroudweldlocationsexhibitingthegreatestextentofcircumferentialcrackingastheringtoshellwelds,i.e.H1,H2,H3,andH6A,H6B.Thehighestsusceptibilitywaslinkedtothefabricationofringscutfromrolledplateandweldedintoaringconfiguration,followedbymachiningtosize.TheNineMilePoint1shroudrings,withtheexceptionoftheshroudsupportring,azeweldedplaterings(seeFigures1-1and1-2).Table2-1hasthedetailsoftheshroudmaterials.ThefabricationrecordsindicatethattheNineMilePoint1shroudsandtheOysterCreekshroudswerefabricatedbyP.F.Averyduringthesametimeperiod.Aspecificbreakdownbetweenthetwoshroudsofwhichspecificitemswentintoeachshroudcouldnotbefound,soalltheheatnumbersrelatedtoeachpartnumberareidentifiedinTable2-1.AllshopP.F.AveryweldsweresubmergedarcweldsusingASTMA-371TypeER-308fillermetalwith5%minimumferritecontentandamaximuminterpasstempezatuzeof350degreesF.Theshroudsupportringisaforged304SSring,however,forNineMilePoint1theH7andHSweldstotheforgedringhaveaplantspecificsusceptibilitybecausetheshroudsupportringforgingwassensitizedduringtheinitialvesselheattreatment.TheH7weldisafieldweldwhichwasnotstressrelievedandthereforeisconsideredtobesuceptabletoIGSCCczackingduetohigherweldstressesandsensitizedbasematerial.ThesusceptibilitytocrackinitiationandcrackgrowthratefoztheH7weldisconsideredsimilartothatusedfoztheweldedplatezingevaluations(HlthroughH6).TheHSlocationsusceptibilityisdiscussedindetailinAppendixA.TheAppendixAanalysisconcludesthatIGSCCthroughtheheataffectedzone(HAZ)oftheHSweldisextremelyunlikelybecausetheresidualstresseswererelievedforthisweldduringtheinitialvesselheattzeatment,andbecausetheHSweldisgenerallycompressiveduringoperation.Inaddition,theAppendixAanalysispredictsthatIGSCCcrackingatHSwouldinitiateattheODsurfaceduetothehighesttensilestressesbeinglocatedontheOD.TheASMEXIinspectionoftheODofHSrevealednoindications.Theinconelshroudsupportconetovesselashroudweldinthisassessment.Thisisconewhichisnotcrevicedandwasstresspostweldheattreatment.Thisplacestheresistantcategorywhichallowsthisweldfurtherdiscussioninthisreport.weld(H9)isnotconsideredaninconelweldtoinconelrelievedduringthevesselweldinamuchmoreIGSCCtobeeliminatedfrom

2.3.2WaterChemistryThegenericassessment'dentifiesthemeanconductivityforthefirstfivecyclesasafactorfozsusceptibilitygrouping.Figure2-1andTable2-2providetheNineMilePoint1specificcyclemeanconductivities.ThisconductivityplacesNineMilePoint1inthesusceptiblecategoryforwhichIGSCCcrackinginweldedplateringweldsislikelytooccur.2.3.3MaterialCarbonContentThegenericassessment'dentifiesthecarboncontentasafactorinsusceptibilitygrouping,with304shroudsbeingmoresusceptiblethan304L.TheNineMilePoint1shroudmatezialis304,withthespecificmaterialcarboncontentidentifiedinTable2-1.2.3.4NeutronFluenceThegenericassessment'idnotselectfluenceasaprimarycontributortoextensivecracking.However,afluenceeffectoncrackingsusceptibility(IASCCatf>3-5E20nvt)orasynergisticinteractionoffluence.inalreadysensitizedmaterial(IGSCCatf>1E19nvt)isexpectedandwasverifiedatBrunswick-1andKKM.TheNineMilePoint1specificfluenceateachweldlocationisprovidedinTable2-3.2.3.5On-LineYearsConsistentwiththegenericassessment',on-lineyearswasusedtoestimatehotoperatingtime.NineMilePoint1on-lineyearsis14.4years.Thegenericassessmentdidnotusehotoperatingtimetogrouptheplants,however,theinspectiondatatodateindicatesthatcrackinginexcessof180degreeswasunlikelyuntilaplantaccumulated10on-lineyears.2.4EstimatedIGSCCSusceptibilityforNineMilePoint1Consistentwiththegenericassessment',thelikelihoodof360degreecrackingatsomedepthisfairlyhigh.Thelikelihoodof360degreecrackingtodepthsapproachinganalysisallowablesisconsideredunlikelyandisdiscussedinSection3.

0TABLE2-1SHROUDMATERIALTYPESPARTNUMBERPARTNAMEQUANTITYTYPEMATERIALHEATNUMBERCARBONCOMMENTSONCONTENT-/MATERIAL/PROCESS1UPPERRING2PIECESA248TYPE38465444-1.864PLATE2UPPERCYLINDER2PIECES3CENTRALRING2PIECESA248TYPE384A248TYPE38465235-IA65235-1865294-1.842~842.856CENTRALUPPER2PIECESCYLINDERCENTRALMIDCYLINDER2PIECESCENTRALLOWER2PIECESCYLINDERA248TYPE384A248TYPE384A248TYPE38465235-165291-lA848784-265298-165295-165298-lA848784-28848784-2A65291-1.842.852.853.847.862'847.853~853~8527LOWERRING2PIECESBLOWERCYLINDER2PIECESA248TYPE384A248TYPE38465444-165291-1848784-2A848784-2B.864~852.853.853SHROUDSUPPORTRING1PIECEASMESA-336FS65298-1AG-23/245352,847NOTKNOWNFORGINGNINEMILEPOINTUNITISHROUDDATANOTES:I.HEATNUMBERDATASHOWNMAYBEAPPLICABLEFORNINEMILEPOINTIANO/OROYSTERCREEK.

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Table2-2NineMilePointj.WaterChemistryHistory.,'::::.".::Cycle.'::::'.:,'.'.:,,'-;::.:::::,-':Mea'ri";:".;,.Va'3u~(j:,'::::.j',;:-',;:.Co'ndue't':i;:v'i.'t'y'.,':.';:.'k,'::,'Ch:1'o'r'i'de',(100.4320.5250.5910.4450.2910.2250.1810.1330.0870.0820.084304658443327262518Table2-3ShroudWeldEstimatedFluenceEstimatedFluences(n/cm',E)lMev)H1H2H3H4H5H6AH6BH78.7E+094.6E+104.0E+117.8E+118.1E+116.2E+072.0E+07<<1.0E+074E+182E+192E+203.5E+203.6E+203E+169E+15<<4E+15BaseonprogecteEFPDatEOCCyce11(EOCCycle11February1995)

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Table2-4ShroudVisualInspectionsi':"""::::We'1d:..",,:.':,.;;:.,",:,:,:,::Numb.er;:.:,,,-'-:<:,::.::.Exam!;d::;:,:,':;;-:;.'::;:!:Etiam.,l'::,d:,',,:',,":iExa'mineddy>>~:'":-',.:::XD/QD~!::;;$N):;Neigh'tilrigj:~",'~:Exa'm':,',:.'d'~g,~jP'i'o'vi;d'ed)',ic3,"e'a'n'ed~':."!.:Yesj<N07p,~,i"..HlH2H3H4H7H8198919891989198919861988199319861988199363"63II29"85"568"568"11%11%15%100%100%ODODODODODODAsneededAsneededAsNeededAsNeededASMEXISIL572ASMEXISIL572NoNoNoNoNoNo10 I

Figure2-1ReactorWaterConductivityMeanValues10.00~1.00~IJ0.10~1MaxWeeldyMeanVa~ycWQhydeMeanVUwswchSId.Oaf.1IAytllace0.01FuelCycleI811

3.0StructuralMarginAssessmentThegenericassessment'iscussedthestructuralmarginsinherentintheshrouddesignandnotedthat304SSisaductilematerialwithhightoughnesspropertiesevenafteraccountingfoztheeffectsofneutronfluence,andthatonlyaminimalremainingligament(5%-10%ofwall)isrequiredtomaintainstructuralmarginsunderpostaccidentloadswhen360degreecrackingispresent.ThegenericassessmentappliesanassumptionthatcrackingisinitiatedafteronefuelcycleandthatcrackgrowthcanbeestimatedanalyticallyusingthePLEDGEModel.InspectionoftheNineMilePoint1hotoperatingtimeandmeancycleconductivitydemonstratesthatNineMilePoint1isboundedbythegenericassessmentconclusionthatfindinga360degreethrough-wallcrackwithanaveragedepthinexcessof90%duringtheFall1994inspectionsisunlikely.However,becauseoftheuncertaintiesassociatedwithresidualstressprofilesandoxidewedgingphenomenon,thegenericassessmentcouldnotruleoutcrackinginexcessof90%.TheuncertaintyassociatedwiththeresidualstzessesisapplicabletotheHlthroughH7welds.ThecrackinguncertaintyassociatedwithHSweldisaddressedseparatelyinAppendixA.ThenextNineMilePoint1refuelingoutageiscurrentlyscheduledforFebruary1995.AdetailedinspectionconsistentwiththeBWRVIPinspectionguidelinescurrentlyunderdevelopmentisscheduledand/orapre-emptiverepairwouldbeimplementedforallshroudhorizontalwelds.Consideringtheuncertaintyintheextentofthrough-wallcrackingprediction,the1994FalloutageinspectionresultsofOysterCreek(scheduledtocommenceattheendofSeptember)willbeusedtodeterminetheuncertaintyassociatedwiththepotentialforupto360degreecrackinginexcessof90%.TheOysterCreekfallinspectionisconsideredtobedirectlyapplicabletothestructuralmarginassessmentforNineMilePoint1becausetheshroudfabricationissimilar(seeSection2.3.1),andtherefore,theuncertaintyassociatedwithresidualstressprofileswillbereduced.Inaddition,theNineMilePoint1first5cyclemeanconductivityisboundedbytheOysterCreekinitial5cycleaverage,andthehotoperatingtimeissimilarinmagnitude.Therefore,theOysterCreekinspectionresultsareexpectedtoallowNiagaraMohawktoassesstheuncertaintyassociatedwiththestructuralmarginintegrityfortheH1throughH7welds.12 I

4.0ShroudDisplacementLikelihoodAsdiscussedinthegenericassessment',severalconditionsmustexistsimultaneouslyinorderforshrouddisplacementtooccur.First,a360degree,)90%deepcrackmustexistintheshroud.Then,adesignbasisguillotinemainsteamlinebreakinsidetheflowlimitersoraDEGBrecirculationlinebreak,oradesignbasisseismiceventmustoccurtogeneratetheloadsassumedontheshroud.Notethatopezationaltransients,smallandintermediatebreakLOCA,mainsteamlinebzeaksoutsidetheflowlimiterandsafeshutdownearthquakeallhavesignificantlyreducedloadsandminimalpotentialshrouddisplacement.InthissectiontheNineMilePoint1specificoveralllikelihoodofthelimitingdesignbasisscenarioisdiscussedusingplantspecificprobabilitiesfromtheIndividualPlantExamination(IPE).4.1CrackingLikelihoodConsistentwiththegenezicassessment',itisconsideredunlikelythatNineMilePoint1has360degreecrackinginexcessof90%depth.Thisissupportedby,thegenericanalysisandpriorvisualinspections.TheuncertaintyassociatedwiththispredictionistobefurtherclarifiedbyreviewoftheFallOysterCreekinspection(zesultsexpectedinOctober1994).Inaddition,360degreecrackinginexcessof90%depthisnotcredibleattheH8inconel182weldbetweentheshroudsupportringandinconnelshroudsupportcone(seeappendixA).NotethatH8isalimitinglocationinthegenericassessmentregardingtheconsequencesoffailureduringaDEGBrecirculationlineLOCA.4'LOCALikelihoodANineMilePoint1specificprobabilisticsafetyassessment(PSA)basedontheNineMilePoint1IPEwasperformedtoevaluatethesafetysignificanceofcontinuedoperationpriortodeterminingthestatusof'eldsrelatedtothereactorshroud.ThePSAevaluatedtheprobabilityofaccidentscenariosresultingfrompotentialfailuresofshroudwelds.Theeventsofprimaryconcernaredoubleendedguillotinebreaks(DEGB)inmainsteamlines,DEGBinreactorrecirculationlines,andearthquakes.Basedontheprobabilityoftheseeventsandtheestimatedconditionalfailureprobabilityoftheshroudwelds,theestimatedoverallincrementalcoredamageandlarge/earlyreleasefrequencyislessthan8.3E-8peryear.ThedetaileddiscussionofthePSAisincludedinAppendixB.4.3InspectionTimingConsistentwiththerecommendationsofthegenericassessment',NineMilePoint1planstoreviewtheresultsoftheOysterCreekFallinspectionandotherFallinspectionstoassesstheuncertaintyassociatedwiththeevaluationthatcrackingisunlikelytobegreaterthan360degreesandgzeatezthan90%deep.13

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5.0Integrated'ShroudAssessmentTheNineMilePoint1susceptibilityassessmenthasconcludedthatthelikelihoodofupto360degreecrackingatsomedepthisfairlyhighattheH1throughH7weldlocation.CrackingtoanysignificantdepthattheHSweldlocationisconsideredextremelyunlikely.ThestructuralmarginassessmentestablishedthatcrackingattheH1throughH7locationsinexcessof90%depthisunlikely.Theuncertaintyinthecrackingpredictionwillbere-assessedbasedupontheresultsoftheOysterCreekFall(October1994)inspection.Theoveralllikelihoodoftheeventscenariodescribed,aLOCAorseismiceventwitha360degree,>90%deepcrack,isextremelyunlikely.TheassessmentofthecoredamagefrequencyassumingshroudweldfailurecombinedwiththedesignbasisseismicorrecirculationlineLOCAorMSLBLOCAisextremelylowconsideringoperationuntilFebruary1995,(4E-8per6months).ThisoverallrisksupportscontinuedoperationofNineMilePoint1untilthescheduledFebruary1995refueloutage.Theconsequencesof360degreethrough-wallcracksapplicabletoNineMilePoint1werereviewedaspartofthegenericassessment'.Thisassessmentreviewedtheshroudresponsetothestzucturalloadingsresultingfromdesignbasiseventsincluding,steamlinebreak,recirculationlinebreakandasymmetricloadsassociatedwiththerecirculationlinebreak.Thisassessmentincludedareviewoftheabilityofplantsafetyfeaturestoperformtheirfunctionsconsideringthedesignbasisaccidentloadswith360degreethrough-wallcracking(e.g.controlrodinsertion,ECCSinjection).ThroughtheBNRVIPassessmentsubcommittee,analysesareunderdevelopmentwhichwillprovidemoredetailedshroudloadsconsidezingboththemainsteamlinebreakLOCAandrecirculationlineLOCA.TheseanalysesareintendedtobetterdefinetheasymmetricloadsassociatedwiththerecirculationsuctionlineLOCAandtheamountofshroudliftfollowingthemainsteamlinebreakLOCA.TheseanalysesareestimatedtobecompletedintheOctober1994timeframe.Intheinterim,additionalinformationisavailabletosupplementthegenericassessmentdiscussionoftherecirculationlinebreakandsteamlinebreak.MainSteamLineBreakAccident:GPUNuclearhascompletedpreliminaryassessments4usingaRELAP5OysterCreekmodelwhichconfirmsthatthemaximumpotentialliftislimitedsuchthatthetopguidedoesnotclearthefuelchannels(e.g.lessthan14inchesoflift)andcontrolrodinsertionisnotexpectedtobeimpacted.Corespraylinesareexpectedtobedamagedbythepossibledisplacement,however,thebreakisaboveTAFsoECCSinjectioninsidethereactorvessel,atorabovethecoresteamingrate,willassureshortandlongtermcooling.RecirculationLineBreakAccident:Thegenericassessmentconsideredtheshroudloadsassociatedwiththerecirculationdischargelinebreakaslimitingandthat14

~c noverticaldisplacementisexpectedatanybuttheverticallyunsupportedH8weld.Theconsequenceofthisfailurewasverticaldisplacement(downward)whichwoulddamagethecorespraylinesandresultinimpairedcorespraycooling.However,additionalstudyoftheH8weldconfiguration(seeAppendixA)hasdeterminedthatfailureoftheH8weldinsuchamannerwhichwouldallowverticaldownwarddisplacementisnotacrediblefailure.WiththeH8weldintegrityassured,thecorespraysystemwouldperformitsdesignbasisfunctionandcontrolrodinsertionisassured.Asdiscussedinthegenericassessment,thelateralforceontheshroudduetotheblowdownasymmetricloadisboundedbytherestoringmomentoftheshroudweightandtherefore,therecirculationlinebreakanalysisresultsareunchanged.Asindicatedabove,additionalanalysesareinprogresstoaddressthisissuegenericallythroughtheBWRVIPassessmentsubcommittee.NineMilePoint1hasalsoreviewedtheguidanceprovidedinthegenericassessmentregardingthrough-wallcrackindicationduringnormaloperation.ThisgenericinformationhasbeenprovidedtooperationsandhasbeenincorporatedintothenormaloperatingprocedurefortheNuclearSteamSupplySystem(N1-OP-1).Theprocedurehasbeenrevisedtoalertoperatorsoftheexpectedplantresponseshouldathrough-wallshroudcrackdevelop.Thistrainingwasprovidedtoalloperationscrewspriortotheirresumptionofshiftduties.6.0ConclusionsTheNineMilePoint1shroudcrackingsafetyassessmentindicatesthat360degree,greaterthan90%through-wallcrackingisunlikelytooccurduringoperationuptothescheduledFebruary1995refueloutage.TheuncertaintyinthisdeterminationwillbeassessedbasedupontheresultsofthescheduledFall1994OysterCreekshroudinspection.Basedonthisconservativeapproach,theprobabilitythattheNineMilePoint1cozeshrouddoesnotsatisfythedesignbasisstructuralintegritymarginsisconsideredextremelylow.Eveniftheextremeconditionof360degree,greaterthan90%through-wallcrackingcoupledwithadesignbasisaccidentisassumed,thesafetyassessmentshowsthatcontrolzodinsertionisnotexpectedtobeimpactedandthecorespraysystemwouldprovideadequatecorecooling.Thislowprobability,combinedwiththeextremelylowoverall'ziskestimate,supportscontinuedoperationuntilthescheduledFebruary1995refuelingoutage.15 SJ

'7.0References2)3)GENE-523-A107P-0794,Revision1"BWRShroudCrackingGenericSafetyAssessment",August1994SIL0572R1,"CoreShroudCracks"4GE-NE-523-148-1193,"BWRCoreShroudEvaluation",April19944)GPUNCalc¹C1302-222-5450-W06,Rev0,"OysterCreekShroudDispacementCalculation"5)NMPCCalc¹SO-VESSEL-M025,rev0,"ResidualstressandremainingligamentcalcualtionfortheshroudringH8weld",ContainsMPRcalculation085-252-01referencedinAppendixA.6)NMPCTechnicalReportSAS-94-005"ProbabilisticRiskAssessmentofPotentialIntegranularStressCorrosionCrackingofNMP1CoreShroud",August5,199416 J

APPENDIXAAnalysisofNineMi3.ePoint1WeldHSShroudSupportRingtoInconelShroudSupportcone17 I)

%1MPRASSOCIATESINC,ENVINEEBSAugust16,1994ANALYSISOFNINEMILEPOINTUNIT1SHROUDSUPPORTRINGTOINCONELSUPPORTCONEWELDH-8WeldH-8attachestheType304forgedstainlesssteelshroudsupportringtotheAlloy600supportconeasshowninFigure1.Theshroudsupportassembly,includingthevesselshell,theconeandthering,butnottheshrouditself,waspostweldheattreated(PWHT)at1150'Fduringvesselfabrication,Asaconsequence,weldH-8wasstressrelievedduringPWHT,andpeaktensileresidualstresseswerereducedbytheheattreatment.Inaddition,thePWHTsensitizedthestainlesssteelringwhichincreasesconcernforIGSCContheringsideofweldH-8.Whiletheweldmetalandconewerealsosensitized,theseareInconelmaterialswhicharemoreresistanttoIGSCCthanthestainlessmaterial,especiallyintheabsenceofcrevices.Normaloperatingstressesinthesupportringareexpectedtobecompressiveduetothedifferenceinthermalexpansioncoefficientsoftheringandthecone/vessel.AfiniteelementstressanalysiswasperformedontheshroudsupportassemblytoquantifynormaloperatingstresslevelsandtodeterminethestressstateduringPWHT(MPRCalculation085-252-01).Fromthelatteranalysis,thestressreliefeffectsforpresumedweldresidualstressescanbeestimated.Theresidualstressesthatremain,whencombinedwithoperatingstresses,determinetheoverallstressstateofweldH-8duringnormaloperation.Theanalysisconfirmedthatthehoop,radialandaxialprincipalstresscomponentsareallgenerallycompressiveinthesupportringduringnormaloperation.Theprincipalstressofconcernistheradialone,sincethisstresscomponentcouldleadtostresscorrosioncrackingwhoseorientationwouldcauseweldH-8toloseitsverticalload-carryingcapability.StresscontourplotsfortheradialstresscomponentduringtheoriginalstressreliefandundernormaloperatingconditionsareshowninFigures2and3.Theprincipalloadduringstressreliefisthethermalload,duringwhichtimetheshroudisnotattached.Duringnormaloperation,theloadsincludethermal,pressure,deadweightandhydraulicupliftforces.InspectionofFigure3revealsthatthehighesttensileradialstressesexistatthetopofweldH-8inthering.Thisisconsideredtobethelimitinglocationforpossiblecrackinitiation.Itispresumedthatlocaltensileweldresidualstressesexistedatthislocationafterwelding,andtheywereattheyieldstresslevel.Duringstressrelief(seeFigure2),18 LI inducedtensilethermalstresses,combinedwiththereducedyieldstrengthatthe1150'ptemperature,reducedtheweldresidualstressestoalowvalue,about7ksi.Duringnormaloperation,thesestressesaddtothenormaloperatingstressesforatotalstressofabout13ksiatthetopofweldH-8inthering.Whileitisunlikelythatcrackingwouldinitiateina13ksistressfield,wenotethatthelocationofhighesttensilestressisanareathat'isinspectable.Further,crackingintheheataffectedzoneofthesupportringadjacenttoweldH-8wouldgrowveryslowly,ifatall,because:(1)itwouldhavetogrowintoanareaofappliedcompressivestresses,and(2)weldresidualstressesarealsoexpectedtobecomecompressiveintheringatthecenterofweldH-8.Finally,thelimitingloadforweldH-8istherecirculationpipebreakdownloadof2millionlbs.Itisestimatedthataligamentofonly1/4inchisrequiredinweldH-8tosupportthisload.Therefore,crackinginweldH-8wouldhavetobequiteextensive,aboutninetypercentthroughwallfor360degrees,inorderfortheweldtofailunderlimitingaccidentconditions.Weconcludethat,becauseofreducedweldtensileresidualstressesinweldH-8,andthefactthatonlyabout1/4inchofweldisrequiredtosupportthelimitingdownloadtransient,weldH-8isextremelyunlikelytobeinaconditionthatcouldfail.19 CI Axial(Y)Shroud(Type304StainlessSteel)Radial(X)WeldH-8(Inconel182)ShroudSupportRing(Type304StainlessSteel)SupportCone(Inconel600)VesselWall(LowAlloySteel)FAIMpQFC65252-OIC6/16/94(IJl)Figure1.ShroudSupportComponentsandWeldH-820 I

Iqir~iANSYS5.0AAUG9199411:18:24PLOTNO.1NODALSOLUTIONSTEP=1SUB=1TIME=1SX(AVG)RSYS=ODMX=1.074SMN=-12442SMNB=-47643SMX=10539SMXB=49670-12442-9889-7335-4782-2228325.24228795432798610539~NINEMILEPOINTUNIT1CORESHROUDTHERMALANALYSISFigure2.RadialStressDuringPWHT

h~E~JtANSYS5.0AAUG9199411:24:12PLOTNO.1NODALSOLUTIONSTEP=1SUB=1TIME=1SX(AVG)RSYS=ODMX=0.440901SMN=-12070SMNB=-23687SMX=6508SMXB=26637-12070-10006-7941-5877-3813-1749315.396238044446508rrJCNINEMILEPOINTUNIT1CORESHROUDTHERMALANALYSISFigure3.RadialStressDuringNormalOperation

APPENDIXBAnalysisandResultsfromNMPCTechnicalReportSAS-94-005"ProbabilisticRiskAssessmentofPotentialIntegranularStressCorrosionCrackingofNMP1CoreShroud",August5,199423 r

Thecrackingofvesselshroudweldscanleadtofailureofvesselinternalssupport.Shouldvesselsupportfail,coreintegritymaybecompromisedand,ofchiefimportance,insertionofcontrolrodsmaynotbepossibleiffuelbundlesarenolongerparalleltocontrolrodmovement.Inaddition,forNMP1,shroudmovementmayresultinfailureofcoresprayspazgersduringsomeevents.BasedontheengineeringreviewandtheinformationinReferences1,2,and3,itisapparentthattheprincipalscenariosofconcernaremainsteamlinebreaks(MSLB),reactorrecirculationlinebreaks(RRLB),andseismicevents.Eachoftheseeventshasthepotentialtoinduceloadingsthatcouldfailcrackedweldsandcausecoremovement.Assuch,thisreportcalculatestheprobabilityofeachoftheevents.TheseprobabilityvaluesshouldbeusefulinassessingthesafetysignificanceoftheissueatNMP1.TheNMP1IPEisadetailedevaluationoftheprobabilityandconsequencesofplantrisk.BecauseitwascompletedpriortotheelevatedconcernregardingshroudIGSCC,itdoesnotexplicitlyincluderecentinsightsassociatedwiththisissue.Inthatregard,theprobabilityofshroudIGSCCeventscanbecalculated,similartotheeventsdevelopedintheIPE,andpresentedasanincrementalriskabove-and-beyondthatcalculatedintheIPE.ThebestwaytodevelopanddescribetheriskassociatedwiththepostulatedIGSCCeventsistotreateachpossiblescenarioseparatelyandthensumtheprobabilityofeachscenariotodevelopthetotalIGSCCeventfrequency.Therefore,thefollowingsectionindividuallytreatstheMSLB,RRLB,andseismicevents.MainSteamLineBreak(MSLB)ShroudIGSCCRiskTheMSLBeventisdefinedbytherapidinitiationofa360'ircumferentialcrackwhichresultsinadoubleendedguillotinebreak(DEGB)ofpipingandanimmediatelossofcoolant(LOCA)event.As'such,makeupflow,fromprimarilythecorespraysystemandfeedwater,isrequired.ThisspecificeventwasmodeledintheNMP1IPEasoneofseveralcontributorstothelargeLOCA(LLOCA)classofinitiators.OthercontributorstothelargeLOCAeventfrequencyinclude:corespraysystemleakage/ruptures,multipleinstrumentpenetrationfailures,SLCsystempipingleakage/rupture,andfeedwaterpipingleakage/rupture.Asdiscussedabove,non-DEGBeventsposelittlethreatrelativetotheshroudissueandarenotincludedinthisriskassessment.LargeLOCAevents,includingDEGB,werenotasignificantcontributortoIPEcalculatedaccidentfrequency.ThepostulatedMSLBinitiatingeventfrequencyrepresentsacertainfractionoftheIPELLOCAinitiatingeventfrequencysinceMSLBisoneofseveraleventsthatazeconsideredtocauseaLLOCA.However,theNMP1IPEdoesnotdifferentiatebetweenspecificLLOCAeventsbecause,fozthepurposesofsevereaccidentmodeling,theplantresponseissimilarbetweenindividualeventsthatfittheIPELLOCAdefinition.AstheNMP1IPELLOCAfrequencyisquantifiedas7E-4peryear,forthisanalysis,theMSLBfrequencycanbereasonablyconsideredless24

than7E-4peryear.TheBWROG'asperformedresearchthatisusefulincharacterizingtheextenttowhichMSLBfrequencyislessthanNMP1LLOCAcalculatedfrequency.TheBWROGestimatesthatrecirculationsystempiping,anditisinferredotherlargepiping,hasarupturefrequencyof"severalordersofmagnitudelowerthan"7.51E-6peryear.ItshouldbepointedoutthatthereisconsiderableuncertaintyastothepossibilityofaninstantaneousDEGBofpipesinanuclearapplication.Awidelyconsideredtheorysuggeststhatthepipewouldleakfozsometimebeforecatastrophicrupture.Assuch,theleakwouldalertoperatorswhowouldshut-downtheplantbeforetheDEGBoccurred.,Inanyevent,nocreditistakenfortheleak-before-breakargumentandtheBWROGvalueisassumedrepresentativeoftheMSLBfrequencyundertheDEGBfailuremode.FollowingaMSLBevent,theintegrityoftheshroudweldswillbechallenged.IPEshavetypicallyassumedthatthispassivefailuremodeisoflowprobability.However,duetotheIGSCCissue,thisassumption,atleasttemporarily,shouldbequestioned.PerPinelli',thepossibilitythatweldfailureswilloccuris"unlikely"evenconsideringIGSCC.Forthisanalysis,"unlikely"isreasonablytranslatedtomeanlessthan1E-2pezevent.Assuch,theprobabilityofaMSLBandresultantshroudfailureisestimatedaslessthan7.51E-8peryear.AccordingtothecurrentIPEmodel,thiseventwouldbeconsideredacoredamageandlarge-earlyreleaseeventsinceanylargeLOCAwithafailuretoSCRAMwasconnectedtocoredamageandlarge/earlyreleaseendstates.Whenaddedtoacoredamagefrequency(CDF)of5.5E-6peryearandalarge/Earlyreleasefrequency(LERF)of6.9E-7peryear,theMSLB-'Shroudeventprobability,7.51E-8peryear,isarelativelyminorcontributor.Inactuality,theimpactisevenlessthantheabovecalculationshows.TheNMP1IPEmodeldoesnotlinkLLOCAeventswithafailuretoSCRAMtotheATWSmodelbutrathertoaClassIVfailureendstate.TheIPEconservativelyassumesthatsuchscenariosresultincoredamage.Thisisdonebecausethelowprobabilityofthesequencesdoesnotjustifythelevelofeffortrequiredtoincorporatethenecessarymodelingdetails.Inreality,evenifcontrolrodsarenotinserted,thereactorcouldpossiblybeshutdownusingSLCinjection.Thisisespeciallyappropriatetoconsidersince,ataminimum,somerodsmaybeatleastpartiallyinsertedevenwiththefuelrodsindisarray.FromtheIPE,SLCfailureprobability,includingtheassociatedoperatoractionstoinitiateSLCandpreventdilution(TopeventsSL,EP,andCH),is1.6E-3perevent.Multiplyingthisbytheabove7.51E-8peryearyieldsaneventprobabilityof1.2E-10peryear.Assuch,ifSLCcouldbecreditedthentheriskimpactwouldbefarless.NotethatthisdoesnotincludeanyconsiderationofSLCequipmentoroperatorfailuresthatcouldrelatetoarelocatedshroud.Inanyevent,theaboveshowsthenatureofsafetyprovidedbytheSLCsystemduringthepostulatedMSLB/shroudevent.25 C

I~~Inaddition,evenifSLCfailed,itispossibletokeepthecorecoveredandestablishheatremovalequaltoorgreaterthanthatgeneratedbythereactor.Thiscouldbeaccomplishedbysomecombinationofcontainmentsprayorcontainmentventoperationinconcertwithsomecombinationofsuccessfulinjection.Theseactionswouldbedirectedviathecurrentsymptombasedemergencyoperatingprocedures(EOP).Itisnotsuggestedthatthesuccessprobabilitywouldbelarge,butrather,itispointedouttoshowtheconservatismintheabovecalculations.ReactorRecirculationLineBreak(RRLB)ShroudIGSCCRiskTheRRLBeventinitiateswhena360'ircumferentialcrackdevelopsinareactorrecirculationlineandveryquicklyruptures.AswiththeMSLB,thiseventresultsinanimmediatelossofcoolant(LOCA)event.TheIPEtreatmentrelativetolargeLOCAisthesameasthatdiscussedabove.Assuch,allrelateddiscussionforMSLBisrelevanthere.Fromabove,agoodestimate,forthepurposesofthisstudyistheBWROG7.51E-6peryearvalue.ShouldaRRLBeventoccur,makeupisimmediatelyrequired.However,sincethebreakcouldbebelowthecore,coresprayisrequiredbecausespraycoolingisnecessarytoprotectthecoreuntilcontainmentfloodingiscompleted.ForNMP1,thecoresprayspargersareattachedtotheshroud.Assuch,followingaRRLB,shouldtheHSshroudcoresupportweldfail,theentireshroudcoulddrop.Thiswouldresultinfailureofthecore'prayfunction;althoughcoresprayflowwillstillreachthevessel.DuetothenatureoftheHSshroudweld,engineeringreviewhasdeterminedthatitisveryreliable;evenconsideringtheIGSCCissueThisreviewhasclassifiedtheH8weldfailureasanextremelyunlikelyevent.Assuch,avalueof1E-3pereventfailurefrequencyhasbeenconservativelyassignedasthefailureprobabilityoftheHSshroudweldfollowingaRRLBevent.Multiplying1E-3pereventbytheabove7.51E-6peryearyieldsaRRLB/Shroud/Cozesprayfailureeventof7.51E-9peryear.Inaddition,theaboveispotentiallyconservativebecausealthoughthecozesprayfunctionisfailed,itsinventory,asinjectionratherthanspray,canreachthevessel.Combinedwithfeedwater,CRD,andSLC,thetotalinventorymightbeenoughtopreventfueldamagepriortocompletionofcontainmentflooding.Thissuccesspathisnotcreditedinthis,ormostlikelyanyotheranalysis,butitismentionedhereasapossiblesuccesspaththatcouldbedevelopedfurther.SeismicEventShroudIGSCCRiskPerNRC',thesafeshutdownearthquake(SSE)isexpectedtoproduceminimalmovementofequipmentrelatedtotheaboveissue.Assuch,itwouldrequireMSLBorRRLBeventscoincidentwiththeSSEtocausepotentialaccidents.Duetothelowlikelihoodofeachindividualevent,thecoincidentoccurrenceoftheSSEandalargebreakis26

~r~g~

consideredverysmall.EveniftheSSEandlargebreakcouldcauseaproblem(assumetheyoccurredonthesamedayratherthaninthesameminuteorhour),aCDFestimateoflessthan1E-10peryearwouldresult.Additionally,abeyondSSEearthquakecouldalsooccursuchthattheearthquakeitselfcausesfailureofalargeline(MSLBorRRLB)andtheshroud.Eventsofthismagnitudeareofverylowprobability(i.e.(1E-7peryear).Also,earthquakesofthismagnitudewouldlikelyfailasignificantportionofotherplantequipmentsuchthatconditionalfailureprobabilityoftheplantasawholewouldbelargeregardlessofthestatusoftheshroudwelds.Assuch,theincrementalriskcausedbypotentiallycrackedshroudweldsisjudgedinsignificant.SummingtheaboveconservativelycalculatedscenariofrequenciesresultsinatotalincrementalCDFandLERFfrequencyof8.27E-8peryear.Consideringthatonlysixmonthsremainuntilthenextrefuelingoutagetheincrementalriskishalfthatabove,or4.14E-8per6months.Also,ithasbeendemonstratedthattheabovecalculationisconservative.Conservativeornot,theaboveincrementalriskisverysmall.REFERENCES(1)Zimmerman,R.P."IntergranularStressCorrosionCrackingofCoreShroudsinBoilingWaterReactors,"GenericLetter94-03,USNRC,July25,1994.(2)Stang,J.F..(USNRC)LettertoFarrar,D.L.(ComEd),"ResolutionofCoreShroudCrackingatDresden,Unit3andQuadCities,Unit1,"7/21/94.(3)Pinelli,R.A.LettertoBWROwner'sGroupExecutives,"BWROGResponsetoNRCRequestforShroudInformation,"GE-NE-523-AI07P-0794,July13,1994.(GEProprietary.)(4)NineMilePointUnitOneFinalSafetyAnalysisReport(Updated).(5)Kirchner,R.F.,et.al.,"NineMilePointNuclearStation-Unit1IndividualPlantExamination(IPE)"NiagaraMohawkPowerCorporation,SAS-TR-93-001,July1993.(6)England,L.A.-LettertoUSNRC(Serkiz,A.W.),"ResponsetoNRCRequestforInformationonPipeBreakFrequencies,"BWROwner'sGroup,BWROG-93149,December8,1993.27 I~~

~~$II,~egATTACHMENT8NINEMILEPOINTUNIT1DOCKETNO.50-220LICENSENO.DPR-63GENERICLETTER94-03HITRYFREHRIPETI

~a~i S>>,~'~NiagaraMohawkhasnotperformedanyshroudinspectionswhichmeetalloftheGeneralElectric(GE)SIL572,Revision1recommendationsforlightinglevel,cameraresolutionandweldpre-cleaning.However,visual(camera)inspectionsofvesselinternalcomponents,whichdirectlyorindirectlyincludedfilmfootageoftheshroudplatesandweldments,havepreviouslybeenperformed.TheseinspectiontapeshavebeenreviewedjointlybyaNiagaraMohawkLevelIIIqualifiedexaminerandaGeneralElectricLevelIIIqualifiedexaminer,whoparticipatedintheexaminationactivitiesatbothQuadCitiesandDresdenandwhoisqualifiedtotheenhancedlevelproposedbythenewstandards.TheresultsofNiagaraMohawk'sreviewofpastinvesselvisualinspectiontapesisprovidedbelowandsummarizedintheaccompanyingtable.CoreshroudweldsHl,H2,H3andH4werefilmedduringa1989accessstudyconductedtoverifyclearancesforthereactorpressurevesselbeltlineinspectiontool.Thelightingprovidedwastothelevelneededforverificationofaccess,andthoughnotspecificallydeployedtoilluminatethewelds,theweldsareclearlyvisible.Thecameraresolutionlevelwasasneededtogaugeaccessibility.Nopriorcleaningoftheweldswasperformed.ThereviewofthesetapesbytheLevelIIIqualifiedexaminersconcludedthattherewasnoevidenceofgrosscrackingatthelocationsinspected.Invesselinspectionsoftheshroudsupportingringtotheshroudsupportskirt(ISIcomponentRV15I)wereconductedin1986,1988and1993inaccordancewithASMESectionXI.TheareasinspectedencompasscoreshroudweldsH7andH8.ThelightinglevelandcameraresolutionrequiredbyASMESectionXImeettherequirementsofGESIL572,Revision1.Nopriorcleaningoftheweldswasperformed.TheinspectionsofISIcomponentRV15Iin1986,1988and1993didnotrevealanyreportableindications.NMP1REHRUDVIALCAMERAEXAMINATION,':;.',:-Numb'e'r',:::,:-:',::::!:.':;Exam!d'::,:::,:;:,:;:;;::;:,:::;::-':::Exnm':,d;'.!:.'",)',:;::ilExIuiiIiiedjjiH1H2H3H4H7H8198919891989198919861988199319861988199363II63"29II85"568"568"11%11%5%15%100%ODODODODODODAsneededAsneededAsneededASMEXI/SIL572ASMEXI/SIL572NoNoNoNoNoNo C~g>I ATTACHMENTCNINEMILEPOINTUNIT1DOCKETNO.50-220LICENSENO.DPR-63GENERICLETTER94-03DRAIFREHRFIATI a'

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