ML17325A125

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Steam Generator Tube Integrity - Apr 1987:Assessment of Next Operating Interval Length. Related Info Encl,Including Description of Steam Generator Manway Cover Closure Repairs for Mar-Apr 1987 & Westinghouse Nuclear Safety Check List
ML17325A125
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Issue date: 05/18/1987
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INDIANA6MICHIGANELECTRICCOMPANYDONALDC.COOKNUCLEARPLANTUNIT2STEAMGENERATORTUBEINTEGRITY-APRIL1987AnAssessmentoftheNextOperatingIntervalLengthAttachment1toAEP:NRC:0936JPreparedby:AmericanElectricPowerServiceCorporationOneRiversidePlazaColumbus,Ohio43216May18,1987870bOCR050003ib0201b9870522pDRADPDR8i TABLEOFCONTENTSLISTOFABBREVIATIONSLISTOFTABLESANDFIGURESREFERENCESUBMITTALS

1.0INTRODUCTION

1.1ReportObjectives1.2OperatingExperienceOverview1.2.11~2.2BackgroundMostRecentOperatingPeriod2.0CONDITXONOFTUBEBUNDLES2.1SteamGeneratorInspectionandTubePlugging-March19872.1.12.1.2EddyCurrentAnalysisCriteria/TubePluggingCriteria6EddyCurrentInspectionResults-------72.2TubeDegradationGrowthRateEvaluation2.2.12.2.22'.3TubePluggingComparison9GrowthRateDetermination10ProbabilisticModelVerification-----ll3.0EVALUATIONOFOPERATIONTHROUGHTHEENDOFFUELCYCLE6123.1USNRCRegulatoryGuide1.121Basis123.1.13.1.2F1.3MinimumAllowableWallDetermination---12LeakBeforeBreakVerification------14EddyCurrentTestingUncertainty-----153.2OperatingIntervalJustification-SafetyAssessment154.0OPERATINGINTERVALDETERMINATION4.1OperationalConsiderations4.2TubeBundleConditionProjection

5.0CONCLUSION

S16161718 LISTOFABBREVIATIONSASMEDIEC,ECTEFPDEFPMgpdgpmIGMECoIGA/SCCMWt-hrNDDR.G.RxxCxxSGxxSLB/FLBAmericanSocietyofMechanicalEngineersDistortedindicationEddycurrent,eddycurrenttestingEffectivefullpowerdayEffectivefullpowermonthGallonsperdayGallonsperminuteIndiana&MichiganElectricCompanyIntergranularattack/stresscorrosioncrackingKilohertzMegawatt,thermalMegawatthours,thermalNodetectabledegradationUSNRCRegulatoryGuideRowandcolumndesignationofsteamgeneratortubeSteamGeneratorNo.21,22,23,or24SteamlinebreakorfeedlinebreakaccidentscenarioSQRSuSquirrelUltimatetensilestressTWUDSThrough-wallpenetrationUndefinedsignal LISTOFTABLESANDFIGURESTable1Table2ListofTablesIndicationsofHotLegSecondarySideCorrosion-March1987A.Includingonlythemostsignificantindicationpertube.B.Includingmultipleindicationspertube.TubesPluggedDuetoIGA/SCC-GeneralComparisonTable3Table4Table5Table6TubesPluggedDuetoIGA/SCC,CompensatedforChangesinAnalysisandPluggingCriteria-ComparisonbyLocationCook2SteamGeneratorTubing-MinimumAcceptableWallRequirementsA.Tubesheetcreviceandtubesheetsurfaceregions.B.Tubesupportplateintersections.Cook2SteamGeneratorTubing-AllowableWallLossDeterminationOperatingIntervalJustification-RemainderofFuelCycle6-R.G.1.121BasisListofFiuresFigure1Figure2Figure3SG21TubesheetMap:March1987SG22TubesheetMap:March1987SG23TubesheetMap:March1987ECInspectionResults-ECInspectionResults-ECInspectionResults-Figure4SG24TubesheetMap:ECInspectionResults-March1987 ListofFiuresCont'dFigure5SGs21,22,23,and24:ECInspectionResults-March1987;IndicationsofIGA/SCCvs.GeneratorElevationsFigure6SGComposite:"Start-of-IntervalTubeBundleCondition-July1986"comparedto"End-of-IntervalTubeBundleCondition-March1987Figure7Figure8Figure9ComparisonofModelPredictiontoActualECInspectionResults,TubesheetCreviceRegionComparisonofModelPredictiontoActualECInspectionResults,TubesheetSurfaceRegionComparisonofModelPredictiontoActualECInspectionResults,TubeSupportPlateIntersectionsFigure10FigurellFigure12A.Fullrange,0to1004TW.B.Blowupof40to100%TWrange.ProjectedEnd-of-IntervalCondition,TubesheetCreviceRegionProjectedEnd-of-IntervalCondition,TubesheetSurfaceRegionProjectedEnd-of-IntervalCondition,TubeSupportPlateIntersections REFERENCESUBMITTALSAEP:NRC:0936G,lettertoMr.HaroldR.Denton,NRR-USNRC,"SteamGeneratorTubeLeakandReturntoPowerOperation,"datedApril9,1987.AEP:NRC:0936E,lettertoMr.HaroldR.Denton,NRR-USNRC,"SteamGeneratorTubeIntegrity,"datedNovember24'986;transmittalofWCAP-11329(proprietaryversion)andWCAP-11330(non-proprietaryversion).AEP:NRC:0936C,lettertoMr.HaroldR.Denton,NRR-USNRC,"SteamGeneratorTubeIntegrity-InterimStatusReport,"datedFebruary7,1986;transmittalofWCAP-11055(Proprietaryversion)andWCAP-11056(non-proprietaryversion).AEP:NRC:0936A,lettertoMr.HaroldR.Denton,NRR-USNRC,"SteamGeneratorTubePlugging-InterimStatusReport,"datedOctober10,1985.

STEAMGENERATORTUBEINTEGRITY-APRIL1987AnAssessmentoftheNextOperatingIntervalLength

1.0INTRODUCTION

1.1ReortObectivesReferenceSubmittal1addressedthecourseofactiontakenasaresultoftheDonaldC.CookNuclearPlantUnit2(Cook2)steamgeneratortubeleakwhichoccurredonMarch3,1987.Theletterdocumentedthepreliminarytubeinspectionresults,addressedrestorationoftubebundleintegritytothesamelevelasatthebeginningofthepreviousoperatingperiod,andpresentedqualitativejustificationforreturntopowerandoperationforastaff-recommendedinitialperiodofthreemonths.Thepurposeofthisfollow-upreportistoprovideamorecompleteevaluationofrecentevents,andtopresentquantitativejustificationforanoperatingintervalinexcessoftheinitialthreemonths.Historically,assessmentofanoperatingintervalbetweensteamgeneratortubeinspectionshasconsideredonlythesafetyissuesofUSNRCRegulatoryGuide1.121.SuchanassessmentwaspresentedforCook2tojustifyoperationthroughtheentirecurrentfuelcycle(ReferenceSubmittal2).However,evenminorsteamgeneratortubeleakage,althoughnotasafetyissueandinfactallowableuptothelimitsetbytheplantTechnicalSpecifications,isundesirablefrombothregulatoryandoperatingperspectives.Inrecognitionofthisfact,determinationofthenextoperatingintervalwillfocusonminimizingthepotentialforaforcedoutageduetoexcessivesteamgeneratorleakage.ThesafetyissuesofR.G.1.121willofcoursebeagainmetbythismoreconservativeapproach.1.20eratinExerienceOverviewl.2.1BackgroundCook2incorporatesanuclearsteamsupplysystemmanufac-turedbyWestinghouse,andislicensedfor3411MWt.InitialcriticalityoccurredonMarch10,1978.Theunitis D.C.CookUnit2AEP:NRC:0936JAttachment1currentlyoperatinginitssixthfuelcycle;at,theendofMarch1987,about5.7effectivefullpoweryearsofoperationhavebeenaccrued.Cook2hasfourWestinghouseSeries51steamgenerators.AdescriptionofsignificantfeaturesandareviewofthetypesoftubedegradationexperiencedpriortoNovember1983arecontainedinReferenceSubmittal3.Alloftheearlytubedegradationwasunrelatedtosecondarysidecorrosion.ThefirstsignificantindicationofsecondarysidetubecorrosionintheCook2steamgeneratorsoccurredinNovember1983,whentheunitwasremovedfromserviceduetosteamgeneratortubeleakage.Detailsofthatandsubsequenteventshavebeendiscussedintwomeetingswiththestaff(December4,1985andSeptember16,1986)andaredocumentedinReferenceSubmittals2,3,and4.Forconvenience,however,followingisachronologyofsignifi-cantsteamgeneratoreventsuptoMarch1987.oNovember7,1983ForcedOutae-firststeamgeneratortubeleakduetosecondarysidecorrosion.Leakrateof0.29gpmLeakidentifiedinSG21,TubeR16C40ECTof1225tubesintwosteamgeneratorsPluggedthreetubes,allduetoindicationsofsecondarysidecorrosionRestartedonNovember22,1983oMarch10,1984RefuelinOutae100percentECTineachsteamgeneratorseventubesamplesremovedforanalysis;confirmedintergranularcorrosionintubesheetregionPlugged402tubes,68ofwhichwereduetoindicationsofsecondarysidecorrosionRestartedonJuly7,1984 D.C.CookUnit2AEP'NRC0936JAttachment1oJuly15,1985ForcedOutae-steamgeneratortubeleakLeakrateof0.22gpmLeakidentifiedinSG23,TubeR16C56ECTof25tubesinSG23Pluggedtwotubes,bothduetoindicationsofsecondarysidecorrosionAttemptedrestartonAugust2,1985oAugust2,1985ForcedOutae-steamgeneratortubeleakduringstart-upLeakratemeasurementsnotpossibleLeaksidentifiedinSG23,TubesR7C28andR14C70ECTof1500tubesinSG23Plugged35tubes,allduetosecondarysidecorrosionInitiatedboricacidtreatmentprogram(30percentpowersoakandon-lineaddition)RestartedonAugust22,1985oAugust23,1985ForcedOutae-steamgeneratortubeleakduring30percentpowersoakLeakrateof0.2gpmLeaksidentifiedinSG22,TubeR14C41andSG24,TubeR19C52100percentECTinSGs21,22,and24;ECTofalltubesinSG23nottestedduringAugust2,outageFirstECindicationsnotedathotlegtubesupportplateintersectionsFivetubesamplesremovedforanalysis;confirmedintergran-ularcorrosionattubesupportplateintersections D.C.CookUnit2AEP:NRC:0936JAttachment1Plugged110tubes,104ofwhichwereduetosecondarysidecorrosionDecidedtoadministrativelylimitunitpowertoabout,80percentRestartedonOctober23,1985oDecember4,1985PresentationtoNRCStaffJustifiedcontinuedoperationuntilscheduledrefuelingoutage,approximately90effectivefullpowerdaysfromtheOctober23restartoFebruary28,1986RefuelinOutaeMinorsteamgeneratorleakage,about0.04gpm,attimeofshutdownLeakidentifiedinSG22,R16C45ECTinaccordancewithTechnicalSpecificationsurveillancerequirementsoninitialsampleof550tubes;classificationofSGs22and24asC-3requiredexpansionofprogramtoalltubesineachsteamgeneratorPlugged151tubes,149ofwhichwereduetosecondarysidecorrosionBoricacidtreatmentprogramcontinued(creviceflushing,30percentpowersoak,andon-lineaddition)RestartonJuly7,1986Unitpoweragainadministrativelylimitedtoabout80percentoSeptember16,1986PresentationtoNRCStaffJustifiedcontinuedoperationthroughentirefuelcyclewithoutshutdownforsteamgeneratorsurveillance-D.C.CookUnit2AEPNRC0936JAttachment1InformedstaffofintenttoreplaceCook2steamgenerators1.2.2MostRecentOperatingPeriodCook2beganoperationinFuelCycle6onJuly7,1986.Thermalpoweroutput,throughoutthecyclehasagainbeenadministrativelylimited-typicallyto80percent,althoughtherehavebeenbriefperiodsofoperationat90percentinordertoperformcertaintestsandtomeethighsystem'loaddemandduringthesummerpeakperiod.Thermalgeneration.throughtheendofMarch1987hasbeen14,990,974MWt-hrs,orabout183EFPDs.Onebriefoutageunrelatedtosteamgeneratortubedegrada-tionoccurredearlyinCycle6.Followingthat,Cook2rancontinuouslyforaperiodof226calendardaysuntilbeingremovedfromserviceonMarch3,1987duetoanindicatedprimary-to-secondaryleakinSG22.Themeasuredleakratewas0.247gpm,wellbelowtheTechnicalSpecificationleakratelimitof500gpd(0.347gpm).TheleakingtubeinSG22wasidentifiedbyhydrostatictestingasTubeR28C53,andwassubsequentlyconfirmedbyeddycurrenttestingtohaveathrough-walldefectinthehotlegtubesheetcreviceabout3.7inchesbelowthetubesheetsurface.ThisdefectistypicalofthesecondarysideIGA/SCCpreviouslyidentifiedintheCook2steamgenerators.Toverifytubeintegritypriortoreturningtoservice,aneddycurrentinspectionprogramconsistentwiththerequirementsofTechnicalSpecification3/4.4.5wasperformed.TestingresultsarepresentedanddiscussedinSection2.0ofthisreport.Afterrestoringtubebundleintegritybypluggingdefectivetubes,theunit,returnedtoserviceonApril21,1987.BeforechangingtoMode3,creviceflushingwithboricacid(1000-2000ppmboron)wasperformed;a32-hoursoakatabout30percentpowerwithboricacid(50ppmboron)wasconducted;on-lineadditionofboricacid(5-10ppmboron)willcontinueduringpoweroperation.Unitthermalpowerwillagainbeadministrativelylimitedtoabout80percent,althoughbriefperiodsofhigherpoweroperationmaybenecessaryfortestingortomeetsystemloaddemand.

D.C.CookUnit2AEP:NRC:0936ZAttachment12.0CONDITIONOFTUBEBUNDLES2.1SteamGeneratorInsectionandTubePluin-March1987AlthoughnotmandatorysincetheTechnicalSpecificationleakratelimitwasnotexceededpriortoshutdown,IGMECoelectedtoverifytheconditionoftheCook2steamgeneratortubebundlesbyperforminganeddycurrentinspectionconsistentwiththerequirementsofTechnicalSpecification3/4.4.5.TestingresultsofaninitialsampleofaboutsixpercentofthetubesineachofSGs22and24necessitatedexpandingtheinspectiontopotentiallyaffectedareasofalltubesineachsteamgenerator.2.1.1EddyCurrentAnalysisCriteria/TubePluggingCriteriaThecriteriausedtoanalyzeeddycurrentdataduringtheMarch1987inspectionwerethesameasthoseusedduringtheMay1986inspection.Thesecriteriaweredevelopedfromacorrelationoffieldbobbincoileddycurrentdatawithmetallographyresultsoftubesamplesremovedin1984and1985,andarediscussedindetailinReferenceSubmittals2and3.Forconvenience,followingisabriefsummaryofpertinenteddycurrentsignalclassifications:oClearIndicationreortedinercentthrouh-wallenetrationor4TW-Asignalwithanunequivocalphaseanglemeasurableat400kHz,confirmedat100kHz;industrypracticeistouseathresholdvoltage,usuallyabout1volt,todiscriminatebetweenreportableandnon-reportableclearin'dications;asaconservatism,however,allclearindications,regard-lessofvoltage,werereportedfordispositionduringtheMay1986andMarch1987inspections.oDistortedIndicationDI-Asignalvisibleat400kHzbelievedbytheinterpretertorepresenttubedegrada-tion,butwithanunquantifiablephaseangle;expectedcorrelationinmixedfrequenciesorothersinglefre-quenciesisnotnecessarilypresent.Qindicationinthetubesheetcreviceregionwhosesignaltraceat400kHziscomplexwithanunquantifiablephaseangle;theseindicationshavehistoricallybeenshowntocompromisetubewallintegrity.

D.C.CookUnit2AEPNRC09367Attachment1oUndefinedSinalUDS-Ananomaloussignal,notnecessarilyindicativeoftubedegradation,but.whichtheinterpreterbelievesshouldbenotedforconsidera-tionanddisposition.oNoDetectableDeradationNDD-Asignalwithnoevidenceoftubewalldegradation;eitherthereisnodegradationoritisbelowthedetectionthreshold.TubepluggingcriteriausedduringtheMarch1987inspectionwerebasicallythesameasthoseusedduringtheMay1986inspection,althoughanadditionalconservatismwasincorporatedforindicationsattubesupportplateintersections,asnotedbelow.DevelopmentandrationaleforthesecriteriaarecontainedinReferenceSubmittal2.Forconvenience,followingisabriefsummaryofthepluggingcriteriaimplementedforsecondarysidecorrosionineachofthethreeareasofconcern:oTubesheetcrevicereionhotle-Allclearindications,DIs,SQRs,andUDSsinthetubesheetcreviceregion(fromthetubesheetrolltransitiontothesecondaryfaceofthetubesheet)wereconsideredpluggable,regardlessofvoltageorphaseangle.oTubesheetsurfacereionhotle-Allclearindications,DIs,andUDSsinthetubesheetsurfaceregion(fromthesecondaryfaceofthetubesheetuptoabout6inchesintothefreespanoftubing)wereconsideredpluggable,regardlessofvoltageorphaseangle.oTubesuortlateintersectionhotle-Clearindicationsmeetingathresholdvoltageof1.75voltsandhavinganindicatedthrough-wallpenetrationof>40percentwereconsideredpluggable.Inaddition,someindicationsnotmeetingthevoltagethresholdwerepluggedonphaseanglealonebased'nrecommendationsofthedatainterpreter.ThisrepresentsanaddedconservatismoverthecriteriausedinMay1986.ITheTechnicalSpecificationpluggingcriteriaof>40percentthrough-wallpenetrationwasappliedtoallotherareasofthesteamgeneratortubing.2.1.2EddyCurrentInspectionResultsSummariesofpertinenthotlegeddycurrentindications,bytypeandlocation,aregiveninTables1-Aand1-B.

D.C.CookUnit2AEP:NRC:09368Attachment1QuantitiesinTable1-Arepresentindividualtubes;fortubeswithmultipleindications,onlytheindicationdeemedmostsevereislisted.Pluggingcriteriaareillustratedbytheboundarylinedrawninthetable.The107tubesinsidetheboundarywereremovedfromservicebyplugging.Inaddition,threetubeswerepluggedduetoreasonsunrelatedtosecondarysidecorrosion(twobecauseeddycurrenttestingcouldnotbeperformedandoneasaprecautionarymeasureduetoaDIatthetubesheetrolltransition).InTable1-B,allindicationshavebeentabulated.ThelargertotalcomparedtoTable1-Areflectsthefactthatsometubeshavemultipleindications,particularlyat.tubesupportplateintersections.Thistotalpopulationofindicationsisusedinlaterdegradationgrowthrateevaluations.Figures1,2,3,and4aretubesheetmapsforeachCook2steamgeneratorshowingthelocationandextentofwalldegradationinthesteamgeneratortubing.IndicationsplottedarethosecontainedinTablel-A.Figure5graphicallydepictsthedataofTable1-Bforeachsteamgenerator.Figure6isacompositeforallfoursteamgenerators,andgivesagraphicalcomparisonoftotalindicationsreportedduringtheMarch1987inspectiontothetotalindicationsleftinservicefollowingthe1986inspection.Thisprovidesanoverviewoftubedegradationprogressionduringthepastoperatingperiod.2.2TubeDeradationGrowthRateEvaluationTheobjectivesofthissectionaretodetermineifthetubedegradationobservedduringthemostrecentoperatingintervalisconsistentwithaveragegrowthratespreviouslydeveloped,andtoattempttoidentifycharacteristicsofthestatisticaldistributionofpreviousgrowthratedatawhichcouldbeusedintheevaluationoffutureoperatingintervals.Threepastoperatingintervalsareofinterestinthissection,andforconveniencearereferredtoas84-85,85-86,and86-87.Pertinent,factorsineachintervalareasfollows:

D.C.CookUnit2AEP:NRC:0936ZAttachment1IntervalDurationEFPDsBoricNominalAcid?Power84-857/07/84to7/15/85291.2No100485-8610/23/85to2/28/8685.0Yes86-877/07/86to3/03/87183.1Yes804804Thegeneral,averagegrowthratesincurrentuseweredevelopedafterthe85-86interval,andarebasedonapplyingidenticalanalysiscriteriatothe1985and1986inspectiondata;specificsofthismethodologyarediscussedinSection2.2.2.The85-86intervalprovidedauniqueopportunitytodevelopagrowthratemethodology,becausemanytubesleftinserviceafterthe1985inspectionwouldhavebeenpluggedhadthelateranalysisandpluggingcriteriabeeninuseatthetime.Thevalidityoftheexistinggeneralgrowthratemethodologywillbeexaminedin,twoways.First,tubeplugginghistorywillbereviewedtoseeiftherecentpluggingisconsistentwithpluggingexperienceduringtheearlierinterval.Thiscomparisoncannotdemonstratethatthemethodologyisvalid,butcanbeusedtoshowthatthemethodologyisnotnecessarilyinvalid.Second,thepopulationofindicationsfromtherecentinspectionwillbeevaluatedtoseeifitstatisticallyfitsthedistributionofthe85-86intervalgrowthratedata.2.2.1TubePluggingComparisonAbroadindicatoroftubedegradationgrowthrateisthetubepluggingrequiredattheendofeachoperatinginter-val,asshowninItem1ofTable2.'Anobviousfallacywiththisgrosscomparisonisthatitdoesnotaccountfordif-ferentoperatingintervallengthsorforchangesindataanalysisandpluggingcriteria.Accountingforoperatingintervalsof9.7,2.8,and6.1EFPMsforthe84-85,85-86,and86-87intervals,respectively,yieldsthecomparisonshowninItem2ofTable2.FurthercompensationforchangesinanalysisandpluggingcriteriaresultsinthemoremeaningfulcomparisongiveninItem3.Thislastcomparisonreflectsthe107tubespluggedattheendofthe85-86intervalwhichwouldhavebeenpluggedattheendofthe84-85intervalifthelatercriteriahadbeenapplied,andthe10tubespluggedattheendofthe86-87interval'hichneednothavebeenplugged.(Theselatter10tubes D.C.CookUnit2AEP:NRC:0936ZAttachment110hadsupport,plateindicationsbelowthe1.75voltthresholdforplugging,butwerepluggedasanaddedconservatismbasedonrecommendationsofthedatainterpreter).ReviewofTable2showsthatthecompensatedtubepluggingrateduringthe86-87intervalcloselymatchesthat.ofthe85-86interval(15.9vs.14.8tubes/EFPM),whichindicatesthatthegeneraltubedegradationgrowthrateobservedinthe86-87intervalisconsistentwiththat.observedinthe85-86interval.Thisisanexpectedresultsincepowerlevelandchemistryparameterswereconsistentduringeachinterval.Sincethegrowthratemethodologyincorporatesdifferentgeneralgrowthratesforthetubesheetcreviceregion,tubesheetsurfaceregion,andtubesupportplateinter-sections,aslightlymorerefinedtestistoevaluatetubepluggingratesateachofthesethreeareas.Table3providesacomparisonofthecompensatedtubepluggingrateforeachareaduringthe85-86and86-87intervals.Reviewofthetableshowsthatthetubepluggingrateineachareaisfairlyconsistentforthetwointervals,andfurthersuggeststhatthegrowthratemetholodogyisvalid.Fromareviewoftubeplugginghistory,itcanbeconcludedthatthepluggingrequiredinMarch1987isconsistentwiththepreviousoperatingperiod.Therefore,thenumericaldegradationgrowthratedatadevelopedduringthatpriorperiodmaybevalidforassessingthenextoperatinginterval.2.2.2GrowthRateDeterminationQuantitativegeneralgrowthrateshavebeenevaluatedafterpastoperatingintervalsforthethreeareasofinterest.Thedeterminationoftheaveragegrowthrateforeachareahasbeenmadebycomparingeddycurrentinspectionresultsbeforeandafteranoperatinginterval.Tubeswithoutevidenceofdegradationorwithverylow,non-quantifiabledegradationhavebeenexcludedfromthecalculations.Thus,thegrowthratesdeterminedreflectthegeneral,averagedegradationgrowthrateoftubesundergoingobservabledegradation-nottheentiretubebundle.Severalmethodsfordeterminingnumericalgrowthrateshavebeenused.Themostobjectiveandreliableisadirectcomparisonofclearindicationsfromoneintervaltothenext("4TW-4TW"Method).Theothermethodsareregardedaslessdependablesincetheyutilizeassumptionsoninitialconditions.Theyareuseful,however,becausetheyallowacomparisontothe"~TW-4TW"Methodresultsandbecausetheyprovidealargersamplesize.Asreportedinprior' D.C.CookUnit:2AEP:NRC:0936JAttachment1submittals,thealternatemethodsandthe"4TW-4TW"Methodyieldconsistentresults.Asnotedearlier,the85-86intervalprovidedauniqueopportunitytoassessgrowthratesusingthe"4TW-4TW"Method.Becauseofnewanalysisandpluggingcriteriathatevolvedafterthe1985outage(fromtubesamplesremovedduringthe1985outage),anumberofnow-pluggableindica-tionswereleftinserviceandgivenanopportunitytogrowduringthe85-86operatinginterval.Comparisonofthereevaluated1985datawiththe1986dataresultedindevelopmentofthegeneralgrowthratemethodologydescribedinReferenceSubmittal2,andsummarizedbelowforconvenience:85-86IntervalIGASCCGrowthRatesLocationMeanGrowthRateSampleSizeTubesheetCreviceRegionTubesheetSurfaceRegion1.600.821918TubeSupportPlateInter-sections0.6638Theabilitytodeterminenewgrowthratesduringthe86-87intervalforthetubesheetcreviceandtubesheetsurfaceregionsusingthe"<TW-~TW"Methodhasbeeneffectivelyeliminatedbecauseofpluggingcriteriawhichremovedallpreviousindicationsfromservice.Thusthepopulation'f4TWsfromthisoperatingintervalrepresentstheextremeingrowthratepossibilities,i.e.tubesclassifiedpreviouslyasNDDwhichgrewtohigh4TWs.Inessence,allthatcanbeobservedisthetailofthestatisticaldistributionofgrowthrates.Iftheextremesofthepopulationcanbeshowntofitthedistributionofthepreviousgrowthratedata,theassumptioncanthenbemadethatthedistributionasawholehasnotchangedandaprobabilisticgrowthratemodeldevelopedfromthe85-86intervaldatawillbevalid.2.2.3ProbabilisticModelVerificationToevaluatetheextremesintubeconditionsobservedinthemost.recentoperatinginterval1)astart-of-intervaltubeconditionprobabilitydistributionwasdetermined,2)thegrowthrateprobabilitydistributionfromthe85-86interval D.C.CookUnit2AEP'NRC0936ZAttachment112wasassumed,3)thetwodistributionswerecombinedtodefineanhypotheticalend-of-intervaltubebundlecondition,and4)thehypotheticalconditionwasthencomparedtotheMarch1987inspectionresultstoconfirmthemodel.Thestart-of-intervaltubeconditionprobabilitydistribu-tionwasestablishedfromthe1986inspectionresultsandtheprobabilityofdetection/non-detectionforvariousindicationsizes.Non-quantifiableindications(DIs,SQRs,andUDSs)wereincludedinthepopulationinanappropriate4TWsizerangebasedondetectionthresholdandothereddycurrentinformationindependentof"sizing"parameterswhichweredevelopedfromcorrelationofprevioustubesampleanalysisandeddycurrentdata(seeReferenceSubmittal3,WCAP-11055,Figure4.1andReferenceSubmittal2,WCAP-11329,Figure2.2.4).Theendresultsoftheabove-describedcomparisonareshowninFigure7forthetubesheetcreviceregion,Figure8forthetubesheetsurfaceregion,andFigures9-Aand9-Bfortubesupportplateintersections.Inthetubesheetsurfaceregionandattubesupportplateintersections,themodeldatawasfitwitha"bestestimate"curve.Inthetubesheetcreviceregion,themodeldatawasfitwithamoreconserva-tive"over-prediction"curveinrecognitionofthefactthatcrevicecorrosionhasbeenthelimitingfactorforcontinuedoperation.Reviewofthesefiguresshowsverygoodagreementbetweenthemodel'spredictionandtheactualinspectionresults.Fromthisitisconcludedthatgrowthratedatafromthe85-86intervalisvalidforassessingthelengthofthenextoperatinginterval.3.0EVALUATIONOFOPERATIONTHROUGHTHEENDOFFUELCYCLE63~1USNRCReulatorGuide1.121Basis3.l.1MinimumAllowableWallDeterminationMinimumwallrequirementsfortheCook2steamgeneratortubingwerecalculatedinaccordancewiththecriteriaofR.G.1.121,entitled"BasesforPluggingDegradedPWRSteamGeneratorTubes".ConfirmationthattherecommendationsoftheguidearemetintheCook2steamgeneratorswasdemonstratedinReferenceSubmittals2and3,andisrestatedhereforconvenience.

D.C.CookUnit2AEPNRC0936ZAttachment113ThebasicrecommendationsofR.G.1.121areoutlinedbelow.I.Allowableminimumwalldeterminationperthefollowing:Fornormalplantoperation,primarytubestressesarelimitedsuchthatamarginofsafetyof3isprovidedagainstexceedingtheultimatetensilestressofthetubematerial,andtheyieldstrengthofthematerialisnotexceeded,consideringnormalandupsetconditionloadings.2.Foraccidentconditionloadings,therequirementsofparagraphNB-3225ofSectionIIIoftheASMECodearetobemet.Inaddition,itmustbedemonstratedthattheappliedloadsarelessthantheburststrengthofthetubesatoperatingtemperatureasdeterminedbytesting.3.Foralldesigntransients,thecumulativefatigueusagefactormustbelessthanunity.II.Leak-Before-BreakVerification,i.e.,thatasinglethrough-wallcrackwithaspecifiedleakagelimit(TechnicalSpecificationleakratelimit)duringnormaloperationwouldnot;propagateandresultintuberuptureduringpostulatedaccidentconditionloadings.Inestabishingthesafelimitingconditionofoperationofatubeintermsofitsremainingwallthickness,theeffectsofloadingsduringbothnormaloperationandpostulatedaccidentconditionsmustbeevaluated.ItemI.3isaddressedindetailinbothReferenceSubmittals2and3.Briefly,fromtheviewpointoffatigueandrelatedimplicationsofcracking,thecausesofcrackingareaccountedforintheverificationofleak-before-break.Inthecalculationoftubeminimumwall,threedistinctareasoftubedegradationwithintheCook2steamgeneratorswereaddressed:thetubesheetcreviceregion,thetubesheet.surfaceregion,andthetubesupportplateintersections.Basedonpreviousmetallography,tubeminimumwalldeterminationforlocalizedtubedegradationoccurringinthetubesheetcreviceoratthetopofthetubesheetassumed:

D.C.CookUnit2AEP:NRC0936JAttachment1142~TubedegradationtobecharacterizedaseithermultipleSCCorIGA/SCC(intergranularSCCcombinedwithshallower,morewidelyspreadIGA).Tubewalldegradationcanbeevaluatedasequivalentthinning(asaresultofIGA)withasuperimposedcrack.3.Theaxialextentoftheequivalentthinnedlengthoftubedegradationis1.5inches.Also,theIGA(equivalentthinning)wasuniformaroundthetubecircumference.Likewise,thetubeminimumwalldeterminationforthe'localizedtubedegradationoccurringatthetubesupportplateelevationsassumed:1.TubedegradationtobemultipleSCC,withindividualcracks0.1to0.2inchinaxialextent.2.Partialthrough-wallcrackingcanbeevaluatedassingleandmultiplecracks.3~Astubesupportplatedegradationwasconfinedtothethicknessofthetubesupportplate,themaximummacrocracklengthisequaltothesupportplatethickness,or0.75inch.4.Link-upofmultipleSCCisimprobableatpostulatedaccidentconditionpressuredifferentialasreflectedinthetubespecimenbursttests.ResultsofthesecalculationsareprovidedinTable4foreachoftheaboveareasoftubedegradation.Moreover,Table5providesasummaryofminimumwalldeterminationforthethreeregionsoflocalizedtubedegradationoccurringintheD.C.CookUnit2steamgenerators.Ineachcase,thelimitingcriterionfordeterminingtheallowablewallreductionistheR.G.1.121criterionfornormaloperationthatrequiresamarginofsafetyof3againstexceedingtheultimatetensilestressofthematerial.3.1.2Leak-Before-BreakVerificationTheleak-before-breakrationaleistolimittheallowableprimary-to-secondaryleakrateduringoperationsuchthattheassociatedcracklengthwhichTechnicalSpecificationleakageoccursisthecriticalcracklengthcorrespondingtotubemaximumnormalthroughlessthanburst.atthe D.C.CookUnit2AEPNRC0936JAttachment115maximumpostulatedpressureconditionloading(SLB/FLB).Again,ReferenceSubmittals2and3showonthebasisofnormaloperationthatunstablecrackgrowthinatubeisnotexpectedtooccurinthetubesheetcrevice,topofthetubesheet,ortubesupportplateintersectionsoftheCook2steamgeneratorsintheunlikelyeventofalimitingaccident.Itisdemonstratedthatgrowthofpartialthrough-wallcracksexhibitalimitedaspectratio.Thischaracteristicresultsincrackextensionthrough-wallpriortoreachingtheSLB/FLBcriticalcracklength.3.2IGMECo'sutilizationofaprimary-to-secondaryleakmonitoring,policywhichemphasizesbothabsoluteleakratemeasurementandrateofchange,andwhichincludestheinitiationofactionpriortoreachingtheTechnicalSpecificationlimit,yieldsadditionalsafetymargin.3.1.3EddyCurrentTestingUncertaintyComparisonofinsitueddycurrentinspectionresultswithlaboratorydestructiveanalysisoftubesamplesremovedfromtheCook2steamgeneratorshasprovidedagoodbasisfordeterminingtheeddycurrent.testinguncertaintyassociatedwiththeparticulartubedegradationexperienced.onCook2.Fortubesamplesinwhichmetallographyrevealedtubewallpenetrationtobeatleast40percentthrough-wall,theinsitueddycurrenttestsyieldamaximumunder-predictionof16percent.Aswallpenetrationgetsdeeper,theeddycurrenttestsmorecloselypredicttheactualdepthofpenetration(seeReferenceSubmittal3,Figure4-3).Tobeconservative,a16percenteddycurrenttestinguncertaintyisusedtoevaluateoperatingintervallength.0eratinIntervalJustification-SafetAssessmentTheinfluenceoftheoperatingenvironmentmayaffectsomeofthetubesinthesteamgeneratorandresultinlocalizedwalldegradation.Aspartofapreventiveprogramtodetecttubedegradation,in-serviceinspectionusingeddycurrenttechniqueswasperformed.Affectedtubeswitharemainingwallthicknessgreaterthantheminimumrequiredwallthicknessareacceptableforcontinuedservice,providededdycurrentmeasurementuncertaintyisaccountedforandanoperationalallowanceforcontinueddegradationuntilthenextscheduledinspectionisconsidered.Table6summarizestheprojectedsafetymarginsforlocallydegradedsteamgeneratortubing,bytubeelevation,uponcompletionofCycle6operationofCook2(about240EFPDsor8.0EFPMsfromstart-uponApril21,1987).Itisdemonstratedfromasafetyperspectivethat,operatingintervalmarginexistsat D.C.CookUnit2AEP:NRC:0936JAttachment116allthreetubeareasinquestionwithrespecttotubeminimumallowablewall.ThesemarginsarebasedonthemaximumpermissiblewalllosscalculatedinaccordancewithR.G.1.121criteria,aneddycurrenttestinguncertaintyof16percent,andthegeneraldegradationgrowthratesdescribedinSection2.2.2.Whiletheaboveevaluationdemonstratesthattherecommenda-tionsofR.G.1.121aremetforanoperatingintervalof8.0EFPMs,theincidenceofprimary-to-secondaryleakageduringthatintervalisnotprecluded.I&MECohasconservativelychosentoestablishanoperatingintervalwhichminimizesthepotentialforforcedoutagesduetosteamgeneratortubeleaks.4.0OPERATINGINTERVALDETERMINATION4.10erationalConsiderationsAsnotedearlier,anoperatingintervalbetweensteamgeneratorinspectionswillbeselectedsuchthatthepotentialforaforcedoutageduetosteamgeneratorleakageisminimized.However,becauseofthehighcostandhighoccupationalradiationexposureassociatedwithsteamgeneratorinspections,theoperatingintervalshouldbeaslongaspossibletominimizethenumberofintermediateinspectionsrequiredpriortoreplacementoftheCook2steamgenerators.The.selectedintervalshouldalsobeconsistentwithfuelcycleconsiderations,andshouldofferIGMECosomeflexibilityforschedulingbasedonsystemloadrequirements.Atstart-uponApril21,1987,Cook2hadabout240EFPDsoffuelremaininginCycle6.Sincetherecenttubeleakoccurredafteronly183EFPDsofoperation,theneedforanintermediateinspectionisapparent.Anobviousintervaltolookatwouldbethemid-pointoftheremainingfuel,orabout120EFPDs.At80percentpower,theearliestthiscouldoccurismid-September1987,whichwouldnotconflictwiththescheduledCook1refueling,andshouldbeafterthesummerpeakloadperiod.However,choosingtheexactmid-pointoftheremainingfuelaffordsIGMEConoflexibilityastowhentoremovetheunitfromservice;alateshutdownwouldviolatethejustifiedintervalandanearlyshutdownwouldmakethesecondintervallongerthanjustified.Anallowanceofaboutthreeweeksshouldbeaddedtoprovidethisneededschedulingflexibility.Therefore,anoperatingintervalof140EFPDs,or4.7-EFPMs, D.C.CookUnit2AEP'NRC'0936ZAttachment117isacceptablefromanoperationalperspective.ThepotentialforsteamgeneratorleakageduringthisintervalisassessedinSection4.2.4.2TubeBundleConditionPro'ectionDuringthemostrecentoperatinginterval,asteamgeneratortubeleakofsufficientmagnitudetoinitiateunitshutdownoccurredsoonerthanexpectedbasedonthepriorsafetyanalysiswhichjustifiedoperationthroughCycle6.AlthoughtheleakwasbelowTechnicalSpecificationlimitsandwaswellwithinoperatorcontrolcapabilitiestopreventanoff-siteradiationrelease,theelementofsignificantcurrentinterestiswhytheleakoccurredinsuchashorttimeframe.Xnanefforttoaddressthisconcern,severalpossibilitieswereidentified.Eachpossibility,alongwithitsassociatedresponserelativetoselectingthenextoperatingintervalandanevaluationofitslikelihoodofbeingtrue,isoutlinedbelow:higherthanduringpreviousperiods.~Resonse-Usethehighermeangrowthratestoadjusttheoperatingintervaltocomplywithsafetyanalysisconsiderations.Evaluation-Littleornoevidencecouldbefoundtosupportthispossibility;asdescribedinSection2.2,growthratesareconsistentwiththe85-86interval.generaldz.stributionsofgrowthratesandinitialconditions,andisthereforearandomevent.~Resonse-Maintaintheprioroperatingintervaljusti-fication,andaccommodateleakagefromanyadditional"outliers"throughleakratemonitoringandmaintenanceshutdownsasrequired.Evaluation-Someevidencesupportingthispossibilityisfoundinthefactthatthereisalownumberofveryhighlevelindicationsseparatedfromthemaindistri-butionofindications.combiningtheextremesofthegeneraldistributionsofgrowthratesandinitialconditions.

D.C.CookUnit2AEPNRC0936JAttachment118~Resonse-Adjusttheoperatingintervaltoreducethepotentialforleakagebyconsideringthestatisticaldistributionofthegrowthratedata.Evaluation-Evidenceinsupportofthispossi-bilitywasdevelopedthroughaprobabilisticmodelcombiningstart-of-intervaltubeconditionsandgrowthrates,asdescribedinSection2.2.3.Theresultsoftheevaluationhavelargelyeliminatedthefirstpossibility.Whilethesecondandthirdcasesarestillpossible,thepresentinformationfavorsthethird.Therefore,undertheassumptionthatextremedegradationconditionsareafunctionofoperatingintervalandnotarandomoccurrence,itseemsprudenttoadjusttheoperatingintervaltominimizethepotentialforleakage.ConsistentwiththeSection4.1discussionofreasonableoperatingintervallengths,anoperatingintervalof4.7EFPMswasconsidered.Toassessthereductioninpotentialforleakage,theprobabilisticmodeldescribedinSection2.2.3wasappliedinthesamemannerasusedtoassessgrowthrate.Theanalysisincludednewstart-of-intervalconditionsresultingfromtheMarch1987inspectionandplugging,andusedthegrowthratedistributionderivedfromthe85-86interval.Theprojectedend-of-intervalconditionsforthetubesheetcreviceregion,tubesheetsurfaceregion,andtubesupportplateintersectionsareshowninFigures10,ll,and12.Sincetheend-of-intervalprojectionsshownoappreciablenumberoftubesatextremewallpenetrations,suchasmightresultinleakage,the4.7EFPMintervalisconsideredappropriate.

5.0CONCLUSION

SThefollowingconclusionshavebeendrawnfromreviewandevaluationoftheMarch1987Cook2steamgeneratortubeleakeventandsubsequenteddycurrentinspectionresults:oTheleakwastypicalofpreviousIGA/SCCdegradationexperiencedintheCook2steamgenerators.Anadequateunderstandingofthisdegradationmechanismhasbeenacquiredthroughpreviousmetallographicexaminationandbursttestingoftubesamples,sonofurtherdestructivetestingisnecessary.oTherecentoveralleddycurrentinspectionresultsand D.C.CookUnit2AEP:NRC:0936JAttachment119thenumberofpluggableindicationsareconsistentwithexperienceintheprioroperatinginterval,andcanbeusedtoshowthat.thegeneral,averagedegradationgrowthratemethodologydevelopedfromthe85-86operatingintervalisstillvalid.oAR.G.1.121safetyevaluationbasedontubestructurallimitsfortheCook2steamgeneratortubing,generaltubedegradationgrowthrates,andaconservativeeddycurrentuncertaintymargincouldbeusedtojustifyoperationthroughtheremaining8.0EFPMsofCycle6.However,thereisadistinctprobabilityofatubeleakoccurringduringthatinterval.oAprobabilisticgr'owthratemodeldevelopedfromthegeneralgrowthratedatabasecanbeusedtopredictextremeconditionsofthetubebundlesfollowingaspecifiedoperatinginterval.Determinationofanoperatingintervalbasedonextremeratherthangeneraltubeconditionsshouldgreatlyreducetheprobabilityofaprimary-to-secondarysteamgeneratortubeleakduringthatinterval,althoughthepossibilityofarandom(outlier)eventcannotbeprecluded.Selectionofaconservativeoperatingintervalbasedonextremetubeconditionsshouldalsoincludeoperationalconsiderationstoreasonablylimittheeconomicpenal-tiesandincreasedpersonnelradiationexposureassociatedwithmorefrequentsteamgeneratorinspec-tions.Anoperatingintervalofabout4.7EFPMsmeasuredfromthereturn-to-powerinApril1987appearsmostappropriatewhenconsideringbothextremetubeconditionsandremainingfuelinthecurrentfuelcycle.IGMECowillremoveCook2fromservicewithinthatintervaltoverifyandrestoreasnecessarytheintegrityofthesteamgeneratortubebundles.ThesubsequentoperatingintervalwouldendattheCycle7refuelingoutage.oSelectionofoperatingintervalsbeyondCycle6shouldconsideroperatingexperienceduringthenexttwointervals,theresultsofthenexttwotubeinspectionprograms,lengthofthenextfuelcycle,andschedulingofthesteamgeneratorreplacementoutage.I&MECorecognizesthatexcessivesteamgeneratortubeleakageresultinginunscheduledshutdownsisnotacceptableonacontinuingbasis,andhasadoptedaconservative.

D.C.CookUnit.2AEP:NRC:0936JAttachment120approachtoselectingthenextoperatingintervalwhichshouldgreatlyreducetheprobabilityofaforcedshutdownduetoleakage.Previouslyinstitutedremedialmeasures(e.g.-bettersecondarywaterchemistry,boricacidtreatment,andadministrativepowerreduction)willbecontinuedduring.theinterval.Intheunlikelyeventthattheincidenceofextremewallpenetrationisarandomeventandisnotpredictedbytheforegoingprobabilisticanalysis,thenIGMECo'sleakratemonitoringprogramandtheTechnicalSpecificationleakratelimitwillensureleak-before-breakconditionsandthatanorderlyshutdowncanbeaffected.IGMECo'sadministrativepolicyofshuttingdownbeforereachingtheactualleakratelimitaddsadditionalmargintoleak-before-breakconsiderations.

Table1IndicationsofHotLeSecondarSideCorrosion-March1987A.Includingonlythemostsignificantindicationpertube,totalforall4SGs.Location<404>404DIUDSSQRTotalTubesheetCrevice64255TubesheetSurface1931TubeSupportPlatesTotal15182159433615042630716B.Includingmultipleindicationspertube,totalforall4SGs.Location<404>40<DIUDSSQRTotalTubesheetCreviceTubesheetSurface196425531TubeSupportPlatesTotal16192383035851042869955 Table2TubesPluedDuetoIGASCC-GeneralComarison0eratinInterval84-8585-8686-872~3~TubespluggedduetosecondarysideIGA/SCC(totaltubes)TubespluggedduetosecondarysideIGA/SCC(tubes/EFPM)TubespluggedduetosecondarysideIGA/SCC,compensatedforchangesinanalysisandpluggingcriteria(tubes/EFPM)14114.525.514952.714.810717.515.9Table3TubesPluedDuetoIGASCCComensatedforChanesinAnalsisandPluinCriteria-ComarisonbLocationLocation0eratinInterval85-8686-87TubesheetCrevice(tubes/EFPM)TubesheetSurface(tubes/EFPM)TubeSupportPlateIntersections(tubes/EFPM)10.92.81~114.89.05.11.815.9 Table4Cook2SteamGeneratorTubinMinimumAccetableWallReirementsA.Tubesheetcreviceandtubesheetsurfaceregions.CriteriaConditionMinimumWallinchesyieldASMECodeSu/3normalfaultednormal0.0150.0170.019B.Tubesupportplateintersections.CriteriaConditionMinimumWallinchesyieldASMECodeSu/3normalfaultednormal0.0120.0130.015Table5Cook2SteamGeneratorTubinAllowableWallLossDeterminationLocationGeometricConditionBasisAllowableWall~LossTubesheetCreviceRegionAxialextent>1.5inchesSu/362TubesheetSurfaceRegionAxialextent>1.5inchesSu/362TubeSupportPlateIntersectionsAxialextent<0.75inchesSu/370 Table60eratinIntervalJustificationRemainderofFuelCcle6-R.G.1.121BasisItemAllowabletubewallloss(>)ECTuncertainty(4).Growth(4/EFPM)Projectedgrowth(+o/8'EFPM)Plugginglevelrequired(4)TubesheetCrevice62*161.612.833.2TubesheetSurface62160.826.639.4TubeSupportPlates70*160.665.348.7Plugginglevelimplemented(%)AllAll40.0*Tubeburstwithinthetubesheetcreviceregionorattubesupportplateintersectionsisconsideredtobeincredible.

ECINSPECTIONRESuLTS-MARCHf987SECONDARYSIDECORROSION,HOTLEGPLANT:DCCOOKUNIT20~PLUGGASLEINOICATIONS.TSCREVICE(2)w~teN-PLUGGASLEINOICATIOHS.TSPS092)GENERATOR:2i0~PLUGGABLEIHOICATIOHS.TSSURFACE(T)TOTALTUBES:3388OUTOFSERVICE(N):f42v~PLUGGASLEIHOICATIOHS.TSPo(5)TOTALTUSESASSIGNER209~~aoOJJ~~JJJ25C/lD~~~++~20IIVAd'DCll~J4~JJJJ~JJJ~JJ~JTJJ~joO~4~~~~~~~~J~~~~~~~~~~~~~~~~~~~~~J~~~~~~~~~~~~~~~~~~~o5IIrgNAHNAYIIIP.INLET(NotLog)IIIIICOLUHHSIIIIIIR88oFigure1I ECINSPECTIONRESULTS-MARCHl987SECONDARYSIDECORROSION,HOTLEGPLANT:DCCOOKUNIT2GENERATOR:22TOTALTUBES:3388OUTOFSERVICE(B):2lOo-pLUBBABLEZNorcAnoNB.TscREvrcEtao)ksNOIR.USSABLEZNOZCATZONS.TSPs(2fB)0~PLUSSABLEZNOZCATZONS.TSSURFACEBO)T>PLUSSABLEZNOZCATZONS.TSPs0)70TALTUBEsAssrsNEo:247k00~~JkJkkkkkJkkkkJ~JkJJ~kkJkJkkJkSkJJJ~~k~~~~~~s~~~~4~~~k~~~~0~JksJJoJSJk20V-XOJkkkkkJ0okkk~J~JkSk~ks4kos~kkk0kkkJ0~J0J0J000~J~~~~~~s~~~~~~~~~~s~~~~s~k~~~sJJk~~~~kkJ~~~~~~~~~~~~J~~~~~~~~~~~~~s~~s~~~~~~~~~~~~s~~IIgIII8RZtLETtNotLay)IIIII=IIIIIIIIIt88800RR-880COLUNNSNOZZLEFigure2 ECINSPECTIONRESULTS-MARCH1987SECONDARYSIDECORROSION,HOTLEGPLANT:DCCOOKUNIT2GENERATOR23TOTALTUBES'388OUTOFSERVICE(0):2100~PUNSABLEINOICATIOHS.TSCREVICE(27)NNRVISSABLEIINICATIONS,TSPOt64)0~PLUSBA))LEIHOICATIONS,TSENFACE(9)v~PLU66ABLEINOICATIONS,TSPs(1)TOTALTLNESASSISNEL121J~~J~JJ~~ssr~~00~0r0~J~J0~~J0~ss~rrr~os~~~0~~~~r44or00~~~~0~JIQR20V10r~~r~~~~00~~~r~~rr~~~~r~~~r~~~r~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~r~~~srr~r~~~~~JJ~re~IIgNAWAYIIIm8RI%ETOhtLsg)IIIIIIIIIIIIII)'38m)800R888880c-COLUMNSHOZZLEFigure3 ECINSPECTIONRESULTS-MARCH1987SECONDARYSIDECORROSION,HOTLEGPLANT:OCCOOKUNIT2CI~PLUSSABLEZ)QICATZOMS,TSCREVICE(8)A~~U68ABLEINOZCATZONS,TSPr(Zfd)GENERATOR24TOTALTUBES:3388OUTOFSERVICE(s)'010~PLUBSASLEI)NICATIONS,TSSNFACE(8)T~PLUSSABLEIHOZCATZNBLTSPs(1i)TOTALT(NESASSZSNE(kf39AA~AAA~~~A~AAAVAAAAAAATA~AAAAAAAA~~~~~~~~~~s~~~~~s~r~~~~s~~~~~20V~~s~ArAss~4A~~4s~~ArA4~sLO8s~ssburrsburrs~s~rsr'~~~r~~~~~rer~~~~~~~~~~~~~~~~~~s~~~~rs~~srsss~r~~~~~rsvpIIIIIIIIIIIIIIII888P888$8))88888)IANNAYI)LET(HotLoO)COL(NNSFigure4 OCCOOKUHIT2SteamGeneratorI2fECINSPECTIONRESULTS-MARCHi987cvCaOCCOOKUIIIT2SteamGenetator:22ECINSPECTIONRESULTS-MARCHi98700to8H820HI"0Ha2HTM4TSiH~aHsHSH~~~sHTHTRHTSHtHSHSH~OHeHVHGENERATORELKVATZONS4R0088HIt.0OI20HI-0HD2HTlOI'tmfHCHtkHsHSH~~~sHTHTRHTSH4HaHSM~sH4MVHGENERATORELEVATZONS>40%TW~DZ<<40KTW~UDSSQRQ>40%TW+DZQ<<40KTWQUDSQSQROCCOOKUIIIT2SteamGenetstoaI23ECINSPECTIONRESULTS-MARCHi987OCCOOKUNIT2SteamGenetstot':24ECINSPECTIONRESULTS-MARCHi98700to8H10000oI8HCOO820HI-0HD2HVlOITSIH4HeHaHatt~~~OH7HTEHT4HCHRHSH~sHOHvHGENERATORELEVATZONS20HI-0HD2HTIHTSfHfHsttSH5H~~~eH7HTCHTSHkHsttaHAHsHOHVHGENERATORELKVATZONS%40XTW~DZ<<40KTW~UDSggSQR>40%TW~DZ<<40%TW~UDSSQRFigure DCCOOKUNIT2SteamGenerator:00START-OF-INTERVALTUBEBUNDLECONDITION-JUL198640000N8HQ.0NZ0HI"00ZH350300250200150100ao0TMHTS-1H1H-2H2H3HSH4H4H-5HSH-SH6H7HTEHTSH1H2HSH4HSHSH7HGENERATORELEVATIONS>40KTW+DI<40KTW+UDSDCCOOKUNIT2SteamGenerator:00END-OF-INTERVALTUBEBUNDLECONDITION-MARCH198740000N8HU0NZ0Hl-0H0ZHSSO900250200150100500THHTs-1H1H-2H2H-SH9H-4H4H-aHSH-SHSH-7HTSHTSH1H2HSH4HSHSH7HGENERATORELEVATIONS>40XTW+DI<40KTW+UDSFigure6 40C0~rfg)30O~IH200InspectionModel1005060708090100TubeWallPenetration,10KIntervalsFigure7ComparisonofModelPredictiontoActualECInspectionResults,TubesheetCreviceRegion i6Co14U12HiO8O6z2'~Y'InspectionModel405060708090iooTubeWallPenetration,iOXIntervalsFigure8ComparisonofModelPredictiontoActualECInspectionResults,TubesheetSurfaceRegion (o500C04003000200z~InspectionModel0iO2030405060708090100TubeWallPenetration,KOXIntervalsFigure9-AComparisonofModelPredictiontoActualECInspectionResults,TubeSupportPlateIntersectionsFullRange,0toKOOKTW 25C0~He20U~HC150c1054'InspectionModel405060708090100TubeWallPenetration,10KIntervalsFigure9-BComparisonofModelPredictiontoActualECInspectionResults,TubeSupportPlateIntersectionsBlowupof40to100KTWRange

10010EDz.01TubeWallPenetration,5%IntervalsFigure10PredictedEnd-of-Interva1Condition,TubesheetCreviceRegion 10010*Sr.14TubeWallPenetration,5XIntervalsFigure11PredictedEnd-of-IntervalCondition,TubesheetSurfaceRegion 100TubeWallPenetration,5XIntervalsFigure12PredictedEnd-of-Interva1Condition,TubeSupportPlateIntersections 03 Attachment2toAEP:NRC:0936JSteamGeneratorManwayCoverClosureRepairsMarch-April1987 h

D.C.CookUnit2AEP'NRC:0936j'ttachment21ESTEAMGENERATORMANWAYCOVERCLOSUREREPAIRSMarch-April1987Eachsteamgeneratorchannelheadhalf(hotlegandcoldleg)hasa16-inchmanway;designoftheboltedclosureisshowninFigure1.WhenopeningthemanwaystoperformtubeinspectionsfollowingtheMarch1987steamgeneratortubeleak,difficultyinremovingtheboltsonbothlegsofSGs22and23wasencountered.Therewasevidenceofgallingundertheboltheadatsomelocations,andanobservationwasmadethatinsufficientthreadlubricantmayhavebeenusedduringthepreviousinstallation.FiveboltsonSG23couldnotberemovedbyde-torquingandweredrilledout.TheboltsonSGs21and24wereremovedwithoutdifficulty.ActionstakenbyI&MECoasaresultoftheboltremovalproblemincluded:oAdesignchange(RFC)toallowuseofhardenedsteelwashersundertheboltheadswasapproved.Thischangeisintendedtoprovideamoreuniformfrictionfactorunderthehead,andthereforeintroducemoreuniformbolttension.oThenewly-approvedwashersandnewmanwaycoverboltswereprocuredforuseinre-installingthemanwaycovers.oWestinghousewashiredtoinspectandgaugetheboltholes.A"go/notgo"gaugewasusedtodeterminetheacceptabilityoftheholepitchdiameter.Thegaugetoleranceswerethoseofanewholeandwerethereforeveryconservative.ResultsoftheboltholegaugingprogramonSGs22and23wereasfollows:oSG22-Fiveholesonthehotlegandfiveholesonthecoldleghadoversizepitchdiametersandrequiredrepair.oSSZZ-Thirteenholesonthehotlegandeightholesonthecoldleghadoversizepitchdiametersandrequiredrepair

D.C.CookUnit2AEP:NRC:0936J'ttachment2Eventhough:nodifficultywasexperiencedonSGs21and24,themanway.coverboltholesonthosetwosteamgeneratorsweregaugedasanaddedprecaution.Resultsofthatinspectionareasfollows:oSG21-AllsixteenholesonbothhotandcoldlegswereslightlyoversizeandcouldnotbedispositionedbyWestinghouse.Znalllikelihood,theholeswereacceptableandacompleteanalysiswouldhavealloweddispositionoftheminthe"as-found"condition.However,duetotheinherentdifficultyinmeasuringinsitufemalethreadparameters(e.g.-threadform,threadangle,andactualpitchdiameter),sufficientdatatodoacompleteanalysiscouldnotbereadilyacquired,soitwasdecidedtorepairthesealso.oSG24-Allholeswereacceptable.Twomethodsoffemalethreadrepairareincommonuse:replacementoftheexistingthreadswithaHeli-coilandinstallationofathreadedinsert.TheHeli-coilmethodwasselectedfortheUnit2repairs,withthethreadedinsertmethodheldasaback-upintheeventtheHeli-coiltechniquewasunsuccessfulonaparticularhole.Westinghouseprovidedasafetyevaluationandinstallationprocedureforeachmethod;anRFCtoallowtheuseofeitherwasapproved.However,useofthreadedinsertswasnotnecessary.TheHeli-coilrepairtechniqueconsistsofdrillingtheexistingboltholeabout1/8inchoverthenominalsizetoremovetheoldthread,threadingtheresultantholewithanappropriatesizedthreadtap,andthenscrewinginastainlesssteelHeli-coil(tradenameforahelicalthreadwhoseoutersurfacemateswiththenewly-tappedholethreadsandwhoseinnersurfaceformsfemalethreadsforthebolthole).Thenewholeacceptsthesamesizedboltasbefore,andactuallyhas"better"threads(closertolerances,moreexactthreadform,and-inthiscase-bettermaterial).Heli-coilsareconsideredapermanentrepair.TheHeli-coilrepairsweremadetoallaffectedboltholesasnotedabove,andthemanwaycoverswereputinplace-usingwashersandnewbolts-withoutfurtherincident.WeareevaluatingthecauseofthisproblemandwewillinformtheNRCoftheresultsofthisevaluationwhenitiscompleted Dia.ofCover26.75D~23bcFigure1PrimaryManveyArrangementGasketDia.16.~~Dia.18.1350.25--"16Bolts1-7/8in,Gasket:I.D.16.0625.O.D.=18.0625 Attachment3toAEP:NRC:0936JWestinghouseNuclearSafetyEvaluationofLooseMechanicalPluginSteamGenerator22 SECLr87-229CustomerReferenceNo(s).WestinghouseReferenceNo(s).~NS-RCS~L-87-450WJ%TEAHOUSENUCLEARSAFETYEVAIIJATIONCKXZIZST1)NUCLZARPRATE(S)D.C.COOKUNIT22)CKKKLESTAPPIZCABIZTO:IlXSEMESCALPIDGPH'MIGENERATOR22(SubjectofChange)3)Ihesafetyevaluationoftherevisedprocedure,designchangeormodificationrequiredby10CFR50.59hasbeenpreparedtotheextentrequiredandisattached.Ifasafetyevaluationisnotre@~orisimxmpleteforanyreason,explainonPage2.PartsAandBofthisSafetyEvaluationCheckListaretobecompletedonlyonthebasisofthesafetyevaluationperformed.CHECKIZST-PARDA(3.1)YesNoXAchangetotheplantasdescribedintheFSAR?(3.2)'esNoXAc1mngetoproceduresasdescribedintheFSAR?(3.3)YesNoXAtestorexperimentnotdescribedintheFSAR?(3.4)YesNoXAchangetotheplanttechnicalspecifications(AppendixAtotheOperatingLicense)?4)CHECKIZST-PARPB(JustificationforPartBanswersmustbe'includedonpage2.)(4.1)YesNoX(4.2)YesNoX(4.3)YesNoX(4.4)YesNoX(4.5)YesNoX(4.6)YesNoX(4.7)YesNoXWilltheprobabilityofanaccidentpreviouslyevaluatedintheFSARbeincreased?WilltheconsequencesofanaccidentpreviouslyevaluatedintheFSARbeincreased?MaythepossibilityofanaccidentwhichisdifferentthananyalreadyevaluatedintheFSARbecreated?WilltheprobabilityofamalfunctionofequipmentimportanttosafetypreviouslyevaluatedintheFSARbeincreased?WilltheconsequencesofamalfunctionofequipmentimportanttosafetypreviouslyevaluatedintheFSARbeinn~sed?Maythepossibilityofamalfunctionofequipmentimportanttosafetydifferentthan,anyalreadyevaluatedintheFSARbecreated?Willthemarginofsafetyasdefinedinthebasestoanytechnicalspecificationbereduced?PAGE1OF7

'h SECL-87-229Iftheanswerstoanyoftheabovequestionsareun)mown,indicateunder5)R12%RESandexplainbelow.Iftheanswertoanyoftheabovequestionsin4)cannotbeansweredinthenegative,basedonwrittensafetyevaluation,thechangecannotbeapprovedwithoutanapplicationforlicenseamen(:hnentsubmittedtotheNRCpursuantto10CFR50.59.5)REMARKS:None'Ihefollowingmamarizesthejustificationuponthewrittensafetyevaluation,(*)foranswersgiveninPartBoftheSafetyEvaluationCheckList:SeeattachedSafetyEvaluation.(*)Referencetodocument(s)containingwrittensafetyevaluation:Section:PagesTables:Figures:Reasonfor/DescriptionofChange:NonePreparedby(NuclearSafety):MATIHENSCcordinatedwithEngineer(e):NIESCNR.+Ccord(hatedGroupManager(e):KEATINGkPNuclearSafetycroupNanager:NNIsrC.Date.S~)~~~~Date:~~~87te:PAGE2OF7 SECL-87-229NS-RCS~/L-87-450PAGE3OF7D.C.COOKUIGT2ZDOSEMECHANICALPIIJGSTEAMGENER%)Rf22SAHH'YEVAIIJATION'Ihisevaluationisprovidedtoact]ressthesafetyimpactofanobjectfoundlodgedinatubeonthehotlegsideofsteamgenerator422ofD.C.CookUnit2.'Iheitemhasbeenidentifiedasamechanicalplugoriginallyinstalledinthehotlegtubeendofanothertubeinthesamesteamgenerator.1hisevaluationconsiderstheeffectofdisengagementoftheplugfrcanthetubeinwhichitwasoriginallyinstalled,theeffectoftheplugonthetubeinwhichitbecamelodgedandtheimpactoftheplugonthehotlegchannelheadccarponentswhiletheplugwasmobileandnotlodgedinanytube.Duringtherec~t100%eddycurrentprogramatD.C.CookUnitg2,aforeignobjectwasreportedtobelodgedinthehotlegofsteamgenerator522.'leobjectwaslocatedapproximately0.75inchesabovethetubeendofRear3Column5.'Xheforeignobjectwasreportedtoberoundanditappearedtocloselyfillthetubeinnerdiameter(ID).Afterprelimir~attemptsweremadetodislodgeandrezmvetheforeignobject,anattemptwasmadebysitepersonneltodrivetheobjectfurtherintothetube.i%iswasintendedtoallerenougha~toinstallamech-micalplugbehindit.Finallytheforeignobjectwassuccessfullyrawvedbyinitiallydrillingapilothole,followedbydrillinga3/8incha~holethroughthematerial,insertingaslidehairandthenpullingitfreefromthetubeID.Onceremved,theforeignobjectwasidentifiedasaWestinghousemechanicalplugthathadlodgedinthetubeendinaninvert~position.Athoroughreviewofvideotapesofthetubesheetinthehotlegofsteamgenerator422showedthatthetubeendatRow40Column39wasmissingamechanicalplug.'ibistubeendwasdocun~tedashavingbeenpluggedintheApril,1986outage,wasdetexnunedtobeopenandwastheapparentsourceofthemechanicalplugfoundinR3-C5.Toinvestigatethepossiblecauseoftheplugmovingfromthetubeendintowhichithadbeeninstalled,theremovedmechanicalplugandthetubeendatR40-C39werevisuallyandmechanicallyinspectedincludingtheexpandeddiametersandthem~ndertranslation.Visualexaminationoftheplugbyexperiencedmeclmnicalpluggingandqualityassurancepersonnelrevealedthattheplugexhibitedscratchesonthesurfaceaswellasthepluglandshadbeenrounded SECXr87-229'S-RCS~/L-87-450PAGE4OF7off.,'IhetubeID(R40~9)inthee1evationrangewheretheplugisdesignedtoseal,wasmeasureat0.5inchintervalsattwoazimtuths.Therecordeddiametersareconsistentwiththencaninalroll.expardeddiametersforsteamgeneratorswith7/8inchdiametertubing.%hetubeendwasvisuallyexaminedtocheckforanycircumferentialindentationsthatareoccasionallyleftinthetubeIDafterasuccessfulinstallationandsubsecpent~ncnralandnonewereevident.%hetubeerdinwhichtheplugbecamelodged(R3-C5)wasinspectedinaccord-mcewiththeproperacceptancecriteriaasspecifiedintheprocedureformechanicalpluggingofsteamgeneratortubes.Itwasevaluatedasacoeptableformeclmnicalplugging.WehotlegtubeendatR40C39wasa1soevaluatedasacceptableforinstallationofanewplug.Botherdsofthetubeinwhichtheplughadbeccalodged(R3-C5)weremechanicallypluggedandthetubevznovedfromserviceasaprecautionarymeasure.%hehotlegtubeendofR40-C39,thatwasmissingthemechmicalplugwasalsomchtanicallyplugged.theprocessparametersforthesepluggingoperationswerewitnessed,verified'arxlrecorded.%heconditionforwhichtheR40-C39tubehadbeenpluggedintheApril1986outagewasaneddycurrent.irdicationtermedasqau~l.Suchanirdicationisasignalinthetubesheetregionwhosetraceat400KHziscomplexandphaseangleunclear,butwhosepresencerepresentschange.Kheseirdicationshavebeenhistoricallypmventocompromisetubewallintegrityifthetuberemainsinserviceandthushavebeenclassifiedastubedegradation.IntheD.C.CookUnit2steamgeneratorstheseirdicationsareassociatedwithdegradationontheoutsidesurfaceofthetubeinthetubetotubesheetcrevice.'Ihecorrosionresistanceofasteamgeneratortubepluggedonthecoldlegonlywasevaluated.Generalformsofcorrosionaretypicallyenviroranentallyard/ormateriallycontrolled.Mostsecond-uysideinitiatedtubingcorrosionfoundinrecirculatingsteamgeneratorshasoccurredinlocalizedregions(mostcananonlycrevices)ofasteamgeneratortubeinwhichdissolvedchemicalspeciescanbeconcentratedtolevelsfargreaterthanthoseinthebulkprimaryorsecondaryfluid.Heattr<msferisnecessarysuchthattheavailablesuperheat(localwalltemperatureminusfluidsaturationtemperature)isincreasedcomparedtovaluesassociatedwithconventionalnucleateboilirgprocessesastheyexistonthetubesurface.'Iheelevatedtemperaturesprovidethedrivingforceforpromotingchemicalconcentrationi.e.,thepotentialfortheformationofalocallyconcentratedsoluti.oncanbecorrelatedwiththeexpectedavailablesuperheatwithintheregion.Astheprimlyfluidwithinatubepluggedonthecoldlegonlywouldbeat SECXr87-229NS-RCS~/L-87-450PAGE5OF7approximatelysecondarysidebulkfluidsaturationtemperatureandinasubcooledstate,noheattransferwouldbeexpectedacrossthetubesurfaceandanylocalizedtubedegradationincludingcontinuingdegradationatthesiteofthepreviouslylocatededdycurrentsignalwouldbeexpecttobeminhnal.'IhesafetyimpactofoperationoftubeR40-C39withwhatisnormallyapluggableindicationismitigatedbythegeometryoftheregion.%hetubetotubesheetcreviceisthespacebetweenthetubesheetandtheunexparxledtubesandisontheorderofafewmills.Tubeplugginglimitsare,establishedinpartbasedonpredictedperformanceofadegradedtubeunderpostulatedfaultedconditions,specificallysteamlinebreakconditions.Forindicationsinthetubesheetcreviceregion,tuberuptureisnotpossibleduetothepresenceofthetubesheetaroundthetubewhichwouldcontainthemnrementofthetubewallrequiredtoeffectabursttubecondition.'lherefore,intheeventofapostulatedsteamlinebreakwiththemechanicalplug,missingfmmoneendoftheR40-C39tubeandthepreviouslyobservededdycurrentindicationwouldnotbeexpectedtoresultinprimarytosecorxteyleakageinexcessofthatusedforaccidentanalyses.'Iheeffectofplantoperationonplugintegrityforuptooneyearwiththesteamgeneratortubepluggedononlythecoldlegsidehasbeenevaluated.'Ihemechanicalplugwasdesignedtoacxxzmnodatethedesignconditionsspecifiedforthesteamgenerator.'lhedesignconditionsenveloptheapproximate10psipressuredifferentialwhichoccursacrossthechannelheadinatubewhichhasbeenpluggedonthecoldlegonlybutnotonthehotleg.'Ihedesignverificationp~msimulatedthesteamgeneratorserviceconditionsofter~ratureandpressureaswellasthermalcyclingassociatedwiththevariousplantconditions.'Ihedesignverificationprogranfortheexpandedmeat~calplugdemonstratedpressurebourxho~integrityundersimulatedfaultedconditionloadingsinadditiontootherplantops~tingconditions.%hedesignoftheSeries51steamgeneratorsatD.C.CookUnit2includesasmallextensionofthetubeendpastthebottomofthetubesheetsurface.Aforeignobjectramvedframthechannelheadduringapreviousoutagehadresultedinsomedeformationofthetubeends.Noneofthetubeendsoftheothertubeshadarestrictionthatwouldpreventinsertionofaneddycurrentprobearxlthetubeendshadnoapparentadditionaldamageduetothelooseplug.%hetubetotubesheetweldsarepartiallyshieldedfromimpactofanobjectofthesizeofamechanicalplugandtheweldshadnoapgm~tdamage.thecladdingofthechannelheadandthetubesheetalsoshowednoapp-~tdamage.'Lhetubes,channelheadandtubesheetcladding,weldmetalandthemechanicalplugareallcarposedofveryductilematerial.Reputedimpactoftheplugonthecladding,tubeends,andtubetotubesheetweldwouldnotbeexpecttocause SECL-87-229NS-RCS~/L-87-450PAGE6OF7crackirgorsmallpiecestobreaklooseframthesurfacesimpactedbythelooseplug.Evaluationsofmeresignificantdeformationoftubeendsinathersteamgenexatorsofsimilardesignhaveshownthatdeformationofthetubeerdwillnotsignificantlydegradethestructuralintegrityofthetubeorthetubetottd~sheetweldorcauseasignificantincreaseintherestrictiontoflawthroughthesteamgenerator'lhemechanicalpluglandouterdiametersapproximatethetubeinnerdiametersintheseatingareaofR40~9.Inorderforthemechanicalplugtohavep~~sealirg,theplugshouldhavebeenlargerthanthetubeIDtoallawforaninterferencefit.DherewasnovisuallydicmernibleevidenceontheIDofthetubeatR40-C39thattheplughadapositiveinterferencefit,withthetube,althoughitisnotmardatorytohavethisforapraperlyinstalledplug.Insametubeerdsthatareapproximatelyashardasthepluglands,however,therearenointerferencemarksandplugsaresuccessfullyinstalled.'lheestimateoftheactualtranslationoftheexparderintherepavedmechanicalplugwouldindicatethatinsufficient~~nsionhadoccurred.'Iheestimatedexpardertranslationdistancedidnotmeetthepzocech.xeinstallationminirttumreguixement.%hepossibileananeliesinthetube-to-tubesheetjointcontributingtothedisengagementofthemechanicalplugwerereviewed.%heavality,notapernoranyotherproblem(suchasalackofrollexpansionintheplugsealingarea),whichwouldirdicatethattheconfigurationofthetubejointcontributedtotheasinstalledconditionofthemechanicalplug.Basedonthefirdirgsoftheinvestigationoutlinedaboveithasbeenconcludedthatsuccessfulinstallationpamnetersformectmu.calplugwerenotachievedanditwaseventuallydisplacedfmmthetubeerdduringtheoperatingperiodpreyingthediscoveryofthemisplacedplug.RelevantWestinghouselogbooks,datasheets,notesardprol.xxiureswerereviewedindetailframtheApril,1986outageinanattend%toidentifyapotentialareatoaccauntfortheasinstalledcorditionoftheplug.%hejobsitecoordinator,shiftsupervisorsandotherkeypeL~nnelwerequeriedtoattempttoidentifyacausativefactor'.Inallcasestherewasnothingidentified.BasedonpriorWestinghousemcpmienceofvirtually100%su~fulinstallationsoveraneightyearperiodofover25,000previousaedmnicalpluginstallations,coupledwithotherinstallationdatacollectedonsurveillancereportsfromalargepercentageofmechanicalplug

~87-229NS-EKS~/L-87-450PAGE7OF7installationsduringtheApril,1986progmn,thejudcpnenthasbeenmadethattheprobabilitythat.theothermechanicalplugsinstalledatD.C.CookVnit42duringtheApril,1986outagewereinstalledcorrectlyapproximates1004.CONCWSIONSOnthebasisoftheinvestigationandevaluationasoutlinedabove,ithasbeenconcludedthatthemechanicalpluglodgedinthehotlegofsteamgenerator422inR3-C5isthesamemechanicalplugthatwasoriginallyinstalledintheR40~9inthesamelegofthesamesteamgeneratorduringthe4/86outage.Duetotheconditionsofthefluidinthepartiallypluggedtube,significant.additionalorcontinuingcorrosionwouldnotbeexpectedtooccur.OperationofthesteamgeneratorwithoneplugintheR40~9tubeisnotexp~tohaveresultedinaconditionwhichwouldhavecausedprimarytosecordaryleakageintheeventofapostulatedsteamlinebreakinexcessofthatassumedforaccidentanalyses.Theintegrityoftheplugonthecoldlegofthetubeframwhichthehotlegsideplugwasdisplaced,wasmaintainedundernormaloperatingandpostulatedaccidentconditionloadings.Theimpactofthelooseplugpriortobeel.'minglodgedintubeR3-C5causednoapparentdamagetothetubeendsorothersurfacesinthechannelhead.Theapparentcauseoftheasinstalledconditionofthesubjectmechanicalplugistheteritunationoftheinstallationprocesspriortoreachingsuccessfulinstallationparameters.ThereforethedisplacementofamechanicalplugframthehotlegendoftubeR40-C39,theimpactofthelooseplugonthechannelheadsurfaces,andthesubsequentlodgingoftheplugintubeR3~didnotresultinthepossibilityofapreviouslyunanalyzedaccidentorincreasetheabilityofapreviouslyanalyzedaccident.Themarginofsafetywasnotreduced.Basedontheinformationoutlinedabove,theloosepluginthehotlegofD.C.Cooksteamgeneratorf22didnotresultinanunrevisedsafetyegestionasdefinedinthecriteriaof10CFR50.59.

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