ML17334B188

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Semiannual Radioactive Effluent Release Rept,Jul-Dec 1987. W/880226 Ltr
ML17334B188
Person / Time
Site: Cook  American Electric Power icon.png
Issue date: 12/31/1987
From: ALEXICH M P
INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG
To:
NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
AEP:NRC:0842K, AEP:NRC:842K, NUDOCS 8803010209
Download: ML17334B188 (27)
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('CCELEMTEDSISI'RxU'HONDEMONSTRATIONSYSTEMREGULATORYINFORMATIONDISTRIBUTIONSYSTEM(RIDS)ACCESSIONNBR:8803010209DOC.DATE:87/12/31NOTARIZED-NOFACIL:50-315DonaldC.CookNuclearPowerPlant,Unit1,Indiana&50-316DonaldC.CookNuclearPowerPlant,Unit2,Indiana6AUTH.NAMEAUTHORAFFILIATIONALEXICH,M.P.IndianaMichiganPowerCo.RECIP.NAMERECIPIENTAFFILIATIONDOCKET0500031505000316

SUBJECT:

"SemiannualRadioactiveEffluentReleaseRept,Jul-Dec1987."W/880226ltr.~viCAAODISTRIBUTIONCODE:IE48DCOPIESRECEIVED:LTENCLSIZE-TITLE:50.36a(a)(2)SemiannualEffluentReleaseReportsNOTESRECIPIENTIDCODE/NAMEPD3-3LAWIGGINGTONIDINTERNAL:AEOD/DOAARMTECHADVNREMPB10AREGFILE01GN2/'DRSEPRPBEXTERNALBNLTICHLERIJ03NRCPDRCOPIESLTTRENCL1011.11114411111111RECIPIENTIDCODE/NAMEPD3-3PDAEOD/DSP/TPABNRR/DEST/PSB8D1NRR/PMAS/ILRB12RGN3FILE02LPDRCOPIESLTTRENCL551111111111A8ATOTALNUMBEROFCOPIESREQUIRED:LTTR22ENCL21 IndianaMichiganPowerCompanyP.O.Box16631Coiumbus,OH43216AEP:NRC:0842K10CFR50.36aDonaldC.CookNuclearPlant:UnitNos.1and2DocketNos.50-315and50-316LicenseNos.DPR-58andDPR-74SEMI-ANNUALRADIOACTIVEEFFLUENTRELEASEREPORTJULY1,1987TODECEMBER31,1987U.S.NuclearRegulatoryCommissionATTN:DocumentControlDeskWashington,D.C.20555ATTN:T.E.MurleyFebruary26,1988

DearDr.Murley:

ThislettertransmitstheRadioactiveEffluentReleaseReportfortheDonaldC.CookNuclearPlantUnits1and2,fortheperiodfromJuly1toDecember31,1987.ThisreportwaspreparedinaccordancewithSection6.9.1.9ofthePlant's"AppendixATechnicalSpecification."ThisdocumenthasbeenpreparedfollowingCorporateprocedureswhichincorporateareasonablesetofcontrolstoensureitsaccuracyandcompletenesspriortosignaturebytheundersigned.Verytrulyyours,M.P.AlechedgEnclosurecc:D.H.Williams,Jr.,w/oenclosureW.G.Smith,Jr.-BridgmanG.BruchmannR.C.CallenG.CharnoffNRCResidentInspector-BridgmanA.B.Davis-RegionIIIAdministrator l

SAIC-88/3122TECHNICALEVALUATIONREPORTFORD.C.COOKNUCLEARPLANT,UNIT2"OPERATIONOFUNIT2THROUGHTHEENDOFTHECURRENTFUELCYCLE"February12,1988~ca~'"ScienceApplicationslnternationalCorporationPreparedfor:U.S.NuclearRegulatoryCommissionWashington,D.C.20555ContractNRC43-87-029TaskOrderNo.09;PostOfficeBox13tU,1710GoodridgeDn've,McLean,Yirginfa22102,f7NI82143M TABLEOFCONTENTSction~PaeINTRODUCTION.2.BACKGROUND.3.DISCUSSION~~~~o~~~~~~~~~~~~~~~~~~3.13.23.33.43.4.13.4.23.4.33.4.43.5EddyCurrentDataAnalysisCriteria.....TubePluggingCriteria..EddyCurrentInspectionResults.JustificationforOperatingIntervalLengthStartinginApril1987.RegulatoryGuide1.121Basis.GrowthRateDetermination.EddyCurrentUncertainty.OperatingIntervalDetermination.JustificationforOperatingIntervalLengthStartinginOctober1987.6781010111515154.EVALUATION.......................18CONCLUSIONS.......................19 LISTOFTABLES~ablePacaeIndicationsofHotLegSecondarySideCorrosion,March1987EddyCurrentInspections..........5IndicationsofHotLegSecondarySideCorrosion,September1987EddyCurrentInspections........9Cook2SteamGeneratorTubing-MinimumAcceptableWallRequirements.............12Cook2SteamGeneratorTubing-AllowableWallLossDetermination................131985to1986IntervalIGA/SCCGrowthRates.......14OperatingIntervalJustification,StartingApril1987-R.G.1.121Basis.............16PluggableIndicationsComparison............17 l.INTRODUCTIONByletterdatedNovember24,1987IndianaandMichiganElectricCompanyprovidedtheNuclearRegulatoryCommission(NRC)staffwithinformationconcerningtheresultsofsteamgeneratortubeeddycurrentinspectionsperformedattheDonaldC.CookNuclearPlantUnit2duringSeptember1987,andwithjustificationforcontinuingoperationthroughtheendofthecurrentfuelcycle(5.2effectivefull-powermonths[EFPMs]sincerestartinOctober1987)withnoscheduledinterimshutdownforsteamgeneratortubeinspections.WhilethisevaluationfocusesonareviewoftheSeptember1987eddycurrentinspectionresultsandjustificationforcontinuingoperation,italsoaddressestherestrictionplacedonpoweroperationbecauseof1985steamgeneratortubeinspectionresults.AlsoincludedinthisevaluationisareviewofthesteamgeneratortubeinspectionsandactionstakenbyIndianaandMichiganElectricPowerCompanytojustifycontinuingoperationasaresultofaMarch3,1987steamgeneratortubeleakatD.C..CookUnit2.Referencedtableshavebeenselectedfromthelicensee'ssubmissions.2.BACKGROUNDD.C.CookUnit2incorporatesanuclearsteamsupplysystemmanufacturedbyWestinghouse,andislicensedfor3411MWt.InitialcriticalityoccurredonMarch10,1978.TheunithasfourWestinghouseSeries51steamgenerators,eachwith3388Inconel600tubes.ThefirstsignificantindicationofsecondarysidetubecorrosionintheD.C.CookUnit2steamgeneratorsoccurredinNovember1983,whentheunitwasremovedfromserviceduetosteamgeneratortubeleakage.Aleakof0.29gallonsperminute(gpm)wasfoundintubeR16-C40ofsteamgenerator21.Eddycurrenttestingof1225tubesintwosteamgeneratorsresultedinthepluggingofthreetubes,allduetoindicationsofsecondarysidecorrosion.

IndianaandMichiganElectricPowerCo.initiatedarefuelingoutageofD.C.CookUnit2onMarch10,1984,atwhichtimeeddycurrentinspectionsofallfoursteamgeneratorswereconducted.Eddycurrentdataresultedinthepluggingof68tubesduetosecondarysidecorrosion;Indicationswereatorabovethetubesheetandinthetubesheetcreviceregion.Secti.onsofseventubeswereremovedformetallurgicalexaminations,whichconfirmedthattubedegradationwasduetointergranularattack/stresscorrosioncracking(IGA/SCC),probablycausedbyacausticenvironment.OnJuly15,1985,D.C.CookUnit2wasremovedfromservicewhenaprimary-to-secondaryleakof0.22gpmdeveloped.VisualinspectionshowedtubeR16-C56leakinginsteamgenerator23.Eddycurrentexaminationoftheleakingtuberevealedadefectabout1inchbelowthetopofthetubesheet.Additionaleddycurrenttestingofablockoftwenty-fourtubesaroundtheleakingtuberevealedanothertube(R15-C56)withapluggableindication.Thetwotubeswerepluggedandtheunitwasreturnedtoservice.OnAugust2,1985,duringrestart,leakagewasdetectedinsteamgenerator23.Theunitwasagainremovedfromserviceandapproximately1500tubeswereinspected.Thirty-fivetubeswerepluggedasaresultoftheseinspections.Twoofthesetubes(R7-C28andR14-C70)weresuspectleakers.Nanyofthe35pluggedtubeshadnopreviousindications,suggestingarapidprogressionofIGA/SCC.AdditionsofboricacidweremadetothesecondarysideofthesteamgeneratorstoneutralizethealkalineenvironmentandthuspossiblyslowtherateofIGA/SCC.TheunitwasrestartedonAugust.22,1985,OnAugust23,duringa30%powerboricacidsoak,anotherleakof0.2gpmwasdetected.Allfoursteamgeneratorswereopenedandthetubeswereleaktested.LeakswerefoundintubeR14-C41ofsteamgenerator22andintubeR19-C52ofsteamgenerator24.Becausetwoleakingtubeswerefound,alltubes,exceptforthe1500inspectedAugust2,1985,wereeddycurrenttested.Asaresultoftheseexaminations,atotalof147tubeswereplugged:93forexceedingthe40%throughwallTechnicalSpecificationsplugginglimit,andtheremaining54

~~forIndianaandMichiganElectricPowerCo.'sself-imposedplugginglimitsthatincludeanyindicationsinthetubesheetcreviceregionorindicationsgreaterthan30%abovethetubesheet.Sectionsoffivetubeswereremovedformetallurgicalandchemicaltests.Thesampleswerefromthetubesheetcreviceareaandsupportplatelocations.IGA/SCCwasfoundatbothlocations.Asaresultoftheseinspectionsandtests,IndianaandNichiganElectricPowerCo.administrativelylimitedthermalpoweroutputto80%inordertoreducetheprimarysidetemperaturesinanattempttoslowtherateoftubedegradation.Secondarysidechemistrytreatmentincludedon-lineboricacidadditionstoinhibitcaustic-inducedtubecorrosion;boronconcentrationwasmaintainedat5to10ppm.Thesemeasureswereexpectedto:a)neutralizethecausticenvironmentwhichhadcontributedtoIGA/SCC,b)changetheenvironmenttoshiftthesusceptibleelectricalpotentialrangeforcorrosionofInconel600,andc)preventmasstransferwithintheinhibitorfilmbyreformationofapassivefilm.Additionally,IndianaandMichiganElectricPowerCo.supportedthereductionofcausticfactorswithprocessestoopenrestrictivecrevicesandremovesludgeandtoreducecontaminationinputthroughimprovedchemistrycontrol.D.C.CookUnit2returnedtoserviceonOctober23,1985andranwithoutsignificantsteamgenerator-relatedproblemsuntilaFebruary28,1986scheduledrefuelingshutdown.Atthetimeoftheshutdown,steamgeneratorprimary-to-secondaryleakagewasintherangeof0.001to0.04gpm.Leaktestingrevealedaleakingtube(R16-C45)insteamgenerator22.Theleakingtubehadanindicationoneinchbelowthetopofthetubesheetonthehotlegsideofthesteamgenerator.Eddycurrentinspectionsofallthetubesresultedinthepluggingof151tubes,OnJuly7,1986,priortorestartofD.C.CookUnit2forFuelCycle6,therewasatotalof763pluggedtubesinD.C.CookUnit2steamgenerators.Therewere142pluggedtubesinsteamgenerator21,210pluggedtubesinsteamgenerator22,210pluggedtubesinsteamgenerator23,and201pluggedtubesinsteamgenerator24, D.C.CookUnit2rancontinuouslyforaperiodof226calendardays,fromthestartofFuelCycle6onJuly7,1986throughMarch3,1987,whentheunitwasremovedfromserviceduetoanindicatedprimary-to-secondaryleakof0.247gpminsteamgenerator22.Althoughthe.measuredleakratewasbelowtheTechnicalSpecificationleakratelimitof500gallons.perday(gpd)or0.347gallonsperminute(gpm),IndianaandMichiganElectricPowerCo.electedtoverifytheconditionoftheD.C.CookUnit2steamgeneratortubebundlesbyperformingeddycurrentinspectionsconsistentwiththerequirementsofTechnicalSpecification3/4.4.5.InalettertotheNRCdatedMay22,1987,IndianaandMichiganElectricPowerCo.attachedareportentitled"SteamGeneratorTubeIntegrity,April1987-AnAssessmentoftheNextOperatingIntervalLength."ThisreportprovidedinformationontheMarch1987steamgeneratorinspectionresults,correctiveactionstakentorestoresteamgeneratortubeintegrity,andjustificationforcontinuingoperationfor4.7effectivefull-powermonths(EFPMs).TheMarch3,1987leakingtubeinsteamgenerator22wasidentifiedbyhydrostatictestingastubeR28-C53andwassubsequentlyconfirmedbyeddycurrenttestingtohaveathroughwalldefectinthehotlegtubesheetcreviceabout3.7inchesbelowthetubesheetsurface.ThisdefectwasnotedtobetypicalofthesecondarysideIGA/SCCpreviouslyidentifiedinD.C.CookUnit2steamgenerators.TheMarch1987eddycurrentinspectionprogramstartedwithaninitialsampleofabout6%ofthetubesinsteamgenerators22and24.Testresultsnecessitatedexpandingtheinspectionstopotentiallyaffectedareasofalltubesineachsteamgenerator.Fortheseinspections,thecriteriausedtoanalyzeeddycurrentdataandthecriteriausedfortubepluggingwerethesameasthoseusedforthe1986inspections(seeSection3,Discussion).Theeddycurrenttestsrevealedatotalof715tubeswithindications,resultinginthepluggingof110tubes.ThebreakdownofthenumberoftubeswitheddycurrentindicationsandthenumberoftubesthatwerepluggedissummarizedinTable1.

TABLE1INDICATIONSOFHOTLEGSECONDARYSIDECORROSIONMARCH1987EDDYCURRENTINSPECTIONS<39%>40%DIUDSSgRTotalSupportPlates14215940N/A629TubesheetSurface3192N/A31TubesheetCrevice04255Total173361542715DIDistortedIndicationSgR-Squirrel(aparticularDIinthecreviceregion)UDS=UndefinedSignalNotes:(a)Pluggingcriteriaareillustratedbytheboundarylineintheabovetable(107tubes);inaddition,3tubeswerepluggedduetoreasonsunrelatedtosecondarysidecorrosion(2becauseECtestingcouldnotbeperformed,and1asaprecautionarymeasureduetoadistortedindicationatthetubesheetrolltransition);110totaltubeswereplugged.(b)Numbersintheabovetablerepresentindividualtubes;fortubeswithindicationsatmultiplelocations,onlytheindicationdeemedmostsevereislisted.

Reference:

AEP:NRC:0936G,datedApril9,1987 Conservativelyusingdegradationgrowthratemodelsbasedon1985-1986and1986-1987degradationrates,IndianaandMichiganElectricPowerCo.establishedanoperatingintervalof4.7EFPMsbeforethenextinspection,whichrepresentedthemidpointoftheremainingfuelcycleplusanallowancetoprovidesomeflexibilityinschedulingthesteamgeneratorinspectionoutage.However,D.C.CookUnit2waselectivelyremovedfromserviceafterapproximately3.0EFPMstoinvestigatepotentialconcernsassociatedwithanchoringofreactorcoolantpumphatchbolts,Sincethepumphatchinvestigationwasscheduledtotakeseveraldays,IndianaandMichiganElectricPowerCo.decidedtoinitiatethesteamgeneratorinspectionoutagetominimizethecompositeoutagetime.3.DISCUSSIONInitslettersubmittalofNovember24,1987,IndianaandMichiganElectricPowerCo.providedthefollowinginformationregardingtheresultsofthesteamgeneratortubeeddycurrentinspectionsofD.C.CookUnit2duringSeptember1987,andpresentedjustificationforcontinuingoperationthroughtheendofthecurrentfuelcycle(5.2EFPMssincerestartinOctober1987)withnoscheduledinterimshutdownforsteamgeneratorinspections.Acompleteeddy'currentinspectionofthehotlegsofallfoursteamgeneratortubeswasperformedbetweenSeptember12andSeptember26,1987.3.1EddCurrentDataAnalsisCriteriaThecriteriausedtoanalyzetheeddycurrentdataduringtheSeptember1987inspectionswerethesameasthoseusedduringtheMarch1987inspections.Thesecriteriaweredevelopedfromacorrelationoffieldbobbincoileddycurr'entdatawithmetallographyresultsoftubesamplesremovedin1984and1985.Thefollowingisabriefsummaryofpertinenteddycurrentsignalclassifications:

oClearIndicationrortedinercentthrouhwallenetrationor%~TW-Asignalwithanunequivocalphaseanglemeasurableat400kHz,confirmedat100kHz.Industrypracticeistouseathresholdvoltage,usuallyabout1volt,todiscriminatebetweenreportableandnon-reportableclearindications.Asaconservatism,however,allclearindications,regardlessofvoltage,arereportedfordisposition.I~~oDistortedIndicationDI-Asignalvisibleat400kHzbelievedbytheinterpretertorepresenttubedegradation,butwithanunquantifiablephaseangle;expectedcorrelationinmixedfrequenciesorothersinglefrequenciesisnotnecessarilypresent.~pi1PR.Aptt1typPdtttdtdttt1tttubesheetcreviceregionwhosesignaltraceat400kHziscomplex,withanunquantifiablephaseangle;theseindicationshavehistoricallybeenshowntocompromisetubewallintegrity.oUndefinedSinalUDS-Ananomaloussignal,notnecessarilyindicativeoftubedegradation,butwhichtheinterpreterbelievesshouldbenotedforconsiderationanddisposition.oNoDetectableDeradationNDD-Asignalwithnoevidenceoftubewalldegradation;eitherthereisnodegradationoritisbelowthedetectionthreshold.3.2TubePluinCriteriaTubepluggingcriteriausedduringtheseinspectionswerebasicallythesameasthoseusedduringtheHarchIQ87inspections,includingconservatismforindicationsattubesupportplateintersections,asnotedbelow.Thefollowingisabriefsummaryofthepluggingcriteriaimplementedforsecondarysidecorrosionineachofthethreeareasofconcern:

oTubesheetcrevicereonhotl-Allclearindications,DIs,S(Rs,andUDSsinthetubesheetcreviceregion(fromthetubesheetrolltransitiontothesecondaryfaceofthetubesheet)areconsideredpluggable,regardlessofvoltageorphaseangle.oTubesheetsurfacereiontl-Allclearindications,DIs,S(Rs,andUDSsinthetubesheetsurfaceregion(fromthesecondaryfaceofthetubesheetuptoabout6inchesintothefreespanoftubing)areconsideredpluggable,regardlessofvoltageorphaseangle.N~~~oTubesuortlateinterectionhotle-Clearindicationsmeetingathresholdvoltageof1.75voltsandhavinganindicatedthroughwallpenetrationof>40percentareconsideredpluggable.Inaddition,someindicationsnotmeetingthevoltagethresholdarepluggedonphaseanglealonebasedonrecommendationsofthedatainterpreter.ThisaddedconservatismwasinitiatedduringtheMarch1987inspection.TheTechnicalSpecificationpluggingcriteriaof>40percentthroughwallpenetrationwasappliedtoallotherareasofthesteamgeneratortubing.3.3EddCurrentInsectionResultsApplicationoftheaboveeddycurrentanalysiscriteria/tubepluggingcriteriaresultedinthepluggingof60tubesbecauseofsecondarysidecorrosionand18tubesbecauseofprimarysideindicationsatthetubesheetrolltransition.Table2givesabreakdownofthenumberoftubeswithhotlegsecondarysideeddycurrentindicationsandthenumberoftubesthatwereplugged.Pointsofinterestintheinspectionresults,asnotedbythelicensee,includethefollowing.

TABLE2INDICATIONSOFHOTLEGSECONDARYSIDECORROSIONSEPTEMBER1987EDDYCURRENTINSPECTIONSA.Includingonlythemostsignificantindicationpertube,total.forall4steamgenerators.<40%>40%DIUDSSgRTotalTubesheetCrevice1636TubesheetSurfaceSupportPlates39133480400To'tal3928371447*TubesinsideboundarywerepluggedB.Includingmultipleindicationspertube,totalforall4steamgenerators.<40%>40%DIUDSSgRTotalTubesheetCrevice01636TubesheetSurface012SupportPlates42134700525Total4228494573

Reference:

AEP:NRC:0936L,datedNovember24,19879 oThenumberofdistortedindications(DIs)reportedattubesupportplateintersectionsdecreasedsignificantlyfromtheMarch1987inspectionresults(470vs.830).Theapparentexplanationforthedecreaseisthattherecentsignalsare"clearer,"thusallowingformoredefinitiveinterpretationofsignalsthatpreviouslywouldhavebeencategorizedasDIs.Theclearerdatamaybeattributedtotheremovalofdepositsbycontinuingsecondarysideboricacidtreatment.oTheincidenceofprimarysideindicationsattubesheetrolltransitions(locatedapproximately18inchesbelowthesecondaryfaceofthetubesheet),firstdetectedin1986,appearstobeslowlyprogressing,buttheprogressionrateis'notofseriousconcernsincetheD.C.CookUnit2steamgeneratorswillsoonbereplaced.Asaprecaution,allindicationsregardlessofdepthwereplugged.3.4Justificationfor0eratinIntervalLenthStartininAril1987Tojustifycontinuingoperationfor5.2EFPMsafterstartupinOctober1987,IndianaandMichiganElectricPowerCo.referenceditsMay22,1987submittal.IntheMay22,1987submittal,IndianaandMichiganElectricPowerCo.documentedoperatingexperiencethroughMarch1987andpresenteddetailedjustificationforsafeoperationoftheD.C.CookUnit2steamgeneratorsfor4.7EFPHsafterstartuponApril21,1987.ThisjustificationwasbasedonmodelsusingRegulatoryGuide1.121safetyevaluationsonsteamgeneratortubestructurallimitsforD.C.CookUnit2tubing,generaltubedegradationgrowthrates,andaconservativeeddycurrentuncertaintymargin.3.4.1ReulatorGuide1.121BasisMinimumwallrequirementsfortheD.C.CookUnit2steamgeneratortubingwerecalculatedinaccordancewiththecriteriaofR.G.1.121,10 entitled"BasesforPluggingDegradedPWRSteamGeneratorTubes."ThebasicrecommendationsofR.G.1.121forallowableminimumwalldeterminationareoutlinedbelow.1.Fornormalplantoperation,primarytubestressesarelimitedsuchthatamarginofsafetyof3isprovidedagainstexceedingtheultimatetensilestressofthetubematerial,andtheyieldstrengthofthematerialisnotexceeded,consideringnormalandupsetconditionloadings.2.Foraccidentconditionloadings,therequirementsofparagraphNB-3225ofSectionIIIoftheASHECodearetobemet.Inaddition,itmustbedemonstratedthattheappliedloadsarelessthantheburststrengthofthetubesatoperatingtemperatureasdeterminedbytesting.3.Foralldesigntransients,thecumulativefatigueusagefactormustbelessthanunity.Tables3and4givethecalculatedR.G.1.121D.C.CookUnit2minimumacceptabletubewallrequirementsandtheallowablewalllossdetermination,3.4.2GrowthRateDeterminationsAveragegeneralgrowthratesweredeterminedforthreeareasofinterestbycomparingeddycurrentinspectionresultsbeforeandafteranoperatinginterval.The1985-1986operatinginterval(at80%powerandwithboricacidsoaking)wasusedtodevelopageneral'growthratemethodologyusingmetallurgicaldatafromtubesamplesremovedduringthe1985outageandanumberofnon-pluggableindicationsthatwereleftinserviceandgivenanopportunitytogrowduringthe1985-1986interval.Table5summarizesthegeneralgrowthratesestablishedforthethreeareasofinterestinthetubebundle.11 P~~~TABLE3COOK2STEAMGENERATORTUBINGMINIMUMACCEPTABLEWALLRE(UIREMENTSA.Tubesheetcreviceandtubesheetsurfaceregions.CriteriaConditionMinimumWallinchesYieldnormal0.015ASMECodefaulted0.017Su/3normal0.019B.Tubesupportplateintersections.CriteriaConditionMinimumWallinchesYieldnormal0.012ASMECodefaulted0.013Su/3normal0.015

Reference:

Attachment1toAEP:NRC:0936J,datedMay18,198712

~~TABLE4COOK2STEAMGENERATORTUBINGALLOWABLEWALLLOSSDETERMINATIONSLocationGeometricConditionAllowable~lh11TubesheetCreviceRegionAxialextent>1.5inchesSu/362TubesheetSurfaceRegionAxialextent>1.5inchesSu/362TubeSupportAxialextentPlateIntersections<0.75inchesSu/370I~I-

Reference:

Attachment1toAEP:NRC:0936J,datedMay18,198713

~~TABLE51985to1986INTERVALIGA/SCCGROWTHRATESLocationMeanGrowthRate~EMSampleSizeTubesheetCreviceRegionTubesheetSurfaceRegion1.600.821918TubeSupportPlateInter-sections0.6638

Reference:

Attachment1toAEP:NRC:0936J,datedNay18,198714 3.4.3ddCurrentTestinUncertaintBycomparingactuallaboratoryresultsoftubewallpenetrationtoinsitueddycurrentinspectionresults,thelicenseefoundthattheinsitueddycurrenttestsyieldamaximumunder-predictionof16percentfortubeswiththroughwallpenetrationofupto40percent.Aswallpenetrationgetsdeeper,theeddycurrenttestsmorecloselypredicttheactualdepthofpenetration.IndianaandMichiganElectricPowerCompanyhasthereforeestablisheda16percenteddycurrenttestinguncertaintytoevaluateoperatingintervallength.3.4.40eratinIntervaleterminationOnthebasisofR.G.1.121criteriafortubestructurallimits,generaltubedegradationgrowthrates,andaconservativeeddycurrentuncertaintymargin,IndianaandMichiganElectricPowerCo.concludedthat8.0EFPMswasanappropriatelengthforanoperatinginterval,measuredfromreturntopowerinApril1987.ThesefindingsaresummarizedinTable6.Intheinterestoffurtherconservatism,IndianaandMichiganElectricPowerCo.requesteda4.7EFPMoperatingintervalstartinginApril1987beforeremovalofD.C,CookUnit2fromservicetoverifyandrestoreasnecessarytheintegrityofthesteamgeneratortubebundles.3.5Justificationfor0eratinIntervalLenthStartininOctober1987BasedontheSeptember1987inspectionresults,IndianaandMichiganElectricPowerCo.concludedthatthemodelsusedinpredictingtubedegradationratesareconservativeorthatactualtubedegradationrateshavebeenreducedasaresultofcorrectivemeasures.IndianaandMichiganElectricPowerCo.citesthedatasummarizedinTable7,whichcomparestheprojectedconditionvs.actualpluggableindicationsfromthe3.0EFPMoperationintervalbetweentheApril1987andSeptember1987inspections.Overall,theactualnumberofpluggableindicationswasnearly50percentlessthanpredictedbythemodelsused.IndianaandMichigan15 TABLE6OPERATINGINTERVALJUSTIFICATIONSTARTINGAPRIL1987-R.G.1.121BASISItemTubesheetCreviceTubesheetSurfaceTubeSupportPlatesAllowabletubewallloss(%)626270ECTuncertainty(%)Growth(%/EFPH)161.6160.82160.66Projectedgrowth(%/8.0EFPH)12.86.65.3Plugginglevelrequired(%)33.239.448.7PlugginglevelimplementedAllAll>40.0%

Reference:

Attachment1toAEP:NRC:0936J,datedHay18,198716 TABLE7PLUGGABLEINDICATIONSCOMPARISONTubesheetCreviceTubesheetSurfaceTubeSupportPlatesTotalProjectedActual753636llI1311260

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AEP:NRC:0936LdatedNovember24,198717 ElectricPowerCo.indicatedthatinthetubesheetcreviceandsurfaceregions,wheretube,leaksduetosecondarysidecorrosionhaveoccurred,largeoverpredictionsweremade.IndianaandMichiganElectricPowerCo.contendsthatunderpredictionofpluggableindicationsattubesupportlocationsislikelytheresultoffewerreportedDIsatsupport.plates;thatis,clearerdataallowedforsizingofsomepre-existingflawsthathadpreviouslybeencalledDIs.IndianaandMichiganElectricPowerCo.concludesthatbecauseofitsconservativepluggingpractices,allindicationsinthevicinityofthetubesheethavebeenremovedfromserviceandthereforenewdegradationgrowthratescannotbereliablycalculatedforthetubesheetcreviceandsurfaceareasandthattheoriginalmodelswillpredictconservativeend-of-intervalconditions.Therefore,inviewoftheinherentandapparentconservatismsintheoriginalmodels,anoperationalintervalof5.2EFPMsstartinginOctober1987representsaninsignificantchangetothe4.7EFPMintervalpreviouslyjustified,andisanappropriateoperatingintervaltominimizethepotentialforsignificantin-servicesteamgeneratortubeleakage.Finally,,IndianaandMichiganElectricPowerCo.believesthatintheunlikelyeventthatextremetubewallpenetrationmightoccurasarandomeventnotpredicted'yprobabilisticanalysis,itsleakratemonitoringprogramandtheTechnicalSpecificationleakratelimitwillensureleak-before-breakconditionsandthatanorderlyshutdowncanbeeffected.IndianaandMichiganElectricPowerCo.furthercontendsthatitsadministrativepolicyofshuttingdownbeforereachingtheactualleakratelimitaddsadditionalmargintoleak-before-breakconsiderations.4.EVALUATIONAreviewofD.C.CookNuclearPlantUnit2eddycurrentinspectionresultsofSeptember1987,degradationgrowthmodelpredictions,anddocumentedoperatingexperiencehasbeenconductedtoassesstheprobabilityofexcessivein-servicesteamgeneratortubeleakageduringpoweroperationthroughtheendofthecurrentfuelcycle.Theprimarypurposeofthis18 evaluationistoprovideatechnicalreviewoftheIndianaandMichiganElectricCompanyjustificationforthenextoperatingintervalandaddresspoweroperationrestrictionsandlicenseeactionsresultingfrompreviousinspectionresults.TheSeptember1987inspectionresultsconfirmthatlicenseeadministrativeandremedialmaintenancemeasureshavebeenadequatetoensuresafeoperatingconditions.Reductionofthermalpoweroutputtoreduceoperatingtemperature,on-lineadditionsofboricacidtoinhibitcaustic-inducedtubecorrosion,andotherimprovedsecondarychemistrycontrolshaveslowedtherateoftubedegradation.PluggableindicationsintwocriticalareasthatsufferIGA/SCC,thetubesheetcreviceregionandthetubesheetsurfaceregion,werealmost50%lessthanpredictedbythedegradationgrowthmodelswhenadjustedtotheactual3.0EFPMsofoperationbetweentheApril1987andSeptember1987inspections,Itshouldbenoted,however,thattheincreaseinpluggableindicationsattubesupportplatelocationsmaybeattributabletothenewoperationalmode.Theconservativeuncertaintymarginintheoriginalpredictivemodels,thecautionarypluggingpractices,whichremovefromserviceallclearindicationsinthevicinityofthetubesheetregardlessofvoltageorphaseangle,andtheleakratemonitoringprogramtoverifyleak-before-breakconditionsareeffectiveelementsthatsupportthejustificationpresentedbyIndianaandMichiganElectricCompanyandminimizethepotentialforsignificantin-servicesteamgeneratortubeleakage.Theinspectionresultsalsoconfirmthelicensee'scontentionthatthemodelsusedtojustifyoperationalintervalsbasedon1985-1986intervaltubedegenerationrates,R.G.1.121tubestructuralintegritycriteria,plugginglevelsforcriticalareas,andeddycurrenttestmarginsareindeedconservative.5.CONCLUSIONSThisreviewandevaluationisbasedonoutageinspectionsconductedtodatebyIndianaandMichiganElectricCompany,thelicensee'slettersofMay22,1987andNovember24,1987,andthereportattachedtotheMay22,1987letterentitled"SteamGeneratorTubeIntegrity,April1987--AnAssessment19 oftheNextOperatingIntervalLength."Conclusionsarebaseduponananalysisofinspectionresults,tubedegradationgrowthmodelpredictionsforsafeoperationof8.0EFPHsbetweeninspections,andextremeorrandomeventprobabilitiescoupledwithlicenseeactionstocontroldegradation,radiationexposureconsiderations,economicpenalties,andacommitmenttosteamgeneratorreplacementplans.Baseduponthisevaluation,ithasbeenconcludedthatD.C.CookUnit2maybeoperatedfor5.2EFPNsfromitsOctober1987startupwithoutunduerisktothepublichealthandsafety.However,inviewoftheincreasednumberofpluggableindicationsdetectedinthetubesupportplateregions,futureeddycurrentinspections,ifrequired,shouldincludeanexpandedinspectionofthetubesupportregions,intothetopsupportplateregionofthecoldlegsideofthesteamgenerators.Previouslyinstitutedremedialmeasuresandadministrativepowerreductionshouldbecontinuedtominimizetheprobabilityofaforcedshutdownduetoleakage.Additionalmarginagainstrandomeventscausingextremewallpenetration'isprovidedbytheleakratemonitoringprogram,thelicensee'sTechnicalSpecificationleakratelimitconditions,andadministrativepolicyoforderlyshutdownbeforereachingactualleakratelimits.20 o~oaaawaoaaoaaaaaaaoaaa;woaoo44aaasaaoaLaScienceApplicakms

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