ML17329A420

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Application for Amend to License DPR-58,revising TSs to Allow Alternate Plugging Criteria to Establish Operability of SG Tubes.Westinghouse Nonproprietary Rept WCAP-13188 & Proprietary Rept WCAP-13187 Encl.Proprietary Rept Withheld
ML17329A420
Person / Time
Site: Cook American Electric Power icon.png
Issue date: 03/20/1992
From: FITZPATRICK E
INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG
To: MURLEY T E
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML17329A421 List:
References
AEP:NRC:1166, NUDOCS 9203260124
Download: ML17329A420 (15)
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Text

ACCEK,ERATED DISTMBUTION DEMONSTPWTION SYSTEM"f.~..p,REGULATOO INFORMATION DISTRIBUTION STEM(RIDE)rkiqi"'ACCESSION NBR:9203260124 DOC.DATE:

92/03/20NOTARIZED:

YESDOCKETFACIL:50-315 Donald,C.CookNuclearPowerPlant,Unit1,IndianaM05000315AUTH.NAMEAUTHORAFFILIATION FITZPATRICK,E.

IndianaMichiganPowerCo.(formerly Indiana&MichiganEleRECIP.NAME RECIPIENT AFFILIATION MURLEY,T.E.

DocumentControlBra@eh(Document ControlDesk)

SUBJECT:

Application foramendtoLicenseDPR-58,revising TSstoallowalternate pluggingcriteriatoestablish operability ofSGtubes.Westinghouse nonproprietary reptWCAP-13188 6proprietary reptWCAP-13187 encl.Proprietary reptwithheld.

DISTRIBUTION CODE:A001DCOPIESRECEZVD:LTRIENCL+SIZERECIPIENT IDCODE/NAME PD3-1LASTANG,JINTERNAL:

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indianaMichiganPowerCompanyP.O.Box1663$Columbus, OH43216AEP:NRC:1166DonaldC.CookNuclearPlantUnit1DocketNo.50-315LicenseNo.DPR-58TECHNICAL SPECIFICATIONS CHANGETOALLOWALTERNATE PLUGGINGCRITERIAU.S.NuclearRegulatory Commission DocumentControlDeskWashington, D.C.'20555Attn:T.E.MurleyMarch20,3.992

DearDr.Murley:

Thisletteranditsattachments constitute anapplication foramendment totheTechnical Specifications (T/Ss)forDonaldC.CookNuclearPlantUnit1inaccordance with10CFR50.90.Thepurposeofthislicenseamendment requestistoobtainauthorization touseanalternate pluggingcriteriatoestablish operability ofCookNuclearPlantUnit1steamgenerator tubes.TheT/Ssnowrequiresteamgenerator tubestobepluggedorrepairedwhenthedegradation exceeds40%tubewallpenetration asdetermined bynon-destructive examination.'e believethatflawindications withintheboundsofthetubesupportplatewithabobbinvoltagelessthanorequalto1.5voltsmayremaininservice.Flawindications greaterthan1.5voltsbutlessthanorequalto4.0voltsmayremaininserviceifarotatingpancakecoil(RPC)probeinspection verifiesthataxialouterdiameterstresscorrosion cracking(ODSCC)isthedegradation mechanism.

Flawindications withavoltagegreaterthan4.0voltswillbepluggedorrepaired.

Wealsobelievethatatubecanremaininserviceifthesignalamplitude islessthanorequalto4.0volts,regardless ofthedepthofpenetration, iftheprojected end-of-cycle distribution ofcrackindications isverifiedtoresultinprimary-to-secondary leakagelessthan120gpminonesteamgenerator duringapostulated steamlinebreak.Westinghouse WCAP-13187, "D.C.CookUnit1SteamGenerator TubePluggingCriteriaforIndications atTubeSupportPlates,"providesthedevelopment ofthe4.0voltalternate pluggingcriteria.

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/foal&/inP Dr.T~E.Murley-2-AEP:NRC;1166Adetaileddescription oftheproposedchangesandouranalysesconcerning significant hazardsconsiderations areincludedinAttachment 1tothisletter.Attachment 2containstheproposedrevisedT/Sspages.Attachment 3containsthemarked-up copiesoftheexi.sting T/Ss.TheWestinghouse reports,WCAP-13187, "D.C,CookUnit1SteamGenerator TubePluggingCriteriaforIndications atTubeSupportPlates"(Proprietary),

andWCAP-13188, "D.C.CookUnit1SteamGenerator TubePluggingCriteriaforIndications atTubeSupportPlates"(Non-Proprietary),

areinAttachment 4.EnclosedinAttachment 5areaWestinghouse authorization letter,CAW-92-282, accompanying affidavit, Proprietary Information Notice,andCopyright Notice.BecauseWCAP-13187 containsinformation proprietary toWestinghouse ElectricCorporation, itissupported byanaffidavit signedbyWestinghouse, the.owneroftheinformation.

Theaffidavit setsforththebasisonwhichtheinformation maybewithheldfrompublicdisclosure bytheCommission andaddresses withspecificity theconsiderations listedinparagraph (b)(4)ofSection2790oftheCommission's regulations.

Accordingly, itisrespectfully requested thattheinformation whichisproprietary toWestinghouse bewithheldfrompublicdisclosure inaccordance with10CFRSection2790oftheCommission's regulations.

Correspondence withrespecttothecopyright orproprietary aspectsoftheitemslistedaboveorthesupporting Westinghouse affidavit shouldreference CAW-92-282 andshouldbeaddressed toN.Liparulo, ManagerofNuclearSafetyandRegulatory Activities, Westinghouse ElectricCorporation, P.0.Box355,Pittsburgh, Pennsylvania 15230-0355.

Webelievethattheproposedchangeswillnotresultin(1)asignificant changeinthetypesofeffluents orasignificant increaseintheamountofanyeffluents thatmaybereleasedoffsite,or(2)asignificant increaseinindividual orcumulative occupational radiation exposure.

TheseproposedchangeshavebeenreviewedbythePlantNuclearSafetyReviewCommittee andwillbereviewedbytheNuclearSafetyandDesignReviewCommittee attheirnextregularly scheduled meeting.Incompliance withtherequirements of10CFR50.91(b)(1),

copiesofthisletteranditsattachments havebeentransmitted totheMichiganPublicServiceCommission andtheNFEMSectionChief.Pleasecontactusifyouhaveanyquestions concerning thislicenseamendment request.NuclearRegulatory Commission staffreviewand Dr.T.E.Murley-3-AEP:NRC:1166approvalofthesechangesarerequested priortoMay22,1992.Thisistheminimumamountoftimenecessary toprepareforimplementation ofthealternate pluggingcriteriaduringtheUnit1refueling outagebeginning approximately June23,1992.Thisdocumenthasbeenpreparedfollowing Corporate procedures thatincorporate areasonable setofcontrolstoensureitsaccuracyandcompleteness priortosignature bytheundersigned.

Sincerely, VicePresident ehAttachments cc:D.H.Williams, Jr.A.A.Blind-BridgmanJ.R.PadgettG.CharnoffA.B.Davis-RegionIIINRCResidentInspector

-BridgmanNFEMSectionChief ATTACHMENT 1toAEP:NRC:1166 NOSIGNIFICANT HAZARDSCONSIDERATION EVALUATION INSUPPORTOPTHEALTERNATE PLUGGINGCRITERIA Attachment 1toAEP:NRC:1166 INTRODUCTION Page1Alicenseamendment isproposedtoprecludeunnecessarily pluggingsteamgenerator tubesduetotheoccurrence ofouterdiameterinitiated stresscorrosion cracking(ODSCC)atthetubesupportplatesintheCookNuclearPlantUnit1steamgenerators.

UsingtheexistingTechnical Specifications (T/Ss)steamgenerator tubepluggingcriteriaof40%tubewallpenetration asdetermined bynon-destructive examination (NDE),manyofthetubeswithcrackindications wouldneedlessly havetoberemovedfromservice.Thealternate pluggingcriteriafortubesupportplateelevation ODSCCoccurring intheCookNuclearPlantUnit1steamgenerators mayresultintubeswithbothpartialandthrough-wall cracksreturning toservice.Inthelimitingcase,itisdemonstrated thatthepresenceofthrough-wall cracksaloneisnotreasonenoughtoremoveatubefromservice.DESCRIPTION OFTHEAMENDMENT REQUESTAsrequiredby10CFR50.91(a)(1),ananalysisis,providedtodemonstrate thattheproposedlicenseamendment toimplement analternate steamgenerator tubepluggingcriteriaforthetubesupportplateelevations atCookNuclearPlantUnit1involvesnosignificant hazardsconsiderations.

Thealternate pluggingcriteriainvolvesacorrelation betweeneddycurrentbobbincoilsignalamplitude (voltage) andtubeburst.andleakagecapability.

Thepluggingcriteriaisbasedontestingoflaboratory-induced ODSCCspecimens, extensive examination ofpulledtubesfromoperating steamgenerators (industry vide),andfieldexperience fromleakageduetoindications atthetubesupportplates(worldvide).Specifically, crackindications withbobbincoilvoltageslessthanorequalto4.0volts,regardless ofindicated depth,donotrequireremedialactionifpostulated steamlinebreakleakagecanbeshowntobeacceptable.

Crackindications withbobbincoilsignalamplitudes exceeding 4.0voltsmustbeeitherpluggedorrepaired.

Bobbincoilsignalamplitudes greaterthan1.5volts,ifleftinserviceatthediscretion oftheowner,mustbeinspected usingamotorized rotatingpancakecoil(RPC).Theproposedamendment wouldmodifyT/Ss3.4.5"SteamGenerators,"

3.4.6,"ReactorCoolantSystemLeakage,"

andtheassociated bases.Theseproposedchangesprovidetubeinspection requirements andacceptance criteriatodetermine thelevelofdegradation forwhichatubeexperiencing ODSCCatthetubesupportplateelevations mayremaininserviceintheCookNuclearPlantUnit1steamgenerators.

Attachment 1toAEP:NRC:1166 EVALUATION SteamGenerator TubeInteritDiscussio Page2Inthe.development ofthealternate pluggingcriteria, Regulatory Guides(RG)1.121,"BasesforPluggingDegradedPWRSteamGenerator Tubes,"and1.83"Inservice Inspection ofPWRSteamGenerator Tubes,"areusedasthebasesfordetermining thatsteamgenerator tubeintegrity considerations aremaintained withinacceptable limits.Regulatory Guide1.121describes amethodacceptable totheNRCstaffformeetingGeneralDesignCriteria2,4,14,15,31,and32byreducingtheprobability andconsequences ofsteamgenerator tuberupturethroughdetermining thelimitingsafeconditions oftubewalldegradation.

Tubeswithunacceptable

cracking, asestablished byinservice inspection, shouldberepairedorremovedfromservicebyplugging.

ThisRGusessafetyfactorsonloadsfortubeburstthatareconsistent withtherequirements ofSectionIIIoftheASMECode.Forthetubesupportplateelevation degradation occurring intheCookNuclearPlantUnit1steamgenerators, tubeburstcriteriaareinherently satisfied duringnormaloperating conditions bythepresenceofthetubesupportplate.Thepresenceofthetubesupportplateenhancestheintegrity ofthedegradedtubesinthatregionbyprecluding tubedeformation beyondthediameterofthedrilledhole.Itisnotcertainwhetherthetubesupportplatewouldfunctiontoprovideasimilarconstraining effectduringaccidentcondition loadings.

Therefore, nocreditistakeninthedevelopment ofthepluggingcriteriaforthepresenceofthetubesupportplateduringaccidentcondition loadings.

Conservatively, basedontheexistingdatabase,bursttestingshowsthatthesafetyrequirements fortubeburstmarginsduringbothnormalandaccidentcondition loadingscanbesatisfied withbobbincoilsignalamplitudes lessthan6.8volts,regardless ofthedepthoftubewallpenetration ofthecracking.

Regulatory Guide1.83describes amethodacceptable totheNRCstaffforimplementing GDC14,15,31,and32throughperiodicinservice inspection forthedetection ofsignificant tubewalldegradation.

Uponimplementation ofthepluggingcriteria, tubeleakageconsiderations mustalsobeaddressed.

Itmustbedetermined thatthecrackswillnotleakexcessively duringallplantconditions.

Forthealternate tubepluggingcriteriadeveloped fortheCookNuclearPlantUnit1steamgenerator tubes,littleornoleakageisexpectedduringnormaloperating conditions evenwiththepresenceofthrough-wall cracks.Industrywide,thecrackmorphology ofSCCattubesupportplateintersections isbestdescribed asashort,tight,axiallyorientedmicrocrack separated byligaments ofnon-degraded material.

Thesamemorphology isjudgedtobepresent Attachment 1toAEP:NRC:1166 Page3intheCookNuclearPlantUnit1steamgenerators.

Tubepullexamination resultsfrom1983indicated axialSCCinitsearlystages.Thedepthsoftheevidenced degradation (determined bydestructive exam)showedthemaximumdepthofpenetration tobeapproximately 10%through-wall.

TheRPCtestingperformed duringthe1989outagehasconfirmed thataxiallyorientedSCCcracksexistatthetubesupportplateintersections.

BasedontheRPCtestingresultsandrelatively smallamplitude bobbinvoltagescoupledwithlowbobbinvoltagegrowthrates,itisconcluded thataxiallyorientedODSCCbestdefinesthedegradation morphology occurring attheCookNuclearPlantUnit1tubesupportplateintersections.

Additional tubeswill'epulledduringthenextrefueling outage(summer1992)fordestructive examination toconfirmthetubedegradation phenomena occurring atthetubesupportplates.Noleakageduringnormaloperating conditions hasbeenobservedinthefieldatsimilarplantsforcrackindications withsignalamplitudes lessthan7.7volts.Additionally, noprimary-to-secondary leakageatthetubesupportplatehasbeendetectedinU.S.plants.Relative.to theexpectedleakageduringaccidentcondition

loadings, thelimitingeventwithrespecttoprimary-to-secondary leakageisapostulated steamlinebreakevent.Laboratory dataforpulledtubesfromotherplantsandmodelboilerspecimens showlimitedleakageforindications under10.0voltsduringapostulated SLBcondition (SeeSection9,0ofWCAP-13187).Additional Considerations Theproposedamendment wouldprecludeapproximately 10manremoccupational radiation exposurethatwouldotherwise beincurredbyplantworkersinvolvedintubepluggingorrepairoperations.

Theproposedamendment wouldminimizethelossofmargininreactorcoolantflowthroughthesteamgenerator inLOCAanalyses.

Theproposedamendment wouldavoidlossofmargininreactorcoolantsystemflowandtherefore assistindemonstrating thatminimumflowratesaremaintained inexcessofthoserequiredforoperation atfullpower.Reduction intheamountoftubepluggingrequiredcanreducethelengthofplantoutagesandreducethetimethatthesteamgenerator isopentothecontainment environment duringanoutage,therebyminimizing airbornecontamination andexposure.

Inaddition, therequired100%bobbincoilinspection tobeperformed ateachoutageasoutlinedinWCAP-13187 willhelptoidentifynewareasofconcernwhichmayariseby.providing alevelofinservice inspection thatisfarinexcessofthecurrentT/Ssrequirements.

Attachment 1toAEP:NRC:1166 NOSIGNIFICANT 1ULEARDSANALYSISPage4Vehaveevaluated theproposedT/Sschangeandhavedetermined thatitdoesnotrepresent asignificant hazardsconsideration basedonthecriteriaestablished in10CFR50.92(c).

Operation oftheCookNuclearplantinaccordance withtheproposedamendment willnot:Involveasinificantincreaseitherobabilit orconseuencesofanaccidetrevousevauatedTestingofmodelboilerspecimens forfreestandingtubesatroomtemperature conditions showburstpressures inexcessof5000psiforindications ofODSCCwithvoltagemeasurements ashighas19volts.Bursttestingperformed onpulledtubesfromotherplantswithupto10voltindications showburstpressures inexcessof5900psiatroomtemperature.

Correcting fortheeffectsoftemperature onmaterialproperties andminimumstrengthlevels(asthebursttestingwasdone,atroomtemperature),

tubeburstcapability significantly exceedstheRG1.121criteria, requiring themaintenance ofamarginofthreetimesnormaloperating pressuredifferential ontubeburstifthrough-wall cracksarepresent.Basedontheexistingdatabase,thiscriteriaissatisfied withbobbincoilindications withsignalamplitudes lessthan6.8volts,regardless oftheindicated depthmeasurement.

Thisstructural limitisbasedona-95%lowertolerance limit(LTL)confidence levelofthedata.The4.0voltpluggingcriteriacomparesfavorably withthestructural limitconsidering expectedgrowthratesofODSCCatCookNuclearPlantUnitl.Alternate crackmorphologies

'ancorrespond to6.8voltssothatauniquecracklengthisnotdefinedbyaburst-pressure-to-voltage correlation.

However,relativetoexpectedleakageduringnormaloperating conditions, nofieldleakagehasbeenreportedatotherplantsfromtubeswithindications withavoltagelevelofunder7.7volts(ascomparedtothe4.0voltproposedalternate tubepluggingcriteriaproposedinthissubmittal).

Also,aqualitative assessment ismadebetweenthebeginning-of-cycle(BOC)4.0volttubepluggingcriteriaandthecurrent40%allowable tubewallpenetration pluggingcriteriaatCookNuclearPlantUnit1.AnODSCC-degraded tubesupportplateintersection witha4.0voltbobbincoilresponseisexpectedtoburstatapproximately 7400psi,usingthemeancurveofFigure9-2ofWCAP-13187.

Whilethe-95'tLTLcurveisusedintheapplication ofthepluggingcriteria, themeancurvemustbeusedforthisspecificcomparison inordertoadequately comparethetwodatasetsused.PerWCAP-13187, Attachment 1toAEP:NRC:1166 Page5acomparison ofthematerialproperties at650Pandroomtemperature condition properties showedthattheelevatedtemperature properties areapproximately 0.86oftheroomtemperature properties.

Therefore, thetemperature-adjusted burstpressurefora4.0voltbobbincoilindication isexpectedtobeapproximately 6400psi.FigurellofNUREG-0718 plotstheburstpressures ofthinned0.875x0,050inchsteamgenerator tubes.At40%actualuniformwallthinning, extending 0.75inchinaxiallength,theburstpressureis6800psi.TheNUREQtestdataisobtainedatatemperature of600P,comparedtotheWestinghouse datanotedabove,whichisadjustedfor650F.TheNUREGresultsat40%actualthinningarecomparable tothe4.0voltBOCcriteriaexpectedburstpressure(6800psiversus6300ps+.Theburstpressurefornon-thinned tubeswithpartialdepthcracksupto0.75inchinlengthisslightlylowerthanforuniformthinninguptodepthsofabout60%.Also,NUREG-0718 information canbeusedtoestimatetheburstpressureforatubewhichhasbeenslotted,simulating anaxialcrack.Theexpectedburstpressurefora40%deep,0.75inchlongEDMslotusingNUREQ-0718isapproximately 6000psi.Therefore, itisjudgedthatthemarginofsafetycorresponding tothecurrent40'%yNDEdepthbasedpluggingcriteriaisnotsignificantly reduceduponimplementation ofthebobbincoilvoltagecriteriaat.CookHuclearPlantUnit1.Relativetotheexpectedleakageduringaccidentcondition

loadings, theaccidents thatareaffectedbyprimary-to-secondary leakageandsteamreleasetotheenvironment are:feedwater systemmalfunction, lossofexternalelectrical loadand/orturbinetrip,lossofallACpowertostationauxiliaries, majorsecondary systempipefailure,steamgenerator tuberupture,reactorcoolantpumplockedrotor,andruptureofacontrolroddrivemechanism housing.Ofthese,themajorsecondary systempipefailureisthemostlimitingforCookHuclearPlantUnit1inconsidering thepotential foroff-sitedoses.Uponimplementation ofthealternate pluggingcriteria, itwillbeverifiedonacycle-by-cyclebasisthatthedistribution ofcrackingindications atthetubesupportplateintersections issuchthatprimary-to-secondary leakagewouldresultinsiteboundarydoseswithinasmallfractionofthe10CFR100guideline, i.e.,30remthyroid,duringapostulated steamlinebreakevent.Dataindicates thatathreshold voltageof2.8voltswouldresultinthrough-wall crackswiththepotential toleakatsteam'inebreak(SLB)conditions.

Application ofthe Attachment 1toAEP:NRC:1166 Page6proposedpluggingcriteriarequiresthatthecurrentdistribution ofnumberofindications versusvoltagebeobtainedduringeachrefueling outage.Theindicated bobbincoilvoltageisthencombinedwiththerateofchangeinvoltagemeasurement toestablish anend-of-cycle (EOC)voltagedistribution and,thus,leakrateduringSLBpressuredifferential.

Ifitisfoundthattheprojected SLBleakagefordegradedintersections plannedtobeleftinserviceexceeds120gpm,thenadditional tubeswillbepluggedtoreduceprojected SLBleakagebelow120gpm.MonteCarloanalysesresultsbasedontheCookNuclearPlantUnit1growthrateandassumededdycurrentuncertainties indicatethatover4000indications, allwitha(BOC)bobbincoilvoltageof2.0volts,'ouldcontribute lessthan1gpmleakageatSLBconditions.

Basedontheinspection resultsfromthelastoutage(1990),indications leftinserviceareexpectedtohaveatotalpredicted SLBleakrateof0.1gpmatEOCconditions.

2)Createtheossibilit oanewordifferent kindofaccidentfromanreviousanal@edImplementation oftheproposedamendment doesnotintroduce anysignificant changestotheplantdesignbasis.Useofthecriteriadoesnotprovideamechanism thatcouldresultinanaccidentoutsideoftheregionofthetubesupportplateelevations.

Neitherasinglenormultipletuberuptureeventwouldbeexpectedinasteamgenerator inwhichthepluggingcriteriahasbeenapplied(duringallplantconditions).

Thebobbincoilsignalamplitude pluggingcriteriaisestablished suchthatneitheroperational leakagenorexcessive leakageduringapostulated steamlinebreakcondition areanticipated.

IndianaandMichiganPowerCompanywillimplement amaximumleakageratelimitof150gpd(0.1gpm)persteamgenerator tohelpprecludethepotential forexcessive leakageduringallplantconditions uponapplication ofthealternate pluggingcriteria.

Thecurrenttechnical specification limitonprimary-to-secondary leakageatoperating conditions isamaximumof1.0gpm(1440gpd)forallsteamgenerators oramaximumof500gpdforanyonesteamgenerator.

TheRG1.121criteriaforestablishing operational leakageratelimitsthatrequireplantshutdownarebaseduponleak-before-break considerations todetectafreespancrackbeforepotential tuberupture.The150gpdlimitprovidesforleakagedetection andplantshutdownintheeventoftheoccurrence ofanunexpected singlecrackresulting inleakagethatis Attachment 1toAEP:NRC:1166 Page7'egulatory Guide1.121acceptance criteria(Item3ofSection3.2ofWCAP-13187) forestablishing operating leakagelimitsarebasedonleak-before-break considerations suchthatplantshutdownisinitiated iftheleakageassociated withthelongestpermissible crackisexceeded.

Thelongestpermissible crackisthelengththatprovidesafactorofsafetyofthreeagainstburstingatnormaloperating pressuredifferential, Avoltageamplitude of6.8voltsfortypicalODSCCcorresponds tomeetingthistubeburstrequirement atthe-95%LTLuncertainty limitontheburstcorrelation.

Alternate crackmorphologies cancorrespond to6.8voltssothatauniquecracklengthisnotdefinedbytheburstpressureversusvoltagecorrelation.

Consequently, typicalburstpressureversusthrough-wall cracklengthcorrelations areusedbelowtodefinethe"longestpermissible crack"forevaluating operating leakagelimits.Thesinglethrough-wall cracklengthsthatresultintubeburstatthreetimesnormaloperating pressuredifferential andSLBconditions areabout0.44inchand0.84inch,respectively.

Nominalleakageforthesecracklengthswouldrangefrom0.1gpmto4gpm,respectively, whilelower95'tconfidence levelleakrateswouldrangefromabout0.01gpmto0.5gpm,respectively.

Anoperating leakratelimitof150gpdwi11beimplemented inapplication ofthealternate tubepluggingcriteria.

Thisleakagelimitprovidesfordetection of0.4inchlongcracksatnominalleakratesand0.6inchlongcracksatthe-95tLTLconfidence levelleakrates.Thus,the150gpdlimitprovidesforplantshutdownpriortoreachingcriticalcracklengthsforSLBconditions atleakrateslessthana-95tLTLconfidence levelandforthreetimesnormaloperating pressuredifferential atlessthannominalleakrates.3)Involveasinificantreduction inamarinofsafetTheuseofthealternate pluggingcriteriaatCookNuclearPlantUnit1isdemonstrated tomaintainsteamgenerator tubeintegrity commensurate withtherequirements ofRG1.121.Regulatory Guide1.121describes amethodacceptable totheNRCstaffformeetingGDCs14,15,31,and32byreducingtheprobability oftheconsequences ofsteamgenerator tuberupture.Thisisaccomplished bydetermining thelimitingconditions ofdegradation ofsteamgenerator tubing,asestablished byinservice inspection.

Tubeswithunacceptable crackingshouldberemovedfromservice.Themostlimitingeffectwouldbeapossibleincreaseinleakageduringasteam Attachment 1toAEP;NRC:1166 Page8linebreakevent.Oncethealternate pluggingcriteriaisapplied,excessive leakageduringasteamlinebreakeventisprecluded byverifying eachfuelcyclethattheexpectedend-of-cycledistribution ofcrackindications atthetubesupportplateelevations wouldresultinminimalandacceptable primary-to-secondary leakageduringallplantconditions.

Thishelpstodemonstrate radiological conditions arelessthanasmallfractionofthe10CFR100guideline.

Inaddressing thecombinedeffectsofaloss-of-coolant accident(LOCA)andasafeshutdownearthquake (SSE)onthesteamgenerator component (asrequiredbyGDC2),ithasbeendetermined thattubecollapsemayoccurinthesteamgenerators atsomeplants.Thisisthecaseasthetubesupportplatesmaybecomedeformedasaresultoflateralloadsatthewedgesupportsattheperiphery oftheplateduetothecombinedeffectsoftheLOCArarefaction waveandSSEloadings.

Theresulting pressuredifferential onthedeformedtubesmaycausesomeofthetubestocollapse.

Therearetwoissuesassociated withsteamgenerator tubecollapse.

First,thecollapseofsteamgenerator tubingreducestheRCSflowareathroughthetubes.Thereduction inflowareaincreases theresistance toflowofsteamfromthecoreduringaLOCAwhich,inturn,maypotentially increasepeakcladtemperature.

Second,thereisapotential thatpartialthrough-wall cracksintubescouldprogresstothrough-wall cracksduringtubedeformation orcollapse.

Consequently, sincetheleak-before-break methodology isapplicable totheCookNuclearPlantUnit1reactorcoolantsystemprimaryloops,theprobability ofbreaksintheprimarylooppipingissufficiently lowthattheyneednotbeconsidered inthestructural designbasisoftheplant.Excluding breaksintheRCSprimaryloops,theLOCAloadsfromthelargebranchlinebreakswereanalyzedforCookNuclearPlantUnit1andwerefoundtobeofinsufficient magnitude toresultinsteamgenerator tubecollapseorsignificant deformation.

Regardless ofwhetherornotleak-before-break isappliedtotheprimarylooppipingatCookNuclearPlantUnit1,anyflowareareduction isexpectedtobeminimal(muchlessthan1t)andPCTmarginisavailable toaccountforthispotential effect.Analysesresultsshowthatnotubesnearwedgelocations areexpectedtocollapseordeformtothedegree Attachment 1toAEP:NRC:1166 Page9thatsecondary-to-primary in-leakage wouldbeincreased overcurrentexpectedlevels.Forallothersteamgenerator tubes,thepossibility ofsecondary-to-primary leakageintheeventofacombinedLOCAandSSEeventisnotsignificant.

Inactuality, theamountofsecondary-to-primary leakageintheeventofacombinedLOCAandSSEisexpectedtobelessthanthatcurrently allowed,i.e.,500gpdpersteamgenerator.

Furthermore, secondary-to-primary in-leakage wouldbelessthanprimary-to-secondary leakageforthesamepressuredifferential sincethecrackswouldtendtocloseunderasecondary-to-primary pressuredifferential.

Also,thepresenceofthetubesupportplateisexpectedtoreducetheamountofin-leakage.

Addressing RG1,83considerations, implementation ofthealternate pluggingcriteriaissupplemented by100%inspection requirements atthetubesupportplateelevations havingODSCCindications, reducedoperating leakratelimits,eddycurrentinspection guidelines toprovideconsistency involtagenormalization, androtatingpancakecoilinspection requirements forthelargerindications leftinservicetocharacterize theprincipal degradation mechanism asODSCC.Asnotedpreviously, implementation ofthealternate pluggingcriteriawilldecreasethenumberoftubeswhichmustberepairedortakenoutofservicebyplugging.

Theinstallation ofsteamgenerator tubeplugsreducestheRCSflowmarginand,thus,implementation ofthealternate pluggingcriteriawillmaintainthemarginofflowthatwouldotherwise bereducedintheeventofincreased tubeplugging.

Basedontheabove,itisconcluded thattheproposedchangedoesnotresultinasignificant reduction inmarginwithrespecttoplantsafetyasdefinedintheFinalSafetyAnalysisReportoranybasesoftheplantTechnical Specifications.

CONCLUSION Basedonthepreceding

analysis, itisconcluded thatusingthetubesupportplateelevation bobbincoilsignalamplitude alternate steamgenerator tubepluggingcriteriaforremovtngtubesfromserviceatCookNuclearPlantUnit1isacceptable andtheproposedlicenseamendment doesnotinvolveaSignificant HazardsConsideration asdefinedin10CFR50.92.
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