ML17332A745
| ML17332A745 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 04/13/1995 |
| From: | FITZPATRICK E INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML17332A746 | List: |
| References | |
| AEP:NRC:1129D, NUDOCS 9504260146 | |
| Download: ML17332A745 (24) | |
Text
RIQRITYCCELERATEDRlDSPROCl'.SSliCREGULATORY INFORMATION DISTRIBUTION SYSTEM(RIDS)ACCESSION NBR:9504260146 DOC.DATE:
95/04/13NOTARIZED:
YESDOCKETNFACIL:50-315 DonaldC.CookNuclearPowerPlant,Unit1,IndianaM05000315AUTH.NAMEAUTHORAFFILIATION FITZPATRICK,E.
IndianaMichiganPowerCo.(formerly Indiana&MichiganEleRECIP.NAME RECIPIENT AFFILIAT10N DocumentControlBranch(Document ControlDesk)
SUBJECT:
Application foramendtolicenseDPR-58,modifying TS3/4.4.5toallowuseoflaser-welded sleevestorepairdefective SG~~tubes.Westinghouse nonproprietary
&proprietary reptsdescribing repairprocessencl.Proprietary reptwithheld.
DISTRIBUTION CODE:APOIDCOPIESRECEIVED:LTR gENCLJSIZE:520TITLE:Proprietary ReviewDistribution
-PreOperating License&Operating RNOTESRECIPIENT IDCODE/NAME PD3-1LAHINTERNAFILECENTER01.EXTERNAL:
NRCPDRCOPIESLTTRENCL11111110RECIPIENT IDCODE/NAME PD3-1PDOGC/HDS2COPIESLTTRENCL1110DCUYOTETOALL"RIDS"RECIPIENTS:
PLEASEHELPUSTOREDUCEiVKSTE!COYTACT'I'I IEDOCL'ifEYT CONTROLDESK,ROOMPI-37IEXT.504.of63)TOI'.LIhflNATEYOI.'RXAifLPl<OilDISTRIBUTION LIS'I'SI'ORDOCK'NlEX'I'SYOI.'ON"I'l.'I'.D!
TOTALNUMBEROFCOPIESREQUIRED:
LTTR6ENCL'
't'E IndianaMichiganPowerCompanyP.O.Box16631Columbus, OH43216IApril13,1995DocketNos.:50-315AEP:NRC:1129D U.S.NuclearRegulatory Commission ATTN:DocumentControlDeskWashington, D.C.20555Gentlemen:
DonaldC.CookNuclearPlantUnit1TECHNICAL SPECIFICATION CHANGESTOALLOWUSEOFLASER-WELDED SLEEVESFORSTEAMGENERATOR TUBESThisletteranditsattachments constitute anapplication foramendment tothetechnical specifications (T/Ss)fortheDonaldC.CookNuclearPlantUnit1.Specifically, weareproposing tomodifyT/Ss3/4.4.5(SteamGenerators) andtheaccompanying Basessectiontoallowuseoflaser-welded sleevestorepairdefective steamgenerator tubes.Adetaileddescription oftheproposedchangesandouranalysisconcerning significant hazardsconsiderations areincludedinAttachment 1tothisletter.Attachment 2containsmarkeduppagesofthecurrentT/Ss.Attachment 3containstheproposedrevisedT/Sspages.Attachment 4containsacopyoftheproprietary reportpreparedbyWestinghouse ElectricCorporation, WCAP-13088 Revision3,describing thesleevingrepairprocess.Attachment 5containsacopyofthenon-proprietary versionofthesameWestinghouse ElectricCorporation report,WCAP-13089 Revision3.Attachment 6containsaWestinghouse authorization letter,CAW-95-786, Application ForWithholding Proprietary Information FromPublicDisclosure andaccompanying affidavit.
Webelievetheproposedchangeswillnotresultin(1)asignificant increaseintheamounts,andnosignificant changeinthetypes,ofanyeffluentthatmaybereleasedoffsite,or(2)asignificant increaseinindividual orcumulative occupational radiation exposure.
TheseproposedchangeshavebeenreviewedbythePlantNuclearSafetyReviewCommittee andwillbereviewedatthenextregularly pu/'/(9504260i46 950413PDRADOCK05000315PPDRscheduled NuclearSafetyandDesignReviewCommittee meeting.:3gegpg/~/~
U.S.NuclearRegulatory Commission Page2AEP'NRC'1129D Incompliance withtherequirements of10CFR50.91(b)(1),
copiesofthisletteranditsattachments havebeentransmitted totheMichiganPublicServiceCommission andtotheMichiganDepartment ofPublicHealth.TheT/Spagessubmitted withthisletterwillbeimpactedbytheT/SpagechangesinourletterAEP:NRC:1166R, "2.0VoltInterimSteamGenerator TubePluggingCriteriaforCycle15."Sincerely, VicePresident SWORNTOANDSUBSCRIBED BEFOREMETHIS~Z4DAYOF1995otaryPublicehAttachments cc:A.A.BlindG.CharnoffJ.B.MartinNFEMSectionChiefNRCResident, Inspector
-BridgmanJ.R.Padgett ATTACHMENT 1TOAEPNRC'1129D DESCRIPTION OFTHEPROPOSEDCHANGESANDANALYSISCONCERNING SIGNIFICANT HAZARDSCONSIDERATIONS
ATTACHMENT 1TOAEP:NRC:1129D Page1INTRODUCTION Thisamendment requestproposesachangetoCookNuclearPlant(CNP)Unit1steamgenerator technical specification (T/S)4.4.5.2,4.4.5.4.a, 4.4.5.4.c, 4.4.5.5.b.l, andBasis3/4.4.5onpageB3/4.4-3,toallowsteamgenerator tubesleevingunderspecificconditions.
Thechangepermitstheinstallation ofAlloy690laser-welded tubesleevesatdegradedtubesupportplate(TSP)intersections andwithinthetubesheet (TS)areaofCNPUnit1steamgenerators,
.-Perthecurrenttechnical specifications, steamgenerator tubeswitheddycurrentindications exceeding thecurrentplugginglimitfortheselocations canberepairedusingexistingsleevingrequirements orberemovedfromservice.Thisproposedamendment permitslaser-welded tubesleevestobeinstalled torepairdegradedsteamgenerator tubeseitherattheTSPintersections (TSPsleeves),
withintheTSarea(TSsleeves),
oracombination ofbothwithinthesametube.DESCRIPTION OFTHEAMENDMENT REQUESTAs'required by10CFR50.91(a)(1),thisanalysisisprovidedtodemonstrate thataproposedlicenseamendment toimplement repairoftubesusinglaser-welded tubesleevesforCNPUnit1steamgenerators represents nosignificant hazardsconsideration.
Inaccordance with10CFR50.92(c),
implementation oftheproposedlicenseamendment wasanalyzedusingthefollowing standards andfoundnotto:1)involveasignificant increaseintheprobability orconsequences foranaccidentpreviously evaluated, 2)createthepossibility ofanewordifferent kindofaccidentfromanyaccidentpreviously evaluated, or3)involveasignificant reduction inamarginofsafety.Thelaser-welded sleevingrepairmethodsecurestotheinsideoftheoriginaltubeashortlengthofsleevetubingwithanouterdiameterslightlysmallerthantheinsidediameterofthetube,spanningthedegradedareaoftheparenttube.TheTSPsleeveisattachedtothedegradedtubebyproducing anautogenous weldbetweentheoriginaltubeandsleeveateachendofthesleeve.TSPsleeveweldsareproducedinthefreespansectionsofthetubeabovethetopofthetubesheet.
Thefreespanweldprovidesthestructural jointbetweenthetubeandsleeve,and,sinceitisahermeticseal,italsoprovidespositive(leaktight) leakageintegrity.
TheTSsleeveissecuredandsupported structurally attheupperjointsectionbyafreespanautogenous weldperformed identically totheTSPsleeveweldswhilethelowerjointissecuredbyamechanical hardroll.
AnoptionalsealweldcanalsobeincludedwithintheTSsleevelowerjointatanelevation coincident withtheapproximate midpointoftheTScladding.
However,fortheTSsleevelowerjoint,thehardrollareasuppliesthenecessary structural requirements forthelowerjointsincethesealweldisoptionalforthislocation.
Boththelowerhardroll 0~~'~'Pol ATTACHMENT 1TOAEP:NRC:1129D Page2andfreespanlaserweldjointsprovidestructural integrity characteristics whichexceedthestructural requirements forthesleeve.Therefore, itisexpectedthatalossofstructural integrity inoneofthesleevejointswillnotresultinalossofstructural integrity forthesleeve.Thesleevestructural integrity requirements includesafetyfactorsinherenttotherequirements oftheASMECode.Installation ofTSPsleevesand/orTSsleevesrestorestheintegrity oftheprimarypressureboundarytoacondition consistent withthatoftheoriginally suppliedtubing.Allweldsmustbeproducedaminimumdistancefromanydetectedtubedegradation asdescribed inWCAP-13088, Rev.3(Attachment 4).Absentprovisions fortuberepairbysleeving, tubeswithindications ofdegradation inexcessofthepluggingcriteriaatTSPand/orTSlocations wouldhavetoberemovedfromserviceinaccordance withtechnical specification tubepluggingcriteria.
Removalofatubefromserviceresultsinasmallreduction ofreactorcoolantflowthroughthesteamgenerator.
Thissmallreduction inflowhasanimpactonthemargininthereactorcoolantflowthroughthesteamgenerator withregardtocorecoolingcapacityandontheheattransferefficiency ofthesteamgenerator.
Repairofatubebysleevingmaintains thetubeinserviceandresultsinamuchsmallerflowreduction asopposedtoplugging.
Therefore, theuseofsleevinginlieuofpluggingwouldminimizelossofmargininreactorcoolantsystemflowandassistinassuringthatminimumflowratesaremaintained inexcessofthatrequiredforoperation atfullpower.Anycombination ofsleevingandpluggingutilizedatCNPUnit1uptoalevelsuchthattheeffectofsleevingwillnotreducetheminimumreactorcoolantflowratetobelowthecurrenttechnical specification limitisacceptable.
Also,minimizing thereduction inflowhasoperational benefitsbylimitingtheincreaseinheatfluxacrossthetubesremaining'n service.Increased heatfluxeshavebeenassociated withanincreased potential fortubecorrosion.
Theproposedamendment wouldmodifyTechnical Specifications 3/4.4.5"SteamGenerators,"
andBasesB3/4.4.5,"SteamGenerators,"
topermittheuseofWestinghouse laser-welded sleevesandwillprovidethesleeve/tube inspection requirements andacceptance criteriatodetermine thelevelofdegradation whichwouldrequirethesleevedtubetosubsequently beremovedfromservice.
~l ATTACHMENT 1TOAEP'NRC'1129D Page3EVALUATION SleeveTubeInteritDuringthedevelopment oflaser-welded
- sleeving, SectionIIIoftheASMECodewasusedfortheminimumwallthickness determination andboundingstressandfatiguelevelsforthesleeve.Byshowingthatthesleevedesignmeetstheapplicable subsections ofSectionIIIoftheCode,thesleevedesignmeetsthedesignrequirements ofthe.original tubing.(Draft)Regulatory Guide(RG)1.121,"BasesforPluggingDegradedPWRSteamGenerator Tubes,"isusedtodeveloptheplugginglimitofthesleevedetermined bynon-destructive examination (NDE),shouldsleevewalldegradation subsequently occur.Potentially degradedsleevesattheplugginglevelwereshown(byanalysis) toretainburststrengthinexcessofthreetimesthenormaloperating pressuredifferential atendofcycleconditions, perRG1.121guidelines.
Thestructural analysisoutlinedinAttachment 4utilizesagenericsetofloadinginputswhichwasintendedtoboundtheoperating regimesofallplantswithWestinghouse Series44and51steamgenerators.
Thecurrentnormaloperating pressuredifferential forCNPUnit1isapproximately 1410psi,whichisboundedbythevalueusedinAttachment 4of1530psifornormaloperating conditions.
Duetotherelatively lowsteampressuredeveloped inModel51steamgenerators, thenormaloperating condition (withappropriate safetyfactorof3applied)resultsinthelimitingloadingcondition fordetermination oftherequiredminimumwallthickness tosatisfytheASMECode,andsubsequently RG1.121.Additionally, thesleevewallplugginglimitforCNPUnit1LWSshasbeenestablished usinganormaloperating condition primarytosecondary pressuredifferential of1600psi(discussed later).Therequirements ofRG1.83,"Inservice Inspection ofPWRSteamGenerator Tubes,"areimplemented, andabaselineeddycurrentinspection oftheinstalled sleevesisperformed priortooperation.
Anultrasonic inspection ofthefreespanweldjointsisalsoperformed priortooperation.
Theultrasonic inspection isusedtoverifythattheminimumacceptable fusionzonethickness oftheweldisachieved.
Aseparateminimumweldfusionzonethickness hasbeenshownbyanalysistosatisfytherequirements oftheASMECodewithregardtoacceptable stresslevelsduringoperating andaccident, conditions'he acceptance criteriafortheultrasonic testing(UT)inspection oftheweldrequiresaminimumweldfusionzonewidth.ThisminimumUTbasedweldwidthisapproximately 50Xlargerthantheminimumacceptable weldwidthbasedonstresslimitations, therefore, structural marginabovethatprovidedmerelybycompliance withtheASMECodeisinherently providedforeachsleeveweld.Additionally, fieldexperience hasindicated thatnominalweldwidthsareapproximately twicetheminimumweldwidthrequiredforUTacceptance.
t41EVI ATTACHMENT 1TOAEP:NRC:1129D Page4Asstatedpreviously, agenericsetofloadingconditions wasusedforstructural analysisofthesleevedtubeassemblyinAttachment 4.Afatigueanalysiswasperformed forthesleevedtubeassembly, thecriticallocationbeingthefreespanlaserweld.Theloadingcyclesthatwereappliedtothesleeveassemblyanalysiswerethosefora40yearplantlifecycle.Therefore, thefatigueanalysisisconservative foranoperating plant.Theresultsofthefatigueanalysisindicateacceptable usagefactorsfortheentirerangeofpermitted weldthicknesses.
Acomparison ofthenumberofloadingcyclesusedin.thegenericanalysisindicates that..the genericinputsareconservative comparedtoCNPUnit1inthisarea.Usingthegenericinputs,thecumulative fatigueusagefactorwasfoundtobemuchlessthan1.0(actualvaluelessthan0.10).Thepressuredifferentials usedforthegenericanalysiswerefoundtobeconservative comparedtoCNPUnit1valuesforthemajorityofthetransient curvesevaluated.
Severaltransients forCNPUnit1involvedslightlyhigherpressuredifferentials comparedtotheinputsusedinthegenericanalysis.
However,thedifference wasdetermined tobeinsignificant withregardtotheappliedrangeofstressintensity andalsoinsignificant withregardtoitsinputtocumulative fatigueusageloading.Recalculation ofcumulative fatigueusageindicates virtually nochangeinthecalculated usagefactor(actualvalueforCNPUnit1remainslessthan0.1).Aconservative setoftransients applicable toCNPUnit1wereusedforthecomparison withthetransient setdefinedinAttachment 4:TheCNPUnit1transients areapplicable forplantoperation atboth2250psiand2100psiRCSpressure.
ArangeofT><<valuesarealsoincludedintheCNPUnit1transient set.Leakagetestingunderconditions considered tobemoreseverethanexpectedduringalloperating plantconditions hasshownthattheLWSdoesnotintroduce additional primarytosecondary leakageduringapostulated steamlinebreakevent.Laser-welded sleevedtubeassemblies weresubjected tothermalandfatiguecyclingandthenleaktestedatpressuredifferences ofupto3110psi,whichfarexceedsthemaximumexpectedCNPUnit1feedlinebreak/steamline break(FLB/SLB) pressuredifferential ofapproximately 2335to2560psid.Noleakagewasdetectedinanyweldedjoint(bothfreespanandTSjoints).LeakagetestinghasalsoshownthatthesealweldoftheTSsleevelowerjointisnotrequiredinordertoprecludeleakageduringnormaloperation oraccidentconditions at600oF.Non-welded lowerjointTSsleeve/tube leakagetestspecimens weresubjected tobothfatigueandthermalcyclingtestspriortofinalleakrateevaluation testing.Theloadlevelappliedduringthefatiguetestingexceededthemaximumaxialloadappliedtothesleeveduringthemostseverepressureloadingcondition.
Thermalcyclingtestssimulated astandardplantheatup/cooldown cycle.Noleakagewasdetectedinanynon-welded TSsleevelowerjointat600oFafterboththermalandfatigueloading.Primarytosecondary leakage
~4'44%4)~ilh44I4I4~I"04hIII4444,~
ATTACHMENT 1TOAEP:NRC:1129D Page5throughnon-welded TSsleevelowerjointswouldnotbeexpectedatOXpower(Tarot547F).SleevtnofPreviousl PluedIndications Thesleeveinstallation requirements applicable toactivetubeswhichhavebeenidentified ascontaining degradation whichexceedstherepairlimitarenodifferent forthesleevingofpreviously pluggedtubes.Anew"baseline" inspection oftheentiretubelengthmustbe...performed priortosleeveinstallation in'previously pluggedtube.Thelocationoftheidentified tubedegradation mustbeverifiedtobeaminimumdistanceofone-inchfromtheweldjoints(sameforactivetubes).Historically, theareasofthetubewhichhavesufferedoutsidediameterinitiated corrosion degradation aretheTSPintersections andthesectionsoftubewithinthethickness oftheTSwheresecondary sidecontaminants havecollected duetotheoperating crevices'he expansion transition regioncanexperience eitherouterdiameterorinnerdiameterinitiated corrosion.
Thesleevefreespan(structural) weldjointsarenotlocatedintheseareas,andshouldnotbeaffectedbyanypreviously identified degradation mechanism whichcausedthetubetoberemovedfromservice.Thestructural analysishasalsosupported sleeveinstallation inacircumferentially separated tube,therefore, theextentofidentified degradation shouldnotaffectsleeveinstallation providedthedegradation isoneinchfromtheweldjoints.Additionally, theareaofthetubewherethetubeplugwasinstalled mustbevisuallyinspected priortosleeveinstallation.
Surfacefinishrequirements forthisareahavebeendeveloped whichhelptomaintaintheabilityofthejointtoformaleaktight seal.Conformance tothesurfacefinishrequirements forthelowerjointwillhelptoensurealeaktight sleevejoint,regardless ofwhetherornotthesealweldhasbeenproduced.
Theabilityoftheweldtosufficiently penetrate thetubewallhasbeenshownbytestincaseswherealocalized gap(upto2mils)existedbetweenthetubeandsleeve.Thepenetrating capabilities oftheweldwillalsohelptoensurealeaktight jointincaseswhereslightsurfaceimperfections duetotubeplugremovalmaybepresent.FlowMarinConsiderations Byreducingthenumberoftubeplugsinstalled inthesteamgenerator, theproposedamendment wouldminimizethelossofmargininreactorcoolantflowthroughthesteamgenerator duringapostulated eventswhencorecoolingcapacityisrequired.
Also,sleevingwillprovidegreatermarginabovetherequiredminimumflowforfullpoweroperation, thanifequalnumbersoftubeswerepluggedasopposedtosleeved.
ATTACHMENT 1TOAEP'NRC'1129D Page6Theinstallation ofasleeveintoatuberesultsinanadditional flowrestriction withintheprimarysystem,withanassociated increaseinpressuredropinthesteamgenerator.
Theeffectsofthisflowrestriction onplantoperation areevaluated inthesamemannerthattubepluggingeffectsareanalyzed.
Attachment 4identifies thereduction inprimarycoolantflowcausedbytheprojected sleevingundernormaloperating conditions andidentifies thenumberofsleevesorcombination ofsleeveswhichresultinaflowreduction equivalent toonepluggedtube.Evaluation ofcorecoolingcapability forthe.minimumreactorcoolantsystemflowratewillboundtheeffectsonallcoreandsystemparameters foracombination ofpluggingandsleevinguptotheequivalent resistance associated withtheminimumreactorcoolantflowrate.Thehydraulic equivalency valuescontained inAttachment 4canbeusedtoestimatetheimpactoflaser-welded sleevingonRCSflowcapability.
Usingworstcaseflowconditions ofAttachment 4(judgedtobeconservative comparedtoCNPUnit1conditions),
asinglehotlegTSsleevewouldrepresent approximately 1/23oftheflowreduction ofapluggedtube.Additional combinations ofTSPsleevesandTSssleevesandtheirflowreduction effectsareincludedinAttachment 4.ANALYSISConformance oftheproposedamendments tothestandards foradetermination ofnosignificant hazardasdefinedin10CFR50.92(threefactortest)isshowninthefollowing:
1)Operation ofCNPUnit1inaccordance withtheproposedlicenseamendment doesnotinvolveasignificant increaseintheprobability orconsequences ofanaccidentpreviously evaluated.
TheTSand/orTSPintersection LWSconfiguration hasbeendesignedandanalyzedinaccordance withtherequirements oftheASMECodeandRG1.121.Fatigueandstressanalysesofthesleevedtubeassemblies producedacceptable results.Mechanical testinghasshownthatthestructural strengthoftheAlloy690sleevesundernormal,faultedandupsetconditions iswithinacceptable limits,Leaktestinghasdemonstrated thatprimarytosecondary leakageisnotexpectedduringallplantconditions, including thecasewherethesealweldisnotproducedinthelowerjointoftheTSsleeve.Testingshowsthatnon-welding TSsleevelowerjointsremainedleaktight attemperature andpressureconditions representative ofnormalandaccidentconditions.
Sincelaserweldingproducesahermeticsealbetweenthetubeandsleeve,noleakpathcanbe'ealizedunderanycondition.
Therefore, installation ofLWSswillnotinfluence offsitedosecalculation forapostulated steamlinebreakevent.
ATTACHMENT 1TOAEP:NRC:1129D Page7Theproposedtechnical specification changetosupporttheinstallation ofAlloy690LWSsdoesnotadversely impactanypreviously evaluated designbasisaccidentortheresultsofaccidentanalysesforthecurrenttechnical specification minimumreactorcoolantsystemflowrate.Theresultsofthequalification testing,analyses, andplantoperating experience demonstrate thatthesleeveassemblyisanacceptable meansofmaintaining tubeintegrity.
Theseaforementioned analysesandtestsdemonstrate thatinstallation ofsleevesspanningdegradedareas,ofthetubewillrestorethetubetoacondition consistent withitsoriginaldesignbasis.Plugginglimitcriteriaareestablished usingtheguidanceofRG1.121.Furthermore, perRG1.83recommendations, thesleevedtubecanbemonitored throughperiodicinspections withpresenteddycurrenttechniques'onformance ofthesleevedesignwiththeapplicable sectionsoftheASMECodeandresultsoftheleakageandmechanical tests,supporttheconclusion thatinstallation oflaser-welded tubesleeveswillnotincreasetheprobability orconsequences ofanaccidentpreviously evaluated.
Depending uponthebreaklocationforapostulated steamgenerator tuberuptureevent,implementation oftubesleevingcouldacttoreducetheradiological consequences tothepublicduetoreducedflowratethroughasleevedtubecomparedtoanon-sleeved tubebasedontherestriction affordedbythesleevewallthickness.
2)Theproposedlicenseamendment doesnotcreatethepossibility ofanewordifferent kindofaccidentfromanyaccidentpreviously evaluated, Implementation oflaser-welded sleevingwillnotintroduce significant oradversechangestotheplantdesignbasis.StressandfatigueanalysisoftherepairhasshowntheASMECodeandRG1.121allowable valuesaremet.Implementation oflaser-welded sleevingmaintains overalltubebundlestructural andleakageintegrity duringallplantconditions atalevelconsistent tothatoftheoriginally suppliedtubing.Leakandmechanical testingofsleevessupportstheconclusions ofthecalculations thatthesleeveretainsbothstructural andleakageintegrity duringallconditions.
Sleevingoftubesdoesnotprovideamechanism resulting inanaccidentoutsideoftheareaaffectedbythesleeves.Anyhypothetical accidentasaresultofpotential tubeorsleevedegradation intherepairedportionofthetubeisboundedbytheexistingtuberuptureaccidentanalysis.
Sincethesleevedesigndoesnotaffectanyothercomponent orlocationofthetubeoutsideoftheimmediate arearepaired, inadditiontothefactthattheinstallation ofsleevesandtheimpactoncurrentplugginglevelanalysesisaccounted for,thepossibility thatlaser-ATTACHMENT 1TOAEP'NRC'1129D Page8weldedsleevingcreatesanewordifferent typeofaccidentisnotsupported.
Thedesignofthermally treatedAlloy600andAlloy690sleevedtubeassemblies haveperformed wellhistorically withregardtocorrosion.
Therearenoreportedinstances ofAlloy600thermally treatedorAlloy690sleevedegradation forthegreaterthan35,000sleevesthatWestinghouse hasinstalled intheU.S.Accelerated corrosion testresultsshowthefreespanlaser-welded joint(LWJ)(withpost-weldheattreatment) iscapableofexhibiting aresistance to"corrosion ofgreaterthan10timesthatofrolledtubetransitions.
MostLWScorrosion specimens didnotexperience degradation andweresubsequently removedfromthecorrosion testmediaafterasubstantial testingperiod(supporting the10xfactorcomparedtorolltransitions) wasachieved.
SeveralmillannealedAlloy600materialheatswereusedforcorrosion specimenpreparation.
Allweredocumented byprevioustesttohavebeenhighlysusceptible toPWSCC.Thepostweldheattreatment processappliedtoLWSfreespanjointsisdesignedtoachieveaminimumtubeODwalltemperature of1400Fadjacenttotheweldandwithinthelaserweldheataffectedzone.Sincethetargettemperature of1400FisachievedonthetubeOD,aslightlyhighertemperature isachievedatthetubeIDsurface,wheretheweldcoolingstressesareconcentrated.
Also,sincetheaxiallengthofthelaserweldandlaserweldheataffectedzonearerelatively narrowcomparedtoothersleeveweldingprocesses, anarrowersectionoftubeisrequiredtobeheattreated.SincethelengthoftuberequiredtobeheattreatedisshorterintheLWSprocessthanwithothersleevingprocesses, lowerresidualstressesinthetubecanbeexpected.
Accelerated corrosion testsalsoshowthatnon-heattreatedlaser-welded freespanjointsexhibitresistance tostresscorrosion crackingequaltoorgreaterthanrolledtubetransitions.
Anextensive databaseexistsonLWSjointperformance inforeignplantsinwhichthefreespanjointsarenotheattreated.Oftheapproximately 18,000non-heattreatedjointsinservice,nonehasexhibited arapidcorrosion potential.
Corrosion testingoftheTSsleevelowerjointLWJsexhibitaresistance tocorrosion crackingofthreetofourtimesthatofrolledtubetransitions.
Thesefactorssuggestpostulated sleeve/tube assemblydegradation wouldoccurataratelessthanrolledtransitions, andthepotential forasleeve/tube assemblywithaccelerated degradation ratecharacteristics moreseverethanrolltransitions isnegligible.
Approximately 800LWSsarecurrently inoperation intheU.S.SomeofthesehavebeeninservicesinceApril1992.Theplantsinwhichthesesleevesareinstalled havenotexperienced anyadverseoperational issues(suchasprimaryto
~'lk'(~4)~4V4 ATTACHMENT 1TOAEP'NRC'1129D Page9secondary leakage)ashasbeendetectedatotherplantswithsleeveswhichhaveexperienced rapidcorrosion oftheparenttube.3)Theproposedlicenseamendment doesnotinvolveasignificant reduction inamarginofsafety.Thelaser-welded sleevingrepairofdegradedsteamgenerator tubesasidentified inWCAP-13088 Rev.3hasbeendemonstrated torestoretheintegrity ofthetube'undle undernormalandpostulated accidentconditions.
Thesafetyfactorsusedinthedesignofsleevesfortherepairofdegradedtubesareconsistent withthesafetyfactorsintheASMEBoilerandPressureVesselCodeusedinsteamgenerator design.Theplugginglimitcriteriaforthesleevehasbeenestablished usingthemethodology ofRG1.121.Thedesignofthesleevejointshavebeenverifiedbytestingtoprecludeleakageduringnormalandpostulated accidentconditions.
Implementation oflaser-welded sleevingwillreducethepotential forprimarytosecondary leakageduringapostulated steamlinebreakwhilemaintaining available primarycoolantflowareaintheeventofaLOCA.Byremovingfromservicedegradedintersections throughrepair,thepotential fortubeleakageduringasteamlinebreakisreduced.Thesedegradedintersections nowarereturnedtoacondition consistent withthedesignbasis.Whiletheinstallation ofasleevecausesareduction inflow,thereduction isfarbelowthereduction incurredbyplugging.
Therefore, fargreaterprimarycoolantflowareaismaintained throughsleeving.
UseofRG1.121.criteria assuresthatthemarginofsafetywithrespecttostructural integrity isthesameforthesleevesasfortheoriginalsteamgenerator tubes.Theportionsoftheinstalled sleeveassemblywhichrepresent thereactorcoolantpressureboundarycanbemonitored fortheinitiation andprogression ofsleeve/tube walldegradation, thussatisfying therequirements ofRG1.83.Portionsofthetubebridgedbythesleevejointsareeffectively isolatedfromthepressureboundary, andthesleevethenformsthepressureboundaryintheseareas.Theareasofthesleevedtubeassemblywhichrequireinspection aredefinedinAttachment 4.Inaddition, sincetheinstalled sleeverepresents aportionofthepressureboundary, abaselineinspection oftheseareasisrequiredpriortooperation withsleevesinstalled.
Asstatedpreviously, weldfusionzonewidthisestablished usingUTtesting.Theminimumacceptable weldwidthasdetermined byUTexamination isapproximately 50Xwiderthantheminimumweldwidthwhichsatisfies thestressconditions oftheASMECode.Thegenericevaluation usesthepressurestressequationofSectionNB3224.1oftheASMECodewhichisusedtoestablish 1~Eg(S\If~aeoIelf ATTACHMENT 1TOAEP'NRC:1129D Page10theminimumrequiredwallthickness forthesleevedesignandsubsequently usedtodetermine thelevel"ofsleevewalldegradation (depthbyeddycurrentdetermination) thatwouldrequirethesleevetoberemovedfromservice.UsingtheBPgoz~ppvalueof1530psifromAttachment 4the1imitingminimumrequiredsleevewallthickness isestablished.
Thesleevewallplugginglimit(usingAttachment 4)'f25Xissubsequently established, andincludesanallowance of10Xforeddycurrentuncertainty and10Xforgrowth,althoughsleevewalldegradation hasnotbeenobservedtodateinWestinghouse sleeves.Thegenericevaluation usedtheASMECodeminimumpropertyvaluestoestablish thesleeveplugginglimit.Certified materialtestreportsindicatethatthesleevematerialproperties aresignificantly higherthantheASMECodeminimumvalues.Thegenericevaluation considered aprimarytosecondary pressuredifferential of1530psia,withasteampressureof720psia,fornormaloperating conditions.
CNPUnit1canoperateatfullpowerwithareducedTh<<valueandRCSpressureof2250psi.Steampressurecanbemaintained aslowas650psi(tokeepTh<<aslowaspossible),
butcannotgolowerthan650psiorthesteamgenerator operating requirement ofaprimarytosecondary aPof1600psi(max)willbeexceeded.
AtthisaP>o~ovalueof1600psi,thesleeveminimumwallthickness requfiement (andsubsequently sleevepressureboundaryplugginglimit)usingASMECodeminimummaterialproperties canberecalculated.
Forthiscondition (normaloperating hPequalto1600psi),thesleeveminimumwallplugginglimitisdefinedtobe23X.Anallowance foreddycurrentuncertainty andcontinued degradation areincludedinthisvalue.Theminimumrequiredwallthickness isdetermined'y examining plantconditions atnormal,upset,faulted,andtestconditions.
ForModel51steamgenerators, thenormaloperating condition resultsinthelimitingminimumwallthickness requirement.
CONCLUSION Basedonthepreceding analysisitisconcluded thatoperation ofCNPUnit1following theinstallation ofAlloy690LWSsatthetubesupportelevations andwithintheTSregionofthesteamgenerators, inaccordance withtheproposedamendment doesnotresultinthecreationofanunreviewed safetyquestion, anincreaseintheprobability ofanaccidentpreviously evaluated, createthepossibility ofanewordifferent kindofaccidentfromanyaccidentpreviously evaluated, norreduceanymarginstoplantsafety.Therefore, thelicenseamendment doesnotinvolveasignificant hazardsconsideration asdefinedin10CFR50.92.