ML17059B241

NMP-1 Core Shroud Repair Mod Summary Rept.

ML17059B241
Person / Time
Site:	Nine Mile Point
Issue date:	08/13/1996
From:	GLEASON T E, RANGANATH S, SCHRAG M R GENERAL ELECTRIC CO.
To:
Shared Package
ML17059B240	List: ML17059B239 ML17059B241 ML17059B242 ML17059B243 ML17059B244 ML18040A180
References
GENE-B13-01739, GENE-B13-01739-31-R0, GENE-B13-1739, GENE-B13-1739-31-R, NUDOCS 9608210135
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ENCLOSMILEPOINT1CORESHROUDREPAIRMODIFICATION SARYREPORT96082iOi35 9608i4'DRADQCK,05000220,.

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GENuclearfnerqyGENEB13-P1739-31 Revision0August1996NineMilePoint1CoreShroudRepairModification SummaryReportPreparedfor.NiagaraMohawkPowerCorporation Preparedby:GENuclearEnergyReactorModification Services175CurtnerAvenue,N/C571SanJose,California 95125

GENuclearE'nergyGENEB13-01739-31 Revision0August1996NineMilePoint1CoreShroudRepairModification SummaryReportPreparedby:&-/Z-K,TE.Gleason,Principal EngineerReactorModification ServicesReviewedby:Approvedby:N.R.Schrag,IncipalEngineerReactorModification Services<l~jg,S.Ranganath, Engineering FellowGENuclearEnergy

GENEB13-01739-31 Revision0August1996REVISIONSTATUSSHEETRevisionApprovalS.Ranganath DateInitialIssueDescription

GENEB13-P1739-31 Revision0August1998IMPORTANT NOTICEREGARDING CONTENTSOFTHISREPORTPleaseReadCarefully ThisreportwaspreparedbyGeneralElectricsolelyfortheuseoftheNiagaraMohawkPowerCorporation.

Theinformation contained inthisreportisbelievedbyGeneralElectrictobeanaccurateandtruerepresentation ofthefactsknown,obtainedorprovidedtoGeneralElectricatthetimethisreportwasprepared.

Theonlyundertakings oftheGeneralElectricCompanyrespecting information inthisdocumentarecontained inthecontractgoverning thiswork,andnothingcontained inthisdocumentshallbeconstrued aschangingsaidcontract.

Theuseofthisinformation exceptasdefinedbysaidcontract, orforanypurposeotherthanthatforwhichitisintended, isnotauthorized; andwithrespecttoanysuchunauthorized use,neitherGeneralElectricCompanynoranyofthecontributors tothisdocumentmakesanyrepresentation orwarranty(expressorimplied)astothecompleteness, accuracyofusefulness oftheinformation contained inthisdocumentorthatsuchuseofsuchinformation maynotinfringeprivately ownedrights;nordotheyassumeanyresponsibility forliability ofdamageofanykindwhichmayresultfromsuchuseofsuchinformation.

GENEB13-01739-31 Revision0August1996CONTENTSl.INTRODUCTION 2.SUMMARYANDCONCLUSIONS 3.TIERODREPLACEMENT MODIFICATION 4.H6ACONTACTEXTENSION 5.DISPLACEMENT SUMMARY6.DESIGNBASIS7.SAFETYCONSIDERATIONS 8.ATTACHMENTS

GENEB13-01739-31 Revision0August1998l.INTRODUCTION Acoreshroudrepairmodification wasinstalled inNineMilePoint1NuclearPowerPlanttoprovideanalternate loadpathfortheType304stainless steelcircumferential welds,HlthroughH7.Thecoreshroudrepairensuresthestructural integrity ofthecoreshroudbyreplacing thefunctionofweldsHlthroughH7with4stabilizer assemblies, andfourcoreplatewedges.Inthecourseofthepost-installation inspection oftheshroudrepair,threedeviations wereidentified, evaluated andwerefoundacceptable forcontinued plantoperation throughthenextcycle.Afteradditional reviewandevaluation, twoadditional modifications areproposedtoprovidethelongtermcorrective actions.1.1Modification 1:270'ieRodReplacement Thelowerspringofonestabilizer assemblybearsontheblendradiusofthe270'ecirculation nozzle.Theproposedmodification istoreplacethetierodandspringassemblywithonehavingthespringontheoppositesideofthetierod.Thisproposedmodification relocates thespringtobearontheRPVasintended.

1.2ThelowerspringcontactwiththeshrouddoesnotextendbeyondweldH6Aatanyofthefourlocations.

Asaresult,ifweldH6Aisfullycracked,andifthedesigncondition ofasteamlineLOCAplusseismiceventweretooccur,theshroudwouldnotbelaterally constrained totheextentintendedbydesign.Theproposedmodification addsanextension piecetoextendthespringcontactbeyondweldH6Aandrestorethisfeaturetoitsintendedfunction.

Theextendedcontactandthecoreplatewedgesalsoprovidearedundant loadpathbetweenthecoreplateandthelowerspringaswasintendedintheoriginaldesign.Thismodification appliestothe90',166'nd350'tabilizer assemblies.

Thedeviation iscorrected forthereplacement assemblyat270'.2.SUMMARYANDCONCLUSIONS 2.1270'ieRodReplacement Theshroudrepairstabilizer assemblies aredesignedwiththelowerspringlocatedonthesideofthetierod.Theproposedmodification istoreplacethetierodandspringassemblywithonehavingthespringontheoppositeside.Themodification movesthespringsufficiently suchthatitwillbearontheRPVasintended.

Themodification utilizes

GENEB13-01739-31 Revision0August1998existinghardwarewhichwasbuiltasasparealongwiththeotherstabilizer assemblies.

Onlyminorreworkisrequiredtorelocatethelowerspringandthereworkhasnoaffectonthehardwarefunction.

Themodification doesnotrequireadditional penetrations throughtheshroudsupportconeoranyadditional EDMwork.Themodification usesthesamelowersupportandupperspringassemblies andthereisnochangetotheactualtierodlocation.

Additional analysishasbeendonetoaddressthedesignwherethelowerspringsarenolongerlocated90'part.Thenon-uniform lowerspringspacingaffectsthenetspringcharacteristic whenthehorizontal seismicloadisdirectedbetweentwosprings.Theanalysisshowtheloadsanddisplacements remainacceptable forallconditions.

2.2H6AContactExtension ThelowerspringcontactswiththeshrouddonotextendabovetheH6Aweldaswasintended.

ThedesignfunctioncanberestoredbyaddingaUshapedextension piecetoextendbeyondweldH6A.Theextension piecefitsovertheexistinglowercontactandiscapturedonthelowerextension inalldirections.

Theextension isdesignedtoprovideapositivespringclampingforceagainstthesidesofthelowercontact.Thespringforceisnotrequiredtocapturethepartbutissufficient topreventanyfreemovementorvibrations.

Withthisarrangement, theaddedextension pieceiscapturedinalldirections andisheldsecurebythespringloadedclampingforce.2.3Conclusions Themodifications totheshroudrepairstabilizers atNineMilePoint1willrestorethemtotheirintendeddesignfunction.

Theplantlicensing baseshavebeenreviewed.

Thisreviewdemonstrates thatthesemodifications canbeinstalled (1)withoutanincreaseintheprobability orconsequences ofanaccidentormalfunction previously evaluated, (2)withoutcreatingthepossibility ofanaccidentormalfunction ofanewordifferent kindfromanypreviously evaluated, (3)andwithoutreducingthemarginofsafetyinthebasesofaTechnical Specification.

3.TIERODREPLACEMENT MODIFICATION

3.1Background

Thelowerwedgeonthe270'ierodwasfoundtobearagainsttheblendradiusonarecirculation nozzleratherthanonthe'vessel wall.Thissituation isdocumented perFDDREAl-0032andfurtherevaluated inGElKB13-01739-25.

Thatreportaddressed concernsaboutthecontactareaandthestability ofthecontactontheinclinedsurfaceofthenozzleblendradius.

GENEB13-01739-31 Revision0August1998Thelowerwedgecanberelocated toapositionwithmorecompleted contact(Figure3.1)onthevesselbymovingthelowerspringtotheoppositesideofthestabilizer assembly.

Byrelocating thelowerspring,theconcernsaboutcontactstability andcontactareaareresolvedandthestabilizer assemblymaintains itsintendedfunctional requirements.

IIIIIIIIIIII1i\'IiNozzleBoundary[2'ldLncaIion//I/Nc~LocnlionII.2ln.FIGURE3.13.2.Description NiagaraMohawkPowerCorporation purchased asparetierodassemblyandthisassemblyisintendedtobemodifiedtothealternate configuration.

Applicable designandassemblydrawingsarerevisedtoincludethenewpartsandgroupswhichdefinethealternate configuration.

Alladditional partsandassemblies aredesignedandfabricated tothesamedesignbasisastheoriginalshroudrepairhardware.

Movingthelowerspringtotheoppositesideofthestabilizer assemblyisaccomplished bythestepslistedbelow.a.Removethelowerspringfromtheexistingspareassemblyandthelowercontactfromtheexistinglowerspring.Thestakedlockingpinswillhavetoberemovedtoaccomplish this.Newlockingpinswillhavetobeinstalled inslightlydifferent locations, butthiswillnotaffectthefunctionofthepart.

GENEB13-01739-31 Revision0August1998b.Modifythelowerspringbyaddingcounterbores totheoppositesideoftheboltholes.Havingcounterbores onbothsidesdoesnotaffectthefunctionofthepart.c.ModifytheC-springbyextending the1.125diameterholethroughthepart.d.Fabricate anewlowercontactwiththeshroudsidedsurfacetaperedtofitontheoppositesideofthestabilizer assembly.

ThenewlowercontactisalsodesignedtoextendbeyondtheH6Aweldtoavoidinstallation ofthecontactextension piece.e.Re-assemble thetierodassembly.

f.Sincethelowerwedgeisatanewposition, newannulusmeasurements arerequiredandthenewlowerwedgemachinedtofitperthemodification drawing.g.Allchangeswillberecordedonamodification drawingrevision.

Nochangesarerequiredfortheuppersupport,theupperspringandthemidsupport.3.3.FunctionThelowerspringisdesignedtorestrictthecoreplatedisplacement duringaseismicevent.Thestabilizer assemblyisdesignedforasinglelowerspringtocarrytheentirehorizontal seismicloadatthecoresupport.However,thedirection oftheloadmaybesuchthatmorethanonespringsharestheload.Thelimitingspringdeflection andspringloadsoccurwhenonlyoneofthelowerspringsreactstotheentirehorizontal load.Relocating thespringhasnoaffectonthemaximumspringloadormaximumspringdeflection.

Relocating thelowerspringdoeschangethespacingbetweenadjacentspringsandthespacingdoesaffectthenetreactionwhentwospringssharethelateralload.ThelowerspringcontactwiththeRPVischangedbyabout4'ymovingittotheoppositesideoftheuerod.The4'hangefromtheas-installed locationresultsinamaximum108'pacing betweenadjacentlowersprings.Theminimumspacingbetweenadjacentlowerspringsis76'.Whenthefourlowerspringsare90'part,theequivalent springconstantisthesameforalldirections oftheappliedload.Theequivalent springconstantisthetotalloadappliedbythelowerspringsdividedbythedisplacement inthedirection oftheappliedload.Becauseofthenon-uniform springspacing,thevariation inequivalent springconstantis 1

GENEB13-D1739-31 RevisionDAugust1998from+24%to-31%.Anincreaseintheequivalent springconstanttendstoincreasethetotalreactionloadanddecreasethetotaldisplacement.

Althoughthetotalreactionloadincreases, theloadissharedbytwospringsandtheloadoneitherspringisboundedbythecasewhereonespringcarriestheentireload.Adecreaseinequivalent springconstantresultsinalargerdisplacement inthedirection oftheload.Additional analysisinAttachments 8.1and8.2showallloadsanddisplacements remainacceptable forthismodification.

4.H6ACONTACTEXTENSION 4.1.Background ThelowercontactsdonotextendabovetheH6Aweldaswasintendedtosatisfytheintendeddesignrequirements.

TheReactorModification Drawing,107E5679Revision6,showstheas-installed positionofthelowercontactsandtheH6Aweld.Thesituation resultedfrominsufficient margininthelowercontactdesigntoaccountfortheuncertainties intheas-builtgeometryoftheshroudsupportcone.Thisabovedeviation fromtheintendeddesigncondition isdescribed andevaluated inFDDREAl-0031.

Theevaluation showedthecoreplateboltsaresufficient tomaintainthecoreplatealignment withoutthelowercontactextending aboveweldH6A.Theevaluation considered theboltclampingloadandtheelasticproperties oftheboltstoshowallowable coreplatedisplacement wasnotexceeded.'dding theextension pieceprovidesadditional designmarginandassurance thatthecoreplatealignment ismaintained.

4.2Description Thelowercontactsatazimuths90',166'nd350'remodifiedtoextendbeyondtheH6AweldbyaddingaUshapedextension pieceshowninFigure4.1.Theextension piecefitsovertheexistinglowercontactwiththelegsoftheUextending aroundthesidesoftheexistinglowercontact.Thestepsattheendsofthelegsfitunderthelowercontacttopreventaxialmovement.

Atangatthetopextension fitsinthegapbetweenthelowercontactandthelowerspringtorestrictthehorizontal movement.

Theaddedextension pieceiscapturedinalldirections ontheexistinglowercontact.Thelegsoftheextension provideapositivespringclampingforce(40lbto50lb)againstthesidesofthelowercontact.Thisforceissufficient topreventanyfreemovementorvibrations.

Withthisarrangement, theaddedextension pieceiscapturedinalldirections andisheldsecurebythespringloadedclampingforce.

GENEB13-01739-31 Revision0August1996TANGLLAi4IPLEGSTEPSFIGURE4.1Theaddedextension piecesareinstalled withaspecialtoolforhandlingandtokeepthelegssprungapart.Whenseatedinplace,thetoolreleasesthelegsallowingthemtoclamparoundthelowercontact.Thismethodallowsthepiecetobeinstalled withoutslidingorhavingtoapplyexcessive force.Thesametoolcanbeusedtoremovetheextension pieceifrequired.

4.3FunctionThelowerspringsaredesignedtolimitthecoreplatedisplacement duringaseismicevent.ThelowerspringbearsagainsttheshroudatthecoresupportledgeandextendsabovetheH6AweldandbelowtheH6Bweld.WhentheH6Aweldremainsincontact,whetheritsfailedorothe+vise, thejointismodeledasahingeintheseismicmodelandiscapableofcarryingashearload.DuringasteamlineLOCA,thedploadontheshroudheadissufficient toopena360'hrough wallcrackattheH6Alocation.

Inthisevent,thejointismodeledasarollerintheseismicmodelandisnotcapableofcarryingashearload.Intheeventoffullseparation atweldH6Athecontactextension limitsthepossibleshroudmovementand,togetherwiththecoreplatewedges,providearedundant loadpathforthehorizontal seismicloads.(Thecoresupportstructure isalsoheldinposition

GENEB13-01739-31 Revision0August1996bythecoresupportboltsandbythecoresupportalignerpins.)Withouttakingcreditforthecoresupportboltsoralignerpins,thelimitinglateraldesignloadontheextension istheentire63,800Ibmaximumhorizontal seismicload.Theanalysisinattachments 8.1and8.2showallloadsanddisplacements remainacceptable withtheextension piecesinstalled.

5.DISPLACEMENT SUMMARYAlthoughallcoresupportdisplacements remainacceptable, bothmodifications described in3and4abovedoaffectthedisplacements andchangethevaluesreportedintheoriginalstressreport,GE-NE-B13-01739-04, Rev.0.Thedisplacement valuesreportedbelowsupersede thedisplacement valuesreportedintheoriginalstressreport.Theallowable permanent andtransient displacements aresummarized below.Theshroudrepairhardwaredesignspecification, 25A5583,providesthebasisfortheallowable displacements andsafetyfactors.TopGuidePermanent

=2.1/SFTopGuideTransient

=notspecified CoreSupportPermanent

=0.75/SFCoreSupportTransient

=1.68/SFNormal/UpsetSF=2.25Emergency SF=1.50FaultedSF=1.1255.1TopGuideTheTopGuidealwaysremainsincontactwiththeupperspringandthereisnopermanent displacement.

Thelimitingcondition foreacheventisthe"allhinge"condition whichhasanequivalent displacement totheHlrollercase.Sincethereisonlyoneseismicevent,thedisplacement isthesamefortheUpset,Emergency andFaultedevents.Thecalculated maximumtransient designdisplacement is0.904inchesforeachevent.Althoughthe0.904inchisatransient displacement, italsosatisfies themostrestrictive allowable permanent displacement requirement foranUpseteventof0.93inches.5.2CoreSupportAfaultedeventwithseparation atweldH6Aistheonlycondition wheretheremaybepermanent displacement atthecoresupport.Forallothereventsthedisplacement resultsfromthespringcompression whichreturnstotheoriginalpositionwhentheloadstops.The"allhinge"case(equivalent tothe"Hlroller"case)isapplicable forUpsetandEmergency andFaultedevents.

GENEB13-D1739-31 RevisionDAugust19965.2.1Permanent Displacement Themaximumpermanent displacement isthedistancetheshroudmovesbeforecontactwithaspringmember.Themachineddistancebetweenthespringloadedshroudcontactsurfaceandtheuppercontactis0.15inches.ThelowercontactalsobearsagainstweldcrownatH68.Theweldcrownisestimated tobelessthan0.13high.Ifthedisplacement isdirectedmidwaybetweenthetwocontactslocated108'part, thedisplacement isincreased to0.48inches.(Attachment 8.2)Theallowable permanent displacement is0.67inches.5.2.2Transient Displacement Theboundingtransient displacement isacombination ofthemaximumpermanent displacement andthemaximumspringcompression.

ForUpset,andEmergency conditions, thereisnopermanent displacement andthemaximumtransient displacement is0.256inches(Attachment 8.1,Table1).Theallowable Upsettransient displacement is0.75inches.Assumingtheworstcasescenarioforloaddirection andspringcharacteristics foraFaultedevent,themaximumspringcompression is0.368inches(Attachment 8.1,Table1).Themaximumtransient displacement becomes0.85incheswhenroundedtotwoplaces.Theallowable Faultedtransient displacement is1.49inches.6.DESIGNBASISThehardwareforbothmodifications isdesignedandfabricated tothesamedesignbasisastheoriginalshroudrepairhardware.

Themodifiedstabilizer assemblyincludesthesamedesignfeaturesastheoriginalhardware.

Allpartsarelockedinplaceorcapturedbymechanical devices.Thefabrication requirements forthetwoproposedmodifications willbeinaccordance withthepreviously approvedfabrication requirements fortheNMP-Icoreshroudstabilizers.

Thereisnoweldingrequiredduringfabrication orinstallation.

Relocating thelowerspringtotheoppositesideofthestabilizer assemblyisconsistent withthecoreshroudrepairdesigncriteriaanddesignbasis.Theadditional counterbores andlockingpinholesneededtoutilizetheexistingpartshavenoaffectonthestabilizer assemblyfunctionorstresses.

Thehandlingandinstallation toolsarethesameasusedfortheoriginalinstallation.

GENEB13-D1739-31 Revision0August19967.SAFETFCONSIDERATIONS Thisevaluation hasinvestigated modifications totheshroudrepairstabilizers atNineMilePoint1whichwillrestorethemtotheirintendeddesignfunction.

Theplantlicensing baseshavebeenreviewed.

Thisreviewdemonstrates thatthesemodifications canbeinstalled (1)withoutanincreaseintheprobability orconsequences ofanaccidentormalfunction previously evaluated, (2)withoutcreatingthepossibility ofanaccidentormalfunction ofanewordifferent kindfromanypreviously evaluated, (3)andwithoutreducingthemarginofsafetyinthebasesofaTechnical Specification.

TheGECoreShroudRepairDesignSafetyEvaluation, GE-NE-B13-01739-05, Rev.1hasbeenreviewedforpossibleadverseconsequences ofmovingthelowerspringtotheoppositesideofthestabilizer assembly.

Thecoreplatedisplacements reportedinB.2.1areupdatedtoincludetheaffectsofthelowerspringspacing.The0.75inchtemporary displacement duringafaultedeventremainswellthe1.49inchallowable forthisevent.GESafetyEvaluation, GE-NE-B13-01739-5.1, Rev.0,entitled, "Modification toGEShroudRepairDesign",wascompleted toevaluatethetwoproposedmodifications inaccordance with10CFR50.59.

Thesafetyevaluation concluded thattheproposedmodifications donotinvolveanyunreviewed safetyquestions.

8.ATI'ACHMENTS 8.1GENEB13-01739-03, Supplement 1,NineMilePoint1SeismicAnalysis, CoreShroudRepairModification 8.2GENEB13-01739-04, Supplement 4,NineMilePoint1ShroudRepairHardwareStressAnalysis8.3Drawing107E5679Rev.7andPartsList107E5679Rev.5,ReactorModification 8.4Specification 25A5585Rev.4,Stabilizer Installation