RIS 2000-22, Issues Stemming from NRC Staff Review of Recent Difficulties Experienced in Maintaining Steam Generator Tube Integrity

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Issues Stemming from NRC Staff Review of Recent Difficulties Experienced in Maintaining Steam Generator Tube Integrity
ML003758988
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Issue date: 11/03/2000
From: Matthews D
Division of Regulatory Improvement Programs
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RIS-00-022
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UNITEDSTATESNUCLEARREGULATORYCOMMISSIONOFFICEOFNUCLEARREACTORREGULATIONWASHINGTOND.C.20555-0001November3,2000NRCREGULATORYISSUESUMMARY2000-22ISSUESSTEMMINGFROMNRCSTAFFREVIEWOFRECENTDIFFICULTIESEXPERIENCEDINMAINTAININGSTEAMGENERATORTUBEINTEGRITY

ADDRESSEES

Allholdersofoperatinglicensesforpressurized-waterreactors(PWRs),exceptthosewhohavepermanentlyceasedoperationsandhavecertifiedthatfuelhasbeenpermanentlyremoved fromthereactorvessel.

INTENT

TheU.S.NuclearRegulatoryCommission(NRC)isissuingthisregulatoryissuesummarytoinformpressurized-waterreactorlicenseesofissuesstemmingfromthestaff'sreviewof

(1)thecircumstancesofthesteamgenerator(SG)tubefailureatIndianPointUnit2(IP-2),

(2)theinabilitytomaintainSGtubeintegrityatArkansasNuclearOneUnit2(ANO-2)and

(3)theanalysesdonetodemonstratethatSGtubeintegrityatthesefacilitieswouldbe maintainedduringsubsequentoperation.ThisRISdoesnottransmitanynewrequirementsor staffpositions.Nospecificactionorwrittenresponseisrequired.

BACKGROUND

INFORMATIONIndianPointUnit2IP-2experiencedasteamgeneratortubefailureeventonFebruary15,2000.Theeventinvolvedthefailureofarow2tubeduetoprimarywaterstresscorrosioncracking(PWSCC)at theapexofthesmallradiusU-bend.Allrow1tubeshadbeenpluggedpriortoinitialplant operation.Thedominantcontributortothecrackwashourglassdeformationofuppersupport plateflowslotsproducingabnormalstressesattheapexoftheU-bend.Thehourglass deformationoftheuppersupportplateflowslotswasassociatedwithin-planedeformationof thesupportplatecausedbydentingatthetube-to-supportplateintersections.Thelast inspectionofthesmallradiusU-bendsbeforethefailureeventwasin1997.Areexaminationof the1997inspectiondatarevealedflawindicationsinfoursmallradiusU-bends,includingthe onewhichfailedonFebruary15,2000.Theflawshadbeenmissedbecauseappropriate correctiveactionhadnotbeentakentoaddressthepoorqualityofthedata.ByletterdatedAugust31,2000(AccessionNo.ML003746339),theNRCstafftransmittedtotheIP-2licenseetheresultsofaspecialNRCteaminspectionaddressingthecausesoftheML003758988 RIS2000-22Page2of10tubefailureeventatIP-2andthelicensee'sperformanceduringthe1997SGinspection(NRCSpecialInspectionReport,IndianPointUnit2SteamGeneratorTubeFailure,ReportNo.

05000247/2000-010).Thestafffoundthatoverallthelicensee's1997SGinspectionwas deficient.Despiteopportunities,thelicenseedidnotrecognizeandtakecorrectiveactionfor significantconditionsadversetoqualityintheSGinspectionprogram.Thelicenseedidnot adequatelyaccountforconditionsthatadverselyaffectedthedetectibilityof,orincreased susceptibilityto,tubeflaws.Asaresult,tubeswithPWSCCflawsinthesmallradiusU-bends wereleftinserviceafterthe1997inspection,andoneofthosetubessubsequentlyfailedon February15,2000.OnOctober11,2000,theNRCstaffissuedatechnicalevaluationreport(TER)(AccessionNo.ML003759418)documentingtheNRCstaff'sreviewoftheFebruary15,2000,tubefailure,its rootcauses,theinspectionsandotheractionstakenbythelicenseetopreventrecurrence,and thelicensee'soperationalassessmentjustifyingcontinuedoperation.Inaccordancewiththe IP-2technicalspecifications,plantrestartfollowingthepost-eventoutagewassubjecttoNRC

approvalbecausetheSGtubeinspectionsperformedduringtheoutageproducedcategoryC-3 resultsintwooffoursteamgenerators(i.e.,greaterthan1%ofthetubesinspectedhad pluggableindications).NRChadnotyetdecidedonwhethertoallowIP-2restartwhenthe licenseedecidedtoinstallreplacementsteamgeneratorsratherthanrestartwiththeexisting steamgenerators.Nevertheless,theTERcontainsanumberofstaffconclusionsabout specifictechnicalaspectsofthelicensee'scorrectiveactionsanditsoperationalassessmentto supportcontinuedoperationwiththeoriginalsteamgenerators.ArkansasNuclearOneUnit2Atubeexhibitingoutsidediameterstresscorrosioncracking(ODSCC)nearaneggcratesupportplatefailedtosatisfytheapplicableburstpressureperformancecriterion(i.e.,thethree timesnormaloperatingpressure(3deltaP)criterion)inaninsitupressuretestduringa refuelingoutageinspectioninJanuary1999.Thelicenseeperformedanoperational assessmentandconcludedtheunitcouldbeoperateduntilmidcycleandstillmaintain adequatetubeintegrity.InsitupressuretestingduringthemidcycleinspectioninNovember

1999wasterminatedwhentheleakageforatubewithanaxialODSCCindicationexceededthe makeupcapacityofthetestsystematapressurebelowthe3deltaPcriterion.Atfirstthe licenseeassumedthepeakpressurereachedduringthetesttobetheburstpressure.The licenseefurtherexaminedthecircumstancesofthetestandconcludedthatthetestwas terminatedwhenligamentsofmaterialinthecracktoreandthatthelikelyburstpressure exceededthe3deltaPcriterion.Usingthisfindingasabenchmark,thelicenseesubmittedits operationalassessmenttotheNRCstaff,forinformation,astechnicaljustificationthattheplant couldbeoperateduntilthescheduledrefuelingoutageinSeptember2000andstillmaintain tubestructuralandleakageintegrityinaccordancewithapplicableperformancecriteria.The staffdisagreedwiththisjustificationandconcludedthatthelicenseehadnotdemonstratedthat theapplicableperformancecriteriawouldcontinuetobemetuntiltheSeptember2000refueling outage(NRClettersdatedMay2andJune23,2000(AccessionNos.ML003710343and ML003726321,respectively)).Accordingly,thelicenseesubmittedarequesttochangetheplant'slicensingbasistoallowoperationofANO-2untiltheSeptember2000refuelingoutageonthebasisofarisk-informed demonstrationthatsteamgeneratortubeintegritywouldmeettheacceptancecriteriainNRC

RIS2000-22Page3of10RegulatoryGuide1.174,"AnApproachforUsingProbabilisticRiskAssessmentinRisk-InformedDecisionsonPlant-SpecificChangestotheLicensingBasis."Inaletterdated July21,2000(AccessionNo.ML003734450),thestafftoldthelicenseethattherequested licenseamendmentcouldnotbeapproved.Theletterenclosedasafetyevaluation documentingthebasisforthisfinding.ANO-2beganshuttingdownforamidcycleinspection onthesameday,i.e.,July21,2000.SUMMARYOFISSUESTheNRCspecialinspectionreportandtechnicalevaluationreportforIP-2,andthesafetyevaluationforANO-2(includingNRClettersdatedMay2andJune23,2000,referencedinthe safetyevaluation)identifyanumberoftechnicalissuesinvolvingdegradationmanagement, tubeinspections,insitupressuretesting,andoperationalassessment.Thestaffbelievesthis informationwillbeusefultotherestoftheindustryinmanagingSGtubeintegrity,andmaybe ofinteresttootherstakeholdersaswell.ByletterdatedOctober6,2000,theNuclearEnergy InstituteprovidedtheNRCwithanindustryevaluationofrecentoperatingexperienceonmany ofthesametopicsdiscussedbelow.Issue1:Considerationofrelevantoperatingexperienceandappropriatediagnostic,corrective,orcompensatorymeasurestoensuretubeintegrity.Issue2:Assessmentoftherootcausesofalldegradationmechanismsataplantandappropriatediagnostic,corrective,orcompensatorymeasurestoensuretubeintegrity.Issues1and2derivefromtwoperformanceissuesidentifiedintheIP-21997inspections(and documentedintheNRCspecialinspectionreportdatedAugust31,2000).ThefailuremechanismthatledtotheFebruary15,2000SGtubefailureatIP-2wasessentiallythesamemechanismthatcausedatuberuptureatSurry2in1976.Thisfailuremechanism wasPWSCCasaresultofabnormallyhighstressattheapexoftheaffectedsmallradiusU-

bend.Theabnormalstresswasassociatedwithanovalizedconditionattheapexcausedby theinwarddisplacementofthelegsoftheU-bendasaresultofhourglassdeformationofthe uppermosttubesupportplateflowslotswhichwasinducedbydentinginthetube-to-tube supportplates.TheamountofhourglassdeformationadjacenttothefailedtubeatIP-2was measuredas0.47inches,afterthefailure.Duringthe1997inspection,aPWSCCindicationwasdetectedforthefirsttimeintheapexofasmallradiusU-bend.Oneperformanceissuecitedinthespecialinspectionreportisthatthe licenseeanditscontractordidnotidentifyorevaluatethepotentialtubeintegrityimplicationsof thistypeofindication.Anotherperformanceissuecitedinthereportisthatthelicenseedidnot haveaprocedure,amethod,orcriteriafordeterminingifsignificanthourglassdeformationof theuppermostsupportplatehadoccurred,eventhoughthetechnicalspecificationsrequired thereportingofsignificanthourglassdeformationoftheuppermostsupportplates.The licenseedidnotassesshourglassdeformationasapotentialcausalfactorfortheapex indicationfoundduringtheinspection,despiteevidenceofactivedentingintheuppermost supportplates.

RIS2000-22Page4of10Issue3:Dataquality

.Dataqualitydependsonthedegreetowhichtheeddycurrentsignalfromaflawcanbemaskedordistortedbysignalsfromsourcesotherthantheflaw.Dataqualitydirectlyaffects theabilitytodetectandsizeflaws.Thesignalsfromsourcesotherthantheflawareoften called"noise".Theamplitudeofthenoisesignalandsignal-to-noiseratioareimportant measuresofdataquality.Issue3derivesfromaperformanceissueidentifiedduringtheIP-21997inspection(anddocumentedintheNRCspecialinspectionreportdatedAugust31,2000).Ahindsightanalysis, completedafterthetubefailureonFebruary15,2000,ofeddycurrentdatacollectedduringthe

1997SGinspectionwithamidrangeplus-pointcoilrevealedfourindicationsweremissed duringthe1997dataanalysis.Oneofthemissedindicationswasinthetubethatfailedon February15,2000.TheNRCspecialinspectionreportfoundthatthe1997eddycurrentdatawasnoisymakingdetectiondifficult.However,in1997,thelicenseedidnotidentifythepotentialmaskingeffectof noiseasasignificantconditionadversetoquality.Thelicenseedidnotincreasethelevelof reviewormorecarefullyexamineexistingdata.Thespecialinspectionreportnotedthatthese omissionswereimportantsinceconditionsindicatinganincreasedsusceptibilitytoPWSCC

wereidentifiedduringthe1997inspection(seeissues1and2).Inaddition,thelicenseedidnot takestepstominimizetheeffectsofnoiseondataquality(e.g.,useofhighfrequencyplus- pointcoilinsteadofmidrangeplus-pointcoil)orestablishdataqualityacceptancecriteria.Theindustryhasdevelopeddraftguidelinesfordataquality.Whenfinalized,theseguidelineswillbeincorporatedintoRevision6oftheElectricPowerResearchInstitute(EPRI)Steam GeneratorExaminationGuidelines.Issue4:Non-destructiveexamination(NDE)qualificationprogramsthatincludetubesampleswithflawsthattrulyrepresentflawsinthefield.Issue4derivesfromtheNRCstaff'sreviewofactionstakenbytheIP-2licenseetojustify restartwiththeexistingsteamgeneratorsfollowingtheFebruary15,2000tubefailureevent,as documentedintheTERdatedOctober11,2000.TheEPRISteamGeneratorExaminationGuidelinesRevision5statethatflawsinqualificationdatasetsshouldproducesignalssimilartothoseobservedinthefieldintermsofsignal characteristics,signalamplitude,andsignal-to-noiselevel.Inpractice,however,thetechnique qualificationsforvariousstresscorrosioncrackingapplicationscontinuetorelyondatasets consistingofspecimensnotchedbyelectro-dischargemachining(EDM).Forexample, techniquequalificationdatasetsforPWSCCandODSCCinsmallradiusU-bendsconsist largelyofEDMnotchedspecimens.EDMnotchedspecimensproducemuchlargeramplitude signalsandhavebettersignal-to-noiselevelsthancomparablysizedcracks.NDEdetection andsizingperformanceforactualcrackswillnotbeasgoodasthatobservedforEDMnotches.

TechniquequalificationsbasedonEDMnotchedspecimensdonotprovideanadequatebasis forevaluatingthetechniquecapabilityparameters(probabilityofdetection(POD),sizing accuracy).

RIS2000-22Page5of10Chemicalmethodstoinducestresscorrosioncrackscanpotentiallyproducecrackswhichexhibithigheramplitudesignalresponsesthancomparablysizedcracksinthefield.Datafrom pulledtubespecimenscanbeusefulfordemonstratingthatthefabricatedflawsand comparablysizedcracksinthefieldproducesignalsofsimilaramplitude.Issue5:Site-specificqualificationsofgenericallyqualifiedtechniquesensuringanapplicationisconsistentwithsite-specificconditionsandthatappropriateNDEperformancecapabilitiesareconsideredinoperationalassessments(e.g.,PODofflawsandflawsizemeasurementerror).Issue5derivesfromtheNRCstaff'sreviewofactionstakenbytheIP-2licenseetojustify restartwiththeexistingsteamgeneratorsfollowingtheFebruary15,2000failureevent,as documentedintheTERdatedOctober11,2000.TheEPRISteamGeneratorExaminationGuidelinesstatethatsite-specificqualificationofNDEtechniquesisnecessarytoensurethatthetechniqueperformancecapabilities(PODandsizing accuracy)obtainedfromthegenerictechniquequalificationareapplicabletosite-specific conditions.Thisisaccomplishedbyadocumentedreviewofaqualifiedtechnique'stubing essentialvariables(e.g.,denting,deposits,tubegeometrychanges,andsignalcharacteristics)

toensuretheapplicationisconsistentwithsite-specificsteamgeneratorconditions.The guidelinesstatethatthereviewshallestablishthattubingessentialvariablesoftheflawed tubesinthegenericqualificationdatasetaresimilarintermsofvoltageandsignal-to-noise ratiotothoseexpectedfromactualsteamgeneratorsignals.TheIP-2licenseewasunabletodemonstratetothestaff'ssatisfactionthattheNDEtechniqueperformancecapabilitiesassumedforthesmallradiusU-bendsduringthepost-failureevent inspectionsperformedin2000wereapplicableforIP-2conditions.Theassumedtechnique performancecapabilitieswereimportantinputparametersinthelicensee'soperational assessmentintendedtosupportplantrestart.Difficultieswereencounteredinthereview becausethesite-specificqualificationprocessdescribedintheEPRIguidelineswasnot performedrigorously.AfterthetubefailureatIP-2onFebruary15,2000,thelicenseeusedahighfrequencyplus-pointprobefordetectingPWSCCinthesmallradiusU-bendsandamidrangeplus-pointprobe forsizingtheflaws.EachoftheseprobeswereAppendixHqualifiedinaccordancewiththe EPRIguidelinesfordetectionofsmallradiusU-bendcracks.However,thequalificationflaw datasetconsistedlargelyofEDMnotchesratherthanactualcracks.Therefore,aspreviously discussed,thetechniquecapabilityparametersderivedfromthisgenericqualificationwerenot representativeofIP-2.Underthesecircumstances,theEPRIguidelinesstatethatatechniquequalificationmeetingthestatisticalrequirementsofAppendixHshouldbeperformedonadatasethavingtubing essentialvariablessimilartothesite-specificconditions.Theguidelinesfurtherstatethatthis maywarrantpullingoneormoretubes.Analternativeapproachusinginsitutestresultsdid notapplytoIP-2sincetheIP-2tubingwasinanunacceptableconditionattheconclusionofthe previouscycle.

RIS2000-22Page6of10Insteadofdoingsuchatechniquequalification,theIP-2licenseeusedNDEperformancecapabilityparametervalues(POD,flawsizemeasurementerrors)initsoperationalassessment thatwerebasedonaperformancedemonstrationwiththemidrangepluspointprobeonadata setconsistingofactualPWSCCflawsinsimulateddentsateggcratesupportintersections.

However,thelicenseewasunabletodemonstratetothestaff'ssatisfactionthatthetubing essentialvariablesoftheperformancedemonstrationdatasetwererepresentativeofthe conditionoftheU-bendsatIP-2.Amajorconsiderationforthestaffwasthatthelicenseewas unabletodemonstratequantitativelytothestaff'ssatisfactionthatnoiselevelsinthe performancedemonstrationdatasetwerecomparabletonoiselevelsfortheIP-2smallradius U-bends.Issue6:Considerationofflawsizemeasurementerrorwhenapplyingthethresholdscreeningcriteriaforselectionofinsitupressuretestresults.Issue6derivesfromphoneconversationsinNovember1999betweentheNRCstaffandthe ANO-2licenseeconcerningthelicensee'splansforinsitupressuretestingduringthe November1999midcycleSGinspectionoutage.AtANO-2sixtubeswerefoundtoexceedthescreeningcriteriaforinsitupressuretesting.ThelicenseeinitiallydeterminedthatfourofthesixtubesdidnotneedtobetestedsincetheNDE

measuredsizeoftherespectiveflawswereboundedbythesizeofflawspressuretestedinsitu duringapreviousinspectionoutage.AfterdiscussionswiththeNRCstaff,thelicenseedecided totestthesetubes.Thestaffnotedthatthescreeningcriteria,inaccordancewiththeEPRI

guidelines,areintendedtoaccountforNDEtestflawsizemeasurementuncertainty.Testingononeofthefourtubeswasterminatedatapressurebelowthe3deltaPcriterionwhenleakagethroughtheflawexceededthecapacityofthesystem.Afterreviewingthe circumstancesofthetest,thestaffconcludedthatthetubewasabouttoburstwhenthetest wasterminated.Thisconclusionisdiscussedunderissue7andinmoredetailintheNRC

letterdatedMay2,2000(AccessionNo.ML003710343).Thisexperienceunderscoresthe importanceofallowingforflawsizemeasurementerrors(inaccordancewiththeEPRI

guidelines)whenselectingtubesforinsitupressuretesting.Issue7:Rigorousanalysesoftheresultsofinsitupressureteststhatareterminatedwhenleakageexceedsthecapacityofthetestsystem.Issue7derivesfromthestaff'sreviewofinsitupressuretestresultsforatubetestedduringthe November1997midcycleinspectionoutageatANO-2.Thestaff'sreviewwasdocumentedin theletterdatedMay2,2000.AtANO-2insitupressuretestingwasconductedforatubeidentifiedduringtheNovember1999inspectionashavinganaxialODSCCflaw.Thistestinvolvedapressurizationrateof about1000psi/minutewithperiodicholdpoints.Initiallowlevelleakagewasobservedatatest pressureofabout3800psi.Thisleakageincreasedtoabout1gpmatatestpressureof

4025psiandto3.7gpmat4147psi,whereupontheleakageexceededthecapacityofthetest RIS2000-22Page7of10systemandthepressuredroppedsuddenlyto600psi.Themaximumtestpressurereachedduringthetestwaslessthantheapplicablestructuralperformancecriterionof4369psi,which correspondstothreetimesnormaloperatingpressureadjustedtoroomtemperatureconditions.Thelicenseedidnotrepeatthetestwithabladdertodeterminewhethertheburstpressurewasactuallyhigherthanthemaximumpressurereachedduringthetest.Instead,onthebasisofan assessmentofthepre-andpost-testeddycurrentflawsizemeasurementsandinsitutest results,thelicenseeconcludedthatthetestwasterminatedwhenligamentsofmaterialinthe cracktoreandthattheactualburstpressureofthetubewasatleast500psihigherthanthe maximumpressurereachedduringthetest.Usingthisfindingasabenchmark,thelicensees didanoperationalassessmenttodemonstratethatANO-2couldbeoperatedwithoutadditional SGinspectionsuntilthenextscheduledrefuelingoutageinSeptember2000andcouldmaintain amarginagainsttuberuptureconsistentwiththeplant'slicensingbasis.Thestaffreviewedthelicensee'sassessmentandconcludedthatthelicenseedidnothaveanadequatebasisforconcludingthattheburstpressurewashigherthanthemaximumpressure reachedduringthetest.Thestaff,therefore,concludedthatthelicenseehadnotsatisfactorily demonstratedthattheapplicableperformancecriteriawouldbemaintaineduntilthescheduled September2000refuelingoutage.Thestaff'sevaluationwasdocumentedintheletterdated May2,2000.TheEPRIinsitupressuretestguidelinesprovideguidanceforassessingburstpressurewhenthetestisterminatedbecauseofexcessiveleakage.Thepreferredapproachistoretestwitha bladderinstalled.Wherethisisnotpossible,theguidelinessuggestthatmarginagainstburst maybeverifiedviavisualoreddycurrenttesting(ECT)examination,orbyextrapolationof leakagedataobtainedduringthetest.Thereislittlespecificguidanceonhowtousevisualor NDEresultsforthispurpose.Licenseesneedtobeawarethatusingtheleakageextrapolation methodssuggestedintheEPRIguidelinescanleadtononconservativeassessmentresults becauseleakratesforactualcrackscanvarybyordersofmagnitudefromtheratesindicated bypredictivemodels.Issue8:Laboratoryandinsitupressuretestproceduresutilizingpressurizationratesthatdonotinfluenceburstpressureresults.ThisissuederivesfromlaboratoryburstandleaktestsperformedtosupporttheANO-2 licensee'sassessmentoftheinsitupressuretestresultsdiscussedunderissue7.The laboratorytestresultsandtheirimplicationshavebeenthesubjectofpublicmeetingswith industryrepresentativesonJuly6andSeptember28,2000.Theaccessionnumberforthe July6,2000meetingsummaryisML003763234,andfortheSeptember28,2000meetingitis ML003760794.

RIS2000-22Page8of10TheANO-2licenseefabricatedanumberofEDMnotchesinlaboratorytubespecimensinanattempttosimulatetheactualflawgeometryinthetubewhichwasthesubjectofthein-situ pressuretestdiscussedunderissue7.Howcloselythesenotchesapproximatedtheactual crackisunderinvestigationbytheindustryandnotrelevanttothisdiscussion.Thelaboratory tubesampleswereleak-testedandburst-tested.Pressurizationratesrangedfromessentially quasi-staticto2000psi/second.Thetestsshowedthatburstpressurewasstronglyaffectedby thepressurizationratesusedduringthetests.Thiswasanunexpectedfindinginviewofprior evidencefromlaboratoriesaroundtheworld.Theindustryisinvestigatingthecausesofthisapparentpressurizationrateeffectandanygenericimplicationsforpressuretestproceduresandexistingburstpressuredatabases.

IndustryrepresentativesdiscussedthestatusofthiseffortwiththeNRCstaffduringthe July6andSeptember28,2000,publicmeetings.Theysaidtheirpreliminaryfindingwasthat thepressurizationrateeffectmaybelimitedtoplanar,part-through-wallaxialflawswith maximumdepthsgreaterthan90%through-wall.Theyalsosaidthatchangestoindustry pressuretestproceduresmaybeneededtoensurethatburstpressuredataisnotinfluenced bypressurizationrate.Theysaidthatinterimindustryguidanceforinsitupressuretestingwill beissuedtotheindustryinOctober2000.Thisguidanceisexpectedtorecommendlimiting pressurizationratestonomorethan200psi/second,withperiodicpressureholdpointsof2- minuteduration.Thepressureholdpointsincludemainsteamlinebreakpressureandthree timesnormaloperatingpressure.Issue9:Useofa"fractionalflaw"methodorothersimilarmethodsfordeterminingabeginning-of-cycleflawdistributionmayleadtononconservativeresultswhenusedinconjunctionwithaPODparameterthatvariesasafunctionofflawsizeorvoltage.Issue9derivesfromthestaff'sreview(documentedinthestaff'sTERdatedOctober11,2000)

ofthelicensee'soperationalassessmenttosupportIP-2restartaftertheSGtubefailureevent onFebruary15,2000.Thefractionalflawmethodisbasedontheassumptionthatforeachflawfoundbyinspection,thereareflawsofthesamesizewhichwerenotdetectedbytheinspection.Foreachdetected flawofagivensize,thenumberofundetectedflawsofthatsizeisassumedequalto1/POD-1.

Thismethodologyhasbeenapprovedbythestaffforimplementingvoltage-basedalternate repaircriteriainaccordancewithNRCGenericLetter95-05andforimplementinganalternate repaircriterionforPWSCCatdentedtubesupportplates.Fortheseapplications,licenseesare currentlyassumingaconstantPODof0.6.ThefractionalflawmethodwasrecentlyusedinanoperationalassessmentofsmallradiusU-bendPWSCCatIP-2.However,theoperationalassessmentusedaPODparameterthat variedwithcracksize.TheeffectofthevariablePODfunctioninconjunctionwiththefractional flawmethodmaketheresultsoftheanalysisinsensitivetothesizeoftheindicationsfoundby inspection.Thestaffconsideredthisfindingunrealistic.TheTERcontainsmoredetailsonthis issueatIP-2.

RIS2000-22Page9of10Issue10:Benchmarkingoperationalassessmentmethodologiesagainstactualoperatingexperiencetoensurerealisticresults.Issue10derivesfromthestaff'sreview(documentedinthestaff'ssafetyevaluationdated July21,2000)oftheANO-2licensee'soperationalassessmentinsupportofitsrisk-informed applicationtochangetheplantlicensingbasistopermitoperationuntilthe September2000inspection.MoreandbiggerflawswerefoundduringtheNovember1999midcycleinspectionthanwerepredictedinthepreviousoperationalassessment.Asdiscussedunderissue7,onetube apparentlyfailedtomeetthe3deltaPcriterion.ThismadethePODandgrowthrate assumptionsusedinthelicensee'sassessmentseemdubious,andthestaffquestionedthe useofthesameapproachintheoperationalassessmentsupportingoperationuntil September2000.ThelicenseerespondedthattheNovember1999bobbincoilinspectionwasmoresensitivethanthepreviousinspectionandthushadahigherPOD.Inbothinspectionsabobbincoil inspectionwasfollowedbyarotatingpancakecoil(RPC)inspectionatlocationswherethe bobbincoilidentifiedpossibleindications.Thelicenseestatedthatadifferentcalibration standardhadbeenusedduringtheNovember1999inspectionresultinginanimproved averageflawsignalvoltageamplitudeandthusamoresensitiveinspection.Thelicenseecited anumberoflesserfactorsalsocontributingtoamoresensitiveinspection.Thestaffreviewedindependentlytheeddycurrentdataandconcludedthatalthoughsignalamplitudehadinfactincreased,noiselevelshadalsoincreased,sothattherewasno improvementinthesignal-to-noiseratio.Basedonthisandthestaff'sreviewoftheother factorscitedbythelicensee,thestaffconcludedthattheinspectioninNovember1999wasno moresensitivethanearlierinspections.Insummary,thelicenseewasunabletoconvincinglybenchmarkitsoperationalassessmentmethodologyagainstactualoperatingexperience.ThiscreateddoubtaboutthePODand growthrateparametersassumedintheassessmentandthusaboutthetubeintegritymargins projectedtoexistatthescheduledSeptember2000refuelingoutage.Accordingly,thestaff wasunabletoapprovethelicensee'srisk-informedapplicationtochangetheplantlicensing basistopermitoperationtotheSeptember2000inspection.BACKFITDISCUSSIONThisRISdoesnotrequireanyactionorwrittenresponse.Therefore,thestaffdidnotperformabackfitanalysis.

RIS2000-22Page10of10FEDERALREGISTERNOTIFICATIONAnoticeofopportunityforpubliccommentonthisRISwasnotpublishedintheFederalRegisterbecauseitisinformational,andthepublicwasaffordednumerousopportunitiestocommentastheIP-2andANO-2matterswerebeingstudied.Furthermore,thisRISrequires noactionorwrittenresponseonthepartofanaddressee.PAPERWORKREDUCTIONACTSTATEMENTThisRISdoesnotrequestanyinformationcollection.

IfthereareanyquestionsconcerningthisRIS,pleasecallthecontactlistedbelow./RA/DavidB.Matthews,DirectorDivisionofRegulatoryImprovementPrograms OfficeofNuclearReactorRegulationTechnicalContact:EmmettL.Murphy,NRR(301)415-2710

E-mail:elm@nrc.govAttachment:ListofRecentlyIssuedNRCRegulatoryIssueSummaries RIS2000-22Page10of10FEDERALREGISTERNOTIFICATIONAnoticeofopportunityforpubliccommentonthisRISwasnotpublishedintheFederalRegisterbecauseitisinformational,andthepublicwasaffordednumerousopportunitiestocommentastheIP-2andANO-2matterswerebeingstudied.Furthermore,thisRISrequires noactionorwrittenresponseonthepartofanaddressee.PAPERWORKREDUCTIONACTSTATEMENTThisRISdoesnotrequestanyinformationcollection.

IfthereareanyquestionsconcerningthisRIS,pleasecallthecontactlistedbelow./RA/DavidB.Matthews,DirectorDivisionofRegulatoryImprovementPrograms OfficeofNuclearReactorRegulationTechnicalContact:EmmettL.Murphy,NRR(301)415-2710

E-mail:elm@nrc.govAttachment:ListofRecentlyIssuedNRCRegulatoryIssueSummariesDistribution:PUBLICRISFile*Seepreviousconcurrence AccessionNo.:ML003758988TemplateNo.:NRR-052Toreceiveacopyofthisdocument,indicateintheboxC=Copyw/oattachment/enclosureE=Copywithattachment/enclosureN=NocopyOFFICEREXBTechEdEMCBEMCBOGCC:EMCB:DENAMEEBennerPKleene*EMurphy*TSullivan*MYoung*WBateman*

DATE//0010/13/0010/13/0010/16/0010/20/0010/16/00D:DEC:REXB:DRIPD:DRIPJStrosnider*LMarsh*DMatthews

10/16/0010/31/0011/02/00OFFICIALRECORDCOPY

______________________________________________________________________________________OL=OperatingLicense CP=ConstructionPermitAttachmentRIS2000-22 Page1of1LISTOFRECENTLYISSUEDNRCREGULATORYISSUESUMMARIES

_____________________________________________________________________________________RegulatoryIssueDateofSummaryNo.SubjectIssuanceIssuedto

_____________________________________________________________________________________2000-21ChangestotheUnplannedScramandUnplannedScramWithLoss ofNormalHeatRemoval PerformanceIndicators10/31/00AllholdersofOLsfornuclearpowerreactors,exceptthosewho havepermanentlyceased operationsandhavecertifiedthat fuelhasbeenpermanently removedfromthereactorvessel2000-20AdvanceNoticeof

Intent

toPursueLicenseRenewalDate pendingAllholdersofOLsfornuclearpowerreactors,exceptthose licenseeswhohavepermanently ceasedoperationsandhave certifiedthatfuelhasbeen permanentlyremovedfromthe reactorvessel2000-19PartialReleaseofReactorSiteforUnrestrictedUseBeforeNRC

ApprovaloftheLicense TerminationPlan10/24/00AllholdersofOLsfornuclearpowerreactors,includingthose licenseeswhohavepermanently ceasedoperationsandhave certifiedthatfuelhasbeen permanentlyremovedfromthe reactorvessel2000-18GuidanceonManagingQualityAssuranceRecordsinElectronic Media10/23/00AllholdersofOLsfornuclearpowerplants,includinglicensees thathavepermanentlyceased operationsandhavecertifiedthat fuelhasbeenpermanently removedfromthereactorvessel.

Inaddition,thosematerials licensees,includingcertificate holdersandvendors,thatare requiredtohaveanNRC

approvedqualityassurance program.2000-17ManagingRegulatoryCommitmentsMadebyPower ReactorLicenseestotheNRC

Staff09/21/2000AllholdersofOLsfornuclearpowerreactors


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