ML17059A522

Structural Evaluation & Justification of Nine Mile Point 1 Core Shroud for Continued Operation.

ML17059A522
Person / Time
Site:	Nine Mile Point
Issue date:	11/04/1994
From:	BRANLUND B J, GORDON B M, RANGANATH S GENERAL ELECTRIC CO.
To:
Shared Package
ML17059A520	List: ML17059A519 ML17059A521 ML17059A522 ML18040A297
References
GENE-523-A161-1, GENE-523-A161-1094, NUDOCS 9411160239
Download: ML17059A522 (84)

Text

GENE-523-A161-1094 DRF137-0010-06 Structural Evaluation andJustification oftheNineMilePoint1CoreShroudforContinued Operation Performed By:BettyI.undSe'EngineerStructural Mechanics ProjectsBarryM.GordonPrincipal EngineerBWRTechnology ApprovedBy:SampathRanganPhDManager,Engineering andLicensing Consulting ServicesGENuclearEnergySanJose,CAT94ilih0239 94ii04PDRADQCK05000220PDR 0

GEiVudcarEnergyGENE-$23-Al6l-lopsIMPORTANT NOTICEREGARDI1VG CONTElVTSOF THISREPORTPleaseReadCarefully Theonlyundertakings oftheGeneralElectricCompany(GE)respecting information inthisdocumentarecontained inthecontractbetweenNiagaraMohawkPowerCompanyandGE,andnothingcontained inthisdocumentshall,beconstnled aschangingthecontract.

Theuseofthisinformation byanyoneotherthanNiagaraMohawkPowerCompanyorforanypurposeotherthanthatforwhichitisintendedundersuchcontractlsnotauthorized; andwithrespecttoanyunauthorized use,GEmakesnorepresentation orwarranty, andassumesnoliability astothecompleteness,

accuracy, orusefulness oftheinformation contained inthisdocument, orthatitsusemaynotinfringeprivately ownedrights.

GErVuclcarEnergyGEJYFS23-A361-1094TableofContentsl.1NTRODUCTION....,.....,......

~~\~oo~o~o~o~too~~~~~o~~112.DESCRIPTION OFINDICATIONS

.......,...~.....,...,....

2.1REFERENCES

.~tttteo~oottoootto212-23.COMPARISON BETWEENNMP-1ANDOYSTERCREEKCORESHROUDS.....................

3-13.1WATERCHEMISTRY 3.2SHROUDEVALUATION.

3.3SHROUDCOMPARISON CONCLUSION

.

3.4REFERENCES

.4.CRACKGROWTHESTIMATE....,.4.1SLIP-DISSOLUTION MODEL4.2CALCULATION OFPARAMETERS 4.3CRACKGROWTHPREDICTION

4.4CONCLUSION

..

4.5REFERENCE 5.FLAWEVALUATION

....,.........,..,...,.,

3-13-33-33o4~o~o~o~o~oo~ooeoo~o~o~o~o~e~o~~~~~~~~ooeee~o~o~o~~~eoe44-14-24-44-544~ooooooeeo ooooooooootoo 515.1LIMITLOADMETHOD..5.2EVALUATION OFPART-THROUGH WALLCRACKS.5.3SAFETYFACTORS..5.4APPLICATION OFFLAWEVALUATION METHODOLOGY TONMP-1SHROUD.5.4./LimitLoad.5.4.2LEFM.

5.5REFERENCES

5-15-35-45-55-55-55-66oCONCLUSIONSoeeoee ootooootooootoeo

~ooooooo~eeeto~ooooteo~o~o~e~oooooooee

~~o~~o~o~~~~eettott

GE(YndearEnergy<EWE-$23-Al6l-tOyg I.INTRODUCTION Thisreportpresentsthestructural evaluation andjustification forcontinued operation oftheNineMilePointUnit1(NMP-1)plantuntilFebruaryof1995.Recently, inspection oftheOysterCreekcoreshroudrevealedsignificant indications atthemid-beltline weld,H4.Duetosimilarities betweenOysterCreekandNMP-1,itisprudenttodetermine ifsimilarcrackingcouldbeexpectedinNMP-1.Itisalsoprudenttodetermine thatiftheOysterCreekcrackingwerepresentinNMP-1,thecrackingisstructurally acceptable foroperation untiltheplannedoutageinFebruaryof1995.Inspection oftheNMP-1coreshroudisplannedforthisnextoutage.Thestructural justification forcontinued operation ispresented inthisreportedasoutlinedinthefollowing analyses:

1.Discussion ofcomparison ofNMP-1andOysterCreekbasedonwaterchemistry, fluenceandon-lineyears.Thiscanbeusedasabasistoestablish thatanycrackingintheNMP-1coreshroudislikelytobeboundedbythatobservedintheOysterCreekcoreshroud.2.GEPLEDGEcrackgrowthratemodelingtoestimateaNMP-1specificcrackgrowthrate.Thiscalculation willshowthattheestimated crackgrowthrateintheNMP-1coreshroudislessthanSxl0'n/hr, whichhasbeentypically usedforcoreshroudcracking.

3.Flawevaluation usingtheOysterCreekindications andconsidering crackgrowthduringthecurrentoperating cycleuntilFebruaryof1995.Resultsofthecomparison betweenNMP-1andOysterCreekshowthatthecrackinginOysterCreekislikelytoboundthatwhichmaybeexpectedintheNMP-1shroud.Inaddition, theflawevaluation andcrackgrowthrateevaluation demonstrate thatthestructural integrity oftheNMP-1coreshroudweldH4isassuredassumingthatthesameindications intheOysterCreekH4weldarepresentintheNMP-1H4weld.1-1

GEivnckurEnergyGEE-$33-A16l-l096 2.DESCRIPTION OFINDICATIONS Theindications foundintheOysterCreekcoreshroudH4weldareusedinthisstructural evaluation.

TheresultsoftheOysterCreekH4inspection areshowninAppendixA.Thesefiguresillustrate theindication depthsatvariousazimuthal locations inthecoreshroud.Atsomelocations, indications werefoundinboththeIDandOD(Insomecasesonecrackwasabovetheweldandtheotherwasbelowtheweld).Forthiscase,theindications wereanalyzedasacombineddepthofthetwoflaws.Fortheareaswhichwerenotinspected, through-wall indications wereassumed.Figure2-1isaschematic showingtheligamentconfiguration basedontheOysterCreekresults.Figure2-1showstheligamentconfiguration afterapplication oftheproximity criteria; thisconfiguration isusedforcalculating thelimitloadcriteria.

Thefollowing conservative assumption wereusedtodetermine theassumedindications:

l.Eachindication wascharacterized bythemaximumdepthoftheindication overtheentirelengthoftheindication.

2.Acrackdepthuncertainty factorof0.3"wasaddedtothedepthofeachcrack.3.Anestimated crackgrowthuntilthenextinspection withacrackgrowthrateofSx10'n/hr wasaddedtoeachcrackdepth.4.Atlocations whereindications werefoundonboththeIDandOD,thedepthwasassumedtobethesumofthetwoindications.

5.Whenflawswerecombinedduetoproximity, themaximumdepthofthecombinedindications wasused.Inaddition, theestimated crackgrowthuntilthenextinspection wasaddedforthisevaluation.

Theshadedareascorrespond toassumedindications.

Theseresultsweredetermined usingtheproximity methodology presented inReference 2-1.2-1

gE>VudcurEnergyGENE-$23-A161-10942.1References 2-1BWRCoreShroudInspection andFlawEvaluation Guidelines, PreparedfortheBWRVesselandInternals ProjectAssessment Subcommittee, GENE-523-A113-0894,August1994.2-2

GESugarEnergyGEM-$23-8161-1094 AT10TFIGURE2-1SCHEMATIC OFOYSTERCREEKINDICATIONS 2-3

GE.VuclearFungyGEM-S23-li l6I-l0943.COMPARISON BET%'EENNMP-1ANDOYSTERCREEKCORESHROUDSAcomparison betweentheNMP-1andOysterCreekcoreshroudsispresented inthissection.Theintentistodemonstrate thatanycrackingintheNMP-1shroudH4weldislikelyboundedbythatobservedintheOysterCreekH4weld.Theevaluation considers waterchemistry, fluence,on-lineyears,andmaterialaspects.3.1WaterChemistry Forthefirstfourcycleofhotoperation, NMP-1operatedwithrelatively highprimarywaterconductivity.

AsseeninTable3-1andFigure3-1,thecyclicconductivity meanvaluesexceeded0.43p,S/cm.Therewasadramaticconductivity improvement duringthefifthfuelcyclewheretheconductivity decreased tolessthan0.3pS/cm.Sincethefourthcycle,conductivity valueshavesteadilyimprovedandwereexcellent atlessthan0.09pS/cmduringthelastthreeoperating cycles.Earlysteadystatechloridelevelsrangedbetween30and58ppb.Inadditiontohighearlylifesteadystateconductivity, therewereafewdocumented waterchemistry transients atNMP-1:l.September 3,1971-NMP-1conductivity reached30pS/cmatpowerduetohighconductivity waterinthe,condensate storagetank.2.November25,1974-NMP-1conductivity reached1.4pS/cmatpowerduetoavalvingerrorduringresintransfer.

ThepHdroppedto5.6and81ppbchloridewas-identified inthewater.3.March9,1977-683ppbchloridewasidentified inthewaterduringshutdown.

OysterCreek'searlywaterchemistry wasconsiderably moreimpurethanNMP-1's.OysterCreekwascharacterized byanaveragefirstsevencyclemeanof0.465ij.S/cm.Onlyafterfuelcycleten,wheredataisagainavailable, didthereactorwaterconductivity 3-1

pGEiVnckarEnergyGENE-$23-A16I-f094 improve.Infact,in1991OysterCreekbeganoperating onhydrogenwaterchemistry (HWC).Thelastthreefuelcyclereactorwaterconductivity atOysterCreekhasbeenexcellent.

OysterCreek'searlysteadystatechloridelevelsrangedoveraslightlywiderrangethanÃvP-1,i.e.,between25and74ppb.Inadditiontolongtermhighearlylifesteadystateconductivity, therewasasingledocumented waterchemistry transient experienced atOysterCreek(Reference 3-1).:1.June6,1972-730ppbchloridewasidentified inthewaterduetodepletedreactorwaterclean-upsystemdemineralizer.

Becauseofthehighearlylifeconductivity history,itislikelythatintergranular stresscorrosion cracking(IGSCC)initiation wasaccelerated insusceptible areasoftheprimarysystem,including theshroud.TheeFectsofconductivity (sulfate) oncrackinitiation inuncreviced materialispresented inFigure3-2.Itisclearthatanincreaseinconductivity resultsinanacceleration incrackinitiation asmeasuredbytheconstantextension ratetest(CERT).Asimilartypeofinitiation acceleration isobservedforchlorideions.Thestrongcorrelation betweenconductivity andIGSCCsusceptibility inuncreviced sensitized stainless steelhasalsobeenexaminedinvariousotherlaboratory studies(Reference 3-2through3-4)anditisevidentthatasignificant decreaseincrackinitiation timeisexpectedwithincreased concentrations ofcertaindeleterious anionicimpurities, inparticular chlorides andsulfates.

ForcrevicedBWRcomponents, thestrongcorrelation ofSCCsusceptibility withactualBWRplantwaterchemistry historyhasbeenDocumented (Reference 3-5).3-2

GEivudcarEnergyGEISTE-$23-Aldl-l0943.2ShroudEvaluation Following isaone-on-one comparison betweentheNMP-1andOysterCreekcoreshrouds:~NMP-1'sfirstfive-cycle meanconductivity was0.457pS/cmcomparedtoOysterCreekat0.526pS/cm.~NMP-1'stotalmeanconductivity is0.280pS/cmcomparedto0.316p,S/cmforOysterCreek.~NMP-1ischaracterized by15.5on-lineyearscomparedto15.7forOysterCreek.~NMP-1peakfastfluenceisapproximately 4.2x10"n/cm.Thiscomparesagainst6.6x10'/cmforOysterCreek.~NMP-1'scoreshroudmaterialandOysterCreekcoreshroudmaterialisessentially thesamewithbothplantsusingthesameheatsofType304stainless steel.~BothNMP-1andOysterCreekshroudsweremanufactured byP.F.Avery.3.3ShroudComparison Conclusion Basedontheexperience ofshroudcrackinginBWRswithrelatively goodwaterchemistry qualityandatlowfluencelocations, independent ofmanufacturer, materialofconstruction andrelativeage,crackinginNMP-1'sH4shroudweldcannotberuledout.However,aon-on-one comparison betweentheoperating historyofNMP-1'sandOysterCreekstronglysuggeststhatNMP-1'sshroudisboundedbyOysterCreek'sshroudcondition.

Althoughthematerialofshroudconstruction isidentical inthetwoplants,theNMP-1shroudcorrosion considerations arefavoredbythelowerfirstfivecyclemeanconductivity oftheplant,lowertotalmeanconductivity andlowerfluenceattheshroud.3-3

GE,Vuelear EnergyGENE-$23-Al61-l0943.4References 3-1.B.H.Dillman etal,"Monitoring ofChemicalContaminants inBWRs,"EPRINP-4134,July1985.3-2.Davis andM.E.Indig,"TheEffectofAqueousImpurities ontheStressCorrosion CrackingofAustenitic Stainless SteelinHighTemperature Water,"paper128presented atCorrosion 83,Anaheim,CA,NACE,April1983.3-3.Ljungberg.

D.Cubiccioti andM.Tolle,"EffectofImpurities ontheIGSCCofStainless SteelinHighTemperature Water,"Corrosion, Vol.44,No.2,February1988.3-4.Ruther, W.K.SoppetandT.F.Kassner,"EffectofTemperature andIonicImpurities atVeryLowConcentrations onStressCorrosion CrackingofType304Stainless Steel,"Corrosion, Vol.44,No.11,November1988.3-5.Brown andG.M.Gordon,"EffectsofBWRCoolantChemistry onthePropensity forIGSCCInitiation andGrowthinCrevicedReactorInternals Components,"

paperpresented attheThrdInt.Symp.ofEnvironmental Degradation ofMaterials inNuclearPowerSystems-Water

Reactors, Transverse City,MI,August1987,published inproceedings ofthesame,TMS-AIME, Warrendale, PA,1988.34

GE'h'uChar EnergyGENE.SZ3-A I61-f094Table3-1.NineMilePoint-1andOysterCreekWaterChemistry HistoryCycleNMP-1CycleMeanValueConduct.pS/cmOysterCrCycleMeanValueConduct.pS/cmOCCl-ppbCl-ppbNMP-ISO4=,ppbOCSO4=,ppb101213140.4320.5250.5910.4450.2910.2250.1810.1330.0870.0820.0840.4260.8690.3290.2940.7140.2980.3240.1430.1440.0880.090.06730465844332726251840742724372825443-5

10.001.00ET<<+00.10OEproonetary haonnaoonleaia NoevenaeeaoaDenan-+MaxWeektyMeanValue<yde QCydeMeanVa(ueawithStd.Oev.21AoH109e0.010FuelCycleFigure3-1NineMilePoint-1ReactorWaterConductivity MeanYaluci3-6 0

Figure3-2.EffectofSulfateonIGSCCInitiation Acceleration forFSType304IAcceleration

'Factor00.2030~~030.101002.30.~0.00.101~0Conductivity (uS/cm)H+0N10Crackinitiation databasedonCERT100Sulfate{ppb)100010000so4wcoN

GEgVaclaarEItargyGENE-S23-AI6l-l094 4.CRACKGRO%THESTIMATEThebasisforthecrackgrowthrateusedinthescreening criteriaisprovidedinthissectionTheNMP-1shroudcylinders werefabricated fromType304stainless steelplate.Therefore, theweldheat-affected-zone (HAZ)islikelysensitized.

Theshroudisalsosubjected toneutronfluenceduringthereactoroperation whichfurtherincreases theeffective degreeofsensitization.

Theotherside-effect ofneutronfluenceinducedirradiation istherelaxation ofweldresidualstresses.

Theslip-dissolution modeldeveloped byGEquantitatively considers thedegreeofsensitization, thestressstateandthewaterenvironment parameters, inpredicting astresscorrosion cracking(SCC)growthrate.Thecrackgrowthratepredictions ofthismodelhaveshowngoodcorrelation withlaboratory andfieldmeasuredvalues.Thismodelwasusedtopredictacrackgrowthrateandaconservative valuewasthenselected.

Theslip-dissolution modeldoesnotexplicitly consideranycontribution tocrackgrowthduetonewcrackinitiations.

Whilenewcrackinitiations duringthenextfuelcycleofoperation cannotberuledout,considerable relaxation inweldresidualstressmagnitudes duetoirradiation islikelytominimizecrackinitiation.

Thisissupported bylimitedfieldevidencefromanoverseasplantwherethesamecrackedregionoftheshroudwasexaminedoverthreerefueling cyclesfollowing thediscovery offirstincidence ofcracking.

SThesubsequent examinations showedsomegrowthoftheexistingcrack,butdidnotshowevidenceofnewinitiations.

Evenifanynewinitiations dooccur,itislikelythatonlyshallowcrackingwilloccurduringonecycleofoperation.

4.1Slip-Dissolution ModelFigure4-1schematically showstheGEslip-dissolution film-rupture model(Reference 4-1)forcrackpropagation.

Thecrackpropagation rateVtisdefinedasafunctionoftwoconstants (Aandn)andthecracktipstrainrate,s.V,=As"where:s=CK"(forconstantload)A=7.8x10n(fromReference 4-2)n=(ef(K)/(eftK)+ef(qi)c))APR)(fromReference 4-2)4-1

gg,Vackar EnergyGENE523rl16l1094Theconstants aredependent onmaterialandenvironmental conditions.

Thecracktipstrainrateisformulated intermsofstress,loadingfrequency, etc.Whenaradiation field,suchasthecasefortheshroud,ispresent,thereisadditional interaction betweenthegammafieldandthefundamental parameters whichaffectintergranular stresscorrosion cracking(IGSCC)ofType304stainless steel(seeFigures4-2and4-3).Theincreaseinsensitization (i.e.,Electrochemical Potentiokinematic Reactivation, EPR)andthechangesinthevalueofconstantAandnasafunctionofneutronfluence(>1MeV)isgivenasthefollowing:

EPR=EPR0+3.36x1024(fluence)1 17(4-2)where,EPRisinunitsofC/cm2,fluenceisinunitsofn/cm2andthecalculated valueofEPRhasanupperlimitof30.TheconstantCisdefinedasthefollowing:

forfluence<1.4x1019n/cm2:C=4.1x10-14 (4-3a)forfluence>1.4x1019n/cm2but<3x1021n/cm2:C=1.14x10-13 ln(fluence)

-4.98x101(4-3b)forfluence<3.0x1021n/cm:C=6.59x1013(4-3c)ThevariableKisthestressintensity vialinearelasticfracturemechanics andistobeusedwiththeaboveexpressions intheunitsofMPa~m.4.2Calculation ofParameters Theparameters neededforthecrackgrowthcalculation bytheGEmodelare:stressstateandstressintensity factor,effective EPR,waterconductivity, andelectro-chemical corrosion potential (ECP).ThestressstaterelevanttoIGSCCgrowthrateisthesteadystatestresswhichconsistsofweldresidualstressandthesteadyappliedstress.Figure4-4showsobservedthrough-'allweldresidualstressdistribution forlarge"diameter pipes.TheresidualstressistensileJ4-2

GEqvualaarEuerg+GEÃE-$23-A26l-1094atboththeinsideandoutsidesurfacesandcompressive inthemiddle.Thistypeofdistribution (characterized byacosinefunction) isaconservative representation forweldsinlargediameterpipesandplates(seeReference 4-3).Themaximumstressatthesurfacewasnominally assumedas35ksi.Thesteadyappliedstressontheshroudisduet'ocorediQerential pressureanditsmagnitude issmallcomparedtotheweldresidualstressmagnitude.

Figure4-5showstheassumedtotalstressprofileusedintheevaluation.

Figure4-6showsthecalculated valuesofstressintensity factor(K)assuminga360'.circumferential crack.Itisseenthatthecalculated valueofKreachesamaximumofapprox.25ksi~in.TheaveragevalueofKwasestimated as20ksi~inandwasusedinthecrackgrowthratecalculations.

Theweldresidualstressmagnitude isexpectedtodecreaseasaresultofrelaxation producedbyirradiation-induced creep.Figure4-7showsthestressrelaxation behaviorofType304stainless steelduetoirradiation at550'.Sincemostofthesteadystressintheshroudcomesfromtheweldresidualstress,itwasassumedthattheKvaluesshowninFigure4-6decreaseinthesameproportion asindicated bythestressrelaxation behaviorofFigure4-7.Thesecondparameter neededintheevaluation istheEPR.Inthemodel,theinitialEPRvalueisassumedas15fortheweldsensitized condition.

UsingEquation(4-2),thepredicted increaseinEPRvalueasafunctionoffiuenceisshowninFigure4-8.Thethirdparameter usedintheGEpredictive modelisthewaterconductivity.

Awaterconductivity ofO.1gS/cmwasusedinthiscalculation whichisareasonable valueformanyplants.Thereactorwaterconductivity atNMP-1isexcellent (approx.0.084p,S/cm).Thishasasignificant impactonthepredicted crackgrowthratebytheGEmodelasseeninFigure4-9,asshownforadomesticBWR/4.Todemonstrate thattheGEmodelconservatively refiectstheeffectofconductivity, Figure4-10showsacomparison oftheGEmodelpredictions withthemeasuredcrackgrowthratesinthecrackadvanceverification system(CAVS)unitsinstalled atseveralBWRs.Thecomparison withCAVSdatainFigureA-10alsodemonstrates theconservative natureofcrackgrowthpredictions bytheGEmode).TThelastparameter neededintheGEprediction modelistheECP.Figure4-11showsthemeasuredvaluesofECPattwolocations inthecore.TheECPvaluesatzeroH2injection arerelevantinFigureA-11fornohydrogeninjection.

ItisseenthattheECP4-3

GEÃuckarEnergy~ELFSZS-~is-iOW valuesatzeroH2injection raterangefrom150mVto225mV.Therefore, avalueof200mVwasusedinthecalculation.

4.3CrackGrowthPrediction Basedonthediscussion inthepreceding section,thecrackgrowthratecalculations wereconducted asafunctionoffluenceassumingthefollowing valuesofparameters:

InitialKEPR0Cond.ECP=20ksi~in=15C/cm2=0.1pS/cm=200mVFigure4-12showsthepredicted crackgrowthrateasafunctionoffluence.Itisseenthatthepredicted crackgrowthrateinitially increases withthefluencevaluebutdecreases laterasaresultofsignificant reduction intheKvalueduetoirradiation inducedstressrelaxation.

Thecrackgrowthratepeaksat4.5x10-5in/hratafluenceoflx10n/cm2.Thus,aboundingvalueofSxl05in/hrcanbeconservatively usedinthestructural integrity evaluation fortheshroud.Theactualrecentwaterconductivity forNMP-1is0.084pS/cm.ANMP-1plantspecificcalculation wasalsoperformed usingtheNMP-1waterconductivity andcurrentfluenceattheH4weld.Resultsofthiscalculation showedthattheNMP-1crackgrowthratewas2.6x10'n/hr.

Forpurposesofthisevaluation, aconservative crackgrowthrateofSx10'n/hr isused.Thisboundingcrackgrowthrateisquiteconservative ascanbeshowninFigureA-13fromNUREG-0313, Rev.2.ItisseenthatthecrackgrowthrateofSx10-5in/hrat20ksi~inisconsiderably higherthanwhatwouldbepredicted byusingtheNRCcurve.Thisfurtherdemonstrates theconservatism inherentintheassumedboundingvalueofcrackgrowthrate.44

GEJVuckarEu~gYGENE-$23-Al6l-l0944.4Conclusion Acrackgrowthratecalculation usingtheGEpredictive modelwasconducted considering thesteadystatestress,EPR,conductivity andECPvaluesforatypicalshroud.Theevaluation accounted fortheeffectsofirradiation inducedstressrelaxation andtheincreaseineffective EPR.Theevaluation showedthataboundingcrackgrowthrateofSx10-5in/hrmaybeusedinthestructural integrity evaluation oftheNMP-1shroud.4-5

gt.fVuckar EnergyGEÃE-$23-gf6g/0944,5Reference 4-1F.P.Fordetal,"Prediction andControlofStressCorrosion CrackingintheSensitized Stainless SteeVWater System,"paper352presented atCorrosion 85,Boston,MA,NACE,March1985.4-2F.P.Ford,D.F.Taylor,P.L.Andresen&R.G.Ballinger, "Environmentally Controlled CrackingofStainless SteelandLowAlloySteelsinLWREnvironments,"

1987,(EPRIReportNP50064M, ContractRP2006-6).

4-3ASMESectionXITaskGrouponReactorVesselIntegrity Requirements, "WhitePaperonReactorVesselIntegrity Requirements forLevelAandBConditions,"

EPRI,PaloAlto,CA,January1993,(EPRIReportTR-100251, Project2975-13).

4-6

GENudcarEnergyGENE-323-8161-1094 CTVTCrack-tip advancebyenhancedoxidation atstrainedcracktipVT--AgWhere:-A,ncrackpropagation rateconstants, dependent onmaterialandenvironmental conditions, crack-tip strainrate,formulated intermsofstress,loadingfrequency, etc.Figure4-1:TheGEPLEDGESlipDissolution

-FilmRuptureModelofCrackPropagation 4-7

6'Egaclcar&erg+GELT-523-A I61-1094SOLUTIONRENEWALRATETOCRACK-TIP STRESSOXIDERUPTURERATEATCRACK-TIP

>/ANIONIC TRANSPORT ENVIRONMENT MICRO-STRUCTURE HARDENING IRELAXATION T-FIELDCRACKTIP4[A],pHPASSIVATION RATEATCRACK-TIP N-FLUENCE G.B.DENUDATION ISEGREGATION Figure4-2:EffectsofFastFluence,Flux&,GammaFieldonParameters Affecting IGSCCofType304Stainless Steel4-8

GEKuCkurEnergyGEIVE-$23-AI61-2094VT=Ai,",QxO~~"A"HoM'EPRP,S,NI~Si~necTz-~ef(x)~(ef(x)+ef(q)cof(EPR)Figure4-3:Parameters ofFundamental Importance toSlipDissolution Mechanism ofIGSCCinSensitized Austenitic Stainless Steel4-9

GEendearEnergyGENE-$23-8161-1094 INSIDEWALL50OUTSIDEWAU403020IOIc/llP-20Oa~ddd44~~QO44oCLd~8d~Q0.2040.60.8l.0Figure4-4:Through-wall Longitudinal ResidualStressDataAdjacenttoWeldsin12to28inchDiameterStainless SteelPiping4-10

GEivnckarEnagyGENE-$23-Al6l-l094STRESSKSIDOD3020TotalStressProfile10AppliedLoadStress0-10-20-30400.20.40.60.8DEPTH(INCHES)1.21.4Figure4-5:Conservative Representation oftheShroudTotalThrough-wall StressProfile4-11

GE/udearEnergyGEÃE-$23-A161-1094 262422201816141210STRESSINTENSITY, K(KSI'INCH" 0.5)0.20.40.60.8CRACKDEPTH,A(INCHES)Figure4-6:ShroudThrough-wall StressIntensity Factor4-12

GE>VudaarEnergyGELT-529-8161-10' 0.8C~~C~~C$EQa:0.6V)V)o04Q~~VC5u-0.2StressRelaxation BehaviorfromIrradiation CreepMinimumAverageData~~Type304Stainless Steel'.at288'Ci.e"g02010NeutronFluence,n/cm2(Eo1MeV}10Figure4-7:StressRelaxation BehaviorofType304Stainless SteelDuetoIrradiation at288'C4-13'

gE,Vuclcar EnergyGEE-$23-rll6l-10943025a-20101E+191E+20FLUENCE1E+21Figure4-8:EPRVersusNeutronFluence4-14 eP GEivudaalEnergyGENE323ill6ll0960.00015.000E-05 PL"0.00001UCl0.000001OFOIAl91992-1993 1975-1984 100mV0mV100mV-200mV300mV0.0000001 00.10.20.30.40.50.60.70.80.9Conductivity, pS/cmPLEDGE:20ksiJin,15C/cm2Figure4-9:GENEPLEDGEModelPrediction foraBWR-4(Sensitized Type304CrackGrowthRate)4-15

GEivnckarEnergyGENE-$23-itl61-10'.0001 5.000E-OS 200mVe0.00001(90.000001O1E-07AGAG0C0CMM(9AG0TMMM0AJ0C0NN0.050.10150.20.25Conductivity, pS/cmPLEDGE:20ksigin,15C/cm2CAV:20-25ksigin,13C/cm2,100-160mV0.30.35Figure4-10:EffectofConductivity onSensitized Type304CrackGrowthRate4-16

GEivuclcarEnergyGM-$23-Al61-l094300200100llJ0E-100OuJ-200-300JustBelowTopGuideLevelJustAboveCorePlateLevel-4000102030405060708090Feedwater H2,SCFMFigure4-11:In-CoreBypassECPversusFeedwater HydrogenforBWR-44-17

GElVF-323-A I6I-I0941.00E-041.00E-061E+191E+20Fluence(n/cm2I1E+21StressIntensity

=20ksigin,InitialEPR=15C/cm2Figure4-12:GrowthRateversusFluence4-18

GE/One!earEnergyGENESZ3II/61109eI0-3I0-4Iin./yrNRCCURVE0-5LLJI-CLI-oI06CDhCCDCLCDI0-7/$8/j/Q~/4r0.04in.iyrIIIIIIIII--I8O.tpps0t',sensltlte4 atIISO'f/th(Eth~ISC/cs)CEO.tPP<<'0tlsensltlte4 at11$0'F/th(Kph~10C/cs)-CEQO.tpps0t'Isensltlte4 at11$0'F/tlhCEO.tpps0t,seecrelysensltlte4 Q0ppsOt.lsensltltH at11$0'F/tlhCEIHITACHICKHKOQNLCKCtO~4pps0t,se<<sltlte4 byvol~l<<$;LfSat$)t'F/tlh(Sll)I01sensltltH at(lt$t'f/10eisn)a($$t'F/tlh)(EPO~lC/cs)0ppsOt,se<<sltltH at(lt$t'f/10min)e($)t'F/tlh)(Epn~lC/cs)f~O.lHt,H~0.$4*0pps0t,sensltlte4 at(It$t'f/IOsin)a(4t'F/tSF h)(EPO~ISC/cs)p0~0,:sensstltH at(It$t'F/10ein) a(4t'F/t57 h)(EPH~'ISC/cs)f~O.lHt,H~0.$i~0ppsOt'IsensltltH atlt$t'f/Ilh(EM~tOC/cs)f~0.000Ht,H~0.$$X0ppsOtlsensltltH atIt$tf/Ilh(EpnItOC/cs)f~0.00Ht,0~0.$$RECENTANLOATA0IO2030405060STRESSINTENSITY, K{I(sile.j 70Figure4-13:NUREG-0313 CrackGrowthRateData4-19

GEtVuclcarEltbargyGEtVE-$23-Al6l.l0945.FLAWEVALUATION Thissectionprovidesthemethodology andevaluation oftheobservedindications intheOysterCreekH4weld.Thismethodincorporates theconservative assumption thattheareasotherthantheinspected ligamentlengthsareassumedtobecrackedthroughwall,andconsiders proximity rules.Abriefdescription ofthetechniques isfirstprovidedfollowedbyadetaileddescription oftheevaluation.

5.1LimitLoadMethodFigure5-1showsaschematic representative planviewofanasymmetric distributed uncracked ligament.

Itisassumedthatthereare1,2,...i,....

nligamentlengthsandthattheilengthisofthickness

'tandextendsfromanazimuthof6;1to6;2.Theligamentlength'loftheithligamentisrelatedtoazimuthangles6;1and6i2bythefollowing relationship:

li=(D/2)~(6;1-6j2)

(5-1)where,Disthediameteroftheshroud.Thecalculation ofmoment'M'hatthisligamentconfiguration canresist,issomewhatcomplicated sinceitisnotaprioriclearastowhichazimuthal orientation oftheneutraVcentral axiswouldproducetheleastvalueofbendingmoment,'M'.Therefore, thevalueofMiscalculated forvariousorientations ofthecentralaxisfrom0'o360'.Thiscalculation isperformed intwosteps:(1)Inthimtep,acentralaxisorientation, e,isfirstselected.

Thelocationoftheneutralaxis(whichisparalleltothecentralaxis)atadistance5fromthecentralaxisisdetermined usingthefollowing (seeFigure5-1):where,IRt(8)d8gm-a+))gm-a+))JRt(6)d6=(am/af)(2nRtg (5-2)a+/AssumedazimuthangleofthecentralaxisAngleoftheneutralaxiswithrespecttocentralaxis,orsin1(5/R)5-1 0

GE.Vuakar EnergyGEÃE-$23-rl16I-I0945=DistancebetweenthecentralaxisandtheneutralRt(e)tnamGfaxisMeanradiusoftheshroudt;(thickness oftheithligament),

ifangle8issuchthate;1<e<62,or0otherwise.

Nominalthickness ofshroudMembranestressMaterialflowstress=3SmThus,thisstephelpsdefinethelocationoftheneutralaxiswhenthecentralaxisisassumedtobeatanazimuthangleofa.(2)Oncethelocationoftheneutralaxisrelativetothecentralaxisisdetermined, themoment,M+,isthenobtainedbyintegrating thebendingmomentcontributions fromindividual ligamentlengths.Themathematical expression usedisthefollowing:

Ma=IafR>At(8)

Sin(a-8)d8(5-3)where,A1.0,if-(n-e+P)<6<a+(,or-1.0,ifa+)<e<-(ii-u+P)

Theorientation

'e'hatproducestheleastvalueofMiscalled'e,min'nd definestheaxiscapableofresisting thelimitingmoment.Whetherthespecified setofuncracked ligamentlengthsprovidestherequiredstructural marginisverifiedbythefollowing:

M(xminI'Z+Pm>SF(Pm+Pb) where,PmPbSFSectionmodulusoftheshroudbasedonuncracked crosssectionAppliedmembranestressAppliedbendingstressSafetyfactor5-2

GEunclearEnergyGENE-323-A l6l-l0945.2Evaluation ofPart-Through WallCracksIfitisnotpossibleobtaintherequiredsafetyfactorsassumingthrough-wall indications, thenevaluation ofacombination ofuncracked ligaments andpartthrough-wall cracksmayberequiredtoassessstructural margins.Forthiscase,theangularlocationoftheuncracked ligaments, andthedepthoftheflaws,mustbedetermined.

Proximity rulesareusedtodetermine effective flawlength.Thedepthdetermination mustalsoincludeanyuncertainty associated withtheNDEmethodused.Allowances forcrackgrowtharealsofactoredin,including effectsonbothlengthofuncracked ligaments, anddepthofflawedportionsoftheareaexamined.

Thisinformation canthenbeanalyzedinaccordance withpreviously outlinedmethods.Themaximumobserveddepthsizingerrortodatehasbeen7.6mm.Basedonthis,theuncertainty assignedtodepthmeasurements is7.6mm,untilbetterinformation canbeobtained.

Itmaybepossibletoconservatively simplifytheaboveapproachbyassumingaflawof360oatthemaximumobserveddepth,a.Thedepth'a'houldincludeanyuncertainty associated withtheNDEmethodused.Therequiredminimum360'igament atacircumferential weldcanbedetermined byiteratively calculating theallowable crackdepth,'d'singthefollowing equations (Reference 5-1):(n(I-d/tn-Pm/af)

}/(2-d/tn)

Pb'(2ag'm)(2-d/tn)sin p(5-5)(5-6)(Pm+Pb)SF

=Pb'+Pmwhere,PmPbdtnSFPrimarymembranestressatthesubjectweldPrimarybendingstressatthesubjectweldAllowable crackdepthShroudwallthickness (awayfromafilletweld)Safetyfactorappropriate fortheoperating condition beingevaluated Materialflowstress(=3Sm)5-3

GEivuckarEnergyGENE-$2$-Al61-l094Itshouldbenotedthatthestresses, PmandPb,arecalculated usingthenominalshroudthickness.

Thecurrentcrackdepth'a'sacceptable iftheprojected crackdepth,afteraccounting forcrackgrowthuntilthenextinspection, islessthantheallowable crackdepth'd'.Thiscriteriaisgivenbythefollowing equation:

(a+CG)<d(5-7)where,CGistheprojected crackgrowthuntilthenextinspection.

5,3SafetyFactorsSafetyfactorsof2.8foroperational conditions and1.4forfaultedconditions wereusedintheevaluation ofcircumferential welds.Thesesafetyfactorvaluesareconsistent withSectionXIvalues.5-4

GEIIudaarEnergyGEM-S23-A I6l-I0945.4Application ofFlawEvaluation Methodology toNMP-1ShroudTheapplication oftheflawevaluation methodology described earlierispresented inthissection.CrackgrowthassumingacrackgrowthrateofSx10Sin/hrwasaddedtotheassumedindications.

5.4.1LimitLoadForlimitload,theflawdistribution patterninSection2.0wasused.Thisflawdistribution patternwasaresultofapplyingtheproximity criteriagiveninReference 2-1.Acomputer.programwasusedwhichusestheReference 2-1methodology.

Resultsofthisevaluation showedsafetyfactorsinexcessofthoserequired.

Theresulting safetyfactorswere:Condition Calculated ReuiredNormalandUpsetEmergency andFaulted6.53.52.81.4Theseresultsillustrate thatduetotherelatively lowloads,theshroudisveryflawtolerant.

5.4.2LEFMTheLEFMcalculation isprovidedeventhoughtheresultsofthiscalculation maynotbemeaningful duetothefluenceattheNMP-1H4weldlocation.

Thecurrentfluenceisjustabove3xlon/cm.Thefracturetoughness usedtodetermine thecriticalflawsizecorrespondMo materialwithafluenceof8x10'/cm.BasedontheOysterCreekflawresults,aconservative combination oftheindications wasconsidered fortheLEFMcalculation.

Usingthisconservative combination, asafetyfactorof1.83wasobtained.

Thiscomparesagainsttherequired1.4forfaultedconditions.

5-5 0

GEPuckarEnergyGENEI-AI6I10945.5References 5-1S.Ranganath andH.S.Mehta,"Engineering MethodsfortheAssessment ofDuctileFractureMargininNuclearPowerPlantPiping,"ASTMSTP803(1983).5-6

OoBll/B12CentralAxis'5?'(:C,.%?5eutraAxisrBuFigure5-1Schematicof Non-Symmetric igiamentDistribution

GEivudcarEnergyGElVE-$2$.1I6l.l0946.CONCLUSIONS Anevaluation oftheNMP-1coreshroudhasbeenperformed.

Theobjective oftheevaluation wastodemonstrate thatcontinued operation ofNMP-1wasjustified onastructural basisbyapplyingtheOysterCreekinspection resultstoNMP-1.Itwasconcluded thatbasedonaone-to-one comparison betweenNMP-1andOysterCreek,theindications intheOysterCreekshroudwilllikelyboundthoseintheNMP-1shroud.Evenwiththisconservative assumption, itwasdetermined thatthesafetyfactorpresentintheNMP-1coreshroud(usingOysterCreekindications) exceededtherequiredsafetyfactorsuntilatleastFebruaryof1995.Thus,itwasconcluded thatcontinued operation oftheNMP-1plantisjustified basedonstructural evaluation ofthecoreshroud.6-1

ATTACHMENT 2NINEMILEPOINTUNIT1DOCKETNO.50-220LICENSENO.DPR-63GENERICLETTER94-03SUPPLEMENTAL INFORMATION "FRACTURE MECHANICS ASSESSMENT OFTHENINEMILEPOINTUNIT1SHROUDH4WELD"REPORTMPM-109439 MPMRESEARCHRCONSULTING OCTOBER1994 0