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{{#Wiki_filter:PENNSYLVANIAPOWER8cLIGHTCCMPANYAREACTIONK)CRACKINGOFAUSTENITICSTAINLESSS9ZELPIPINGINBOILINGWATERREACTORS(INCLUDESSUSQUEHANNASESDESIGNMODIFICATIONS)EarleM.Mead./ProgectEngineeringManagerSusquehannaSES TableofContentsl.Introduction2.ProblemStatementSafetySignificancePrimaryConsiderations4.1Environmental(CoolantChemistry)4.2Stress4.3Material5SusquehannaSESPreventiveMeasures5.1Environment5.1.1ChemicalControl5.1.2MechanicalControl5.1.2.1ControlRodDrive(CRD)PumpSuctionRelocation5.1.2.2MechanicalVacuumDeaeration5.1.3OperatingProcedures5.2Stress5.2.1'DesignStresses5.2.2FabricationStresses5.2.2.1Fit-up5.2.2.2InitialFabrication(Shop)5'2.2.3Welding-Induced.Stress5.2.2.3.1HeatInput5.2.2.3.2JointDesign5.2.2.3.3FillerMetal5.2.2.3.4Cleanliness TableofContentsPage5.2.3'ethodsofStressReduction105.2.3.1SolutionHeatTreatment5.2.3.2HeatSinkMelding5.2.3.3InductionHeatingStressImprovement105.3Material5~3-1503~2CoreSpraySystemReactorRecirculationSystemDischargeGateValveBypassLine13135~3~353~.6.ReferencesControlRodDriveReturnLineRecirculationRiserpipes1315 TableandIllustrationTable1Figure1
{{#Wiki_filter:PENNSYLVANIA POWER8cLIGHTCCMPANYAREACTIONK)CRACKINGOFAUSTENITIC STAINLESS S9ZELPIPINGINBOILINGWATERREACTORS(INCLUDESSUSQUEHANNA SESDESIGNMODIFICATIONS)
~~'1.IntroductionThisreportoriginallyresultedfromaninformalteleconbetweenrepresentativesofPPM.andtheNRCwhichoccurredinFebruary1976.AtthattimeproposedSusquehannaSteamElectricStation(SSES)designchangeswerebrieflydiscussedanditwasagreedthatthisadditionalinformationshould.besubmitted.,SubsequenttotheoriginalissueofthisreporttherehavebeennumerousincidentsattributedtoIntergranularStressCorrosion.Cracking(IGSCC).Based.ontheseincidents,PPM,hasmodifiedourpositiononIGSCC,whichincludedadditionaldesignchangesatSSES..FortheabovereasonandtoprovidetheNRCwithPAL'spositiononNUHEG-0313,thisreporthasbeenrevisedandupdated.
EarleM.Mead./ProgectEngineering ManagerSusquehanna SES TableofContentsl.Introduction 2.ProblemStatement SafetySignificance PrimaryConsiderations 4.1Environmental (CoolantChemistry) 4.2Stress4.3Material5Susquehanna SESPreventive Measures5.1Environment 5.1.1ChemicalControl5.1.2Mechanical Control5.1.2.1ControlRodDrive(CRD)PumpSuctionRelocation 5.1.2.2Mechanical VacuumDeaeration 5.1.3Operating Procedures 5.2Stress5.2.1'DesignStresses5.2.2Fabrication Stresses5.2.2.1Fit-up5.2.2.2InitialFabrication (Shop)5'2.2.3Welding-Induced.
2.ProblemStatementFromSeptember,1974toOctober,1976crackinghad.beendiscovered.inrecirculationbypassloops,corespraylinesand.controlrod.drivereturnlinesof10GEboilingwaterreactors.Theaffectedunitswere:a)Corespraylines-Dresden2,Fukushima1,and.Tsurugab)Recirculationbypasslines-Dresden2,QuadCities1,QuadCities2,PeachBottom3,MillstonePoint1,Monticello1,Fukushima1,Hamaoka1,Brunswick2,Hatch1,and.Pilgriml.c)Contxolroddrivereturnlines-TarapurPP8cLbelievedthatsufficientJustificationexisted.torecognizethecauseasbeingIntergranularStressCorrosionCracking.ThisreportwasoriginallyissuedonOctober12,1976and.summarizedPP8cL'sconcernsaswellasmodificationsthatwereimplementedforSSES.FromOctober1976tothepresenttherehavebeen'numerousreportsofcrackingatotherplantswhichhasbeenattributedtoIGSCC.Notonlyhavetheabovelinesbeenaffected,buttherearereportsofcrackinginheadventlines,recirculationriserlines,instrumentlines,andalso,mainrecirculationandfeedwaterlines.ThisreporthasbeenrevisedtoreflectPPM'spositiononIGSCCand.thelatestmodificationswhichhavebeenmadeatSSES.  
Stress5.2.2.3.1 HeatInput5.2.2.3.2 JointDesign5.2.2.3.3 FillerMetal5.2.2.3.4Cleanline ss TableofContentsPage5.2.3'ethodsofStressReduction 105.2.3.1SolutionHeatTreatment 5.2.3.2HeatSinkMelding5.2.3.3Induction HeatingStressImprovement 105.3Material5~3-1503~2CoreSpraySystemReactorRecirculation SystemDischarge GateValveBypassLine13135~3~353~.6.References ControlRodDriveReturnLineRecirculation Riserpipes1315 TableandIllustration Table1Figure1
~~'1.Introduction Thisreportoriginally resultedfromaninformalteleconbetweenrepresentatives ofPPM.andtheNRCwhichoccurredinFebruary1976.AtthattimeproposedSusquehanna SteamElectricStation(SSES)designchangeswerebrieflydiscussed anditwasagreedthatthisadditional information should.besubmitted.,
Subsequent totheoriginalissueofthisreporttherehavebeennumerousincidents attributed toIntergranular StressCorrosion.
Cracking(IGSCC).Based.ontheseincidents, PPM,hasmodifiedourpositiononIGSCC,whichincludedadditional designchangesatSSES..FortheabovereasonandtoprovidetheNRCwithPAL'spositiononNUHEG-0313, thisreporthasbeenrevisedandupdated.
2.ProblemStatement FromSeptember, 1974toOctober,1976crackinghad.beendiscovered.
inrecirculation bypassloops,corespraylinesand.controlrod.drivereturnlinesof10GEboilingwaterreactors.
Theaffectedunitswere:a)Corespraylines-Dresden2,Fukushima 1,and.Tsurugab)Recirculation bypasslines-Dresden2,QuadCities1,QuadCities2,PeachBottom3,Millstone Point1,Monticello 1,Fukushima 1,Hamaoka1,Brunswick 2,Hatch1,and.Pilgriml.c)Contxolroddrivereturnlines-TarapurPP8cLbelievedthatsufficient Justification existed.torecognize thecauseasbeingIntergranular StressCorrosion Cracking.
Thisreportwasoriginally issuedonOctober12,1976and.summarized PP8cL'sconcernsaswellasmodifications thatwereimplemented forSSES.FromOctober1976tothepresenttherehavebeen'numerous reportsofcrackingatotherplantswhichhasbeenattributed toIGSCC.Notonlyhavetheabovelinesbeenaffected, buttherearereportsofcrackinginheadventlines,recirculation riserlines,instrument lines,andalso,mainrecirculation andfeedwater lines.ThisreporthasbeenrevisedtoreflectPPM'spositiononIGSCCand.thelatestmodifications whichhavebeenmadeatSSES.  


3.SafetySignificancePPM,considersthestatementinNUREG-0313,whichreadsinpart,"Althoughtheprobabilityisextremelylowthatthesestresscorrosioncrackswillpropagatefarenoughtocreateasignificantsafetyhazardtothepublic,thepresenceofsuchcracksisundesirable"tobeanaccurateassessmentofthesafetysignificance.Beyond,thatPPMbelievesthesignificanceofthefailurestorelateonlytoplantreliability.Based,onpreviousBWRexperience,itcanbeexpected.thatbrittlecrackingwillnotoccurinausteniticType304stainlesssteeland.thatsmallleakswillbedetected,v5.suallyand/orbyleakdetectioninstrumentationiftheyoccurinsidetheprimarycontainment.Theimportanceofdetectabilityhasbeenrecognized,andtheSSESdrywellleakdetectionsystemwillcomp~withNRCRegulatoryGuide1.45(May1973).TheInserviceInspectionProgramatSSESisinaccordancewiththerequirementsoftheASMEBoilerandPressureVesselCode,SectionXI,"RulesforInserviceInspectionofNuclearPowerPlantComponents",1974edition,includingaddendathroughSummer1975,asmodified.byAppendixIIItoMinter1975addenda,"UltrasonicExaminationMethod.forClass1andClass2PipingSystemsMadefromFerriticSteels",andINA-2232ofthe,Summer1976Addenda,using50+pofthereferencelevelascriteriaforinvestigatingreflectors.TheISIProgramwillbeupdated,asrequired/allowedby10CFR50.55a(g).ItwillalsobeaugmentedtocomplywiththerecommendationsofNUREG-0313.ThedegreeofaugmentationwilldependontheoutcomeofPPM,'sdetailedevaluationofIGSCCatSSES.Thisevaluationwillbecompleted.byJanuary1,1990and.willaddressallapplicablelineswhichcontainreactorcoolant.Itwilldelineateallmaterialsandanyfabricationprocesseswhichwillprovideacomprehensivelisting'ofsusceptiblelinesintheasinstalledcondition.ThestudywillthenprovideanevaluationofallIGSCCcountermeasureswhichareavailableforuseatSSES.Theconclusionofthestudywillbearecommendationofwhat"courseofaction"shouldbetakenforeachsusceptibleline>fromwhichcountermeasuresshould.beusedtohowtheISIProgramshould.beaugmented..  
3.SafetySignificance PPM,considers thestatement inNUREG-0313, whichreadsinpart,"Although theprobability isextremely lowthatthesestresscorrosion crackswillpropagate farenoughtocreateasignificant safetyhazardtothepublic,thepresenceofsuchcracksisundesirable" tobeanaccurateassessment ofthesafetysignificance.
Beyond,thatPPMbelievesthesignificance ofthefailurestorelateonlytoplantreliability.
Based,onpreviousBWRexperience, itcanbeexpected.
thatbrittlecrackingwillnotoccurinaustenitic Type304stainless steeland.thatsmallleakswillbedetected, v5.sually and/orbyleakdetection instrumentation iftheyoccurinsidetheprimarycontainment.
Theimportance ofdetectability hasbeenrecognized, andtheSSESdrywellleakdetection systemwillcomp~withNRCRegulatory Guide1.45(May1973).TheInservice Inspection ProgramatSSESisinaccordance withtherequirements oftheASMEBoilerandPressureVesselCode,SectionXI,"RulesforInservice Inspection ofNuclearPowerPlantComponents",
1974edition,including addendathroughSummer1975,asmodified.
byAppendixIIItoMinter1975addenda,"Ultrasonic Examination Method.forClass1andClass2PipingSystemsMadefromFerriticSteels",andINA-2232ofthe,Summer1976Addenda,using50+pofthereference levelascriteriaforinvestigating reflectors.
TheISIProgramwillbeupdated,asrequired/allowed by10CFR50.55a(g).
Itwillalsobeaugmented tocomplywiththerecommendations ofNUREG-0313.
Thedegreeofaugmentation willdependontheoutcomeofPPM,'sdetailedevaluation ofIGSCCatSSES.Thisevaluation willbecompleted.
byJanuary1,1990and.willaddressallapplicable lineswhichcontainreactorcoolant.Itwilldelineate allmaterials andanyfabrication processes whichwillprovideacomprehensive listing'ofsusceptible linesintheasinstalled condition.
Thestudywillthenprovideanevaluation ofallIGSCCcountermeasures whichareavailable foruseatSSES.Theconclusion ofthestudywillbearecommendation ofwhat"courseofaction"shouldbetakenforeachsusceptible line>fromwhichcountermeasures should.beusedtohowtheISIProgramshould.beaugmented..  


4'r1maryConsiderations4.1Environment(CoolantChemi,stry)ThecoolantchemistryinBoilingWaterReactorsisestablished.primarilytoensurecompat1bilitywithmaterialsusedthroughouttheNuclearSteamSupplySystem.Hence,neutral,high-puritywaterisusedand.halogensarestringentlylimited..Limitationsarealsoplacedonthesilicaand.copperconcentrationstopreventtheirdepositionintheturbine.Dissolved.oxygenconcentrationisnotnormallycontrolledbychemicaladditionormechanicaldeaeration.Withoutchemicalormechanicalcontrolthesteadystatelevelofdissolved.oxygenatSSESduringnormaloperationwillbeamaximumof7.1ppb.However,duringlowloadornoload.cond1tionstheoxygenconcentrationcanapproachsaturationwhich,underconditionsofstandardtemperatureandpressure,is8.0ppm.Underthecombinedinfluencesofsensitizationandhightensilestressthisoxygenlevelismorethansufficienttoenablestresscorrosioncrackingofausteniticstainlesssteeltooccur.Since,forconstantvaluesofsensitizationand.stress,tim-to-failure1sd.irectlyproportionaltodissolved.oxygenconcentration,lowflowandstagnantlinesarehigh+suspect.Itwould.,therefore,beverybeneficialtoreducetheoxygenleveltoaslowaspossibledur1ngallphasesofplantoperat1on.4.2StressThedesignstresslevelsforNuclearSteamSupp+System(NSSS)pipingareestablished.withintheconstraintsoftheAQSCodeaswellasanyloadingrestrictionswhichmightbeimposed.bytheNSSSvendor.StresslevelssufficienttoresultinIGSCCgenerallyarenot'usttheresultofordinarily-appliedengineeringloadsorstresses.Rather,theyresultfromthecombind'ffectsofallsourcesofstressand.strain:i.e.,residuals,thermal,surface,service,etc.IItisverybeneficialtomin1mizetheamountofstressactingonthesens1tized.material.Therefore,theamountofresidualand.applied.stressesshouldbereducedwhereverpossible.4.3NaterialBoilingWaterReactorpipingisfabricatedfromsteelswhichare:corrosionresistant,tough,stabledimnsional+,sufficientlystrongforanticipatedloadings,resistanttoradiat1ondamage,resistanttobothacidicandbasicchemicalattack,economical,and.anticipated.tobeavailableintheforeseeablefuture.Themostprominentmaterialsused.areausteniticstainlesssteels(Types304and,316)and,carbonsteel.  
4'r1maryConsiderations 4.1Environment (CoolantChemi,stry)
"l However,ithasbeendeterminedthatthestandardgradesof304and.316stainlesssteelwithhighcarboncontentsofapproximately.06to.08percentarethegradeswhichproducethemostseveresensitizationand.thus,thegreatestsusceptibilitytoIGSCC.Thelowcarbon((.03percentcarbon)gradesof304and316stainlesssteelaredemonstratingamuchgreaterresistancetoIGSCC.Theseand,otheralternatematerialsareundergoingextensivedevelopmentand,evaluationforreducingtheprobabilityofIGSCC.
Thecoolantchemistry inBoilingWaterReactorsisestablished.
primarily toensurecompat1bility withmaterials usedthroughout theNuclearSteamSupplySystem.Hence,neutral,high-purity waterisusedand.halogensarestringently limited..
Limitations arealsoplacedonthesilicaand.copperconcentrations topreventtheirdeposition intheturbine.Dissolved.
oxygenconcentration isnotnormallycontrolled bychemicaladditionormechanical deaeration.
Withoutchemicalormechanical controlthesteadystatelevelofdissolved.
oxygenatSSESduringnormaloperation willbeamaximumof7.1ppb.However,duringlowloadornoload.cond1tions theoxygenconcentration canapproachsaturation which,underconditions ofstandardtemperature andpressure, is8.0ppm.Underthecombinedinfluences ofsensitization andhightensilestressthisoxygenlevelismorethansufficient toenablestresscorrosion crackingofaustenitic stainless steeltooccur.Since,forconstantvaluesofsensitization and.stress,tim-to-failure 1sd.irectly proportional todissolved.
oxygenconcentration, lowflowandstagnantlinesarehigh+suspect.Itwould.,therefore, beverybeneficial toreducetheoxygenleveltoaslowaspossibledur1ngallphasesofplantoperat1on.
4.2StressThedesignstresslevelsforNuclearSteamSupp+System(NSSS)pipingareestablished.
withintheconstraints oftheAQSCodeaswellasanyloadingrestrictions whichmightbeimposed.bytheNSSSvendor.Stresslevelssufficient toresultinIGSCCgenerally arenot'usttheresultofordinarily-applied engineering loadsorstresses.
Rather,theyresultfromthecombind'ffectsofallsourcesofstressand.strain:i.e.,residuals, thermal,surface,service,etc.IItisverybeneficial tomin1mizetheamountofstressactingonthesens1tized.
material.
Therefore, theamountofresidualand.applied.stressesshouldbereducedwhereverpossible.
4.3NaterialBoilingWaterReactorpipingisfabricated fromsteelswhichare:corrosion resistant, tough,stabledimnsional+,
sufficiently strongforanticipated
: loadings, resistant toradiat1on damage,resistant tobothacidicandbasicchemicalattack,economical, and.anticipated.
tobeavailable intheforeseeable future.Themostprominent materials used.areaustenitic stainless steels(Types304and,316)and,carbonsteel.  
"l However,ithasbeendetermined thatthestandardgradesof304and.316stainless steelwithhighcarboncontentsofapproximately
.06to.08percentarethegradeswhichproducethemostseveresensitization and.thus,thegreatestsusceptibility toIGSCC.Thelowcarbon((.03percentcarbon)gradesof304and316stainless steelaredemonstrating amuchgreaterresistance toIGSCC.Theseand,otheralternate materials areundergoing extensive development and,evaluation forreducingtheprobability ofIGSCC.
IIi~
IIi~
5.SSESPreventiveMeasuresPP&LeffortshavecenteredonreducingtheprobabilityofoccurrenceofIGSCCforSSES.RecommendedmodificationstotheexistingSSESdesignwereevaluated,priortoimplementationagainstthefallowingcriteria:1.TheirpotentialforsubstantiallyreducingtheprobabilitythatXGSCCwilloccur;2.Theirpotentialforsubstantiallyreducingthetimerequired.todetectcracksorleaksresultingfromXGSCC;3.Theirpotentialforcreatingotherproblemswhichwouldeitherbeasbad.as,orworsethan,thecurrentproblem.5.1EnvironmentCurrent'nalysesindicatethatamongtheenvironmentrelated.contributorstothecurrentZGSCCprobleminBWR's,thedissolvedoxygenconcentrationofthereactorcoolantisprobablythemostsignificant.Oxygenlevelscanbecontrolled,eitherchemically,mechanically,oroperationally.5.1.1ChemicalControlSincethereisnouniversalinhibitor'forimprovingBMRwaterchemistryand.sincetherearelimited.dataconcerningtheuseofoxygenscavengersandneutralizersinBNR's,theiruseintheprimarycoolantisnotconsidered.atthistime.Futuredevelopmentsinthisarea,however,willbefallowed..5.1.2MechanicalControlPrimaryoxygenremovalisaccomplishedinthecondenserduringnormaloperation.Duringthisphasetheoxygenlevelismaintained.atapproximately'$.0ppb.Duringanycombinationofpartialload.(startup,shutdown,hotstandbyandsomeabnormalevents)theoxygenleveltend.stoincreasetowardsaturation(approximately8.0ppm).TherehavebeentwomajordesignchangeswhichPPRLhasmadetoimprovethewaterchemistryatSSES.5.1.2.1ControlRod.Drive(CRD)PumpSuctionRelocationPPMpreviouslyrelacatedtheCRDpumpsuctionfromthecondensatestoragetanktothecondensatemakeup/rejectline.Thepurposeofthislineistocontrolprimary.cyclewaterinventorybymakingupfromorrejectingtothecondensatestoragetank.Understeadyloadconditionsthislinereceivesaconstantdischargefromthecondenserdue toprimarycycleinfluentwatersourcessuchastheCRDsystemitself.Hence',locatingtheCRDpumpsuctiononthemakeup/regectlineresultsinutilizationofwaterwiththelowestoxygenconcentrationsavailable(essentiallywaterwithfeedwaterquality)mostofthetime.Atthetimetheabovechangewasmade,PALbelievedthatthischange,inadditiontootherchangesmade,wasadequatetosufficientlyreducetheprobabilityofIGSCC.Sincethattime,however,ppM,hasfound.thatcontrollingthe02concentrationasaneffectivemeansofcontrollingIGSCCrequires02controlduringallphasesofplantoperation,notgustnormaloperation.Forthisreason,PHkLadded,amechanicaldeaerationsystem(seesection5.1.2.2),5.1.2.2MechanicalVacuumDeaerationBasedonmorerecentdata,pp&Lhastakenthestepstoadd.amechanicalvacuumdeaerationsystematSSES.This02controlsystemwilloperateduringallphasesofplantoperationexceptnormaloperation.Itwillmaintainthe.02concentrationintheprimarycoolanttolessthan250ppb.Thisrecentchangewasmadeinanefforttoreducethecorrosivenatureoftheprimaryfluidaslowaspossible.ItisPP8cL'spreferencetohavethe02controlsysteminstalledand.operatingpriortoplantstartup.$4143OperatingProceduresLinesconnectedtothereactorvesselwhicharenormallystagnantorexperiencelowflowconditionsmayaccumulatedissolvedoxygenconcentrationswhicharehighrelativetogeneralreactorwater.Startup,Shutdown,HotStandbyand.abnormaleventsareofparticularsignificance.Totheextentpractical,procedureswillbedevelopedwhichwillminimizedissolvedoxygenconcentrationsinstagnantorlowflowlinesand/orreducethetotaltimeofstagnantconditions.ThewaterqualitysamplingsystemhasbeenupgradedinordertoalerttheplantoperatorsofadversewaterconditionsconducivetoIGSCC.Itincludescontinuousmonitoringoffeedwaterandreactorwaterfordissolvedpxygenconcentration,conductivityand.pHand.continuousmonitoringoftheCRDsystemwaterfordissolvedoxygenconcentrationand.conductivity."Thesamplingsystem,automaticallyalarmswhenwaterqualityconditionsconsideredtobeadversetoBWRoperationarereached.  
5.SSESPreventive MeasuresPP&Leffortshavecenteredonreducingtheprobability ofoccurrence ofIGSCCforSSES.Recommended modifications totheexistingSSESdesignwereevaluated, priortoimplementation againstthefallowing criteria:
1.Theirpotential forsubstantially reducingtheprobability thatXGSCCwilloccur;2.Theirpotential forsubstantially reducingthetimerequired.
todetectcracksorleaksresulting fromXGSCC;3.Theirpotential forcreatingotherproblemswhichwouldeitherbeasbad.as,orworsethan,thecurrentproblem.5.1Environment Current'nalyses indicatethatamongtheenvironment related.contributors tothecurrentZGSCCprobleminBWR's,thedissolved oxygenconcentration ofthereactorcoolantisprobablythemostsignificant.
Oxygenlevelscanbecontrolled, eitherchemically, mechanically, oroperationally.
5.1.1ChemicalControlSincethereisnouniversal inhibitor'for improving BMRwaterchemistry and.sincetherearelimited.dataconcerning theuseofoxygenscavengers andneutralizers inBNR's,theiruseintheprimarycoolantisnotconsidered.
atthistime.Futuredevelopments inthisarea,however,willbefallowed..
5.1.2Mechanical ControlPrimaryoxygenremovalisaccomplished inthecondenser duringnormaloperation.
Duringthisphasetheoxygenlevelismaintained.
atapproximately
'$.0ppb.Duringanycombination ofpartialload.(startup,
: shutdown, hotstandbyandsomeabnormalevents)theoxygenleveltend.stoincreasetowardsaturation (approximately 8.0ppm).TherehavebeentwomajordesignchangeswhichPPRLhasmadetoimprovethewaterchemistry atSSES.5.1.2.1ControlRod.Drive(CRD)PumpSuctionRelocation PPMpreviously relacated theCRDpumpsuctionfromthecondensate storagetanktothecondensate makeup/reject line.Thepurposeofthislineistocontrolprimary.cyclewaterinventory bymakingupfromorrejecting tothecondensate storagetank.Understeadyloadconditions thislinereceivesaconstantdischarge fromthecondenser due toprimarycycleinfluentwatersourcessuchastheCRDsystemitself.Hence',locatingtheCRDpumpsuctiononthemakeup/regect lineresultsinutilization ofwaterwiththelowestoxygenconcentrations available (essentially waterwithfeedwater quality)mostofthetime.Atthetimetheabovechangewasmade,PALbelievedthatthischange,inadditiontootherchangesmade,wasadequatetosufficiently reducetheprobability ofIGSCC.Sincethattime,however,ppM,hasfound.thatcontrolling the02concentration asaneffective meansofcontrolling IGSCCrequires02controlduringallphasesofplantoperation, notgustnormaloperation.
Forthisreason,PHkLadded,amechanical deaeration system(seesection5.1.2.2),
5.1.2.2Mechanical VacuumDeaeration Basedonmorerecentdata,pp&Lhastakenthestepstoadd.amechanical vacuumdeaeration systematSSES.This02controlsystemwilloperateduringallphasesofplantoperation exceptnormaloperation.
Itwillmaintainthe.02concentration intheprimarycoolanttolessthan250ppb.Thisrecentchangewasmadeinanefforttoreducethecorrosive natureoftheprimaryfluidaslowaspossible.
ItisPP8cL'spreference tohavethe02controlsysteminstalled and.operating priortoplantstartup.$4143Operating Procedures Linesconnected tothereactorvesselwhicharenormallystagnantorexperience lowflowconditions mayaccumulate dissolved oxygenconcentrations whicharehighrelativetogeneralreactorwater.Startup,Shutdown, HotStandbyand.abnormaleventsareofparticular significance.
Totheextentpractical, procedures willbedeveloped whichwillminimizedissolved oxygenconcentrations instagnantorlowflowlinesand/orreducethetotaltimeofstagnantconditions.
Thewaterqualitysamplingsystemhasbeenupgradedinordertoalerttheplantoperators ofadversewaterconditions conducive toIGSCC.Itincludescontinuous monitoring offeedwater andreactorwaterfordissolved pxygenconcentration, conductivity and.pHand.continuous monitoring oftheCRDsystemwaterfordissolved oxygenconcentration and.conductivity."
Thesamplingsystem,automatically alarmswhenwaterqualityconditions considered tobeadversetoBWRoperation arereached.  


Procedureswillbedeveloped.whichwillminim1zeexcessiveoxygenconcentrationsintheprimarycycleand,toenableplantoperatorstotakeimmediateactiontoprotecttheplantfromprolongedoperationwithadversewaterqualitycond.itions.5.2StressStressaloneisnotparticularlys1gnificantsofarastheoverallcorrosionofmetalsisconcerned.Whencombinedwithacorrosiveenv1ronment,however,theappl1cationofsufficienttensilestressinsusceptiblematerialscanlead.tostresscorrosioncracking.Areduction1ntotaltensilestressinlinesconsidered.susceptibletoIGSCCcould.thereforebeconsidered.beneficial.Inanattempttoreduceoveralltensilestress,pipinglocatedinsidecontainmentand.connected.directlytoeithertheReactorPressureVessel(RPV)ortheReactorRecirculationSystemwasreviewed,todetermineifdesignand/orfabricatingcontributionstotensilestresslevelscouldbereduced..5.2.1DesignStressesThecombinedeffectsofservice,internalpressure,deadweightand.thermalstresseswerereviewedand.allpipingsystemswereconfirmedtohavelayoutswhichlimited.theircontributionstototalstresstoalevelconsideredtobeaslowasreasonablyach1evable.RecognizingtheparticularsusceptibilityoftheCoreSpraySysteminfectionlines,alternateroutingswerechoseninorderthatthethermalstresscomponentoftotalstressisred.ucedby25$.522FabricationStressesThedifficultyinassuringcomplianceunderallshopand.fieldfabricatingconditions,limitstheeffectivenessofprocedureswhichmightbedeveloped.inthisarea.However,s1ncestresslevelsinnon-stressrelieved.austeniticstainlesssteelpipingcanequalorexceed.yield.,anyprocedureswhichmightsignificantlyreducefit-up,initialfabrication,orwelding-induced.stressescannotbeoverlooked..5.2.2.1Fit-upCodetoleranceforalignmentareccmpliedwithtoassureminimumstressfrommisalignmntandminimumdegradat1onoffatigueresistance.5.2.2.2Initial.Fabrication(shop)Thepipematerialispurchased.1nthesolutionannealed.condition.Normally,spoolp1ecesarenotsolutionannealed.duetothedifficultyofmaintainingdesireddimensions.
Procedures willbedeveloped.
5.2.2.3Melding-InducedStressPALrecognizesthatwhenausteniticsta1nlesssteelsarewelded,somelevelofresidualstressand.sens1tizationispresent.Acompromisebetweenheatinputcontrolandtheresultingcoolingratemustbeachievedinorderthatacceptablelevelsofres1dualstressand.sensit1zationcanbeachievedwithoutsacrificinggoodpenetrationandfusion.Unfortunately,precisequantitativevaluesofheatinput,coolingrate,etc.,whichwi.llinsureconsistentlygoodqualityweldsresistanttoIGSCCarenotavailable.Therefore,PPMreliesonpastindustrialexper1enceforguidance.PP8Lhasadoptedthefollowingmeasuresforfieldweldingtheapplicable11nes.Thesemeasureshelpreducewelding-inducedstresses,w1thoutcreatingadditionalproblems,toalevelaslowascanbeexpectedusingnormalweldingpractices.5.2.2.3.1HeatInputNopreheat(inexcessoftheacceptableworkingrangeof60Fto150F).b.C~dOInterpasstemperaturelimitedto350F.Blockweldingprohibited.Electrodesize11mitedto5/32"h1ax.forSMAMandl/8"Max.forGTAMwhicheffectivelylimitstheheatinput.5.2.2.3.2JointDesigna.TherootismadewithGTAMut111'z1nghandfedfillerwireoraconsumable1nserttoinsurecompletepenetrationandgoodfusion.b.Theextended-land)ointdesignhasnoinherentproblemswithlackofpenetration,lackoffusionorexcessiveresidualstress.C~Aninertgaspurge1susedpriortoweld.ingandinertgasbackingisused.duringtheweld1ngofthefirstpassestoinsureagood.rootcontourminimizing'theoccurrenceofanycreviceswhichmightleadtocorrosionproblems.Asmoothfinishcontourisspecified(1.e.,noexcessiveundercut,excessivereinforcement,coarser1pples,etc.)toreducetheoccurrenceof"notches"whichcandetrimental+affectfatiguestrengthorcorrosionresistance.
whichwillminim1zeexcessive oxygenconcentrations intheprimarycycleand,toenableplantoperators totakeimmediate actiontoprotecttheplantfromprolonged operation withadversewaterqualitycond.itions.
105.2.2.3.3FillerMetalTominim1zemicrofissuringand,sensitizationproblems,308Lfillermetalor309and.309Lfillermetalisspecified.w1thminimumdeltaferritecontentsof8percentand.5percentrespectively.5.2.2.3.4CleanlinessTopreventcontaminationofthejoint:a.Grease,oilandothercontaminantsareremoved.fromthejointand.thef1llermetalpriortomakingtheweld.b.Onlymarkingcrayons,chalk,1nkandtemperatureindicatingcrayonswhicharecertified.tobelowinhalogenand,sulfurcontentareused.c.Onlycleaningsolventswh1charenotharmfultoausteniticstainlesssteelareused,.d..Stainlesssteelwirebrushesareused,.e.Grindingwheelsusedonothermaterialsarenotused.onstainlesssteel.f.GrindingwheelsarenotusedonI.D.pipesurfaces.Ifcleaningisnecessary,flapperwheelsshallbeused.TheexistingmethodsandproceduresforQualityControl/QualityAssuranceoftheaboveareadequatetoinsurethattheseprovisionsarefollowedand.thattheresultswillbeconsistentw1thwhatwasspecified..Restrictionsconsistentwiththoseaboveapplyequallytoshopand.fieldsubcontractwelding.5.2.3MethodsofStressReductionDuetocontinuedreportsofIGSCCsincePPMfirstformd.apositiononthesubject,PP&Lhassteppeclupitsmonitoringoftheproblemanditspossiblecountermeasures.Thosecountermeasuresthatarebeinginvestigated./evaluated.whichdealwithstressreductionareSolutionHeatTreatment(SHT),HeatSinkWelding(HSW),and.Induct1onHeatingStressImprovement(IHSI).5.2.3.1SolutionHeatTreatmentThisIGSCCcountermeasurestressrelievesshopwelcls.beforethesectionsofpipeareshipped.tothefieldforinstallation.Thismethod.canonlybeusedonshopweld.s,and.then,onlywhenthepipeshavenotbeeninstalled..
5.2StressStressaloneisnotparticularly s1gnificant sofarastheoverallcorrosion ofmetalsisconcerned.
ForSSESmostofthetargetlinesforwhichnoothercountermeasures(i.e.,materialchanges)havebeentaken,havealreadybeeninstalled..However,theshopweldsontherecirculationgetpumpr1sersunderwentSHTbecausePPMbelievedtheselinestobeextremelysusceptibletoIGSCC.Thef1eld.weldendsoftheriserswerealsocorrosionresistantclad..Thisprocesswillbed.iscussedinalatersection.5.2.3.2HeatS1nkWeldingThisIGSCCcountermeasurerequirescoolingtheIDofthepipewithcoolingwateraftertherootpassoftheweldhasbeencompleted.Thisprocesscauses-theresultantresidualstressesontheIDofthepipetobecompressiveratherthantensileaswould.befound.withnormalweldingpractices.ResultantcompressivestressespreventXGSCC,ThiscountermeasurehasnotbeenusedatSSES.However,BechtelispresentlyperformingafeasibilityevaluationontheuseofHSWforselected.linesatSSES.5.2.3.3.InductionHeatingStressXmprovementThisIGSCCcountermeasureisused.afterthefieldweldshavebeencompleted..TheprocessinvolvesheatingtheO.D.ofthepipewithaninductioncoilwhilecoolingtheI.D.withcoolingwater.ThisprocesscausestheresultantstressesontheI.D.ofthepipetobecompressiveratherthantensile,thuspreventingIGSCC.ThisprocesshasnotbeenusedatSSES.PresentlyGE1sintheprocessofdeveloping/qualifyingthisprocedureforuseonBWR'sintheUnitedStates(Reported.lytheJapanesehaveused.thisproceduresuccessfullyontheirnuclear~powerplants,).PP8cLintend,stotracktheprogressofGEand.usetheprocedureonsusceptiblelinesifand,whentheprocedureisdetermined.tobefeasible.5.3hfaterialDuetotherestrictionsofcoolantchemistryandtotaltens1lestresslevels,theuseofsubstitutematerialswhicharelesssusceptibletoXGSCCwereconsidered..ThelackofsignificantoperatingdataformaterialsotherthancarbonsteelorType304and.Type316stainlesssteelslimitstheoptions,however.Dur1ngthedesignoftheplant,attentionwasgiventominimizingproblemsrelatedtogrosscorrosion.StainlesssteelwaschosenforCoreSpraylinesinsidecontainment,condenserand.'feedwaterheatertubes,and.ASSAMA155GradeKC70,Class1feedwaterpipe.PP8cLis,therefore,unwillingtousecarbonsteelasanIGSCCf1x.
Whencombinedwithacorrosive env1ronment, however,theappl1cation ofsufficient tensilestressinsusceptible materials canlead.tostresscorrosion cracking.
TheprincipaldrawbacktothecontinueduseofType304and.Type316stainlesssteelforNSSSpipingistheirsusceptibilitytoIGSCC.PP8cLbelievesthissusceptib1lityisrelatedtosensitizationwhichoccursadjacenttoaweldintheheat-affectedzone.Sensitizationisatemperaturedependentmetallurgicalphenomenonwhichresultsintheformationofchromiumcarbideatgrainboundarieslocatedintheheat-affected.zoneofaweld.Therefore,1twaslogicalto11mitthecarboncontentofsusceptiblelines.Originally,thehistoryoftheIGSCCproblemformedthebasisoftheassumptionthatthecomb1nationofresidualstressandsensitizationwasinsufficienttoresultinahighprobabilityoffailureduetoIGSCCforlinesinthereactorcoolantpressureboundarylargerthan12"diameterNPS.Thefocusforpossiblematerialsubstitutionwas,therefore,onthoselineswh1chwerelessthanorequalto12"diameterNPS.Anysuchsubstitutionswouldapplyequallytopipefittings.However',valvesand.containmentpenetrationflued,headsarenotincludedastheyareofsufficientmasstobesubstantiallylesssusceptibletoIGSCC.~Basedontheaboveassumption,Type304Lstainlesssteelwasusedforallstainlesspipingwithinthereactorcoolantpressureboundarywhichis4"diameterNPSorsmallerwithasupplementalrequirementof0.030percentmaximumcarbon(withtheexceptionoftheRecirculat1onSystemDischargeGateValve'ypassLine).Sta1nlesspipinglocatedwithinthereactorcoolantpressureboundarywhichisgreaterthan4"butlessthan12"diameterNPSwillbeType304stainlesssteelwithamaximumcarboncontentof0.030percent.1hesetwomaterialsarevirtuallyidenticalmetallurgicallybutPPEcLisunwill1ngtosacrificethemechanicalpropertiesof304forcertainpipingsystems.Tablelident1fiespipingforwhichachangeinmaterialwasjustified,thematerialprevious+specified,andthereplacementmaterialchosentomitigatetheprobabilityofIGSCC.Sincethetimetheabovematerialchangesweremade,additionalinc1dentsofIGSCChaveshownthattheassumptionthatonlythoselineswhichare12"d1ameterNPSorlessaresusceptibletoIGSCCisincorrect.Therefore,alllinesmustbeconsideredwhenattemptingtoeliminateorreduceIGSCC.Inadditiontosimplemater1alreplacement,theother"mater1al"relatedIGSCCcountermeasurewhichcanbeevaluatedisCorrosionRes1stantCladding(CRC).Thiscountermeasurecombinescladdingthefieldweldedpipeendswithahighlycorrosionresistantmetalwithsolutionannealingwhicheffect1velyprovidesacorrosionresistantbarrierbetweentheheataffectedbasemetaland,theoxygenatedreactorcoolant(corrosivefluid.).
Areduction 1ntotaltensilestressinlinesconsidered.
13Asdiscussed.inSection5.3.4ofth1sreport,PPM,utilizedCRContherecirculationgetpumprisers.Duetotheirparticularsignificancewithregardtothecurrentproblem,theCoreSpray,ReactorRecirculationSystemDischargeGateValveBypassLine,ControlRodDriveReturnLine,andRecirculationR1serPipesarediscussedbelow.5.3.1CoreSpraySystemThatportionofthecorespraysystemwhichislocatedwithintheprimarycontainmntwill,forSusquehannaSES,bema'defrom12"diameterNPS,Type304StainlessSteelPipewithsupplementalmaximumcarbonlim1tationof0.030percent.pipeandfittingswillbehandledsimilarly.532ReactorRecirculationSystmDischargeGateValveBypassZineFromanoperationalstandpointpp&Ldoesnotwishtodeletethislin.Itisconsideredimportantfromthefollowingstandpoints;l.Itprovidesameansofpreheatinganidlerecirculationloop.2.Itreducesthermalshockseenbythecomponentsofan1dleloop+/3.Itprovidespressureequalization.onbothsidesofthedischargegatevalvetoassureproperventingandclosureofthevalve.Iteliminatescuttingandwiredrawingofthedischargegatevalveseat.The4"diameterNPSlinewillbefabricated.fromType304stainlesssteelwithasupplementalmaximumcarbonlimitationof0.030percent.Thismaterialchoiceresultsfromthedes1retolimittheprobabilityofIGSCCwhileretainingthemechanicalpropertiesofandtheexistingstressanalysisforType304stainlesssteel.Pipeandfittingswillbehandledsimilarly.533ControlRodDriveReturnLineThis3"diameterlinewaschang'edfrom304SSto304LSSwhich,1twasbelieved.,would.solvetheproblemofIGSCC.Subsequenttothischangetherewerenumerousreportedinc1dentsofcrackingintheCRDReturnLinenozzle.Theseincidentsofcrackingwereattributedtoexcessivethermalgradientsacross thenozzleratherthanIGSCC.GeneralElectric'srecommendationwastodeletethereturnlineand.makeotherchangestothesystemtomainta1nthesystemdesignfunction.PPEcLconcurred..withGE'srecommendationand.deleted.thereturnlin.Thisaction(1)eliminatedtheproblemofnozzlecrackingduetothermalgrad.1entsand.(2)eliminatedthepossibilityofpipcrackingduetoIGSCC.5.34Rec1rculationRiserPipesThe10'ecirculationriserp1pesleadingfromtherecirculationheadertothegetpumpshaverecentlyexperiencedIGSCCatotheroperatingplants.Thecrackshavebeenformed.intheheataffected.zonesofthethermalsleevetosafeend.attachmentweld.s.Thepipeshavebeenfabricatedfrom304sta1nlesssteel.Thesafeend.sareImonel600,and.thenozzlesarecarbonsteelclad.withstainlesssteel.PP8:LhasmadethefollowingchangeswhichwillminimizethepossibilityofthesepipescrackingduetoIGSCCofSusquehannaSES.1.ThepipetosafeendandpipetoteeweldswillhavetheirID'scladwith308Lweld,materialintheheataffected.areapriortowelding.2.Theriserpipeswillbesolutionheattreated.toeliminateresidualstressesfromtheelbowtopipeshopweld.s,andtheCRCprocess.3.Theseweldswillthenbefieldwelded.using308Lweldingrods.Thisprocesswillprevent304stainlesssteelintheheataffectedareafromcomingincontactwiththeprocessfluid.
susceptible toIGSCCcould.therefore beconsidered.
156.ReferencesSourceGENRCAS%1DocumentNEDO-21000NUHEG75/067"StressCorrosionCrackingofMetals-AStateoftheArt"DateJu~,1975October,1975October,1971NATO"TheTheoryofStressCorrosionCrackinginAlloys"October,1971"FundamentalAspectsofStressCorrosionCracking"September,1967UnitedStatesSenateJointHearingConcerning"NuclearRegulatoryCommissionActionRequiringSafetyInspectionsWhichResultedinShutdownofCertainNuclearPowerPlants"February,1975 16SUSQUEHANNASTEAMELECTRICSTATIONTABLZ1MA'JRRIALCHANGESPipeDescriptionHead.SprayCoreSprayInfluentSize~NPS12IIpreviousMaterialType304SSNewMaterialCarbon-Limited.Type304SSControlRod,Drive3"HydraulicReturnCRDReturnLineHasBeenDeleted.StandbyLiquid.ControlReactorWaterCleanupEffluent1-1/2"4IIType304SStofirstvalvepthenCarbonSteelType304LSStofirstvalve,thentoCarbonSteelInstrumentpipingVent,Drain,and.TestConnectionsShownonFigure11",2"Type304SS4IIType304SSType304LSSType304LSSRecirculation'ystemBypassBottomDrain4II4IIType304SSType304SSCarbon-Limited,Type'304SSType304LSSTFO:bah 17M~1MCONTAINMENTPENETRATIONHEADSPRAYREACTORVENTTOINSTATMVENTVENTTOlASt,VESSEI.VENTNLIAINSTEAMlFEEOIVATERTOVESSELI6>>MAINSTEAMFEEOWATERTOVESSELSLCTESTCONN'ECTIONVENTVCONNECTIONDRAINCONNfCTIONSTANDBYLIGVIDCONTROLSYSTEMREACTORIYATERCLEANUPSYSTEMRESIDUALNEATREMOVALSYSTEMCONTROLAODDRIVESYSTEM12"CORESPRAYM1>>121>>12"REACTORPRESSUREVESSEL12"I>>1>>>>COR'ESPRAY,CRORETURN(DELETED}LINE>>RHRRETURN24"AECIRCYLOOPJ24RECIRC+LOOP24"24RHRRETURNI>>M120RHRSUCTIONRECIRCg26"PILOO20>>20"4GOTTOMDRAIN4>>4>>4>>RECIRC9LOOPINSTCONN11/2"SLCRWCUSUCTION6"6"INSTCONNV1>>41"LTM0IOOISOBGIFigure1}}
beneficial.
Inanattempttoreduceoveralltensilestress,pipinglocatedinsidecontainment and.connected.
directlytoeithertheReactorPressureVessel(RPV)ortheReactorRecirculation Systemwasreviewed, todetermine ifdesignand/orfabricating contributions totensilestresslevelscouldbereduced..
5.2.1DesignStressesThecombinedeffectsofservice,internalpressure, deadweight and.thermalstresseswerereviewedand.allpipingsystemswereconfirmed tohavelayoutswhichlimited.theircontributions tototalstresstoalevelconsidered tobeaslowasreasonably ach1evable.
Recognizing theparticular susceptibility oftheCoreSpraySysteminfection lines,alternate routingswerechoseninorderthatthethermalstresscomponent oftotalstressisred.ucedby25$.522Fabrication StressesThedifficulty inassuringcompliance underallshopand.fieldfabricating conditions, limitstheeffectiveness ofprocedures whichmightbedeveloped.
inthisarea.However,s1ncestresslevelsinnon-stress relieved.
austenitic stainless steelpipingcanequalorexceed.yield.,anyprocedures whichmightsignificantly reducefit-up,initialfabrication, orwelding-induced.stressescannotbeoverlooked..
5.2.2.1Fit-upCodetolerance foralignment areccmpliedwithtoassureminimumstressfrommisalignm ntandminimumdegradat1on offatigueresistance.
5.2.2.2Initial.Fabrication (shop)Thepipematerialispurchased.
1nthesolutionannealed.
condition.
: Normally, spoolp1ecesarenotsolutionannealed.
duetothedifficulty ofmaintaining desireddimensions.
5.2.2.3Melding-Induced StressPALrecognizes thatwhenaustenitic sta1nless steelsarewelded,somelevelofresidualstressand.sens1tization ispresent.Acompromise betweenheatinputcontrolandtheresulting coolingratemustbeachievedinorderthatacceptable levelsofres1dualstressand.sensit1zation canbeachievedwithoutsacrificing goodpenetration andfusion.Unfortunately, precisequantitative valuesofheatinput,coolingrate,etc.,whichwi.llinsureconsistently goodqualityweldsresistant toIGSCCarenotavailable.
Therefore, PPMreliesonpastindustrial exper1ence forguidance.
PP8Lhasadoptedthefollowing measuresforfieldweldingtheapplicable 11nes.Thesemeasureshelpreducewelding-inducedstresses, w1thoutcreatingadditional
: problems, toalevelaslowascanbeexpectedusingnormalweldingpractices.
5.2.2.3.1 HeatInputNopreheat(inexcessoftheacceptable workingrangeof60Fto150F).b.C~dOInterpass temperature limitedto350F.Blockweldingprohibited.
Electrode size11mitedto5/32"h1ax.forSMAMandl/8"Max.forGTAMwhicheffectively limitstheheatinput.5.2.2.3.2 JointDesigna.TherootismadewithGTAMut111'z1ng handfedfillerwireoraconsumable 1nserttoinsurecompletepenetration andgoodfusion.b.Theextended-land
)ointdesignhasnoinherentproblemswithlackofpenetration, lackoffusionorexcessive residualstress.C~Aninertgaspurge1susedpriortoweld.ingandinertgasbackingisused.duringtheweld1ngofthefirstpassestoinsureagood.rootcontourminimizing
'theoccurrence ofanycreviceswhichmightleadtocorrosion problems.
Asmoothfinishcontourisspecified (1.e.,noexcessive
: undercut, excessive reinforcement, coarser1pples,etc.)toreducetheoccurrence of"notches" whichcandetrimental+
affectfatiguestrengthorcorrosion resistance.
105.2.2.3.3 FillerMetalTominim1zemicrofissuring and,sensitization
: problems, 308Lfillermetalor309and.309Lfillermetalisspecified.
w1thminimumdeltaferritecontentsof8percentand.5percentrespectively.
5.2.2.3.4 Cleanliness Topreventcontamination ofthejoint:a.Grease,oilandothercontaminants areremoved.fromthejointand.thef1llermetalpriortomakingtheweld.b.Onlymarkingcrayons,chalk,1nkandtemperature indicating crayonswhicharecertified.
tobelowinhalogenand,sulfurcontentareused.c.Onlycleaningsolventswh1charenotharmfultoaustenitic stainless steelareused,.d..Stainless steelwirebrushesareused,.e.Grindingwheelsusedonothermaterials arenotused.onstainless steel.f.GrindingwheelsarenotusedonI.D.pipesurfaces.
Ifcleaningisnecessary, flapperwheelsshallbeused.Theexistingmethodsandprocedures forQualityControl/QualityAssurance oftheaboveareadequatetoinsurethattheseprovisions arefollowedand.thattheresultswillbeconsistent w1thwhatwasspecified..
Restrictions consistent withthoseaboveapplyequallytoshopand.fieldsubcontract welding.5.2.3MethodsofStressReduction Duetocontinued reportsofIGSCCsincePPMfirstformd.apositiononthesubject,PP&Lhassteppeclupitsmonitoring oftheproblemanditspossiblecountermeasures.
Thosecountermeasures thatarebeinginvestigated.
/evaluated.
whichdealwithstressreduction areSolutionHeatTreatment (SHT),HeatSinkWelding(HSW),and.Induct1on HeatingStressImprovement (IHSI).5.2.3.1SolutionHeatTreatment ThisIGSCCcountermeasure stressrelievesshopwelcls.before thesectionsofpipeareshipped.tothefieldforinstallation.
Thismethod.canonlybeusedonshopweld.s,and.then,onlywhenthepipeshavenotbeeninstalled..
ForSSESmostofthetargetlinesforwhichnoothercountermeasures (i.e.,materialchanges)havebeentaken,havealreadybeeninstalled..
However,theshopweldsontherecirculation getpumpr1sersunderwent SHTbecausePPMbelievedtheselinestobeextremely susceptible toIGSCC.Thef1eld.weldendsoftheriserswerealsocorrosion resistant clad..Thisprocesswillbed.iscussed inalatersection.5.2.3.2HeatS1nkWeldingThisIGSCCcountermeasure requirescoolingtheIDofthepipewithcoolingwateraftertherootpassoftheweldhasbeencompleted.
Thisprocesscauses-the resultant residualstressesontheIDofthepipetobecompressive ratherthantensileaswould.befound.withnormalweldingpractices.
Resultant compressive stressespreventXGSCC,Thiscountermeasure hasnotbeenusedatSSES.However,Bechtelispresently performing afeasibility evaluation ontheuseofHSWforselected.
linesatSSES.5.2.3.3.Induction HeatingStressXmprovement ThisIGSCCcountermeasure isused.afterthefieldweldshavebeencompleted..
TheprocessinvolvesheatingtheO.D.ofthepipewithaninduction coilwhilecoolingtheI.D.withcoolingwater.Thisprocesscausestheresultant stressesontheI.D.ofthepipetobecompressive ratherthantensile,thuspreventing IGSCC.ThisprocesshasnotbeenusedatSSES.Presently GE1sintheprocessofdeveloping/qualifying thisprocedure foruseonBWR'sintheUnitedStates(Reported.ly theJapanesehaveused.thisprocedure successfully ontheirnuclear~powerplants,).
PP8cLintend,stotracktheprogressofGEand.usetheprocedure onsusceptible linesifand,whentheprocedure isdetermined.
tobefeasible.
5.3hfaterial Duetotherestrictions ofcoolantchemistry andtotaltens1lestresslevels,theuseofsubstitute materials whicharelesssusceptible toXGSCCwereconsidered..
Thelackofsignificant operating dataformaterials otherthancarbonsteelorType304and.Type316stainless steelslimitstheoptions,however.Dur1ngthedesignoftheplant,attention wasgiventominimizing problemsrelatedtogrosscorrosion.
Stainless steelwaschosenforCoreSpraylinesinsidecontainment, condenser and.'feedwater heatertubes,and.ASSAMA155GradeKC70,Class1feedwater pipe.PP8cLis,therefore, unwilling tousecarbonsteelasanIGSCCf1x.
Theprincipal drawbacktothecontinued useofType304and.Type316stainless steelforNSSSpipingistheirsusceptibility toIGSCC.PP8cLbelievesthissusceptib1lity isrelatedtosensitization whichoccursadjacenttoaweldintheheat-affectedzone.Sensitization isatemperature dependent metallurgical phenomenon whichresultsintheformation ofchromiumcarbideatgrainboundaries locatedintheheat-affected.
zoneofaweld.Therefore, 1twaslogicalto11mitthecarboncontentofsusceptible lines.Originally, thehistoryoftheIGSCCproblemformedthebasisoftheassumption thatthecomb1nation ofresidualstressandsensitization wasinsufficient toresultinahighprobability offailureduetoIGSCCforlinesinthereactorcoolantpressureboundarylargerthan12"diameterNPS.Thefocusforpossiblematerialsubstitution was,therefore, onthoselineswh1chwerelessthanorequalto12"diameterNPS.Anysuchsubstitutions wouldapplyequallytopipefittings.
However',
valvesand.containment penetration flued,headsarenotincludedastheyareofsufficient masstobesubstantially lesssusceptible toIGSCC.~Basedontheaboveassumption, Type304Lstainless steelwasusedforallstainless pipingwithinthereactorcoolantpressureboundarywhichis4"diameterNPSorsmallerwithasupplemental requirement of0.030percentmaximumcarbon(withtheexception oftheRecirculat1on SystemDischarge GateValve'ypass Line).Sta1nless pipinglocatedwithinthereactorcoolantpressureboundarywhichisgreaterthan4"butlessthan12"diameterNPSwillbeType304stainless steelwithamaximumcarboncontentof0.030percent.1hesetwomaterials arevirtually identical metallurgically butPPEcLisunwill1ng tosacrifice themechanical properties of304forcertainpipingsystems.Tablelident1fies pipingforwhichachangeinmaterialwasjustified, thematerialprevious+
specified, andthereplacement materialchosentomitigatetheprobability ofIGSCC.Sincethetimetheabovematerialchangesweremade,additional inc1dents ofIGSCChaveshownthattheassumption thatonlythoselineswhichare12"d1ameterNPSorlessaresusceptible toIGSCCisincorrect.
Therefore, alllinesmustbeconsidered whenattempting toeliminate orreduceIGSCC.Inadditiontosimplemater1alreplacement, theother"mater1al" relatedIGSCCcountermeasure whichcanbeevaluated isCorrosion Res1stant Cladding(CRC).Thiscountermeasure combinescladdingthefieldweldedpipeendswithahighlycorrosion resistant metalwithsolutionannealing whicheffect1vely providesacorrosion resistant barrierbetweentheheataffectedbasemetaland,theoxygenated reactorcoolant(corrosive fluid.).
13Asdiscussed.
inSection5.3.4ofth1sreport,PPM,utilizedCRContherecirculation getpumprisers.Duetotheirparticular significance withregardtothecurrentproblem,theCoreSpray,ReactorRecirculation SystemDischarge GateValveBypassLine,ControlRodDriveReturnLine,andRecirculation R1serPipesarediscussed below.5.3.1CoreSpraySystemThatportionofthecorespraysystemwhichislocatedwithintheprimarycontainmntwill,forSusquehanna SES,bema'defrom12"diameterNPS,Type304Stainless SteelPipewithsupplemental maximumcarbonlim1tation of0.030percent.pipeandfittingswillbehandledsimilarly.
532ReactorRecirculation SystmDischarge GateValveBypassZineFromanoperational standpoint pp&Ldoesnotwishtodeletethislin.Itisconsidered important fromthefollowing standpoints; l.Itprovidesameansofpreheating anidlerecirculation loop.2.Itreducesthermalshockseenbythecomponents ofan1dleloop+/3.Itprovidespressureequalization.
onbothsidesofthedischarge gatevalvetoassureproperventingandclosureofthevalve.Iteliminates cuttingandwiredrawingofthedischarge gatevalveseat.The4"diameterNPSlinewillbefabricated.
fromType304stainless steelwithasupplemental maximumcarbonlimitation of0.030percent.Thismaterialchoiceresultsfromthedes1retolimittheprobability ofIGSCCwhileretaining themechanical properties ofandtheexistingstressanalysisforType304stainless steel.Pipeandfittingswillbehandledsimilarly.
533ControlRodDriveReturnLineThis3"diameterlinewaschang'edfrom304SSto304LSSwhich,1twasbelieved.,
would.solvetheproblemofIGSCC.Subsequent tothischangetherewerenumerousreportedinc1dents ofcrackingintheCRDReturnLinenozzle.Theseincidents ofcrackingwereattributed toexcessive thermalgradients across thenozzleratherthanIGSCC.GeneralElectric's recommendation wastodeletethereturnlineand.makeotherchangestothesystemtomainta1nthesystemdesignfunction.
PPEcLconcurred..with GE'srecommendation and.deleted.thereturnlin.Thisaction(1)eliminated theproblemofnozzlecrackingduetothermalgrad.1ents and.(2)eliminated thepossibility ofpipcrackingduetoIGSCC.5.34Rec1rculation RiserPipesThe10'ecirculation riserp1pesleadingfromtherecirculation headertothegetpumpshaverecentlyexperienced IGSCCatotheroperating plants.Thecrackshavebeenformed.intheheataffected.
zonesofthethermalsleevetosafeend.attachment weld.s.Thepipeshavebeenfabricated from304sta1nless steel.Thesafeend.sareImonel600,and.thenozzlesarecarbonsteelclad.withstainless steel.PP8:Lhasmadethefollowing changeswhichwillminimizethepossibility ofthesepipescrackingduetoIGSCCofSusquehanna SES.1.ThepipetosafeendandpipetoteeweldswillhavetheirID'scladwith308Lweld,materialintheheataffected.
areapriortowelding.2.Theriserpipeswillbesolutionheattreated.toeliminate residualstressesfromtheelbowtopipeshopweld.s,andtheCRCprocess.3.Theseweldswillthenbefieldwelded.using308Lweldingrods.Thisprocesswillprevent304stainless steelintheheataffectedareafromcomingincontactwiththeprocessfluid.
156.ReferencesSourceGENRCAS%1DocumentNEDO-21000 NUHEG75/067"StressCorrosion CrackingofMetals-AStateoftheArt"DateJu~,1975October,1975October,1971NATO"TheTheoryofStressCorrosion CrackinginAlloys"October,1971"Fundamental AspectsofStressCorrosion Cracking" September, 1967UnitedStatesSenateJointHearingConcerning "NuclearRegulatory Commission ActionRequiring SafetyInspections WhichResultedinShutdownofCertainNuclearPowerPlants"February, 1975 16SUSQUEHANNA STEAMELECTRICSTATIONTABLZ1MA'JRRIAL CHANGESPipeDescription Head.SprayCoreSprayInfluentSize~NPS12IIpreviousMaterialType304SSNewMaterialCarbon-Limited.
Type304SSControlRod,Drive3"Hydraulic ReturnCRDReturnLineHasBeenDeleted.StandbyLiquid.ControlReactorWaterCleanupEffluent1-1/2"4IIType304SStofirstvalvepthenCarbonSteelType304LSStofirstvalve,thentoCarbonSteelInstrument pipingVent,Drain,and.TestConnections ShownonFigure11",2"Type304SS4IIType304SSType304LSSType304LSSRecirculation'ystem BypassBottomDrain4II4IIType304SSType304SSCarbon-Limited, Type'304SSType304LSSTFO:bah 17M~1MCONTAINMENT PENETRATION HEADSPRAYREACTORVENTTOINSTATMVENTVENTTOlASt,VESSEI.VENT NLIAINSTEAMlFEEOIVATER TOVESSELI6>>MAINSTEAMFEEOWATER TOVESSELSLCTESTCONN'ECTION VENTVCONNECTION DRAINCONNfCTIONSTANDBYLIGVIDCONTROLSYSTEMREACTORIYATERCLEANUPSYSTEMRESIDUALNEATREMOVALSYSTEMCONTROLAODDRIVESYSTEM12"CORESPRAYM1>>121>>12"REACTORPRESSUREVESSEL12"I>>1>>>>COR'ESPRAY,CRORETURN(DELETED}
LINE>>RHRRETURN24"AECIRCYLOOPJ24RECIRC+LOOP24"24RHRRETURNI>>M120RHRSUCTIONRECIRCg26"PILOO20>>20"4GOTTOMDRAIN4>>4>>4>>RECIRC9LOOPINSTCONN11/2"SLCRWCUSUCTION6"6"INSTCONNV1>>41"LTM0IOOISOBGIFigure1}}

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Susquehanna Units 1 and 2 - a Reaction to Cracking of Austenitic Stainless Steel Piping in Boiling Water Reactors (Includes Susquehanna Ses Design Modifications)
ML18024A114
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PENNSYLVANIA POWER8cLIGHTCCMPANYAREACTIONK)CRACKINGOFAUSTENITIC STAINLESS S9ZELPIPINGINBOILINGWATERREACTORS(INCLUDESSUSQUEHANNA SESDESIGNMODIFICATIONS)

EarleM.Mead./ProgectEngineering ManagerSusquehanna SES TableofContentsl.Introduction 2.ProblemStatement SafetySignificance PrimaryConsiderations 4.1Environmental (CoolantChemistry) 4.2Stress4.3Material5Susquehanna SESPreventive Measures5.1Environment 5.1.1ChemicalControl5.1.2Mechanical Control5.1.2.1ControlRodDrive(CRD)PumpSuctionRelocation 5.1.2.2Mechanical VacuumDeaeration 5.1.3Operating Procedures 5.2Stress5.2.1'DesignStresses5.2.2Fabrication Stresses5.2.2.1Fit-up5.2.2.2InitialFabrication (Shop)5'2.2.3Welding-Induced.

Stress5.2.2.3.1 HeatInput5.2.2.3.2 JointDesign5.2.2.3.3 FillerMetal5.2.2.3.4Cleanline ss TableofContentsPage5.2.3'ethodsofStressReduction 105.2.3.1SolutionHeatTreatment 5.2.3.2HeatSinkMelding5.2.3.3Induction HeatingStressImprovement 105.3Material5~3-1503~2CoreSpraySystemReactorRecirculation SystemDischarge GateValveBypassLine13135~3~353~.6.References ControlRodDriveReturnLineRecirculation Riserpipes1315 TableandIllustration Table1Figure1

~~'1.Introduction Thisreportoriginally resultedfromaninformalteleconbetweenrepresentatives ofPPM.andtheNRCwhichoccurredinFebruary1976.AtthattimeproposedSusquehanna SteamElectricStation(SSES)designchangeswerebrieflydiscussed anditwasagreedthatthisadditional information should.besubmitted.,

Subsequent totheoriginalissueofthisreporttherehavebeennumerousincidents attributed toIntergranular StressCorrosion.

Cracking(IGSCC).Based.ontheseincidents, PPM,hasmodifiedourpositiononIGSCC,whichincludedadditional designchangesatSSES..FortheabovereasonandtoprovidetheNRCwithPAL'spositiononNUHEG-0313, thisreporthasbeenrevisedandupdated.

2.ProblemStatement FromSeptember, 1974toOctober,1976crackinghad.beendiscovered.

inrecirculation bypassloops,corespraylinesand.controlrod.drivereturnlinesof10GEboilingwaterreactors.

Theaffectedunitswere:a)Corespraylines-Dresden2,Fukushima 1,and.Tsurugab)Recirculation bypasslines-Dresden2,QuadCities1,QuadCities2,PeachBottom3,Millstone Point1,Monticello 1,Fukushima 1,Hamaoka1,Brunswick 2,Hatch1,and.Pilgriml.c)Contxolroddrivereturnlines-TarapurPP8cLbelievedthatsufficient Justification existed.torecognize thecauseasbeingIntergranular StressCorrosion Cracking.

Thisreportwasoriginally issuedonOctober12,1976and.summarized PP8cL'sconcernsaswellasmodifications thatwereimplemented forSSES.FromOctober1976tothepresenttherehavebeen'numerous reportsofcrackingatotherplantswhichhasbeenattributed toIGSCC.Notonlyhavetheabovelinesbeenaffected, buttherearereportsofcrackinginheadventlines,recirculation riserlines,instrument lines,andalso,mainrecirculation andfeedwater lines.ThisreporthasbeenrevisedtoreflectPPM'spositiononIGSCCand.thelatestmodifications whichhavebeenmadeatSSES.

3.SafetySignificance PPM,considers thestatement inNUREG-0313, whichreadsinpart,"Although theprobability isextremely lowthatthesestresscorrosion crackswillpropagate farenoughtocreateasignificant safetyhazardtothepublic,thepresenceofsuchcracksisundesirable" tobeanaccurateassessment ofthesafetysignificance.

Beyond,thatPPMbelievesthesignificance ofthefailurestorelateonlytoplantreliability.

Based,onpreviousBWRexperience, itcanbeexpected.

thatbrittlecrackingwillnotoccurinaustenitic Type304stainless steeland.thatsmallleakswillbedetected, v5.sually and/orbyleakdetection instrumentation iftheyoccurinsidetheprimarycontainment.

Theimportance ofdetectability hasbeenrecognized, andtheSSESdrywellleakdetection systemwillcomp~withNRCRegulatory Guide1.45(May1973).TheInservice Inspection ProgramatSSESisinaccordance withtherequirements oftheASMEBoilerandPressureVesselCode,SectionXI,"RulesforInservice Inspection ofNuclearPowerPlantComponents",

1974edition,including addendathroughSummer1975,asmodified.

byAppendixIIItoMinter1975addenda,"Ultrasonic Examination Method.forClass1andClass2PipingSystemsMadefromFerriticSteels",andINA-2232ofthe,Summer1976Addenda,using50+pofthereference levelascriteriaforinvestigating reflectors.

TheISIProgramwillbeupdated,asrequired/allowed by10CFR50.55a(g).

Itwillalsobeaugmented tocomplywiththerecommendations ofNUREG-0313.

Thedegreeofaugmentation willdependontheoutcomeofPPM,'sdetailedevaluation ofIGSCCatSSES.Thisevaluation willbecompleted.

byJanuary1,1990and.willaddressallapplicable lineswhichcontainreactorcoolant.Itwilldelineate allmaterials andanyfabrication processes whichwillprovideacomprehensive listing'ofsusceptible linesintheasinstalled condition.

Thestudywillthenprovideanevaluation ofallIGSCCcountermeasures whichareavailable foruseatSSES.Theconclusion ofthestudywillbearecommendation ofwhat"courseofaction"shouldbetakenforeachsusceptible line>fromwhichcountermeasures should.beusedtohowtheISIProgramshould.beaugmented..

4'r1maryConsiderations 4.1Environment (CoolantChemi,stry)

Thecoolantchemistry inBoilingWaterReactorsisestablished.

primarily toensurecompat1bility withmaterials usedthroughout theNuclearSteamSupplySystem.Hence,neutral,high-purity waterisusedand.halogensarestringently limited..

Limitations arealsoplacedonthesilicaand.copperconcentrations topreventtheirdeposition intheturbine.Dissolved.

oxygenconcentration isnotnormallycontrolled bychemicaladditionormechanical deaeration.

Withoutchemicalormechanical controlthesteadystatelevelofdissolved.

oxygenatSSESduringnormaloperation willbeamaximumof7.1ppb.However,duringlowloadornoload.cond1tions theoxygenconcentration canapproachsaturation which,underconditions ofstandardtemperature andpressure, is8.0ppm.Underthecombinedinfluences ofsensitization andhightensilestressthisoxygenlevelismorethansufficient toenablestresscorrosion crackingofaustenitic stainless steeltooccur.Since,forconstantvaluesofsensitization and.stress,tim-to-failure 1sd.irectly proportional todissolved.

oxygenconcentration, lowflowandstagnantlinesarehigh+suspect.Itwould.,therefore, beverybeneficial toreducetheoxygenleveltoaslowaspossibledur1ngallphasesofplantoperat1on.

4.2StressThedesignstresslevelsforNuclearSteamSupp+System(NSSS)pipingareestablished.

withintheconstraints oftheAQSCodeaswellasanyloadingrestrictions whichmightbeimposed.bytheNSSSvendor.Stresslevelssufficient toresultinIGSCCgenerally arenot'usttheresultofordinarily-applied engineering loadsorstresses.

Rather,theyresultfromthecombind'ffectsofallsourcesofstressand.strain:i.e.,residuals, thermal,surface,service,etc.IItisverybeneficial tomin1mizetheamountofstressactingonthesens1tized.

material.

Therefore, theamountofresidualand.applied.stressesshouldbereducedwhereverpossible.

4.3NaterialBoilingWaterReactorpipingisfabricated fromsteelswhichare:corrosion resistant, tough,stabledimnsional+,

sufficiently strongforanticipated

loadings, resistant toradiat1on damage,resistant tobothacidicandbasicchemicalattack,economical, and.anticipated.

tobeavailable intheforeseeable future.Themostprominent materials used.areaustenitic stainless steels(Types304and,316)and,carbonsteel.

"l However,ithasbeendetermined thatthestandardgradesof304and.316stainless steelwithhighcarboncontentsofapproximately

.06to.08percentarethegradeswhichproducethemostseveresensitization and.thus,thegreatestsusceptibility toIGSCC.Thelowcarbon((.03percentcarbon)gradesof304and316stainless steelaredemonstrating amuchgreaterresistance toIGSCC.Theseand,otheralternate materials areundergoing extensive development and,evaluation forreducingtheprobability ofIGSCC.

IIi~

5.SSESPreventive MeasuresPP&Leffortshavecenteredonreducingtheprobability ofoccurrence ofIGSCCforSSES.Recommended modifications totheexistingSSESdesignwereevaluated, priortoimplementation againstthefallowing criteria:

1.Theirpotential forsubstantially reducingtheprobability thatXGSCCwilloccur;2.Theirpotential forsubstantially reducingthetimerequired.

todetectcracksorleaksresulting fromXGSCC;3.Theirpotential forcreatingotherproblemswhichwouldeitherbeasbad.as,orworsethan,thecurrentproblem.5.1Environment Current'nalyses indicatethatamongtheenvironment related.contributors tothecurrentZGSCCprobleminBWR's,thedissolved oxygenconcentration ofthereactorcoolantisprobablythemostsignificant.

Oxygenlevelscanbecontrolled, eitherchemically, mechanically, oroperationally.

5.1.1ChemicalControlSincethereisnouniversal inhibitor'for improving BMRwaterchemistry and.sincetherearelimited.dataconcerning theuseofoxygenscavengers andneutralizers inBNR's,theiruseintheprimarycoolantisnotconsidered.

atthistime.Futuredevelopments inthisarea,however,willbefallowed..

5.1.2Mechanical ControlPrimaryoxygenremovalisaccomplished inthecondenser duringnormaloperation.

Duringthisphasetheoxygenlevelismaintained.

atapproximately

'$.0ppb.Duringanycombination ofpartialload.(startup,

shutdown, hotstandbyandsomeabnormalevents)theoxygenleveltend.stoincreasetowardsaturation (approximately 8.0ppm).TherehavebeentwomajordesignchangeswhichPPRLhasmadetoimprovethewaterchemistry atSSES.5.1.2.1ControlRod.Drive(CRD)PumpSuctionRelocation PPMpreviously relacated theCRDpumpsuctionfromthecondensate storagetanktothecondensate makeup/reject line.Thepurposeofthislineistocontrolprimary.cyclewaterinventory bymakingupfromorrejecting tothecondensate storagetank.Understeadyloadconditions thislinereceivesaconstantdischarge fromthecondenser due toprimarycycleinfluentwatersourcessuchastheCRDsystemitself.Hence',locatingtheCRDpumpsuctiononthemakeup/regect lineresultsinutilization ofwaterwiththelowestoxygenconcentrations available (essentially waterwithfeedwater quality)mostofthetime.Atthetimetheabovechangewasmade,PALbelievedthatthischange,inadditiontootherchangesmade,wasadequatetosufficiently reducetheprobability ofIGSCC.Sincethattime,however,ppM,hasfound.thatcontrolling the02concentration asaneffective meansofcontrolling IGSCCrequires02controlduringallphasesofplantoperation, notgustnormaloperation.

Forthisreason,PHkLadded,amechanical deaeration system(seesection5.1.2.2),

5.1.2.2Mechanical VacuumDeaeration Basedonmorerecentdata,pp&Lhastakenthestepstoadd.amechanical vacuumdeaeration systematSSES.This02controlsystemwilloperateduringallphasesofplantoperation exceptnormaloperation.

Itwillmaintainthe.02concentration intheprimarycoolanttolessthan250ppb.Thisrecentchangewasmadeinanefforttoreducethecorrosive natureoftheprimaryfluidaslowaspossible.

ItisPP8cL'spreference tohavethe02controlsysteminstalled and.operating priortoplantstartup.$4143Operating Procedures Linesconnected tothereactorvesselwhicharenormallystagnantorexperience lowflowconditions mayaccumulate dissolved oxygenconcentrations whicharehighrelativetogeneralreactorwater.Startup,Shutdown, HotStandbyand.abnormaleventsareofparticular significance.

Totheextentpractical, procedures willbedeveloped whichwillminimizedissolved oxygenconcentrations instagnantorlowflowlinesand/orreducethetotaltimeofstagnantconditions.

Thewaterqualitysamplingsystemhasbeenupgradedinordertoalerttheplantoperators ofadversewaterconditions conducive toIGSCC.Itincludescontinuous monitoring offeedwater andreactorwaterfordissolved pxygenconcentration, conductivity and.pHand.continuous monitoring oftheCRDsystemwaterfordissolved oxygenconcentration and.conductivity."

Thesamplingsystem,automatically alarmswhenwaterqualityconditions considered tobeadversetoBWRoperation arereached.

Procedures willbedeveloped.

whichwillminim1zeexcessive oxygenconcentrations intheprimarycycleand,toenableplantoperators totakeimmediate actiontoprotecttheplantfromprolonged operation withadversewaterqualitycond.itions.

5.2StressStressaloneisnotparticularly s1gnificant sofarastheoverallcorrosion ofmetalsisconcerned.

Whencombinedwithacorrosive env1ronment, however,theappl1cation ofsufficient tensilestressinsusceptible materials canlead.tostresscorrosion cracking.

Areduction 1ntotaltensilestressinlinesconsidered.

susceptible toIGSCCcould.therefore beconsidered.

beneficial.

Inanattempttoreduceoveralltensilestress,pipinglocatedinsidecontainment and.connected.

directlytoeithertheReactorPressureVessel(RPV)ortheReactorRecirculation Systemwasreviewed, todetermine ifdesignand/orfabricating contributions totensilestresslevelscouldbereduced..

5.2.1DesignStressesThecombinedeffectsofservice,internalpressure, deadweight and.thermalstresseswerereviewedand.allpipingsystemswereconfirmed tohavelayoutswhichlimited.theircontributions tototalstresstoalevelconsidered tobeaslowasreasonably ach1evable.

Recognizing theparticular susceptibility oftheCoreSpraySysteminfection lines,alternate routingswerechoseninorderthatthethermalstresscomponent oftotalstressisred.ucedby25$.522Fabrication StressesThedifficulty inassuringcompliance underallshopand.fieldfabricating conditions, limitstheeffectiveness ofprocedures whichmightbedeveloped.

inthisarea.However,s1ncestresslevelsinnon-stress relieved.

austenitic stainless steelpipingcanequalorexceed.yield.,anyprocedures whichmightsignificantly reducefit-up,initialfabrication, orwelding-induced.stressescannotbeoverlooked..

5.2.2.1Fit-upCodetolerance foralignment areccmpliedwithtoassureminimumstressfrommisalignm ntandminimumdegradat1on offatigueresistance.

5.2.2.2Initial.Fabrication (shop)Thepipematerialispurchased.

1nthesolutionannealed.

condition.

Normally, spoolp1ecesarenotsolutionannealed.

duetothedifficulty ofmaintaining desireddimensions.

5.2.2.3Melding-Induced StressPALrecognizes thatwhenaustenitic sta1nless steelsarewelded,somelevelofresidualstressand.sens1tization ispresent.Acompromise betweenheatinputcontrolandtheresulting coolingratemustbeachievedinorderthatacceptable levelsofres1dualstressand.sensit1zation canbeachievedwithoutsacrificing goodpenetration andfusion.Unfortunately, precisequantitative valuesofheatinput,coolingrate,etc.,whichwi.llinsureconsistently goodqualityweldsresistant toIGSCCarenotavailable.

Therefore, PPMreliesonpastindustrial exper1ence forguidance.

PP8Lhasadoptedthefollowing measuresforfieldweldingtheapplicable 11nes.Thesemeasureshelpreducewelding-inducedstresses, w1thoutcreatingadditional

problems, toalevelaslowascanbeexpectedusingnormalweldingpractices.

5.2.2.3.1 HeatInputNopreheat(inexcessoftheacceptable workingrangeof60Fto150F).b.C~dOInterpass temperature limitedto350F.Blockweldingprohibited.

Electrode size11mitedto5/32"h1ax.forSMAMandl/8"Max.forGTAMwhicheffectively limitstheheatinput.5.2.2.3.2 JointDesigna.TherootismadewithGTAMut111'z1ng handfedfillerwireoraconsumable 1nserttoinsurecompletepenetration andgoodfusion.b.Theextended-land

)ointdesignhasnoinherentproblemswithlackofpenetration, lackoffusionorexcessive residualstress.C~Aninertgaspurge1susedpriortoweld.ingandinertgasbackingisused.duringtheweld1ngofthefirstpassestoinsureagood.rootcontourminimizing

'theoccurrence ofanycreviceswhichmightleadtocorrosion problems.

Asmoothfinishcontourisspecified (1.e.,noexcessive

undercut, excessive reinforcement, coarser1pples,etc.)toreducetheoccurrence of"notches" whichcandetrimental+

affectfatiguestrengthorcorrosion resistance.

105.2.2.3.3 FillerMetalTominim1zemicrofissuring and,sensitization

problems, 308Lfillermetalor309and.309Lfillermetalisspecified.

w1thminimumdeltaferritecontentsof8percentand.5percentrespectively.

5.2.2.3.4 Cleanliness Topreventcontamination ofthejoint:a.Grease,oilandothercontaminants areremoved.fromthejointand.thef1llermetalpriortomakingtheweld.b.Onlymarkingcrayons,chalk,1nkandtemperature indicating crayonswhicharecertified.

tobelowinhalogenand,sulfurcontentareused.c.Onlycleaningsolventswh1charenotharmfultoaustenitic stainless steelareused,.d..Stainless steelwirebrushesareused,.e.Grindingwheelsusedonothermaterials arenotused.onstainless steel.f.GrindingwheelsarenotusedonI.D.pipesurfaces.

Ifcleaningisnecessary, flapperwheelsshallbeused.Theexistingmethodsandprocedures forQualityControl/QualityAssurance oftheaboveareadequatetoinsurethattheseprovisions arefollowedand.thattheresultswillbeconsistent w1thwhatwasspecified..

Restrictions consistent withthoseaboveapplyequallytoshopand.fieldsubcontract welding.5.2.3MethodsofStressReduction Duetocontinued reportsofIGSCCsincePPMfirstformd.apositiononthesubject,PP&Lhassteppeclupitsmonitoring oftheproblemanditspossiblecountermeasures.

Thosecountermeasures thatarebeinginvestigated.

/evaluated.

whichdealwithstressreduction areSolutionHeatTreatment (SHT),HeatSinkWelding(HSW),and.Induct1on HeatingStressImprovement (IHSI).5.2.3.1SolutionHeatTreatment ThisIGSCCcountermeasure stressrelievesshopwelcls.before thesectionsofpipeareshipped.tothefieldforinstallation.

Thismethod.canonlybeusedonshopweld.s,and.then,onlywhenthepipeshavenotbeeninstalled..

ForSSESmostofthetargetlinesforwhichnoothercountermeasures (i.e.,materialchanges)havebeentaken,havealreadybeeninstalled..

However,theshopweldsontherecirculation getpumpr1sersunderwent SHTbecausePPMbelievedtheselinestobeextremely susceptible toIGSCC.Thef1eld.weldendsoftheriserswerealsocorrosion resistant clad..Thisprocesswillbed.iscussed inalatersection.5.2.3.2HeatS1nkWeldingThisIGSCCcountermeasure requirescoolingtheIDofthepipewithcoolingwateraftertherootpassoftheweldhasbeencompleted.

Thisprocesscauses-the resultant residualstressesontheIDofthepipetobecompressive ratherthantensileaswould.befound.withnormalweldingpractices.

Resultant compressive stressespreventXGSCC,Thiscountermeasure hasnotbeenusedatSSES.However,Bechtelispresently performing afeasibility evaluation ontheuseofHSWforselected.

linesatSSES.5.2.3.3.Induction HeatingStressXmprovement ThisIGSCCcountermeasure isused.afterthefieldweldshavebeencompleted..

TheprocessinvolvesheatingtheO.D.ofthepipewithaninduction coilwhilecoolingtheI.D.withcoolingwater.Thisprocesscausestheresultant stressesontheI.D.ofthepipetobecompressive ratherthantensile,thuspreventing IGSCC.ThisprocesshasnotbeenusedatSSES.Presently GE1sintheprocessofdeveloping/qualifying thisprocedure foruseonBWR'sintheUnitedStates(Reported.ly theJapanesehaveused.thisprocedure successfully ontheirnuclear~powerplants,).

PP8cLintend,stotracktheprogressofGEand.usetheprocedure onsusceptible linesifand,whentheprocedure isdetermined.

tobefeasible.

5.3hfaterial Duetotherestrictions ofcoolantchemistry andtotaltens1lestresslevels,theuseofsubstitute materials whicharelesssusceptible toXGSCCwereconsidered..

Thelackofsignificant operating dataformaterials otherthancarbonsteelorType304and.Type316stainless steelslimitstheoptions,however.Dur1ngthedesignoftheplant,attention wasgiventominimizing problemsrelatedtogrosscorrosion.

Stainless steelwaschosenforCoreSpraylinesinsidecontainment, condenser and.'feedwater heatertubes,and.ASSAMA155GradeKC70,Class1feedwater pipe.PP8cLis,therefore, unwilling tousecarbonsteelasanIGSCCf1x.

Theprincipal drawbacktothecontinued useofType304and.Type316stainless steelforNSSSpipingistheirsusceptibility toIGSCC.PP8cLbelievesthissusceptib1lity isrelatedtosensitization whichoccursadjacenttoaweldintheheat-affectedzone.Sensitization isatemperature dependent metallurgical phenomenon whichresultsintheformation ofchromiumcarbideatgrainboundaries locatedintheheat-affected.

zoneofaweld.Therefore, 1twaslogicalto11mitthecarboncontentofsusceptible lines.Originally, thehistoryoftheIGSCCproblemformedthebasisoftheassumption thatthecomb1nation ofresidualstressandsensitization wasinsufficient toresultinahighprobability offailureduetoIGSCCforlinesinthereactorcoolantpressureboundarylargerthan12"diameterNPS.Thefocusforpossiblematerialsubstitution was,therefore, onthoselineswh1chwerelessthanorequalto12"diameterNPS.Anysuchsubstitutions wouldapplyequallytopipefittings.

However',

valvesand.containment penetration flued,headsarenotincludedastheyareofsufficient masstobesubstantially lesssusceptible toIGSCC.~Basedontheaboveassumption, Type304Lstainless steelwasusedforallstainless pipingwithinthereactorcoolantpressureboundarywhichis4"diameterNPSorsmallerwithasupplemental requirement of0.030percentmaximumcarbon(withtheexception oftheRecirculat1on SystemDischarge GateValve'ypass Line).Sta1nless pipinglocatedwithinthereactorcoolantpressureboundarywhichisgreaterthan4"butlessthan12"diameterNPSwillbeType304stainless steelwithamaximumcarboncontentof0.030percent.1hesetwomaterials arevirtually identical metallurgically butPPEcLisunwill1ng tosacrifice themechanical properties of304forcertainpipingsystems.Tablelident1fies pipingforwhichachangeinmaterialwasjustified, thematerialprevious+

specified, andthereplacement materialchosentomitigatetheprobability ofIGSCC.Sincethetimetheabovematerialchangesweremade,additional inc1dents ofIGSCChaveshownthattheassumption thatonlythoselineswhichare12"d1ameterNPSorlessaresusceptible toIGSCCisincorrect.

Therefore, alllinesmustbeconsidered whenattempting toeliminate orreduceIGSCC.Inadditiontosimplemater1alreplacement, theother"mater1al" relatedIGSCCcountermeasure whichcanbeevaluated isCorrosion Res1stant Cladding(CRC).Thiscountermeasure combinescladdingthefieldweldedpipeendswithahighlycorrosion resistant metalwithsolutionannealing whicheffect1vely providesacorrosion resistant barrierbetweentheheataffectedbasemetaland,theoxygenated reactorcoolant(corrosive fluid.).

13Asdiscussed.

inSection5.3.4ofth1sreport,PPM,utilizedCRContherecirculation getpumprisers.Duetotheirparticular significance withregardtothecurrentproblem,theCoreSpray,ReactorRecirculation SystemDischarge GateValveBypassLine,ControlRodDriveReturnLine,andRecirculation R1serPipesarediscussed below.5.3.1CoreSpraySystemThatportionofthecorespraysystemwhichislocatedwithintheprimarycontainmntwill,forSusquehanna SES,bema'defrom12"diameterNPS,Type304Stainless SteelPipewithsupplemental maximumcarbonlim1tation of0.030percent.pipeandfittingswillbehandledsimilarly.

532ReactorRecirculation SystmDischarge GateValveBypassZineFromanoperational standpoint pp&Ldoesnotwishtodeletethislin.Itisconsidered important fromthefollowing standpoints; l.Itprovidesameansofpreheating anidlerecirculation loop.2.Itreducesthermalshockseenbythecomponents ofan1dleloop+/3.Itprovidespressureequalization.

onbothsidesofthedischarge gatevalvetoassureproperventingandclosureofthevalve.Iteliminates cuttingandwiredrawingofthedischarge gatevalveseat.The4"diameterNPSlinewillbefabricated.

fromType304stainless steelwithasupplemental maximumcarbonlimitation of0.030percent.Thismaterialchoiceresultsfromthedes1retolimittheprobability ofIGSCCwhileretaining themechanical properties ofandtheexistingstressanalysisforType304stainless steel.Pipeandfittingswillbehandledsimilarly.

533ControlRodDriveReturnLineThis3"diameterlinewaschang'edfrom304SSto304LSSwhich,1twasbelieved.,

would.solvetheproblemofIGSCC.Subsequent tothischangetherewerenumerousreportedinc1dents ofcrackingintheCRDReturnLinenozzle.Theseincidents ofcrackingwereattributed toexcessive thermalgradients across thenozzleratherthanIGSCC.GeneralElectric's recommendation wastodeletethereturnlineand.makeotherchangestothesystemtomainta1nthesystemdesignfunction.

PPEcLconcurred..with GE'srecommendation and.deleted.thereturnlin.Thisaction(1)eliminated theproblemofnozzlecrackingduetothermalgrad.1ents and.(2)eliminated thepossibility ofpipcrackingduetoIGSCC.5.34Rec1rculation RiserPipesThe10'ecirculation riserp1pesleadingfromtherecirculation headertothegetpumpshaverecentlyexperienced IGSCCatotheroperating plants.Thecrackshavebeenformed.intheheataffected.

zonesofthethermalsleevetosafeend.attachment weld.s.Thepipeshavebeenfabricated from304sta1nless steel.Thesafeend.sareImonel600,and.thenozzlesarecarbonsteelclad.withstainless steel.PP8:Lhasmadethefollowing changeswhichwillminimizethepossibility ofthesepipescrackingduetoIGSCCofSusquehanna SES.1.ThepipetosafeendandpipetoteeweldswillhavetheirID'scladwith308Lweld,materialintheheataffected.

areapriortowelding.2.Theriserpipeswillbesolutionheattreated.toeliminate residualstressesfromtheelbowtopipeshopweld.s,andtheCRCprocess.3.Theseweldswillthenbefieldwelded.using308Lweldingrods.Thisprocesswillprevent304stainless steelintheheataffectedareafromcomingincontactwiththeprocessfluid.

156.ReferencesSourceGENRCAS%1DocumentNEDO-21000 NUHEG75/067"StressCorrosion CrackingofMetals-AStateoftheArt"DateJu~,1975October,1975October,1971NATO"TheTheoryofStressCorrosion CrackinginAlloys"October,1971"Fundamental AspectsofStressCorrosion Cracking" September, 1967UnitedStatesSenateJointHearingConcerning "NuclearRegulatory Commission ActionRequiring SafetyInspections WhichResultedinShutdownofCertainNuclearPowerPlants"February, 1975 16SUSQUEHANNA STEAMELECTRICSTATIONTABLZ1MA'JRRIAL CHANGESPipeDescription Head.SprayCoreSprayInfluentSize~NPS12IIpreviousMaterialType304SSNewMaterialCarbon-Limited.

Type304SSControlRod,Drive3"Hydraulic ReturnCRDReturnLineHasBeenDeleted.StandbyLiquid.ControlReactorWaterCleanupEffluent1-1/2"4IIType304SStofirstvalvepthenCarbonSteelType304LSStofirstvalve,thentoCarbonSteelInstrument pipingVent,Drain,and.TestConnections ShownonFigure11",2"Type304SS4IIType304SSType304LSSType304LSSRecirculation'ystem BypassBottomDrain4II4IIType304SSType304SSCarbon-Limited, Type'304SSType304LSSTFO:bah 17M~1MCONTAINMENT PENETRATION HEADSPRAYREACTORVENTTOINSTATMVENTVENTTOlASt,VESSEI.VENT NLIAINSTEAMlFEEOIVATER TOVESSELI6>>MAINSTEAMFEEOWATER TOVESSELSLCTESTCONN'ECTION VENTVCONNECTION DRAINCONNfCTIONSTANDBYLIGVIDCONTROLSYSTEMREACTORIYATERCLEANUPSYSTEMRESIDUALNEATREMOVALSYSTEMCONTROLAODDRIVESYSTEM12"CORESPRAYM1>>121>>12"REACTORPRESSUREVESSEL12"I>>1>>>>COR'ESPRAY,CRORETURN(DELETED}

LINE>>RHRRETURN24"AECIRCYLOOPJ24RECIRC+LOOP24"24RHRRETURNI>>M120RHRSUCTIONRECIRCg26"PILOO20>>20"4GOTTOMDRAIN4>>4>>4>>RECIRC9LOOPINSTCONN11/2"SLCRWCUSUCTION6"6"INSTCONNV1>>41"LTM0IOOISOBGIFigure1

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