ML17329A091

Metallurgical Investigation of Wall Thinning & Leakage of Bmi Thimble Tubing at DC Cook Unit 2.

ML17329A091
Person / Time
Site:	Cook
Issue date:	01/31/1991
From:	RAO G V, RISHEL R D WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML17329A090	List: ML17329A089 ML17329A091
References
MT-MNA-035(91), MT-MNA-35(91), NUDOCS 9107230292
Download: ML17329A091 (46)

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MT-MNA-035(91)9i072302929i07i5PDRADOCK050003ihPPDRMETALLURGICALINVESTIGATIONOFWALLTHINNINGANDLEAKAGEOFTHEBMITHIMBLETUBINGATD.C.COOKUNIT2GuttiV.RaoJanuary1991n-Approved:R.D.Rishel,ManagerMetallurgical5NondestructiveAnalysisWorkperformedundershoporderAIAP-138WESTINGHOUSEELECTRICCORPORATIONNuclearandAdvancedTechnologyDivisionP.0.Box2728Pittsburgh,Pennsylvania15230-27281990WestinghouseElectricCorp.5069s:10/012991 TABLEOFCONTENTS1INTRODUCTION2EXAMINATIONSANDTESTS2.1SurfaceExaminations2.2Metal1ographicExaminations2.3NearMorphologyExaminationsbySurfaceReplication2.4HardnessMeasurements2.5FuelNozzleGeometryExaminations3RESULTSANDDISCUSSION44CONCLUSIONS5069s/013091:10 LISTOFTABLESTableNo.TitleSummaryofHardnessMeasurementsS069s/013091:10 00 FigureNoLISTOFILLUSTRATIONSTitleSchematicRepresentationoftheReactorVesselBottomMountedInstrumentationThimbleTubeSystem2.1MacrophotographIllustratingtheAs-ReceivedConditionoftheLeaked(Perforated)ThimbleTube"C-7"2.2MacrophotographIllustratingtheAs-ReceivedAppearanceofSeverelyHornThimbleTube"A-9"2.3MetallographicExaminationResultsofaTransverseSectionThroughtheLeakRegionoftheThimbleTube"C-7"MetallographyResultsofanAxialSectionThroughtheSeverlyHornRegionoftheThimbleTube"A-9"2.5ScanningElectronMacrographIllustratingtheOverviewofthePlasticReplicaoftheHornRegioninThimbleTubeC-7IdentifyingLocationsandMicrographNumbersWhereHigherMagnificationSEMwasConducted.2,6ScanningElectronMacrographofthePlasticReplicaTakenfromtheHornRegionofThimbleTube"A-9"IdentifyingLocationsandMicrographNumbersWhereHigherMagnificationSEMwasConducted.2.7ScanningElectronMacrographofthePlasticReplicaTakenfromtheWornRegionoftheThimbleTubeC-7,IdentifyingLocationsWhereNigherMagnificationSEMwasConducted.2.8SEMPhotomicrographsIllustratingtheSurfaceMorphologyoftheUnscarredandScarredRegionsinSampleC-7.5069s/01309110 SEMPhotomicrographsIllustratingtheSurfaceMorphologyoftheUnscarredand.ScarredRegionsinSampleC-7.SEMPhotomicrographsIllustratingtheWearMorphologySeenatLocations39and41Identi.fied(inFigure2.5)ontheReplicaFrom"C-7"2.11Higher'MagnificationSEMPhotomicrographsIllustratingtheWearMorphologySeenatLocation39oftheReplicafromC-7(Figure2.10).2.12SEMPhotomicrographsIllustratingtheWearMorphologySeen'tLocations31,33and34ofReplica(Figure2.5)fromC-7Sample.2.13SEMPhotomicrographsIllustratingtheHearMorphologySeenatLocations19,22and24(Figure2.5)oftheReplicaTakenfromSampleC-7.SEMPhotomicrographsIllustratingtheWearMorphologySeenatLocations29and30(Figure2-5),ClosetotheThroughHallLeakageRegionoftheSampleC-7.2.15SEMPhotomicrographsIllustratingtheWearMorphologySeenatLocations8,9,and10(Figure2.6)oftheReplicaFromA-9Sample.2.16SEMPhotomicrographsIllustratingtheWearMorphologySeenatLocations21,22and23(Figure2.6)oi'heReplicafromSampleA-9.2.17SEMPhotomicrographsIllustratingtheHearMorphologySeenatLocations24and25(Figure2.6)oftheReplicafromSampleA-9.SchematicRepresentationofFuelBundl.eBottomNozzle.5069s/013091:101V

~J-00 SECTION

1.0INTRODUCTION

Thisreportsummarizesthefindingsofthemetallurgicalinvestigationofthewearandleakageofthereactorvesselbottommountedinstrumentation(BMI)thimbletubesatD.C.CookUnit2.Thereactorvesselinstrumentationthimbleisasmalltubingwithanoutsidediameterrangingfrom0.300in.to0.385in.andawallthicknessrangingfrom0.05in.to0.06in.respectively,dependingontheplant.Thethimbletubingismadeof'coldworked316stainlesssteelmaterialalthoughmostrecentlycoldworked316Lgradehasbeenappliedtolimitthecobaltcontent.AschematicrepresentationofthereactorvesselBHIthimblesystemisillustratedinFigure1.1.ThecurrentreportsummarizestheevaluationsandresultsofoneseverelywornandoneleakythimbletubefromD.C.CookUnit2.Theevaluations,conductedattheHestinghousehotcellfacilitiescenteredontwo,approximatelythreefeetlongthimbletubesegmentscontainingthewearaffectedregionsandincludedthefollowingmajortasks:oSurfaceexaminationsoHetallographicexaminationsoDetailedwearmorphologyevaluations,andoHardnessmeasurementsTheoverallpurposeoftheinvestigationwastoestablishthemechanismandcauseofthethimbletubeleakageandfurthertodevelopinformationthatwouldbehelpfulfortakingcorrectiveactions.5069s:10/020591 oo0 SECTION2.0TESTSANDEXAMINATIONS2'urfaceExaminainTheas-receivedconditionofthethimbletubesampleswereexaminedvisuallyandbylowmagnificationlightopticalmicroscopyforevidenceofcracks,wear,surfaceattackorotherdamageanddeposits.TheresultsofthesurfaceexaminationweredocumentedbythemacrophotographsillustratedinFigures2.1and2.2.2.2Mt11rhiExamininsMetallographicexaminationswereconductedonthethimbletubesamplessectionedaxiallyandtransverselythroughthewornand/orleakregionstoexaminethelocationandextentofweardamage,thewearscargeometryandthematerialmicrostructure.TheresultsofthemetallurgicalexaminationsareillustratedinFigures2.3and2.4.2.3WarMrh1ExmintinrfRlitinPriortosectioningformetallography,thewornandleakregionofthethimbletubesampleswerepreparedforsurfacereplicationandplasticreplicaswerepulledfromtheaffectedregion.Thereplicaswerepreparedbygoldsputteringundervacuumandwereexaminedbyscanningelectronmicroscopyto'stablishthemorphologyandmechanismoftheweardamage.Theresultsofthes'eexaminationsareillustratedinFigures2.5through2.17.2.4HrnMrmnHardnesstraversemeasurementswereconductedonpolishedsectionsofthewornregionofthethimbletubestoexaminethe'natureofdeformationandworkhardeningassociatedwiththeweardamage.TheresultsofthehardnesstraversemeasurementsaresummarizedinTable1,5069s:10/020591 00 2.5FuelNozz1mtrExamintinTheinsidediametersurfacegeometryofthefuelbundlebottomnozzleattheentryoftheinstrumenttubewasexaminedandcomparedwiththimblewearscargeometrytoestablishtheirrelationshipifany.ThenozzlegeometryisschematicallyillustratedinFigure2.18.5069s:10/020591

SECTION3.0RESULTSANDDISCUSSIONTheresultsofthesurfaceexaminationoftheas-receivedthimbletubesamplesareillustratedinFigures2.1and2.2.Figure2.1illustratesthesurfaceappearanceofthewearscarinflictedontheleakedthimbleC-7.Thescarwhichextendedapproximatelyover0.5in.inlengthismadeupoftwosteps.Thedeepeststepwhichcorrespondstothemostseverelywornregioncontainedathrough-wallperforationcontributingtotheleakage.Thesideviewshowninthetopphotomacrographclearlyshowsthepresenceof1circumferentiallyorientedwearmarksassociated.withthewearscar.Inadditiontothetwosteppedwearscar,thepresenceofanaxiallyorientedwavyscarcanalsobeseenhere.Thescarappearancesuggeststhatitmayhavebeeninflictedbysurfacescrapingortoolingactionagainstasharpcornermostlikelyduringinsertionorretractionofthethimble.Figure2.2illustratesthesurfaceappearance(sideandtopviews)ofthewearscarinthimbleA-9.ThescarappearanceisverysimilartotheoneseeninthimbleC-7.Thetwosteppedwallthinningandthepresenceofcircumferentialwearmarkscanbeclearlyseen.Thethinningatthedeepestscarlocationappearstohavejustfallenshortofathrough-wallperforation.Thetotallengthofthetwosteppedwearregionagaincorrespondedtoapproximately0.5in.inlength.TheresultsofthemetallographicexaminationofthethimbletubesamplesareillustratedinFigures2.3and2.4.Figure2.3illustratesthemetallographyresultsofatransversesectionthroughthethrough-wallperforationonthimbletubeC-7.Thelocationswherehardnessmeasurementsweretakenfromarealsoindicatedhere.Severalsignificantobservationsareapparentfromtheillustration.Thethimble.tubewear(thinning)appearstohaveextendedcircumferentiallyoveranangularregionof240'.Thegeneralmicrostructuredidnotrevealanyevidenceofsubstructurecharacteristicsofdeformationexceptatthethinnestregionoftheterminationsneartheperforation.Thethinnestsectionneartheterminationsmeasuredapproximately0.06in.thick.Noevidenceofanycoldworkwasapparentatthewearsurface.Thehardnessmeasurements(summarizedinTable1)confirmedsomeworkhardeningofthethin5069s:10/020591 terminationspresumablyduetobendingattheperforation.Figure2.4illustratesthemetallographyresultsofanaxialsectionthroughthewornregionofthethimbleA-9.,Hereagain,althoughthereisasignificantreductioninwallthicknessduetowear,'ogrossdeformation'orcoldworkisseeninthematerial.ThisisfurtherevidencedbythehardnessvalueslistedinTable1.Thehardnessvaluesatthethinnestregionherearecomparabletothehardnessvaluestakenfromtheregionaffectedbywear.Theseobservationssuggestthatthecontactand/orimpactloadsinvolvedinthewearprocessmayhavebeenrelativelylow.NoticeableisthelackofdeformationorbendingatthethinligamentsectionofthewearscarinFigure2.4.ThehighermagnificationscanningelectronmicroscopyresultsofthewearmorphologybysurfacereplicationareillustratedinFigures2.5through2.17.Figures2.5through2.7illustratethelowmagnificationphotomacrographsofthesurfacereplicastakenfromthewornregionsoftheC-7andA-9thimblesidentifyinglocationswherehighermagnificationSEHwasconducted.Figures2.8through2.17illustratethehighermagnificationscanningelectronmicrographsdetailingthewearmorphologyseenatdesignatedlocations(indicatedinFigures2.5through2.7).Figure2.8illustratesthesurfacemorphologyoftheunaffected(asfinished)andwearaffectedregionsinthimbleC-7.Theunaffectedregion(micrograph¹16)suggeststhepresenceofmechanicaltoolingmarksperhapscharacteristicofthetubefabricationprocesswhilethemorphologyseenattheaffectedregionappearsdistinctlydifferent,characterizingthewearprocess.Figure2.9illustratestheregionofintersectionofwornandunaffectedregionsinthimbleC-7.Theaxiallyoriented(horizontal)toolingmarksrepresentingtheunaffectedsurfaceregionterminatesintoawornregionofcircumferentiallyoriented(vertical)wearscars.SimilarobservationsseenattheunaffectedandwearregionsofthimbleA-9areillustratedinFigures2.13and2.16.Figures2.10and2.17illustratethetypicalwearmorphologyseenatthelessseverelywornregions(upperstepregion'fwearscar)ofthethimblesC-7andA-9.Themorphologyresemblescircumferentiallyoriented,regularlyspaced"boatshaped"shallowmarks.Highermagnificationviewsofthesemarks,illustratedinFigures2.10(b)and2.11suggestsasurfaceformedbyrubbingorfrettingaction.Themorphologyseenherealsosuggestssomerateofjettingorerrosiveactionofthefluid.Asecondtypeofwearmorphologyseenatthemoreseverely(deep)5069s:10'/020591 0

'k~~wornlowerstepregionsofthewearscarareillustratedinFigures2.12and2.13,Themorphologyseenheresuggestsmateriallossintheformofirregularlyshapedflakes,presumablyduetohigherdeformationorloads.Thistypeofplanarflake-likemorphologyisseenatthedeeperstepsurfaceandclosertotheperforationregions.ThesurfacemorphologyseenattheterminationsimmediatelyadjacenttotheperforationisillustratedinFigure2.14.Thesurfacemorphologyseenhereresemblesdeformationbandscharacteristicofslipbandsineachgrain.Thethicknessofthethimbletubehereisconsideredverysmallapproachingthatofagrainsizesothatthedeformationslipbandsineachcrystal(grain)areclearlyapparenthere.AschematicrepresentationofthegeometryofthefuelbundlebottomnozzleisillustratedinFigure2.18.Closeexaminationsofthenozzleinsidediametersurfacegeometryatthethimblepenetrationclearlyrevealsacloseandconsistentrelationshipwiththetwosteppedgeometryofthethimbletubewearscar.Thenozzlepenetrationwidth(0.5in)isalsoincloseagreementwiththeaxiallengthofthewearscar.Thisclearlyestablishesthatthethimbletubewearoccurredbythemovementofthethimbleatthenozzlepenetration.Theprimarywaterflowvelocitiesandflowconditionsinthisregionareknowntoinducethimbletubevibrations.Itisbelievedthatthesevibrationsmayhavecausedadequatemotionandcontactloadsresultingintheobservedthimbletubewear.5069s:10/020591 0

TABLE1SUMMARYOFHARDNESSMEASUREMENTRESULTS(LOCATIONSASMARKEDINFIGURES2.2AND2.3)LocationI.D.HarnVHN4msTransverse1n2852742902972703093922504102803742605069s:10/020591 0

SECTION

4.0CONCLUSION

SoBasedontheoverallresultsoftheevaluationsitisconcludedthatleakageintheD.C.CookthimbletubeoccurredbytheODsurfacewearatthebottomfuelnozzlepenetration,mostlikelycausedbyflowinducedvibrationsofthethimbletube.oThewearmorphologyofthethimbletubeshowedatleasttwodisti.nctlydifferenttypesofwearconditionsdependingonthelocationanddepthofthewearsuggestingvaryingdegreesofdisplacement,contactloadsand~fluidjettingconditionsalongthelengthofthethimbletubesatthenozzlepenetration.oCircumferentialconfigurationofthewearscarsuggestedthatthethimbletubetonozzleborecontactoccurredonlyononesideofthethimbletubeduringthewearprocess.oLackofcoldworkatthewearscarsuggestedthatrelativelylowimpactloadswereinvolvedinthewearprocess.5069s:10/020591 I~I4f!,'/If/J.w//+</whr~lg)IRSSp!,!,Ill"(fjj-g~IIg.;g,(II--ggI~g~Is-!~s~.s 0

Itlif/IU.S.A.Jd.iljiiIilflff*'*"ITrttrliS.A.I4~Ave"(~~Circumferential1'itWearScarCWaveyScarklFigure2.1HacrophotographIllustratingtheAs-ReceivedConditionoftheLeaked(Perforated)ThimbleTube"C-7" Figure2.2HacrophotographIllustratingtheAs-ReceivedAppearanceofSeverelyHornThimbleTube"A-9" 240o.6200X,~~ter200Xr4g4tA.IL~W>>50X200XFigure2.3Metal1ographicExaminationResultsofaTransverseSectionThroughtheLeakRegionoftheThimbleTube"C-7"(HardnessMeasurementLocationsareMarked) 200X200X.200XCt((>>w~(XX23.50Xr.Ih>>5,~.Figure2.4200X200X200XMetallographyResultsofAnAxialSectionThroughtheSeverlyHornRegionoftheThimbleTube"A-9"(HardnessMeasurementLocationsareIndicated) 00 LeakagePerforationFLUl'HAI(BLR:..kEYLIAf~K'Ilx142191V~9091>l421OkVirnrA",~L'(JR'rHiH8x14.299'.LE"~REPLiCA191:V09093Figure2.5ScanningElectronHacrographIllustratingtheOverviewofthePlasticReplicaoftheHornRegioninThimbleTubeC-7IdentifyingLocationsandHicrographNumbersHhereHigherHagnificationSEHwasConducted.

4zi:t-3-iFLVYiTREPLICAx14.5..@8001H:.,-,C3FLUB'THIl1BLE-,x1Q,510LV~lINIMBLE=>FLUXT.1x<ssAlNBLE'O'EPLli'n110kVo6002Figure2.6ScanningElectronMacrographofthePlasticReplicaTakenfromtheWornRegionofThimbleTube"A-9"IdentifyingLocationsandMicrographNumbersWhereHigherMagnificationSEMwasConducted.

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FlUR-iH-i*tiSLEREPLICA"8'"i,x998t00prs~18kV¹88iZ~;~.T,,-gQ'.glq)L)f$<FLIILlTHI)'l)LEI10pm18kV¹88i8E'VFLHTHIIBLE::kEFLICBILOS~2888i8kV.~.yBr.E='t$jg¹88i6Figure2.8SEHPhotomicrographsIllustratingtheSurfaceMorphologyoftheUnscarredandScarredRegionsinSampleC-7.

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!;<'!j'~~g~~~.~I'0P.QFDNTAIti5LE"REPL"I~R'V"'.:Cbbprn,xi9919kVCc,%':iDi'i%iA'~it'.F".:"=(Fri'ita~~V4]4bprnxi99818kVe8986',PL4TAA~fN"h.:hEPLKKR"B"<4'~Sbptnxi88818kV~8889Figure2.9SEMPhotomicrographs.IllustratingtheSurfaceMorphologyoftheUnscarredandScarredRegionsinSampleC-7.

¹8839x258i8kVCwg'CO'0'fH'Ihe'L.'E----,'AE'.WKI-CA'fi"'~~.'.I1OCtlrr.w~f,'%*-4'Ia)"~~+.w-jL,F,LUXtHINBL.C',REBELf5'8'h>>.:xi888I8f;V¹884(b)Figure2.10SEHPhotomicrographsIllustratingtheWearMorphologySeenatLocations39and41Identified(inFigure2.5)ontheReplicafrom"C-7" 0

I~h~I50~-'pBI~'--PL'UXTi-i(ik2666~..>>S~~,~E'.-'-'-,KEiCiih'QPts'e6kV~88ii'.,:';m','i4,."'...'\-*"',fz,'.,gg~fp'~Il--';."'--l.Ž--.;""::-'.~!~g~ggTA6'ih~+QgQ~tA~xa58e6669~66i6~~'SC"~xi888i8k~>Figure2.11HigherHagnificationSEHPhotomicrographsIllustratingtheHearHorphologySeenatLocation39oftheReplicafromC-7(Figure2.10).

0188t44'~~';-".'*Lg5;g,'V'""-','~URTAINSLE;.:.:~BCPLkbaal"8'"'""kCOurn18kV¹883i.jp).'4p.gf,',~~gt.4'lqqj,~aov~'.x188818kV¹8834~Tg>>I.(c...z,-A.,ag8PXOptAixi88818kV¹8833Figure2.12SEHPhotomicrographsIllustratingtheWearHorphologySeenatLocations31,33and34ofReplica(Figure2.5)fromC-7Sample.

~~If~jIF~"w*~"\a~%\hEIJQHABlE.:~RVPIiC!Pmx288818kV08824tIr".."'~f1OVfAx266616kVe66Q-Figure2.13SENPhotomicrographsIllustratingtheHearMorphologySeenatLocations19,22and24(Figure2.5)oftheReplicaTakenfromSampleC-7.

Figure2.14SEMPhotomicrographsIllustratingtheHearMorphologySeenatLocations29and30(Figure2-5),ClosetotheThroughWallLeakageRegionoftheSampleC-7.

P-Figure215SEHPhotomicrographsIllustratingtheHearHorphologySeenatLocations8,9,and10(Figure2.6)oftheReplicaFromA-9Sample.Ii8.8~28

$7/~:+k~,~,.9A,jfAgg~'~REP~882iA~/'.,.T~kINB~E+1OO~3<58818)Y~8822+7$Ã]>~gp.,;t24)P<>>p+$E+)peWIFigure2.16.SEHPhotomicrographsIllustratingtheWearHorphologySeenatLocations2l,22and23(Figure2.6)oftheReplicafromSampleA-9.XOptn18lY-

011 ANFBOTTOMNOZZLETHIMBLETUBEAPPARENTWEARSCARFROMC7ANDA9THIMBLESTHROUGHWALLLEAKAGE5QTTIIHEXNUTI-lCOREPLATECRUCIFORMGUIDETUBEFigure2.18SchematicRepresentationoftheGeometryattheThimbleTubetoFuelBundleBottomNozzleIntersectionIllustratingtheWearLocation.