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)9i07230292 9i07i5PDRADOCK050003ihPPDRMETALLURGICAL INVESTIGATION OFWALLTHINNINGANDLEAKAGEOFTHEBMITHIMBLETUBINGATD.C.COOKUNIT2GuttiV.RaoJanuary1991n-Approved:

R.D.Rishel,ManagerMetallurgical 5Nondestructive AnalysisWorkperformed undershoporderAIAP-138WESTINGHOUSE ELECTRICCORPORATION NuclearandAdvancedTechnology DivisionP.0.Box2728Pittsburgh, Pennsylvania 15230-2728 1990Westinghouse ElectricCorp.5069s:10/012991 TABLEOFCONTENTS1INTRODUCTION 2EXAMINATIONS ANDTESTS2.1SurfaceExaminations 2.2Metal1ographicExaminations 2.3NearMorphology Examinations bySurfaceReplication 2.4HardnessMeasurements 2.5FuelNozzleGeometryExaminations 3RESULTSANDDISCUSSION 44CONCLUSIONS 5069s/013091:

10 LISTOFTABLESTableNo.TitleSummaryofHardnessMeasurements S069s/013091:10 00 FigureNoLISTOFILLUSTRATIONS TitleSchematic Representation oftheReactorVesselBottomMountedInstrumentation ThimbleTubeSystem2.1Macrophotograph Illustrating theAs-Received Condition oftheLeaked(Perforated)

ThimbleTube"C-7"2.2Macrophotograph Illustrating theAs-Received Appearance ofSeverelyHornThimbleTube"A-9"2.3Metallographic Examination ResultsofaTransverse SectionThroughtheLeakRegionoftheThimbleTube"C-7"Metallography ResultsofanAxialSectionThroughtheSeverlyHornRegionoftheThimbleTube"A-9"2.5ScanningElectronMacrograph Illustrating theOverviewofthePlasticReplicaoftheHornRegioninThimbleTubeC-7Identifying Locations andMicrograph NumbersWhereHigherMagnification SEMwasConducted.

2,6ScanningElectronMacrograph ofthePlasticReplicaTakenfromtheHornRegionofThimbleTube"A-9"Identifying Locations andMicrograph NumbersWhereHigherMagnification SEMwasConducted.

2.7ScanningElectronMacrograph ofthePlasticReplicaTakenfromtheWornRegionoftheThimbleTubeC-7,Identifying Locations WhereNigherMagnification SEMwasConducted.

2.8SEMPhotomicrographs Illustrating theSurfaceMorphology oftheUnscarred andScarredRegionsinSampleC-7.5069s/013091 10 SEMPhotomicrographs Illustrating theSurfaceMorphology oftheUnscarred and.ScarredRegionsinSampleC-7.SEMPhotomicrographs Illustrating theWearMorphology SeenatLocations 39and41Identi.fied (inFigure2.5)ontheReplicaFrom"C-7"2.11Higher'Magnification SEMPhotomicrographs Illustrating theWearMorphology SeenatLocation39oftheReplicafromC-7(Figure2.10).2.12SEMPhotomicrographs Illustrating theWearMorphology Seen'tLocations 31,33and34ofReplica(Figure2.5)fromC-7Sample.2.13SEMPhotomicrographs Illustrating theHearMorphology SeenatLocations 19,22and24(Figure2.5)oftheReplicaTakenfromSampleC-7.SEMPhotomicrographs Illustrating theWearMorphology SeenatLocations 29and30(Figure2-5),ClosetotheThroughHallLeakageRegionoftheSampleC-7.2.15SEMPhotomicrographs Illustrating theWearMorphology SeenatLocations 8,9,and10(Figure2.6)oftheReplicaFromA-9Sample.2.16SEMPhotomicrographs Illustrating theWearMorphology SeenatLocations 21,22and23(Figure2.6)oi'heReplicafromSampleA-9.2.17SEMPhotomicrographs Illustrating theHearMorphology SeenatLocations 24and25(Figure2.6)oftheReplicafromSampleA-9.Schematic Representation ofFuelBundl.eBottomNozzle.5069s/013091:101V

~J-00 SECTION

1.0INTRODUCTION

Thisreportsummarizes thefindingsofthemetallurgical investigation ofthewearandleakageofthereactorvesselbottommountedinstrumentation (BMI)thimbletubesatD.C.CookUnit2.Thereactorvesselinstrumentation thimbleisasmalltubingwithanoutsidediameterrangingfrom0.300in.to0.385in.andawallthickness rangingfrom0.05in.to0.06in.respectively, depending ontheplant.Thethimbletubingismadeof'coldworked316stainless steelmaterialalthoughmostrecentlycoldworked316Lgradehasbeenappliedtolimitthecobaltcontent.Aschematic representation ofthereactorvesselBHIthimblesystemisillustrated inFigure1.1.Thecurrentreportsummarizes theevaluations andresultsofoneseverelywornandoneleakythimbletubefromD.C.CookUnit2.Theevaluations, conducted attheHestinghouse hotcellfacilities centeredontwo,approximately threefeetlongthimbletubesegmentscontaining thewearaffectedregionsandincludedthefollowing majortasks:oSurfaceexaminations oHetallographic examinations oDetailedwearmorphology evaluations, andoHardnessmeasurements Theoverallpurposeoftheinvestigation wastoestablish themechanism andcauseofthethimbletubeleakageandfurthertodevelopinformation thatwouldbehelpfulfortakingcorrective actions.5069s:10/020591 oo0 SECTION2.0TESTSANDEXAMINATIONS 2'urfaceExaminainTheas-received condition ofthethimbletubesampleswereexaminedvisuallyandbylowmagnification lightopticalmicroscopy forevidenceofcracks,wear,surfaceattackorotherdamageanddeposits.

Theresultsofthesurfaceexamination weredocumented bythemacrophotographs illustrated inFigures2.1and2.2.2.2Mt11rhiExamininsMetallographic examinations wereconducted onthethimbletubesamplessectioned axiallyandtransversely throughthewornand/orleakregionstoexaminethelocationandextentofweardamage,thewearscargeometryandthematerialmicrostructure.

Theresultsofthemetallurgical examinations areillustrated inFigures2.3and2.4.2.3WarMrh1ExmintinrfRlitinPriortosectioning formetallography, thewornandleakregionofthethimbletubesampleswerepreparedforsurfacereplication andplasticreplicaswerepulledfromtheaffectedregion.Thereplicaswerepreparedbygoldsputtering undervacuumandwereexaminedbyscanningelectronmicroscopy to'stablish themorphology andmechanism oftheweardamage.Theresultsofthes'eexaminations areillustrated inFigures2.5through2.17.2.4HrnMrmnHardnesstraversemeasurements wereconducted onpolishedsectionsofthewornregionofthethimbletubestoexaminethe'natureofdeformation andworkhardening associated withtheweardamage.Theresultsofthehardnesstraversemeasurements aresummarized inTable1,5069s:10/020591 00 2.5FuelNozz1mtrExamintinTheinsidediametersurfacegeometryofthefuelbundlebottomnozzleattheentryoftheinstrument tubewasexaminedandcomparedwiththimblewearscargeometrytoestablish theirrelationship ifany.Thenozzlegeometryisschematically illustrated inFigure2.18.5069s:10/020591

SECTION3.0RESULTSANDDISCUSSION Theresultsofthesurfaceexamination oftheas-received thimbletubesamplesareillustrated inFigures2.1and2.2.Figure2.1illustrates thesurfaceappearance ofthewearscarinflicted ontheleakedthimbleC-7.Thescarwhichextendedapproximately over0.5in.inlengthismadeupoftwosteps.Thedeepeststepwhichcorresponds tothemostseverelywornregioncontained athrough-wall perforation contributingtotheleakage.Thesideviewshowninthetopphotomacrograph clearlyshowsthepresenceof1circumferentially orientedwearmarksassociated.

withthewearscar.Inadditiontothetwosteppedwearscar,thepresenceofanaxiallyorientedwavyscarcanalsobeseenhere.Thescarappearance suggeststhatitmayhavebeeninflicted bysurfacescrapingortoolingactionagainstasharpcornermostlikelyduringinsertion orretraction ofthethimble.Figure2.2illustrates thesurfaceappearance (sideandtopviews)ofthewearscarinthimbleA-9.Thescarappearance isverysimilartotheoneseeninthimbleC-7.Thetwosteppedwallthinningandthepresenceofcircumferential wearmarkscanbeclearlyseen.Thethinningatthedeepestscarlocationappearstohavejustfallenshortofathrough-wall perforation.

Thetotallengthofthetwosteppedwearregionagaincorresponded toapproximately 0.5in.inlength.Theresultsofthemetallographic examination ofthethimbletubesamplesareillustrated inFigures2.3and2.4.Figure2.3illustrates themetallography resultsofatransverse sectionthroughthethrough-wall perforation onthimbletubeC-7.Thelocations wherehardnessmeasurements weretakenfromarealsoindicated here.Severalsignificant observations areapparentfromtheillustration.

Thethimble.tubewear(thinning) appearstohaveextendedcircumferenti allyoveranangularregionof240'.Thegeneralmicrostructure didnotrevealanyevidenceofsubstructure characteristics ofdeformation exceptatthethinnestregionoftheterminations neartheperforation.

Thethinnestsectionneartheterminations measuredapproximately 0.06in.thick.Noevidenceofanycoldworkwasapparentatthewearsurface.Thehardnessmeasurements (summarized inTable1)confirmed someworkhardening ofthethin5069s:10/020591 terminations presumably duetobendingattheperforation.

Figure2.4illustrates themetallography resultsofanaxialsectionthroughthewornregionofthethimbleA-9.,Hereagain,althoughthereisasignificant reduction inwallthickness duetowear,'ogrossdeformation

'orcoldworkisseeninthematerial.

Thisisfurtherevidenced bythehardnessvalueslistedinTable1.Thehardnessvaluesatthethinnestregionherearecomparable tothehardnessvaluestakenfromtheregionaffectedbywear.Theseobservations suggestthatthecontactand/orimpactloadsinvolvedinthewearprocessmayhavebeenrelatively low.Noticeable isthelackofdeformation orbendingatthethinligamentsectionofthewearscarinFigure2.4.Thehighermagnificationscanningelectronmicroscopy resultsofthewearmorphology bysurfacereplication areillustrated inFigures2.5through2.17.Figures2.5through2.7illustrate thelowmagnification photomacrographs ofthesurfacereplicastakenfromthewornregionsoftheC-7andA-9thimblesidentifying locations wherehighermagnification SEHwasconducted.

Figures2.8through2.17illustrate thehighermagnification scanningelectronmicrographs detailingthewearmorphology seenatdesignated locations (indicated inFigures2.5through2.7).Figure2.8illustrates thesurfacemorphology oftheunaffected (asfinished) andwearaffectedregionsinthimbleC-7.Theunaffectedregion (micrograph

¹16)suggeststhepresenceofmechanical toolingmarksperhapscharacteristic ofthetubefabrication processwhilethemorphology seenattheaffectedregionappearsdistinctly different, characterizing thewearprocess.Figure2.9illustrates theregionofintersection ofwornandunaffected regionsinthimbleC-7.Theaxiallyoriented(horizontal) toolingmarksrepresenting theunaffected surfaceregionterminates intoawornregionofcircumferentially oriented(vertical) wearscars.Similarobservations seenattheunaffected andwearregionsofthimbleA-9areillustrated inFigures2.13and2.16.Figures2.10and2.17illustrate thetypicalwearmorphology seenatthelessseverelywornregions(upperstepregion'fwearscar)ofthethimblesC-7andA-9.Themorphology resembles circumferentially

oriented, regularly spaced"boatshaped"shallowmarks.Highermagnification viewsofthesemarks,illustrated inFigures2.10(b)and2.11suggestsasurfaceformedbyrubbingorfrettingaction.Themorphology seenherealsosuggestssomerateofjettingorerrosiveactionofthefluid.Asecondtypeofwearmorphology seenatthemoreseverely(deep)5069s:10'/020591 0

'k~~wornlowerstepregionsofthewearscarareillustrated inFigures2.12and2.13,Themorphology seenheresuggestsmateriallossintheformofirregularly shapedflakes,presumably duetohigherdeformation orloads.Thistypeofplanarflake-like morphology isseenatthedeeperstepsurfaceandclosertotheperforation regions.Thesurfacemorphology seenattheterminationsimmediately adjacenttotheperforation isillustrated inFigure2.14.Thesurfacemorphology seenhereresembles deformation bandscharacteristic ofslipbandsineachgrain.Thethickness ofthethimbletubehereisconsidered verysmallapproaching thatofagrainsizesothatthedeformation slipbandsineachcrystal(grain)areclearlyapparenthere.Aschematic representation ofthegeometryofthefuelbundlebottomnozzleisillustrated inFigure2.18.Closeexaminations ofthenozzleinsidediametersurfacegeometryatthethimblepenetration clearlyrevealsacloseandconsistent relationship withthetwosteppedgeometryofthethimbletubewearscar.Thenozzlepenetration width(0.5in)isalsoincloseagreement withtheaxiallengthofthewearscar.Thisclearlyestablishes thatthethimbletubewearoccurredbythemovementofthethimbleatthenozzlepenetration.

Theprimarywaterflowvelocities andflowconditions inthisregionareknowntoinducethimbletubevibrations.

Itisbelievedthatthesevibrations mayhavecausedadequatemotionandcontactloadsresulting intheobservedthimbletubewear.5069s:10/020591 0

TABLE1SUMMARYOFHARDNESSMEASUREMENT RESULTS(LOCATIONS ASMARKEDINFIGURES2.2AND2.3)LocationI.D.HarnVHN4msTransverse 1n2852742902972703093922504102803742605069s:10/020591 0

SECTION

4.0CONCLUSION

S oBasedontheoverallresultsoftheevaluations itisconcluded thatleakageintheD.C.CookthimbletubeoccurredbytheODsurfacewearatthebottomfuelnozzlepenetration, mostlikelycausedbyflowinducedvibrations ofthethimbletube.oThewearmorphology ofthethimbletubeshowedatleasttwodisti.nctly different typesofwearconditionsdepending onthelocationanddepthofthewearsuggesting varyingdegreesofdisplacement, contactloadsand~fluidjettingconditions alongthelengthofthethimbletubesatthenozzlepenetration.

oCircumferential configuration ofthewearscarsuggested thatthethimbletubetonozzleborecontactoccurredonlyononesideofthethimbletubeduringthewearprocess.oLackofcoldworkatthewearscarsuggested thatrelatively lowimpactloadswereinvolvedinthewearprocess.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"(~~Circumferential 1'itWearScarCWaveyScarklFigure2.1Hacrophotograph Illustrating theAs-Received Condition oftheLeaked(Perforated)

ThimbleTube"C-7" Figure2.2Hacrophotograph Illustrating theAs-Received Appearance ofSeverelyHornThimbleTube"A-9" 240o.6200X,~~ter200Xr4g4tA.IL~W>>50X200XFigure2.3Metal1ographicExamination ResultsofaTransverse SectionThroughtheLeakRegionoftheThimbleTube"C-7"(Hardness Measurement Locations areMarked) 200X200X.200XCt((>>w~(XX23.50Xr.Ih>>5,~.Figure2.4200X200X200XMetallography ResultsofAnAxialSectionThroughtheSeverlyHornRegionoftheThimbleTube"A-9"(Hardness Measurement Locations areIndicated) 00 LeakagePerforation FLUl'HAI(BLR:

..kEYLIAf~K'I lx142191V~9091>l421OkVirnrA",~L'(JR

'rHiH8x14.299'.LE"~REPLiCA191:V09093Figure2.5ScanningElectronHacrograph Illustrating theOverviewofthePlasticReplicaoftheHornRegioninThimbleTubeC-7Identifying Locations andHicrograph NumbersHhereHigherHagnification SEHwasConducted.

4zi:t-3-iFLVYiTREPLICAx14.5..@8001H:.,-,C3FLUB'THIl1BLE-,x1Q,510LV~lINIMBLE=>FLUXT.1x<ssAlNBLE'O'EPLli'n 110kVo6002Figure2.6ScanningElectronMacrograph ofthePlasticReplicaTakenfromtheWornRegionofThimbleTube"A-9"Identifying Locations andMicrograph NumbersWhereHigherMagnification SEMwasConducted.

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FlUR-iH-i*tiSLE REPLICA"8'"i,x998t00prs~18kV¹88iZ~;~.T,,-gQ'.glq)L)f

$<FLIILlTHI)'l)LEI10pm18kV¹88i8E'VFLHTHIIBLE::kEFLICBILOS~2888i8kV.~.yBr.E='t$jg¹88i6Figure2.8SEHPhotomicrographs Illustrating theSurfaceMorphology oftheUnscarred andScarredRegionsinSampleC-7.

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!;<'!j'~~g~~~.~I'0P.QFDNTAIti5LE"REPL"I~R'V"'.:Cbbprn,xi9919kVCc,%':iDi'i%iA'~it'.F".:

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4bprnxi99818kVe8986',PL4TAA~fN"h.:hEPLKKR"B"<4'~Sbptnxi88818kV~8889Figure2.9SEMPhotomicrographs

.Illustrating theSurfaceMorphology oftheUnscarred andScarredRegionsinSampleC-7.

¹8839x258i8kVCwg'CO'0'fH'Ihe'L.'E----,'AE'.WK I-CA'fi"'~~.'.

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f,'%*-4'Ia)"~~+.w-jL,F,LUXtHINBL.C',REBELf5'8'h>>.:xi888I8f;V¹884(b)Figure2.10SEHPhotomicrographs Illustrating theWearMorphology SeenatLocations 39and41Identified (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~>Figure2.11HigherHagnification SEHPhotomicrographs Illustrating theHearHorphology SeenatLocation39oftheReplicafromC-7(Figure2.10).

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'~URTAINSLE;.:.:~BCPLkbaal"8'"'""kCOurn18kV¹883i.jp).'4p.gf,',~~gt.4'lqqj,

~aov~'.x188818kV¹8834~Tg>>I.(c...z,-A.,ag8PXOptAixi88818kV¹8833Figure2.12SEHPhotomicrographs Illustrating theWearHorphology SeenatLocations 31,33and34ofReplica(Figure2.5)fromC-7Sample.

~~If~jIF~"w*~"\a~%\hEIJQHABlE.:~RVPIiC!Pmx288818kV08824tIr".."'~f1OVfAx266616kVe66Q-Figure2.13SENPhotomicrographs Illustrating theHearMorphology SeenatLocations 19,22and24(Figure2.5)oftheReplicaTakenfromSampleC-7.

Figure2.14SEMPhotomicrographs Illustrating theHearMorphology SeenatLocations 29and30(Figure2-5),ClosetotheThroughWallLeakageRegionoftheSampleC-7.

P-Figure215SEHPhotomicrographs Illustrating theHearHorphology SeenatLocations 8,9,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.SEHPhotomicrographs Illustrating theWearHorphology SeenatLocations 2l,22and23(Figure2.6)oftheReplicafromSampleA-9.XOptn18lY-

011 ANFBOTTOMNOZZLETHIMBLETUBEAPPARENTWEARSCARFROMC7ANDA9THIMBLESTHROUGHWALLLEAKAGE5QTTIIHEXNUTI-lCOREPLATECRUCIFORM GUIDETUBEFigure2.18Schematic Representation oftheGeometryattheThimbleTubetoFuelBundleBottomNozzleIntersection Illustrating theWearLocation.