NL-14-0672, Updated Status/Analysis of Core Shroud

Updated Status/Analysis of Core Shroud

ML14139A178
Person / Time
Site:	Hatch
Issue date:	05/14/2014
From:	Pierce C R Southern Co, Southern Nuclear Operating Co
To:	Croteau R Document Control Desk, Division Reactor Projects II
References
NL-14-0672
Download: ML14139A178 (11)

Text

Charles R.Picrcc Southern Nuclear Rcgiilatcry Alfaiis Diicrtui Operating Company, Inc.'10 liivstiiess Center Parkway Posl Offics Box 1235 Bitiii:ngl)a:n.

Alabana 35201 lol 205.9927872 Fax 205.992.7601 MAY14 2014 Docket Nos.: 50-321 NL-14-0672 50-366U.S.Nuclear Regulatory Commission ATTN: Mr.Richard Croteau Director Reactor ProjectsOfficeof the Regional Administrator.

Region II 245 Peachtree Center Avenue, NE Suite 1200 Atlanta, Georgia 30303-1257 Edwin I.Hatch Nuclear Plant Unit 1 Updated Status/Analysis of Core Shroud Ladies and Gentlemen:Thisletterisbeing providedattherequestofNuclear Regulatory Commission (NRC)managementtosupportamore complete understandingoftheresults fromrecentinspectionsoftheHatch Unit1coreshroud as well as resulting actions (taken/planned) and evaluations performedthatwereassociated with that activity.By letters dated December 3.2004 (ML043430471)

Southern Nuclear Operating Company (SNC)providedtothe Nuclear Regulatory Commission (NRC), an updated analysisofthe findings for the Edwin I.Hatch Nuclear Plant Unit 1flawedCore ShroudVerticalwelds baseduponexamination results obtained during the Spring 2004 RefuelingOutage.The resultsofthat examination andevaluationindicatedthatthe endofinterval (EOl)forre-examinationshouldbe10 years for the two flawed core shroud vertical welds designated V5 and VG.This analysis was reviewedbythe NRC staff and responses to requests for additional information were providedinaletterdated April 15, 2005 (ML051100309).

Thestaffconcludedinaletter dated November 10, 2005 (ML053110060) thattheflawevaluationmettheintentoftheAmericanSocietyofEngineersCodeSection XI (ASME XI)and demonstratedthatthe unit could be operated without repair offlawedvertical welds\/5 and ve for the analyzedintervalof 10 years.Accordingly, SNC perfonned a re-examinationofthe two flawed vertical welds during the twenty-sixth refuelingoutageinthe spring of 2014.During the Spring 2014 Refueling Outage, SNC also performed activities intended to provide a broader structural and aging management assessment oftheHatch1coreshroud.Thiseffortwas partly based on indications previously identifiedviavisual examinationtechniquesthat while not structurally significant U.S.Nuclear Regulatory Commission NL-14-0672 Page 2wereatypicalandpossibly indicative of irradiation effects.Includedinthisinspectioncampaignwas volumetric examination of additional vertical welds, volumetricexaminationoftheatypicalvisualindicationsoftheshroudandobtainingaboatsample from a highlyin'adiatedshroud location.Asummaryoftheinspectionresultsis providedinEnclosure1.Alsoenclosedis the Core ShroudWeldIdentification sketch (Enclosure2).Asofthis date theboatsampleobtained duringtheSpring2014 outage is awaitingsubmittaland subsequentNRCapprovalofthevendor-suppliedshippingcontainer.ThislettercontainsnoNRCcommitments.Ifyouhaveany questions, please contact Ken McElroy at (205)992-7369.Respectfully submitted, c.^C.R.Pierce RegulatoryAffairsDirector

Enclosures:

1.PlantHatchUnit1Spring 2014CoreShroudInspection and Evaluation Summary 2.Drawing,CoreShroud Weld Identification Roll Out (Inside View)cc: Southern Nuclear Operating Company Mr.S.E.Kuczynski,Chainnan,President&CEO Mr.D.G.Bost,ExecutiveVice President&ChiefNuclearOfficer Mr.D.R.Vineyard, VicePresident-Hatch Mr.B.L Ivey,VicePresident-Regulatory AffairsMr.D.R.Madison, Vice President-Fleet OperationsMr.B.J.Adams.Vice President-Engineering Mr.G.L.Johnson.Regulatory AffairsManager-Hatch RTYPE: CHA02.004 U.S.Nuclear Regulatory CommissionMr.V.M.McCree, Regional AdministratorMr.R.E.Martin,NRR Senior Project Manager-HatchMr.E.D.Mom's, Senior Resident Inspector-Hatch Edwin 1.Hatch Nuclear Plant Response to Request for Additional Information Plant HatchUnit1 Spring 2014 Core Shroud inspection and Evaluation Summary Background/HistoryTheHatch Unit1Core shroud is fabricated withtype304 stainless steel plate rolled andweldedvertically and horizontally as depictedinEnclosure2.

Allofthesimilarmetalweldswereperformedatthefabricator's facilityandshippedinthe"as-welded"condition.The Boiling Water Reactor (BWR)fleet beganexperiencingIntergranular StressCorrosionCracking (IGSCC)incoreshroud welds as early 1992.SouthernNuclearOperatingCompany(SNC)preemptivelyinstalledatierodmodificationin 1994tostructurally replace shroud horizontal welds H1-H8.Thetierod modification dependsuponverticalweldintegritythusrequiringa regimenofverticalweld inspection.

Visual examinationswereperformedonthe shroudverticalweldsbeginningin HI R16 (1996)and detectedcrackingatV5andV6which was evaluated as acceptable.

An ultrasonic volumetric examination (UT)was performed on weldsV3throughV8during H1R17 (1997)and repeated during H1R21(2004)forwelds V5 andV6.At thetimeofinitialUT, the technique wasnotfully demonstrated for sizing.Therefore, the examinations were consideredfor"informationonly"butdidnotyield results that necessitated a revised flaw evaluation.

Indications ofvaryinglengthwere recordedonV5,V6,V4andV8during H1R18(1999)visual examinations.

The indicationsonV4 and V8 weresufficientlysmallto meet Boiling Water Reactor Vessel Inspection Program, BWRVIP-76, guidancefora 10-year re-inspection interval.The indicationsonV5 and V6 were somewhat longer and promptedaplant specific analyses which determined a re-inspection in 2004.The 2004 evaluation of V5 and V6 was based on the UT examination during HIR21(2004).This analysis was submitted to andreviewedbytheNuclearRegulatoryCommission(NRC)staffin 2005 (ML053110060]

and establishedaten year re-inspectioninterval.As partofthe recoveryeffortfromtierod upper support cracking detected in H1R22 (2006), shroudhorizontalweld UT examinations were conducted which established acceptable structuralintegrityofthehorizontal welds to demonstrate redundancytothe degraded tie rod assemblies.

During H1R23 (2008)the planned replacementofallfourtierod upper supportscouldnot be completed.

The existing upper supportsintwo locations wereleftin place.As part of theefforttojustify structuralintegrityfor anotherfuelcycle, shroudhorizontalweldUT examination was again conducted during H1R23 (2008).In H1R24 (2010), thefinaltwo upgraded upper supportswereinstalled and the shroud repair returned to fulllongtermfunctionality.Duringthe HIR23(2008)outage two-sided visual examinations of shroud verticalweldsV3,V4,V7, and V8, and single-sided visual examinations of shroud vertical welds VI,V2,V9, VI0 and V11 were completed.

Some new indications were recorded at the inner surfaceofV4,V7, and V8.The indicationsonV7 and V8 appearedtobeverticalbranchingcomponentsof horizontalweldH5flawsandweresmallenoughtomeet BWRVIP-76-A screeningcriteria.TheindicationsonV4requiredevaluationand appeared to traversethroughthehorizontalweldH4whichisatypicalofIGSCC.

AlltheIndicationsonV4have aspects suggesting Im'adiation Assisted StressCorrosionCracking (lASCC).An INPO operating experiencereport,OE 080614-004, was issuedtoalerttheindustry and re-examinations were performed during H1R24(2010)to better interrogatetheInner diameter (ID)high fluence intersections.Priorto H1R24 (2010),theflawswere evaluated basedonthe H1R23(2008)flawlengths.DuringH1R24(2010), these locations were visually reexamined in ordertoobtainimprovedflaw characterization.Nonewflaws were detected and the evaluation prepared prior to H1R24 (2010)was determinedtobe conservative andstillapplicable.This operating experience was sharedwiththeindustry.

H1R26 Shroud inspection scope Basedonflaws characterized during HIR21and evaluated per BWRVIP guidance, a re-examination was due In 2014 (1R26).In conjunction with theBWRVIP-requiredexaminationan extensive inspection campaign was planned to facilitate an assessment of theoverallUnit1 shroud material condition.

The planincludedUT examinationofadditional shroudverticalwelds,off-axisUT scanning to better characterize indications visually detected outside the heat affected zone (HAZ)ofhigh fluence vertical-horizontal weld intersections and a boat sample to determine material properties and accumulated fluence.This campaign was supported by the BWRVIP and intendedtoprovide sufficient infomiation to developalongterm strategyfortheUnit1 shroud andfortheBWRVIPto assess current shroud inspection and evaluation strategies.Belowisa summary of shroud examinations completed during H1R26:*VolumetricUTof8 out of 11 vertical welds (BWRVIP-76-A)*V5 and V6 repeated UT examinations from 2004 (BWRVIP-76-A)

• VolumetricUTof horizontal/vertical weld intersections H4A/4, H5A/8&H5/V7 (augmented examinationstofurther characterize atypical Indications visually detected during 2008)*Visual examinationfromthe outer diameter(OD)of3vertical welds, inaccessibleviaUTorIDvisual(BWRVIP-76-A)*Visual examination of-36%of shroud ID surfaces (ASME Code Section XI, surfaces made accessible by scheduledremovaloffuel)

• Visual examination of=50%of shroud OD surfaces (ASME Code Section XI)Aspartofthe augmented examinations SNC'sinspectionvendor,inajointeffort with SNC, the BWRVIP and the EPRI-NDE center, successfully demonstrated a UT procedure and transducer package capableofdetecting andsizingatypical indications similar to those seen at Hatch.The intent was to use the UTinformationof theseatypicalindicationsto chooseanoptimumlocationfromwhichtoobtainthe planned boat sample.Boat Sample decision process The boat sample location wastobe basedonUT examination results at the H4A/4, H5A/8 or H5A/7 intersections as these were the locations of the atypicalindications.Locationswere pre-selected for planning/execution purposes as candidate boat samplelocationsatboth H4/V4 and H5A/8 intersections,withadecisiontree providingoptionsto choose elsewhere if UT criteriawerenotmet.Oneofthe pre-selectedvisualindications at H5A/7mettheUTcriteriafortheboatsample.The remaining2locationsat H5/V7werenot detected via UT.However, the H5/V7 intersection is atalower fluence in comparison to the H4/V4intersectionandthus less desirableformaterialtestingifahigherfluencelocation othenwisemetthecriteria.

Allthreepre-determinedaxialflawsat H4A^4failedthe UT criteria for takingaboatsamplebecause leaving a through-wall remnant flawhadnot beenincludedintheanalysisforanas-leftconfiguration.Thedecision criteriawerecomparedagainstother newly identified part-through-wall (UT)flawsinthe vicinityofthe H4/V4intersection.A flawlocatedat-9.5inchescounterclockwisefromV4, and-1.5 inches aboveH4,approximately0.8 inches deep, was chosen basedonthepre-outagedecisioncriteriaandaboatsamplewasobtained.The sample currentlyresidesinthePlantHatch Unit1FuelPool awaiting submittalandsubsequent NRC approvaloftheClassB shippingcontainersothatitcanbe senttothe hot-cellequippedlaboratorycontractedby the BWRVIP.H1R26 Shroud Exam Results As described earlier the intent of the shroud examinations was to comply with BWRVIP requirements which had established a re-examination interval of ten years for the long, limiting flaw in the HAZ of vertical weld V6.This weldandtheflawedV5weld were UT examined from theIDin essentially the same manner as the previous examinationin2004.The limiting flawinthe HAZ of V6didnot change in length (20.3")since 2004 but depth progressed from 78%through-wall (TW)maximum to 100%TW for 13" of the flaw length, well within predicted crack grovirth rates (CGR)from BWRVIP guidance.The longest flaw along V5 had little change in length and depth progressed from 61%TW to 80%TW.A summary ofverticalwelds examinedwithUTis depictedinthe table below: Weld Identification Weld length%of Examined Weld length%of Examined length flawed V3@140°36" 82.0%0%V4@320°36" 91.0%10.2%V5@50°98" 97.1%21.7%V6@230°CD 96.9%32.2%V7@140°36" 84.8%12.7%

VS@320>>36" 86.4%1.9%V9@50°CVJ in 63.2%0%VI0@170" CM in 90.0%0%Visual VT-3examinationswereperformedofthe shroud inner diameter per ASME Code Section XI Table IWB-2500-1 B-N-2 Item B13.40"accessiblesurfaces".Inadditiontodetectingindications associated with welds/HAZ, 4 indications at 3 azimuths were detected in the base metal plates at locations unassociatedwithaweld.

Three of these indications were>>3"long (one was 5/16"),andallwereinhigher fluence areas withclearvisualevidenceofsurface grinding.Oneofthe3" long flaws was examined with UT with a maximum depthof0.52" and withlengthin agreementwiththevisual measurement.

UT examination conducted at the intersections of H4A/4, H5A/7 and H5/V8 providedsomeexpectedandsome unanticipatedresults.The2 flaws detected at the intersection of H5/V7 were associated with horizontal weld HAZIGSCC, initiated from the IDandwereparalleltoH5inthe HAZbelowH5.Indications ofthistypeat H5A/7thusdidnot yield unanticipated or atypicalresults.Seventeen flaws were detected at the intersection of H5/V8 with surface-connection to both the ID (9 flaws)andOD(8 flaws).Thescanlengthswere28"onthetopsideof H5 and30"onthebottom sideofH5.Theflawswereallrelatively shallow withnodepth recordedtobegreaterthan23%

through-wall (0.34")and allbutone flaw were in the HAZ above H5.This intersection alsodidnotexhibit atypical or unanticipated indications.

Unanticipated flawsweredetectedbythe UTofthe H4/V4 intersection.

Similar totheother intersection scans, approximately 15" clockwise and counterclockwise from the verticalweldintersection (30" total scanlength),aboveandbelowH4 was scanned with transducers oriented left/rightandup/down.Four axially oriented through-wall flawsweredetectednearthe intersection of H4/V4.Threeofthese flawswerethe pre-selected candidates foraboatsampleandthe fourth was newly identified during H1R26.The lengths varied from=5.3"-8" long.The through-wall natureofthese flaws was unexpected.

Two additional ID connected axial flaws>50%through-wallweredetectedandoneofthese flawswasselected fortheboatsample.The H4/V4 intersection UTscanalsodetected=40 axially oriented, part-through-wall flawsthatwere ODsurfaceconnected (3.3" maximumlength,0.3"maximumdepth).

SNC Actions in Response to Shroud Exam Results SNC prepared structural evaluations priortotheoutage.The evaluations assumed that all existing flaws were through-wall for the assessment of structural integrityandwere grown in length in accordance with BWRVIP-99-A requirements.

Tlie limitingflawatV6continuedto pass structurallyfora 10-yearreexaminationinterval wlien extrapolated.

The structural evaluation was updated during H1R26toincludealladditional flaws and updated flaw inspection results.Tfiis updated structural evaluation demonstratedstructuralflaw toleranceforanadditional 10 years.Per BWRVIP-76-A guidance,thethrough-wall observations prompted a leakage assessmentforcomparison against LOCA analysis assumptions.

The resultsofthis assessment showed adequatemarginin assumed ECCSflowsto bound conservatively assumed shroud leal<age rates and the existing LOCA analysis is acceptable for continued operation.

This assessment was initially madeforflaw growth projected over one cycle of operation and shortly thereafter updated to include two cycles of crack growth and accompanying leakage.This assessment results in more frequent inspections.

ASME Code Section XI and BWRVIP scope expansion requirements were reviewed and determined to be satisfied, as documented in corrective action program technical evaluations.

The ASiy/IE Code examinations will be repeated under successive examination criteria no later than I-I1R28.Theflawsat the vertical welds and shroud weld intersections were structurally evaluatedtobe acceptablefora10 yearinspectioninterval, and are assessed for leakage with cracks extendingfortwo cycles.SNCplansto re-examine the through-wall flaws no later than H1R28 (2018)unless a re-evaluation is successful in demonstrating adequate leakage margin existstoallow continuedgrowthofthethrough-wallflawsforadditionalfuel cycles.It should be noted thatSNCistransitioningtoGNF-2fuel beginning in 2016 on i-latchUnit1 and as partofthistransitionan updated LOCA analysis will be prepared which will take into account the most recent shroud examination results.SNC response-Communications to industry/NRC to-dateSNCnotified theBWRVIPof unexpected through-wall cracking at H4A/4 and base metal indications.Industrycalls wereheldwiththeBWRVIPIntegration, andMaterialsExecutive committees to communicate these unexpected conditions, as well as the evaluation status of the shroud via PowerPoint presentation.

The Institute of Nuclear Power Operations wasnotifiedpriorto the BWRVIPIntegrationcommittee teleconference, and was also representedduringthe teleconference.

The Hatch NRC senior resident was briefed during the outage.Program engineers respondedtoinformal questionsfromtheRegion 11 NRC-ISIinspectorviaemail.Asrequiredby ASMECodeSection XI, SNC will include shroud evaluationsinthe HIR26OARForm within 90 daysaftercompletionof the refuelingoutage.Asrequiredby participationinthe BWRVIP, SNC willdocumentasummaryofthe H1R26 BWRVIPinspectionresultstothe BWRVIP within 120 daysofthe outage per BWRVIP-g4 guidance.

BWRVIP Actions The BWRVIPisfundingand facilitating the boat sample destmctive examination and analysis.Anindustry team is overseeing the sample analysis.TheNuclear Reactor Regulation (NRR)branch chief wasbriefedbytheIntegrationChair during the Hatch outage.The BWRVIP hasformeda focus group to assess the recent shroud Operating Experience which conducteditsfirst teleconference on 4/18/14.The results of the material testing of the boat sample planned for 2015 could factorintofuture inspection and repair contingency planning whether plantspecifictoHatchorwithpotentiallyneworrevised BWRVIP guidance.

Edwin i.Hatch Nuclear Plant Response to Request for Additional Information Drawing, Core Shroud Weld Identification Roll Out (Inside View)

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