Information Notice 2000-20, Potential Loss of Redundant Safety Related Equipment Due to Lack of a High-Energy Line Break Barriers

Potential Loss of Redundant Safety Related Equipment Due to Lack of a High-Energy Line Break Barriers
	ML003760571
Person / Time
Issue date:	12/11/2000
From:	Marsh L; Operational Experience and Non-Power Reactors Branch
To:	;
References
	IN-00-020
	Download: ML003760571 (5)
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UNITEDSTATESNUCLEARREGULATORYCOMMISSIONOFFICEOFNUCLEARREACTORREGULATIONWASHINGTON,D.C.20555December11,2000NRCINFORMATIONNOTICE2000-20:POTENTIALLOSSOFREDUNDANTSAFETY-RELATEDEQUIPMENTBECAUSEOFTHELACK

OFHIGH-ENERGYLINEBREAKBARRIERS

Addressees

Allholdersofoperatinglicensesorconstructionpermitsfornuclearpowerreactors.

Purpose

TheU.S.NuclearRegulatoryCommission(NRC)isissuingthisinformationnoticetoalertaddresseestothediscoveryofseveralhigh-energylinebreak(HELB)concernsabout

redundantsafety-relatedequipmentatD.C.CookNuclearPlant,Units1and2.Afailureof

redundantsafety-relatedequipmentmayresultinrisk-significantconfigurations.Itisexpected

thattherecipientswillreviewtheinformationforapplicabilitytotheirfacilitiesandconsider

correctiveactions,asappropriate.However,suggestionscontainedinthisinformationnotice

arenotNRCrequirements;therefore,nospecificactionorwrittenresponseisrequired.BackgroundAsaresultofthenumeroussafetyissuesidentifiedatCook1and2sinceAugust1997,theNRCanalyzedtherisksignificanceofCookissuesusingtheAccidentSequencePrecursor

(ASP)programmethodology.Ofthe141issuesanalyzed,fourwerefoundtobeaccident

sequenceprecursorssincetheirconditionalcoredamagefrequenciesweregreaterthan

1.0x10-6/year.TwoofthesefourissuesinvolvedpostulatedHELBscenariosthatmayleadtofailureofredundantsafety-relatedsystems(seeLicenseeEventReports(LERs)316/98-005 and315/99-026fordetails).Withinthesetwoissuestherearethreescenariosthataredescribedbelow:

ÿAbreakinaUnit2mainsteamlineormainfeedwaterlinecoulddegradetheabilityofthecomponentcoolingwater(CCW)pumpsofbothunitstoperformtheirfunction.All

fiveCCWpumpsforCook1&2areinthesameroom.Thepumpsarenotqualifiedfor

theharshenvironmentofaHELB.Therefore,allofthepumpsmayfailonexposureto

thehighhumidityandhightemperaturescausedbyamainsteamlineoramain

feedwaterlinebreakinthepipechaseadjoiningtheroom.ML003760571 IN2000-20Page2of3ÿAbreakinthehigh-pressurefeedwaterheatersorassociatedpipingnearthedoortotheswitchgearroomcoulddegradetheabilityofbothtrainsof600Vsafety-relatedbuses.

Thedoorbetweentheswitchgearroomandtheturbinebuildingisnormallyopenand

maynotcloseintheeventofaHELB.Bothtrainsof600Vsafety-relatedbusesarein

theswitchgearroomandthebusesarenotqualifiedforaharshenvironment.

Therefore,bothtrainsofsafety-related600Vbusesmayfailonexposuretothehigh

humidityandhightemperaturesofaHELB.

ÿAHELBintheturbinebuildingcoulddegradetheabilityofallthreeauxiliaryfeedwater(AFW)pumps.Thedoortotheturbine-drivenAFWpumpisnormallyopenandmaynot

closeintheeventofaHELB.Thetwomotor-drivenAFWpumpsareinroomswhose

ventilationintakeisfromtheturbinebuilding.AFWpumpsarenotqualifiedforaharsh

environment.Therefore,allAFWpumpsmayfailonexposuretothehighhumidityand

hightemperaturesofaHELBintheturbinebuilding.

DiscussionConditionsconducivetoarisk-significantconfiguration

Fourconditionsmustcoexisttoproducearisk-significantconfigurationlikethatatCook.Thesefourconditionsare(1)lackofaHELBbarrierbetweentheredundanttrainsofasystemthatis

neededtomitigateaccidents,(2)thelackofenvironmentalqualificationfortheredundant

componentsoftrainslocatedinthesamearea,(3)thepresenceofhigh-energypipingin

adjacentareas,and(4)thelackofaHELBbarrierbetweenadjacentpipingandtheredundant

safetysystemtrains.Relationshipoftherisk-significantconfigurationtoregulatoryguidance:Section3.6.1oftheStandardReviewPlan(SRP)andNRRPlantSystemsBranchTechnicalPositionSPLB3-1(formerlyAPCSB3-1)provideregulatoryguidanceontheplantdesignfor

protectionagainstpostulatedpipingfailuresoutsidecontainment.WhenSPLB3-1isusedasa

guidetomeettherequirementsoftheGeneralDesignCriterion4of10CFRPart50,

AppendixA,themethodusedtoconformwiththatregulatoryguidancedependsuponwhenthe

constructionpermitapplicationsweretenderedandtheoperatinglicensesissued.SectionB.4 ofSPLB3-1providesdetailsonthedependenceofitsapplicabilitytothedatesonwhich

constructionpermitsweretenderedoroperatinglicenseswereissued.GenericLetter87-11,issuedonJune11,1987,transmittedRevision2oftheMechanicalEngineeringBranch(MEB)TechnicalPositionMEB3-1.Thisrevisionprovidedadditional

guidanceonlocationswherepipebreaksshouldbepostulated.Revision2ofMEB3-1allows

theeliminationofpipe-whiprestraints,jet-impingementshields(placedtomitigatetheeffectsof

arbitraryintermediateruptures),andotherrelatedchanges.However,therevisiondoesnot

relievelicenseesfromtheneedtoconformtotheguidancerelatingtoHELBeffectsonessential

systemsandcomponents.Essentialsystemsandcomponentsaresystemsandcomponents

requiredtoshutdownthereactorandmitigatetheconsequencesofapostulatedpipingfailure, withoutoffsitepower.EventhoughapplicationofRevision2oftheMEB3-1pipebreakcriteria

maynotrequirepostulatingbreaksnearareasthathousetheredundantequipmentand

installingpiperestraints,licenseesareexpectedtocomplywiththeirlicensingbasisand

regulatorycommitmentsforpostulatingacrackatthelocationmostdamagingtothe

IN2000-20Page3of3essentialstructuresandsystems.Forexample,theGiambussoletterof1972(NUREG-0800,StandardReviewPlan3.16.1,AppendixB,Rev.2,October1999)specifiesthatwherepipes

carryinghigh-energyfluidsareroutednearstructuresandsystemsnecessaryforsafe

shutdownoftheplant,supplementalprotectionofthosestructuresandsystemsshallbe

providedtocopewiththeenvironmentaleffects(includingtheeffectsofjet-impingement)ofa

singlepostulatedopencrackatthelocationmostdamagingtothoseessentialstructuresand

systems.NUREG-1728,"AssessmentofRiskSignificanceAssociatedWithIssuesIdentifiedatD.C.CookNuclearPowerPlant,"Volumes1&2werepublishedinOctober2000.Thisreport

documentstheresultsofananalysisoftherisksignificanceatD.C.CookNuclearPowerPlant, Units1&2sinceAugust1997.ThisNUREGmaybeaccessedelectronicallyattheNRC's

PublicElectronicReadingRoomatwww.nrc.gov/NRC/ADAMS/index.html

.Thisinformationnoticerequiresnospecificactionorwrittenresponse.Ifyouhaveanyquestionsabouttheinformationinthisnotice,pleasecontactoneofthetechnicalcontactslisted

below,theappropriateregionaloffice,ortheappropriateOfficeofNuclearReactorRegulation

(NRR)projectmanager./RA/LedyardB.Marsh,ChiefEventsAssessment,GenericCommunicationsandNon-PowerReactorsBranchDivisionofRegulatoryImprovementPrograms

OfficeofNuclearReactorRegulationTechnicalcontacts:S.D.Weerakkody,RESY.C.Li,NRR301-415-6374301-415-2772 E-mail:sdw1@nrc.govE-mail:ycl@nrc.govC.D.Petrone,NRR301-415-1027 E-mail:cdp@nrc.govAttachment:ListofRecentlyIssuedNRCInformationNotices