ML102570807
| ML102570807 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 09/13/2010 |
| From: | Price J A Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 10-050A | |
| Download: ML102570807 (23) | |
Text
10CFR50.55a VIRGINIA ELECTRIC AND POWER C O MPAN Y RICHMOND, VIRGINIA 23261September13
, 2010U.S.NuclearRegulatoryCommissionAttention:DocumentControlDeskWashington,D.C.20555SerialNo.NL&OS/ETSDocketNos.LicenseNos.
10-050A RO 50-338/339 NPF-4/7 VIRGINIA ELECTRICANDPOWER COMPANY (DOMINION)NORTHANNA POWER STATIONUNITS1AND2 ASME SECTION XI INSERVICE INSPECTION PROGRAM RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION RELIEF REQUEST N1-14-RI-001 AND N2-14-RI-001 REQUEST FOR ALTERNATIVE-IMPLEMENTATIONOFA RISK-INFORMED INSERVICE INSPECTION PROGRAMBASEDONASME CODECASEN-716InaFebruary23
,2010letter(SerialNo.10-050),Dominionrequestedauthorizationtoimplementarisk-informedinserviceinspection(RI-ISI)programbasedontheAmericanSocietyofMechanicalEngineers(ASME)CodeCaseN-716
,asdocumentedintheRequestsforAlternative N1-14-RI-001 and N2-14-RI-001forUnits1and2,respectively.
N1-14-RI-001 and N2-14-RI-001weresubmittedinatemplateformat.InanAugust12,2010e-mailfromDr.V.Sreenivas,theNRCrequestedadditionalinformationtocompletethereviewoftheRI-ISIprogram.Theattachmenttothisletterprovidestherequestedinformation
.Dominionplanstoimplementthisalternativefortheentire4thlSIIntervalforNorthAnnaUnits1and2.NorthAnnaUnit1's4th10-YearInte rvalbeganMay1,2009andwillendApril30
,2019.NorthAnnaUnit2
's4th10-YearIntervalbeginsDecember14
,2010andwillendDecember13
,2020.Therefore,Dominioncontinuestorequestreviewandapprovalof N1-14-RI-001 and N2-14-RI-001byFebruary
, 2011inordertoplanandcompletethefirstperiodexaminations.Ifyouhaveanyquestionsorrequireadditionalinformation
,pleasecontactMr.ThomasShaubat(804)273-2763.
Respectfully, J.aPrice Vi peresident-NuclearEngineering Attachment 1.ResponsetoRequestforAdditionalInformation-ReliefRequests N1-14-RI-001 and N2-14-RI-001with3Enclosures SerialNo.10-050ADocketNos.
50-338/339ResponsetoRequestforAdditionalInformationFourthIntervalRisk InformedReliefRequests N1-14-RI-001
&N2-14-RI-001Page2of2cc:U.S.Nuclear Regulatory CommissionRegionII Marquis One Tower 245 Peachtree CenterAvenue,NE,Suite1200 Atlanta, Georgia 30303-1257Mr.J.E.Reasor,Jr.
Old Dominion Electric Cooperative Innsbrook Corporate Center 4201 Dominion Blvd.Suite300GlenAllen, Virginia 23060 NRC Senior Resident InspectorNorthAnnaPowerStationMs.K.R.CottonNRCProject ManagerU.S.Nuclear Regulatory CommissionOneWhiteFlintNorthMailStop 0-8 G9A11555RockvillePike Rockville, Maryland 20852Dr.V.Sreenivas NRC Project ManagerU.S.Nuclear Regulatory CommissionOneWhiteFlintNorthMailStop 0-8 G9A11555RockvillePike Rockville, Maryland 20852 Ser ial No.10-050ADocketNos.
50-338/339 ResponsetoRequestfor Additional InformationFourthIntervalRisk InformedReliefRequests N1-14-RI-001
&N2-14-RI-001 Attachment RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION INSERVICE INSPECTION PLAN RISK INFORMED FOURTH INTERVAL RI RELIEF REQUESTS N1-14-RI-001 AND N2-14-RI-001NorthAnna Power StationUnits1and2 Virginia Electric and Power Company (Dominion)
Serial No.10-050A Docket Nos.50-338/339 Response to Request for Additional Information Fourth Interval Risk Informed Relief Requests N1-14-RI-001&N2-14-RI-001Page1of13 BackgroundByletterdatedFebruary23,2010,VirginiaElectricandPowerCompany(Dominion),submittedforstaffreviewandapprovallSIProgramReliefRequests N1-14-RI-001 and N2-14-RI-001,whichrequestapprovaltousealternativerisk-informedinserviceinspection(RI-ISI)selectionandexaminationcriteriaforCategoryB-F,B-J, C-F-1 andC-F-2pressureretainingpipingweldsfortheNorthAnnaPowerStation(NAPS)Units1
&2.Tocompletetheirreview,theNRCstaffrequestedthefollowingadditional information.
Probabilistic Risk Assessment Licensing BranchTheNRChasnotendorsedEPRI(ElectricPowerResearchInstitute)Topical Report1018427.ThequestionslistedbelowaddressthequalityofNorthAnnaprobabilisticriskassessment(PRA)model.Question1.A self assessment performedontheNorthAnnaPRA model in August 2007 identifiedPRAmodeling and documentationsupportingrequirements(SRs)wherethePRA modeldidnot meet Capability Category (CC)" of the ASME(AmericanSocietyof MechanicalEngineers)PRAstandard.In December2009,a modelupdatewas performedtomeet Category" of the ASME PRA standard and RegulatoryGuide1.200 Rev 1.Pleaseidentify anddispositionanyremainingdifferenceswithCC"requirements(i.e.
,openitems)thatmay affectthisapplication.DominionResponseAselfassessmentwasperformedontheNorthAnnaPRAmodelinJune2010identifyingremainingopenitemsthatdonotmeetRegulatoryGuide1.200Rev1CapabilityCategory(CC)IIrequirements.Theseopenitemsareidentifiedandevaluatedfor theirpotentialtoimpacttheriskassessmentperformedfortheRI-ISIprogramatNorthAnna.Specifically,theunmetsupportingrequirements(SRs)areconsideredfortheirabilitytoimpactthequantificationofalargebreakLOCA,whichwastheboundingcasethatwasusedforthechangeinriskanalysis,ortheinternalfloodinganalysis,whichwasusedforscopedetermination.Basedontheevaluationinthetablebelow,noneoftheopenitemsidentifiedinthecurrentNorthAnnaPRAmodelaffecttheinputsorresultsofthisapplication.
Ser ialNo.10-050ADocketNos.50-338
/339 Respo nsetoRequestforAdd it ional Information Fourth Interva l R isk Informed Relie f Requests N1-14-RI-001&N2-14-RI-001Page2of13 Gap Description Self Assessment ImpactontheRI-ISIApplicat ion AS-A4Forkey safety functions SR remainsasNOTMETuntil 1)The importanceoftheSBOD iesel (e.g.,powerrestoration)1)anhumaneventprobability islowwith respec ttofloodi ng events identify operator actio ns (HEP)isaddedtothestation andalargeb reakLOGAeventi n the toac hievethedef ined B lackout (SBO)nodes for No rth A nnaPRAmode l.TheR isksuccesscriteria.restoringtheEGGSfunctions;Ach ievemen t Worth (RAW)ofth eand2)text insec tion 2.3.3.1isSBOfor flooding even ts is1.00 , and revisedtoclarifytheneed fortheSBORAW foralargebrea k operatoractiontorestartEGGSLOGAevent is1.01.Basedonthis functions.lowriskworth,addinganHEPt o theSBOnodesforrestoringtheEGGS fu nctions wou ld no t impact the resultso fther isk assessment perfo rmedtosupportth is application.2)No t S ign ificant.Th is is judgedtobea documentation consideration on lyanddoesnotaffect the technical adequacy of thePRA mode l.AS-B5aDefineandmodelplantTheNAPS modelscredituseofFora lloft he crosst ie systems , e ither configurationsandtheopposite unit systems , e.g., the unava ilability duri ng refuel ing alignmentsthatreflect chargingsystemandd iesel-outages is accountedforinthePRA dependenc ies.generators
, for accident unavailabilitieso r the system/trains mitigation.However,n o do nothavesignificant unavailability documentation was identifiedduringoutages.Theo nly exceptionthatwou ldshowhowopposite arethe electrica lbuseswhere the unit outageswereconsidered.unavailability duringatpower For example , during a refueling operationisnot included i n thePRA outage,aTrain-Aoutagemaymodel.Thees t imated unavailabilitymakecharg ing or component is1-2days , whichislesst han1E-2 cooling(GC)cross-t ie change i n estimated unavailability.
unavailableforasignificant Thissmallchange i n unavailability pe riodoft ime.Suchwouldnot impacttheflooding unavailability va lues cou ld evaluationort he quantification o f areach5%overal l.If la rge break LOGA.u navailability dur ing opposite-un it outagesi s included in theoverallsys tem unavailability, then thatcou ldbestatedinth e accide nt seque nce (AS)docume ntation.DA-D2W henusingexpert DocumentationneedstobeNotS ignif icant.Thisisjudgedtobe judgment docume nt the enhanced fortheseveralcases a documentatio n consideratio n only rationa lebehindthewhereexpertopinionisused
.anddoesnota ffectthetechnicalchoiceof parameterTheexpe rt opinioni s adequacy of thePRAmodel.
val ues.reasonableandshouldnot cha nce.
SerialNo.10-050A Docket Nos.50-338/339 ResponsetoRequestforAddit ional InformationFourthIntervalRisk InformedReliefRequestsN1-14-RI-001&N2 RI-001Page3of13 Gap Description Self Assessment ImpactontheRI-ISIApplicat ionQU-B1Identify method-specific Although key assumptionsareNotSign ificant.Thisisjudgedtobe limitat ions and features documented,thesedonot a documentation consideration onlythatcould impact the include l imitationsoftheanddoesnot affectthetechnicalresultsand applications.
quantification method or adequacyofthePRAmodel.
featuresthatimpactresults(asidefromreferencestocode l imitations
, guidance documents and procedures).
QU-F5 Identify method-specific Although key assumptionsareNotS ignificant.Thisisjudgedtobe limitations and features documented,thesedonota documentation consideration onlythatcouldimpactthe include limitationsoftheanddoesnot affectthetechnicalresultsand applications
.quantif ication method or adequacyofthePRAmodel.
features that impact resu lts(asidefrom referencestocode limitations , guidance documents and procedures).
SC-A6Includea discussionofSomeofthesuccesscri teriaNotS ignificant.Thisisjudgedtobe operator actions discussion includesgenerala documentation consideration only assumedaspartofthe operator actions ,butt heanddoesnotaffectthetechnical success criteria discussiondoesnot include adequacyofthePRAmodel.
development
,andhow proceduresandnotallevent those actionsaretree sectionscontainthe consistentwithplant discussion.
procedures and practices.SY-A2Useresultsofplant The DominionPRAstaffhasNotSign ificant.Thisis judgedtobe walkdownsandplant performedmanysystem a documentation cons ideration on ly personnel interviews walkdowns dur ing theanddoesnot affectthetechnical (system engineers and development and maintenance adequacyofthePRAmodel.
operators)asasourceofofthemodels
.Inaddition
, informat ion for modeling DominionPRAstaffworkstheas-built, as-operated closelywithNorthAnnasystem plant.engineers and operators onnearlyadailybas is w hile supporting the various r isk informed programs.However ,noformal documentation existsatthistimeto allowclosureof these supporting requirements (SRs).It isNOT anticipatedthatnotmeetingthis requirementwillhavea siqnificantimpactonthemodel.
SY-B15IdentifySSCsthatmay Currently ,theNAPSPRA Including a specific fa ilure probabilityberequiredto operate inmodeldoesnotdistingu ishfora pressurizer PORV fa iling to condit ionsbeyondthe irbetweenPZRPORVs failing to reseat afterpassingwaterwouldnot env ironmentalrecloseonwaterorsteam impacttheinternalflooding qualifications.relief.SeeEPRI TR-1011047 evaluationorlargebreakLOCA "ProbabilityofSafetyVa lve quantif ication,sothisopenitemdoes Failure-to-Reseat Following not impacttheRI-ISIapplication
.SteamandLiquidRelief
."
Ser ial NO.1 0-050A Docket Nos.50-338/339 Response to Request for Additional Information Fourth Interval Risk Informed Relief RequestsN1-14-RI-001&N2-14-RI-001Page4of13 Gap Descr iption Self Assessmen t ImpactontheRI-ISI Applicat ion SY-B8 Use resultsofp lant The Domin ion PRAstaffhasNot Significant.
Th is is judgedtobe walkdowns and plant performed many system a documentation cons ideration only personnel interviews walkdowns during the and does not affect the techn ical (system engineers and development and maintenance adequacyofthe PRA model.operators)asa sourceofofthe models.In addition , informat ion for model ing Domin ionPRAstaff workstheas-bu ilt, as-operated close ly w ith North Anna system plant.engineers and operators on nearly a daily basis while supporting the various risk informed programs.However , no formal documentation ex istsatthist ime to allow closure of theseSRs.Itis NOT anticipated that not meeting this requirement will have a significant impactonthe model.HR-G4Basethe time available Time windows for successfulAspartofthe 2009 model update , to complete actions on complet ionofact ions in some new MAAPrunswere performed for appropr iate realistic instances may needtobe someofthekey operator act ions.generic thermal-updated (for example, those This includesrunsto support the hydrau lic ana lyses , or thatarebasedonest imates est imat ionofHEP-1FRH:1-11and simulat ion from similar madefortheIPE).HEP-1FRH 1-15-0NE ,whicharethe plants only HEPs that could significantly affect the internal flood ing evaluat ion.TheHEPfor transferring to hotleg recirculation
, HEP-1ES1:4 , isthe only HEP importantforlarge break LOCA quantification
.Updatingthe timingforaddit ional HEPs to meetCCIIofthisSRwould not impacttherisk assessment performed fortheRI-ISI application
.HR-G5Basethe required t ime No documentation cu rrently Not Signif icant.This i s judgedtobe tocompleteactions fo r exists and thisSRwill remain a documentation cons ideration only significant HFEs on NOTMET.Asa footnote the and does not affect the techn ical action time timingsarenot expected to adequacyofthe PRA model.measurements i n either change significantly as they are walkthroughs or talk-based on comparisons with throughsofthe similar actionsatSurry.procedures or simulato r observations
.SY-A4Useresu lts of plant The Dominion PRAstaffhasNot Signif icant.This is judgedtobe walkdowns and plant performed many system a documentation consideration only personnel interv iews walkdowns during the and does not affectthetechn ical (system engineers and development and maintenance adequacyofthePRA model.operators)asa source ofofthe models.In addition , informationfor modeling Domin ionPRAstaffworks the as-built , as-operated closelywithNorth Anna system plant.engineers and operators on nearly a daily bas is wh ile Serial No.1 0-050A Docket Nos.50-338/339 Response to Request for Additiona l Information Fourth Interval Risk Informed Relief Requests N1-14-RI-001&N2-14-RI-001Page5of13 Gap Description Self Assessment ImpactontheRI-ISI Application support ing the various r isk informedprog rams.However , no forma l documentation ex istsatthis time to allow closure of these SRs.Itis NOT anticipatedthatnot meet ing this requi rement will have a significant impactonthe model.AS-A7 Delineate accidentSRis NOT ME T until: 1)1)Inclusion of consequent ial RCP sequence (e.g.,Lossof inclusion of consequent ial loss seal cooling for transientswouldnotRCPseal cooling)forofRCPseal cooling for affecttheapplication because onlyeachin itiating even t trans ients ,and2)the large break LOCA and flooding (e.g., trans ients).documentat ion enhancement of events were quantified.
the U1-RCPSL nodes.ConsequentiallossofRCPcooli ng is considered for flooding eventsinthe North Anna PRA model ,anddoes not applyfora large break LOCA scenario.2)Not Significant.
Th is is judgedtobea documentat ion consideration onlyanddoesnot affect the technical adequacyofthe PRA model.QU-E1 Identify key sources of Each PRA element notebookNotSign ificant.This i s judgedtobe mode l uncerta inty.(IE ,AS,SC,SY , DA ,HR,LE)a documentation cons ideration only has identified potent ial sources and does not affect the technical of model uncertainty.
A adequacyofthePRA model.characterization of those sou rces of uncertainty and evaluat ionofthe generic sources of uncertaintyhasnotyetbeen completed however.QU-F4 DOCUMENT key Although the different element Not Significant.
This is judgedtobe assumptionsandkey notebooks (IE , AS , SC , SY , a documentat ion considerat ion only sources of uncertainty
,etc.)do include specific and does not affectthetechn icalsuchas: possible assumptions relatedtothe adequacyofthe PRA model.optimistic or development of that element , conservative success thereisno discussion inthe criteria, suitabilityoftheQU.1 (input)and QU.2 (results)rel iability data , possible notebooksofthe sources of modeling uncertaint ies uncertainty inthe NAPS model, (model ing limitations duenorofthe assumptions to the method selected), associated with those degree of completeness uncertaint ies.inthe selection of initiating events , possible spatial dependencies
, etc.
Ser ial No.10-050A Docket Nos.50-338/339 ResponsetoReques t for Additional Information Fourth Interval Risk InformedReliefRequestsN1-14-RI-001&
N2-14-RI-001Page6of13 Gap Description Self Assessment ImpactontheRI-ISI Application LE-D4 PERFORM a realistic Secondary side isolationisNotSignificant.
This iswithregards secondary side isolat ion explicitly and realistically to SGTR init iating eventandwould capab ility analysis for modeledintheLevel1System not impact t he flood ing evaluation orthesign ificant accident Analys is notebooks for pre-core the quantificationofalargebreak progression sequences damage cons ideration.
LOCA.causedbySGt ube However , secondary side release.USEa isolation during a SGTR should conservativeoraalso consider the additional combination of number of demandsonthe conservat ive and relief valvesinthe progress ion realistic evaluationoftocore damage.Itis possible secondary side isolationthatsome sequences capabilityfornon-considered"isolated"inthe signif icant accidentLevel1 analysiscouldbe progression sequences unisolated intheLevel2 result ingina large early analysis.Also , vers ion4ofthe release.JUSTIFY MAAP codeprovidesbetter applicabilitytotheplant SGTR analysisthanhadbeen be ing evaluated.usedfortheIPEwith version 3 Analysesmayco ns iderofthecode.
realistic comparison with similar isolation capability in similar containment designs.QU-E2 IDENTIFY keyTheQU.1(input) notebook Not Significant.Aspartofthe2009 assumptions madeinthe indicatesthatkey modelingmodelupdate,withineachPRA developmentofthePRA assumptions are documented in element notebook(IE,AS,SC,SY
, model.PartIIofthePRAmodel DA , HR , LE), potent ialsourcesof notebook ,butthisparthasnot mode l uncerta intyhavebeenyetbeen developed (although identified.
A characterization of thosesomekey assumptionsmaybe sources of uncertainty and available intheIPE submittal), evaluationofthe genericsourcesof The different element uncertaintyhasnotyetbeen notebooks (IE , AS , SC , SY , completed however.Thisis judgedetc.)do include specif ictobea documentation consideration assumptionsrelatedtotheonlyand does not affect the developmentofthat elemen t, technical adequacyofthePRAbutthereis typically no model.discussionofthesourcesof uncertainty those assumptionsrelatetoandthe impacts of those assumptions.
QU-E3 ESTIMATE theTheQU.1(input)and QU.2 Not Significant.
The parametric uncerta inty intervalof(resul ts)notebooksdonot uncerta inty analysishasbeentheoverallCDFresults
.include a parametric uncertainty drafted and documented in notebook ESTIMATE the analysis.AlthoughQU.1does QU.3 , whichi s currently undergoing uncertainty intervalsnotethatthebasis event data acceptancereview.The parametr ic associated with(BED)file contains uncertainty uncertainty analysishasbeen parameter uncertainties d istributiondataandthebasic performed with correlated basic (DA-D3 , HR-D6 , HR-G9 , event u ncertaintydatainthe events in ordertoreflect"state-of-IEC13), taking into parameterfileis documented in knowledge" dependencies
.Thisis SerialNo.10-050ADocketNos.50-338/339ResponsetoRequestforAdditionalInformat ionFourthIntervalRiskInformedRe lief Requests N1-14-RI-001
&N2-14-RI-001Page7of13 Gap Description Self AssessmentImpactontheRI-ISIApplicationaccountthe "state-of-thedatanotebooks(section judgedtobea documentation knowledge" correlation
.2.5),andthat uncertainty cons iderationonlyanddoesnotanalysescanbe performedonaffectthetechn icaladequacyofthetheequationf iles (sect ion 4.0),PRAmodel.thereisnosuchanalysismentionedinQU.2
.Thereareafewbasiceven ts in the parameter file (N05A_16C.prm)thatdonot contain uncertainty d istribution data.
SerialNo.10-050A Docket Nos.50-338/339 ResponsetoRequestforAddit ional InformationFourthIntervalRiskInformedReliefRequests N1-14-RI-001&N2-14-RI-001Page8of13Question2Thesupporting requirement(SR),IF-C6andIF-C8,permits screeningoutoffloodareas based on , in part ,thesuccessofhumanactionstoisolate andterminatethe flood.TheendorsedRI-ISImethodsrequiredetermination ofthefloodscenariowithandwithouthumaninterventionwhichcorrespondstothecapability category/1/,i.e.,scenariosare not screened out basedonhumanactions.Therefore a category/1/analysiswouldbe acceptable
.Toprovideconfidencethatscenariosthat might exceedthequantitativeCDFand LERFguidelineareidentified
,pleasedescribe how creditisgiventohumanactionsifthe currentapplicationanalysisdoesnotmeetCapability Category/1/forthesesupportingrequirements.DominionResponseFloodswerenotscreenedoutbasedontheabilityofhumanactionstoisolateormitigateafloodintheNorthAnnaPRAmodel.Themodelmeets CapabilityCategoryIIIforIF-C6andIF-C8,whichisappropriateforthisapplication.NDEBranchQuestion1TableIWB-2500-1 of ASME ,SectionXI,2001Editionwith 2003Addendarequires volumetric and/orsurfaceexamination ofallCategoryB-ForB-JPressureRetainingDissimilarMetalWelds greaterthanNPS 1.Basedonrecentfindings of primary waterstresscorrosioncracking(PWSCC)in Alloy 82/182 dissimilar metalweldsthe staffwouldlikemoreinformationon yourinspectionplansfortheseweldsinthe 4 h IntervallSIPlanforNAPSUnits 1&2.Describetheinspectionplanof Alloy 82/182 dissimilar metal welds greaterthanNPS1inthe4thIntervallSIPlanforNAPSUnits 1 and 2 (e.g.,aretheseweldsincludedinthe number of welds selectedforexaminationintheRI-ISIprogram
,howmanyoftheseweldsare selectedforexamination
,whatexaminationmethodes)arebeingemployed
,whatisthefrequency ofexamination,howisdisposition oflimitedcoverage
<<90%)examinations handled , etc.).DominionResponsePWSCCisanactivedegradationmechanism(OM)includedintheCodeCaseN-716(RIS-B)analysis.ThechecklistcriteriaforPWSCCis:a.pipingmaterialisInconel(Alloy600),and SerialNo.10-050ADocketNos.50-338/339 ResponsetoRequestfor Additional Informat ionFourthIntervalRisk InformedReliefRequests N1-14-RI-001
&N2-14-RI-001Page9of13b.exposedtoprimarywaterattemperaturesgreaterthan570 0 F , andc.thematerialismill-annealedandcoldworked,orcoldworkedandweldedwithoutstressrelief.ThemethodofexaminationforPWSCCsusceptibleweldsisavolumetricexaminationusingASMESectionXIFigureIWB-2500-8(c).Thevolumeshallbeincreasedbyenoughdistance
, approximately1/2inch,toincludeeachsideofthebasemetalthicknesstransitionorcounterboretransition.TwoareasatNorthAnnawererecognizedassusceptibletoPWSCCintheRIS-Banalysis:1)Unit1SteamGeneratorhotlegnozzles,and2)thepressurizernozzletosafe-endwelds,includingthoseforthesurgeline,spraylineandsafetyandreliefvalvelinesforbothunits
.TheUnit2Steam Generatorhotlegnozzles,whichcontaintheAlloy82/182materialthatissusceptibletoPWSCCwereinlaidwithAlloy52duringpreserviceconstruction.Therefore
,theAlloy82/182materialhasneverbeenexposedtoprimarygradewater.ForUnit1 ,sevencomponentswereassignedPWSCC susceptibilityandfour(57%)wereselectedforexamination.TwoUnit1componentswereassignedDMsforbothPWSCCandTT(ThermalTransients).Bothofthesetwocomponentshavebeenselectedforexamination
.ForUnit2,fourcomponentswereassignedPWSCCsusceptibilityandone(25%)wasselectedforexamination.TwoUnit2componentswereassignedbothPWSCCand ITDMsandbothwereselectedforexamination.BytheCodeCasecriteriaaminimumof25%oftheDMsor combinationofDMsshouldbeselectedforexaminationperinterval.Theseselectionswillbeexaminedonceperinterval.Inthismanner
,theClass1Alloy82/182dissimilarmetalweldswereincludedinthepopulationanalyzedbytheCodeCaseN-716applicationtomakecomponentselectionsforexamination.AllofthedissimilarmetalweldsonbothUnit1and2 pressurizershavebeenoverlaidwithPWSCCresistantmaterialtoreinforcethestructuralintegrity.ReliefRequestNDE-005forNorthAnnaUnit1Interval4wasdevelopedtoaddresstheinspectionmethodandfrequencyforthepressurizeroverlaysandwasapprovedbytheNRCinaletterdatedSeptember28,2009(ML092530274).DominionplanstoinspecttheUnit1overlaidweldsinaccordancewiththisreliefrequestatthistime.Thesamesamplingselectionof25%isrequiredbythereliefrequest
,sothenumberofinspectionsisconsistentwiththeRIS-Bapproach
.However,CodeCaseN-716doesnotaddressweldsthathavebeenoverlaid.Theinspectiontechniquesandallaspectsofthereliefrequest(includingdeterminationofadditionalexamsandevaluatingindications)willbefollowedforUnit1overlaidselectedexaminations.DominionanticipatesCodeCaseN-770,"AlternativeExaminationRequirementsandAcceptanceStandardsforClass1PWRPipingandVesselNozzleButtWelds SerialNo.10-050A Docket Nos.50-338/339 Response to Request for Additional InformationFourthIntervalR isk Informed Relie f RequestsN1-14-RI-001&
N2-14-RI-001 Page 10of13FabricatedWithUNSN06082orUNSW86182WeldFillerMaterialWithorWithoutApplicationofListedMitigationActivities"willbeincorporatedbytheNRCintothenextrulechangeoftheFederalRegisterbyMay2011.ThisnewruleshouldbeeffectiveintimetoestablishtheexaminationrulesforUnit2pressurizeroverlaidweldinspections.IfincorporationofCodeCaseoccursasanticipated,DominionwillthenusetherequirementsofCodeCaseN-770togoverninspectionrequirementsforweldsfabricatedwithAlloy82/182materialandwithdrawtheUnit1reliefrequest.TheinspectionselectionsdeterminedbytheRIS-BProgramwillremainunchanged.However,theguidanceofthisCodeCasewilldeterminetheexaminat ionmethods.Ifneeded,areliefrequestsimilartoUnit1willbesubmittedfortheUnit2pressurizeroverlaidAlloy600welds,toaddressinspectionmethodandtechnique.NorthAnnacurrentlyhasanAugmentedPlanthataddressesMRP-139,"MaterialReliabilityProgram:PrimarySystemPipingButtWeldInspectionandEvaluation Guideline.
"ExaminationsmustbeperformedonAlloy600weldsuntiltheweldshavebeenmitigated.
Currently ,theUnit1SteamGeneratorhotandcoldlegnozzletosafeendweldsmustbeexaminedasfollows:*Onehotlegnozzleweld:Baremetalvisualinspectioneveryrefuelingoutage,UTeveryperiod*Onecoldlegnozzleweld:Baremetalvisualinspectioneveryrefuelingoutage,UTeveryfiveyearsCodeCaseN-722wasincorporatedintothelastpublicationoftheCodeofFederalRegulationsandwasimplementedbyJanuary2009atNorthAnna.TheCodeCaserequiresavisualbaremetal(VE)inspectiononunmitigated,Class1,Alloy600welds.
Steam Generatorhotlegnozzle-to-pipe-weldsmustreceiveaVEinspectioneveryrefuelingoutageandtheSteam GeneratorcoldlegnozzlesmustbeVEinspectedonceperinterval.IfanyRIS-Bselectionsaremadeonweldsthathavenotbeenmitigated(i.e.,Steam Generator hotlegs)theywillbevolumetricallyexaminedinaccordancewithCodeCaseN-716usingASMESectionXIFigureIWB-2500-8(c).Thevolumeshallbeincreasedbyenoughdistance, approximately1/2inch,toincludeeachsideofthebasemetalthicknesstransitionorcounterboretransition.DominionhasusedthephasedarrayUTtechniquepreviouslyontheSteamGeneratornozzleweldstoachievemaximumcoverageandobtainacceptableresultsandplanstocontinuetousethephasedarraytechniqueontheSteam Generator welds..PartoftheinitialselectionprocessfordeterminingRIS-B examinationsistochoosecomponentsthatareknowntomeetfullcoveragerequirements.Iflimitedexaminations Ser ialNo.10-050ADocketNos.50
-338/339ResponsetoRequestfor Additional Information Fourth Interva l Risk InformedReliefRequests N1-14-RI-001&N2-14-RI-001Page11of13(coverage90%orless)dooccur,Dominionwilladdressthelimitationsbyareliefrequestinaccordancewith10CFR50.55a(g)(5)(iii)
.Tosummarize,presentlythereareseveraldriverstoinspectAlloy600weldssusceptibletoPWSCC:CodeCaseN-722,MRP-139andtheproposedRiskInformedInserviceInspections.NorthAnnahasprogramsinplacetoaddresseachoftheseindependently.TheRIS-BanalysiswasperformedwithoutconsiderationofanyotherProgramsforinspectingAlloy600welds;suchasMRP-139andCodeCaseN-722.TheanalysisoftheRIS-BProgramdidnotcreditexamsscheduledtomeetN-722ortheAugmentedProgram(MRP-139)inanymannertoreducetheneedforinspections.IfweldshavebeenoverlaidtheyarestillnotedintheRIS-BProgramassusceptibletoPWSCCandwillbeselectedforexaminationasrequired.ThetechniqueforexaminingtheoverlaidweldswillfollowcriteriaofeitheranacceptedreliefrequestorCodeCaseN-770ifincorporatedintotheCodeofFederalRegulations.Examinationoverlapmayoccurandcredit foroneweldexammaybetakenformultipleprogramsifthe examination specifications/requirementsforeachprogramcreditedaremet.NRCQuestion2 Section 3.3 of the February 23 , 2010submittalstatesthat,"In contrasttoanumberofRI-ISIProgramapplicationswherepercentageofClass 1pipinglocationsselectedforexaminationhasfallen substantially below 10%,CodeCaseN-716mandatesthat10
%bechosen." Immediately belowthisparagrapha brief summary is providedshowingthe numberofweldsinClass 1 , 2 andnon-classsystemsalongwiththe numberofwelds selectedforexaminationforNAPSUnits 1&2.Accordingtothis summarythenumberofClass 1 welds selectedforexaminationonUnit 2 is significantlylessthan10
%ofthe total numberofClass 1welds.Pleaseexplainthis discrepancy
.DominionResponseAtNorthAnna,theClass1boundarieshavebeenunnecessarilyextendedbeyondthesecondisolationvalvefromthereactorpressurevessel.Thiswasdonetocoordinate the"Q"Qualityboundarydesignationsthatweremadeduringsystemdesignand construction.IndeterminingtheHighSafetySignificant(HSS)componentsthataresubjecttoselectionforexamination,CodeCaseN
-716definesHSSweldsas:(1)Class1portionsofthereactorcoolantpressureboundary(RCPB)
,exceptasprovidedin10CFR50.55a(c)(2)(i)and(c)(2)(ii).10CFR50.55a(c)ReactorCoolantPressure Boundary(2)(ii)states "Thecomponentisorcanbeisolatedfromthereactorcoolantsystembytwovalvesinseries(both SerialNO.10-050A Docket Nos.50-338/339ResponsetoRequestforAddit ional InformationFourthIntervalRisk InformedReliefRequests N1-14-RI-001
&N2-14-R I-001Page12of13closed,bothopen
,oroneclosedandtheotheropen).Eachopenvalvemustbecapableofautomaticactuationand
,assumingtheothervalveisopen
,itsclosuretimemustbesuchthat,intheeventofpostulatedfailureofthecomponentduringnormalreactoroperation,eachvalveremainsoperableandthereactorcanbeshutdownandcooleddowninanorderlymanner,assumingmakeupisprovidedbythereactorcoolantmakeupsystemonly.
"Part(2)oftheCodeCasefurtherdefinesHSScomponents:(2)applicableportionsoftheshutdowncoolingpressureboundaryfunction.Thatis,Class1and2weldsofsystemsorportionsofsystemsneededtoutilizethenormalshutdowncoolingflowpatheither: (a)aspartoftheRCPBfromthereactorpressurevessel(RPV)tothesecondisolationvalve(Le.,farthestfromtheRPV)capableofremoteclosureortothecontainmentpenetration,whicheverencompassesthelargernumberofwelds;or (b)othersystemsorportionsofsystemsfromtheRPVtothesecondisolationvalve(i.e.,farthestfromtheRPV)capableofremoteclosureortothecontainmentpenetration,whicheverencompassesthelargernumberof welds.Section3.1oftheFebruary10
,2010submittalreiteratesthisinformation.BasedonthedefinitionsinCodeCaseN
-716,263ofUnit2Class1SafetyInjectionweldsareLowSafetySignificant(LSS),513ofClass1ChargingweldsareLSS.ForUnit1,38ofClass1SafetyInjectionweldsareLSSand77Class1ChargingweldsareLSS.TheseweldsarenotrequiredtobeincludedintheHSSpopulation,butareincludedinthetotalClass1weldcountinthetableofSection3.3ofthe February 10,2010 submittal.ThestatementinSection3.3whenaddressingtheuniqueclassificationdefinitionsatNorthAnna,wouldbebetterstated,"IncontrasttoanumberofRI-ISIProgramapplicationswherethepercentageofHSSClass1pipinglocationsselectedforexaminationhasfallensubstantiallybelow10%
,CodeCaseN-716mandatesthat10%bechosen
."AtmostplantsthetotalnumberofClass1componentswillbeHSS;however,atNorthAnnaUnits1and2,theyarenot.
Dominion'sengineeringdocument"RiskInformedInserviceInspectionProgramforNAPS1and 24thIntervals,CodeCaseN-716Based "waswrittentosupporttheRI-ISIsubmittal.Enclosure1containspagesofthatEngineeringdocument.TheWeldCounttablesshowtheLSSandHSStotals
.UsingtheRIS-Bapplication,10%oftheHSSweldsarerequiredtobeexamined,whichis10%of1433forUnit1and SerialNo.10-050A Docket Nos.50-338/339 Response to Request for Additional Information Fourth Interval R isk Informed Relief RequestsN1-14-RI-001&
N2-14-RI-001Page13of1310%of1528forUnit2.ThetotalnumberselectedshownintheSection3.3tableoftheSubmittal
,178forUnit1and183forUnit2iscorrect.NRCQuestion3Alsothetotal number ofweldsshowninthe summaryinSection 3:3forUnit 2doesnotagreewiththe "Weld Count" columntotalvalue showninTable 3.1 b of the February 23 , 2010submittal.Pleaseexplainthisdiscrepancy.DominionResponse Table 3.1bforNAPS2wasnotcorrectandcontainederroneoustotalsforLowSafetySignificantwelds.ThefollowingarethecorrectvaluesfortotalLSSwelds:Main Steam--171versus160,ResidualHeat-141versus139,SafetyInjection
-736versus734,QuenchSpray-167versus165,RecirculationSpray-88versus86.TotalLSSweldsshouldbe2244versus2234andthetotalweldcountshouldbe3772versus3762.Enclosure2tothislettercontainsacorrectedtable.PleasereplaceTable 3.1 bintheor iginalsubmittalwiththeupdatedinformationpresentedinEnclosure2.ThetotalweldcountsandnumberofselectionsintheSection3.3tableofthesubmittalis correct.Duringthe developmentofthisresponsewediscoveredatypographicalerror.OnTable3.3a ,fortheRCsystemTT(ThermalTransients)shouldpairwithPWSCC,notTASCS(ThermalStratification,CyclingandStriping)
.Enclosure3isthecorrectedTable3.3aforNAPS1.PleasereplacethisTableintheoriginalsubmittal.
Serial NO.1 0-050ADocketNos.50-338/339ResponsetoRequestforAdditionalInformationFourthlntervalRisk Informed Rel ief Requests N1-14-RI-001
&N2-14-RI-001 NorthAnnaPowerStationUnits1and2 Virginia ElectricandPower Company (Dominion)
ET-ISI-2010-0001Rev.1NAPS1CodeCaseN-716Selection S u mmary Attachment 10 pg1of2 System D M Welds (25%)HSS (1 0%)R CPB (1 0%)R CPBu (2/3 of RCPB)B ER(10%)Total Selected%DM Total HSS%Total Selected 0/0 Total Selected%R CPB Total Selected%BER C H-C harging18527.8%16.0%31951 1 6.0%5949 96.1%000.0%F W-MainF eedwater 0 0 0.0%1 1.3%00 0.0%00 0.0%4310 23.3%MS-MainStea m 000.0%20.0%000.0%000.0%30620.0%RC-Rea ctor Coo lant 772228.6%10.9%57062 10.9%452 62 100.0%000.0%RH-Residual Heat00 0.0%12.9%314 12.9%9250.0%000.0%SI-Safety Injection 9333.3%1 1.4%368421 1.4%0 0 0.0%000.0%Tota l To ta l Check 104 104 30 30 28.8%28.8%178 12.4%1 288 1288 159 159 12.3%12.3%520 520 1 13 113 7 1.1%71.1%73 73 16 16 21.9%21.9%TotalSelected 17 8 TotalSec tion XIInspe , 294 Weld Count System T ota l HSS LSS C H-Charg i ng811319492 FW-Mai n Feedwater11 5 115 0MS-M ain Steam19930 1 69 R C-ReactorCoolant570570 0RH-Re sidualHeat16831 137 S I-Saf ety Injection860368 492 QS-Quench Spray 143 0 143 RS-Recirc Spray730 7 3 Tot al 293914331506 ET-ISI-2010-0001 Re v.1NAPS2Cod e Case N-716 Selection Summary Attachment 10 pg 2of2 S ystem DMWe ld s (25%)H SS (10'10)R CPB (10%)R CPB u (2/3ofR CP B)B ER (1 0%)Tota l S e lecte d%DMTotal HSS%.Total S e lec t e d%Total S e lecte d%RCPB TotalS e lecte d%B E R C H-C har g ing 20 6 30.00%11.90%420501 1.90%5 8 4 7 9 4.00%0FW-Feedwater 000.00%1 3.27%0 0 0.00%00 0.0%4 4 1 5 34.1%MS-MainSteam00 0.00%18.18%00 0.00%000.0%26 6 23.1%R C-ReactorCoo lan t 7 8 27 34.62%11.87%57368 11.87%472 68 100.0%0 0 0.0%RH-Resid u al HeatRemoval000.00%13.79%29413.79%1 0 2 50.0%0 0 0.0%S I-SafetyInjection 9 3 33.33%11.11%360401 1.11%00 0.0%0 0 0.0%Tot a l Tot a l C he ck 107 10 7 36 3 6 33.64%33.64%183.00 1 1.98%1382 1382 162 162 11.72%5 40 1 1.72%54 0 1 17 117 72.2%72.2%70 7 0 21 21 30.0%3 0.0%Tot a l Se lected 1 83 Tot a l Sectio n XIIn spected27 9 W eld C o unt System TotalHSSLSS CH-Charg ing 1340 420 920 FW-Main Feedwater 1 341132 1 MS-Ma in Stea m 204331 7 1 R C-ReactorCoo la nt 573 573 0RH-Residual Heat Remo val 170 29 1 41 S I-SafetyInjection1096360 736 QS-QuenchSpray 167 0 167 RS-RecircSpray 88 0 88 Total 3772 15282244 Serial No.1 0-050A Docket Nos.50-338/339 Response to Request for Add itional Information Fourth Interval Risk Informed Relief Requests N1-14-RI-00 1&N2-14-RI-001 NorthAnnaPower StationUnits1and2 VirginiaElectricandPower Company (Dominion) 10-050Pg16 of 26Table3.1b N*716 Safety Significance Determination:
NAPS2 System Description Weld N-716 Safety Significance Determination Safety Count SignificanceRCPSSOCPWR:
BER>1E_6cDF High Low FW>1E_7LERF CH-Charging 420"" 920"FW-Ma in Feedwater 44"" 69"" 21"MS-MainS team 33"" 171" RC-Reactor Coo lant 573""RH-ResidualHeat 29""" 141" S I-Safety Inject ion 360"" 736"QS-QuenchSpray 167"R8-RecirculationSpray 88"
SUMMARY
RESULTS FOR 1353"" ALL SYSTEMS 77"" 69.;" 29"" 2244" TOTALS 3772 1528 2244 Serial No.1 0-050A Docket Nos.50-338/339 Response to Request for Additional Information Fourth Interval Risk Informed Rel ief RequestsN1-14-RI-001&
N2-14-RI-001 Enclosure 3NorthAnnaPower StationUnits1and2 Virginia ElectricandPower Company (Dominion) 10-050Pg18 of 26 Table 3.3a N-716 ElementSelections:NAPS1 System(1)Selections HSS(2)DMs(3)RCPB(4)RCPB1RV(5)RCPB OC(6j BER(7)CH Required32of319 rr 50f832of31937n/an/a Made 51 n5 51 49 n/a n/a FW Required12of115 n/a n/a n/an/a5of43 Made 13 n/an/an/an/a 10 MS Required3of30 n/an/an/an/a3of30Made6 n/a n/an/an/a 6 RC Required57of570TASCS
, rr457of57041n
/a n/aTASCS11of41 rr 30f11 PWSCC 20f7 PWSCC , r r1of2 Made 62 TASCS , rr 76262n/a n/aTASCS5 n4PWSCC4 PWSCC, rr 2 RH Required3of31 n/a3of31 3 n/a n/aMade4 n/a 4 2 n/a n/a SI Required37of368IGSCC2of637of3680 n/a n/a rr ,IGSCC1of3Made42IGSCC2 42 0 n/a n/a n ,IGSCC 1 TOTALMade178 30 159 113 nJa 16 Notes (1)SystemsaredescribedinTables3
.1aand3.1 b.(2)HighSafetySignificant(3)Deg radationMechanismsNomorethan10
%ofHSSp ipingweldsarerequiredtobeselectedforexaminat ion.OMselectionsmaybereducedtomeetthisrequirement.
(4)ReactorCoolantPressu re Boundary(5)ForRCPB 1 F IV(ReactorCoolantPressureBoundaryins ide first isolation valve)2/3requirement isfortotalofRPCB1RV and isnot requiredtobemetpersystem.
(6)ReactorCoolantPressureBoundaryoutsidecontainment(7)BreakExclusionRegion