ML19088A210

Review of NuScales Design Certification Application with Respect to Mitigation of Beyond-Design-Basis Events Final Rule

ML19088A210
Person / Time
Site:	NuScale
Issue date:	03/28/2019
From:	Bergman T NuScale
To:	Document Control Desk, Office of New Reactors
References
LO‐0319‐64989
Download: ML19088A210 (13)

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LO031964989 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com DocketNo.52048 March28,2019 U.S.NuclearRegulatoryCommission ATTN:DocumentControlDesk OneWhiteFlintNorth 11555RockvillePike Rockville,MD208522738

SUBJECT:

ReviewofNuScalesDesignCertificationApplicationwithRespecttoMitigationofBeyond DesignBasisEventsFinalRule

REFERENCES:

1. NuScalePower,LLC,NuScaleStandardPlantDesignCertificationApplication,Rev.2, October30,2018(ML18311A006)Tier2Chapter20,MitigationofBeyondDesignBasis Events.

2. NuScalePower,LLC,MitigationStrategiesforExtendedLossofACPowerEvent,TR 081650797Rev.0,November2016.

3. U.S.NuclearRegulatoryCommission,StaffRequirementsAffirmationSession,SRM M190124A,January24,2019,ADAMSAccessionNumberML19023A038.

4. U.S.NuclearRegulatoryCommission,SummaryoftheFebruary21,2019,PublicMeeting withNuScalePower,LLC,ADAMSAccessionNumberML19084A136.

NuScalePower,LLC(NuScale)understandsthattheU.S.NuclearRegulatoryCommission(NRC)Staffare developingaCommissionissuepaper(SECY)todiscussoptionsforreviewingNuScalesDesignCertification Application(DCA)contentpertainingtothemitigationofbeyonddesignbasisevents(MBDBE).TheStaff requestedthatNuScaleprovideourpositionforconsiderationinthatSECY,whichisthepurposeofthisletter.

NuScalesapproachtoMBDBEisprovidedinChapter20oftheDCAfinalsafetyanalysisreport(FSAR)andin technicalreportTR081650797,MitigationStrategiesforExtendedLossofACPowerEventinanticipationof NRCsfinalMBDBErule.Inarecentaffirmationsession,theCommissionapprovedthefinalrule[Reference3].

ThefinalrulesimplifiestheMBDBErequirements,doesnotrequireathreephasecopingstrategy,and anticipatesthepotentialtorelyoninstalledplantequipmentforboththeinitialandlongtermresponsetoa lossofallacpower.

TheNuScaledesignjustifiesrelyingsolelyoninstalledplantequipmentfortheinitialandlongtermresponseto alossofallacpower.NuScalesdesignevolved,inpartinresponsetoFukushimalessonslearned,toeliminate relianceonelectricalpower(bothacanddc)andoperatoractionstoperformsafetyfunctions.WhiletheDCA reviewisnotcomplete,onthebasisofthereviewtodateincludingdraftsafetyevaluationreports,itappears theNRCstaffacceptsboththesefeatures.Further,NuScalehasunprecedentedcopingcapabilitycomparedto designsconsideredindevelopmentoftherule.Usingonlysafetyrelateddesignfeatures,thestoredinventory inthereactorbuildingpools,andtheautomaticplantresponse,thecopingdurationexceeds50daysforcore coolingandcontainment,and150daysforspentfuelcooling.Beyondthesedurations,whichNuScalebelieves exceedthosenecessarytosatisfythenewrule,onlyasmallamountofwater(approximately28gpm)added throughagravityfedpipingsystemwouldmaintaintheremainingpoolinventory.

AlthoughtheMBDBErulewillnotapplytoNuScaleasaDCapplicant,NuScaleseeksfinalityandissueresolution concerningtheequipmentalicenseewillrelyonfortheirmitigationstrategiesandspentfuelpoollevel monitoring.NuScaleandstaffagreedduringpreapplicationthatNuScalecouldaddressthependingrule,and

LO-0319-64989 Page 2 of 2 03/28/2019 NuScale has invested substantial resources developing this portion of its DCA and in supporting the staff review. Early resolution of this issue is consistent with the intent of 10 CFR Part 52, and is also consistent with the approach taken on control room staffing requirements in 10 CFR 50.54(m), another requirement that does not apply to design certification applicants. NuScale has not seen the Staff SECY, but based on discussions in a recent public meeting [Reference 4] understands Staff intend to propose three options: (1) Postpone all review of NuScale mitigating strategies until the combined-license (COL) review, providing no finality during design certification, (2) provide finality for the design certification up to the first 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, and the COL applicant would be responsible for "Phase 2 and Phase 3" of the MBDBE strategies, or (3) NuScale would modify the design to include instrumentation beyond 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> for monitoring key safety functions and full finality could be achieved during design certification. As the first two options defer resolution until the COL stage, NuScale does not support them because it negates the investment made by NuScale on this issue. The third option presents the staff's interpretation of the rule: that instrumentation is required regardless of a design's capability.

Based on the final rule approved by Commission, NuScale believes that installed plant features as currently described in the application provide the only equipment necessary for satisfying the language and intent of the final rule, and therefore a licensee's mitigation strategies need not address the acquisition and use of portable and offsite resources. The key issue related to this outcome is whether monitoring capability is required where the plant's coping capability relies only on installed, safety-related design features to achieve and maintain core, containment, and spent fuel cooling for an extended period, and does not rely on any operator actions. As detailed in the enclosure, NuScale believes requiring such monitoring independent of the expected plant response is not warranted for safety reasons and runs counter to the intent of the final rule. Based on a determination that such instrumentation is not required, NuScale requests Staff review of FSAR Chapter 20 and TR-0816-50797 with respect to the full extent of equipment required under the forthcoming rule (i.e., the entire duration encompassed by the rule).

NuScale appreciates the engagement with NRC Staff on this issue, and Staff's solicitation of NuScale's position on the preferred path forward. NuScale understands that the staff is seeking to submit its SECY as soon as possible, and asks Staff to include this letter and its Enclosure as an enclosure to the SECY paper as an additional option to those currently planned.

This letter makes no regulatory commitments and no revisions to any existing regulatory commitments.

If you have any questions, please contact Carrie Fosaaen at 541-452-7126 or at cfosaaen@nuscalepower.com.

Distribution: Robert Taylor, NRC, OWFN-7H4 Samuel Lee, NRC, OWFN-8G9A Greg Cranston, NRC, OWFN-8G9A Omid Tabatabai, NRC, OWFN 8H12

Enclosure:

NuScale's Position on Staff Review of Design Certification Application with Respect to Mitigation of Beyond-Design-Basis Events Final Rule NuScale Power, LLC 1100 NE Circle Blvd. Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com

LO031964989 Enclosure Page1of11

Enclosure:

NuScalesPositiononStaffReviewofDesignCertificationApplicationwithRespect toMitigationofBeyondDesignBasisEventsFinalRule I.

Introduction NuScalerequeststhatNRCStaffrecommendwithintheirCommissionissuepaper(SECY)thefull resolution,viathedesigncertification(DC)rulemaking,oftheportionsofforthcoming10CFR50.155 pertainingtoequipmentforthemitigationofbeyonddesignbasisexternalevents(MBDBE).NuScale believesthattheinstalledfeaturesoftheNuScalepassivedesignfulfilltherequirementsandintentof theforthcomingfinalrule,suchthatalicenseewouldnotneedtoprovideorassureadditional capabilities(installedequipment,portableequipment,orpre-stagedoffsiteresources)indeveloping mitigationstrategiesfortheassumedevent(alossofallacpowerconcurrentwithalossofnormal accesstothenormalheatsink).

ThattheNuScaleDCcanresolvethefullscopeofequipmentrequiredforthenewruleisbasedupon NuScalespositionontwokeyissuesaddressedherein.First,NuScalesunderstandingoftheneedfor instrumentationandmonitoringcapabilityunderthenewrule.TheNuScaledesignprovidesforatleast 72hoursofmonitoringcapabilitythatwouldallowoperatorstoverifytheplantrespondsasexpected.

However,byrelyingexclusivelyonpassive,failsafe,safetyrelateddesignfeaturestomaintaincore cooling,containment,andspentfuelcoolingforanextendedperiodwithnorelianceonelectrical poweroroperatoractionsNuScaleconcludesthatmonitoringcapabilityisnotrequiredtomaintain safetyortosatisfythemitigationstrategiesportionoftherule.Second,NuScalebelievesthat maintainingtherequiredsafetyfunctionswithonlyinstalledplantequipmentforasufficientduration satisfiestherequirementsoftherule,withoutneedforportableoroffsiteresources.Basedonthe NuScaledesignandprecedent,NuScalebelievesaminimumof14daysprovidesadequatetimeto establishanalternatemeansofremovingheat.NuScalehasunprecedentedcopingcapabilitycompared todesignsconsideredindevelopmentoftherule.Usingonlysafetyrelateddesignfeatures,thestored inventoryinthereactorbuildingpools,andtheautomaticplantresponse,thecopingdurationexceeds 50daysforcorecoolingandcontainment,and150daysforspentfuelcooling.Beyondthesedurations, whichNuScalebelievesexceedthosenecessarytosatisfythenewrule,onlyasmallamountofwater (approximately28gpm)addedthroughagravityfedpipingsystemwouldmaintaintheremainingpool inventory.

UnderNuScalesapproach,theDCAwouldaddress,andtheStaffsSafetyEvaluationReport(SER)would reachfindingson,thesufficiencyoftheinstalledequipmenttosupportalicenseesmitigationstrategies tothefullextentnecessarytosatisfythenewrule.TheNuScaleFSARandsupportingtechnicalreport wouldberevisedtoalignwiththefinalrulelanguageandtheapproachdescribedherein.Finally, NuScalerecommendsthatthereviewandfinalityoutcomebereflectedintheApplicableRegulations portionoftheDCrule,whichwoulddescribetheapplicabilityof10CFR50.155tolicenseesreferencing theNuScaleDC.

NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com

LO031964989 Enclosure Page2of11

NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com II.

NuScalePowerPlantdesigncapabilitiesforcorecooling,containment,andspentfuelpool coolingandmonitoring Followingalossofallacpower(anextendedlossofacpower,orELAP)concurrentwithalossofnormal accesstothenormalheatsink,automaticresponsesofsafetyrelatedequipmentestablishandmaintain thekeysafetyfunctionsbyplacingthereactormodulesintoasafe,stable,shutdownstatewithpassive coreandcontainmentcooling.Followingtheinitial,automaticresponseofsafetyrelatedequipment whichrequiresnooperatoractionandnoelectricalpower(acordc)thereactormodulesandthe spentfuelpoolrelyonlyonthelargeinventoryofthereactor,refueling,andspentfuelpools,which comprisetheultimateheatsink(UHS),tomaintainuninterruptedandlongtermheatremoval.

Corecooling:

DuringanELAP,reactorcoolantsysteminventoryispreservedbycontainmentisolationthat occurswithinthefirstminuteoftheevent.

Ifdcpowerisavailable,thedecayheatremovalsystem(DHRS)passivelyremovesdecayheatfor thefirst24hoursfollowinganELAP.Ifdcpowerisnotavailableorislostearlierthan24hours, ECCSvalvesautomaticallyopentoremovedecayheat.

Theemergencycorecoolingsystem(ECCS)coolsthecorefortheremainderofanELAP.Reactor coolantwateraccumulatesinthecontainmentvessel(CNV)andpassivelyreturnstothereactor vesselbynaturalcirculationafterECCSvalvesopen.Thereisnoplausiblemechanismbywhich theECCSvalvescouldbechangedfromtheirsafeopenposition.

Thereactormodulesaresubmergedinthereactorpool,whichispartoftheUHS.Passiveheat removaltotheUHSusingDHRSandECCSmaintainscorecoolingformorethan50dayswithout poolinventorymakeuporoperatoraction.

Containment:

Containmentisolationvalves(CIVs)andtheCNVprovidepassivecontainmentfunction.Without operatoractionorelectricalpower,thesafetyrelatedCIVsclosetoisolatetheCNV.

HeatremovaltotheUHSpassivelycontrolstemperatureandpressuretoensurecontainment integrity.PeakpressureandtemperatureconditionsfortheCNVoccurearlyintheeventwhen theECCSvalvesopenanddonotchallengecontainmentintegrity.

Containmentcoolingismaintainedformorethan50dayswithoutpoolinventorymakeupor operatoraction.

Spentfuelpoolcooling:

Thespentfuelpool(SFP),aspartoftheUHS,communicateswiththerefuelingpoolandreactor poolabovetheSFPweirwall.Assuch,thepoolsrespondasasinglevolumeduringanELAP, untilUHSlevellowersbelowtheweirwall.

TheUHSinventorymaintainspassivecoolingofthespentfuelintheSFPformorethan150days followinginitiationofanELAPwithoutpoolinventorymakeuporoperatoraction.

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NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com Monitoring:

Nooperatoractionisrequiredtoestablishormaintaintherequiredsafetyfunctionsforatleast 50daysfollowingtheonsetofanELAP.Therefore,noinstrumentationisnecessarytosupport operatoractions.

Althoughnotnecessarybecauseofthefailsafeandpassivedesign,monitoringinstrumentation (safetydisplayinstrumentationsystem,SDIS)ismaintainedinthemaincontrolroomforatleast 72hourstoprovideadditionalassurancethatsystemshaverespondedasdesigned.

AlthoughsufficientUHSlevelexistsforatleast50days,UHSlevelmonitoring,whichincludes SFPlevel,isassuredforatleast72hoursusinginstalledequipmentalone.

III.

KeyIssues

1. Instrumentation

a. Monitoringtosupportmitigationstrategies Tworequirementsfrom10CFR50.155raisetheissueofwhatinstrumentationisrequiredbytherule andforhowlong.First,NuScaleunderstandsthatthekeytechnicalissuethatmustberesolvedto achievefullresolution(i.e.,notlimitedto72hours)oftheequipmentaspectsoftheforthcomingruleis theextenttowhichmonitoringcapabilityisnecessarytosatisfythemitigationstrategiesrequirements of50.155(b)(1)and(c).Under10CFR50.155(b)(1),alicenseemusthavestrategiesandguidelinesto mitigatebeyonddesignbasisexternaleventstoaddressthesafetyfunctionsofmaintainingor restoringcorecooling,containment,andspentfuelpoolcoolingcapabilitiesinresponsetothedefined ELAPdamagestate.Perparagraph(c),theequipmentreliedonforthemitigationstrategiesand guidelinesrequiredbyparagraph(b)(1)ofthissectionmusthavesufficientcapacityandcapabilityto performthosefunctions.

ThequestionforresolutioniswhethertheNuScaledesignreliesoninstrumentationtomaintainthe requiredsafetyfunctionsduringanELAP.NuScalebelievesmonitoringisonlynecessarytotheextent requiredtosupportrequiredactionsunderthemitigationstrategies;i.e.,theneedformonitoringis dependentonthecopingstrategy.BecausetheNuScaleapproachdoesnotdependonoperatoractions duringtheinstalledequipmentcopingperiod,NuScalebelievesthatnomonitoringisrelieduponas contemplatedbythefinalrule.NuScaleunderstandsStaffspositionisthatmonitoringoftherequired safetyfunctionsisrequiredregardlessoftheoperatorsexpectedactions;i.e.,monitoringisa requirementindependentofthedesignedcopingcapability.NuScaleunderstandsthattheintentofthis positionistosupportalicenseesabilitytoverifykeysafetyfunctionsaremaintainedandtofacilitate decisionmaking,whichmayinformcontingencyactionsbeyondthosethatarenecessarytorespondto theprescribedMBDBEboundaryconditions.

Asdetailedabove,theNuScaleplantresponsetoanELAPreliesentirelyuponsafetyrelateddesign featuresthatperformtheirsafetyfunctionautomaticallywithorwithoutdcpoweravailableand,once actuated,havenoplausiblemechanismforchangingthemtoanunsafeconfiguration.Dependingupon theavailabilityofdcpower,theplantresponseiscompletedwithin24hoursaftertheonsetoftheELAP, bywhichpointtheplantisinalongterm,safe,passivecooledstate.Nooperatoractionisrequiredat anypointtoestablishormaintainsafetyfunctionsduringthe50plusdaycopingperiod,beyondwhich

LO031964989 Enclosure Page4of11

NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com pointasmallamountofwateraddedtotheUHSbygravityfeedthroughaninstalled,externalpiping connectionwouldmaintainpoolinventory.

ItisimportanttonotethatsomeofthesekeyfeaturesoftheplantresponsetoanELAPwerenotalways partoftheNuScaledesign.Thedesignevolved,inpartinresponsetoFukushimalessonslearned,to eliminaterelianceonelectricalpowerandoperatoractionstoperformsafetyfunctions.TheELAP boundaryconditionsareequivalenttoadesignbasiseventfortheNuScaleplant,andthustheinitial designresponseiscarefullyanalyzedinaccordancewithalltherulesandconservatismsappliedtoa designbasisanalysisinChapter15oftheFSAR.WhiletheELAPeventmayendurelongerthanan analyzeddesignbasisevent,NuScaledoesnotbelievethereisaplausiblemechanismfortheplantto changestateduringtheextendedperiod.

InaFebruary21,2019publicmeeting(summaryatADAMSaccessionnumberML19084A136),Staff expressedtheirbeliefthatmonitoringcapabilitymustbeavailabletooperatorsthroughoutabeyond designbasisexternalevent,becauseofuncertaintiesinthermalhydraulicphenomenaandboron distributionduringlongtermcooling.AccordingtoStaff,suchinstrumentationwouldbeneededby operatorstomonitormodulestatusandfacilitatecontingencyactionsbeyondtheinstalledcoping capacity.

NuScalenotesthatconcernsaboutthepossibilityforboronplateout,riseruncovery,andovercooling returntopowerrelatetoconditionspostulatedtodevelopduringlongtermcoolingfollowinga transientwithconservative,designbasisanalysisassumptions.Inimportantrespects,certainChapter 15conservatisms(e.g.,astuckcontrolrod)exceedthedefinedELAPdamagestate.Forthepurposesof FSARChapter15,NuScaleexpectstoresolvetheseconcernsinthecourseoftheDCAreview.Thus, NuScalebelievesthatsuchresolutionalsoprovidesadegreeofassurancethatexceedsthatdemanded forthebeyonddesignbasiscopinganalysisthatsupportsChapter20.Therefore,NuScaledoesnot believethatthesemechanismswarrantcontingencycopingstrategiesthatcouldimplyaneedfor monitoringcapabilitytosupportthemitigationstrategies.NuScalefurtherbelievesthatsuchaposition wouldruncountertotheintentofthenewrule,andtheobjectivesoftheAdvancedReactorPolicy Statementwithrespecttodesignsimplificationandenhancedsafety.

Inadditiontothesafetyandpolicyconsiderations,NuScalenotesthatthefinalrulerequiressufficient capacityandcapabilityfortheequipmentreliedonforthemitigationstrategies.NuScaleunderstands thatreliedonisanalogoustothetermrelieduponasusedinthedefinitionofsafetyrelatedunder 10CFR50.2.Underthatdefinition,anSSCisunderstoodtobereliedupon,e.g.,ifitiscreditedinthe safetyanalysisofadesignbasisevent.IntheNuScaledesign,postaccidentmonitoringisanonsafety relatedfunctionbecauseitisnotrelieduponbyoperatorsinresponsetodesignbasisevents.Whilethe DCAreviewisnotcomplete,onthebasisofthereviewtodateitappearsthatstaffacceptsthisposition.

Likewise,instrumentationisnotrelieduponbyoperatorsinresponsetoanELAPforMBDBEmitigation strategies.Therefore,NuScalebelievesnoinstrumentationiswithinscopeoftheequipmentreliedon forthemitigationstrategiesandguidelinesasaddressedbyfuture10CFR50.155(c).Toadd instrumentationnotrequiredforDBEssolelyforthepurposeoftheMBDBEruleseemsillogical,and addscomplexitytoadesignthathastakenpassivesafetyandsimplicitytoanunprecedenteddegree.

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NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com WhileNuScaledoesnotbelieveanymonitoringisnecessary,theELAPcopingcapabilitydoesincludethe capabilitytomonitorimportantsafetyfunctions(reactormoduleparametersandUHSlevelmonitoring) foraminimumof72hoursusinginstalled,highlyreliabledcpowersupplies.Theabilitytomonitor reactormodulevariablesandpoollevelsfor72hoursprovidesampletimeforoperatorstoconfirmthat theplantrespondedtotheELAPasanticipatedandthatthepoolinventoryistrendingasexpected.

PlantconditionsmorechallengingthanthepostulatedELAPconditions,andcontingencyactionsto respondtosuchconditions,arebeyondthescopeofthefinal10CFR50.155(b).

Insum,NuScalespositionisthattheplantcopingperiodfarexceedsthatrequiredtofullysatisfythe rule(seenextsection),andthatnooperatoractionsarenecessaryduringthatcopingperiod.

Accordingly,NuScalebelievesthatmonitoringcapabilityisnotrequiredinordertomeetthemitigation strategiesportionoftherulebecauseitwouldnotbereliedonbyalicenseeinperformingexecuting thosestrategies.TheNuScaledesignincludesmonitoringcapabilitiesthatcomplementtheplantcoping capability,butarenotrequiredbythemitigationstrategiesportionoftherule.

b. Spentfuelpoolmonitoring MonitoringduringanELAPisonlyexplicitlyaddressedbythenewrulewithrespecttoSFPmonitoring, forwhich10CFR50.155(c)willrequire:

Inordertosupporteffectiveprioritizationofeventmitigationandrecoveryactions,eachlicensee shallprovidereliablemeanstoremotelymonitorwiderangewaterlevelforeachspentfuelpool atitssiteuntil5yearshaveelapsedsinceallofthefuelwithinthatspentfuelpoolwaslastused inareactorvesselforpowergeneration....

ArequireddurationforSFPlevelmonitoringisnotdefinedbythenewruleordiscussedinthe statementsofconsideration.Asstatedwithintherequirement,though,theintentoftheruleisto supporteffectiveprioritizationofeventmitigationandrecoveryactions.AsNRCstatedinrescinding theSFPinstrumentationorder,EA12051,fromthepermanentlyshutdownOysterCreekstation:

IntheeventofachallengetothesafetyoffuelstoredintheSFP,thefocusofthefacilitystaff wouldbetheSFPcondition,withoutthepossibilityofaconcurrentchallengetothereactorand primarycontainmentsafetyfunctions.Thus,intheeventofabeyonddesignbasisexternal event,effectiveprioritizationofeventmitigationandrecoveryactionswouldbesimplified,and theapplicationoftheOrderrequirementswouldnolongerbenecessarytoservetheOrder's underlyingpurpose.

SimilarreasoningappliestotheNuScaleplant.NooperatoractionsarerequiredtomitigateanELAP, andUHSinventoryassurescorecooling,containment,andSFPcooling,andoperatorshaveatleast50 daystoarrangeforasmallamountofwatertobeaddedtotheUHSthroughaninstalledexternal connectiontomaintainsufficientpoolinventoryindefinitely.Accordingly,NuScalebelievesSFP monitoringisnotneededtosupporteffectiveprioritizationofeventmitigationandrecoveryactions.

However,theNuScaledesignassuresatleast72hoursofUHSlevelmonitoring,includingtheSFP,using installedinstrumentationandpowersources,therebyfulfillingtheintentofthisrequirement.

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NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com

2. CopingDuration Asrequiredbynew10CFR50.155(b)(1)(ii),alicenseesmitigationstrategieswillberequiredtoaddress theacquisitionanduseofoffsiteassistanceandresourcestosupportthe[MBDBEsafetyfunctions]

indefinitely,oruntilsufficientsitefunctionalcapabilitiescanbemaintainedwithouttheneedforthe mitigationstrategies.NuScaleexpectsfuturelicenseestorelyononlyinstalledequipmentforboththe initialandlongtermresponsetotheELAPevent,withnorelianceonportableequipmentandoffsite resources.Thus,asecondissuethatshouldbedecidedtoachievefullresolutionoftheforthcomingrule isthetotalcopingdurationexpectedforthemitigationstrategies.

NuScaleseekstoestablish,forlicenseesthatwillreferencetheNuScaleDC,adesignapproachfor supportingmitigationstrategiesdifferentfromthethreephasecopingstrategylicenseeshaveusedto addresstheMBDBEOrdersthusfar(OrderModifyingLicenseswithRegardtoRequirementsfor MitigationStrategiesforBeyondDesignBasisExternalEvents,EA12049,March12,2012).As acknowledgedbytheCommissionintheforthcomingrulesstatementsofconsideration:

Newreactorsmayestablishdifferentapproachesfromthoseofoperatingreactorsindeveloping strategiestomitigatebeyonddesignbasisevents.Forexample,newreactorsmayuseinstalled plantequipmentforboththeinitialandlongtermresponsetoalossofallacpowerwithless relianceonportableequipmentandoffsiteresourcesthancurrentlyoperatingnuclearpower plants.TheNRCwouldconsiderthespecificplantapproachwhenevaluatingtheSSCsreliedon aspartofthemitigationstrategiesforbeyonddesignbasisevents.

Withrespecttothecopingduration,theCommissionalsoexplains:

Theacquisitionanduseofoffsiteassistanceandresourcestosupportthefunctionsrequiredby

§50.155(b)(1)(i)ofthissectionindefinitely,oruntilsufficientsitefunctionalcapabilitiescanbe maintainedwithouttheneedforthemitigationstrategiesmeansthatlicenseesneedtoplanfor obtainingsufficientresources(e.g.,fuelforgeneratorsandpumps,coolingandmakeupwater) tocontinueremovingdecayheatfromtheirradiatedfuelinthereactorvesselandSFPaswellas toremoveheatfromcontainmentasnecessaryuntilanalternatemeansofremovingheatis established.Thealternatemeansofremovingheatcouldbeachievedthroughrepairstoexisting SSCs,commissioningofnewSSCs,orreductionofdecayheatlevelsthroughthepassageoftime sufficienttoallowheatremovalthroughlossestotheambientenvironment.

NuScaleseekstodemonstratethatbyrelyingexclusivelyoninstalledSSCs,alicenseecanmaintainthe requiredfunctionsofcorecooling,containment,andSFPcoolinguntilsufficientsitefunctional capabilitiescanbemaintainedwithouttheneedforthemitigationstrategies.Inotherwords,ifthe installedequipmentcopingdurationissufficientlylong,thelicenseesmitigationstrategieswouldnot addresstheacquisitionanduseofoffsiteresourcesbecausethereisnoperiodoftimeforwhichsuch resourcesarerequired.

NuScalerequeststhattheStaffaddressintheirSECYpaperaminimumcopingdurationthatwould satisfythepurposeoftheruleandwouldthereforeobviatetheneedforoffsiteresources.Althoughthe currentNuScaledesignprovidesformorethan50daysofcoping,thatdurationmayfluctuatewith

LO031964989 Enclosure Page7of11 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com futuredesignchanges.Asdiscussednext,basedontheFukushimaeventandrecentprecedentas appliedtotheNuScaleplantdesign,NuScalebelievesthata14daycopingdurationissufficientto establishanalternatemeansofremovingheatfortheNuScaledesign.

IntheFukushimaDaiichiaccident,personnelbeganaddingwatertothespentfuelpoolofUnit4viafire andconcretepumptrucks9daysafterthetsunami,andbeganinjectingwaterviathefuelpoolcooling system14daysafterthetsunami(InternationalAtomicEnergyAgency,TheFukushimaDaiichi Accident,TechnicalVolume1).Theseactionsoccurredwithnopreplanningorprestagingof resources,withoutthebenefitofahardenedpoolmakeupconnection,anddespitewidespread destructionlimitingaccesstooffsiteresources.

InevaluatingrequeststorelaxtheMitigationStrategiesOrder,EA12049,forpermanentlyshutdown reactors,NRChasaddressedtheissueofanacceptabledurationtomaintainsafetyfunctions.For example,OysterCreekestimatedthat,followingrequestedrescissionoftheOrder,theSFPwater inventorywouldlastaminimumof7dayspriortoreducingtoaleveloflessthan10feetabovethetop ofthespentfuelrack,whichwouldensurespentfuelcoolingandshielding(seeADAMSAccession numberML18150A249).InwithdrawingtheOrderasnolongernecessary(seeADAMSAccession numberML18176A071),NRCagreedandconcludedthatthe7daysofinventorysatisfiedtheintentof theSFPcoolingrequirement,suchthatmitigationstrategiesfortheSFPwerenotneeded.Staff explained:thelowdecayheatandthelongboiloffperiodoftheSFPprovidessufficienttimeforthe licenseetoobtainoffsiteresourcesonanadhocbasistosustaintheSFPcoolingsafetyfunction indefinitely,eliminatingtheneedforthefinalphaseoftheguidanceandstrategiesformaintainingor restoringSFPcoolingcapabilities.

FortheNuScaledesign,thesamereasoningappliesnotonlytoSFPcooling,butalsoforcorecoolingand containment.AllthreefunctionsareassuredbymaintainingUHSinventoryalone.Afteranextended copingduration,theonlyactionthatmaybeneededtomaintainpoolinventoryindefinitelyistoadd waterbygravityfeedtotheSFP,whichhasahardenedmakeuplinetotheexterioroftheReactor Buildingforthatpurpose.Thus,forthesimplifiedNuScaledesign,14daysisareasonablyconservative copingdurationthatwouldallowthelicenseetoestablishalternatemeansofremovingheat, includingthroughrepairofexistingSSCs,commissioningofnewSSCs,orobtainingoffsiteresourceson anadhocbasis.

NuScalestechnicalreportTR081650797,MitigationStrategiesforExtendedLossofACPowerEvent, willdemonstratethatcorecoolingandcontainmentwillbemaintainedbytheUHSwaterinventoryfor greaterthan50dayswithoutanyoperatoraction,electricalpower,ormakeupwater.Awaterlevelof 10feetabovethetopofthespentfuelrackwouldbemaintainedforapproximately135days,andthe spentfuelwouldremaincooledforapproximately150days.Becausethisdesigncopingduration providessubstantialmargintotheproposedminimumdurationof14days,alicenseesmitigation strategieswouldnotneedtoaddresstheacquisitionanduseofoffsiteassistanceandresources.After 50days,makeupoflessthan28gallonsperminutewouldmaintainpoolinventoryindefinitely,an amounteasilyprovidedbygravitythroughtheexistingexternalpipingconnection,facilitatingtheuseof offsiteresourcesonanadhocbasisshouldmakeupbewarranted.

LO031964989 Enclosure Page8of11 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com IV.

RegulatoryAssessment Withtheaboveissuesresolved,NuScalebelievesthattheaboveinstalledcapabilitiesfullysatisfythe equipmentrelatedrequirementsforlicenseesprescribedby10CFR50.155(b)(1),(c),and(e).NuScale seeksNRCStaffsconclusionthatsuchequipmenthassufficientcapacityandcapabilitytoperformthe corecooling,containment,andSFPcoolingfunctionsforaminimumof14days,oranotherminimum durationthattheNRCdeterminesissufficienttoallowthelicenseetoestablishalternatemeansof removingheat,asdiscussedabove.Eachoftheserequirementsisassessedbelow,assuminga minimum14daycopingdurationisrequired.

(b)(1)Alicenseemustdevelop,implement,and maintainstrategiesandguidelinestomitigate beyonddesignbasisexternaleventsfromnatural phenomenathataredevelopedassumingaloss ofallacpowerconcurrentwith...alossof normalaccesstothenormalheatsink.

AlicenseereferencingtheNuScaledesignwill develop,implement,andmaintainMBDBE strategiesandguidelines,relyingontheinstalled plantfeaturesandequipmenttorespondtoan ELAP.

(b)(1)(i)Thestrategiesandguidelinesmustbe capableofbeingimplementedsitewideand mustincludemaintainingorrestoringcore cooling,containment,andspentfuelpoolcooling capabilities.

Thelicenseesstrategiesandguidelineswill addressthefullsiteandtherequiredsafety functions.Nooperatoractionsarerequiredto restoreormaintainthesafetyfunctions.Thus, NuScaleexpectsthestrategiesandguidelinesto addresssupplementaryactionssuchas confirmingtheexpectedplantresponse,placing thesecondarysystemsinasafestate,and restorationofpowertorestorenormalplant conditions.

(b)(1)(ii)Thestrategiesandguidelinesmust includetheacquisitionanduseofoffsite assistanceandresourcestosupportthefunctions requiredbyparagraph(b)(1)(i)ofthissection indefinitely,oruntilsufficientsitefunctional capabilitiescanbemaintainedwithouttheneed forthemitigationstrategies.

ThecopingdurationensuredbyinstalledSSCs exceeds14days,whichprovidessufficienttime forthelicenseetoestablishanalternatemeans ofremovingheat,suchasobtainingoffsite resourcesonanadhocbasis,throughrepairsto existingSSCsorcommissioningofnewSSCs,or heatremovalthroughlossestotheambient environment.Therefore,thereisnoperiodof timeforwhichoffsiteresourcesneedtobe acquiredandused.Thestrategiesandguidelines mayaddressoffsiteresourcesbeyondtheplants minimumcopingduration(e.g.,greaterthan50 days),butthiswouldbebeyondthe requirementsoftherule.

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NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com (c)(1)Theequipmentreliedonforthemitigation strategiesandguidelinesrequiredbyparagraph (b)(1)ofthissectionmusthavesufficientcapacity andcapabilitytoperformthefunctionsrequired byparagraph(b)(1)ofthissection.

Theinstalledequipmentreliedontoensurecore cooling,containment,andSFPcoolinghas sufficientcapacityandcapabilitytoperform thosefunctionsforatleast50days,exceeding the14daysrequired.Monitoringisnotreliedon forthemitigationstrategiesandguidelines,but installedinstrumentationprovidesatleast72 hoursofmoduleandUHSmonitoringasa supplementarycapability.

(c)(2)Theequipmentreliedonforthemitigation strategiesandguidelinesrequiredbyparagraph (b)(1)ofthissectionmustbereasonably protectedfromtheeffectsofnaturalphenomena thatareequivalentinmagnitudetothe phenomenaassumedfordevelopingthedesign basisofthefacility.

Theinstalledequipmentreliedonforthe mitigationstrategiesandguidelinesissafety related,andthereforereasonablyprotectedfrom theeffectsofnaturalphenomenathatare equivalentinmagnitudetothephenomena assumedfordevelopingthedesignbasisofthe facility.Monitoringisnotreliedonforthe mitigationstrategiesandguidelines,butthe safetydisplayandinformationsystemandthe highlyreliabledcpowersystemsarealsoSeismic CategoryIandenvironmentallyqualified.

(e)Inordertosupporteffectiveprioritizationof eventmitigationandrecoveryactions,each licenseeshallprovidereliablemeanstoremotely monitorwiderangewaterlevelforeachspent fuelpoolatitssiteuntil5yearshaveelapsed sinceallofthefuelwithinthatspentfuelpool waslastusedinareactorvesselforpower generation TheNuScaledesignprovidesatleast72hoursof UHSlevelmonitoring,includingtheSFP,fromthe controlroomusinginstalledinstrumentationand powersources.Becausemitigationactionsare notrequiredtomaintaincorecooling, containment,orSFPcoolingforanextended duration,thiscapabilityprovidessufficienttime tosupporteffectiveprioritizationofevent mitigationandrecoveryactions.

V.

DCAUpdates,Review,andResolutionProcess NuScalebelieves10CFR50.155canandshouldbeaddressedwithintheNuScaleDCrulemaking.

AlthoughthenewrulewillnotdirectlyapplytoaDCapplicantsuchasNuScale,NRCprecedent establishesthatitisfeasibleandsometimesappropriatetoresolvedesignaspectsofaruleapplicableto licenseesattheDCstage.OneofNRCsobjectivesofdesignstandardization,includingthroughdesign certification,istoenhanceplantsafetyandreduceregulatoryuncertaintythroughearlyresolutionof designissues(see,e.g.,September15,1987,52FR34884,NuclearPowerPlantStandardization).

Accordingly,certaindesignfeatureswitharelationshiptooperationalrequirementsarereviewedand resolvedattheDCstage.Forexample,NuScaleisseekingtoresolvecontrolroomoperatorstaffing requirementsattheDCstage,aconditionoflicensesunder10CFR50.54thatisnotapplicabletoDC

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NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com applicants,becauseofthecloserelationshipbetweenoperatorstaffingandthecontrolroomdesign.

WithrespecttotheMBDBErule,inresponsetoNuScalecomments,NRCrecognizedinthedraftfinal rulethatareactordesignermayaddress,atleastinpart,theprovisionsoftheMBDBEruleinthe designcertificationapplication(SECY160142:Enclosure2,NRCResponsetoPublicComments,ADAMS AccessionNo.ML16271A063).

Accordingly,NuScalebelievesitisallowableandappropriatetoresolvetheequipmentaspectsofthe new10CFR50.155ruleduringthedesigncertificationprocess.BasedonNuScalesinterpretationofthe requirementspresentedinSectionsIIIandIV,above,issueresolutionandfinalitycanbefullyachieved (i.e.forthefulldurationcoveredbytherule)fortheportionsoftheruledescribed.

WiththesemattersresolvedattheDCstage,aCOLAsremainingscope,addressedbyaCOLItematthe DCStage,wouldbelimitedtodevelopingthemitigationstrategiesrequiredby10CFR50.155(b)(1),to addressactionssupplementarytotheplantsinherentcopingresponsetoanELAP.Alicenseewould alsoaddressotherportionsoftherulenotdiscussedherein,includingtheextensivedamagemitigation guidelinesrequiredunder10CFR50.155(b)(2)andthetrainingrequirementsofparagraph10CFR 50.155(d).TheseitemswouldbeaddressedbyCOLItemsintheNuScaleFSAR.

NuScaleproposestoresolvetheseequipmentaspectsoftheforthcomingruleattheDCstage.NuScales preferredapproachistoexcludeportionsof10CFR50.155asApplicableRegulationsforlicense applicantsandlicensees.Thisapproachiseffectivelyanexemptionfromportionsoftheruleforfacilities referencingtheNuScaledesign,consistentwiththeapproachbeingusedforthecontrolroomstaffing requirementsof10CFR50.54(m).NuScalewouldincludeanadditionalsectionwithinPart7oftheDCA similartoanexemptionrequesttosupporttherequest,andthelicenseeexemptionwouldbeincluded asaparagraphinSectionV,ApplicableRegulations,oftheNuScaleDCRule.Foratechnicalbasisforthe request,NuScalewouldrelyontherevisedTR081650797tosupportthenecessarydesigndescription andsafetyfindings,similartothoseinthetableabove.

InordertoachieveissueresolutionandsupportStaffsreview,NuScaleintendstosubstantiallyrevise FSARChapter20andTR081650797.Currently,theNuScaleFSARcomparesNuScalesmitigation strategytoNEI1206,whichhasledtosomeconfusion.Undertheforthcomingrule,NuScalebelieves thattheCommissionhasclearlyestablishedthattheNEI1206approachofthreephasecopingisnot requiredforfuturedesigns.Accordingly,referencestoNEI1206willberemovedandFSARChapter20 andTR081650797willberewrittentodirectlyaddressthenewrulesrequirementsinamanner similartothatdescribedherein.Chapter20willdescribetheplantcopingdurationusingonlyinstalled SSCsandnooperatoractionsinresponsetotherulesprescribedboundaryconditionoflossofallac powerandlossofnormalaccesstothenormalheatsink.

IntheFebruary21publicmeetingwithNRCStaff,Staffidentifiedanapparentinconsistencybetween FSARChapter20andTR081650797regardingtheuseofmonitoringinstrumentation.Therevisionsto bothdocumentswillconformtotheapproachdescribedherein,whichwillremovethisinconsistency.

Specifically,thedocumentswilldescribethedesigncapabilityofatleast72hoursofmonitoringusing installedinstrumentsandpowersourcesasasupplementaryfeature.Thedocumentswillmakeclear thatthiscapabilityisnotreliedupontomaintaincorecooling,containment,orSFPcooling,and thereforenotrequiredbythefinalrule.

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NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com IftheNRCagreesthattheapproachdescribedhereisanacceptablemeanstosatisfytheMBDBErule, thenNuScaleexpectstosubmittherevisionstoFSARChapter20andTR081650797withinnomore than60daysofthatdecision.

VI.

Conclusion BasedonthefinalMBDBEruleapprovedbyCommission,NuScalebelievesthatinstalledplantfeatures currentlydescribedintheDCAprovidetheonlyequipmentnecessaryforsatisfyingthelanguageand intentofthefinalrule,andthereforealicenseesmitigationstrategiesandguidelineswillnotneedto addresstheacquisitionanduseofportableandoffsiteresources.Thekeyissuerelatedtothisoutcome iswhethermonitoringcapabilityisrequiredwheretheplantscopingcapabilityreliesonlyoninstalled, safetyrelateddesignfeaturestoachieveandmaintaincore,containment,andspentfuelcoolingforan extendedperiod,anddoesnotrelyonanyoperatoractions.Asdetailedabove,NuScalebelievesthat suchmonitoringisnotrelieduponwithinthemeaningoftherule,andisthusnotrequired,because theplantsautomaticresponseachievestherequiredsafetyfunctionsandmaintainsthemforaduration thatexceedsaminimumcopingdurationappropriatefortheNuScaledesign.Therefore,althoughthe NuScaledesignprovidesatleast72hoursofmoduleandpoollevelmonitoring,thiscapabilityis complementaryto,andnotrequiredtosupport,alicenseesmitigationstrategiesandguidelines.With agreementonthisinterpretation,NuScaleexpectstoreviseFSARChapter20andTR081650797to alignwiththefinalrulesrequirements,andseekstoachievefinalitywithrespecttothefullextentof equipmentrequiredundertheforthcomingrule.