ML20149M119
| ML20149M119 | |
| Person / Time | |
|---|---|
| Site: | NuScale |
| Issue date: | 05/28/2020 |
| From: | Rad Z NuScale |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LO-0520-70261 | |
| Download: ML20149M119 (12) | |
Text
LO-0520-70261 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com May 28, 2020 Docket No.52-048 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738
SUBJECT:
NuScale Power, LLC Summary of Impacts to eRAI 8930 Response and Discussion on the Exemption from General Design Criterion 33
REFERENCES:
- 1. Nuclear Regulatory Commission, Request for Additional Information No. 484 (eRAI No. 8930), dated May 29, 2018 (ML18149A640) 2.
NuScale Response to NRC Request for Additional Information No.
484 (eRAI 8930), dated September 14, 2018 (ML18257A308) 3.
NuScale Supplemental Response to NRC Request for Additional Information No. 484 (eRAI 8930), dated July 18, 2019 (ML19199A117) 4.
NuScale Supplemental Response to NRC Request for Additional Information No. 484 (eRAI 8930), dated November 27, 2019 (ML19332A120) 5.
Letter from NuScale Power, LLC to Nuclear Regulatory Commission, Submittal of Second Updates to NuScale Power, LLC Standard Plant Design Certification Application, Revision 4, dated May 20, 2020 (ML20141L787)
During public teleconferences on April 1 and April 14, 2020 with NRC staff, including reviewers from Reactor Systems Branch, NuScale Power, LLC (NuScale) discussed potential updates to the actuation of the emergency core cooling system described in the Final Safety Analysis Report (FSAR). As a result of these discussions, NuScale provided changes to the FSAR in Reference 5. to this letter provides a summary on the impacts of this update to NuScales previous response to eRAI 8930 (Reference 4) due to the design changes discussed in Reference 5. to this letter provides a discussion of analyses performed to support the exemption requested from General Design Criterion 33 in Part 7 of the NuScale Design Certification Application, for events which led to the design changes provided in Reference 5.
While the discussion in Attachment 2 shows that NuScale was able to demonstrate the events addressed were acceptable using deterministic assumptions and methods, NuScale would like to recognize that an opportunity was lost to take a risk-informed approach in lieu of performing these analyses. Specifically, as summarized in Attachment 2, implementation of
LO-0520-70261 Page 2 of 2 05/28/2020 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com Commission direction in Staff Requirements - SECY-19-0036 - Application of the Single Failure Criterion to NuScale Power LLCs Inadvertent Actuation Block Valves, dated July 2, 2019 would seem to have resolved this issue. Although the opportunity to apply the Staff Requirement Memorandum (SRM) was missed in this case, we look forward to continue working with the NRC Staff to implement the Commissions SRM in the most effective manner for the scope and content of this application, and future NRC staff reviews.
This letter makes no regulatory commitments or revisions to any existing regulatory commitments.
If you have any questions, please feel free to contact Matthew Presson at 541-452-7531 or at mpresson@nuscalepower.com.
Sincerely, Zackary W. Rad Director, Regulatory Affairs NuScale Power, LLC Distribution: Gregory Cranston, NRC Prosanta Chowdhury, NRC Michael Dudek, NRC Michael Snodderly, NRC Christiana Liu, NRC Christopher Brown, NRC Marieliz Johnson, NRC Bruce Bavol, NRC : ECCS Setpoint and Riser Design Change Impact on NuScales Response to eRAI 8930 : Review of the NuScale Design Certification Application Exemption Request from General Design Criterion 33 (GDC 33) y, Zackary W. Rad Director Regulatory Affairs
LO-0520-70261 Page 1 of 2
NuScale Nonproprietary ECCSSetpointandRiserDesignChangeImpactonNuScalesResponsetoeRAI8930
TheRAI8930supplement2responsesubmittedinNuScaleletterRAIO111968093anddated
November27,2019(ML19332A120)completelyreplacedtheprevioussupplementalresponseandthe
originalresponsesubmittedinRAIO071966323,datedJuly17,2019(ML19199A117),andRAIO0918 61810,datedSeptember15,2018(ML18257A308),respectively.TheRAI8930supplement2responseis
notimpactedbytheemergencycorecoolingsystem(ECCS)setpointchangesortheriserdesignchange
toaddflowholesasdiscussedbelow.
TheRAI8930responseevaluatedtheborondistributionintheNuScalePowerModule(NPM),with
focusonborontransportafterECCSactuation,andconcludedthattheboronconcentrationinthecore
remainedabovetheinitialconcentrationfor72hoursaftereventinitiation.Threeeventswere
evaluated:RCCW(ReactorCoreCoolingWater)linebreak,RRV(ReactorRecirculationValve)inadvertent
opening,andanRVV(ReactorVentValve)inadvertentopening.TheRRVinadvertentopeningeventwas
foundtobelimitingforborondistributionanalysis.
Alongtermcoolingtechnicalreport(LTC)(TR091651299)assessmentcomparedanRVVsteamspace
break(fivepercentandfull),aninjectionlineliquidbreak(fivepercentandfull),anddecayheatremoval
system(DHRS)cooldowneventsprogressionswithandwithouttheECCSsetpointchangesandriser
holeaddition.ThefullinjectionlineliquidbreakbehavessimilarlytotheRRVinadvertentopeningevent.
Thelowreactorcoolantsystem(RCS)pressureECCSsignalwasfoundtohavenoimpactonLTCanalyses
sincealllossofcoolantaccident(LOCA)casesassumelossofDCpower,sothatECCSactuationoccursas
soonastheinadvertentactuationblock(IAB)releasesetpointisreached.Inaddition,thesignalis
designedtopreventactuationduringnonLOCAevents.LoweringtheECCSactuationsetpointon
containmentvessel(CNV)levelhasnoimpactforsimilarreasoning,andthereforethechangestothe
ECCSsetpointshavenoimpactontheLTCanalyses.Forthelimitingborondilutionanalysispresentedin
responsetoRAI8930,likewise,theECCSsetpointchangeswillhavenoimpact,sinceallECCSvalvesare
openverysoonaftereventinitiationataboutthesametimeasseeninthefullinjectionlineliquidbreak
intheassessment.
Asshownintheassessment,theriserholesdonotsignificantlyimpactthelongtermmodulecooldown.
ForLOCAevents,theriserholeswillbeuncoveredafterECCSactuationandhavenoimpactlongterm.
Forsmallbreaks,asmalldifferenceinRCSdepressurizationratescanimpactthetimingofECCS
actuationonIABreleasepressure,butlongtermconditionstrendtowardthesamevalueregardlessof
differencesintiming.Forthefivepercenthighpointventlinebreak,coreinlettemperatureandRCS
pressuremergedatsevenhours,andtherewasnodeviationintheseparametersforthefullbreak.For
theinjectionlinebreak,boththefivepercentandfullbreaksexhibitedessentiallynodifferenceincore
inlettemperatureandRCSpressure.
TheRAI8930responseevaluated:
- 1. borontransportbetweentheCNV,downcomer,andcore;
- 2. boronvolatilityinthesteamgeneratedinthecoreandriser;
- 3. boronlossmechanisms;
LO-0520-70261 Page 2 of 2
NuScale Nonproprietary
- 4. coreandriserboronmixing;
- 5. criticalheatinglength;and
- 6. reactivitybalanceinthecore Anevaluationfortheborondistributionwasalsoperformedforanextendedperiodoftimeoutto7
days,withmorerealisticassumptionsforthelimitingRRVinadvertentopeningevent,andisdiscussedin
theRAI8930supplementalresponse.
PriortoECCSactuation,theriserholeshavenegligibleimpactontheRCSthermalhydraulicresponse,
andprovideabenefittotheborontransportbehaviorforsmallerbreaksbeforeECCSactuation.TheLTC
assessmentshowednegligiblechangesintheRCSthermalhydraulicresponseand,byextension,
negligiblechangesintheborontransportbehaviorfollowingECCSactuation.Theremaybelocalflow
distributionchangesduetotheadditionoftheriserholes,howevertheimpactislimitedgiventheholes
arerelativelysmall,andonlyimpacttheliquidflowforashortperiodoftimeintheinitialtransient
phase.
Itisconcludedthatcoreandrisermixingassumptionsarenotadverselyimpactedbytheadditionof
riserholesduetominimalchangesintheRCSthermalhydraulicresponseandtheholesareuncovered
followingECCSactuation.Additionally,itisconcludedthatthecoreinletconditionsarenotimpacted
suchthatthecriticalboilinglengthcalculation,demonstratingthattheconservatismofthereturnto
poweranalysis,isnotadverselyaffected.
Volatilityandboronlossmechanismsarelikewisenotnegativelyimpactedduetotheminimalchanges
intheRCSthermalhydraulicresponse.Volatilityismainlydependentonthecoreandriserboron
concentrationandthermalhydraulicconditions.Asvolatilityisarelativelysmallerboronlossterm,and
themostsignificantlossterm(boronintheCNVliquidbelowtheRRVelevation)isnotdependentonthe
designchanges,boronlossmechanismsarenotsignificantlyimpacted.
Fortheextended7dayevaluation,thethermalhydraulicconditionsbeyond72hoursarequasisteady stateandcoreheatremovalisperformedbyECCS.TheRCSthermalhydraulicresponseintheLTC
evaluationshowedthattheeventsevaluatedwithandwithouttheriserholesproducedidenticalresults
beyondaboutsevenhoursaftereventinitiation.Thiscomparisoncanbeextendedtotheendofthe
7dayperiodduetotheRCSquasisteadystateconditions.Therefore,theconclusionsofthe7day
analysisdiscussedinthelastsupplementtotheRAI8930responseisstillapplicable.
Inconclusion,thepriordiscussiondemonstratesthattheECCSsetpointchangesandtheriserhole
additionhaveminimalimpactontheRAI8930response.Inaddition,itisnotedthatnocredithasbeen
givenfortheriserholeadditionintheRAI8930transientcasestomitigatetheadverseimpactsofboron
redistributionpriortoriserholeuncovery.
LO-0520-70261 Page 1 of 8
NuScale Nonproprietary ReviewoftheNuScaleDesignCertificationApplicationExemptionRequestfromGeneralDesign
Criterion33(GDC33)
AspartoftheNuScaleDesignCertificationApplication(DCA),anexemptionwasrequestedfromGDC33
anddescribedinDCAPart7.TheFinalSafetyAnalysisReport(FSAR)providesanalysesthat
conservativelydemonstratethattheautomaticemergencycorecoolingsystem(ECCS)functionsensure
thatspecifiedacceptablefueldesignlimit(SAFDL)violationswillnotoccurforeventsresultingindesign
basiseventleakage,i.e.,thatfallwithinthedefinedscopeofapplicabilityandcriteriain10CFR50.46.
Additionally,NuScalehasperformedanalysesthatdemonstrateautomaticECCSfunctions(safety relatedactuationsorinherentdesignfeatures)willensurenoSAFDLviolationswilloccurforleakrates
belowthatscopewithassumedinitialconditionsbeyondthoseexpectedorlikelytooccurduringnormal
operations.Theseconditionsconservativelyoverlaypotentialnormaloperationalcoolantleaks
describedinthetechnicalspecificationlimits.
Coolantlossandeffectsduringnormaloperationarerequiredtobeidentifiedandrespondedtoby
operatoractionsspecifiedintheplantoperatinglicenseastechnicalspecificationrequirements.These
actionsarerequiredtobetakenandsubjecttocontrolatthesamelevelasotherlimitsestablishedin
theplanttechnicalspecifications.
ReviewofAnalyses
Thefollowingdescriptionssummarizetheanalysesprovidedfortheconsiderationofboron
redistributionandpotentialforcoredilution.
NonLossofCoolantAccident(NonLOCA)Transients
NonLOCAtransientswereevaluated,includingaspectrumofprimaryandsecondaryinventory
conditions(reflecting,forexample,achemicalandvolumecontrolsystem(CVCS)breakoutside
containment,orincreaseinfeedwaterflowtransients).Resultsshowedacceptableborondistribution
resultsthatprecludecoredilutionconcernsbyensuringthedowncomerconcentrationsremain
conservativelyabovecriticalboronconcentration(CBC),accountingforuncertainties,foruptoa7day
period.
LossofCoolantAccident(LOCA)Transients
LOCAtransientswereanalyzedforthefullLOCAspectrum,asdefinedbyCVCSmakeupcapacity,to
demonstratesufficientlyearlyECCSactuationpriortoanysignificantdowncomerdilutionoccurring.Due
totherapidnatureofECCSactuationandlowCBCsatthetimeofECCSactuation,thesescenariosare
wellboundedbyextendeddecayheatremovalsystem(DHRS)operatingscenarios.
ReactorCoolantSystem(RCS)Leakage
RCSleakratefromarangeofapproximately6gpmupto40gpmwasalsoevaluatedinsupportofthe
NuScaleGDC33exemptionrequest.TheanalysisconcludesthatearlyECCSactuationonlowRCS
LO-0520-70261 Page 2 of 8
NuScale Nonproprietary pressurecanbeexpectedforallleakage,exceptinthecaseofverycoldinitialpooltemperature
conditions.ForthesecoldinitialpooltemperaturecasesitisexpectedthattheRCSpressurewilldrop
sufficientlyfortheECCSvalvestoopenthemselvespassivelywithinapproximately20hours.IfthisECCS
valvefunctionisignoredbyanalysis,therisermixturelevelisconservativelycalculatedtoprovide
sufficientflowthroughtheriserholestomaintainthedowncomerconcentrationabovethecritical
boronconcentrationforaperiodof24hours.At24hours,ECCSwouldbeactuatedforlossofACpower
scenarios.IfACpowerisavailable,avalidECCSactuationsignalwouldnotbeexpectedwithina72hour
periodduetothelackofcontainment(CNV)levelaccumulation.
Whileitisnotdeterministicallyconsidered,ifthepossibilityofECCSactuationwereassumedatany
pointafter24hoursandbefore72hours,thereisapossibilitythattherisermixturelevelcoulddrop
belowtheriserholeswhichcouldgenerateaborongradientbetweenthecoreanddowncomer.The
analysisforthecoreconcentrationwhenECCSisactuatedat24hoursindicatesthatalaterECCS
actuationwouldnotgenerateacoredilutionconcernevenifthedowncomerisdiluted.Thisisbecause
duringtheECCStransient,thereisanetmassflowoutofthecoreduetotheincreasedmixturelevel
duringthedepressurizationperiod.Eventually,pressuresandfluidlevelsstabilize,atwhichpointdiluted
coolantfromtheCNVentersthedowncomerthroughtheRRVs,whichisaconditionthatwasanalyzed
indetailinthefinalsupplementalresponsetoRAI8930(ML19332A120).
Fromariskperspective,RCSleakageevents,inwhichoperatorshypotheticallyfailtooperatetheplant
withinTechnicalSpecificationsthattransitionsafelytoECCS,areattributedafrequencyof6E7peryear
andwouldnotresultinacoredamage.Thelikelihoodofacommoncausefailureofall5ECCSvalvesto
passivelyopenonlowdifferentialpressureissignificantlylesslikely(5E12permodulecriticalyear)and
alsowouldnotresultinacoredamageevent.ThemoreprobablescenarioofasubsetoftheECCSvalves
notopeningcorrectlyisalreadycapturedintheprobabilisticriskassessment(PRA)asanincomplete
ECCSactuationwithafrequencyofapproximately7E12peryearandresultsinsubsequentcore
damage,asRCSmakeupwouldalsobenominallyavailable,butisassumedtofailinthisscenario.
Becausetheeventsofinterestincludeanisolatedcontainment,thereisnolargereleasefrequencyand
thusnosignificantradiologicalconsequences.Thisprovidesadditionalsupporttoconcludethatthe
eventspostulatedabovearenotrisksignificant.
RequirementforActionbythePlantOperatingStaff
TechnicalspecificationsareincorporatedintotheoperatinglicenseofnuclearpowerplantsasAppendix
A.Theydescriberequirementsthatmeetthecriteriain10CFR50.36thathelpensuretheplantwillbe
operatedinaccordancewiththesafetyanalysesthatprotectthehealthandsafetyofthepublic.
Thetechnicalspecificationsincluderequirementsregardingtheuseandapplicationoftherequirements
specifiedwithinthem.ThesearespecifiedinChapter1,UseandApplication,withadditional
requirementsforimplementingLimitingConditionsforOperationspecifiedinSectionLCO3.0,Limiting
ConditionforOperation(LCO)Applicability,andSR3.0,SurveillanceRequirements(SR)Applicability.
LO-0520-70261 Page 3 of 8
NuScale Nonproprietary Theformerapplytoallsectionsofthespecificationsanddefinetermsusedthroughoutthedocument
(andpresentedinALLCAPS),aswellasthemeaningofformattingelementsusedinthedocument.The
latter,sections3.0specifyrequirementsandrulesappliedtoactionsandsurveillancerequirements.For
example,LCO3.0.1statesthatLCOsshallbemetduringMODESorotherspecifiedconditions,and
LCO3.0.2states[u]pondiscoveryofafailuretomeetanLCO,theRequiredActionsoftheassociated
Conditionsshallbemet.1
Controlsandrequirementsarealsoprovidedbythesurveillancetestingrequiredbythetechnical
specifications.TheapplicabilityrulesinSR3.0providerequirementsforperformanceoftestingand
actionstobetakenifafailuretomeetasurveillanceoccurs.Specifically,SR3.0.1states
FailuretomeetaSurveillance,whethersuchfailureisexperiencedduringtheperformanceofthe
SurveillanceorbetweenperformancesoftheSurveillance,shallbeafailuretomeettheLCO.
FailuretoperformaSurveillancewithinthespecifiedFrequencyshallbefailuretomeettheLCO
Ifsuchafailureoccurs,therequirementsofLCO3.0.2apply.
Technicalspecification5.2specifiestherequiredstafffortheplant,includingthemanagerresponsible
foroverallsafeoperationoftheplant,andthefacilitystaffrequiredtobeatthefacilitytoimplement
therequirementsoftheoperatinglicense,includingthetechnicalspecifications.
Plantoperationsarerequiredtobeconductedinaccordancewithwrittenproceduresasspecifiedin
technicalspecification5.4,Procedures.
Insummary,theCommissionhasissuedregulationsdescribingtherequiredcontentofthose
specificationsas10CFR50.36and10CFR50.36a.Thestaffandindustryhavedevelopedguidanceand
expectationsregardingtheformatanduseofthetechnicalspecifications.NuScalehasproposed
technicalspecificationsinconformancewiththeserequirementsandguidancedocuments.Andthe
technicalspecificationsincluderequirementsfortheplanttobeoperatedbyqualifiedstaffin
accordancewithwrittenproceduresthatwillrequireLCOstobemet,orupondiscoveryofafailureto
meetanLCOthespecifiedRequiredActionsmustbetaken.
Theserequirementsarethespecificbasisfortheoperatinglicenserequirementthattheoperatingstaff
takeactioninaccordancewithwrittenproceduresifanLCOorSRisnotmet.
RCSLeakageLimitsandRequiredActions
TechnicalspecificationsrequirethatRCSOperationalLEAKAGEbelimitedtolessthanthevalueslistedin
LCO3.4.5.AsnotedintheBasesforLCO3.4.5,
1 The LCO 3.0 and SR 3.0 sections include exceptions and allowances that address other, special, and limited circumstances that occur during implementation of the requirements. They have evolved over decades of use, however the discussion provided is the fundamental requirements of the subsections quoted. For additional details see the NuScale, or generic technical specifications (NUREG-1431, etc.)
LCO 3.0 and SR 3.0 sections and associated bases.
LO-0520-70261 Page 4 of 8
NuScale Nonproprietary ExceptforprimarytosecondaryLEAKAGE,thesafetyanalysesdonotaddressRCSOperational
LEAKAGE.However,otherformsofRCSOperationalLEAKAGEarerelatedtothesafetyanalyses
forLOCA.TheamountofLEAKAGEcanaffecttheprobabilityofsuchanevent.
LCO3.4.5includeslimitsonpressureboundary,unidentified,identifiedRCS,andprimarytosecondary
LEAKAGE.Theselimitsarestructuredsimilartothoseinlargepressurizedwaterreactors,howeverthe
NuScaledesignmakesidentificationofleakagechallengingandinmostconditionsthe0.5gpm
unidentifiedLEAKAGEmaximumislikelytobethelimitappliedduringtheconditionsofapplicability.
IftheidentifiedRCSorunidentifiedLEAKAGElimitsareexceeded,ConditionAofLCO3.4.5willapply
andtheRequiredActionisthattheLEAKAGEmustberestoredtowithinlimitswithin4hours,as
requiredbyLCO3.0.2.
IftheLEAKAGEcannotberestoredtowithinlimitswithinfourhours,orpressureboundaryorprimary tosecondaryLEAKAGElimitsarenotmet,thenConditionBmustbeenteredasrequiredbyLCO3.0.2.
RequiredActionsB.1andB.2requiretheoperatorstotakeactioninaccordancewithLCO3.0.2forthe
planttobeinMODE2(subcritical)within6hoursandtobeinMODE3withtheRCShottemperature
below200ºFwithin48hours.
TheseactionsarerequiredbyLCO3.0.2,anddesignedtoverifyleakageratesandeitheridentify
unidentifiedLEAKAGEorreduceRCSOperationalLEAKAGEtowithinlimitsbeforethereactormustbe
shutdown.ThecompletiontimesforConditionBaredesignedtoprovideareasonableopportunityto
reachtherequiredunitconditionsfromfullpowerconditionsinanorderlymanner.
RCSLeakageInstrumentationRequirements
GDC30ofAppendixAto10CFR50requiresmeansfordetectingand,totheextentpractical,identifying
thesourceofRCSLEAKAGE.RegulatoryGuide1.45describesacceptablemethodsforselectingLEAKAGE
detectionsystems.
LEAKAGEdetectionsystemsmusthavethecapabilitytodetectsignificantreactorcoolantpressure
boundarydegradationassoonafteroccurrenceaspracticaltominimizethepotentialforpropagationto
agrossfailure.Thus,anearlyindicationorwarningsignalisnecessarytopermitproperevaluationofall
unidentifiedLEAKAGE.AsnotedintheBasesofLCO3.4.5RCSLEAKAGEisrelatedtothesafetyanalyses
forLOCA.TheamountofLEAKAGEcanaffecttheprobabilityofsuchanevent.
TheNuScaledesignincludesthreedistinctmethodsfordetectionandmonitoringofRCSleakageas
describedinFSARsection5.2.5.1.
x ContainmentEvacuationSystem(CES)CollectedCondensate
x ContainmentPressure
x RadioactivityMonitoring
AllthreemethodsutilizefeaturesoftheCESthatisusedtomaintainthecontainmentvesselatavery
lowpressureduringoperations.
LO-0520-70261 Page 5 of 8
NuScale Nonproprietary AllthreemethodsarerequiredtobeOPERABLEasspecifiedinLCO3.4.7,RCSLeakageDetection
Instrumentation.TheLCOprescribestherequirementsthateachoftheinstrumentationmethodsbe
availablewhenthereactorcoolantsystem(RCS)isabove200ºF,withtheECCSvalvesclosedandthe
containmentnotflooded.
Thefirsttwoofthethreemethodsdescribedaboveincludetwochannelseachofinstrumentationused
tomeasuretherelevantparameters,i.e.,therearetwochannelsformeasuringcondensatecollection,
andtwochannelsformeasuringcontainmentpressure.Onechannelofradioactivitymonitoringis
availableinadditiontotheothertwomethods.Eachofthemethodsandchannelsaresubjectedto
CHANNELCHECKS,CHANNELOPERATIONALTESTS,andCALIBRATIONSinaccordancewiththe
surveillancerequirementsinLCO3.4.7.
PlantproceduresdescribedinFSARchapter13,andrequiredbytechnicalspecification5.4,willdescribe
themeansandmethodstheoperatingstaffwillusetodetectandrespondtoleakagefromtheRCS.
Thesewillincludealarms,indications,andsurveillancetestingresults.Eachofthethreemethods
provideindicationtotheplantoperatorsoftheplantcompliancewiththespecifiedlimits.Detailed
descriptionsofthefunctions,instrumentation,capability,andrequiredconditionstoensure
OPERABILITYaredescribedinFSAR5.2.5.1.
LCO3.4.7includesRequiredActionsthatmustbetakeniftheLCOcannotbemetinaccordancewith
LCO3.0.1andLCO3.0.2.TheConditionsaremorecomplexthantypicalPWRspecificationsbecauseof
thedesignoftheNuScaleleakagedetectioninstrumentation.
InaccordancewiththerequirementsofLCO3.0.2,ifonlyonechannelofthefirsttworequiredmethods
isinoperable,operationsareallowedtocontinueforupto14daysifasurveillancerequirementofthe
RCSleakageLCOisperformedevery24hours.ThisisacceptablebecausethreemethodsofRCSleakage
remainOPERABLE,albeitwithasinglechannelOPERABLEfortheaffectedmethod.Therequired
surveillanceperformsanRCSwaterinventorybalanceprovidingfurtherassuranceofleakagedetection
withaninoperablechannel.
Ifbothchannelsofamethodwithtwochannels,orthesinglechannelradioactivitymonitormethod,are
inoperablethenatleastonechannelmustberestoredforfunctionswithtwochannels,orthe
radioactivitymonitormustberestoredtoOPERABLEwithin72hours,asrequiredbyLCO3.0.2.Ifthe
inoperablefunctionisnotrestored,thenConditionCisrequiredtobeimplementedandtheplantmust
beplacedinMODE2(subcritical)within6hours,andbeinMODE3withtheRCShottemperaturebelow
200ºFwithin48hours.Thecompletiontimesaredesignedtoprovideareasonableopportunitytoreach
therequiredunitconditionsfromfullpowerconditionsinanorderlymanner.
OperationalImplementationofLeakageRequirements
TheoperationsstaffinthecontrolroomareprovidedwithextensivecapabilitytomonitortheRCS
leakageandassuretherequirementsofLCO3.4.5and3.4.7aremet.Technicalspecification5.2requires
minimumstaffingintheplantcontrolroom.
LO-0520-70261 Page 6 of 8
NuScale Nonproprietary Plantproceduresrequiredbytechnicalspecification5.4willensurethatappropriateoperational
awarenessoftheplantconditionsismaintainedbytherequiredoperators.
x COLItem13.51requiresaCOLapplicanttodescribethesitespecificproceduresthatprovide
administrativecontrolforactivitiesthatareimportantforthesafeoperationofthefacility
consistentwiththeguidanceprovidedinRegulatoryGuide1.33,Revision3.
x COLItem13.52requiresaCOLapplicanttodescribethesitespecificproceduresthatoperators
useinthemaincontrolroomandlocallyintheplant,includingnormaloperatingprocedures,
abnormaloperatingprocedures,andemergencyoperatingprocedures.
x COLItem13.53requiresaCOLapplicanttodescribethesitespecificmaintenanceand
operatingprocedures,includingcalibrationandtestprocedures,andmaintenanceprocedures.
TheseCOLitemsandtheprogramsandproceduresrequiredtobepreparedbyaCOLapplicantwill
ensuretheoperatingstaffinthecontrolroommaintainscontinuousawarenessoftheplantstatus.The
designofthesystemsensurethatoperatorsarenotifiedifparametersaretrendingtowardorexceed
limits,andresponseproceduresthatimplementthetechnicalspecificationrequirementswillensure
operatorstakeaction.
TheavailableleakagemonitoringcapabilitiesaredescribedindetailinFSAR5.2.5.1andinclude:
CondensateCollection
x Collectionvessellevelinstrumentationincludesquantificationandtrendingofleakratechanges.
x Indicationandalarminthecontrolroomtomonitorandtrendliquidleakageintothe
containmentatmosphere.
x Controlroomalarmbeforereachingthemaximumallowablepressuretemperaturetoensure
methodfunctionality.
x CapabilitytodetectanRCSleakrateoflessthan1gpmwithinonehour.
x Minimumdetectableleakrateoflessthan0.05gpm.
ContainmentPressure
x Theinlettothecontainmentevacuationsystemincludespressuresensorsthatmonitors
containmentpressure.
x Controlroomindicationofpressureandcapabilitytoalarmandtrendchangesinpressure.
x Controlroomalarmbeforereachingthemaximumallowablepressuretemperaturetoensure
methodfunctionality.
x Capableofdetectinganincreaseof0.1psiinlessthanoneminuteofa1gpmleakfromtheRCS.
x CapableofdetectingaminimumleakratefromtheRCSof0.007gpm.
RadioactivityMonitor
x Monitorsbothgaseousandliquideffluentremovedfromthecontainmentatmosphere.
x Capabilitytoevaluateisotopicmakeup(includingtracergasesifused)toidentifyleakagesource.
x Indication,alarm,andcapabilitytotrendradioactivitylevelsinthecontrolroom.
TheNuScaledesignisinherentlymoresensitivetodetectingRCSleakagethanotherdesigns.The
containmentvesselisoperatedatanactivelymaintainedlowpressurethatminimizesthepresenceof
LO-0520-70261 Page 7 of 8
NuScale Nonproprietary anygasorliquid.Thissensitivitymakesanychangecausedbypostulatedleakagemoreapparentand
readilyquantifiablethanpreviousdesigns.
Additionally,theOPERABILITYoftwoleakdetectionfunctionsthatdependonthecontainment
evacuationsystemrequiresthatthepressureinthecontainmentbemaintainedbelowthesaturation
pressureofthesurroundingpoolwaterasdescribedinFSARsection5.2.5.1.Thispressureisalarmed
andcanbecontinuouslymonitoredinthecontrolroomifthepressureapproachesthatwhichwould
renderthedetectionfunctionsinoperable.AsshowninFSARFigure5.23,thenominalUHSpool
temperatureof100ºFwillresultinanalarmbeforethecontainmentpressureapproachesabout
0.8psia.
IntheNuScaledesignthecontainmentpressure,i.e.,vacuum,becomesakeyoperatingparameterbeing
maintainedandmonitoredbytheplantstaffusingthecontainmentevacuationsystemdescribedin
FSARsection9.3.6.2.1.WhileexistinglargePWRsmonitorcontainmentpressureandincorporatealarms
andactuations,thelargevolumeofthosecontainmentstructurestypicallyresultinslowerpressure
variationsandnosensitivitytoliquidleaksintothecontainmentvolume.
Basedontheabove,theNuScaledesignensuresthatanyleakageintothecontainmentwillberapidly
detected,evaluated,andacteduponinaccordancewiththerequirementsofthetechnicalspecifications
limitsandactionsrequiredtobeimplementedbytheunitoperatinglicense.
RiskInformedSummary
AlthoughinthiscaseNuScaleisabletodemonstratetheeventsaddressedinthisattachmentwere
acceptableusingChapter15assumptionsandmethods,anopportunitywaslosttotakeariskinformed
approachinlieuoftheseanalyses,whichwouldhaveresultedinlesstimeandcost,whilestillproviding
reasonableassuranceofadequateprotectionofpublichealthandsafety.Specifically,assummarized
below,implementationofCommissiondirectioninStaffRequirementsSECY190036-Applicationof
theSingleFailureCriteriontoNuScalePowerLLCsInadvertentActuationBlockValves,datedJuly2,
2019wouldseemtohaveresolvedthisissue.Inthatstaffrequirementsmemorandum(SRM),the
Commissionrequiredthat,theStaffshouldapplyriskinformedprincipleswhenstrict,prescriptive
applicationofdeterministiccriteriaisunnecessarytoprovideforreasonableassuranceofadequate
protectionofpublichealthandsafety.
Thestrict,prescriptiveapplicationofdeterministiccriteriaimposedinthiscasewerethat,forthe
durationoftheanalyses:
x ACandDCpowerwereassumedavailable,and
x Operatorswereassumedtonottakeanyactions,includingthoserequiredbytheoperating
licenseviatechnicalspecifications.
UndertheseassumptionsandusingChapter15methods,ECCSactuationwouldbeindefinitelydelayed
forverysmall(612gpm)reactorcoolantsystemleaks.Thus,Staffquestionedwhetherthishypothetical
scenariowouldleadtoananalyzedplantconditionoutsidetheNuScalelicensingbasis.Becauseitis
LO-0520-70261 Page 8 of 8
NuScale Nonproprietary plausiblethattheNuScaleplantmaybelesssafewithelectricpoweravailableincertainrare
circumstances,performinganalysisassumingelectricpowerisavailableisnormallyanappropriate
approachforChapter15.However,couplingthatassumptionwithanassumptionthatoperatorsviolate
technicalspecificationrequiredactions(whichinallcaseswouldhavemitigatedtheeventswithin10
hours)wasunnecessaryinthiscase.
TheNuScaleplantisdesignedtoremainsafeindefinitely,withacompletelossofallACandDCpower,a
situationthatiscatastrophicformostdesignswhetheranalyzedunderChapter15ormorerealistically
underChapter19methods.WhiletheNuScaledesignissafewithoutACandDCpower,itshouldbe
obviousthattheplantwillbeevensaferwhenACandDCpowerareavailable,regardlessofconclusions
fromChapter15.ThisisevidentfromtheProbabilisticRiskAnalysisdocumentedinthisattachmentand
inChapter19.ForthesmallRCSleaksequencepostulatedhere,theriskofcoredamageisseveralorders
ofmagnitudebelowtheNRCscoredamagefrequency(CDF)goal,andalargereleaseisprecludedbyan
intactcontainment.Therefore,applyingriskinformedprincipleswouldhaveshownthatstrict,
prescriptiveapplicationofdeterministiccriteriawasunnecessaryinthiscasetoprovideforreasonable
assuranceofadequateprotectionofpublichealthandsafety.PursuanttotheCommissionsdirectionin
SRMSECY190036,thedeterministicanalysisdescribedinthisattachmentwasunnecessary.
AlthoughtheopportunitytoapplytheSRMwasmissedinthiscase,itisanimportantlessonlearnedto
carryforwardtotheSDAapplication.Goingforward,NuScalerecommendsthatpreapplication
engagementwiththeNRConourplannedStandardDesignApproval(SDA)applicationfocuson
identifyingareaswheretheSRMmaybeimplementedtoyieldamoresafetyfocusedapplicationand
review.WelookforwardtoworkingwiththeNRCstafftoimplementtheCommissionsSRMinthemost
effectivemannerforthescopeandcontentoftheapplication,andtheNRCstaffreview.