L-16-337, Mitigating Strategies Assessment (MSA) for Flooding

Mitigating Strategies Assessment (MSA) for Flooding

ML16348A010
Person / Time
Site:	Davis Besse
Issue date:	12/12/2016
From:	Boles B FirstEnergy Nuclear Operating Co
To:	Document Control Desk, Office of New Reactors
References
L-16-337, TAC MF3721
Download: ML16348A010 (18)

Text

FENOCŽ FirstEnergy Nuclear Operating Company Brian D. Boles Vice President , Nuclear December 12, 2016 L-16-337 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852

SUBJECT:

Davis-Besse Nuclear Power Station Docket No. 50-346, License No. NPF-3 5501 North State Route 2 Oak Harbor, Ohio 43449 419-321-7676 Fax: 419-321-7582 10 CFR 50.54(f) Mitigating Strategies Assessment (MSA) for Flooding CT AC No. MF3721) On March 12, 2012, the Nuclear Regulatory Commission (NRC) issued a letter titled, "Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3, of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident," to all power reactor licensees and holders of construction permits in active or deferred status. Enclosure 2 of the 10 CFR 50.54(f) letter addresses Near-Term Task Force (NTTF) Recommendation 2.1 for flooding.

One of the required responses is for licensees to submit a hazard reevaluation report (HRR) in accordance with the NRC's prioritization plan. By letter dated March 11, 2014, FirstEnergy Nuclear Operating Company (FENOC) submitted the flood HRR for Davis-Besse Nuclear Power Station (DBNPS). Additional information was provided by FENOC letters dated August 25, 2014, December 10, 2014, February 25, 2015, and August 11, 2015. As indicated in NRC letter dated March 1, 2013, the NRC staff considers the reevaluated flood hazard to be "beyond the current design/licensing basis of operating plants." Concurrent to the flood hazard reevaluation, FENOC developed and implemented mitigating strategies in accordance with NRC Order EA-12-049, "Order Modifying Licenses with Regard to Requirements for Mitigation Strategies for Basis External Events." By letter dated September 1, 2015, the NRC staff confirmed that licensees need to address the reevaluated flooding hazards within their mitigating strategies for beyond-design-basis (BDB) external events. Guidance for performing mitigating strategies assessments (MSAs) for reevaluated flooding hazards is contained in Appendix G of Nuclear Energy Institute 12-06, Revision 2, which was endorsed by Davis-Besse Nuclear Power Station L-16-337 Page 2 the NRC in JLD-ISG-2012-01, Revision 1. In the NRC interim staff assessment for DBNPS, dated September 3, 2015, the NRC concluded that the "reevaluated flood hazards information, as summarized in the Enclosure

[Summary Tables of Reevaluated Flood Hazard Levels], is suitable for the assessment of mitigating strategies developed in response to Order EA-12-049" for DBNPS. The enclosure to this letter provides the MSA for flooding for DBNPS. This assessment indicated that the FLEX strategy design basis did not bound the reevaluated flood hazard (that is, mitigating strategies flood hazard information) for the local intense precipitation (LIP) flood and the probable maximum storm surge (PMSS) flooding, which could challenge the successfully implementation of the FLEX strategy as designed.

As a result, use of alternate staging areas and trigger points for pre-deployment of FLEX N+1 equipment are being developed.

This will remove the challenges to the FLEX mitigating strategies from LIP and PMSS. There are no new regulatory commitments contained in this letter. If there are any questions or if additional information is required, please contact Mr. Thomas A. Lentz, Manager -Fleet Licensing, at 330-315-6810.

I declare under penalty of perjury that the foregoing is true and correct. Executed on 2016. Sincerely, Brian D. Boles

Enclosure:

Mitigating Strategies Assessment for Flooding cc: Director, Office of Nuclear Reactor Regulation (NRR) NRC Region Ill Administrator NRC Resident Inspector NRR Project Manager Utility Radiological Safety Board

Page1of16MitigatingStrategiesAssessmentforFloodingAcronyms:BDBEEBeyondDesignBasisExternalEventDBDavisBesseNuclearPowerStationEFWFEmergencyFeedwaterFacilityFHRRFloodHazardReevaluationReportFIPFinalIntegratedPlanLIPLocalIntensePrecipitationMSFHIMitigatingStrategiesFloodHazardInformation(fromtheFHRRandMSFHIletter)NORMNuclearOperatingReferenceMaterialNSRCNationalSAFERResponseCenterPMSSProbableMaximumStormSurgePMWEProbableMaximumWindEventRAIRequestforAdditionalInformationUSAR-UpdatedSafetyAnalysisReportDefinitions:FLEXDesignBasisFloodHazardThecontrollingfloodparametersusedtodeveloptheFLEXfloodstrategies.FLEXDiverse&FlexibleCopingStrategiesPhase1Initiallycopebyrelyingoninstalledplantequipment.Phase2Transitionfrominstalledplantequipmenttotheon siteFLEXequipment.Phase3Obtainadditionalcapabilityandredundancyfromoff siteequipmentuntilpower,water,andcoolantinjectionsystemsarerestoredorcommissioned.FLEXNEquipmentEquipmentusedisprotectedfromallBDBEEhazardsandistheprimaryFLEXresponseequipment.FLEXN+1EquipmentEquipmentusedisNOTprotectedfromallBDBEEhazardsandisusedasanalternatetoFLEXNequipment.FLEXNSRCEquipmentEquipmentprovidedbytheNSRCtosupportFLEXPhase3strategy.Unitabbreviations

ft-feetin-inchespsf-poundspersquarefootfps-feetpersecond

Page2of161.SummaryTheMitigatingStrategyFloodHazardInformation(MSFHI)providedintheDavis BesseFloodHazardReevaluationReport(FHRR)(Ref.1)hasconcludedthattheLocalIntensePrecipitation(LIP)andProbableMaximumStormSurge(PMSS)canchallengeimplementationoftheFLEXstrategies.TheexistingFLEXstrategiesfortheseeventscanbemodifiedtoaddresstheimpactsoftheMSFHI.Otherreevaluatedfloodhazardmechanisms(i.e.tsunami,channelmigrations/diversions,etc.),areboundedbytheplantdesignbasisandhavenoimpactonthesite.TheMSFHILIPfloodinglevelsdevelopadepthabovecriticaldoorsillsforalimitedperiodoftime.Doorsareclosedininclem entweatherbasedonexistingplantprocedures.Asstatedinreferences1,2and3nointernalfloodingwillbeexperiencedthatcouldjeopardizeeithersafetyrelatedorFLEXequipment.SufficientmarginexistsintheFLEXstrategiestoallowforwaterrecessionaroundthepowerblocktherebypreventingachalleng etoPhase1andPhase2FLEXstrategies.FLEXN+1andNSRCequipmentareaffectedbytheLIPstandingwaterinthedeploymentroutes.Phase3strategiesrelyonNSRCequipment.AlternatestagingareashavebeenconfirmedtobeavailableduringandafteraLIPevent,whichwillallowimplementationofallphasesoftheFLEXstrategies.TriggerpointswillbedevelopedtoallowforpredeploymentofN+1equipment.UseofalternatestagingareasandpredeploymentofN+1equipmentwillremovechallengestotheFLEXmitigationstrategyfromtheLIP.SimilartotheLIPtheMSFHIPMSSaffectscriticalstationdoorsforashortperiodoftime.Theseimpactsandtheirmitigationarethesameasdescribedabove.ThePMSSflooddurationabove585ft.inthepowerblockareais2.5hours.SufficientmarginexistintheFLEXstrategytodelayimplementationuntilfloodlevelsdropbelow585ft.Thetotalabovegradeflooddurationissixhours,butthedepthandvelocitiesallowforFLEXactionsanddeploymenttobecompletedduringthisminorflooding.ThePMSSalsoimpactsNSRCsitestagingareaandN+1equipmentdeploymentduetostandingwater.ThedepthanddurationofthestandingwaterisgreaterthantheLIPeffects.Alternatestagingareashavebeenconfirmedtobeavailable,whichwillallowimplementationofallphasesoftheFLEXstrategies(Ref.5).TriggerpointswillbedevelopedtoallowforpredeploymentofN+1equipment.Useofalternatestagingareasandpredeployme ntofN+1equipmentwillremovechallengestotheFLEXmitigationstrategyfromthePMSSevent.TheFLEXresponsetimelinehasbeenreviewedandverifiedtoensureFLEXstrategiescanbeimplementedtoaddresstheLIPandPMSSimpactsthroughtheuseofalternatestagingareasandpre deploymentofN+1equipment(Ref.5).Developmen toftriggerpointsforLIPandPMSSpredeploymentofN+1equipmentanddocumentationofthealternatestagingareasarebeingtrackedintheFENOCcorrectiveactionprogram.TheEFWFandauxiliarybuildingwhichhousetheFLEXNequipmentarenotaffectedbytheLIPorPMSS.

Page3of162.Documentation2.1NEI12 06,Rev.2,SectionG.2-CharacterizationoftheMSFHILocalIntensePrecipitation(LIP)FloodHeightThereevaluatedLIPanalysis,documentedintheDBFHRR(Ref.1),isashortdurationlowvelocityevent.Themaximumfloodingdepthofaccumulatedwaterinthepowerblockareais0.5ft.FloodEventDurationAsdescribedinSection5oftheFHRR(Ref.1)andpage2oftheRAIresponse(Ref.3)theLIPdoesnotaffectsafety relatedequipment.Totaleventdurationis2.5hoursinthepowerblockareawithwaterlevelabovecriticaldoorsills(11doors)fornotmorethan33minutes.Oneturbinebuildingdoorhaswaterabovethesillfor54minutes,butthepotent ialtoaffectsafety relatedequipmentisprecludedbyacurblocatedintheturbinebuilding.Residualwaterinlowlyingnonpowerblockareaswillexistforanextendedperiodoftime.RelevantAssociatedEffectsTheimpactoftheLIPontheFLEXstrategieswasevaluatedinNORM LP 7221(Ref.5).ThisevaluationdeterminedthatthereissufficientmarginintheFLEXstrategytodelayPhase1andPhase2FLEXexternalactions,ifneeded,untilthewaterlevelrecededbelowcriticaldoorsilllevels.Italsodeterminedthatduetotheshallowdepthsofthefloodandthelowvelocitiesofthefloodwater,Phase1andPhase2externalactivitiescouldbecompletedifnecessary.TheevaluationidentifiedthattheN+1equipmentdeploymentpathandPhase3NSRCstagingareawereaffectedbytheLIP.BoththestagingareaandtheN+1deploymentpatharesubjecttoLIPfloodingandresidualwate rinlowlyingareasforanextendedperiodoftime.Additionalengineeringevaluationswereperformedtodeterminetheflooddurationandidentifyalternateviablestagingareas(Ref.5).Twoviablestagingareaswereidentified.AtriggerpointforaLIPeventwillbedevelopedtoallowpre deploymentofN+1equipment.Thesechange swillallowsuccessfulimplementationoftheFLEXstrategiesasdesigned.WarningTimeALIPeventresultingfromasynopticstorm(i.e.largefrontalsystem)provideslimitedwarningtime.BasedonexistingDBsiteproceduresandtheMSFHIevaluationperformedinNORM LP 7221(Ref.5),thesitehasapproximatelyonehourofpreparationtime.ThetriggerpointtobedevelopedwillallowforenoughtimetopredeploytheN+1equipment.TheamountofN+1equipmentrequiringpredeploymentislimitedtoa480voltgenerator,cablecart,andtwopumps(Ref.5).Intheeventpredeploymentwasunsuccessful,theFLEXNequipmentremainsavailabletosupportFLEXimplementation.

Page4of16ProbableMaximumStormSurge(PMSS)FloodHeightThereevaluatedPMSSanalysis,documentedintheDBFHRR(Ref.1),isashortdurationlowvelocityeventinthepowerblockarea.PMSSwithwaverun upwasalsoanalyzedresultingina.1ftwaverunup.Themaximumfloodingdepthofaccumulatedwater,includingwaverun up,inthepowerblockareais10.8inches(in)abovethepowerblockflooranddoorsillelevationsof585ft.FloodEventDurationAsdescribedinSection5oftheFHRR(Ref.1)andtheRAIresponse(Ref.3)thePMSSdoesnotaffectsafety relatedequipment.Totaleventdurationissixhoursinth epowerblockareawithwaterlevelabove585ftdoorsillelevationfor2.5hours.RelevantAssociatedEffectsTheimpactofthePMSSontheFLEXstrategieswasevaluatedinNORM LP 7221(Ref.5).ThisevaluationdeterminedthatthereissufficientmarginintheFLEXstrategytodelayPhase1andPhase2FLEXexternalactions,ifneeded,untilthewaterlevelrecededbelowcriticaldoorsilllevels.ItalsodeterminedthatduetotheshallowdepthsofthefloodandthelowvelocitiesofthefloodwaterPhase1andPhase2externalactivitiescouldbecompletedifnecessary.TheevaluationidentifiedthattheN+1equipmentdeploymentpathandPhase3NSRCstagingareawereaffectedbythePMSS.BoththestagingareaandtheN+1deploymentpatharesubjecttoPMSSfloodingandresidualwaterinlowlyingareasforanextendedperiodoftime.Additionalengineeringevaluationswereperformedtodeterminetheflooddurationandidentifyalternateviablestagingareas(Ref.5).Twoviablestagingareaswereidentified.AtriggerpointforthePMSSeventwillbedevelopedtoallowpre deploymentofN+1equipment.ThesechangeswillallowsuccessfulimplementationoftheFLEXstrategiesasdesignedWarningTimeThePMSSeventtakesseveralhourstodevelop.Oncetheprobablemaximumwindevent(PMWE)developsittakesapproximatelythreehoursforfloodinginlowlyingareastodevelopandsixhourstocausefloodingabovethesitegradeelevation(584ft)inthepowerblockarea.ThisallowsampletimeforsitepreparationsaswellasN+1equipmentpre deployment.

Page5of162.2NEI12 06,Rev.2,SectionG.3-ComparisonoftheMSFHIandFLEXDBFloodTable1a-FloodCausingMechanismA(LIP)orBoundingSetofParameters FloodScenarioParameterLIPPlantDesignBasisFloodFLEXDesignBasisFloodHazardMSFHIMSFHIBounded(B)orNotBounded(NB)FloodLevelandAssociatedEffects1.MaxStillwaterElevation584.5ft584.5ft585.5ftNB2.MaxWaveRun upElevationN/AN/AN/AN/A3.MaxHydrodynamic/DebrisLoading(psf)NotdiscussedinUSARNotdiscussedinUSARSeeNote3NB4.EffectsofSedimentDeposition/ErosionNotdiscussedinUSARNotdiscussedinUSARSeeNote4NB5.Otherassociatedeffects(identifyeacheffect)N/AN/AN/AN/A6.ConcurrentSiteConditionsN/AN/AN/AN/A7.EffectsonGroundwater250psf250psfSeeNotes3&7BFloodEventDuration8.WarningTime(hours)VariesVariesVariesSeeNote8NB9.PeriodofSitePreparation(hours)NotdiscussedinUSARNotdiscussedinUSAR1NB10.PeriodofInundation(hours)NotdiscussedinUSARNotdiscussedinUSAR0.5NB11.PeriodofRecession(hours)NotdiscussedinUSARNotdiscussedinUSAR1NBOther12.PlantModeofOperationsNotdiscussedinUSARNotdiscussedinUSARMode16NB13.OtherFactorsN/AN/AN/AN/A

Page6of16Additionalnotes,'N/A'justifications(whyaparticularparameterisjudgednottoaffectthesite),andexplanationsregardingthebounded/non boundeddetermination.1.AllelevationvalueswillbeintheSiteDatum,IGLD55,unlessnotedotherwiseastheMSFHIvalueisabovedesignbasisitisconsiderednotbounded(NB).

References:

C CSS 020.13 014Rev1,FHRRSection3.8&FHRRTable1,FHRRSection2.1.1,USARSection2.4.2.32.Thereisnowaverun upassociatedwiththeLIP.Theeventhasashortdurationandthestandingwaterrecedesquickly.TheUSARdidnotaddressfloodingfromtheLIP,specificallywithregardtostandingwater,sonowaverun updiscussionexists.SinceneitherthedesignbasisnortheMSFHIidentifiedthi sasanissue,thesevaluesaremarkedN/A.

References:

USARChapter2,FHRR3.DebriswasaccountedforintheLIPmodelbyassuming55%blockageofthespacesbetweenthevehiclebarriersystem(VBS)concreteblocks.Thisblockagehastheeffectofincreasingthewaterretentiontimearoundthepowerblock.ThehydrodynamiceffectsontheVBSareminimalsincetherestillaresufficientflowpathstopr eventexcessivehydrodynamicandhydrostaticloading.TheVBSisasecurityfeature,notafloodbarrier.Basedonthelackoffreedebrisinthesurroundingareathereisnoloadingexpectedfromdebris.BuildingloadsidentifiedincalculationC CSS 020.013 014Rev.1areasfollows:*Themaximumfloodvelocityandwaterdeptharoundeachbuildingisusedforloadcomputation.BasedontheshortdurationandsmalllocalizedloadsthereisnoeffectonthestructuresasaresultofaLIPevent.ThesestructuresareeitherCategory1orCategory2andareevaluatedformoresignificantloadsthanthosepresentedbytheLIP.PertheDesignCriteriaManual,allwallsforCategory1seismicstructuresandCategory2nonseismicstructuresared e signedwithhydrostaticandhydrodynamicloadsuptothe584ftlevel.Theseloadsincludesoilandwaterloads.SeismicCategory1structuresareevaluatedwithloadsappliedinconjunctionwiththeseismicloads.TheseTable5.0.2MaximumLoadsonBuildingsBuildingMaxVelocity*(fps)MaxDepth*(ft)MaxHydrostaticLoad(psf)MaxHydrodynamicLoad(psf)ContainmentStructure3.871.308129AuxiliaryBuilding2.461.237712TurbineBuilding2.311.026410PersonnelShop2.040.90568LLRadwasteStorage1.470.76474ContainmentAccess1.840.53337WaterTreatmentBuilding6.141.308173IntakeStructure5.480.392458DieselGeneratorBuilding2.821.559715

Page7of16loadsaresignificantlygreaterthantheloadsfromtheLIPevent;thereforenoadverseconsequencesresultfromtheLIP.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsiderednotbounded(NB).

References:

C CSS 020.13 014Rev1,DesignCriteriaManualSectio nII.G.2,USARChapter2&3.44.Davis Besseislocatedonflatterrain.TheaveragevelocityofthefloodwatersatthepeakoftheLIPis4.3fpsinthevicinityofthepowerblock.Verylittledebrisorsedimentwillbedepositedbasedontheshortdurationoftheeventandtheimpermeablematerialsurroun dingthepowerblockarea,preventingdebrisandsedimentbeingentrainedinfloodwaters.Thisareaisconcreteormacadam.Thishardmaterialwillalsopreventscour,soitisnotconsideredanissue.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsiderednotbounded(NB).

References:

C CSS 020.13 014Rev1,USARChapter25.Noadditionaldetrimentaleffectswereidentified.SinceneitherthedesignbasisnortheMSFHIidentifiedanyothersignificantdetrimentaleffects,thesevaluesaremarkedN/A.

References:

USARChapter2,FHRR6.NospecificadditionaleffectshavebeenidentifiedduringaLIPevent.Itisreasonabletoassumetherewillbewindsassociatedwiththestorm.However,theraindurationoftheLIPeventisonly60mins.ThepowerblockinternalareasarenotfloodedasaresultoftheLIP.Sincenei t herthedesignbasisnortheMSFHIidentifiedthisasanissue,thesevaluesaremarkedN/A.

References:

USARChapter2,FHRR,FIP7.Therewillbenoadversegroundwatersurchargeeffects.Theshortdurationofinundationandimpermeablematerialssurroundingthepowerblockareawouldpreventanychangeinthegroundwater.Criticalstructuresareratedforanadditional250psfsurchargeloading.Thisitemisconsideredbounded(B)bytheexistingdesignbasis.Referenc es:C CSS 020.13 014Rev1,DesignCriteriaManualSectionII.G.28.Nospecificwarningtimeisidentified.AsoutlinedintheRAIresponsediscussingtheinterimactions,siteprocedureswillprovideguidanceintheeventofsevereweather.Theseactionscommencebasedonweatherreportsoronexternalagencycontactingthecontrolroomwithnotificationofimpendingsevereweather.Theshiftmanagerthendire ctsactionsbasedontheenvironmentalthreat.Basedontherun upofthefloodlevelsassociatedwithaLIP,thereisadequatetimeforthesitetorespondbyshuttingdoors,hatchesandotheractionsneededtoprecludefloodingofvitalareas.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsider ednotbounded(NB).

References:

C CSS 020.13 014Rev1,FHRRSection5,RAIResponsetoInterimActions,RA EP 02830Flooding,RA EP 02810TornadoorHighWinds,RA EP 02870StationIsolation,USARChapter2

Page8of169.AsdiscussedinItem8thereisnospecifiedwarningtime.However,ascanbeseeninthevarioushydrographsinAttachment17ofCalcC CSS 020.13 014Rev.1,floodingabovegradefromLIPtakesapproximately51minutestoaffectthecriticaldoors.Thisallowstheonsitepers onnelsufficienttimetoensuredoors,hatchesetc.tobeclosedtopreventwateringress.AsstatedintheFHRRandsubsequentRAIassociatedwithInterimactions,ithasbeendeterminedthattheseactionsaresufficienttoprotectsafety relatedequipment.Onedoordoesfloodpriorto51minutes,Door334.Thisdooropensintotheturbinebuildingandwaterrisesabovethefloorelevationatapproximately21minutes.AsdiscussedinSection5oftheFHRR,thereisacurbthatprotectssafety relatedequipmentbelow585ftifwaterweretoenterthisdoor.Ascanbeseenbythehydrograph,theactualdept hofthewateris6.1in,whichisbelowthefloodheightprotectionprovidedbythecurb(8inperDrawingA0005).Therearemanydrainagepathstothelowerelevationsandthevolumeissufficienttoprecludefloodingofsafety relatedequipmen t.Th isdoorisclosedaspartofsiteresponsetoincreasingwaterlevels.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsiderednotbounded(NB).CalculationC CSS 020.13 014Rev.2,whichusedrefinedmethodology,reducedthewaterlevelstoa585ftelevat ion,whichisthedoorsillheight,forallcriticaldoorsexceptforDoor334discussedaboveanddeterminedtonotbeanimpact.Threeadditionaldoorstothewatertreatmentbuildingaresubjecttominorfloodingandhavenoimpactonsafetyrelatedequipment.

References:

C CSS 020.13 014Rev1Attachment17,USARChapter2,FIP,FHRRSection5,RAIResponsetoInterimActions,USARChapter2.10.Thetotalsiteinundationperiodinthepowerblockareais0.5hourswithonlyshortdurationsoftimeabovethesillsforcriticaldoors.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsiderednotbounded(NB).CalculationC CSS 020.13 014Rev.2,whichusedrefi nedmethodology,reducedthewa terlevelstoa585ft.elevation,whichisthedoorsillheight,forallcriticaldoorsexceptforDoor334discussedaboveanddeterminedtonotbeanimpact.Threeadditionaldoorstothewatertreatmentbuildingaresubjecttominorfloodingandhavenoimpactonsafetyrelatedequipment.Ref.C CSS 020.13 014Rev.1Attachment17,USARChapter2,FIP,FHRRSection5,RAIResponsetoInterimActions,USARChapter211.ThesiteremainsaccessibleduringtheLIP.AsshowninFigure4.7.3ofcalculationC CSS 020.13 014Rev.1,accessroadswillhavevaryingdepthsofwater.Thereareseveraldifferentaccesspointstothesite.Thelowlyingareaswillhavepondingbutwillnotpreventsiteaccess.TheLIPisofsh ortduration,hasrelativelyshallowdepthsandhaslowwatervelocity.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsiderednotbounded(NB).

References:

C CSS 020.13 014Rev.1Attachment17,USARChapter2,FIP,FHRRSection5,RAIResponsetoInt e rimActions,USARChapter212.PlantmodesarenotdiscussedintheUSARrelatedtofloodingevents.TheUSARdidnotidentifyanyfloodingimpactstothepowerblockorsafetyrelatedequipment.TheFLEXstrategydoesidentifydifferentresponsesbasedonplantmodeandtheavailabilityofsteamgeneratorsforheattransfer.Sincethedesignbasisdoesnotdis c ussthisissueandtheMSFHIdoes,itisconsiderednotbounded(NB).

References:

USARChapter2,FIP,RAIResponsetoInterimActions

Page9of1613.NoadditionalfactorswereidentifiedassociatedwiththeLIP.Theeventisshortdurationandhaslowwatervelocity,sowaterborneprojectilesarenotexpected.SinceneitherthedesignbasisnortheMSFHIidentifiedthisanissue,thesevaluesaremarkedN/A.

References:

USARChapter2,FHRR

Page10of16Table1b-FloodCausingMechanismA(PMSS)orBoundingSetofParametersFloodScenarioParameterPMSSPlantDesignBasisFloodFLEXDesignBasisFloodHazardMSFHIMSFHIBounded(B)orNotBounded(NB)FloodLevelandAssociatedEffects1.MaxStillwaterElevation583.7ft583.7ft585.81ftNB2.MaxWaveRun upElevation590.3ft583.7ft589.88ftB3.MaxHydrodynamic/DebrisLoading(psf)NotdiscussedinUSARNotdiscussedinUSARSeeNote3NB4.EffectsofSedimentDeposition/ErosionNotdiscussedinUSARNotdiscussedinUSARSeeNote4NB5.Otherassociatedeffects(identifyeacheffect)N/AN/AN/AN/A6.ConcurrentSiteConditions590.3ft585ft585.9ftNB7.EffectsonGroundwater250psf250psfSeeNote7BFloodEventDuration8.WarningTime(hours)VariesVariesSeeNote8NB9.PeriodofSitePreparation(hours)NotdiscussedinUSARNotdiscussedinUSARSeeNote9NB10.PeriodofInundation(hours)NotdiscussedinUSARNotdiscussedinUSAR2.5inthepowerblockareaNB11.PeriodofRecession(hours)NotdiscussedinUSARNotdiscussedinUSARSeeNote11NBOther12.PlantModeofOperationsNotdiscussedinUSARNotdiscussedinUSARMode16NB13.OtherFactorsN/AN/AN/AN/A

Page11of16Additionalnotes,'N/A'justifications(whyaparticularparameterisjudgednottoaffectthesite),andexplanationsregardingthebounded/non boundeddetermination1.AllelevationvalueswillbeintheSiteDatum,IGLD55,unlessnotedotherwise.SincetheMSFHIvalueisabovethedesignbasis,itisconsiderednotbounded(NB).

References:

C CSS 020.13 017Rev.0,C CSS 020.13 022Rev.0,FHRRSections2.1.4,2.1.8&3.7.4,USARSection2.4.2.2.12.WaverunupisdiscussedinNote6asitrelatestostormsurgeinpowerblockarea.SincetheMSFHIvalueisbelowthedesignbasis,itisconsideredbounded(B).

Reference:

FHRRSections2.1.4&2.1.83.Nospecificdebrisloadingwasprovidedinthestormsurgecalculationsrelatedtotheeffectsonpowerblockstructures.However,thestormsurgewaterdepthisonlyslightlygreaterthantheLIPwaterdepth,andthewatervelocitiesaresignificantlyless.AsshownintheLIPtable,thesafetyrelatedstructureshavesignificantmarginsre latedtotheeffectsfromflooding.Ther efore,nodetrimentaleffectsareexpectedfromthePMSS(SeeNote7).NospecificdebrisloadingwasaccountedforinthePMSSmodel.Thesiteisflatterrainandsurroundedbymarshland.NosignificantdebrisisexpectedtobetransportedtothepowerblockareabasedonthelowvelocitiesofthePMSSeventandthemultitudeofobstacles,i.e.fencelines,aroundthepowerblockareapreventingdebristransport.CalculationC CSS 020.13 017Rev.0assumptionsstatethattheVBScouldbeaffectedduringthestormsurgeeventinthatsomeoftheblockscouldbedislodge d.Theeffectofanydislodgedbarriersisassumedtobeminimalsincebarrierovertoppingisthefloodingmechanism.TheVBSisasecurityfeature,notadesignfloodbarrier.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsiderednotbounded(NB).

References:

C CSS 020.13 022Rev.0,FHRRSection3.7.4,C CSS 020.13 017Rev.04.Davis Besseislocatedonflatterrain.TheUSARdoesnotdiscussfloodinginthepowerblockareaandthereforevelocityandscourwerenotaddressed.ThePMSSisashortdurationandlowvelocityevent(seeNote7).Thepowerblockandsurroundingareaaremostlymacadamandconcrete.Basedonthesehardmaterials,shortdurationandlowwatervelocities,scourisnotanissue.Thesesameparametersminimizesoildepositioninthepowerblockarea.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsiderednotbounded(NB).

References:

C CSS 020.13 017Rev.05.Noadditionaldetrimentaleffectswereidentified.SinceneitherthedesignbasisnortheMSFHIidentifiedthisasanissue,thesevaluesaremarkedN/A.

Reference:

C CSS 020.13 022Rev.0,FHRRSection3.7.4,C CSS 020.13 017Rev.0.6.Discussconditionsthatcouldexistconcurrentwiththisflood causingmechanismorcombined effectflood(e.g.highwinds,iceformation,etc.)ThespecificadditionaleffectidentifiedduringaPMSSeventisthePMWE,whichisrequiredtogeneratethePMSS.ThepowerblockareaisfloodedasaresultofthePMSS.Waverun upvaluesassociatedwiththePMSSincreasethefloodheightaroundthepowerblockby0.1ftduetowind.Thisincreasesthestandingwaterelevationfrom585.81ftto585.9ft.ThePMSSisashortdurationevent,andthestandingwaterinthepowerblockarearecedesinap proximately2.5hours.Th enewhazardremainsboundedwithregardtothestormsurgeimpactontheearthenberms.Thedesignvaluefortheseberms

Page12of16is590.3ftandtheMSFHIvalueis589.88ft.TheUSARdoesnotspecificallyaddressfloodingfromthePMSSwithregardtostandingwaterandwaverunupeffectsinthepowerblockarea.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsiderednotboun ded(NB).CalculationC CSS 020.13 017Rev.1usedarefinedanalysistoevaluatethePMSSevent,whichresultedinnofloodinginthepowerblockarea.

References:

C CSS 020.13 022Rev.0,FHRRSection3.7.4,C CSS 020.13 017Rev.07.Therewillbenogroundwatersurchargeeffects.Theshortdurationofinundation,approximately2.5hours,andimpermeablematerialssurroundingthepowerblockareawouldpreventanychangeinthegroundwater.Thepowerblockstructuresaredesignedforgroundwaterlevelsupto584ft.Theauxiliarybuilding,containmentstructureandturbinebuildingde signincludesa250psfsurchargeload.Theintakestructurehas500psfsurchargeloadinitsdesign.ThesestructuresareeitherCategory1orCategory2andareevaluatedformoresignificantloadsthanthosepresentedbythePMSS.PertheDesignCriteriaManual,allwallsforCategory1seismicstructuresan dCategory2nonseismi cstructuresaredesignedwithhydrostaticandhydrodynamicloadsuptothe584ftlevel.Theseloadsincludesoilandwaterloads.SeismicCategory1structuresareevaluatedwithloadsappliedinconjunctionwiththeseismicloads.TheseloadsaresignificantlygreaterthantheloadsfromthePMS Sevent;thereforenoadverseconsequencesresultfromthePMSS.ThehydrostaticloadingfromthePMSSisasfollows:Ifthehydrostaticloadweredirectlyappliedtothewallasagroundwatersurchargeload,thestructuredesignshavesufficientmarginstoprecludeanyadverseeffects.Also,thegrou ndwaterst udyperformedin2007indicatesthatgroundwatertendstoflowawayfromthepowerblockarearatherthanaccumulatingagainstthepowerblocksubgradewalls.Thiswouldreduceanysurcharge.Sincethedesignbasisdoesdiscussthisissue,itisconsideredbounded(B).CalculationC CSS 020.13 017Rev.1usedarefinedan alysistoevaluatethePMSSevent,whichresultedinnofloodinginthepowerblockarea.

References:

C CSS 020.013 017Rev.0,Groundwaterstudy,DesignCriteriaManualSectionII.G.2.6MaximumLoadsonBuildingsObservationSiteNearestBuildingsMaxVelocity(fps)MaxFlowDepth(ft)MaxHydrostaticLoad(psf)MaxHydrodynamicLoad(psf)C4AuxBuildingNorth0.42.45152.880.31C13ContainmentStructure0.32.03126.670.17C14AuxBuildingWest0.61.1873.6320.69C20IntakeStructure/Turbine1.12.08129.792.34C22TurbineBuilding1.12.40149.762.34

Page13of168.Nospecificwarningtimeisidentified.AsoutlinedintheRAIresponsediscussinginterimactions,siteprocedureswillprovideguidanceintheeventofsevereweather.Theseactionscommencebasedonweatherreportsoranexternalagencycontactingthecontrolroomwithnotificationofimpendingsevereweather.Theshiftmanage rthendirectsactionsbasedontheenvironmentalthreat.ReviewofthedatapresentedincalculationC CSS 020.03 017Rev.0indicatestheactualstormsurgetakeshourstodevelop.Theshortesttimeshownfortheonsetofsitefloodingissixhours.ThePMSSdevelopmentrequireshighwindstooc cur.BasedonthelengthoftimerequiredandthehighwindconditionneededaswellastheantecedentlakelevelrequiredthesitewouldhaveenteredtheTornadoandHighWindsandtheStationFloodingprocedures.Thesitewouldhaveamplewarningtimetopreparebyshuttingdoors,hatches,andotheractionstoprecludefloodingofvitalareas.Additionally,theEmergencyResponseOrganization(ERO)wouldbestaffediftheseconditionsweretooccur,providingadditionalstaffasneeded.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsiderednotbounded(NB).Referen c es:C CSS 020.013 017Rev.0,FHRR,USARChapter2,RAIResponse,RA EP 0283Flooding,RA EP 02870StationIsolation,RA EP02810TornadoorHighWinds9.AsdiscussedinItem8thereisnospecifiedwarningtime.However,ascanbeseeninthevarioushydrographsandENERCONReportFNOCDB101 PR 001,thebuildupforthePMSStakesseveralhours.Theshortesttimeidentifiedfortheonsetoffloodinginlowlyingsiteareasisthreehours.Areasclosertothepowerblockdonotbegintoflooduntilsixhoursafterthebeginningofthestorm.Thisallowstheonsitepersonnelsufficienttimetoensuredoors,hatchesetc.tobeclosedtopreventwateringress.AsstatedintheFHRRandsubsequentRAIassociatedwithinterimactions,proceduralactionsaresufficienttoprotectsafetyrelatedequipment.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsiderednotbounded(NB).CalculationC CSS 020.13 017Rev.1usedarefinedanalysistoevaluatethePMSSevent,whichresultedinnofloodinginthepowerblockarea.

References:

C CSS 020.013 017Rev.0,FHRR,USARChapter2,ENERCONReportFNOCDB101 PR 001,RAIResponse,RA EP 0283Flooding,RA EP 02870StationIsolation,RA EP 02810TornadoorHighWinds.10.AreasaroundthepowerblockbegintofloodatT+6hourswithwaterrisingabovesitegradeof584ft.Watercontinuestoriseforapproximatelytwohoursandthenbeginstorecede.Waterwillrecedebelow584ftbyT+12hoursforatotaldurationabove584ftofsixhours.Criticaldoorsandopeningsarelocatedatthe585fteleva t ion.Theperiodofinundationabove585ftisapproximately2.5hoursinthepowerblockarea.StagingAreaBisflooded,precludingthereceiptofNSRCequipmenttosupportPhase3activities.Thedesignatedstagingarea,StagingAreaB,andtheassociatedhaulpathareinunda tedforapproximately44hours.FloodingbeginsatT+3hours,peaksbyT+8hoursandslowlyrecedes.Thestormsurgewillalsoimpactthesiteaccessviatheroadways.AsdiscussedinNote11,someofthesiteaccessroadsarefloodedfor14hours.AlternatesstagingareashavebeenevaluatedinENERCONReportFNOCDB101 PR 001.ThesealternateareasaredryorhaveminimalfloodingandwillbeavailableduringaPMSSevent.AsdiscussedinNote8thesitewouldprepareforthepotentialinundationandroadwayfloodingthroughexecutionoftheEPproceduresuptoandincludingthestationisolationproce d ure.AsthesitesaccessbecomesthreatenedtheEROwillmobilizeandadditionalsitepersonnelwillbedesignatedtosupportthestation.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsiderednotbounded(NB).CalculationC CSS 020.13 017Rev.1usedarefinedan alysistoevaluatethePMSSevent,whichresultedinnofloodinginthepowerblockarea.

Page14of16

References:

C CSS 020.013 017Rev.0,FHRR,USARChapter2,ENERCONReportFNOCDB101 PR 001,RAIResponse,RA EP 0283Flooding,RA EP 02870StationIsolation,RA EP 02810TornadoorHighWinds11.ThePMSSinthepowerblockisabovethe585ftelevationfor2.5hours.Thefloodedareasaroundthesite,includingtheaccessroads,remainfloodedforasignificantlylongerperiod.Asdiscussedabove,StagingareaBisfloodedinexcessof44hoursasitisalowspotonthesite.Th enorthacces sroadbeginstofloodatT+3hours,peaksatT+5hours,andisfloodedfor14hours.Severalotherroadwaysarealsofloodedforasignificantperiod.ThePMSScalculationsdidnotevaluateroadwaysexternaltothesite.AsdiscussedinNote10,thesitehasastationisolationproce durethataddressesactionsintheeventafloodwouldpreventsiteaccess.ENERCONReportFNOCDB101 PRestimatesthefloodwatersrecedingfromthelowspotsonsitewithin44hoursoftheonsetofflooding,butbasedontopographyandnaturaldrainageofStagingAreaB,itsavailabilityisindeterm inate.AlternatestagingareasareavailableasdiscussedinNote10.ExistingEROprocessesrecognizetheneedtobeabletosupportthesitesneedsintheeventofastationisolationevent,includingdeliveryofadditionalpersonnelandsupplies.Asdiscussedinthestationfloodingpro cedure,higherelevationroadwaysaredesignatedasthemostlikelytoclearfirstintheeventofflooding,basedontheirelevations.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsiderednotbounded(NB).

References:

ENERCONReportFNOCDB101 PR 001,C CSS 020.13 017Rev.0,RAIResponse,RA EP 0283Flooding,RA EP 02870Stat ionIsolation,RA EP02810TornadoorHighWinds12.PlantmodesarenotdiscussedintheUSARrelatedtofloodingevents.TheFLEXstrategydoesidentifydifferentresponsesbasedonplantmodeandtheavailabilityofsteamgeneratorsforheattransfer.SincethedesignbasisdoesnotdiscussthisissueandtheMSFHIdoes,itisconsiderednotbounded(NB).Referen c es:FIP,USARChapter213.NoadditionalfactorswereidentifiedassociatedwiththePMSS.Thefloodinginthepowerblockareahasashortdurationandlowwatervelocity,sowaterborneprojectilesarenotexpected.SinceneitherthedesignbasisnortheMSFHIidentifiedthisasanissue,thesevaluesaremarkedN/A.

References:

FHRR,FIP,USARChapter2

Page15of162.3.NEI12 06,Rev.2,SectionG.4-EvaluationofMitigatingStrategiesfortheMSFHI2.3.1NEI12 06,Rev.2,SectionG.4.1-AssessmentofCurrentFLEXStrategiesTheoverallplantresponsestrategiestoanELAPandlossofultimateheatsinkeventcanbeimplementedasdescribedintheFinalImplementationPlanusingthecurrentFLEXprocedures,equipmentandpersonnel,providedthefollowingmodificationsareimplemented:a.TriggerpointsestablishedtoallowforpredeploymentofN+1equipment.b.UtilizationofalternateNSRCstagingareas,ifrequired.2.3.1.1Conclusion-ModifyFLEXStrategy.2.3.2NEI12 06,Rev.2,SectionG.4.2-AssessmentforModifyingFLEXStrategies:TheexistingFLEXmitigationstrategiescanbeimplementedwithrelativelyminormodifications.

TheMSFHILIPeventproducesrainfallamountsthatchallengethecurrentFLEXmitigationstrategies.LI PwaterlevelsfloodtheN+1equipmentdeploymentpath,anditremainsfloodedforanextendedperiodoftime.TheLIPalsofloodsthedesignatedsitestagingareaforNSRCequipmentreceiptaffectingPhase3activities.

AlternatestagingareashavebeenidentifiedandverifiedtobeavailableduringaLIPeventtosupportreceiptofNSRCequipment.Atriggerpointwillbedevelopedtoallowforpre deploymentofN+1equipmentpriortofloodingofthedeploymentpath.ThecurrentmitigationstrategytimelinecontainssufficientmarginforlocalfloodwaterstorecedepriortotherequiredFLEXNactionsorequipmentdepl oymentasdescribedintheFIPforFLEXPhase1andPhase2actions.TheuseofalternatestagingareasisalsoanoptionthatiscurrentlyaddressedintheSAFERPlaybook,whichwouldallowforcompletionofFLEXPhase3actions.TheMSFHIPMSScausesfloodingoftheNSRCsta gingareaatthesiteprecludingitsuse.ThePMSSalsofloodstheN+1equipmentdeploymentpath.Thefloodingofthispathdoesnotoccuruntilthreehoursintotheeventallowingsufficienttimeforthepre deploymentofN+1equipment.AlternatestagingareashavebeenidentifiedandverifiedtobeavailableduringaPMSSeventtosupportreceiptofNSRCequipment.Atriggerpointwillbedevelopedtoallowforpre deploymentofN+1equipmentpriortofloodingofthedeploymentpath.

Page16of16ThecurrentmitigationstrategytimelinecontainssufficientmarginsanddiversitytoallowsuccessfulimplementationoftheFLEXstrategyusingFLEXNequipmentforPhase1andPhase2actions,aswellastheversatilitytousethealternatestagingareastosupportPhase3activities.NorevalidationisrequiredasthesechangesdonotaffecttheFLEXstrategyimplementationtimelines.2.4.References1.FHRRRev1-ML14070A108LetterFENOCtoNRC-Dated3/11/2014,L 14 04,FirstEnergyNuclearOperatingCompany(FENOC)ResponsetoNRCRequestforInformationPursuantto10CFR50.54(f),RegardingtheFloodingAspectsofRecommendation2.1oftheNearTermTaskForce(NTTF)ReviewofInsightsfromtheFukushimaDai ichiAccident2.FHRRRev2-ML15750A023-LetterFENOCtoNRC-Dated2/25/2015,L 15 043,RevisiontoFloodHazardReevaluationReportinResponsetoNearTermTaskForceRecommendation2.1(TACNo.MF3721)3.RAIresponse-ML14198A400-LetterFENOCtoNRCDated7/17/2014,L 14 235,SupplementtoFloodHazardReevaluationsReportinResponsetoNearTermTaskForceRecommendation2.14.StaffAssessment-ML15239B212LetterNRCtoFENOC-Dated9/3/2015,Davis BesseNuclearPowerStation,Unit1InterimStaffResponseToReevaluatedFloodHazardsSubmittedInResponseTo10CFR50.54(f)InformationRequestFloodCausingMechanismReevaluation(TACNO.MF3721)5.NORM LP 7221,Davis BesseFloodingMitigatingStrategyAssessmentSupportDocument