View source for L-14-104, Firstenergy Nuclear Operating Co. Response to NRC Request for Information Pursuant to 10 CFR 50.54 (F) Regarding the Flooding Aspects of Recommendation 2.1 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident

{{Adams
| number = ML14070A108
| issue date = 03/11/2014
| title = Firstenergy Nuclear Operating Co. Response to NRC Request for Information Pursuant to 10 CFR 50.54 (F) Regarding the Flooding Aspects of Recommendation 2.1 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident
| author name = Lieb R
| author affiliation = FirstEnergy Nuclear Operating Co
| addressee name = 
| addressee affiliation = NRC/Document Control Desk, NRC/NRR
| docket = 05000346
| license number = NPF-003
| contact person = 
| case reference number = L-14-104
| document type = Letter type:L, Report, Miscellaneous
| page count = 36
}}

=Text=
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\riia. i. l.atr,.tri i..f tJ iviri i'i:', t j March11, 2A14 L44-144                                                                                   10cFR 50.54(fj ATTN: Document                        ControlDesk U.S.NuclearRegulatory                         Commission 11555Rockville                    Pike Rockville,                 MD ?fr852

==SUBJECT:==

Davis-Besse                   NuclearPowerStation DocketNo.50-346.LicenseNo.NPF-3 FirgtEnerqy                  NucleFIOperatinq       Companv(FENOC)Respgnsqt_o           NRCReo.uest   fqr tnformation                  pursuant     to tg CFR50.54{flReqardino      the F,loodir}oAg0ects3f Recommendation                        2.1of the Near-Term    TaskForce{NTTF}Rqview_of       Insiqhtsffomthe Fukushima                    Dai-ichi  Accident On March12,2A12,                         theNuclear  Regulatory  Commission    {NRC)issueda lettertitled, "Requestfor Informstion                       Pursuantto Title10of the Codesf FederalRegulatisns 50.54{0Regarding                       Recommendations      2.1,2.3,and9.3of the Near-Term     TaskForce Reviewof lnsights                     fromthe Fukushima      Dai-ichiAccident," to all powerreactorlicensees andholdersof construction                         permitsin activeor deferredstatus.Enclosure   2 of the 10 CFR50.54{0letteraddresses                          NTTFRecommendation        2.1forflooding.Oneof the required                 respon$es      is for licenseesto submita HazardReevaluation      Report(HRR)in accordance                   withthe NRC'sprioritization      plan By letterdatedMay11,2A12,      the NRC placedthe Davis-Besse                        NuclearPowerStation(DBNP$)in Category         2 requiring    a response                  by March12,2414.TheFloodHRRfor DBNPSis enclosed.
As discussed                  in the enclcsedreport,twofloodlevels(localintenseprecipitation           and probable                  maximumstorrnsurge)determined           duringthe hazardreevaluatian   exceedthe currentlicensing                   basis(CLB)floodlevels.Theincreased          levelsarethe resultof newer methodologies                   and notthe resultof errorswithinthe CLBevaluations.          Currentplant procedures                   addressing     floodingat thesiteprovideactionsto be takenin theevent flooding                 is imminent     or hasoccurred   at or nearthe DBNP$site. No additional    actions beyondthosecurrently                        in placearenecessary    at thistime.

Davis-Besse     NuclearPowerStation L-14-104 Page2 ln accordance    withthe guidanceprovidedby NRCletterdatedDecember3, 2fi12,titled "TriggerConditions      for Performing an IntegratedAssessment    and Due Datefor Respon$,"    an integrated    assessment  is requiredif floodlevelsdetermined  duringthe hazardreevaluation       are not boundedby the CLBfloodlevels.The 10 CFR50.54(f) specifiesthatthe integratedassessment         be compfetedand a repartsubmittedwithin twoyearsof submitting        the HRR. Therefore,  FENOCintendsto submitan Integrated Assessment               for Report DBNPS         priorto March12,241&.
Thereare no regulatorycsrnmitments        containedin this letter. lf thereare anyquestions or if additional information              pleasecontactMr.ThomasA. Lentz,Manager-is required, FleetLicensing,    at 330-31   5-6810.
I declareunderpenaltyof perjurythatthe foregoingis trueandeorrect.Executedon M a r c hf l , 2 A 1 4 .
Respectfully,

==Enclosure:==

FloodHazardReevaluation          Report cc: Director,Officeof NuclearReactorRegulation           (NRR)
NRCRegionlll Administrator NRCResidentInspector NRRProjectManager UtilityRadiological    SafetyBoard

Enclosure L-14-104 FloodHazardReevaluationReport (33 pagesfollow)

FLOODHAZARDREEVALUATION                            REPORT tN RESPONSE    TO THE50.54(f)fNFORMATTON                      REQUE$TREGARDING NEAR-TERM    TASKFORCERECOMMENDATION                              2'1: FLOODING for the DAVIS-BESSE   NUCLEARPOWERSTATIOTII 5501North State Route 2 Oak Harbor,OH 43449 FlrstEnergyCorporation 76 SouthMalnStreet Akron,OH 44308 Prepared        by:
ET ENERCON
( relhnce - - twty projxl tvay day EnerconServicesInc, 12420Mllestone   CenlerDrive,$uite200 Germantown,          MD 20876 Revislon1 Submlttedto FENOC;March06, zAlH PrlntedName                          Affiliatlon                Date Preparer:                       AnubhavGaur                            Enercon Verifier:                       AbiotGemechu                           Enercon "sl*l+rt ollo$lt4
_.7--]-
Verifier:                      LanaLawrence                                                             i,',1/
                                                                                               .A          7 Approver:                       RaySacramo LeadResponslbleEngineers:      ThomasGulvas MichaelSobota                                                     t lbla.rr1 DesignEngineering Supervisor     GregoryMichael                                                 s l,.ltL DeslgnEnglneering Manager        Jon Hook                                FENOC

NTTFRecommendation               2.1 (HazardReevaluations):         Flooding                     Revision1 FirstEnergyCorporation                                                                        March06, 2014 2.1,2. Flooding           in Streamsand Rivers                                                    ..........6 2.1.3. DamBreaches                 andFailures..                                                   .....,.,.7 2.1.7. Channel            Migration      or Diversion    ..                                         ........7 2.1.8. CombinedEffectFlood(including                        Wind-GeneratedWaves)                     .......7 2.2. Flood-Related            Changesto the LicenseBasis                                      .................7 2.3. Changesto the Watershed                        and LocalAreasinceLicenselssuance          .............,..7 2.4. CurrentLicensing         BasisFloodProtection          and Pertinent             Features............8 FloodMitigation
: 3. 

==SUMMARY==
OF FLOODHAZARDREEVALUATION                                                                    ........8 3.1. Floodingin Streamsand Rivers(ReferenceDBNPS2013a,DBNPS2013b,and DBNPS 2013c)                                                                                              ..........9 3 . 1 . 1 . B a s i so f I n p u l s : . . . . . .                                                ........10 3.1.2. Computer             Software        Programs..                                               .....11 3.1.3. Methodology.                                                                                  .....11 3 . 2 . 1 . B a s i so f l n p u t s                                                              ........15 3.2.2. Computer             Software        Programs..                                           .........15 3.2.3. Methodology.                                                                                .......15 3 . 3 . 1 . B a s i so f I n p u t s                                                                  ....16 3.3.2. Computer             Software        Programs..                                             .......16 3.3.3. Methodology..                                                                               .......16 3.4. ChannelMigration              or Diversion        (ReferenceDBNPS2013d)                    .............17 3,4.1. Basisoflnputs                                                                              ........17 DAVIS-BESSE       NUCLEARPOWERSTATION                                                          Page 1 of 32

NTTFRecommendation     2.1 (HazardReevaluations):
Flooding                     RevisionI FirstEnergyCorporation                                                March06, 2014 3.4.2. Computer  SoftwarePrograms.....                                ............17 3.4.3. Methodology..                                                     ,.....,,.17 3.4,4. Results                                                            ........17 3,5. Storm Surge (ReferenceDBNPS20139,DBNPS2013h, DBNPS2013i and DBNFS 2 0 13 m )                                                                     . . . . .1.B 3.5.1. Basisof Inputs                                                         ....18 3.5.2. Computer  SoftwarePrograms..                                        .......18 3.5.3. Methodology..
3.5.4. Results                                                              ......21 3.6. Tsunami  Assessrnent (ReferenceDBNPS2013j)                                  ....21 3.6.1. Basisof lnputs 3.6.2. ModelsUsed                                                      .."........22 3.6.3. Methodology....                                       ,.r...,,.... .....22 3.6.4. Results                                                              ..,...23 3.7. CombinedEffectFlood(including           Waves)(Reference
                                       \Mnd-Generated             DBNPS2013n).23 3.7.1. Basisof Inputs                                                  ...,.......24 3.7.2. Computer$oftwarePrograms..                                            .....24 3.7.3. Methodology...                                                   .........24 3.7.4, Results                                                      ..............25 3.8. LocalIntensePrecipitation(Reference DBNPS2013eand DBNPS20130......        .....,..26 3.8.1. Basisoflnputs                                                        ......26 3.8.2. ModelsUsed                                                      ............26 4 , COMPARISON     WITHCURRENTDESIGNBASIS 5.
6.
DAVIS-BESSE    NUCLEARPOWERSTATION                                      Page2 ol 32

NTTFRecommendation      2.1 (HazardReevaluations):   Flooding                          Revision1 FirstEnergyCorporation                                                             March06, 2014
{. PURPOSE 1.1.Background ln responseto the nuclearfueldamageat the FukushimaDai-ichipowerplantdue to the March 11, 2011 earthquakeand subsequenttsunami, the United States Nuclear Regulatory Commission(NRC) establishedthe Near Term Task Force (NTTF)to conducta systematic reviewof NRC processesand regulations,and to make recornmendations           to the NRC for its policydirection.The NTTFreporteda set of recommendations       that were intendedto clarifyand strengthenthe regulatoryframeworkfor protectionagainstnaturalphenomena.
On March 12,2012the NRC issuedan informationrequestpursuantto Title 10 of the Code of FederalRegulations,   Section50.54(D(10 CFR50.54(f)or 50.54(f)lette$whichincludedsix (6) enclosures:
1 . NTTF Recommendation      2.1:Seismic 2 , NTTF Recommendation      2.1:Flooding
: 3. NTTF Recommendation       2.3:Seismic
: 4. NTTF Recommendation       2.3:Flooding 5 . NTTF Recommendation      9.3:EP 6 . Licenseesand Holdersof Construction    Permits fn Enclosure2 of the NRC-issued    information request(ReferenceNRCMarch2A12),the NRC requestedthat licenseesreevaluatethe floodinghazardsat their sites against present-day regulatory  guidanceand rnethodologies   beingusedfor earlysite permits(ESP)and combined operatinglicensereviews.
On behalfof First EnergyCorporation(FENOC)for the Davis-BesseNuclearPower Station (DBNPS),this FloodHazardReevaluation        Report(Report)providesthe informationrequested in the March 12, 2012 50.54(f)letter;specifically, the informationlistedunderthe "Requested
                                                                 'e').The "Reque$ted fnformation"  sectionof Enclosure2, paragraph1 ('a' through                        Information" sectionof Enclosure2, paragraph2 ('a' through      'd'), IntegratedAssessmentReport,will be addressedseparatelyif the currentdesignbasisfloods do not boundthe reevaluatedhazard for all flood-causing mechanisms.
1.2.RequestedActlons Per Enclosure2 of the NRC-issued     informationrequest,50.54(f)Ietter,FENOCis requestedto performa reevaluation   of all appropriateexternal  floodingsourcesfor DBNPS,includingthe effectsfrom localintenseprecipitation  (LlP)on the site,the probablemaximumflood(PMF)on streamsand rivers,lakefloodingfromstormsurges,seichesand tsunamis,and dam failures.lt is requestedthat the reevaluationapply present-dayregulatoryguidanceand methodologies being used for ESPs, and calculationreviewsincludingcurrenttechniques,software,and methodsused in present-daystandardengineeringpracticeto developthe flood hazard.The requestedinformationwill be gatheredin Phase 1 of the NRC staffs two-phaseprocessto irnplementRecornmendation      2,1, and will be used to identifypotential"vulnerabilities"(see definition below).
DAVIS-BESSE     NUCLEARPOWERSTATION                                                  Page3 of 32

NTTFRecommendatisn       2.1 (HazardReevaluations):  Flooding                           Revision1 FirstEnergyCorporation                                                              March46,2014 For the siteswherethe reevaluatedfloodexceedsthe designbasis,addresseesare requested to submitan interimactionplan documenting       plannedactionsor measuresimplemented            to addressthe reevaluated    hazards.
Subsequently,   addresseesshall performan integratedassessmentof the plantto fully identify vulnerabilities and detail actionsto addressthem. The scope of the integratedassessment reportwill includefull poweroperationsand otherplantconfigurations      that couldbe susceptible due to the statusof the flood protectionfeatures.The scopealso includesthosefeaturesof the ultimateheat sink (UHS)that could be adverselyaffectedby flood conditions(the loss of UHS from non-floodassociatedcauses is not included).lt is also requestedthat the integrated asses$ment    addressthe entiredurationof the floodconditions.
A definition of vulnerability in the context of Enclosure 2 is as follaws: Plant-specific are thosefeaturesimpoftantto safetythat whensubjectta an increaseddemand vulnerabilities due lo the newly calculated hazard evaluation have not been shown to be capable of performingtheirintendadfunctiorts.
1.3.RequestedInformation Per Enclosure2 of the NRC-issuedinformationrequest 50.54(0 letter, the Report should providedocumentedresults,as well as pertinentDBNPSinformationand detailedanalysis,and includethe following:
: 1. Site informationrelaledto the flood hazard.Relevantstructure,systems,and components (SSCs)importantto safetyand the UHS are includedin the scopeof this reevaluation,        and pertinentdata concerningtheseSSCsshouldbe included.Otherrelevantsite data includes the following:
: 1. Detailedsite information(both designedand as-built),includingpresent-daysite layout, elevation of pertinentSSCs importantto safety, site topography,and pertinentspatialandtemporaldatasets;
: 2. Currentdesignbasisfloodelevations     for all flood-causing mechanism$;
: 3. Flood-relatedchangesto the licensingbasis and any flood protectionchanges (includingmitigation) sincelicenseissuance;
: 4. Changesto the watershedand localareasincelicenseissuance;
: 5. Currentlicensingbasisfloodprotectionand pertinentfloodmitigationfeaturesat the site:and
: 6. Additionalsite details,as necess?ry,to assessthe flood hazard(e.9.,bathymetry andwalkdownresults).
: 2. Evaluationof the flood hazardfor each flood-causingmechanism,based on present-day methodologiesand regulatoryguidance.Provide an analysis of each flood-causing mechanismthat may impactthe site,includingLIP and site drainage,floodingin streams and rivers, dam breachesand failures,storm surge and seiche, tsunamis,channel migrationor diversion,and combinedeffects.Mechanisms        that are not applicableat the site may be screenedout; however,a      justification shouldbe    provided. A basisfor inputsand assumptions,  methodologies  and modelsused,includinginputand outputfiles,and other pertinentdatashouldbe provided.
DAVIS-BESSE     NUCLEARPOWERSTATION                                                    Page4 of 32

NTTFRecommendation        2.1 (HazardReevaluations):  Flooding                          Revision1 FirstEnergyCorporation                                                            March06, 2014
: 3. Cornparisonof currentand reevaluatedflood-causingmechanisrnsat the site. Providean asse$$ment    of the currentdesignbasisfloodelevationto the reevaluated  floodelevationfor each flood-causing    mechanism.Includehow the findingsfrom Enclosure2 of the 50.54(f) letter(i.e., Recommendation                                  supportthis determination.
2.1, flood hazardreevaluations)                           lf the current design basis flood bounds the reevaluated       hazard   for  all flood-causing mechanisms,    includehowthisfindingwas determined.
: 4. Interimevaluationand actionstaken or plannedto addre$sany higherfloodinghazards relativeto the design basis, prior to completionof the integratedassessmentdescribed below,if necessary.
: 5. Additionalactions beyond requestedinformationitem l.d taken or plannedto address floodinghazards,if any.
: 2. SITEINFORMATION DBNPSis locatedon the shore of Lake Erie in Oak Harbor,Ohio" The majorhydrological featuresof the terrain are the broad expanseof Lake Erie to the north and east, and the ToussaintRiver,which flows east into the lake along the south side of DBNPS,DBNPS is approximately    3,000 feet (ft) from the Lake Erie shorellne(USAR, Section1.2.1.1)and approximately    2,000ft from the ToussaintRiver.Site areas surroundingthe stationstructures havebeenbuiltup from 6 to 14 feet abovethe existinggradeelevationto an elevationof 584 ft International GreatLakesDatumof 1955(lGLD55)or 15.4ft abovethe LakeErie Low Water Datumof 568.6ft-lGLDs5.Topographyat and aroundDBNPSis relativelyflat,with a mean station elevation of approximately584 ft-lclDss. The site safety-relatedstructuresare protectedagainsthighwaterlevelsup to an elevationof 585 ft-lGLDs5.A LakeEriedike,which is locatedalongthe shoreof Lake Erie,protectsthe site from lakesurges.Additionally,    a wave protectiondike is situatedalongthe northern,eastern,and a small    portionof southernsidesof DBNPS.The elevationat the top of the wave protectiondike is 591 ft-lGLDs5. Present-Day SiteLayoutis shownin Figures2.0.1.
DAVIS.BESSE     NUCLEARPOWERSTATION                                                   Page5 of 32

NTTFRecommendation        2.1(HazardReevaluations): Flooding                        Revision1 FirstEnergyCorporation                                                         March06,2014 Figure2.0.1- Present-Day  Site Layout 2.1,CurrentDesignBasis The currentdesignbasisis definedin the DBNPSUpdatedSafetyAnalysisReport(USAR).
The followingis a list of flood-causingmechanismsand their associatedwater surface elevations    thatwereconsidered for the DBNPScurrentdesignbasis.
2 . 1 . 1 .L t P The USARindicatesthat the precipitation    valueof 24.l-inchesover a 6 hour periodis utilized for the LIP analysis.As indicatedin the USAR,the averageinvertelevationof rnanholesand catchbasinsis 582ft-lcLD55;with 24.5inchesof estimatedaccumulation,     watercouldbuildup to 584.5ft-lclDss     (USAR, Section2.4.2.3).
2.1.2. Floodingin Streamsand Rivers The USAR indicatesthat a flow rate of 78,500cubicfeet per second(cfs) in the Toussaint Riverat DBNPS(USAR,Section2,4.3)wouldresultin a maximumwatersurfaceelevationof 579 ft-lclDss. As indicatedin the USAR,the elevationof 579 ft-lGLDs5was derivedusingthe conservative               that noneof the wateris discharged assumption                                 to LakeErie,assumingthat the PMFflowis hypothetically    dammedup atthat   point(USAR,        2.4.3.5).
Section DAVIS.BESSE        NUCLEARPOWERSTATION                                            Page6 of 32

NTTFRecommendation      2.1 (HazardReevaluations):  Flooding                       Revision1 FirstEnergyCorporation                                                         March06, 2014 2.1.1. Dam Breachesand Failures The USAR indicatesthat there are no dams or other regulatinghydraulicstructureson the ToussaintRiverwhichwouldaffectthe flowhydrograph      at DBNPS(USAR,Section2.4.31.
2.1.4, StormSurge& Seiche The probablemaximummeteorological      eventin LakeErie resultsin a maximumwatersurfece elevationof 583.7 ft-lGLD5s. This meteorologicalevent is caused by a maximumeast-northeast  windat any locationof 100 milesper hourfor a 1O-minute duration,anda windspeed of 70 milesper hourduringthe six-hourperiodboth beforeand afterthe maximumwind speed (USAR,Section2.4.5).
2.1.5. Low Water No wateris takenfromthe ToussaintRiverfor plantcoolingwaterrequirements. Therefore,low flows in the Toussaint River will not affect DBNPS operation.The probable maximum meteorological  event in Lake Erie resultsin the probableextremelow water level of 556.8ft-lGLD55(USAR,Section2.4.11).
2.1,6. lce-lnduced   Flooding Floodingof the safety-relatedstructuresand equipmentat DBNPS due to ice jams in the ToussaintRiveris not credible.The USARindicatesthat the elevationof the pfantstructuresis abovethe level of normallake ice formations.Category1 wave protectiondikesare designed to withstand the impactof ice (USAR,Section2.4.7).
2.1.7. GhannelMigrationor Diversion As indicatedin the USAR,the mean lake levelis not subjectta variationsdue to diversionsor sourcecutoff(USAR,Section2.4.9).
2.1.8. CombinedEffectFlood(lncludingWind-Generated          Waves)
Wind-waveactivity,includingrunup,was evaluatedfor its effecton the wave protectiondikes on the north,east,and southsidesof DBNPS.As indicatedin the USAR,the maximumwave run-upon the dike is 6.6 ft abovethe probablemaximumwater surfaceelevationof 583.7ft-lGLD55.The resultingmaximumwave runupelevationis 590.3ft-lGLDs5,whichis belowthe top of the dike(USAR,Section2.4.2.2.1).
2.2. Flood-Related  Changesto the LicenseBasis There were no changesto the licensebasissince the            licenseissuance with regardto I flooding.
2.3.Changesto the Watershedand Local Area since Licenselssuance The watershedcontributory   to the ToussaintRiverupstreamof DBNPSis approximately    139.0 square miles (ReferenceDBNPS 2013c).Based on aerial imagesof the watershed,the changesto the watershedincludecommercialdevelopment       withinthe watershedarea,whichis a very small percentageof the overallwatershedarea. The changesto the local area sub-watershedfor DBNPSincludebuifdings,parkingfots,and securitybarrierupgradesthat have beenaddedto the sitesincelicenseissuance.
DAVIS-BESSE     NUCLEARPOWERSTATION                                              Page7 at 32

NTTFRecommendation      2.1 (HazardReevaluations):   Flooding                       Revision1 FirstEnergyCorporation                                                          March06, 2014 2.4. Cunent LicensingBasis Flood Protectionand PertinentFlood MitigationFeatures The maximumflood level in the designbasis is belowthe site finishfloor elevationof 585 ft-lGLD55.Therefore,therewere no mitigationactionsinitiatedor takenfor floodingat the site.
: 3. 

==SUMMARY==
OF FLOODHAZARDREEVALUATION NUREG/CR-7046,Design-BasisFlood Estimationfor Srfe Cfiaracterization       at NuclearPawer Planfs in the united Sfafes of America (ReferenceNUREG/CR-7046),by referenceto the AmericanNuclearSociety(ANS),statesthat a singleflood-causing       eventis inadequateas a design basis for power reactorsand recommendsthat combinationsshouldbe evaluatedto determinethe highestflood water elevationat the site. For DBNP$, the combinationthat producesthe highestflood water elevationat the site is the probablemaximumsurge and seicheon Lake Eriewith the effectsof coincidentwind wave activity.
The USARreportselevationscorresponding        to lGLDSSverticaldatum.The recentsite survey, UnitedStatesGeologicalSurvey       (USGS)   topographicrnaps,and other referencedocuments reportelevationin NorthAmericanVerticalDatumof 19BB(NAVDBB).         In orderto comparethe reevaluatedflood elevatienswith the existingdesign basis    reportedin USAR,final pertinent elevationshave been convertedto lGLD55 datum. The conversionbetween lGLD55 and NAVDBBat DBNPSis represented        as-- ft-lGLDsS= ft-NAVD88* 1.07ft.
Calculation  C-CSS-020.13-017    (Reference  DBNPS2013i)definesthe maximumwatersurface elevationof 585.81ft-lGLDs5at DBNPSadjacentto the powerblock.This elevationis due to a probablemaximumstorm surge (PMSS)during a probablemaximumwind storm (PMWS) event.The revisedmaximumwater surfaceelevationis abovethe site finishfloor elevationof 585 ft-tGLD55.
CalculationC-CSS-020.13-022      (ReferenceDBNPS2013n)definesthe coincidentwind wave runup.The maximumwave runupelevationof the PMSScoincidentwith wind wave activityis determinedby addingthe wind wave runup to the water surfaceflood elevationdue to the PMS$.The maximumrunupon the wave protectiondike is 589.88ft-lcLD55,whichis below the top of the wave protectiondike elevationof 591 ft-lclDss. The maximumwave runup elevationin the vicinityof the powerblockis 585.90feet-lGLD55. The wave runupelevationsin the vicinityof the powerblockare abovethe sitefinishfloorelevationof 585 ft-lGLD55.
Calculation  C-CSS-020.13-014   (Reference   DBNPS20130definesthe maximumwatersurface elevationresultingfrom the LIP event.The watersurfaceelevationdue to the LIP eventvaries from 585.17ft-lGLDS5to 585.44ft-lGLDsS.The LIP maximumwater surfaceelevationsare abovethe site finishfloorelevationof 585ft-lGLD55 The methodologyused in the floodingreevaluation     for DBNPSis consistentwith the following standardsand guidancedocuments:
    . NRC StandardReview Plan, NUREG-0800,revised March 2007 (ReferenceNUREG-0800)
    . NRC Officeof StandardsDevelopment,       RegulatoryGuides,RG 1.102- "FloodProtection for NucfearPowerPfants",Revision1, datedSeptember1976(Reference         NRC RG 1.102) and RG 1.59-"Design     BasisFloodsfor NuclearPowerPlants",Revision2, datedAugust 1977(Reference   NRCRG 1.59)
DAVIS-BESSE     NUCLEARPOWERSTATION                                                PageB of 32

NTTFRecomrnendation      2.1 (HazardReevaluations):Flooding                           Revision1 FirstEnergyCorporation                                                           March06, 2014
    . NUREGICR-7046,    "Design-Basis  Flood Estimationfor $ite Characterizationat Nuclear Power Plants in the United States of America," dated November z0fi (Reference NUREG/CR-7046)
    . NUREG/CR-6966,     "TsunarniHazardAssessmentat NuclearPower Plant Sites in the UnitedStatesof America",datedMarch2009(ReferenceNUREGICR-6966) r     "AmericanNationalStandardfor DeterminingDesignBasis Floodingat Power Reactor Site$",datedJuly28, 1992(ReferenceANSI/ANS-2.8-1992)
    . NEI Report12-08,"Overviewof ExternalFloodingReevaluations"     (ReferenceNEI August 2412)-
r     NRC JLD-ISG-2012-06,    "Guidancefor Performinga Tsunami,Surgeor SeicheFlooding HazardAssessment",   Revision0, datedJanuary4,2A13(Reference     JLD-lSG-2012-06)
    . NRC JLD-lSG-2013-01,     "Guidancefor Assessmentof FloodingHazardsdue to Dam Failure",Revision0, datedJuly29, 2013(Reference  JLD-ISG-2O13-01)
The followingprovidesthe flood-causingmechanistnsand their associatedwater surface elevationsthat are consideredin the DBNPSfloodhazardreevaluation     study:
3.f . FloodingIn $treamsand Rivers(ReferenceDBNPS2013a,DBNPS20{3b,and DBNPS2013c)
The PMF in rivers and streams adjoiningthe site is determinedby applyingthe probable maximumprecipitation     (PMP)to the drainagebasinin whichthe site is located.The PMF is based on a translationof PMP rainfall in the watershedto flood flow. The PMP is a deterministic  estimateof the theoreticalmaximumdepthof precipitation that can occurat a time of year for a specifiedarea. A rainfall-to-runoff transforrnation function,as well as runoff characteristics,  based on the topographicand drainagesystem networkcharacteristics       and watershedproperties,are neededto appropriatelydevelopthe PMF hydrograph.The PMF hydrographis a time historyof the dischargeand serves as the input parameterfor other hydraulicmodelswhichdevelopthe flowcharacteristics,    includingfloodflow and elevation.
The PMF is a functionof the combinedeventsdefinedin NUREG/CR-7046           for floodscaused by precipitation  events.
Alternative1 - Combinationof:
r   Meanmonthlybaseflow
        . Mediansoilmoisture
        . Antecedentrain:lesserof (1) rainfallequalto 40 percentof the PMP,or (2) a 500-year rainfall
        . TheAll-SeasonPMP
        ,   Wavesinducedby 2-yearwindspeedappliedalongthe criticaldirection Afternative  2 - Combination of:
        . Meanmonthlybaseflow DAVIS-BESSE      NUCLEARPOWERSTATION                                                 PageI of 32

NTTFRecommendation      2.1 (HazardReevaluations): Flooding                        Revision1 FirstEnergyCorporation                                                         MarchA6,2014
      . Snowmeltfromthe Probablemaximumsnowpack o fi 10O-year,   cool-seasonrainfall
      . Wavesinducedby Z-yearwindspeedappliedalongthe criticaldirection Alternative3 - Combination  of:
      . Meanmonthlybaseflow
      . Snowmeltfrom a 100-yearsnowpack
       . The cool-seasonPMP
       . Wavesinducedby Z-yearwind speedappliedalongthe criticaldirection 3.1,1. Basis of lnputs:
The inputsusedin the PMP,snowmelt,and PMFanalysesare basedon the following:
All-SeasonPMPAnalysisand Cool-SeasonPMPwith $nourmeltAnalysis
          . DBNPS and Toussaint River watershed locations, areas, boundaries and configurations; I  Historicflow ratedatacollectedby USGSat gage04195820on the PortageRiver; a  HMR-52-standardisohyetal patterns, storm orientation,percentage of 6-hour incrementof PMP,and standardisohyetalgeometryinformation; a  HMR-s3-seasonal    PMPvalues:
I The 100-yearall-seasonpoint rainfallestimatesfrom the NationalOceanic and Atmospheric   Administration(NOAA)Precipitation  FrequencyData$erver; Medianand extremedaily snow cover by      month for Ohio-data is downloadedfrom NOAA;and
          ' Snowmeltrate (energybudget)equationsand constantsare based on U.S. Army Corpsof Engineers   (USACE)Engineering   ManualEM-1110-2-1406, PMFanalysis-Hydrologic     & HydraulicAnalysis
          ' Digitalelevationmodel(DEM):The DEM used for the PMF calculation        is obtained from the U.$, Departmentof Agriculture(USDA) NationalResourceConservation Services(NRCS),nationalelevation   data; r Probablemaximumprecipitation     (PMP):72-hourPMP and associated     snowmelt,as applicable,for the subjectwatershed area;
          . Baseflow:Historicflow rate data collectedby USGS at gage 04195820on the PortageRiver,whichis usedas the baseflowfor the ToussaintRiver;
          . Soil Type: The soil types within the projectwatershedare developedusing USDA NRCSsoilinformation;
          . Land Use:The land use information   for the watershedis obtainedfrom USDANRCS soilsurveygeographic  database; DAVIS.BESSE    NUCLEARPOWERSTATION                                              Page10 of 32

NTTFRecommendation     2.1 (HazardReevaluations):Flooding                        Revision1 FirstEnergyCorporation                                                       March06, 2014
          . Manning'sroughnesscoefficientsare based on a visual assessmentof aerial photographyand selected using standard applicable engineeringguidance references;
          . Bridge informationobtainedfrom the Ohio Departmentof Transportation      (ODOT);
and
          . Supporting  Geographic            System(GlS)input(Reference Information                             DBNPS2013k).
3.1.2, ComputerSoftwarePrograms PMPand Snowmeltanalysis r   AutoCADCivil3D 2012
          . ArcGlSDesktop10.1
          . HMR-52software
          . MicrosoftExcel PMFanalysis
          . ATcGIS  Desktop10.1
          . HEC-HMS   3.5 r   HEC-RAS   4.1
          . HEC-GeoRAS    10.1 r   lGLD8SHeightConversion    OnlineTool
          . MicrosoftExcel 3.{.3. Methodology The PMFanalysisincludedthe followingsteps:
          '   Delineatewatershedand sub-watersheds,   then calculatesub-watershed  areas for inputintothe USACEHEC-HMSrainfall-runoff   hydrologic computermodel.
e Determine   rainfall.
          ' EstimateHEC-HMS rainfall-runoff     model initial input parameters:Snyder unit hydrographmethod,peakingand lag coefficient.
          . CalculateHEC-HMSmodellossinputparameters:       initiallossand constantlossrate.
          . CalculateHEC-HMSriverreachroutingmodelinitialinputparameters:       Muskingum-Cunge.
          . Method:B-pointcross-section,   reach        slope, and Manning'sroughness coefficient.
          . PerformPMFsimufation    with PMPinputusingHEC-HMSmodel.
          . Estimatewater surfaceelevationusing HEC-RA$unsteady-state      model by using runofffromthe HEC-HMSmodelas an input.
WatershedDelineation For the purposesof the hydrologicmodelingeffort,the ToussaintRiverwatershedis subdividedinto three (3) sub-watersheds(PackerCreek,UpperToussaintCreek,and LowerToussaintCreek)basedon the hydrologic   unitcode(HUC)boundaries.
DAVIS-BESSE    NUCLEARPOWERSTATION                                            P a g e1 1 o f 3 2

NTTFRecommendation     2.1 (HazardReevaluations):  Flooding                       Revision1 FirstEnergyCorporation                                                         March06, 2014 Rainfall& Snowmelt Eachalternative  containsrainfalldefinedeitherby the all-seasonPMP (Alternative   1),
the 1O0-year,  cool-season rainfall(Alternative                     PMP (Alternative 2), or the cool-season 3). Each rainfallevent is consideredto be a 72-hourdurationevent.Note that an antecedentrainfalloccurspriorto the all-seasonPMP.An antesedentstormequivalent to 40 percentof the all-seasonPMP is appliedto the HEC-HMSmodelwith a 72-hour dry periodbetweenthe antecedentstormand the PMPevent.
Snowmeltis includedin the two cool seasonalternatives.For rain-on-snow   conditions, the air temperature,dew point temperature,and averagemaximurndaily wind speed are obtained from representativeweather stations. The basin wind coefficientis determinedbasedon the densityof foreststandsin each sub-basin.lt is conservatively assumedthat the ToussaintRiverwatershedis unforestedplainto maximizesnowmelt.
For rain-freeconditions,the snowmeltparametersare selectedbasedon the USACE guidance.
The snowpackis assumedto be at its maximumat the onset of rainfallevents and cover the entire watershed.Soil is assumedto be frozen with no lassesduring the monthsof OctoberthroughApril. For the probablemaximumsnowpack,snowpack depthis assumedto be availablefor the durationof the coincidentrainfallevent.
Alternative{ -All-SeasonPMP The locationof the DBNPSwatershedis withinthe domainof the HMR-51and HMR-52 guidance.The all-seasonPMP is determined      by usingthe generalized PMP estimates definedby the HMR-51and HMR-52guidance.Differentstormcentersthroughoutthe watershedare examinedto determinethe criticalstorm centerthat maximizesrunoff.
HMR-52softwareis usedto optimizethe stormand definethe PMP estimatesfor each sub-basin.
HMR-52softwareis based on a standardtemporaldistribution.The HMR guidance indicatesthe greatestprecipitation may occurat othertimesthroughoutthe durationof the storm. The temporaldistributionof the PMP is calculatedin accordancewith recommendationsin HMR-52, wherein individual rainfall incrementsdeerease progres$ivelyto either side of the greatest rainfall increment.Various temporal for each rainfallscenarioare then evaluatedto furthermaximizethe runoff.
distributions Front, one-third, center, two-third, and end-loading temporal distributions are consideredin an effortto capturethe distributionthat maximizesrunoff.
Alternative2 - ProbableMaximumSnowpackand 1O0-Year             Cool-SeasonRainfall The probablemaximumsnowpackis assumedto be equalto an unlimitedsnowpack during the entire coincidentrainfall.While the snowpackcan be determineddirectly from the snow depth, there is not adequate data to extrapolateany historical observations up to the magnitudeof the probablemaximumevent.
The 1O0-year,cool-seasonrainfallis determinedfor the watershedlocationusing precipitationfrequencyestimatesdefinedby NOAA Atlas 14 guidanceand applying regionalseasonalguidance.NOAA Atlas 14 providesall-seasonpoint precipitation rainfallestimatesvia the NOAAprecipitation   frequencydata server.As NOAAAtlas 14 values are  point  precipitationvalues,the estimatesare adjustedusing area-depth reductionfactors.NOAAAtlas 14 valuesare also adjustedto reflectcool-season    rainfall ratherthanall-season  rainfall.
DAVIS-BESSE   NUCLEARPOWERSTATION                                               Page12 af 32

NTTFRecommendation     2.1 (HazardReevaluations):    Flooding                          Revision1 FirstEnergyCorporation                                                            March06, 2014 The 3-day (72-hour)snowmeltduration is assumedin order to correspondto the precipitationevents(PMP and 100-yearrainfall).A 10O-year,          cool-sea$onrainfallis equivalentfor all the cool-seasonmonths,However,the snowmeltis expectedto be differentfor each cool-seasonmonth becauseit is highlydependenton ternperature, which variessignificantlyfrom monthto month.Therefore,the monthwith the highest expectedsnowmeltis identifiedand usedfor the calculations     of the snowmeltrates Alternative3 - 100-YearSnowpackand Cool-SeasonPMP A 1O0-year  snow depth is calculatedby performinga statisticalanalysisbasedon the historicaldata obtainedfrom the NOAA Annual ObservationData website.A Fisher-Tippett Type l (FT-l) distributionfrequencyanalysisis performedto determinethe maximumsnowdepthwith an annualexceedanceprobabilityof 1 percent(i.e. 10O-year snow depth).The FT-l distributionis applicablefor long{erm statisticalanalysesand specificallyfor extremevalue calculations.The cool-seasonPMP is determinedby applyingseasonalHMR-53guidanceto the all-season        PMPestimates.
HydrologicModel(HEC-HMS)
The PMF is the floodresultingfrom the PMP.The temporaldistribution        of the PMP is calculatedin accordancewith the recommendations          in HMR-52,whereinindividual incrementsdecreaseprogressivelyto either side of the greatestincrement.For each sub-watershed,  a 9-dayPMP hyetographis constructed       usinga rainfallequivalentto 40 percentof the PMP during the first 72 hours,followedby a dry 72-hourperiod,and finallyfollowedby the full 72-hourPMPstorm.
USACEHEC-HMShydrologicsoftwareis used to convertrainfallts runoff.A rainfall hyetographis appliedto each sub-watershedand transformedto runoff using unit hydrographmethodology.Generallya unit hydrographis developedusing historical data obtainedfrom various rain and stream gages in the watershed.The DBNPS watershedis ungaged.Thus,there are no historicalobservationsavailableto use as a basisto createa unit hydrograph.Therefore,a syntheticunit hydrographis developed.
The Snyderunithydrographmethodology                                   transformation.
is usedfor rainfall-to-runoff Routing accounts for change in the flow hydrographas a flood wave passes downstreamand accountsfor storageand attenuationduring a floodingevent. The Muskingum-Cunge     routingmethodis utilizedin the HEC-HMSmodel,with the streams represented  by B-pointcrosssections.
ANSIIANS-2.8-1992    suggeststhat baseflowshouldbe basedon meanmonthlyflow.As mean monthly flow is not available for the Toussaint River, the baseflow is approximatedbased on the mean monthlyflow in an adjacentwatershed.The only gagestationavailablein the samehydrologic      unitis on the PortageRivernearElmore, OH. The watershedsof the ToussaintRiverand PortageRiverare locatedin the same HUC and have similar watershed characteristics.Therefore,it is an acceptable approachto use the base flow informationfor the Portage River as the basis for estimationof the baseflow at ToussaintRiver.
lnitiallossesare ignored.Infiltration,  or constantlosses,is determinedbasedon the hydrologiccharacteristics  of the soilswithineachbasin.Constantlossesare not applied to impervious areas.Additionally,  constantlossesare ignoredfor the cool-season    PMF alternativesdueto the assumption    thatgroundis frozen.
DAVIS-BESSE   NUCLEARPOWERSTATION                                                  Page13 of 32

NTTFRecommendation     2.1 (HazardReevaluations):      Flooding                          Revision1 FirstEnergyCorporation                                                              March06, 2014 The unit hydrographs   for each sub-watershed    are modifiedto accountfor the effectsof nonlinearbasin   response   in accordance  with  NUREGICR-7046. The peakof eachunit hydrographis   increased  by  one-fifthand  the time-to-peak is reduced  by one-third.The remaininghydrographordinates        are adjusted  to preserve the  runoffvolumeto a unit depthoverthe drainagearea.
HydraulicModel(HEC-RAS)
The unsteadyflow modulewithinthe USACEHEC-RASsoftwareis used to transform the resultingflow hydrographsfrom the controllingalternativeinto a water surface elevationhydrographunderunsteadyflow conditions.For referenceand comparison,           all threealternatives  are evaluatedwith the HEC-RASmodel.
Channeland floodplaingeometryfor the ToussaintRiver is modeledby developing cro$s sectionsof the stream.The cross sectionsare placed at locationsthat define geometriccharacteristics    of the river valley and overbanks.Cross sectionsare also placedat representative   locationswherechangesoccurin discharge,slope,shape,and roughness,as well as at hydraulicstructures(e.9. bridges). River banks,blocked obstructions,and ineffective   flow areasare alsoincorporated   intothe HEC-RASmodel.
Two bridgesare modeled(the CR19 Bridgeand the CR2 Bridge)using information receivedfrom ODOT.Thereare two additionalbridgesover the modeledportionof the ToussaintRiver:the N. Benton-Carroll       Rd Bridgeand the CR590 Bridge.These two bridgesare locatedfarther away from DBNPS (approximately             7 and 10 river miles respectively).lt is not expectedthat thesetwo bridgeswould havea measurableeffect on the computational   resultsbecauseof the distance,Any possibleeffectproducedby the bridgesupstreamof the riverwill be lost due to attenuationin the stream.Therefore, theyare not includedin the model.
The PMF flow hydrographsobtainedfrom the HEC-HMSmodelare enteredinto the HEC-RAS model. The highest observedwater level in Lake Erie is used as a downstreamboundaryconditionin the HEC-RASsoftwareprogram.
The HEC-RASmodel is evaluatedfor both all-seasonPMF (Alternative1) and cool-seasonPMF alternatives     (Alternatives 2 and 3).
3.1.4. Results The Alternative1 PMF is the controlling     combination   and is a resultof the all-season PMP.The maximumwatersurfaceelevationat DBNPSis 575.96fi-lGLDs5(576.93ft-NAVDBB),  witha maximumflowof 100,436cfs.
For Alternative 2, the maximumwatersurfaceelevationis 574.15ft-lGLD5s(575.12tt-NAVD88)witha maximumflowof 31,747cfs.
For Alternative3, the maximumwatersurfaceelevationis 575.06ft-lGLDs5(576.03ft-NAVDBB)   witha maximumflowof 61,943cfs.
The all-seasonPMF is determinedto be the controllingPMF scenarioand an additionalcombinedeventanalysisis performed         in CalculationC-CSS-020.13-022.
DAVIS.BESSE    NUCLEARPOWERSTATION                                                    Page14 o{ 32

NTTFRecommendation     2.1 (HazardReevaluations):  Flooding                          Revision1 FirstEnergyCorporation                                                           March06, 2014 3.2. DamAssessment(ReferenceDBNPS2013d) 3.2.1. Basisof Inputs Inputsusedfor the dam assessment    evaluation r   HEC-RASmodeldevelopedin the PMFanalysis" r   Dam information:   The Nationallnventoryof Dams (NlD) is used to identifythe watersheddams.
3,2.2. ComputerSoftwarePrograms n ArcGlSDesktop10.1
         . HEC-RAS      4.1 3.2.3. Methodology The criteriafor dam a$sessmentis providedin the hlRC Guidancefor Assessmenfof FloadingHazardsdue to Dam Failure,JLD-lSG-2O13-01.        Only two dams reportedby NID are locatedin the DBNPSwatershed      - the Genoa  UG  SewageDisposalLagoons and the GraymontSludgeLagoons.
Effectsof the failureof the two dams are analyzedusing a simplifiedapproachas outlinedin JLD-ISG-2013-01. The peakoutflowwithout   attenuation  methodis basedon summingestimateddischarges    fromsimultaneou$   failuresof upstreamdamsarrivingat the sitewithoutattenuation.
The peakdischargeusingthe simplifiedequation$wa$ calculated        to be 4,642cfs and 13,651cfs for GenoaUG SewageDisposalLagoon$and GraymontSludgeLagoons respectively.A cumulativepeakbreachdischargeequalto 18,253cfs from bothdams is included in the HEC-RAS model as additionaftateral inflow at the cros$ section immediatelyupstreamof the DBNPS site. Conservatlvely,        the peak breach flow is apptiedto the HEC-RASmodelat the time corre$ponding the PMF peak discharge to determined  in the PMFanalysis.
3,2,4, Results The maximumwater surface elevationat the site resultingfrom the PMF event combinedwith the cumulativeupstreamdam failuresis 577.09ft-NAVDBB.           Compared to the PMF results,the water surfaceelevationincrease      due  to  the additional  dam
                                                 -         =
breachflowis equalto 0.16ft (577.09ft 576.93ft 0.16ft).The maximum          PMF    water surfaceelevationat DBNPSis 8.04ft belowthe sitegradeelevationof 584.0ft-lGLD5s.
Consequently,   the increasedue to the dam failureresultsin a water surfaceelevation thatis 7.88ft belowsitegrade(8.04ft - 0.16ft = 7.88ft).
The maximumwater surface elevation at the site resultingfrom the PMF event combinedwith the cumulativeupstreamdam failuresis well belowthe plantsite grade elevation,Therefore,the upstreamdams are determinedto be noncriticaldams as referredto in the JLD-lSG-2O13-01 . No furtherdamfailureanalysisis required.
Thereare no damsdownstreamof DBNPSon the ToussaintRiver.
DAVIS.BESSE   NUCLEARPOWERSTATION                                                 P a g e1 5 o f 3 2

NTTFRecommendation        2.1 (HazardReevaluations):  Flooding                       Revision1 FirstEnergyCorporation                                                          March06, 2014 3.3. lce-lnducedFlooding(Reference          DBNPS2013d)
As identifiedby NUREG/CR-7046,         ice jams and ice dams can form in rivers and streams adjacentto a site,and may leadto floodingby two mechanisms:
      '   Collapseof an ice jam or an ice dam upstreamof the site can result a dam breach-likefloodwave that may propagateto the site;and
      . An ice jam or an ice dam downstreamof a site may impoundwater upstreamof itself, thuscausinga floodvia backwatereffects.
3.3.{. Basisof Inputs
          . USACEicejam database.
          . Bridgegeometry(upstreamand downstreamof DBNPS)- Information          relativeto the bridgestructuresprovidedby ODOT.
e DBNPSHEC-RASmodeldeveloped              in the PMFanalysis.
3.3.2. ComputerSoftwarePrograms
          '   HEC-RAS      4.1 3.3.3. Methodology Per NUREG/CR-7046,       ice-inducedfloodingis assessedby reviewingthe USACEice jam databaseto determinethe mostseverehistoricaleventsthat haveoccurred.There are no historicalrecordsavailablefor the ToussaintRiver.The nonexistence    of ice jam recordsis explainedby the absenceof stream monitoringstationson the Toussaint River.Basedon ice jam occurrencewithinadjacentstreamsin the samehydrologicunit code(HUC),it is determined     thaticejam eventsare possiblein the ToussaintRiver.
The maximumice jam is determinedby selectingthe historicevent that producedthe maximumflood stage relativeto the normalwater surfaceelevationat that location.
Regardlessof specificconditionsthat producedthe historicflood stage at a specific location,the full heightis conservatively assumedto representthe icejam.
Historicalice jam data for PortageRiver,RockCreek,BayouDitch,and LacarpeCreek are consideredas they are locatedin the same HUC area. The maximumrecorded stagedue to an icejam is used, The peakwater surfaceelevationat DBNPSas a resultof an upstreamice jam breach
{i.e., failure of ice dam) is estimated.A hypotheticalice jam is incorporatedinto the HEC-RASmodelat the locationof the firstbridgeupstreamof DBNPS,the CR2 Bridge.
lce dam breachparametersare selectedso the entireice jam withinthe main channel wouldbreachwhenthe waterlevelbehindthe icejam is at its maximumelevation.
The recorded ice jams have a maximum reported stage of approximately13 ft; however,thereare no recordsfor the heightof the ice damsthemselves. The clearance between the bottom of the Toussaint River and the low          point of the bridge is approximatelyI ft, which is less than the maximum reported stage. Therefore, conservatively,   the postulatedlce dam couldcompletelyblockthe bridgeclearance.
DAVIS-BESSE    NUCLEARPOWERSTATION                                                Page16 of 32

NTTFRecomrnendation      2.1 (HazardReevaluations):  Flooding                        Revision1 FirstEnergyCorporation                                                          March06, 2014 Per NUREG/CR-7046,      floodingdue to an ice jam is not requiredto be combinedwith otherextremefloodingevents.However,to representnormalflow in the ToussaintRiver during the cool-seasonmonth, a smaller cool-seasonPMF alternativeis utilized (Alternative2 PMF).The Alternative2 PMF is a combinationof the snowmeltfrom a probable maximum snowpack and a 10O-year,cool-seasonrainfall.The inflow hydrographsrepresenting    the Alternative2 PMF eventare usedin the HEC-RASmodel evaluatingthe effectof a postulatedice dam failure.
3.3.4. Results The maximumwater surfaceelevationat DBNPSresultingfrom the upstreamice jam breachingwas calculatedto be 574.05ft-lGLDSs(575.12ft-NAVD88).There are no bridgesor structuresdownstreamof DBNPSon ToussaintRiverthat couldcreatean ice damor icejam.
The watersurfaceelevationat DBNPSdue to the PMF is equalto 575.96ft-lclDss.
Therefore,the ice-inducedfloodingat DBNPSis boundedby the PMF, and no further consideration  is required.
3.4. ChannelMigratlonor Diversion(ReferenceDBNPS20f gd)
NUREGICR-7046       indicateshistoricalrecordsand hydrogeomorphological data shouldbe used to determinewhetheran adjacentchannel,stream,or river has exhibitedthe tendencyto meandertowardsthe site.
3.4.1. Basisof lnputs
          . USGStopographic    maps r    Aerialimages 3.4.2. ComputerSoftwarePrograms
          . Arc GIS10.1 3.4.3. Methodology Historicand currenttopographicmaps and aerialimagesare reviewedto examinethe conditionand alignment   of riversand streamsovertime.
Historicalmapsfor the yearsof 1900,1952,1967,1986,and 2011 were reviewedto assess historic channel migration of the Toussaint River. Toussaint River is approxirnately2,000 ft south of the DBNPS. The locationsof the river and lake shorelinesshown on the historicalmaps are comparedto the present-daylocations
( 2 0 11 ) .
3.4,4. Results Fromthe comparisonof the historicalmaps,the mostsignificantdiscrepancies      between the present-dayand historicalstreambank and shorelinelocationsare observedon the USGS map for 1900. More recent USGS maps show both stream and shoreline locationsapproximately   the sameas the currentlocation(within+/- 0.1 miledifference).
DAVIS-BESSE      NUCLEARPOWERSTATION                                              Page17 of 32

NTTFRecommendation      2.1 (HazardReevaluations): Flooding                         Revision1 FirstEnergyCorporation                                                         March06, 2014 Basedon the comparisonbetweenthe currentlocationof the ToussaintRiverand the river locationas shownon the historicalmaps which cover a periodof approximately 110 years,it is determinedthat channeldiversiontowardsthe site is not probable.The same comparisonis performedfor the lake shorelineand similarly,Lake Frie shorefine diversiontowardsthe site is not probable.
3.5. StormSurge(ReferenceDBNPS20139,DBNPS2013h,DBNPS20131and DBNPS 2013m)
Probqhlef.Ulaximum   Stofm Surse (PMSSI In accordancewith JLD-ISG-2012-06,    all coastalnuclearpowerplantsites and nuclearpower plantsites adjacentto coolingpondsor reservoirssubjectto potentialhurricanes,windstorms and squalllinesmust considerthe potentialfor inundationfrom storm $urgeand waves.JLD-ISG-2012-06   alsosuggeststhatfor the stormsurgehazardas$e$sment,    historicalstormevents in the region should be augmentedby a syntheticstorm parameterizedto account for conditionsmoreseverethan thosein the historicalrecordsand consideredreasonablypossible on the basisof technicalreasoning.
3.5.1. Basisof Inputs The inputsusedin PMSSanalysisare basedon the following:
r   Historicalwind and pressurefielddatafrom NOAAfor the GreatLakeRegion r   Probablemaximumwindstorm(PMWS)
          . LakeEriebathymetryfromthe NOAAgeophysical        database
          . Supporting GISdata  (Reference  DBNPS   2013o) 3.5.2. Computer$oftware Programs
          . ArcMap10.1
          . Deft3D sofhnraresuite (Delft3D-FLOWDelft3D-WAVE,Delft3D-RGFGRID,             and Delft3D-QUICKIN) 3.5.3. Methodology Several physical processescontributeto the generationof a storm surge. The contributionof wind to a stormsurgeis oftencalledwind setup.Wind blowingover the watercausesa shearstressthat is exertedon the surfaceof the water,pushingwater in the directionof the wind. Atmosphericpressuregradients are another forcing mechanismthat contributesto changesin waterlevel,as wateris forcedfromregionsof highatmospheric   pressuretowardregionsof low pre$sure.
The followingdescribesthe methodologies    usedin the PMSScalculation:
Developmentof the PMWS The PMWS storm-basedapproachis specificto the characterislicsof the site. Past extremeeventsin a regionare analyzedand consideredtranspositionable.      As part of the PMWS, differentstorm types       (such as synoptic,squall line, and  hybrid) that DAVIS-BESSE    NUCLEARPOWERSTATION                                              Page18 of 32

NTTFRecommendation     2.1 (HazardReevaluations):    Flooding                          Revision1 FirstEnergyCorporation                                                           March06, 2014 impactedthe GreatLakesregionare consideredin orderto determinethe stormevent that will generatethe maximumsurgeand seiche.Eachstorm'sinputparameter$              are quantifiedand plottedbasedon the locationof lodhigh pressurecenters,concurrent wind/pressure  fields,and how they evolvethroughtime and space, Mostof the synopticstormsoccurin associationwith deep areasof low pressurewhich movethroughthe regionfrom southwestto northeast.The generalsynopticpatternis one in which the deep area of low pressureresultsin a very strongpressuregradient force betweenits low pressurecenterand a corresponding      regionof higherpressureto the north or west. The larger the      gradient betweenthe two systemsover a given distanceis, the strongerthe resulting  winds.
Squall line (or derecho)events create a widespreadstraight-linewindstormthat is associatedwith a fast-movingband of severe thunderstorms.These winds have producedsome of the highestinstantaneous        gusts on record,but last for only a short time (lessthan 30 minutes)at a given location.The shortdurationof theseevents,as they quicklytraversea given location,mean they will not controlthe PMSS. Further, these events do not occur within deep low pressuresystems or remnanttropical systems.Therefore,theirwind and pressuredata are not combinedwith the olherstorm typesin thisanalysis,as thiswouldresultin a PMWSthatis not physically      possible.
Althoughdeep low pressuresystemsoften producethe longestdurationlarge-scale winds,otherstormtypesalso producestrongwindsoverthe region.In rarecases,land-fallingtropicalsystemsalongthe Gulf Coast or AtlanticSeaboardmove inlandacross the Appalachians   or up the Mississippi and OhioRivervalleys.By the timethesestorms reach the Great Lakes region,they are no longertropicalsystems,but insteadhave transitioned intoextra-tropical cyclones.Theirgeneralcirculationand centerof deep low pressurepersists.Much like the deep low pressurescenariopreviouslydiscussed, strong and persistentwinds can result.The remnantsof HurricaneHazel (October 1954)and HurricaneSandy (Octoberz}ftl are classicexamplesof this storm type.
This storm scenarioprovidedsome of the strongestwindsfrom the northwestthrough the northeastdirectionsoverLakeErie(withdurationsat 12 hoursor more).
Delft3DCalibration The Delft3Dhydrodynamicmodel is set up based on the Delft3Dsoftwaresuite.The wave setup contributionto the total storm surge valuesare modeledby couplingthe Delft3D-WAVE    and Delft3D-FLOW      surgemodels.The generalapproachto stormsurge modelingusing coupled Delft3D-FLOWand Delft3D-\ffAVEmodels consistsof the followingsteps:
I   Developing  the bathymetric  datasetand modelgrid meshfor the lakesystem; a   Assemblinginputfilesfor atmospheric     forcing(windand pressurefields);
Assembling   inputfilesfor initialwaterlevel,boundaryconditions, andthe physical and numericalparameters     of the model; Assemblingmeasuredwaterlevelsand wavedatafor modelcalibrationand verification; a   Testingand refiningthe initialmodelsetup; t   Validatingthe modelfor historicalextremestormevents;and DAVIS-BESSE   NUCLEARPOWERSTATION                                                   Page19 of 32

NTTFRecommendation     2.1 {HazardReevaluations):  Flooding                         Revision1 FirstEnergyCorporation                                                          March00, 2014
         . Assessingmodelsensitivityto variousfactorsand adjustableparameterssuchas bottomfrictionand wind drag coefficient.
The Delft3D model is calibrated based on historicaldata obtained from NOAA meteorological  and waterlevelrecordingstationslocetedin the LakeErieregion.
Reviewof lristoricaldata shows that variousparts of Lake Erie responddifferentlyto aRyone particularstorm.The stormthat producesextremewater levelsin one part of Lake Erie might not, and probablydoes not, produceextremelevels in other parts.
Thereforethe numberof calibrationand validationstorms selected,to assess model predictionaccuracy,coveredall partsof the lakeshoreline.
Calibrationand verificationof the coupledDelft3D-FLOW      and DelflSD-WAVE  modelsis performedby a time series comparisonof measuredand predictedlmodeledstorm surge values at differentwater level recordingstationson Lake Erie. A similartime seriescomparisonis also performedfor wave heights.
The Deltt3Dmodelsare calibratedusing extremehistoricwind and pressuredata from multiplemeteorological  and waterlevelrecordingstations.Calibrat*on                 of and verification the coupled Delft3D-FLOWand Delft3D-WAVEmodels demonstratesthat the hydrodynamic   modelis capableof computingthe stormsurgeand seichedynamicsfor Lake Erie,as well as the signiticantwave heightsand periodsat DBNPSfrom PMWS events.
PMSS The calibratedDelft3Dmodelis used to determinethe PMSS.The historicwind and pre$surefield data is replacedwith candidatePMWSevents,and the modelis run to determinethe criticalPMWS.
JLD-ISG-2A12-06    and ANSI/ANS2.8-1992requirethe antecedentwater levelequalto the 100-yearmaximumrecordedwater level to be appliedas the initialslorm surge modelstill water level.The 100-yearwater levelof 175.05meters-IGLDBS       is used as the initialcondition/antecedent water level in all the Delft3D-FLOW  models.$ince the probableminimumlow water level at DBNPScouldoccurat a time when the monthly meanlakelevelis at the long-termmeanlow probablelevel,the anteeedentwaterlevel for low waterevaluationis set to the long-ternrlow probablelevelat Lake Erie,whichis equalto 173.13meters-IGlD    85 Varioustopographicfeaturesmay affectthe storm$urgepropagationtowardsDBNP$.
The elevatedareaaroundDBNPSis protectedalongthe northern,eastern,and alonga smallportionof the southernsidesby an earthfillwaveprotection    dikebuiltup to 591.00 ft-lGLD55.The purposeof the wave protectiondike is to protectagainstthe surgeand associatewave run-up.Additionally,     the DBNPSarea along the soulhern,western, northern,and easternsidesof the plantis protectedby a vehiclebarriersystem(VBS).
MaximumHistoricaland 26-yearStorm $urge The historicalmaximumstorm surge is the largestof the determinedyearlymaximum storm surge heights.The historicalmaximumstorm surge height will be used in combinedfloodingscenariosin a separatecalculation.
         $torm surges are calculatedfrom monthlydata as the differencebetweenmonthfy maximumand monthly mean based on guidanceprovidedby U$ACE. The Log PearsonType lll distributionis the commonlyacceptedfrequencyprocedurefor annual DAVIS.BESSE    NUCLEARPOWERSTATION                                               Page20 ot 32

NTTFRecommendation       2.1 (HazardReevaluations):    Flooding                        Revision1 FirstEnergyCorporation                                                            March06, 2014 maximumwater levels. A frequencyanalysison the yearly maxlmumstorm surge heightsobtainedfrom the Toledoand Marbleheadstationsis performedusing a Log Pearsonlll statisticalanalysis.The 2S-yearstormsurgeheightwas used in combined floodingscenarios.
3.5.4. Results Simulations   of all the candidatePMWSeventsshowedthat the criticalPMWSeventis the October2012 wind stormevent,which is the remnantsof HurricaneSandy.This storm is the most intenseof all the PMWS events with a maximumwind speed of 103.12mileslhourand is alignedalongthe axis of LakeEriewhichis in the northeast direction.The maximumPMSSresultingfrom this PMWSeventproduceda maximum watersurfaceelevationof 585.90ft-lcLD55at the intakeforebaylocation, The Delft3Dmodelingresultsshow that the Lake Erie dike,will be overtoppedfrom the PMSSevent.Overtoppedwaterwill accumulatebehindthe LakeErie dike in the marsh and low elevationareasaroundDBNPS,establishing           a highermean water level (i.e.
pondedwater)aroundthe plant.As the surge recedesto Lake Erie,the accumulated wateris forcedto returnto LakeErie (returnflow) alongthe westernand southernVBS.
Eventually,  the waterwill overtopthe southernand westernVBS duringthe recessionof surgewaterto LakeErie,and floodDBNPS.
The maximumPMSSwater surfaceefevationin the vicinityof the power blockdue to the criticalPMWSis 585.81ft-lGLD5S.The PMS$ watersurfaceelevationswill remain abovethe site finishfloorelevation(585ft-lGLD55)for approximately     2.5 hours.
          $urge, Seiche,and Resonance Resultsfrom CalculationC-CSS-020.13-016          show that the level of the rise due to seicheis significantly   lessthan the calculatedsurgeheight.For this rea$on,seichesare not the controlling  floodeventat DBNPS.
Resonancegeneratedby wavescan causeproblemsin enclosedwaterbodiessuch as harborsand bayswhen the periodof oscillationof the waterbodyis equalto the period of the incomingwaves. The periodof oscillationof Lake Eriedelerminedin Calculation C-CSS-020.13-016       is in the rangeof 12 to 15 hours.This is muchgreaterthan that of the peak spectralperiod of the incidentshallowwater storm waves. Consequently, resonanceis not a detrimentat DBNPSduringthe criticalPMWSevent.
ProbableMinimumLow WaterLevel resultingfrom the PMW$
Simulationsof all the candidatePMWSstormeventsshowthat the criticalPMWSevent that would result in probableminimumlow water level (drawdown)is the transposed January1978stormevent.This stormhad the most intensewest and southwestwinds of the examinedstormevents,with maximumsouthwestwindspeedof 89.0 miles/hour.
The probableminimumlow waterelevation(drawdown)associatedwith the transposed January1978stormproducesa probableminimumlow waterlevelof 547.46ft-lGLD5s at the westernbasinof LakeErie.At this probableminimumlowwaterlevel,the DBNPS intakecanalis completelycut off from LakeEriefor approximately    43 hours.
3.6.TsunamiAssessment(Reference            DBNPS2013J)
NUREG/CR-6966      identifies  that earthquakes,           and volcanoescan initiatetsunamis, landslides, with earthquakesbeing the most frequent cause. Dip-slip earthquakes(due to verlical movement)are more efficientat generatingtsunamisthan strike-slipearthquakes(due to DAVIS-BESSE    NUCLEARPOWERSTATION                                                  Page21 of 32

NTTFRecommendation      2.1 (HazardReevaluations):  Flooding                        Revision1 FirstEnergyCorporation                                                          March06, 2014 horizontalrnovement). To generatea majortsunami,a substantial    amountof slip and a large rupturearea is required.Consequently,   only largeearthquakes  with magnitudes  greaterthan 6.5 on the Richterscalegenerateobservable    tsunamis.
3,6.1. Basisof Inputs
           . NOAAnaturalhazardstsunamidatabase r   NOAAnaturalhazardsvolcanodatabase r   Historical earthquake hazardsdatabase
           . OhioDepartment  of NaturalResources(ODNR)database 3.6.2. ModelsUsed
           . None 3.6.3. Methodology As identifiedby NUREGICR-7046,     tsunamiassessmentis referenced     to NUREGICR-6966 and NOAA TechnicalMemorandumOAR PMEL-136.In addition,the more recentlyissuedNRCguidance,JLD-lSG-2012-06,      alsoaddresses  tsunamiassessment.
However,JLD-lSG-2012-06     providesguidanceon detailedtsunamimodelingand is beyondthe scopeof this assessment. TechnicalMemorandumOAR PMEL-136reflects a similartsunamiscreening  assessment  describedby NUREGICR-6966.
The NUREGICR-6966      screeningassessmentis basedon a regionalscreeningand a site screening.The regionalscreeningconsistsof researchinghistoricalrecordsfor tsunamirecordsand the potentialfor tsunami-generating     sources.The site screening evaluatesthe site based on the horizontaldistancefrom a coast, the longitudinal distancemeasuredalonga river,and the gradeelevationin comparisonto the effectsof a tsunami.This assessmentapproachis basedon a reviewof historicalrecordsand databases.
NUREG/CR-6966identifies that tsunamis are generated by rapid, large-scale disturbances of a bodyof water.The mostfrequentcauseof tsunamisis an earthquake; however,landslidesand volcanoescan also initiatetsunamis.Becauseof the tsunami-generationsequenceassociatedwith earthquakes,     dip-slipearthquakes(dueto vertical movement)are rnoreefficientat    generating tsunamisthan strike-slipearthquakes(due to  horizontalmovement).Furthermore,to generatea major tsunami,a substantial amount of slip and a large rupture area is required.Consequently,only large earthquakes  with magnitudes  greaterthan6.5 on the Richterscalegenerateobservable tsunamis.
As part of the assessment,  the NOAA naturalhazardstsunamidatabasewas used to reviewhistoricaltsunamieventsand associatedrun-upsfor the east coastof the United Statesand Canada.Of the total events,therewere 7 tsunamieventsthat produced14 run-upsoccurringin the GreatLakesregionfrom 1755to 1954"The USGShazardfault databasefindingswere reviewedfor strongearthquakesor the verticaldisplacements necessaryto inducea tsunami.Additionally,   the USGSeadhquakehazardsprogramis reviewedfor historicalearthquakesin the region.Lastly,the NOAA naturalhazards volcanodatabaseis reviewedto assessvolcanoesin the LakeErieregion.
An earthquake-generated   tsunamiin Lake Erie would requirea very large earthquake on the order of magnitude7.0 or greateralong with significantverticaldisplacement.
DAVfS-BESSENUCLEARPOWERSTATfON                                                   Page22 of 32

NTTFRecommendation      2.1 (HazardReevaluations):   Flooding                         Revision1 FirstEnergyCorporation                                                           March06, 20f 4 Historically,in the Lake Erie region,the largestearthquakes   are in the magnitude5.0 range. Preliminaryanalysisof post-glacial     sedimentsin the region has not yielded evidence of a large earthquakein the last few thousand years. Furthermore, earthquakesin the region, for which sufficientdata are available,show primarily horizontalrather than vertical movement,which is not as conduciveto tsunami generation.
Tsunamiscan also be generatedby the downslopemovementof a very largevolumeaf rock or sedirnent,eitherfrom a rockfallabovethe water or fiom a submarinelandslide.
Althoughlarge amountsof unconsolidated       sedimentsare washedinto Lake Erie each year when shorelinebluffsare undercutby wave action,these masseslack sufficient volumeand rapid collapseto displacea volumeof water that would createa tsunami.
Lake Erie afso has a very gentlebottomprofile,particularlyin the westernand central basins.The easternbasinhas steeperslopes,but not steepenoughfor a largeamount of sedimentto suddenlyflowdownslopein a submarinelandslide.
Lastly, according to the NOAA natural hazards volcano database,there are no volcanoesin the LakeErieregion.
3.S.4. Results The NOAA naturalhazardstsunamidatabaseidentifiesonly two ocsurrencesof non-seiche (or non-wind-induced)    tsunami events in the Great Lakes region. The two occurrencesyielded slight or small wave effects. Various earthquakedatabases, includingthe USGS EarthquakeHazardsProgramearthquakedatabase,the National Centerfor EarthquakeEngineeringresearchcatalog,and NaturalResourcesCanada, identifythat the largesteventsin the vicinityare no greaterthan magnitude5.0.
Accordingta the USGS EarthquakeHazards Program,the hazard fault database containsno knownQuaternaryfaults(or currentfaults)in this regionbecausegeologists have not found any faultsat the Earth'ssurface.Consequently,    thereis nol a potential for strongearthquakesor the verticaldisplacement    necessaryto inducea tsunami.
Therefore,a tsunamiis not expectedto be the controllingfloodeventat DBNP$.
3.7,CombinedEffect Flood (includingWlnd-Generated          Waves){ReferenceDBNP$
2013n1 Evafuationof the shoresidelocationis coveredin H.4.1of NUREGICR-7046         and includesone alternative:
Combinationof:
Probablemaximumsurgeand seichewithwind-waveactivity, The lesserof the 1OO-year or the maximumcontrolledwaterlevelin the enclosed bodyof water.
There are three alternativesspecified in H.4.2 af NUREG/CR-7046for streamside locatione.Each of the alternatives  consideredhas three componentscontributingto the watersurfaceelevation.
          . Alternative1 - Comblnationof:
          - The lesserof one-halfof ttrePMFor the 500-yearflood;
          - $urge and seiche from the worst regionalhurricaneor windstormwith wind-wave activity;and DAVIS.BES$E    NUCLEARPOWERSTATION                                                 Page23 af 32

NTTFRecommendation     2.1 (HazardReevaluations):   Flooding                        Revision1 FirstEnergyCorporation                                                         March06,2A14
         -   The lesserof the 1O0-year     or the maximumcontrolledwater level in the enclosed bodyof water.
         . Alternative2 - Combinationof:
         -   PMF;
         -   A 25-yearsurgeand seichewithwind-waveactivity;and
         -   The lesserof the 10O-year     or the maximumcontrolledwater level in the enclosed bodyof water.
r   Alternative3 - Combinationof:
         -   A 2S-yearflood;
         -   Probablemaximumsurgeand seichewith wind-waveactivity;and
         -   The lesserof the 1O0-year     or the maximumcontrolledwater level in the enclosed bodyof water.
3.7.1. Basis of Inputs lnputsincludethe following:
r   Toussaint River sub-watershedproperties for rainfall-runotfmodeling from CalculationC-CSS-020. 13-011
         . ToussaintRiverHEC-RASmodelfromCalculation       C-CSS-020.13-011 r   PMFdischargehydrographs       fromCalculation C-CSS-020.13-01  1
         . One-halfPMFdischargehydrographs
         . Z5-yeareventrainfallfor inputintoHEC-HMSmodelfromNOAAAtlas 14
         . 2S-yeareventdischargehydrographs
         . Lake ErieProbablePMSSelevationsfrom CalculationC-CSS-020.      rc-417 3.7.2. ComputerSoftwarePrograms
         . ArcGlSDesktop10.1 r   Delft3D r   HEC-HMS    3.5
         . HEC-RAS4.1
         . MicrosoftExcel 3,7.3. Methodology Eachcombinationincludescoincidentwind-waveactivity.Coincidentwind-waveactivity is determined                                   usingthe USACEguidanceoutlinedin for the criticalfloodingcombination USACECoaslalEngineeingManual.Runupis the maximumelevationof wave uprush abovestillwaterlevel.
H 4.1 Combination Probablemaximumsurgeand seicheis estimatedin CalculationC-CSS-020.13-017.
Wind-waveactivityincludeswave height,wind set-up,and wave runup.Wave height andwindset-upare includedas partof the PMSSdevelopedusingDelft3Dmodel.
DAVIS.BESSE   NUCLEARPOWERSTATION                                               Page24 af 32

NTTFRecommendation      2,1 (HazardReevaluations):   Flooding                           Revision1 FirstEnergyCorporation                                                              March06,2414 H.4.2Alternative1 Alternative 1 requiresusingthe lesserof one-halfof the PMF or the 500-yearevent.In this case,the PMF was alreadydetermined        as part of Calculation C-CSS-020.13-011.
Therefore,  the one-halfPMF is utilizedas describedin C-CSS-020.13-022.        The surge and seiche height from the worst regionalhurricaneor windstormwith wind-wave activityis estimatedusing statisticalanalysisof the historicaldata. Lake Erie has no outletcontrolstructures.Therefore,the 10O-year     watersurfaceelevationis usedwithout furtherconsideration  of the maximumcontrolledwater elevation.The HEC-RASmodel developedas part of the PMF analysisis revisedto use the one-halfPMF as the inflow boundarycondition and 100-year surge-seicheelevation from the worst regional hurricaneas the downstreamboundarycondition.The HEC-RASmodel providesthe watersurfaceelevationfor this alternative.
H.4,2Alternative2 Alternative 2 requiresusingthe PMFestimatedin Calculation        C-CSS-020.13-011. The
          $urgeand   seiche  height from the 25-year event  is estirnatedusing           analysis statistical       of the historicaldata. Similar to Alternative1, the HEC-RAS     model was  updated  to obtain the resuttingwatersurfaceelevation.
H.4.2Alternative3 Afternative3 requiresusingthe 21-yearfloodin the ToussaintRiver.Pointrainfalfdata from NOAAwas used to estimatethe 2S-yearrainfallevent. This rainfallis input into the HEC-HMSmodeldevelopedas part of the PMF analysisto estimaterunoffdue to 25-yearevent.The watersurfaceelevationfor the probablemaximumsurgeand seiche in combinationwith the 100-yearwater level is determinedin CalculationC-CSS-02A13-017.Similarto Alternatives1 and 2, the HEC-RASmodelwas updatedto obtain the resultingwatersurfaceelevation.
3.7.4. Results The predictedwater surfaceelevationat the site for Alternative3 is found to be the maximumfor the alternativesspecifiedin H.4.2.lt is also concludedthat the Toussaint Riverwater surfaceelevationsat the site are completelycontrolledby the backwater conditionsat Lake Erie for that alternative(i.e.,the predictedwatersurfaceelevationin the river is equal to the lake elevation,extendingfor about one mile upstreamof DBNPS).
The watersudaceelevationof 585.93ft-lGLD5Sfor combination           H.4.1is equalto the criticalwater surfaceelevationfor combination     H.4.2  Alternative3 and representsthe criticalwater sudace elevationat the site       resulting from  the combined   events as specifiedin NUREGCR-7046,AppendixH.4.
DBNPSis protectedagainstfloodingdue to wave runup during a PMWS by wave protectiondikesinstalledalongthe northern,eastern,and alonga smallportionof the southernsidesof the site to an elevationof 591 ft-lclDss. Wave actionat DBNPSis governedby the maximumsupportablewave at the toe of the north dike duringthe PMSS.Waveactionanalysisconcludes         thata maximumwaverunupof 3.98ft on top of the PMSSlevelof 585.90ft-lGLDsSmay be generatedat the toe of the northdike,The maximumwave runup elevationduringthe controllingfloodingAlternativeis therefore equalto 589.88ft-lGLD5S.This elevationis less than the top of the wave protection dikes(591ft-lGLD55).Therefore,the wave runupanalysisshowsthat wave protection DAVIS-BESSE    NUCLEARPOWERSTATION                                                   Page25 of 32

NTTFRecommendation       2.1 (HazardReevaluations):    Flooding                          Revision1 FirstEnergyCorporation                                                              March46,2414 dikes are sufficientto protectDBNPSfrom wave runup during the criticaleombined floodingevent.
DBNPS is iloodedduringthe PMWS event along the non-dikedwest and south site boundaries.The maximumPMSSwater surfaceelevationin the vicinityof the power block is 585.81ft-lGLDsS.The maximumwave runup elevationin the vicinityof the powerblockis 585.90feet-lGLD55.
3.8.Local lntensePrecipitation(ReferenceDBNPS2013eand DBNF$2013f1 The LIP is an extremeprecipitation     event (high intensity/shortduration)at a given location.
The durationof the event and the coveragearea are needed to quantify an extreme precipitationevent fully. Generally,the amountof precipitationdecreaseswith increasing durationand increasingarea. NUREG/CR-7046           specifiesthat the LIF shouldbe equivalent to the 1-hr, 1-mizprobablemaximumprecipitation      (PMP)at the locationof the site.
3.8.{. Basisof Inputs
               . Sitetopography
               . LIP(cumulative   and incremental)
               . Manning'sroughnesscoefficients
               . Supporting GISdata(Reference      DBNPS20131) 3.8.2. ModelsUsed r   ArcGlSDesktop10.1
             . FLO-ZDPro r   MicrosoftExcel 3.8.3. Methodotogy The LIP event was evaluatedto determinethe associatedfloodingelevationand velocitiesassumingthe activeand passivedrainagefeaturesare non-functional.        The entire roof drainage  is  assumed  to  be contributing to  the surface runoff.The LIP evaluationwas   performed   in accordance with the NUREG/CR-7046.
The runoffcausedby the LIP eventwas estimatedusing the FLO-2Dsoftware. The softwareuses shallowwater equationsto route stormwaterthroughoutthe site. FLO-2D depicts site topography,using a digitalelevationmodel (DEM),to characterize grading,slopes,drainagedivides,and low areasof the site.The DEM is a grid model devetopedfrom compositegroundsurfaceinformation.The methodologyused within the FLO-ZD software included the rainfall function and the levee function (to incorporate site security features which could impact the natural drainage characteristicsof the site).
Per NUREG/CR-7046,      the 1-hr,1-mi2PMPeventwas developedusingHMR-52. The total PMP depth per squaremite for the l-hr event was interpolatedfrom the PMP depth contour map providedin HMR-52.The distributionof the 1-hr PMP was developedfor the 5-, 15-, and 3O-minutetime intervals,with the 60-minuteinterval being the 1-hr PMP depth.The depth for each time intervalwas calculatedusingthe DAVIS.BESSE      NUCLEARPOWERSTATION                                                  Page26 of 32

NTTFRecommendation      ?.1 (HazardReevaluations): Flooding                        Revision1 FirstEnergyCorporation                                                        March06, 2014 guidanceprovidedin HMR-52.The 1-hrPMPwas modeledin FLO-2Dto calculatethe subsequent  siteflooding.
Active and passivedrainagesystem components(e.9., pumps, gravity storm drain systems,smallculverts,and inlets)were considerednon-functional    or cloggedduring the LIP event, per  Case 3 in NUREG/CR-7046. The Manning's  roughnes$ coefficient valuesare selectedbasedon the land covertype usingthe      guidance  providedin the FLO-2D manual.Two types of obstructionsare modeled:buildingslstructures        that completelyblockthe waterpassage,and securitywalt barriersthat couldbe overtopped if the waterdepthincreasesto abovethe top of the wall.
To determinethe floodingelevationassociatedwith the LlP, the 1-hr,1-mizstormwas appliedevenlyacrossthe site, and the model was allowedto run for 2.5 hours to ensurethat only the areas of staticpondingwould remain.Five temporaldistributions similarto the PMFanalysiswereconsidered.
3.8.4. Results The end temporaldistributionof the LIP eventresultedin the highestwaterdepthsand consequentlyin the highestwater surfaceelevations.The water surfaceelevationsat SSCs,are listedin Tabfe1.
criticaldoorlocations,or doorsleadingto safety-related TableI - LIP FloodingElevationand Durationat DBNPS Door      MaximumWaterSurface          Flood Durationabove Structure        Number       Elevation(ft-lGLD56)     S85ft-lcLD55 (minutes)
AuxiliaryBuilding        300               585.25                        6 AuxiliaryBuilding        361               585.20                        15 AuxiliaryBuifding        362               585.20                        15 AuxiliaryBuilding        315               585.17                        15 AuxiliaryBuilding       320A               585.17                        15 AuxiliaryBuilding        324               585.1B                        18 TurbineBuilding          330               585.1B                        18 TurbineBuilding         399A               585.19                        1B TurbineBuilding          339               585.20                        1B TurbineBuilding          333               585.22                        18 TurbineBuilding          334               585.41                       57*
IntakeStructure          224               585.44                        30
* The differencein the floodingdurationat Door 333 and Door 334 is causedby the groundsurfaceelevations.The groundat Door 334 is higherthan the groundat Door 333 (585.92vs. 585.67ft NAVDBB). Therefore,minimalfloodingdepthsresultin the water fevel increaseabove the floor elevation.Betweenminute27 and minute54 of floodingeventthewaterdepthabove585.0is 0.01to 0.05ft.
DAVIS.BESSE     NUCLEARPOWERSTATION                                             Page27 ol 32

NTTFRecommendation        2.1 (HazardReevaluations): Flooding                      Revision1 FirstEnergyCorporation                                                        March06, 2014 The hydrodynamicloads, or impact loads, on the structuresdue to the LIP are presentedin Table 2. FLO-2Dreportsthe impact pressurea$ a force per unit length (impactpressuretimes flow depth).The maximumimpactforce on the structurewas estimatedby multiplying  the impactpressureby the structurelength.
Table2 - MaximumlmpactLoadson Buildings Bulldlng                Max lmpact (tblft)
Containment Structure             0.46 AuxiliaryBuilding               1.53 TurbineBuilding                7.14 IntakeStructure                5.27
: 4. COMPARISON         WITHCURRENTDESIGNBASIS The reevaluatedmaximumwater surfaceelevationdue to the riverineflooding(Toussaint River)is belowthe currentlicensingbasis.The reevaluatedmaximumwater surfaceelevation due to the LIP and PMSSeventsexceedthe currentlicensingbasis.
For lake flooding,the currentdesignbasisassumesthe surgeonly in one direction.A site-specificwind and pressurefield is developedas part of the re*analysis. More recentstorms providedthe controllingwind for surgefloodingat DBNP$.
For LIP flooding,the currentdesign basis assumes24.5 inchesof rainfallwill pond evenly acros$ the site. As part of the re-analysis,recent site topographywas used in a two-dimensionalhydraulicmodel(FLO-2DPro)and additionalrainfallestimateswere obtainedfrom the morerecentHMR-52guidance.
ln the interim,it is understoodthat an event of such magnitudeto approachthe postulated accumulationof rainfalfis a low probabilityevent. Such an eventwould likelybe associated with a significanttropicalstorm.Meteorological   forecastingwould providesufficientwarning well in advanceof such an event.The InterimActionsdiscussedin Section5 will provide adequateprotectionuntilpermanent              are implemented.
solutions The comparisons                              floodhazardsare providedin Table3, of existingand reevaluated DAVIS-BESSE     NUCLEARPOWERSTATION                                             Page28 af 32

NTTFRecommendation     2.1 (HazardReevaluations):Flooding                          Revision1 FirstEnergyCorporation                                                         March06, 2014 Table3 - Gomparisonof Existingand ReevaluatedFlood Hazardsat DBNP$
Flood-Causing Mechanism          DesignBasis      Comparison      Flood HazardReevaluationResults Flooding in        PMF Etevation   -   Bounded       All-Season PMF Elevation   - 575.96ft-streamsand         579ft-tGLD55                      IGLD55, All-Season     PMF Flow-rivers                                               100,436cfs PMFFlow- 78,500 cfs                               Cool-Season  PMF Elevalion- 575.06ft-IGLD55, Cool-$eason      PMFFlow-Cool-season  PMP                  61,943cfs was not evaluated.
Dam breaches       No damsor other     Bounded       Dam as$es$mentindicatedno critical and failures       regulatinghydraulic               dams.
structures.
Stormsurge         Watersurface        Not           Watersurfaceelevation-585.81 ft-elevation- 583.7    bounded.      lGLDSSat powerblock, IGLD55              Exceeds current designbasis.
Seiche             Thisflood-causing   Thisflood-    Not a crediblescenario.Boundedby mechanism   is not  causing       stormsurge.
describedin the     mechanism USAR.               is not describedin the USAR.
Tsunami            Thisflood-causing   Thisflood-    Tsunamiasses$ment      indicatesthereis mechanismis not     causing       a slightpossibilityof tsunamisin Great describedin the     mechanism     lakes.However,the seismicityin the USAR.               is not        regionsuggeststhereis no potentialfor describedin   strongearthquakes   or the vertical the USAR. displacement necessaryto inducea tsunami.
substantial lce-induced        Notplausible        Bounded       lce-inducedfloodingis boundedby the flooding                                             all-seasonPMFevent.
Channel            As indicatedin the  Bounded       Channeldiversiontowardsthe site is not migration          USAR,the mean                     probable.
diversion          lakelevelis not subjectto variationsdue to diversionsor sourcecutoff.
DAVIS-BESSE   NUCLEARPOWERSTATION                                               Page29 of 32

NTTFRecommendation        2.1 (HazardReevaluations): Flooding                          Revision1 FirstEnergyCorporation                                                             March08,2014 Table3 - Comparisonof Existingand ReevaluatedFlood Haeardsat DBNPS(Continued)
Flood-Causing Mechanism           DesignBasis        Comparison      Flood HazardReevaluationResults Combinedeffect       Waverunupon          Bounded         Wave runupon wave protectiondike-flood(including      wave protection                      589.88ft-lclDss.
wind-generated       dike-590.3ft-waves)               IGLD55.
Maximumwaverunupelevationin the vicinityof the powerblock- 585.90ft-IGLD55.
LIP                  Maximumwater         Not bounded. Maximumwatersurfaceelevaiion-surfaceelevation Exceeds             585.44ft-lGLD55.
                     - 584.5fr-lGLDs5. currentdesign basis.
DamFailure           As indicatedin the                   Damslocatedin the DBNPgwatershed USAR,thereare                        are determinedto be noncritical.
no structureson ToussaintRiver that can affectthe flow hydrographat DBNPS.
: 5. INTERIM    AND PLANNEDFUTUREACTIONS The FloodingHazardReevaluation       Reportevaluatedapplicablefloodinghazardsfor DBNPS, Two of the postulatedreevaluated   floodhazardevents,the PMS$ and the LtP events,resulted in maxirnumflood water elevationshigher than previouslycalculatedfor DBNPS. The assessmentof the buildings,resultingfrom the flood hazardreevaluation,     founda numberof doorsfeadingto areascontainingsafetyrelatedequipmentto be susceptibleto the postulated water infiltration.These postulatedflooding events are consideredbeyond design basis events.The reevaluatedflood levels are small increaseswith short durations.These low probabilityeventswould likelybe identifiedin advanceby meteorological                Current forecasting.
plant proceduresaddressingfloodingat the site provideactions to be taken in the event floodingis imminentor has occurredat or nearthe DBNPSsite. No additionalactionsbeyond thosecurrentlyin placeare nece$saryat this time. The totalplantresponseto the reevaluated hazardis to be determinedby the Integrated   Assessment.
The integratedassessmentwill be performedto addressthe needandlorpotentialdesignsfor temporaryor permanentbarriers(or alternativecountermeasures)        to preventpostulatedflood water infiltrationand/ormitigationof the postulatedfloodwater infiltration.This evaluationwill also includea study of emergencyprocedures.The evaluationof the mitigatingstrategyand schedulefor the implementation                    (as necessary)will be documentedin the of modifications CorrectiveActionProgram.The evaluationwill addressthe followingitems:
DAVIS-BESSE      NUCLEARPOWERSTATION                                                Page30 of 32

NTTFRecommendation       2.1(HazardReevaluations):  Flooding                          Revision1 FirstEnergyCorporation                                                            March06, 2014 L!E As indicated earlier,the watersurfaceelevation    exceedsthe finish ffoor elevationof 585 ft-lGLD55by a maximumvalueof 0.44ft for a totaldurationof approximately        1.0 hrs at one (1) doorand0.5 hrs or lessat the remaining   eleven(11)affecteddoors,due to the LIP event.The LIP storm mechanismswill be reviewedin the integratedassessmentto establishtrigger pointswhichsupportimplementation     of proceduralized            measures.This includesan mitigation evaluationof the forecastinformationavailableto personnelthat would allow for advanced monitoringand warningof meteorological     conditionsthat could potentiallyresult in an LIP eventoccurringat the site.Modifications wilf afsobe consideredto affordprotectionfor the site vulnerabilities or to furtherreducethe impactof the LlP, PMSS As indicatedearlier,the water surfaceelevationexceedsthe finish floor elevationof 585 ft-IGLD55by a maximumvalueof 0.81 ft for a totaldurationof approximately       2.5 hrs due to the PMSSevent.The PMSSstorm mechanismswill be reviewedin the integratedassessmentto establishtriggerpointswhich supportimplementation       of proceduralizedmitigationmeasures.
This includesan evaluationof the forecastinformationavailableto     personnel that wouldallow for advancedmonitoringand warningof meteorological       conditionsthat could potentiallyresult in a surgeeventaffectingthe site.Modifications   will also be consideredto affordprotectionfor the sitevulnerabilities.
: 6. REFERENCES (ANSf/ANS-2.8-1992)     ANS, American National Standardfor DeterminingDesign Basis Flooding at Power Reactor Sites, Prepared by the American Nuclear Society Standards Committee  WorkingGroupANS-2.8,1992.
(JLD-ISG-2A13-01)    NRC,Guidancefor Assessmentof FloodingHazardsdue to Dam Failure, Revision0, June2A13.
(JLD-lSG-2012-06)    NRC, Guidancefor Performinga Tsunami,Surge and SeicheFlooding SafetyAnalysis,Revision0, June2012 (NElAugust2012,NEl,Report12-08,Overview           of External  Flooding Reevaluations,  August 2012.
(NRCMarch20121NRC,Letterto Licensees,          Requestfor Inforrnation Pursuant  to Title10 of theCodeof Federal    Regulations50.54(0  Regarding    Recommendations  2.1 ,2.3,and  9.3of the NearTermTaskForceReviewof Insightsfromthe Fukushima               Dai-ichiAccident, March  12, 2012.
(NRC RG 1.59) NRC, DesrgrrBasis Flood for NuclearPower Plants,RegulatoryGuide Revision 2r 1977.
(NRC RG 1.102)NRC, FtoodProtectionfor NuclearPower Plants,RegulatoryGuide 1.1A2, Revision1, 1976.
(NUREG-0800)    NRC, NUREG-0800,StandardReviewPlanfor the Reviewof SafetyAnalysis Repods for NuclearPower Plants: LWR Edition - S#e Charccterisftbsand Sr'fe Parameters (Chapter2), M107c400364,     March2A07.
(NUREG/CR-7046)      NRC, NUREG/CR-7046,      PNNL-20091    , Design-8asisFloodEsfttnaffonfor Stle Characterization at NuclearPower Plantsin the UnitedSfafesof America,ML11321,{195, November   2011.
DAVIS-BESSE    NUCLEARPOWERSTATION                                                 Page31 of 32

NTTFRecommendation     2.1 (HazardReevaluations):
Flooding                       Revision1 FirstEnergyCorporation                                                     March06, 2014 (NUREG/CR-6966)    NRC,NUREG/CR-6966,    TsunamiHazardAssessment    at NuclearPower PlantSitesin theUnitedSfafesof America,NationalTechnicallnformationService,March 2009.
(DBNPS 2013a) FENOC CalculationC-CSS-020.13-009,         A//-SeasonPrabableMaximum PrecipitationAnalysisfor Davis-BesseNuclearPowerSfafion,Revision0.
(DBNPS 2013b) FENOC CalculationC-CSS-020.13-010,          Coo/-SeasonPrecipitation and SnowmeltAnalysisfor Davis-BesseNuc/earPowerSfaflon,Revision    0.
(DBNPS2013c)FENOCCalculationC-CSS-020.13-01        1, ProbableMaximumFload Analysis for Davis-BesseNuclearPower Station,Revision0.
(DBNPS 2013d) FENOC CalculationC-CSS-02A13-A12,         Dam Assessmenli lce Jam, and ChannelMigrationfor Davis-8esseNuclearPawerSfafion,Revision0.
(DBNPS2013e)FENOCCalculationC-CSS-020.13-013,          Local lntenseProbableMaximum PrecipitationAnalysrsfor Davis-BesseNuc/earPowerSfafion,Revision0.
(DBNPS20130 FENOC CalculationC-CSS-020.13-014,        Effecfsof Local lntenseProbable MaximumPrecipitationAnalysisfor Davis-BesseNuc/earPowerSfaffon,Revision0.
(DBNPS2013g)FENOCCalculationC-CSS-020.13-015,                   Windand PressureField Sife-specifie Analysisfar Davis-Besse NuclearPowerSfafion,Revision0.
(DBNPS2013h) FENOC CalculationC-CSS-020.13-016,         Su4geand Seiche Screeningfor Davis-BesseNuclearPowerSfafion,Revision0.
(DBNPS2013i)FENOCCalculation      C-CSS-020.13-017, Surgeand SeicheAnalysisfor Davis-EesseNuclearPowerSfaflon,Revision0.
(DBNPS 2013j) FENOC CalculationC-CSS-020.13-018,         Tsunami Screening/Analysis for Davis-BesselVuclearPawerSfafion,Revision0.
(DBNPS 2013k) FENOC CalculationC-CSS-020.13-019,         Probable MaximumFlood GIS Analysisfar Davis-BesseNuclearPawerSfafion,Revision0.
(DBNPS 20131)FENOC CalculationC-CSS-020.13-020          Locat lntense PrecipitationGtS Analysisfor Davis-BesseNuclearPowerStafion,Revision0.
(DBNPS2013m) FENOC CalculationC-CSS-020.13-A21,        Surge and Seiche Calibrationfar Davis-BesseNuc/earPowerSfafion,Revision0.
(DBNPS 2013n) FENOC CalculationC-CSS-02A13-022,Combined Event includingWind Wave Analysisfor Davis-8esseNuclearPower Statian,Revision0.
(DBNPS2013o)FENOCCalculation      C-CSS-020.13-023, Surgeand SeicheGIS Analysis  for Davis-BessefVuc/earPawerStafion,Revision0.
(USAR)Davis-Besse   NuclearPowerStation,UpdatedFinalSafetyAnalysisReport,Revision 29.
DAVIS-BESSE    NUCLEARPOWERSTATION                                          Page32 of 32}}