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

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

ML14070A108
Person / Time
Site:	Davis Besse
Issue date:	03/11/2014
From:	Lieb R A FirstEnergy Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-14-104
Download: ML14070A108 (36)

Text

FENOC," Fi r stEne rgy Nt r:l,earr;ratrnq Ct-trn pany'::ti.j l Ntrtl r sl.t/f l]ilillir

..'i-):tk I't,y I:t r. illtii;, I, iC"lll Rty*rutd A. Lieb\riia. i. l.atr,.tri i..f tJ iviri i'i:', t j March 11 , 2A14 L44-144 ATTN: Document Control DeskU.S. Nuclear Regulatory Commission 1 1555 Rockville Pike Rockville, MD ?fr852 10 cFR 50.54(fj

SUBJECT:

Davis-Besse Nuclear Power StationDocket No.

50-346. License No. NPF-3 FirgtEnerqy NucleFI Operatinq Companv (FENOC) Respgnsqt_o NRC Reo.uest fqr tnformation pursuant to tg CFR 50.54{fl Reqardino the F,loodir}o Ag0ects3f Recommendation 2.1 of the Near-Term Task Force

{NTTF} Rqview_of Insiqhts ffom the Fukushima Dai-ichi AccidentOn March 12,2A12, the Nuclear Regulatory Commission

{NRC) issued a lettertitled,"Request for Informstion Pursuant to Title 10 of the Code sf Federal Regulatisns50.54{0 Regarding Recommendations 2.1 ,2.3, and 9.3 of the Near-Term Task Force Review of lnsights from the Fukushima Dai-ichi Accident," to all power reactor licensees and holders of construction permits in active or deferred status. Enclosure 2 of the 10 CFR 50.54{0 letter addresses NTTF Recommendation 2.1 forflooding. One of the required respon$es is for licensees to submit a Hazard Reevaluation Report (HRR) in accordance with the NRC's prioritization plan By letter dated May 11,2A12, the NRC placed the Davis-Besse Nuclear Power Station (DBNP$) in Category 2 requiring a response by March 12,2414. The Flood HRR for DBNPS is enclosed.As discussed in the enclcsed report, two flood levels (local intense precipitation and probable maximum storrn surge) determined during the hazard reevaluatian exceed the current licensing basis (CLB) flood levels. The increased levels are the result of newer methodologies and not the result of errors within the CLB evaluations.

Current plant procedures addressing flooding at the site provide actions to be taken in the eventflooding is imminent or has occurred at or near the DBNP$ site.

No additional actions beyond those currently in place are necessary at this time.

Davis-Besse Nuclear Power Station L-14-104Page 2 ln accordance with the guidance provided by NRC letter dated December 3, 2fi12, titled"Trigger Conditions for Performing an Integrated Assessment and Due Date for Respon$*," an integrated assessment is required if flood levels determined during thehazard reevaluation are not bounded by the CLB flood levels. The 10 CFR 50.54(f) specifies that the integrated assessment be compfeted and a repart submitted within two years of submitting the HRR. Therefore, FENOC intends to submit an Integrated Assessment Report for DBNPS prior to March 12,241&.There are no regulatory csrnmitments contained in this letter.

lf there are any questions or if additional information is required, please contact Mr. Thomas A. Lentz, Manager-Fleet Licensing, at 330-31 5-68 1 0.I declare under penalty of perjury that the foregoing is true and eorrect. Executed on March f l ,2A14.

Enclosure:

Flood Hazard Reevaluation Report cc: Director, Office of Nuclear Reactor Regulation (NRR)NRC Region lll Administrator NRC Resident Inspector NRR Project ManagerUtility Radiological Safety Board Respectfully, Enclosure L-14-104Flood Hazard Reevaluation Report (33 pages follow)

FLOOD HAZARD REEVALUATION REPORT tN RESPONSE TO THE 50.54(f) fNFORMATTON REQUE$T REGARDING NEAR-TERM TASK FORCE RECOMMENDATION 2'1: FLOODINGfor the DAVIS-BESSE NUCLEAR POWER STATIOTII5501 North State Route 2 Oak Harbor, OH 43449Flrst Energy Corporation76 South Maln Street Akron, OH 44308Prepared by:

ET ENERCON ( relhnce - - twty projxl tvay day Enercon Services Inc,12420 Mllestone Cenler Drive, $uite 200 Germantown, MD 20876 Revislon 1Submltted to FENOC; March 06, zAlH Preparer: Verifier: Verifier: Approver: Lead Responslble Engineers:Design Engineering Supervisor Deslgn Englneering Manager Thomas Gulvas Abiot Gemechu EnerconPrlnted Name Anubhav Gaur Affiliatlon Enercon Date"sl*l+rt ollo$lt4_.7--]-.*A i,',1/ 7 t lbla.rr1 s l,.l tLLana Lawrence Ray Sacramo Michael SobotaGregory MichaelJon Hook FENOC NTTF Recommendation

2.1 First

Energy Corporation (Hazard Reevaluations):

FloodingRevision 1March 06, 2014 2.1,2. Flooding in Streams and Rivers ..........6 2.1.3. Dam Breaches and Failures..

.....,.,.7

2.1.7. Channel

Migration or Diversion

.. ........7 2.1.8. Combined Effect Flood (including Wind-Generated Waves) .......7 2.2. Flood-Related Changes to the License Basis

.................7

2.3. Changes

to the Watershed and Local Area since License lssuance .............,..7

2.4. Current

Licensing Basis Flood Protection and Pertinent Flood Mitigation Features............8

3.

SUMMARY

OF FLOOD HAZARD REEVALUATION

........83.1. Flooding in Streams and Rivers (Reference DBNPS 2013a, DBNPS 2013b, and DBNPS201 3c) . .... .....93.1.1. Basis of Inpuls:......

........103.1.2. Computer Software Programs..

.....113.1.3. Methodology.

.....113.2.1. Basis of lnputs

........15

3.2.2. Computer

Software Programs..

.........15 3.2.3. Methodology.

.......153.3.1. Basis of Inputs ....163.3.2. Computer Software Programs..

.......163.3.3. Methodology..

.......163.4. Channel Migration or Diversion (Reference DBNPS 2013d)

.............173,4.1. Basisoflnputs

........17 DAVIS-BESSE NUCLEAR POWER STATIONPage 1 of 32 NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding First Energy CorporationRevision I March 06, 2014 3.4.2. Computer Software Programs.....

............17 3.4.3. Methodology..

,.....,,.17 3.4,4. Results ........17 3,5. Storm Surge (Reference DBNPS 20139, DBNPS 2013h, DBNPS 2013i and DBNFS 201 3m) ...... 1B 3.5.1. Basis of Inputs

....18 3.5.2. Computer Software Programs..

.......18 3.5.3. Methodology..3.5.4. Results

......21 3.6. Tsunami Assessrnent (Reference DBNPS 2013j)

....213.6.1. Basis of lnputs

3.6.2. Models

Used .."........223.6.3. Methodology....

,.r...,,....

.....223.6.4. Results

..,...23 3.7. Combined Effect Flood (including

\Mnd-Generated Waves) (Reference DBNPS 2013n).23 3.7.1. Basis of Inputs

...,.......243.7.2. Computer $oftware Programs..

.....243.7.3. Methodology...

.........243.7.4, Results

..............253.8. Local Intense Precipitation (Reference DBNPS 2013e and DBNPS 20130...... .....,..26

3.8.1. Basisoflnputs

......26 3.8.2. Models Used ............26COMPARISON WITH CURRENT DESIGN BASIS 4, 5.6.DAVIS-BESSE NUCLEAR POWER STATION Page 2 ol 32 NTTF Recommendation 2.1 (Hazard Reevaluations):

FloodingFirst Energy Corporation{. PURPOSE Revision 1 March 06, 20141.1. Backgroundln response to the nuclear fuel damage at the Fukushima Dai-ichi power plant due to the March 11, 201 1 earthquake and subsequent tsunami, the United States Nuclear Regulatory Commission (NRC) established the Near Term Task Force (NTTF) to conduct a systematic review of NRC processes and regulations, and to make recornmendations to the NRC for its policy direction. The NTTF reported a set of recommendations that were intended to clarify and strengthen the regulatory framework for protection against natural phenomena.On March 12,2012 the NRC issued an information request pursuant to Title 10 of the Code of Federal Regulations, Section 50.54 (D (10 CFR 50.54(f) or 50.54(f) lette$ which included six (6)enclosures:

1.2, 3.NTTF Recommendation 2.1: SeismicNTTF Recommendation 2.1: Flooding NTTF Recommendation 2.3: Seismic NTTF Recommendation 2.3: Flooding NTTF Recommendation 9.3: EP Licensees and Holders of Construction Permits 4.5.6.f n Enclosure 2 of the NRC-issued information request (Reference NRC March 2A12), the NRC requested that licensees reevaluate the flooding hazards at their sites against present-day regulatory guidance and rnethodologies being used for early site permits (ESP) and combinedoperating license reviews.On behalf of First Energy Corporation (FENOC) for the Davis-Besse Nuclear Power Station (DBNPS), this Flood Hazard Reevaluation Report (Report) provides the information requestedin the March 12, 2012 50.54(f) letter; specifically, the information listed under the "Requestedf nformation" section of Enclosure 2, paragraph 1 ('a' through 'e'). The "Reque$ted Information"section of Enclosure 2, paragraph 2 ('a' through 'd'), Integrated Assessment Report, will be addressed separately if the current design basis floods do not bound the reevaluated hazardfor all flood-causing mechanisms.

1.2. Requested

ActlonsPer Enclosure 2 of the NRC-issued information request, 50.54(f)

Ietter, FENOC is requested to perform a reevaluation of all appropriate external flooding sources for DBNPS, including theeffects from local intense precipitation (LlP) on the site, the probable maximum flood (PMF) on streams and rivers, lake flooding from storm surges, seiches and tsunamis, and dam failures.

lt is requested that the reevaluation apply present-day regulatory guidance and methodologies being used for ESPs, and calculation reviews including current techniques, software, and methods used in present-day standard engineering practice to develop the flood hazard. The requested information will be gathered in Phase 1 of the NRC staffs two-phase process to irnplement Recornmendation 2,1, and will be used to identify potential "vulnerabilities" (see definition below).DAVIS-BESSE NUCLEAR POWER STATIONPage 3 of 32 NTTF Recommendatisn 2.1 (Hazard Reevaluations):

Flooding Revision 1 First Energy Corporation March 46,2014 For the sites where the reevaluated flood exceeds the design basis, addressees are requestedto submit an interim action plan documenting planned actions or measures implemented toaddress the reevaluated hazards.Subsequently, addressees shall perform an integrated assessment of the plant to fully identify vulnerabilities and detail actions to address them. The scope of the integrated assessment report will include full power operations and other plant configurations that could be susceptible due to the status of the flood protection features.

The scope also includes those features of theultimate heat sink (UHS) that could be adversely affected by flood conditions (the loss of UHS from non-flood associated causes is not included). lt is also requested that the integratedasses$ment address the entire duration of the flood conditions.

A definition of vulnerability in the context of Enclosure 2 is as follaws: Plant-specific vulnerabilities are those features impoftant to safety that when subject ta an increased demand due lo the newly calculated hazard evaluation have not been shown to be capable of performing their intendad functiorts.

1.3. Requested

InformationPer Enclosure 2 of the NRC-issued information request 50.54(0 letter, the Report should provide documented results, as well as pertinent DBNPS information and detailed analysis, and include the following:

1. Site information relaled to the flood hazard. Relevant structure, systems, and components (SSCs) important to safety and the UHS are included in the scope of this reevaluation, and pertinent data concerning these SSCs should be included. Other relevant site data includes the following:1. Detailed site information (both designed and as-built), including present-day site layout, elevation of pertinent SSCs important to safety, site topography, and pertinent spatial and temporal data sets;2. Current design basis flood elevations for all flood-causing mechanism$;3. Flood-related changes to the licensing basis and any flood protection changes (including mitigation) since license issuance;4. Changes to the watershed and local area since license issuance;5. Current licensing basis flood protection and pertinent flood mitigation features at thesite: and6. Additional site details, as necess?ry, to assess the flood hazard (e.9., bathymetryand walkdown results).

2. Evaluation of the flood hazard for each flood-causing mechanism, based on present-day methodologies and regulatory guidance. Provide an analysis of each flood-causing mechanism that may impact the site, including LIP and site drainage, flooding in streamsand rivers, dam breaches and failures, storm surge and seiche, tsunamis, channelmigration or diversion, and combined effects. Mechanisms that are not applicable at the site may be screened out; however, a justification should be provided. A basis for inputs and assumptions, methodologies and models used, including input and output files, and other pertinent data should be provided.DAVIS-BESSE NUCLEAR POWER STATION Page 4 of 32 NTTF Recommendation 2.1 (Hazard Reevaluations):

FloodingFirst Energy Corporation

4. Interim evaluation and actions taken or planned relative to the design basis, prior to completion below, if necessary.5. Additional actions beyond requested informationflooding hazards, if any.Revision 1 March 06, 2014to addre$s any higher flooding hazards of the integrated assessment described item l.d taken or planned to address 3. Cornparison of current and reevaluated flood-causing mechanisrns at the site. Provide anasse$$ment of the current design basis flood elevation to the reevaluated flood elevation foreach flood-causing mechanism. Include how the findings from Enclosure 2 of the 50.54(f)letter (i.e., Recommendation 2.1, flood hazard reevaluations) support this determination.

lf the current design basis flood bounds the reevaluated hazard for all flood-causingmechanisms, include how this finding was determined.

2. SITE INFORMATIONDBNPS is located on the shore of Lake Erie in Oak Harbor, Ohio" The major hydrological features of the terrain are the broad expanse of Lake Erie to the north and east, and the Toussaint River, 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, Section 1.2.1.1) and approximately 2,000 ft from the Toussaint River.

Site areas surrounding the station structureshave been built up from 6 to 14 feet above the existing grade elevation to an elevation of 584 ft International Great Lakes Datum of 1955 (lGLD55) or 15.4 ft above the Lake Erie Low WaterDatum of 568.6 ft-lGLDs5.

Topography at and around DBNPS is relatively flat, with a meanstation elevation of approximately 584 ft-lclDss. The site safety-related structures are protected against high water levels up to an elevation of 585 ft-lGLDs5.

A Lake Erie dike, which is located along the shore of Lake Erie, protects the site from lake surges.

Additionally, a wave protection dike is situated along the northern, eastern, and a small portion of southern sides of DBNPS. The elevation at the top of the wave protection dike is 591 ft-lGLDs5.

Present-Day Site Layout is shown in Figures 2.0.1.DAVIS.BESSE NUCLEAR POWER STATION Page 5 of 32 NTTF Recommendation

2.1 First

Energy Corporation (Hazard Reevaluations):

Flooding Revision 1 March 06, 2014Figure 2.0.1- Present-Day Site Layout2.1, Current Design Basis The current design basis is defined in the DBNPS Updated Safety Analysis Report (USAR).The following is a list of flood-causing mechanisms and their associated water surface elevations that were considered for the DBNPS current design basis.2.1.1. LtP The USAR indicates that the precipitation value of 24.l-inches over a 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> period is utilized for the LIP analysis. As indicated in the USAR, the average invert elevation of rnanholes and catch basins is 582 ft-lcLD55; with 24.5 inches of estimated accumulation, water could build upto 584.5 ft-lclDss (USAR, Section 2.4.2.3).

2.1.2. Flooding

in Streams and RiversThe USAR indicates that a flow rate of 78,500 cubic feet per second (cfs) in the Toussaint River at DBNPS (USAR, Section 2,4.3) would result in a maximum water surface elevation of 579 ft-lclDss. As indicated in the USAR, the elevation of 579 ft-lGLDs5 was derived using the conservative assumption that none of the water is discharged to Lake Erie, assuming that the PMF flow is hypothetically dammed up atthat point (USAR, Section 2.4.3.5).DAVIS.BESSE NUCLEAR POWER STATIONPage 6 of 32 NTTF Recommendation 2.1 (Hazard Reevaluations):

Flooding First Energy Corporation Revision 1 March 06, 2014 2.1.1. Dam Breaches and Failures The USAR indicates that there are no dams or other regulating hydraulic structures on the Toussaint River which would affect the flow hydrograph at DBNPS (USAR, Section 2.4.31.2.1.4, Storm Surge & Seiche The probable maximum meteorological event in Lake Erie results in a maximum water surfece elevation of 583.7 ft-lGLD5s.

This meteorological event is caused by a maximum east-northeast wind at any location of 100 miles per hour for a 1O-minute duration, and a wind speed of 70 miles per hour during the six-hour period both before and after the maximum wind speed (USAR, Section 2.4.5).

2.1.5. Low Water No water is taken from the Toussaint River for plant cooling water requirements. Therefore, low flows in the Toussaint River will not affect DBNPS operation.

The probable maximum meteorological event in Lake Erie results in the probable extreme low water level of 556.8 ft-lGLD55 (USAR, Section 2.4.11).2.1,6. lce-lnduced Flooding Flooding of the safety-related structures and equipment at DBNPS due to ice jams in the Toussaint River is not credible.

The USAR indicates that the elevation of the pfant structures is above the level of normal lake ice formations. Category 1 wave protection dikes are designed to withstand the impact of ice (USAR, Section 2.4.7).2.1.7. Ghannel Migration or DiversionAs indicated in the USAR, the mean lake level is not subject ta variations due to diversions orsource cutoff (USAR, Section 2.4.9).

2.1.8. Combined

Effect Flood (lncluding Wind-Generated Waves)Wind-wave activity, including runup, was evaluated for its effect on the wave protection dikes on the north, east, and south sides of DBNPS.

As indicated in the USAR, the maximum wave run-up on the dike is 6.6 ft above the probable maximum water surface elevation of 583.7 ft-lGLD55. The resulting maximum wave runup elevation is 590.3 ft-lGLDs5, which is below thetop of the dike (USAR, Section 2.4.2.2.1).

2.2. Flood-Related Changes to the License Basis There were no changes to the license basis since the flooding.license issuance with regard to I 2.3. Changes to the Watershed and Local Area since License lssuance The watershed contributory to the Toussaint River upstream of DBNPS is approximately 139.0 square miles (Reference DBNPS 2013c). Based on aerial images of the watershed, the changes to the watershed include commercial development within the watershed area, which isa very small percentage of the overall watershed area.

The changes to the local area sub-watershed for DBNPS include buifdings, parking fots, and security barrier upgrades that havebeen added to the site since license issuance.DAVIS-BESSE NUCLEAR POWER STATIONPage 7 at 32 NTTF Recommendation 2.1 (Hazard Reevaluations):

Flooding First Energy Corporation Revision 1 March 06, 20142.4. Cunent Licensing Basis Flood Protection and Pertinent Flood Mitigation Features The maximum flood level in the design basis is below the site finish floor elevation of 585 ft-lGLD55. Therefore, there were no mitigation actions initiated or taken for flooding at the site.3.

SUMMARY

OF FLOOD HAZARD REEVALUATIONNUREG/CR-7046, Design-Basis Flood Estimation for Srfe Cfiaracterization at Nuclear Pawer Planfs in the united Sfafes of America (Reference NUREG/CR-7046), by reference to the American Nuclear Society (ANS), states that a single flood-causing event is inadequate as adesign basis for power reactors and recommends that combinations should be evaluated to determine the highest flood water elevation at the site.

For DBNP$, the combination that produces the highest flood water elevation at the site is the probable maximum surge and seiche on Lake Erie with the effects of coincident wind wave activity.The USAR reports elevations corresponding to lGLDSS vertical datum. The recent site survey, United States Geological Survey (USGS) topographic rnaps, and other reference documents report elevation in North American Vertical Datum of 19BB (NAVDBB). In order to compare the reevaluated flood elevatiens with the existing design basis reported in USAR, final pertinentelevations have been converted to lGLD55 datum. The conversion between lGLD55 andNAVDBB at DBNPS is represented as-- ft-lGLDsS

= ft-NAVD88

• 1.07 ft.Calculation C-CSS-020.13-017 (Reference DBNPS 2013i) defines the maximum water surface elevation of 585.81 ft-lGLDs5 at DBNPS adjacent to the power block. This elevation is due to a probable maximum storm surge (PMSS) during a probable maximum wind storm (PMWS)event. The revised maximum water surface elevation is above the site finish floor elevation of585 ft-tGLD55.

Calculation C-CSS-020.13-022 (Reference DBNPS 2013n) defines the coincident wind wave runup. The maximum wave runup elevation of the PMSS coincident with wind wave activity isdetermined by adding the wind wave runup to the water surface flood elevation due to thePMS$. The maximum runup on the wave protection dike is 589.88 ft-lcLD55, which is belowthe top of the wave protection dike elevation of 591 ft-lclDss. The maximum wave runupelevation in the vicinity of the power block is 585.90 feet-lGLD55.

The wave runup elevations in the vicinity of the power block are above the site finish floor elevation of 585 ft-lGLD55.

Calculation C-CSS-020.13-014 (Reference DBNPS 20130 defines the maximum water surfaceelevation resulting from the LIP event.

The water surface elevation due to the LIP event variesfrom 585.17 ft-lGLDS5 to 585.44 ft-lGLDsS. The LIP maximum water surface elevations are above the site finish floor elevation of 585ft-lGLD55 The methodology used in the flooding reevaluation for DBNPS is consistent with the followingstandards and guidance documents:. NRC Standard Review Plan, NUREG-0800, revised March 2007 (Reference NUREG-0800). NRC Office of Standards Development, Regulatory Guides, RG 1 .102 - "Flood Protectionfor Nucfear Power Pfants", Revision 1, dated September 1976 (Reference NRC RG 1.102)and RG 1.59-"Design Basis Floods for Nuclear Power Plants", Revision 2, dated August 1977 (Reference NRC RG 1.59)

DAVIS-BESSE NUCLEAR POWER STATION Page B of 32 NTTF Recomrnendation 2.1 (Hazard Reevaluations):

Flooding First Energy Corporation. NUREGICR-7046, "Design-Basis Flood Estimation for $itePower Plants in the United States of America," dated Revision 1March 06, 2014 Characterization at Nuclear November z0fi (Reference NUREG/CR-7046). NUREG/CR-6966, "Tsunarni Hazard Assessment at Nuclear Power Plant Sites in the United States of America", dated March 2009 (Reference NUREGICR-6966) r "American National Standard for Determining Design Basis Flooding at Power Reactor Site$", dated July 28, 1992 (Reference ANSI/ANS-2.8-1992). NEI Report 12-08, "Overview of External Flooding Reevaluations" (Reference NEI August 2412)-r NRC JLD-ISG-2012-06, "Guidance for Performing a Tsunami, Surge or Seiche Flooding Hazard Assessment", Revision 0, dated January 4,2A13 (Reference JLD-lSG-2012-06). NRC JLD-lSG-2013-01, "Guidance for Assessment of Flooding Hazards due to Dam Failure", Revision 0, dated July 29, 2013 (Reference JLD-ISG-2O13-01)

The following provides the flood-causing mechanistns and their associated water surface elevations that are considered in the DBNPS flood hazard reevaluation study:3.f . Flooding In $treams and Rivers (Reference DBNPS 2013a, DBNPS 20{3b, and DBNPS 2013c)The PMF in rivers and streams adjoining the site is determined by applying the probable maximum precipitation (PMP) to the drainage basin in which the site is located. The PMF is based on a translation of PMP rainfall in the watershed to flood flow. The PMP is adeterministic estimate of the theoretical maximum depth of precipitation that can occur at a time of year for a specified area. A rainfall-to-runoff transforrnation function, as well as runoff characteristics, based on the topographic and drainage system network characteristics and watershed properties, are needed to appropriately develop the PMF hydrograph.

The PMF hydrograph is a time history of the discharge and serves as the input parameter for otherhydraulic models which develop the flow characteristics, including flood flow and elevation.The PMF is a function of the combined events defined in NUREG/CR-7046 for floods caused by precipitation events.Alternative 1 - Combination of:

r Mean monthly base flow. Median soil moisture. Antecedent rain: lesser of (1) rainfall equal to 40 percent of the PMP, or (2) a 500-year rainfall. The All-Season PMP , Waves induced by 2-year wind speed applied along the critical directionAfternative 2 - Combination of:. Mean monthly base flow DAVIS-BESSE NUCLEAR POWER STATION Page I of 32 NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding First Energy CorporationRevision 1 March A6,2014 and from. Snowmelt from the Probable maximum snowpack o fi 10O-year, cool-season rainfall. Waves induced by Z-year wind speed applied along the critical directionAlternative 3 - Combination of:. Mean monthly base flow. Snowmelt from a 100-year snowpack. The cool-season PMP. Waves induced by Z-year wind speed applied along the critical direction3.1,1. Basis of lnputs: The inputs used in the PMP, snowmelt, and PMF analyses are based on the following:All-Season PMP Analysis and Cool-Season PMP with $nourmelt Analysis. DBNPS and Toussaint River watershed locations, areas, boundaries and configurations; Historic flow rate data collected by USGS at gage 04195820 on the Portage River;HMR-52-standard isohyetal patterns, storm orientation, percentage of 6-hourincrement of PMP, and standard isohyetal geometry information;HMR-s3-seasonal PMP values:

I a a IThe 100-year all-season point rainfall estimates from the National OceanicAtmospheric Administration (NOAA) Precipitation Frequency Data $erver;Median and extreme daily snow cover by month for Ohio- data is downloaded NOAA; and' Snowmelt rate (energy budget) equations and constants are based on U.S. Army Corps of Engineers (USACE) Engineering Manual EM-1110-2-1406,PMF analysis-Hydrologic & Hydraulic Analysis

' Digital elevation model (DEM): The DEM used for the PMF calculation is obtainedfrom the U.$, Department of Agriculture (USDA) National Resource Conservation Services (NRCS), national elevation data; r Probable maximum precipitation (PMP): 72-hour PMP and associated snowmelt, asapplicable, for the subject watershed area;. Baseflow: Historic flow rate data collected by USGS at gage 04195820 on thePortage River, which is used as the baseflow for the Toussaint River;. Soil Type: The soil types within the project watershed are developed using USDANRCS soil information;. Land Use: The land use information for the watershed is obtained from USDA NRCSsoil survey geographic database;DAVIS.BESSE NUCLEAR POWER STATION Page 10 of 32 NTTF Recommendation 2.1 (Hazard Reevaluations): FloodingFirst Energy Corporation. Manning's roughness coefficients are based photography and selected using standard Revision 1March 06, 2014 on a visual assessment of aerial applicable engineering guidance references;. Bridge information obtained from the Ohio Department of Transportation (ODOT);and. Supporting Geographic Information System (GlS) input (Reference DBNPS 2013k).3.1.2, Computer Software ProgramsPMP and Snowmelt analysis r AutoCAD Civil 3D 2012. ArcGlS Desktop 10.1. HMR-52 software. Microsoft Excel PMF analysis. ATcGIS Desktop 10.1. HEC-HMS 3.5 r HEC-RAS 4.1. HEC-GeoRAS 10.1 r lGLD8S Height Conversion Online Tool. Microsoft Excel3.{.3. MethodologyThe PMF analysis included the following steps:

' Delineate watershed and sub-watersheds, then calculate sub-watershed areas for input into the USACE HEC-HMS rainfall-runoff hydrologic computer model.

e Determine rainfall.' Estimate HEC-HMS rainfall-runoff model initial input parameters: Snyder unit hydrograph method, peaking and lag coefficient.. Calculate HEC-HMS model loss input parameters: initial loss and constant loss rate.. Calculate HEC-HMS river reach routing model initial input parameters:

Muskingum-Cunge.. Method: B-point cross-section, reach coefficient.

slope, and Manning's roughness. Perform PMF simufation with PMP input using HEC-HMS model.. Estimate water surface elevation using HEC-RA$

unsteady-state model by usingrunoff from the HEC-HMS model as an input.Watershed Delineation For the purposes of the hydrologic modeling effort, the Toussaint River watershed is subdivided into three (3) sub-watersheds (Packer Creek, Upper Toussaint Creek, andLower Toussaint Creek) based on the hydrologic unit code (HUC) boundaries.

DAVIS-BESSE NUCLEAR POWER STATION Page 11 of32 NTTF Recommendation 2.1 (Hazard Reevaluations):

Flooding First Energy Corporation Revision 1 March 06, 2014Rainfall & SnowmeltEach alternative contains rainfall defined either by the all-season PMP (Alternative 1), the 1O0-year, cool-season rainfall (Alternative 2), or the cool-season PMP (Alternative 3). Each rainfall event is considered to be a 72-hour duration event. Note that an antecedent rainfall occurs prior to the all-season PMP. An antesedent storm equivalent to 40 percent of the all-season PMP is applied to the HEC-HMS model with a 72-hour dry period between the antecedent storm and the PMP event.Snowmelt is included in the two cool season alternatives.

For rain-on-snow conditions,the air temperature, dew point temperature, and average maximurn daily wind speedare obtained from representative weather stations. The basin wind coefficient is determined based on the density of forest stands in each sub-basin. lt is conservatively assumed that the Toussaint River watershed is unforested plain to maximize snowmelt.For rain-free conditions, the snowmelt parameters are selected based on the USACE guidance.The snowpack is assumed to be at its maximum at the onset of rainfall events andcover the entire watershed. Soil is assumed to be frozen with no lasses during themonths of October through April. For the probable maximum snowpack, snowpackdepth is assumed to be available for the duration of the coincident rainfall event.

Alternative

{ -All-Season PMPThe location of the DBNPS watershed is within the domain of the HMR-51 and HMR-52 guidance.

The all-season PMP is determined by using the generalized PMP estimates defined by the HMR-51 and HMR-52 guidance.

Different storm centers throughout thewatershed are examined to determine the critical storm center that maximizes runoff.HMR-52 software is used to optimize the storm and define the PMP estimates for each sub-basin.HMR-52 software is based on a standard temporal distribution. The HMR guidance indicates the greatest precipitation may occur at other times throughout the duration of the storm. The temporal distribution of the PMP is calculated in accordance withrecommendations in HMR-52, wherein individual rainfall increments deerease progres$ively to either side of the greatest rainfall increment. Various temporal distributions for each rainfall scenario are then evaluated to further maximize the runoff.Front, one-third, center, two-third, and end-loading temporal distributions areconsidered in an effort to capture the distribution that maximizes runoff.Alternative 2 - Probable Maximum Snowpack and 1O0-Year Cool-Season Rainfall The probable maximum snowpack is assumed to be equal to an unlimited snowpack during the entire coincident rainfall.

While the snowpack can be determined directlyfrom the snow depth, there is not adequate data to extrapolate any historicalobservations up to the magnitude of the probable maximum event.The 1O0-year, cool-season rainfall is determined for the watershed location using precipitation frequency estimates defined by NOAA Atlas 14 guidance and applying regional seasonal guidance. NOAA Atlas 14 provides all-season point precipitation rainfall estimates via the NOAA precipitation frequency data server. As NOAA Atlas 14 values are point precipitation values, the estimates are adjusted using area-depthreduction factors. NOAA Atlas 14 values are also adjusted to reflect cool-season rainfallrather than all-season rainfall.DAVIS-BESSE NUCLEAR POWER STATION Page 12 af 32 NTTF Recommendation 2.1 (Hazard Reevaluations):

Flooding First Energy Corporation Revision 1 March 06, 2014 The 3-day (72-hour) snowmelt duration is assumed in order to correspond to the precipitation events (PMP and 100-year rainfall). A 10O-year, cool-sea$on rainfall isequivalent for all the cool-season months, However, the snowmelt is expected to be different for each cool-season month because it is highly dependent on ternperature,which varies significantly from month to month.

Therefore, the month with the highest expected snowmelt is identified and used for the calculations of the snowmelt rates Alternative 3 - 100-Year Snowpack and Cool-Season PMPA 1O0-year snow depth is calculated by performing a statistical analysis based on the historical data obtained from the NOAA Annual Observation Data website. A Fisher-Tippett Type l (FT-l) distribution frequency analysis is performed to determine the maximum snow depth with an annual exceedance probability of 1 percent (i.e. 10O-year snow depth). The FT-l distribution is applicable for long{erm statistical analyses and specifically for extreme value calculations. The cool-season PMP is determined by applying seasonal HMR-53 guidance to the all-season PMP estimates.

Hydrologic Model (HEC-HMS)The PMF is the flood resulting from the PMP. The temporal distribution of the PMP is calculated in accordance with the recommendations in HMR-52, wherein individual increments decrease progressively to either side of the greatest increment. For eachsub-watershed, a 9-day PMP hyetograph is constructed using a rainfall equivalent to 40 percent of the PMP during the first 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, followed by a dry 72-hour period, and finally followed by the full 72-hour PMP storm.

USACE HEC-HMS hydrologic software is used to convert rainfall ts runoff. A rainfall hyetograph is applied to each sub-watershed and transformed to runoff using unit hydrograph methodology. Generally a unit hydrograph is developed using historical data obtained from various rain and stream gages in the watershed. The DBNPS watershed is ungaged. Thus, there are no historical observations available to use as a basis to create a unit hydrograph. Therefore, a synthetic unit hydrograph is developed.

The Snyder unit hydrograph methodology is used for rainfall-to-runoff transformation.

Routing accounts for change in the flow hydrograph as a flood wave passes downstream and accounts for storage and attenuation during a flooding event. TheMuskingum-Cunge routing method is utilized in the HEC-HMS model, with the streams represented by B-point cross sections.ANSIIANS-2.8-1992 suggests that baseflow should be based on mean monthly flow. Asmean monthly flow is not available for the Toussaint River, the baseflow is approximated based on the mean monthly flow in an adjacent watershed. The only gage station available in the same hydrologic unit is on the Portage River near Elmore, OH. The watersheds of the Toussaint River and Portage River are located in the same HUC and have similar watershed characteristics.

Therefore, it is an acceptable approach to use the base flow information for the Portage River as the basis for estimation of the base flow at Toussaint River.lnitial losses are ignored. Infiltration, or constant losses, is determined based on the hydrologic characteristics of the soils within each basin. Constant losses are not appliedto impervious areas.

Additionally, constant losses are ignored for the cool-season PMF alternatives due to the assumption that ground is frozen.

DAVIS-BESSE NUCLEAR POWER STATION Page 13 of 32 NTTF Recommendation 2.1 (Hazard Reevaluations):

Flooding First Energy Corporation Revision 1 March 06, 2014The unit hydrographs for each sub-watershed are modified to account for the effects ofnonlinear basin response in accordance with NUREGICR-7046.

The peak of each unit hydrograph is increased by one-fifth and the time-to-peak is reduced by one-third.

Theremaining hydrograph ordinates are adjusted to preserve the runoff volume to a unitdepth over the drainage area.Hydraulic Model (HEC-RAS)The unsteady flow module within the USACE HEC-RAS software is used to transform the resulting flow hydrographs from the controlling alternative into a water surfaceelevation hydrograph under unsteady flow conditions. For reference and comparison, all three alternatives are evaluated with the HEC-RAS model.Channel and floodplain geometry for the Toussaint River is modeled by developingcro$s sections of the stream. The cross sections are placed at locations that define geometric characteristics of the river valley and overbanks.

Cross sections are also placed at representative locations where changes occur in discharge, slope, shape, and roughness, as well as at hydraulic structures (e.9. bridges).

River banks, blocked obstructions, and ineffective flow areas are also incorporated into the HEC-RAS model.Two bridges are modeled (the CR19 Bridge and the CR2 Bridge) using information received from ODOT. There are two additional bridges over the modeled portion of the Toussaint River: the N. Benton-Carroll Rd Bridge and the CR590 Bridge. These two bridges are located farther away from DBNPS (approximately 7 and 10 river miles respectively). lt is not expected that these two bridges would have a measurable effect on the computational results because of the distance, Any possible effect produced by the bridges upstream of the river will be lost due to attenuation in the stream. Therefore, they are not included in the model.The PMF flow hydrographs obtained from the HEC-HMS model are entered into the HEC-RAS model. The highest observed water level in Lake Erie is used as a downstream boundary condition in the HEC-RAS software program.The HEC-RAS model is evaluated for both all-season PMF (Alternative 1) and cool-season PMF alternatives (Alternatives 2 and 3).3.1.4. ResultsThe Alternative 1 PMF is the controlling combination and is a result of the all-season PMP. The maximum water surface elevation at DBNPS is 575.96 fi-lGLDs5 (576.93 ft-NAVDBB), with a maximum flow of 100,436 cfs.For Alternative 2, the maximum water surface elevation is 574.15 ft-lGLD5s (575.12tt-NAVD88) with a maximum flow of 31 ,747 cfs.For Alternative 3, the maximum water surface elevation is 575.06 ft-lGLDs5 (576.03 ft-NAVDBB) with a maximum flow of 61,943 cfs.The all-season PMF is determined to be the controlling PMF scenario and an additional combined event analysis is performed in Calculation C-CSS-020.13-022.

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Flooding First Energy Corporation3.2. Dam Assessment (Reference DBNPS 2013d)3.2.1. Basis of Inputs Revision 1 March 06, 2014 Inputs used for the dam assessment evaluation r HEC-RAS model developed in the PMF analysis" r Dam information: The National lnventory of Dams (NlD)watershed dams.is used to identify the 3,2.2. Computer Software Programs n ArcGlS Desktop 10.1. HEC-RAS 4.13.2.3. MethodologyThe criteria for dam a$sessment is provided in the hlRC Guidance for Assessmenf of Floading Hazards due to Dam Failure, JLD-lSG-2O13-01. Only two dams reported byNID are located in the DBNPS watershed - the Genoa UG Sewage Disposal Lagoonsand the Graymont Sludge Lagoons.Effects of the failure of the two dams are analyzed using a simplified approach as outlined in JLD-ISG-2013-01.

The peak outflowwithout attenuation method is based on summing estimated discharges from simultaneou$

failures of upstream dams arriving at the site without attenuation.

The peak discharge using the simplified equation$

wa$ calculated to be 4,642 cfs and13,651 cfs for Genoa UG Sewage Disposal Lagoon$ and Graymont Sludge Lagoons respectively. A cumulative peak breach discharge equal to 18,253 cfs from both dams is included in the HEC-RAS model as additionaf tateral inflow at the cros$ section immediately upstream of the DBNPS site. Conservatlvely, the peak breach flow isapptied to the HEC-RAS model at the time corre$ponding to the PMF peak discharge determined in the PMF analysis.3,2,4, Results The maximum water surface elevation at the site resulting from the PMF event combined with the cumulative upstream dam failures is 577.09 ft-NAVDBB.

Compared to the PMF results, the water surface elevation increase due to the additional dambreach flow is equal to 0.16 ft (577.09 ft - 576.93 ft

= 0.16 ft). The maximum PMF water surface elevation at DBNPS is 8.04 ft below the site grade elevation of 584.0 ft-lGLD5s.

Consequently, the increase due to the dam failure results in a water surface elevation that is 7.88 ft below site grade (8.04 ft - 0.16 ft = 7.88 ft).The maximum water surface elevation at the site resulting from the PMF event combined with the cumulative upstream dam failures is well below the plant site grade elevation, Therefore, the upstream dams are determined to be noncritical dams asreferred to in the JLD-lSG-2O13-01 . No further dam failure analysis is required.

There are no dams downstream of DBNPS on the Toussaint River.DAVIS.BESSE NUCLEAR POWER STATIONPage 15of32 NTTF Recommendation 2.1 (Hazard Reevaluations):

Flooding First Energy Corporation3.3. lce-lnduced Flooding (Reference DBNPS 2013d)As identified by NUREG/CR-7046, ice jams and ice dams can form adjacent to a site, and may lead to flooding by two mechanisms:

Revision 1 March 06, 2014 in rivers and streams' Collapse of an ice jam or an ice dam upstream of the site can resultlike flood wave that may propagate to the site; anda dam breach-. An ice jam or an ice dam downstream of a site may impound water upstream of itself, thus causing a flood via backwater effects.

3.3.{. Basis of Inputs. USACE ice jam database.. Bridge geometry (upstream and downstream of DBNPS) - Information relative to the bridge structures provided by ODOT.e DBNPS HEC-RAS model developed in the PMF analysis.3.3.2. Computer Software Programs

' HEC-RAS 4.1

3.3.3. MethodologyPer

NUREG/CR-7046, ice-induced flooding is assessed by reviewing the USACE ice jam database to determine the most severe historical events that have occurred. Thereare no historical records available for the Toussaint River.

The nonexistence of ice jam records is explained by the absence of stream monitoring stations on the Toussaint River. Based on ice jam occurrence within adjacent streams in the same hydrologic unit code (HUC), it is determined that ice jam events are possible in the Toussaint River.The maximum ice jam is determined by selecting the historic event that produced the maximum flood stage relative to the normal water surface elevation at that location.Regardless of specific conditions that produced the historic flood stage at a specific location, the full height is conservatively assumed to represent the ice jam.Historical ice jam data for Portage River, Rock Creek, Bayou Ditch, and Lacarpe Creek are considered as they are located in the same HUC area.

The maximum recorded stage due to an ice jam is used, The peak water surface elevation at DBNPS as a result of an upstream ice jam breach{i.e., failure of ice dam) is estimated. A hypothetical ice jam is incorporated into theHEC-RAS model at the location of the first bridge upstream of DBNPS, the CR2 Bridge.lce dam breach parameters are selected so the entire ice jam within the main channel would breach when the water level behind the ice jam is at its maximum elevation.

The recorded ice jams have a maximum reported stage of approximately 13 ft;however, there are no records for the height of the ice dams themselves. The clearance between the bottom of the Toussaint River and the low point of the bridge is approximately I ft, which is less than the maximum reported stage. Therefore, conservatively, the postulated lce dam could completely block the bridge clearance.

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Flooding First Energy CorporationRevision 1March 06, 2014and hydrogeomorphological data should be used stream, or river has exhibited the tendency to Per NUREG/CR-7046, flooding due to an ice jam is not required to be combined with other extreme flooding events. However, to represent normal flow in the Toussaint River during the cool-season month, a smaller cool-season PMF alternative is utilized (Alternative 2 PMF). The Alternative 2 PMF is a combination of the snowmelt from a probable maximum snowpack and a 10O-year, cool-season rainfall.

The inflow hydrographs representing the Alternative 2 PMF event are used in the HEC-RAS modelevaluating the effect of a postulated ice dam failure.3.3.4. ResultsThe maximum water surface elevation at DBNPS resulting from the upstream ice jambreaching was calculated to be 574.05 ft-lGLDSs (575.12 ft-NAVD88).

There are nobridges or structures downstream of DBNPS on Toussaint River that could create an ice dam or ice jam.The water surface elevation at DBNPS due to the PMF is equal to 575.96 ft-lclDss.

Therefore, the ice-induced flooding at DBNPS is bounded by the PMF, and no further consideration is required.3.4. Channel Migratlon or Diversion (Reference DBNPS 20f gd)NUREGICR-7046 indicates historical recordsto determine whether an adjacent channel, meander towards the site.3.4.1. Basis of lnputs. USGS topographic maps r Aerial images3.4.2. Computer Software Programs. Arc GIS 10.1 3.4.3. Methodology Historic and current topographic maps and aerial images are reviewed to examine the condition and alignment of rivers and streams over time.Historical maps for the years of 1900, 1952, 1967, 1986, and 2011 were reviewed to assess historic channel migration of the Toussaint River. Toussaint River is approxirnately 2,000 ft south of the DBNPS. The locations of the river and lakeshorelines shown on the historical maps are compared to the present-day locations (201 1).3.4,4. ResultsFrom the comparison of the historical maps, the most significant discrepancies between the present-day and historical stream bank and shoreline locations are observed on the USGS map for 1900. More recent USGS maps show both stream and shoreline locations approximately the same as the current location (within +/- 0.1 mile difference).

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FloodingFirst Energy Corporation Revision 1March 06, 2014 Based on the comparison between the current location of the Toussaint River and theriver location as shown on the historical maps which cover a period of approximately1 10 years, it is determined that channel diversion towards the site is not probable.

Thesame comparison is performed for the lake shoreline and similarly, Lake Frie shorefine diversion towards the site is not probable.3.5. Storm Surge (Reference DBNPS 20139, DBNPS 2013h, DBNPS 20131 and DBNPS 2013m)Probqhle f.Ulaximum Stofm Surse (PMSSI In accordance with JLD-ISG-2012-06, all coastal nuclear power plant sites and nuclear power plant sites adjacent to cooling ponds or reservoirs subject to potential hurricanes, windstorms and squall lines must consider the potential for inundation from storm $urge and waves. JLD-ISG-2012-06 also suggests that for the storm surge hazard as$e$sment, historical storm events in the region should be augmented by a synthetic storm parameterized to account for conditions more severe than those in the historical records and considered reasonably possibleon the basis of technical reasoning.

3.5.1. Basis

of Inputs The inputs used in PMSS analysis are based on the following:

r Historical wind and pressure field data from NOAA for the Great Lake Region r Probable maximum windstorm (PMWS). Lake Erie bathymetry from the NOAA geophysical database. Supporting GIS data (Reference DBNPS 2013o)3.5.2. Computer $oftware Programs. ArcMap 10.1. Deft3D sofhnrare suite (Delft3D-FLOW Delft3D-WAVE, Delft3D-RGFGRID, and Delft3D-QUICKIN)3.5.3. Methodology Several physical processes contribute to the generation of a storm surge. The contribution of wind to a storm surge is often called wind setup. Wind blowing over the water causes a shear stress that is exerted on the surface of the water, pushing water in the direction of the wind. Atmospheric pressure gradients are another forcing mechanism that contributes to changes in water level, as water is forced from regions ofhigh atmospheric pressure toward regions of low pre$sure.The following describes the methodologies used in the PMSS calculation:Development of the PMWSThe PMWS storm-based approach is specific to the characterislics of the site. Pastextreme events in a region are analyzed and considered transpositionable.

As part ofthe PMWS, different storm types (such as synoptic, squall line, and hybrid) that DAVIS-BESSE NUCLEAR POWER STATION Page 18 of 32 NTTF Recommendation 2.1 (Hazard Reevaluations):

FloodingFirst Energy Corporation Revision 1 March 06, 2014 impacted the Great Lakes region are considered in order to determine the storm event that will generate the maximum surge and seiche. Each storm's input parameter$

are quantified and plotted based on the location of lodhigh pressure centers, concurrent wind/pressure fields, and how they evolve through time and space,Most of the synoptic storms occur in association with deep areas of low pressure whichmove through the region from southwest to northeast.

The general synoptic pattern isone in which the deep area of low pressure results in a very strong pressure gradient force between its low pressure center and a corresponding region of higher pressure tothe north or west. The larger the gradient between the two systems over a given distance is, the stronger the resulting winds.

Squall line (or derecho) events create a widespread straight-line windstorm that is associated with a fast-moving band of severe thunderstorms.

These winds have produced some of the highest instantaneous gusts on record, but last for only a short time (less than 30 minutes) at a given location. The short duration of these events, as they quickly traverse a given location, mean they will not control the PMSS. Further, these events do not occur within deep low pressure systems or remnant tropicalsystems. Therefore, their wind and pressure data are not combined with the olher storm types in this analysis, as this would result in a PMWS that is not physically possible.Although deep low pressure systems often produce the longest duration large-scalewinds, other storm types also produce strong winds over the region. In rare cases, land-falling tropical systems along the Gulf Coast or Atlantic Seaboard move inland across the Appalachians or up the Mississippi and Ohio River valleys. By the time these storms reach the Great Lakes region, they are no longer tropical systems, but instead have transitioned into extra-tropical cyclones.

Their general circulation and center of deep lowpressure persists.

Much like the deep low pressure scenario previously discussed,strong and persistent winds can result. The remnants of Hurricane Hazel (October1954) and Hurricane Sandy (October z}ftl are classic examples of this storm type.

This storm scenario provided some of the strongest winds from the northwest throughthe northeast directions over Lake Erie (with durations at 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> or more).Delft3D CalibrationThe Delft3D hydrodynamic model is set up based on the Delft3D software suite. Thewave setup contribution to the total storm surge values are modeled by coupling the Delft3D-WAVE and Delft3D-FLOW surge models. The general approach to storm surgemodeling using coupled Delft3D-FLOW and Delft3D-\ffAVE models consists of thefollowing steps:

Developing the bathymetric dataset and model grid mesh for the lake system;Assembling input files for atmospheric forcing (wind and pressure fields);Assembling input files for initial water level, boundary conditions, and the physical and numerical parameters of the model;Assembling measured water levels and wave data for model calibration and verification; Testing and refining the initial model setup;Validating the model for historical extreme storm events; and I a a t DAVIS-BESSE NUCLEAR POWER STATIONPage 19 of 32 NTTF Recommendation 2.1 {Hazard Reevaluations):

Flooding First Energy Corporation Revision 1 March 00, 2014. Assessing model sensitivity to various factors and adjustable parameters such as bottom friction and wind drag coefficient.

The Delft3D model is calibrated based on historical data obtained from NOAAmeteorological and water level recording stations loceted in the Lake Erie region.

Review of lristorical data shows that various parts of Lake Erie respond differently to aRy one particular storm. The storm that produces extreme water levels in one part ofLake Erie might not, and probably does not, produce extreme levels in other parts.Therefore the number of calibration and validation storms selected, to assess model prediction accuracy, covered all parts of the lake shoreline.Calibration and verification of the coupled Delft3D-FLOW and DelflSD-WAVE models is performed by a time series comparison of measured and predictedlmodeled stormsurge values at different water level recording stations on Lake Erie. A similar time series comparison is also performed for wave heights.The Deltt3D models are calibrated using extreme historic wind and pressure data from multiple meteorological and water level recording stations.

Calibrat*on and verification ofthe coupled Delft3D-FLOW and Delft3D-WAVE models demonstrates that the hydrodynamic model is capable of computing the storm surge and seiche dynamics for Lake Erie, as well as the signiticant wave heights and periods at DBNPS from PMWS events.PMSS The calibrated Delft3D model is used to determine the PMSS. The historic wind and pre$sure field data is replaced with candidate PMWS events, and the model is run todetermine the critical PMWS.JLD-ISG-2A12-06 and ANSI/ANS 2.8-1992 require the antecedent water level equal to the 100-year maximum recorded water level to be applied as the initial slorm surge model still water level. The 100-year water level of 175.05 meters-IGLDBS is used asthe initial condition/antecedent water level in all the Delft3D-FLOW models. $ince the probable minimum low water level at DBNPS could occur at a time when the monthlymean lake level is at the long-term mean low probable level, the anteeedent water level for low water evaluation is set to the long-ternr low probable level at Lake Erie, which is equal to 173.13 meters-IGlD 85 Various topographic features may affect the storm

$urge propagation towards DBNP$.The elevated area around DBNPS is protected along the northern, eastern, and along a small portion of the southern sides by an earthfill wave protection dike built up to 591.00 ft-lGLD55.

The purpose of the wave protection dike is to protect against the surge andassociate wave run-up. Additionally, the DBNPS area along the soulhern, western,northern, and eastern sides of the plant is protected by a vehicle barrier system (VBS).Maximum Historical and 26-year Storm $urgeThe historical maximum storm surge is the largest of the determined yearly maximum storm surge heights. The historical maximum storm surge height will be used incombined flooding scenarios in a separate calculation.

$torm surges are calculated from monthly data as the difference between monthfy maximum and monthly mean based on guidance provided by U$ACE. The Log Pearson Type lll distribution is the commonly accepted frequency procedure for annual DAVIS.BESSE NUCLEAR POWER STATION Page 20 ot 32 NTTF Recommendation 2.1 (Hazard Reevaluations):

FloodingFirst Energy CorporationRevision 1 March 06, 2014 maximum water levels. A frequency analysis on the yearly maxlmum storm surgeheights obtained from the Toledo and Marblehead stations is performed using a Log Pearson lll statistical analysis. The 2S-year storm surge height was used in combined flooding scenarios.

3.5.4. Results

Simulations of all the candidate PMWS events showed that the critical PMWS event is the October 2012 wind storm event, which is the remnants of Hurricane Sandy. Thisstorm is the most intense of all the PMWS events with a maximum wind speed of 103.12 mileslhour and is aligned along the axis of Lake Erie which is in the northeastdirection. The maximum PMSS resulting from this PMWS event produced a maximum water surface elevation of 585.90 ft-lcLD55 at the intake forebay location,The Delft3D modeling results show that the Lake Erie dike, will be overtopped from thePMSS event. Overtopped water will accumulate behind the Lake Erie dike in the marsh and low elevation areas around DBNPS, establishing a higher mean water level (i.e.ponded water) around the plant. As the surge recedes to Lake Erie, the accumulatedwater is forced to return to Lake Erie (return flow) along the western and southern VBS.Eventually, the water will overtop the southern and western VBS during the recession ofsurge water to Lake Erie, and flood DBNPS.The maximum PMSS water surface efevation in the vicinity of the power block due tothe critical PMWS is 585.81 ft-lGLD5S.

The PMS$ water surface elevations will remainabove the site finish floor elevation (585 ft-lGLD55) for approximately 2.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />.$urge, Seiche, and Resonance Results from Calculation C-CSS-020.13-016 show that the level of the rise due toseiche is significantly less than the calculated surge height. For this rea$on, seiches arenot the controlling flood event at DBNPS.Resonance generated by waves can cause problems in enclosed water bodies such as harbors and bays when the period of oscillation of the water body is equal to the period of the incoming waves. The period of oscillation of Lake Erie delermined in CalculationC-CSS-020.13-016 is in the range of 12 to 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br />. This is much greater than that of the peak spectral period of the incident shallow water storm waves.

Consequently, resonance is not a detriment at DBNPS during the critical PMWS event.

Probable Minimum Low Water Level resulting from the PMW$Simulations of all the candidate PMWS storm events show that the critical PMWS event that would result in probable minimum low water level (drawdown) is the transposedJanuary 1978 storm event. This storm had the most intense west and southwest windsof the examined storm events, with maximum southwest wind speed of 89.0 miles/hour.

The probable minimum low water elevation (drawdown) associated with the transposedJanuary 1978 storm produces a probable minimum low water level of 547.46 ft-lGLD5sat the western basin of Lake Erie. At this probable minimum low water level, the DBNPS intake canal is completely cut off from Lake Erie for approximately 43 hours4.976852e-4 days <br />0.0119 hours <br />7.109788e-5 weeks <br />1.63615e-5 months <br />.3.6. Tsunami Assessment (Reference DBNPS 2013J)NUREG/CR-6966 identifies that earthquakes, with earthquakes being the most frequentmovement) are more efficient at generating DAVIS-BESSE NUCLEAR POWER STATIONlandslides, and volcanoes can initiate tsunamis, cause. Dip-slip earthquakes (due to verlicaltsunamis than strike-slip earthquakes (due to Page 21 of 32 NTTF Recommendation 2.1 (Hazard Reevaluations):

Flooding First Energy Corporation Revision 1March 06, 2014 horizontal rnovement). To generate a major tsunami, a substantial amount of slip and a large rupture area is required.

Consequently, only large earthquakes with magnitudes greater than 6.5 on the Richter scale generate observable tsunamis.3,6.1. Basis of Inputs. NOAA natural hazards tsunami database r NOAA natural hazards volcano database r Historical earthquake hazards database. Ohio Department of Natural Resources (ODNR) database 3.6.2. Models Used. None 3.6.3. Methodology As identified by NUREGICR-7046, tsunami assessment is referenced to NUREGICR-6966 and NOAA Technical Memorandum OAR PMEL-136.

In addition, the morerecently issued NRC guidance, JLD-lSG-2012-06, also addresses tsunami assessment.

However, JLD-lSG-2012-06 provides guidance on detailed tsunami modeling and is beyond the scope of this assessment. Technical Memorandum OAR PMEL-136 reflectsa similar tsunami screening assessment described by NUREGICR-6966.

The NUREGICR-6966 screening assessment is based on a regional screening and a site screening.

The regional screening consists of researching historical records fortsunami records and the potential for tsunami-generating sources. The site screeningevaluates the site based on the horizontal distance from a coast, the longitudinal distance measured along a river, and the grade elevation in comparison to the effects ofa tsunami. This assessment approach is based on a review of historical records and databases.

NUREG/CR-6966 identifies that tsunamis are generated by rapid, large-scale disturbances of a body of water. The most frequent cause of tsunamis is an earthquake; however, landslides and volcanoes can also initiate tsunamis.

Because of the tsunami-generation sequence associated with earthquakes, dip-slip earthquakes (due to vertical movement) are rnore efficient at generating tsunamis than strike-slip earthquakes (due to horizontal movement).

Furthermore, to generate a major tsunami, a substantialamount of slip and a large rupture area is required.

Consequently, only large earthquakes with magnitudes greater than 6.5 on the Richter scale generate observable tsunamis.As part of the assessment, the NOAA natural hazards tsunami database was used to review historical tsunami events and associated run-ups for the east coast of the UnitedStates and Canada. Of the total events, there were 7 tsunami events that produced 14 run-ups occurring in the Great Lakes region from 1755 to 1954" The USGS hazard faultdatabase findings were reviewed for strong earthquakes or the vertical displacements necessary to induce a tsunami. Additionally, the USGS eadhquake hazards program is reviewed for historical earthquakes in the region. Lastly, the NOAA natural hazards volcano database is reviewed to assess volcanoes in the Lake Erie region.

An earthquake-generated tsunami in Lake Erie would require a very large earthquake on the order of magnitude 7.0 or greater along with significant vertical displacement.

DAVf S-BESSE NUCLEAR POWER STATf ON Page 22 of 32 NTTF Recommendation 2.1 (Hazard Reevaluations):

Flooding First Energy Corporation Revision 1March 06, 20f 4 Historically, in the Lake Erie region, the largest earthquakes are in the magnitude 5.0 range. Preliminary analysis of post-glacial sediments in the region has not yielded evidence of a large earthquake in the last few thousand years. Furthermore, earthquakes in the region, for which sufficient data are available, show primarily horizontal rather than vertical movement, which is not as conducive to tsunami generation.Tsunamis can also be generated by the downslope movement of a very large volume af rock or sedirnent, either from a rockfall above the water or fiom a submarine landslide.

Although large amounts of unconsolidated sediments are washed into Lake Erie each year when shoreline bluffs are undercut by wave action, these masses lack sufficient volume and rapid collapse to displace a volume of water that would create a tsunami.Lake Erie afso has a very gentle bottom profile, particularly in the western and centralbasins. The eastern basin has steeper slopes, but not steep enough for a large amountof sediment to suddenly flow downslope in a submarine landslide.

Lastly, according to the NOAA natural hazards volcano database, there are novolcanoes in the Lake Erie region.3.S.4. Results The NOAA natural hazards tsunami database identifies only two ocsurrences of non-seiche (or non-wind-induced) tsunami events in the Great Lakes region. The two occurrences yielded slight or small wave effects.

Various earthquake databases, including the USGS Earthquake Hazards Program earthquake database, the National Center for Earthquake Engineering research catalog, and Natural Resources Canada, identify that the largest events in the vicinity are no greater than magnitude 5.0.According ta the USGS Earthquake Hazards Program, the hazard fault databasecontains no known Quaternary faults (or current faults) in this region because geologists have not found any faults at the Earth's surface.

Consequently, there is nol a potential for strong earthquakes or the vertical displacement necessary to induce a tsunami.Therefore, a tsunami is not expected to be the controlling flood event at DBNP$.3.7, Combined Effect Flood (including Wlnd-Generated Waves) {Reference DBNP$2013n1 Evafuation of the shoreside location is covered in H.4.1 of NUREGICR-7046 and includes one alternative:

Combination of: Probable maximum surge and seiche with wind-wave activity, The lesser of the 1OO-year or the maximum controlled water level in the enclosed body of water.There are three alternatives specified in H.4.2 locatione.

Each of the alternatives considered has water surface elevation.. Alternative 1 - Comblnation of:- The lesser of one-half of ttre PMF or the 500-year flood;- $urge and seiche from the worst regional hurricane or windstorm with wind-wave activity; andaf NUREG/CR-7046 for streamside three components contributing to the DAVIS.BES$E NUCLEAR POWER STATION Page 23 af 32 NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding Revision 1 First Energy Corporation March 06,2A14- The lesser of the 1O0-year or the maximum controlled water level in the enclosedbody of water.. Alternative 2 - Combination of:- PMF;- A 25-year surge and seiche with wind-wave activity; and- The lesser of the 10O-year or the maximum controlled water level in the enclosed body of water.r Alternative 3 - Combination of:- A 2S-year flood;- Probable maximum surge and seiche with wind-wave activity; and- The lesser of the 1O0-year or the maximum controlled water level in the enclosedbody of water.

3.7.1. Basis

of Inputs lnputs include the following:

r Toussaint River sub-watershed properties for rainfall-runotf modeling from Calculation C-CSS-020. 1 3-01 1. Toussaint River HEC-RAS model from Calculation C-CSS-020.13-011 r PMF discharge hydrographs from Calculation C-CSS-020.13-01

1. One-half PMF discharge hydrographs. Z5-year event rainfall for input into HEC-HMS model from NOAA Atlas 14. 2S-year event discharge hydrographs. Lake Erie Probable PMSS elevations from Calculation C-CSS-020. rc-417

3.7.2. Computer

Software Programs. ArcGlS Desktop 10.1 r Delft 3D r HEC-HMS 3.5. HEC-RAS 4.1. Microsoft Excel 3,7.3. Methodology Each combination includes coincident wind-wave activity. Coincident wind-wave activity is determined for the critical flooding combination using the USACE guidance outlined in USACE Coaslal Engineeing Manual. Runup is the maximum elevation of wave uprushabove stillwater level.H 4.1 Combination Probable maximum surge and seiche is estimated in Calculation C-CSS-020.13-017.

Wind-wave activity includes wave height, wind set-up, and wave runup.

Wave height and wind set-up are included as part of the PMSS developed using Delft3D model.DAVIS.BESSE NUCLEAR POWER STATION Page 24 af 32 NTTF Recommendation 2,1 (Hazard Reevaluations):

FloodingFirst Energy Corporation Revision 1 March 06,2414 H.4.2 Alternative 1 Alternative 1 requires using the lesser of one-half of the PMF or the 500-year event. Inthis case, the PMF was already determined as part of Calculation C-CSS-020.13-011.

Therefore, the one-half PMF is utilized as described in C-CSS-020.13-022. The surgeand seiche height from the worst regional hurricane or windstorm with wind-wave activity is estimated using statistical analysis of the historical data. Lake Erie has nooutlet control structures.

Therefore, the 10O-year water surface elevation is used withoutfurther consideration of the maximum controlled water elevation. The HEC-RAS modeldeveloped as part of the PMF analysis is revised to use the one-half PMF as the inflowboundary condition and 100-year surge-seiche elevation from the worst regionalhurricane as the downstream boundary condition.

The HEC-RAS model provides the water surface elevation for this alternative.H.4,2 Alternative 2Alternative 2 requires using the PMF estimated in Calculation C-CSS-020.13-011.

The$urge and seiche height from the 25-year event is estirnated using statistical analysis of the historical data.

Similar to Alternative 1, the HEC-RAS model was updated to obtain the resutting water surface elevation.H.4.2 Alternative 3Afternative 3 requires using the 21-year flood in the Toussaint River. Point rainfalf datafrom NOAA was used to estimate the 2S-year rainfall event. This rainfall is input into the HEC-HMS model developed as part of the PMF analysis to estimate runoff due to25-year event. The water surface elevation for the probable maximum surge and seichein combination with the 100-year water level is determined in Calculation C-CSS-02A13-017. Similar to Alternatives 1 and 2, the HEC-RAS model was updated to obtainthe resulting water surface elevation.3.7.4. Results The predicted water surface elevation at the site for Alternative 3 is found to be the maximum for the alternatives specified in H.4.2. lt is also concluded that the ToussaintRiver water surface elevations at the site are completely controlled by the backwaterconditions at Lake Erie for that alternative (i.e., the predicted water surface elevation in the river is equal to the lake elevation, extending for about one mile upstream of DBNPS).The water sudace elevation of 585.93 ft-lGLD5S for combination H.4.1 is equal to the critical water surface elevation for combination H.4.2 Alternative 3 and represents the critical water sudace elevation at the site resulting from the combined events asspecified in NUREG CR-7046, Appendix H.4.DBNPS is protected against flooding due to wave runup during a PMWS by wave protection dikes installed along the northern, eastern, and along a small portion of thesouthern sides of the site to an elevation of 591 ft-lclDss. Wave action at DBNPS is governed by the maximum supportable wave at the toe of the north dike during thePMSS. Wave action analysis concludes that a maximum wave runup of 3.98 ft on top ofthe PMSS level of 585.90 ft-lGLDsS may be generated at the toe of the north dike, Themaximum wave runup elevation during the controlling flooding Alternative is thereforeequal to 589.88 ft-lGLD5S.

This elevation is less than the top of the wave protection dikes (591 ft-lGLD55).

Therefore, the wave runup analysis shows that wave protection DAVIS-BESSE NUCLEAR POWER STATION Page 25 of 32 NTTF Recommendation 2.1 (Hazard Reevaluations):

FloodingFirst Energy Corporation dikes are sufficient to protect DBNPS from wave runup during the flooding event.Revision 1March 46,2414 critical eombined DBNPS is ilooded during the PMWS event along the non-diked west and south site boundaries. The maximum PMSS water surface elevation in the vicinity of the power block is 585.81 ft-lGLDsS.

The maximum wave runup elevation in the vicinity of the power block is 585.90 feet-lGLD55.3.8. Local lntense Precipitation (Reference DBNPS 2013e and DBNF$ 2013f1 The LIP is an extreme precipitation event (high intensity/short duration) at a given location.The duration of the event and the coverage area are needed to quantify an extreme precipitation event fully. Generally, the amount of precipitation decreases with increasing duration and increasing area.

NUREG/CR-7046 specifies that the LIF should be equivalentto the 1-hr, 1-miz probable maximum precipitation (PMP) at the location of the site.3.8.{. Basis of Inputs. Site topography. LIP (cumulative and incremental). Manning'sroughnesscoefficients. Supporting GIS data (Reference DBNPS 20131)3.8.2. Models Used r ArcGlS Desktop 10.1. FLO-ZD Pro r Microsoft Excel 3.8.3. Methodotogy The LIP event was evaluated to determine the associated flooding elevation andvelocities assuming the active and passive drainage features are non-functional.

Theentire roof drainage is assumed to be contributing to the surface runoff. The LIPevaluation was performed in accordance with the NUREG/CR-7046.The runoff caused by the LIP event was estimated using the FLO-2D software.

Thesoftware uses shallow water equations to route stormwater throughout the site. FLO-2D depicts site topography, using a digital elevation model (DEM), to characterize grading, slopes, drainage divides, and low areas of the site. The DEM is a grid model devetoped from composite ground surface information.

The methodology used withinthe FLO-ZD software included the rainfall function and the levee function (toincorporate site security features which could impact the natural drainage characteristics of the site).Per NUREG/CR-7046, the 1-hr, 1-mi2 PMP event was developed using HMR- 52. The total PMP depth per square mite for the l-hr event was interpolated from the PMP depth contour map provided in HMR-52. The distribution of the 1-hr PMP was developed for the 5-, 15-, and 3O-minute time intervals, with the 60-minute interval being the 1-hr PMP depth. The depth for each time interval was calculated using the DAVIS.BESSE NUCLEAR POWER STATIONPage 26 of 32 NTTF Recommendation

?.1 (Hazard Reevaluations):

FloodingFirst Energy Corporation Revision 1 March 06, 2014in FLO-2D to calculate the guidance provided in HMR-52. The 1-hr PMP was modeledsubsequent site flooding.

Active and passive drainage system components (e.9., pumps, gravity storm drainsystems, small culverts, and inlets) were considered non-functional or clogged during the LIP event, per Case 3 in NUREG/CR-7046.

The Manning's roughnes$

coefficient values are selected based on the land cover type using the guidance provided in the FLO-2D manual. Two types of obstructions are modeled:

buildingslstructures that completely block the water passage, and security walt barriers that could be overtoppedif the water depth increases to above the top of the wall.

To determine the flooding elevation associated with the LlP, the 1-hr, 1-miz storm wasapplied evenly across the site, and the model was allowed to run for 2.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> to ensure that only the areas of static ponding would remain. Five temporal distributions similar to the PMF analysis were considered.

3.8.4. Results

The end temporal distribution of the LIP event resulted in the highest water depths and consequently in the highest water surface elevations.

The water surface elevations at critical door locations, or doors leading to safety-related SSCs, are listed in Tabfe 1.ground surface elevations.

The ground at Door 334 is higher than the ground at Door 333 (585.92 vs. 585.67 ft NAVDBB). Therefore, minimal flooding depths result in the water fevel increase above the floor elevation. Between minute 27 and minute 54 of flooding event the water depth above 585.0 is 0.01 to 0.05 ft.Table I - LIP Flooding Elevation and Duration at DBNPS Structure Door Number Maximum Water Surface Elevation (ft-lGLD56)

Flood Duration above S85 ft-lcLD55 (minutes)Auxiliary Building 300 585.25 6 Auxiliary Building 361 585.20 15 Auxiliary Buifding 362 585.20 15 Auxiliary Building 315585.1 7 15Auxiliary Building 320A585.1 7 15 Auxiliary Building 324585.1 B 18 Turbine Building 330585.1 B 18 Turbine Building 399A 585.19 1B Turbine Building 339 585.20 1BTurbine Building 333 585.22 18Turbine Building 334 585.41 57*Intake Structure 224 585.44 30* The difference in the flooding duration at Door 333 and Door 334 is caused by the DAVIS.BESSE NUCLEAR POWER STATION Page 27 ol 32 NTTF Recommendation 2.1 (Hazard Reevaluations):

FloodingFirst Energy Corporation Revision 1 March 06, 2014The hydrodynamic loads, or impact loads, on the structures due to the LIP are presented in Table 2. FLO-2D reports the impact pressure a$ a force per unit length (impact pressure times flow depth). The maximum impact force on the structure wasestimated by multiplying the impact pressure by the structure length.Table 2 - Maximum lmpact Loads on Buildings Bulldlng Max lmpact (tblft)Containment StructureAuxiliary Building Turbine BuildingIntake Structure 0.46 1.53 7.14 5.27 4. COMPARISON WITH CURRENT DESIGN BASISThe reevaluated maximum water surface elevation due to the riverine flooding (ToussaintRiver) is below the current licensing basis. The reevaluated maximum water surface elevationdue to the LIP and PMSS events exceed the current licensing basis.

For lake flooding, the current design basis assumes the surge only in one direction.

A site-specific wind and pressure field is developed as part of the re*analysis.

More recent storms provided the controlling wind for surge flooding at DBNP$.For LIP flooding, the current design basis assumes 24.5 inches of rainfall will pond evenlyacros$ the site. As part of the re-analysis, recent site topography was used in a two-dimensional hydraulic model (FLO-2D Pro) and additional rainfall estimates were obtained from the more recent HMR-52 guidance.ln the interim, it is understood that an event of such magnitude to approach the postulated accumulation of rainfalf is a low probability event. Such an event would likely be associated with a significant tropical storm. Meteorological forecasting would provide sufficient warningwell in advance of such an event. The Interim Actions discussed in Section 5 will provide adequate protection until permanent solutions are implemented.The comparisons of existing and reevaluated flood hazards are provided in Table 3, DAVIS-BESSE NUCLEAR POWER STATION Page 28 af 32 NTTF Recommendation 2.1First Energy Corporation (Hazard Reevaluations):

Flooding Revision 1 March 06, 2014Table 3 - Gomparison of Existing and Reevaluated Flood Hazards at DBNP$Flood-Causing MechanismDesign Basis Comparison Flood Hazard Reevaluation Results Flooding in streams and rivers PMF Etevation

-579 ft-tGLD55 PMF Flow - 78,500 cfsCool-season PMPwas not evaluated.

Bounded All-Season PMF Elevation - 575.96 ft-IGLD 55, All-Season PMF Flow -100,436 cfs Cool-Season PMF Elevalion - 575.06 ft-IGLD 55, Cool-$eason PMF Flow -61,943 cfsDam breachesand failures No dams or other regulating hydraulic structures.

BoundedDam as$es$ment indicated no critical dams.Storm surge Water surface elevation - 583.7 IGLD55 Not bounded.Exceeds current design basis.Water surface elevation

-585.81 ft-lGLDSS at power block, Seiche This flood-causingmechanism is not described in the USAR.This flood-causing mechanismis not described inthe USAR.Not a credible scenario.

Bounded by storm surge.Tsunami This flood-causingmechanism is notdescribed in the USAR.This flood-causing mechanism is not described in the USAR.Tsunami asses$ment indicates there is a slight possibility of tsunamis in Great lakes. However, the seismicity in the region suggests there is no potential for strong earthquakes or the vertical displacement necessary to induce a substantial tsunami.lce-induced flooding Not plausible Bounded lce-induced flooding is bounded by the all-season PMF event.Channel migration diversion As indicated in the USAR, the mean lake level is notsubject to variations due todiversions or source cutoff.Bounded Channel diversion towards the site is not probable.DAVIS-BESSE NUCLEAR POWER STATION Page 29 of 32 NTTF Recommendation

2.1 First

Energy Corporation (Hazard Reevaluations):

Flooding Revision 1 March 08,2014Table 3 - Comparison of Existing and Reevaluated Flood Haeards at DBNPS (Continued)

Flood-Causing Mechanism Design Basis ComparisonFlood Hazard Reevaluation Results Combined effect flood (including wind-generated waves)Wave runup on wave protection dike- 590.3 ft-IGLD55.Bounded Wave runup on wave protection dike-589.88 ft-lclDss.

Maximum wave runup elevation in thevicinity of the power block - 585.90 ft-IGLD55.LIP Maximum watersurface elevation- 584.5 fr-lGLDs5.Not bounded.

Exceeds current design basis.Maximum water surface elevaiion

-585.44 ft-lGLD55.Dam FailureAs indicated in the USAR, there areno structures onToussaint River that can affect theflow hydrograph at DBNPS.Dams located in the DBNPg watershedare determined to be noncritical.5. INTERIM AND PLANNED FUTURE ACTIONSThe Flooding Hazard Reevaluation Report evaluated applicable flooding hazards for DBNPS, Two of the postulated reevaluated flood hazard events, the PMS$ and the LtP events, resultedin maxirnum flood water elevations higher than previously calculated for DBNPS. The assessment of the buildings, resulting from the flood hazard reevaluation, found a number ofdoors feading to areas containing safety related equipment to be susceptible to the postulatedwater infiltration.

These postulated flooding events are considered beyond design basisevents. The reevaluated flood levels are small increases with short durations.

These low probability events would likely be identified in advance by meteorological forecasting.

Current plant procedures addressing flooding at the site provide actions to be taken in the event flooding is imminent or has occurred at or near the DBNPS site.

No additional actions beyondthose currently in place are nece$sary at this time.

The total plant response to the reevaluatedhazard is to be determined by the Integrated Assessment.

The integrated assessment will be performed to address the need andlor potential designs for temporary or permanent barriers (or alternative countermeasures) to prevent postulated floodwater infiltration and/or mitigation of the postulated flood water infiltration. This evaluation willalso include a study of emergency procedures.

The evaluation of the mitigating strategy and schedule for the implementation of modifications (as necessary) will be documented in the Corrective Action Program. The evaluation will address the following items: DAVIS-BESSE NUCLEAR POWER STATION Page 30 of 32 NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding First Energy Corporation L!E As indicated earlier, the water surface elevation exceeds theRevision 1 March 06, 2014 finish ffoor elevation of 585 ft-of Flooding Hazards due to Dam Failure,a Tsunami, Surge and Seiche FloodinglGLD55 by a maximum value of 0.44 ft for a total duration of approximately 1.0 hrs at one (1)door and 0.5 hrs or less at the remaining eleven (11) affected doors, due to the LIP event. The LIP storm mechanisms will be reviewed in the integrated assessment to establish trigger points which support implementation of proceduralized mitigation measures.

This includes an evaluation of the forecast information available to personnel that would allow for advanced monitoring and warning of meteorological conditions that could potentially result in an LIP event occurring at the site. Modifications wilf afso be considered to afford protection for the site vulnerabilities or to further reduce the impact of the LlP, PMSSAs indicated earlier, the water surface elevation exceeds the finish floor elevation of 585 ft-IGLD55 by a maximum value of 0.81 ft for a total duration of approximately 2.5 hrs due to the PMSS event. The PMSS storm mechanisms will be reviewed in the integrated assessment to establish trigger points which support implementation of proceduralized mitigation measures.This includes an evaluation of the forecast information available to personnel that would allow for advanced monitoring and warning of meteorological conditions that could potentially result in a surge event affecting the site. Modifications will also be considered to afford protection for the site vulnerabilities.

6. REFERENCES (ANSf/ANS-2.8-1992) ANS, American National Standard for Determining Design Basis Flooding at Power Reactor Sites, Prepared by the American Nuclear Society Standards Committee Working Group ANS-2.8, 1992.(JLD-ISG-2A13-01) NRC, Guidance for Assessment Revision 0, June 2A13.(JLD-lSG-2012-06)

NRC, Guidance for PerformingSafety Analysis, Revision 0, June 2012 (NEl August 2012, NEl, Report 12-08, Overview of External Flooding Reevaluations, August 2012.(NRC March 20121 NRC, Letter to Licensees, Request for Inforrnation Pursuant to Title 10 of the Code of Federal Regulations 50.54(0 Regarding Recommendations 2.1 ,2.3, and 9.3 of theNear Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, March 12, 2012.(NRC RG 1.59) NRC, Desrgrr Basis Flood for Nuclear Power Plants, Regulatory GuideRevision 2r 1977.(NRC RG 1.102) NRC, Ftood Protection for Nuclear Power Plants, Regulatory Guide 1.1A2, Revision 1 , 1976.(NUREG-0800) NRC, NUREG-0800, Standard Review Plan for the Review of Safety AnalysisRepods for Nuclear Power Plants: LWR Edition - S#e Charccterisftbs and Sr'fe Parameters (Chapter 2), M107c400364, March 2A07.(NUREG/CR-7046) NRC, NUREG/CR-7046, PNNL-20091 , Design-8asis Flood Esfttnaffon forStle Characterization at Nuclear Power Plants in the United Sfafes of America, ML11321,{195,November 2011.

DAVIS-BESSE NUCLEAR POWER STATIONPage 31 of 32 NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding Revision 1First Energy Corporation March 06, 2014 (NUREG/CR-6966) NRC, NUREG/CR-6966, Tsunami Hazard Assessment at Nuclear Power Plant Sites in the United Sfafes of America, National Technical lnformation Service, March 2009.(DBNPS 2013a) FENOC Calculation C-CSS-020.13-009, A//-Season Prabable Maximum Precipitation Analysis for Davis-Besse Nuclear Power Sfafion, Revision 0.(DBNPS 2013b) FENOC Calculation C-CSS-020.13-010, Coo/-Season Precipitation and Snowmelt Analysis for Davis-Besse Nuc/ear Power Sfaflon, Revision 0.(DBNPS 2013c) FENOC Calculation C-CSS-020.13-01 1, Probable Maximum Fload Analysis for Davis-Besse Nuclear Power Station, Revision 0.(DBNPS 2013d) FENOC Calculation C-CSS-02A13-A12, Dam Assessmenli lce Jam, and Channel Migration for Davis-8esse Nuclear Pawer Sfafion, Revision 0.(DBNPS 2013e) FENOC Calculation C-CSS-020.13-013, Local lntense Probable Maximum Precipitation Analysrs for Davis-Besse Nuc/ear Power Sfafion, Revision 0.(DBNPS 20130 FENOC Calculation C-CSS-020.13-014, Effecfs of Local lntense Probable Maximum Precipitation Analysis for Davis-Besse Nuc/ear Power Sfaffon, Revision 0.(DBNPS 2013g) FENOC Calculation C-CSS-020.13-015, Sife-specifie Wind and Pressure FieldAnalysis far Davis-Besse Nuclear Power Sfafion, Revision 0.(DBNPS 2013h) FENOC Calculation C-CSS-020.13-016, Su4ge and Seiche Screening for Davis-Besse Nuclear Power Sfafion, Revision 0.(DBNPS 2013i) FENOC Calculation C-CSS-020.13-017, Surge and Seiche Analysis for Davis-Eesse Nuclear Power Sfaflon, Revision 0.(DBNPS 2013j) FENOC Calculation C-CSS-020.13-018, Tsunami Screening/Analysis for Davis-Besse lVuclear Pawer Sfafion, Revision 0.(DBNPS 2013k) FENOC Calculation C-CSS-020.13-019, Probable Maximum Flood GIS Analysis far Davis-Besse Nuclear Pawer Sfafion, Revision 0.(DBNPS 20131) FENOC Calculation C-CSS-020.13-020 Locat lntense Precipitation GtSAnalysis for Davis-Besse Nuclear Power Stafion, Revision 0.(DBNPS 2013m) FENOC Calculation C-CSS-020.13-A21, Surge and Seiche Calibration far Davis-Besse Nuc/ear Power Sfafion, Revision 0.(DBNPS 2013n) FENOC Calculation C-CSS-02A13-022, Combined Event including Wind Wave Analysis for Davis-8esse Nuclear Power Statian, Revision 0.(DBNPS 2013o) FENOC Calculation C-CSS-020.13-023, Surge and Seiche GIS Analysis for Davis-Besse fVuc/ear Pawer Stafion, Revision 0.(USAR) Davis-Besse Nuclear Power Station, Updated Final Safety Analysis Report, Revision 29.DAVIS-BESSE NUCLEAR POWER STATION Page 32 of 32