ML16272A217

Oconee, Units 1, 2, and 3 - Revision 1 to Flood Hazard Reevaluation Report on Oconee Nuclear Station, Pp. 1-70, Dated March 6, 2015 (Redacted)

ML16272A217
Person / Time
Site:	Oconee
Issue date:	03/06/2015
From:	HDR Engineering
To:	Office of Nuclear Reactor Regulation
Shared Package
ML16070A295	List: ML16070A284 ML16070A287 ML16070A288 ML16070A290 ML16272A216 ML16272A217 ML16272A218 ML16272A220 ONS-2015-028, Supplemental Information Re NRC 2008 and 2012 Request for Information Pursuant to 10 CFR 50.54(f) Pertaining to External Flooding, Dated March 6, 2015 (Redacted)
References
FOIA/PA-2016-0071
Download: ML16272A217 (83)

Text

ML13UfZAlU(_^ __ __ .--h l .....ntzn 8!-- ...I. fz t l..lti- ----. 10l CFRIm l)Enclosure 1Revision 1 to Flood Hazard Reevaluation ReportOconee Nuclear StationRevision 1 Summary1. Revisions made as applicable to a revised Jocassee Dam Break flood analysis whichapplied multiple alternate breach-parameter estimations in accordance withJLD-ISG-201 3-1.2. Revisions made as applicable to incorporate the Jocassee specific seismic analysis intothe report (satisfies RAl 1 from March 20,2014 RAI).3. Addresses revised responses to RAls 11 -15 from the March 20, 2014 PAI.4. Changes to errata in the use of the terms "licensing basis" and/or "design basis"throughout the document.Sections Affected by Revision 1:* Executive Summary* Section 2.3* Section 2.8* Section 3.3* Section 4* Section 5* Section 6* Appendix D

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• lf................ 1Prepared for:DUKE ENERGY CAROLINAS, LLCCharlotte, North CarolinaPrepared by:HOR ENGINEERING, INC. OF THE CAROLINASCharlotte, North CarolinaRevision 1January 29, 2015 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORT~~REPORT VERIFICATION 'lJ¶L,'REPORT VERIFICATIONPROJECT: ONS FLOODING HAZARD, REEVALUATION REPORT REVISION 1TITLE: RESPONSE TO REQUEST FOR INFORMATION PURSUANT TO TITLE 10 OF THECODE OF FEDERAL REGULATIONS 50.54 (F) REGARDING RECOMMENDATION 2.1:FLOODING OF THE. NEAR-TERM TASK FORCE REVIEW OF INSIGHTS FROM THEFUKUSHIMA DAI-ICHI ACCIDENTThis ,document has been reviewed for accuracy and quality commensurate .with the intended application.-Prepared b-: J. ChritphrE, ,P.E.-7112121Checked.by: Tim Banta, P.E. 'ot J4L.1Dae 12901Qualhty Review by: -Angie Scangas, PE.E 9 5CfaA5:o4. Date: 1129/2015Approved by: .J. Christophere P. E. 112912015This document has been reviewed for accuracy and quality commensurate with the intended application.Corporate Seal:Professional Engineer Seal:HDR Engineering, Inc. the Carolinas440 S. Church Street, Suite 900Charlotte, NC 28202South Carolina License No. C03i 8 "QI 3° .. "~ .. ....~nv~iI~m~u .n .lu... uH. m ~rDuke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTTable of ContentsTable of Contents*REPORT VERIFICATION.............................. .......... .... .., .., ................ ..:.... ..... ...Table of Contents .... ....................... ., .. ................iList of Figures .... ....;........................;................,....... ...................... ......List of Acronyms ...........................................................................................viiE x e c u tiv e S u m m a ry ..... ..... ........... ...... ... ... .. ..................... ...... ........................E S -ISection 1 -Site Information Related to the Flood Hazard ..... .. ....... .................... 11.1 Detailed Site Information!.. ... ., ...... ..... ..... ..,................ ,.......................141.2 Current Licensing Basis Flood Elevations .. .. .. ... ......................... ......... 1.2.1 Local Intense Precipitation..................................,. .. ............11.2:2 Flooding in Reservoirs ... ........: .......... -........ .. .....: .. .. 51 .2 .3 D a m F a ilu re s .............. ..... ....... ............ ...,.. ......... ...... ..... ..........61.2.4 Storm Surge and Seiche ..............................................61.2.5 Tsunami ......,............................................................................ 61 .21.6 Ice-Induced Flooding.........................................,... ......................... 61.2.7 Channel Diversion ....................................................,..................... 71.2.8 Combined Effects .....................................,.... ...........71.3 Licensing Basis Flood-Related and Flood Protectioni Changes .....1.4 Watershed and Local Area Changes ...........,............; .... ... ..... ..81.5 Current Licensing Basis Flood Protection and Mitigation Features ....,;. ........ .9Section 2 -Flooding H azard Reevaluation ................,......... ................ ............... ,...1 i2.1 Local Intense Precipitation ................................................................... 112.2 Flooding in Reservoirs : ...................... .... .. ....................172.2..1 Probable Maximum Flood -Keowee 1............................,.........72..2.2 Probable MaXimum Flood -Jocassee .................................,......,..........242.3 Dam Failures ..................,.. ............. , .. ..,.,.......................... 312.3.1 Potential Dam Failure ........ ........ ,..,.................,............. 312.3.2 Dam Failure Permutations .... ......... ., ..........,. .......... ,.............. .322.3.2.1 Potential Hydrologic Overtopping ..............,............,........................... 322.3.2.2 Potential Seismic Failure .................;.......................................... 32JI Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTTable 0o" Contents2.3.2.3 Site Geology Characteristics ......,.................,.................. ,.................. 332.3.2.4 Seismic Hazard Methodology Description ..... ... .... ... ..., ....362.3.2.5 Seismic Hazard for Hard-Rock Conditions ..... ..............,..... ,... .............362.3.2.6 Site Response Analysis .... .372.3.2.7 Seismic Hazard for Soil Conditions............... ............ ..,....... 2.3.2.8 Seismic Performance Evaluation .........;....... ...................... ;............. 392.3.2.9 Seismic Performance.................i............................................... 402.3.2.1.0 Appurtenant Structures ....................... ...... .............................. 412.3.3 Unsteady Flow Analysis of Potential Dam Failures ............................ ......422.3.4 Water Level at the Plant Site..,....,.... ....... ...:..., ..... :...................... ,...... 522.5 Tsunami ...................... ........................ .................,....... ... ...... ...,....562.6 Ice-Induced Flooding ............................... .......,................................... 562.6.1 e Efe ts..... Ice. ...... .Effects.., .. .......*............ ............ ..... .56. ;.52.6.2 Ice Jam Events .................................... ........... ,. ........ ........562.7 Channel. Diversions...................................................................... ........ 562.8 Combined Effects..... ............. .......................................................... 56Section 3 -Comparison of Current Licensing Basis .and Reevaluated Flood-CausingMechanisms ..... ............. ....... ......................... ,...........,,.................. 583.1 Local Intense Precipitation. ...,......... .................................................,.....583.2 Probable Maximum Flooding ....................................... ......................... 593.3 Dam Failures ...........................593.4 Storm Surge and Seiche ........................ .....,. .... ........593.5 Tsunami ........................, ............................................. .,....., ........ ...593.6 Ice-Induced Flooding .............,,............. .............................................. 593.7 Channel Diversion................ ........... ..........,................. .......... 593.8 Combined Effects ... ..I............ .......59Section 4 -Interim Evaluation and Actions Taken or Planned..................................... 60Section 5 -Additional Actions.............................,........................ ..................... 615.1 RAI-14: Hazard input to the integrated assessment: Flood event duration parameters615.1.1 Response to pRAl-14 ............... ,...... ........... , .... .. .......,..:....,,............ 625.2 RAI 15: Input to integrated assessment: Flood height and associated effects., .......63ill L.onlalns oe~uriiy ae,,uiuvu ;,.,,,.v, w,,,, ;,~ .~....Lv;;, -i. ..... Duke Energy Carolinas,, LLC I ONS FLOODING HAZARD REEVALUATION REPORTTabre of Contents5.2.1 Response to RAI 15....................,.................................................. .64.Section 6-- References.... .............. ... ......-..............................:......................... .67Reference CalcUlations: ..... .. ..... ........,........ .... ..... 70APPENDICESAPPENDIX A -FIGURES AND TABLESAPPENDIX B -CURRENT LICENSING BASIS, LIP MODEL ANALYSIS INUNDATIONLEVELSAPPENDIX C -FLOOD HAZARD REEVALUATION BEYOND DESIGN BASIS LIP MODELANALYSIS INUNDATION LEVELSAPPENDIX D -DAM BREACH MODEL UNSTEADY FLOW MODELING.DETAILS9iv¸ C,-, .. ,.3,.u .,ai,h,aveu,;ul,, wmu;[~uuu .zfuzJu puUDiw per ,u ='Duke Energy Carolinas. LLC I ONS FLOODING HAZARD REEVALUATION REPORTList of FiguresList of FiguresFigure 1. Probable Maximum Precipitation Depth Duration Curve .... ............................ 13Figure 2L incremental precipitation during the 6-hour PMP for six different temporal distributions........................................'............................................................... 14Figure 3. Incremental precipitation during the 72-hour PMP for six different temporaldistributions........*............ .... .................................................. 15Figure 4. PMP DAD curves for Keowee watershed PMP depth vs. Duration: .................... 18,Figure 5. PMP DAD curves for Keowee watershed PMP depth vs. Drainage Area .............. 19Figure 6. Keowee watershed sub-basins ...............................,...............*........... .....22Figure Table 6.2 PMS from HMR 52 which generates PMF..................................... 23Figure 8. KeoweePMF hydrographs ...................,...........;............. ........................... 24Figure 9. Jocassee PMP DAD curves PMP depth vs. Area....... ................................. 25Figure 10. Jocassee watershed sub-basins ................................................ ........27Figure 11. Jocassee PMF hydrographs ............................................................. 31Figure 12. Map of Jocassee Main Dam location showing Latitude and Longitude. North is to thetop of the figure.....;.............. .............................. .....,...................... 34Figure 13. Composite profile 1 representing geologic conditions below the control pointelevation at Jocassee Dam (LCI, 2014). Profiles JD-1 and JD-5 are individual profilesat Jocassee from AMEC (AMEC, 2014b) that are combined into, composite 1. "Lower"and "Upper" profiles correspond .to the lower-range and upper-range cases,respectively, to capture epistemic uncertainty in mean shear wave velocity per theSPID (EPRI, 2013a)................ .........:................................................ 35.Figure 14. Site-specific mean soil hazard curves for seven sPectral frequencies at Jocassee(LCI, 2014) .............,........ .............. ;.............................. ... ........... 38Figure 15. Horizontal mean UHRS for MAFEs of 10-4, 10"s, and 10"e at Jocassee (LCI, 2014). ,39V

• Duke Energy Carolinas, LIC I ONS FLOODING HAZARD REEVALUATION REPORTList of TablesList of TablesTable 1. Reservoir Flooding Results...................*............................................... 5Table 2. Calculation Results................. ........................................... ...... .........6Table 3. Probable Maximum Precipitation Depths for the Site Using HMR 51 and 52 ........... 12Table 4. 5-Minute Interval Duration Depths ....... ................................................... 13Table 5. Keowee Damn -Normal and probabie-maximum flood freeboard (ft)......................18Table 6. Jocassee Dam -Normal and probable maximum flood freeboard (It)................... 24Table 7. Final ,Jocassee Dam Breach Parameters ................................................. 48Table 8. Final Jocassee Dam Breach Formation Pattern (HEC-RAS Input) ...... ..........49Table 9. Comparison of 1 -D and 2-D model results -time to breach and maximum watersurface elevations (Elevation in ft msl and Time in hours) ... .., ....................... 54Table 10. Wind-driven wave run-up results .................. .............. ................. ............55Table 11. 2-year wind velocity results ..................... ........55Table 12. Combined effects flood elevations... .....,... .................................... ...... ..... 57Table 13. Current licensing basis and reevaluation flood elevations .............................. 58vi

-- --i,- C..:t...._ Lf;......tL,- , .1t'iht.r'l~ frtr ....kri, IAl r~Q'2 Qfll~l4~1Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTList of AcronymsList of AcronymsBWST Borated Water.Storage TankCAL Confirmatory Action LetterCAP Corrective Action ProgramCCW Condenser Circulating Watercfs cubic feet per secondCM compensatory measuresCN curve numberCPE control point elevationDAD depth-area-durationDEM digital elevation modelEAP emergency action planEPRI Electric Power Research InstituteFERC Federal Energy Regulatory CommissionGIS Geographic Information SystemsGMRS Ground Motion Response SpectrumHEC-RAS Hydrologic Engineering Center's -River Analysis SystemHHA Hierarchical Hazard AssessmentHMR Hydrometeorological ReportIDF Inflow Design FloodISFSI Independent Spent Fuel Storage InstallationIWCS InfoWorks CSLCl Lettis Consultants InternationalLIP local intense precipitationmsl mean sea levelNED National Elevation Data SetNGVD National Geodetic Vertical DatumNLSWE non-linear shallow water equationsNRC Nuclear Regulatory CommissionNTTF Near-Term Task ForcePGA peak ground accelerationPMF probable maximum floodPMP probable maximum precipitationPMS probable maximum stormPSHA probabilistic seismic hazard analysisSCS Soil Conservation ServiceSE Safety EvaluationSPID Screening Prioritization and Implementation DetailsSRM Staff Requirements MemorandumSSC systems, structures, and components,SSF Standby Shutdown Facilityvii Sa*..it ~.: l..r-::: .LL IJ f- ... pl:.ti : 410 FF £l'l~ 20")tnl,)4Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTList of AcronymsSri Supporting Technical InformationSWMM storm water management modelTIN triangulated irregular networkUFSAR Updated Final Safety Analysis ReportUHR~S uniform hazard response spectraUSACE United States Army Corps of EngineersUSGS United States Geological Surveyviii Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTExecutive SummaryExecutive SummaryFollowing the accident at the Fukushima Dai-ichi nuclear power plant resulting from the 2011Great Tohoku Earthquake and Tsunami, the Nuclear" Regulatory Commission (NRC)established the Near-Term Task Force (NTTF) and tasked it with conducting a systematic andmethodical .review of NRC. processes and regulations to determine whether improvements arenecessary.The resulting NTTF report concludes that continued United States (U.S.) nuclear plant operationdoes not pose an imminent risk to public health and safety and provides a set ofrecommendations to the NRC. The. NRC directed its staff to determine which recommendationsshould be implemented without unnecessary delay (Staff Requirements Memorandum [SRM] onSECY-1 1-0093).The NRC issued its request for information pursuant to Title 10 of the Code of FederalRegulations, Section 50.54(f) (10 CFR 50.54[f]) on March. 12. 2012, based on the followingNTTF flood-related recommendations:* Recommendation 2.1: Flooding* Recommendation 2.3: FloodingEnclosure 2 to the NRC 50.54(f) letter addresses Recommendation 2.1 and requests a writtenresponse from licensees to:1. Gather information with respect to NTTF Recommendation 2.1, as amended by SRM onSECY-1 1-01 24 and SECY-1 1-0137, and the Consolidated Appropriations Act for 2012,Section 402, to reevaluate seismic and flooding hazards at operating reactor sites.2. Collect information to facilitate NRC's determination of the need to update the safety-related design basis and systems, structures, and components (SSCs) that areimportant to protect the updated hazards at operating reactor sites.3. To collect information to address Generic Issue 204 regarding the flooding of nuclearpower plant sites following upstream darn failures.A 'Flood Hazard Reevaluation Report" was prepared for the Oconee Nuclear Station (ONS),Units 1, 2, and 3 in response to NTTF Recommendation 2.1 and submitted March 12, 20i3.By E-mail dated September 15, 2014, the NRC transmitted a Request for Additional Information(RAI) regarding Oconee's flood analysis of a postulated upstream dam failure. TheSeptember 2014 RAI requests that the dam failure be re-analyzed by applying alternate breachmethodologies.This report is the revised "Flood Hazard Reevaluation Report"for Oconee Nuclear Station.There are two major changes encompassed by the revision. The first is that it incorporates theresults of a revised analysis which utilizes alternate breach methodologies, as requested by theSeptember 15, 2014 RAt. Secondly, it incorporated a recently completed seismic analysis,ES-I

• .:,oL- w,.,,i~ purntu per mu ..l)Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTExecutive Summaryspecific to the Jocassee Dam. By incorporating this seismic analysis, the revised FHRR nowcontains the information being sought by PAL 1, from the March 20, 2014, RAI.When preparing Duke Energy's October 15, 2014, response, RAls 11 through 15 were identifiedas possibly being affected by the revision. The answers to RAls 11 and 12 are now contained inthe appropriate sections of the report body. RAl 13 requested the dam breach model'selectronic input and output files. This information is provided on electronic media discs as anattachment to the submittal letter for this report. The new responses to RAls 14 and 15 areincluded in Section 5 of the revised FHRR.The revised report addresses the request of the September 15, 2014 RAl and satisfies the"Flood Hazard Reevaluation Report~' response of NTTF Recommendation 2.1 for the OconeeNuclear Station (ONS) Generating Plant Units 1, 2, and 3 (ONS).ES-2 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 1 -Site Information Related to the Flood HazardSection 1 -Site Information Related to the FloodHazard1.1 Detailed Site InformationOconee Nuclear Station (ONS) is located in eastern Oconee County, South Carolina,approximately 8 miles northeast of Seneca, South Carolina. Duke Energy Carolinas, LLC's(Duke Energy) Lake Keowee occupies the area immediately north and west of the site. TheUnited States Army Corps Of Engineers' (USACE) Hartwell Reservoir is south (downstream) ofthe site. Duke Energy's Lake Jocassee lies approximately 11 miles to the north.The location and description of ONS presented in the Updated Final Safety Analysis Report(UFSAR) Chapter 1 and Chapter 2 include reference to figures showing the generalarrangement, layout, and relevant elevations of the station. The original design of the ONSYard (Yard) grade was nominally 796.ft mean sea level (msl) (all elevations referenced in thisreport are based on National Geodetic Vertical Datum [NGVD] 1929). The mezzanine floorelevation in the Turbine, Auxiliary, and Service Buildings is 796.5 ft msl. ExteriOr accesses tothese buildings are at an elevation of 796.5 ft msl. Section 4.0 provides further discussion ofmodifications to the Yard grade.All of the man-made dikes and dams forming the Keowee Reservoir rise to a minimum elevationof 815 ft msl including the ONS Intake Canal Dike.The ONS site, as per the original licensing basis, is a "flood-dry site," which is not subject toflooding from the nearby streams and Lake Keowee River (excluding postulated dam breakscenarios). The full pond water elevation of Lake Keowee is 800 ft msl.1.2 Current Licensing Basis Flood Elevations1.2.1 Local Intense PrecipitationThe flood water elevation due to a maximum local intense precipitation (LIP) (also known as theprobable maximum precipitation [PMP]) was reevaluated by HDR Engineering, Inc. of theCarolinas (HDR) in the last quarter of 2012 using the current licensing basis case PMP andstate-of-the-practice engineering software. The analysis evaluated the maximum water surfaceelevation within the ONS power block area resulting from the occurrence of'the PMP and*assuming three different site drainage scenarios an updated site topogr'aphy and buildinglayout. Figures and tables referenced in this section are presented in Appendices A andB.Rainfall precipitation for the ONS site was based on the UFSAR 2.4.2.2 stated depth andduration of 26.6 inches in 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. As prescribed by the UFSAR 2.4.2.2, the temporaldistribution applied to the rainfall was derived from the normalization Of mass rainfall curveslocated at Clemson College from the historical precipitation event of mid-August 1940. FiguresA-I and A-2 illustrate the cumulative and incremental precipitation, as well as rainfall masscurve used in the model analysis. The maximum 1-hour rainfall intensity for the normalized

" "" ~.,........... r....i.,..l..L ....a .. .;~ ....L ,. .uui., v '.r' £.U "flIDuke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection* 1 -Site information Related to the Flood Hazardrainfall precipitation event was approximately 3.5 inches per hour. Figure A-3 is an output fromthe rainfall/runoff simulation model showing the rainfall distribution as input in the analysis.The coupled one-dimensional (l-D) and two-dimensional (2-0) hydraulic model was used forthe basis of this study. This model encompasses the main Yard and extends to include the 230kilovolt (kV) switchyard east of the main Yard and the Independent Spent Fuel StorageInstallation (ISFSI) south of the main Yard (Figures A-4 and A-5-A). A separate model wascreated for the Keowee Hydro Powerhouse sub-basin (Figure A-5-B).The topography terrain data for the Yard and ISFSI was supplied by Duke Energy and was usedas the basis for generating the modeling surface for the main Yard. The 3-inch topography datawas extended using the 1-foot topography contours for areas outside the coverage of the 3-inchtopography. The areas using the 1-foot topography contours are the 230-kV switchyard,extension to the ISFSI area, and the Keowee Hydro Powerhouse sub-basin. The extension tothe ISFSI area is mainly between the main Yard and !SFSI where there is no 3-inch topographycoverage, extending towards the inlet channel and extending to the drainage basin boundary.The supplied data was processed in ESRI ArcGIS software to create a triangulated irregularnetwork (TIN) file, which waS imported into the. hydraulic mOdeling software, Inf0Works CS,Version 11.5 (IWCS).The modeling of the Yard reflects the up-to-date configuration of the Yard, based on 2010surveyed data. There were some locations in the. terrain model that had to be modified due totemporary construction (excavation) that was taking place at the time the site was surveyed.These areas were identified and the mesh for the 2-D simulation was modified to either raise thearea locally or lower the area locally. The approach used was to raise an area by specifying aminimum elevation to use for that zone. If a terrain value was lower than this defined minimumelevation, this minimum elevation was substituted for the actual elevation for determining the 2-D element elevation. Similarly for lowering a zone, a maximum elevation was chosen and anyvalue in the terrain data would be capped by this value for determining the 2-D mesh elementelevation. The final mesh elevations used for the simulation are illustrated in Figures A-6-A andA-6-B.Soil and terrain surface characteristics for the Yard and off-site sub-basins were used todevelop the hydrology characteristics Using the Soil Conservation Service (SCS) curve number(ON) method. Figure A-i-A shows the various off-site boundary areas by color designation.The flow coming off these sub-basins was further subdivided to be applied where it would enterthe Yard as shown in Figure A-i-B. In addition, model node l~s are shown in Figure A-7-B.Flow hydrographs were calculated for the downstream loCation of these sub-basins and typicallyapplied directly to the 2-0 mesh at locations where it had been determined by contOurs that theflow would naturally concentrate. For off-site Basins 1, 2, and 5 shown in Figure A-i-A that areon the western side of the site, the calculated flows were routed along overland flow paths,through culverts, or over weirs that represent roadways to adjacent overland flow paths thatconnect to the 2-D mesh of the Yard. The flow coming off the sub-basins was furthersubdivided to be applied where it would enter the Yard.2 I~,, .* .. ...... .... ..... ........ --t ... .iu .... -.2. (~lDuke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 1 -Site Information Related to the Flood HazardThe Keowee Hydro Powerhouse area has no additional modeled routed drainage. Rainfall isdirectly applied to the 2-D mesh. This assumption was used because the subject drainage areais fairly small (at less than 10 acres) and with the pervious areas being grassY and steep, initialand continual losses would be minimal and thus the approach taken would yield a moreconservative result.Physiographic characteristics were derived from the following resources:* Soil Characteristics (UFSAR 2.5.4.2; 2.5.6.3) (Contractor determined) (NaturalResources Conservation Service)* Surface Characteristics (Contractor determined by aerial photographs provided by Duke.Energy)The Yard drainage was created from drawings and walkdown information of the current sitelayout. This data was used to build the existing conditions model (Figure A-7-A) where colorshading represents differ'ent sub-basins in the runoff model. The layout of the site, including thelocation of building and drainage information, was taken from the Duke Energy-suppliedMicroStation drawing files. These files were also used to input pipe size and elevation of theelements within the system along with the associated supplied Spreadsheet of the catch basindata. Duke Energy catalogued the site drainage catch basins. This information is representedin the model as an equivalent-sized orifice for each catch basin.The roof drainage (Figure A-8) for the Reactor, Auxiliary, and Turbine buildings was createdfrom drawing and photograph files. Each roof section was modeled as a conceptual volumedefined by an elevation-area relationship. An orifice was used to drain the roof area to therespective segments of the roof drainage system. Overflow of the roof gutter or parapet wasaccounted for by use of a conceptual weir of appropriate elevation and length that discharges toa location based on determined flow paths. These locations are typically directly applied to the2-D mesh, at downspout locations, where appropriate, or other roof sections depending on roofgeometry. Details for parts of the Auxiliary Building and the other buildings on site werereviewed by the modeler; and where extensive detail was not deemed necessary (based onexperience), a more simplified roof catchment and orifice drainage system was defined tosimulate the roof drainage that connected directly to the Yard drainage system.The roofs that drain to the Yard directly (no downspouts) and those with downspouts weremodeled by defining a catchment area for each roof area and connecting this to the 2-D YardSurface (Figure A-9). An orifice was. used to represent each downspout to discharge to the Yardat the appropriate location. A weir was also used at each downspout location to allowovertopping of the gutter to add flow to the same location the downspouts discharge to. Roofswith a direct response to the Yard and overflow from gutters were represented by the use of aweir to direct the flow to the 2-D surface.The modeling software used for this effort was IWCS with 2-0 -a Coupled 1 -D and 2-Dsimulation model produced by Innovyze (formerly Wallingford Software). This modelingpackage allows the hydrology and hydraulics for 1 -D pipe flow and 2-D overland flow to bemodeled-within one software environment. The hydrology was divided into three areas: off-site3 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 1 -Site Information Related to the Flood Hazarddrainage, which is modeled as SCS basins and derived flows loaded onto the Yard 2-D mesh atappropriate locations; the Yard, which is the 2-D surface directly around the Reactor andTurbine buildings where the rainfall is applied directly to the mesh; and roof drainage. The roofsurfaces use the storm water management model (SWMM) routing and direct flow to the roofdrains, Yard drains, or directly to the Yard as appropriate. Two models were developed: onefor the main Yard to the 230-ky switchyard and ISFSI area, and one for the Keowee HydroPowerhouse sub-basin.Figure A-i0-A shows catch basins and other nodes located within the Yard study area. The linkbetween the 1-D and 2-D simulations can be an important factor in the model results along withthe simulation time step used. The 1-D and 2-D simulation engines are separate with a linkbetween them which, in this IWCS model, represents the catch basin nodes. The simulationengines Calculate depth and flow in the pipes and across the surface at every pointsimultaneously for each "major" time step. If a result cannot be determined at a particular timestep, then the time step is halved to a "minor" time step and the simulation engines try tocalculate again until a result is achieved. The interaction between the 1-D and 2-D Simulationstakes place at the major time steps at the catch basins. Thus, it is important to use anappropriate time step for the simulation to ensure proper exchange of flow between the 1-Dpipes and 2-D surface. A 1-second time step has been used for these simulations to preventexcess flow from building up on the suJrface over the catch basins between major time steps,which would artificially increase the water surface elevations on the 2-0 surface.The 2-D mesh is comprised of an irregular array of triangles known as computational mesh.These triangles have a defined maximum size. The mesh also has a minimum element sizedefined for simulation. If mesh triangles have an area less than the minimum mesh elementsize, then triangles are merged together to create a 2-D element greater than the minimummesh element size. This is to maintain simulation stability. The main Yard has a maximumtriangle size of 250 square ft and a minimum mesh element size of 30 squareft.The average mesh element size in highly detailed areas around buildings is approximately 80square ft with an average size of about 150 Square ft across the open part of the Yard. Thismesh is tighter around features of hydraulic significance such as buildings, swales, and catchbasins; and the mesh is looser in areas that are open and reasonably flat. The Keowee HydroPowerhouse sub-basin mesh has a maximum triangle size of 90 square ft and a minimum meshelement size of 30 square ft.. The average mesh element size is about 60 square ft.Three scenarios were investigated and are summarized below.All three scenarios use the 26.6 inches in 48-hours rainfall event with temporal distributionmodeled after the August 11-14, 1940, storm event for the area.* Scenario 1: Complete system with fully functioning roof and Yard drainage.* Scenario 2: Yard and roof drainage considering the Yard drainage catch basins to beblocked (not functioning).* Scenario 3: Yard drainage (surface) only considering both the roof inlets and Yarddrainage (sub-surface) catch basins to be blocked (not functioning).4 "c h :C :. ,C ~ .....v..... ,,.,i wv~pIJIU *ab puu si, I iu !.rtK -'.,su~a)'I,Duke Energy Carolinas. LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 1 -Site Information Related to the Flood HazardThe simulations were run for a period of 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br /> to allow enough time for all of the water fromthe rainfall event to flow off or out of the system. Site inundation elevations under currentlicensing basis PMP and existing site layout are provided in Appendix B.Table B-I quantifies the increase in flood depth around the Reactor, Auxiliary, Turbine, andAdministrative buildings due to modeling the Yard by simulating the Yard drainage catch basinsbeing blocked. The average increase in water depth due to the catch basins being blocked is0.67 ft. The average increase in flood depth east of the Turbine Building is 0.77 ft. The averageincrease west of the Auxiliary and Reactor buildings is 0.83 ft.The Yard flood depths are the same for Scenario 2 and Scenario 3 where only the Yard drainsare modeled as blocked and where the Yard drains and roof drains are both modeled asblocked.Figures B-2 and B-4 show the location of maximum water surface elevations and durations forpoints in the Yard around the Standby Shutdown Facility (SSF), Protected Service Water(PSW), and Essential Siphon Vacuum (ESV) structures and in the CT-5 area when Yarddrainage is effective.The maximum depth of water for the current licensing basis case around the Keowee HydroPowerhouse sub-basin is shown in Figures B-3 and B-5. The 2-D terrain in this area is showinglocal low areas in paving next the powerhouse but the base map contours around thepowerhouse are 1 foot while the modeled water depths are around 0.5 ft.The efficiency of the Yard drainage and roof drainage systems was evaluated using the IWCSmodel but for this review, the drainage systems were assumed to be blocked, producing a moreconservative LiP inundation condition at the site.1.2.2 Flooding in ReservoirsSince ONS is located near the ridgeline between the Keowee and Little River valleys, or morethan 100 ft above the maximum known flood in either valley, the records of past floods are notdirectly applicable to siting considerations.Original ProJect studies were conducted to evaluate effects on reservoirs and spillways ofmaximum hypothetical precipitation (PMP) occurrin~g over the entire Lake Keowee drainagearea. This rainfall was estimated to be 26.6 inches within a 48-hour period. Unit hydrographswere prepared based on a distribution in time of the storms of October 4-6, 1964, for Jocasseeand August 13-15, 1940, for Keowee. Reservoir flooding results are summarized as follows:Table I. Reservoir Flooding ResultsKeowee JocasseeMaximum spillway discharge 147,800 cfs 70,500 cfsMaximum reservoir elevation 808.0 ft 1,114.6 ftFreeboard below top of dam 7.0 ft 10.4 ftNote: Data above from UFSAR.S Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 1 -Site Information Related to the Flood HazardWhile spiliway capacities at Keowee and Jocassee have been designed to pass the inflowdesign flood (IDF) with no surcharge on full pond, the damns and other hydraulic structures havebeen designed with adequate freeboard and structural safety factors to safely accommodate theeffects of PMP. Due to the time-lag characteristics of the runoff hydrograph after a storm, it isextremely unlikely the maximum reservoir elevation due to the PMP would occur simultaneouslywith winds causing maximum wave heights and run-ups.Considering this assessment, the ONS site can be characterized as a "flood-dry site," asdescribed in Section 5.1.3 of the American National Standard Report, "Determining DesignBasis Flooding at Power Reactor Sites," because the safety-related structures of the existingONS are above spillway discharge flooding elevations. The Yard is nominally 796 ft msl andduring the passing of a probable maximum flood (PMF) through the Keowee spillway,discharged water (approximately 145,000 cubic feet per second [cfs]) is not expected to backupsignificantly over the river elevation of approximately 686 ft msl. This meets the intent of thedefinition of a "flood-dry site."1.2.3 Dam FailuresThere were no dam failures postulated in the original licensing or design basis of the plant. Adam failure event was postulated more recently and is described below in Section 1.3.1.2.4 Storm Surge and SeicheStorm surge and seiche events were never postulated to affect the site, and no flood elevationis given in the original licensing basis of the plant. The maximum wave height and wave run-upwere calculated for Lake Keowee and Lake Jocassee by the Sverdrup-Munk formulae. Theresults of these calculations are as follows:Table 2. Calculation ResultsLake --Wave Height' Wave Run-Up -Maximum Fetch,Keowee' (Keowee.River Arm) 3.70 ft 7.85 ft 8 milesJocassee 3.02 ft 6.42 ft 4 milesKeowee (Little River Ar~m)' 3.02 ft 6.42 ft 4 milesNote: Data above from UFSARThe wave height and wave run-up figures are vertical measurements above normal full pondelevations as tabulated above. The design freeboard at each dam is 15 ft which is adequate toprevent overtopping of wind-driven waves.1.2.5 TsunamiTsunamis were never postulated to affect the site, and no flood elevation is given in the originallicensing or design basis of the plant.1.2.6 Ice-Induced FloodingIce-induced flooding were never postulated to affect the site, and no flood elevation is given inthe original licensing or design basis of the plant.6 C .nbr fm ~r i ..... J ...... ......... .* ....... .:t -I ...... ~vIrT -- ir .... .... o( J(Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 1 -Site Information Related to the Flood! Hazard1.2.7 Channel [DiversionChannel diversions were never postulated to, affect the site and no flood elevation -is given in theoriginal licensing or design basis of the plant.1.2.8 Combined EffectsCombined flooding effects (PMP, PMF, dam failure and/or wind-driven waves) were neverto affect the site and no flood elevation is given in the original licensing ordesignbasis of the plant.1.3 Licensing Basis Flood-Related and Flood ProtectionChangesONS has made the following flood-related and flood protection changes described below.Thereis one exception to the Keowee ReServoir Retention dikes and dams minimum elevationof 815 ft msl. This .exception is described as two reinforced concrete trenches extendingthrough the ONS Intake Canal Dike with a minimUm elevation Of 810 ft msl. This exception onlyoccurs during very rare occasions when the covers would be removed for maintenance. Thesetrenches are protected from wave action by the Condenser Circulating water (CCW) IntakeStructure and the Causeway at the west end of the CCW Intake Structure. Therefore only themaximum reservoir elevation of 808 ft msl is applicable with regard to flooding through thereinforced concrete trenches.An additional licensing caveat exists in ONS's Updated Final Safety Analysis Report (UFSAR).UFSAR Section 9.6.3.1 describes the design basis loads for the SSF. The original design basis.for the SSF stated, "Flood studies show that Lake Keowee and Lake Jocassee are designedwith adequate margins to contain and cOntrol floods... The Final Safety Analysis Report (FSAR)addresses Oconee's location as on a ridgeline 100' above maximum known floods. Therefore,external flooding due to rainfall affecting rivers and reservoirs is not a problem. The SSF is,within the site boundary and, therefore, is not subject to flooding from lake waters" (UFSARSection 9.6.3.1). In 1983, a JocaSsee Dam failure studY was completed to determine themaximum water surface elevation around the SSF if a postulated fair-weather failure of theJocassee Dam is considered. The results of the study estimated a peak flood elevation of817.45 ft msl at the Keowee dam, and a Yard flood level of 4.71 ft. In resPonse to this study,ONS erected several walls approximately 5 ft tall, around the entrances to the SSF as a riskreduction measure. This was not part of the design basis. ,Based on O NS's September 26,2008. response to a Title 10 of the Code of Federal Regulations, Section (10 CFR50.54[f]) request for information, ONS increased the height of the flood wall around theS5SF by2.5 ft as a risk reduction measure with a resulting elevation of 803.5 ft ins!.The UFSAR Section 9.6.3.1 was updated to say:"As a PRA enhancement the SSF is providedwith a five foot external flood wall which is equipped with a water tight door near the southentrance of the SSF. A stairway Over the wall provides accessto 'the north entrance. The yard.elevation at both the north and the south entrances to the SSF is 796.0 ft msl. Based on the as-7 Duke Energy Carolinas, .LLC j ONS FLOODING HAZARD REEVALUATION REPORTSection 1 -Site Information Related to the Flood Hazardbuilt configuration of the 5' flood wall provided at the north entrance and the flood wall at thesouth entrance to the SSF, SSF external flood protection is provided for flooding *that does notexceed 801 ft above mean sea level." In its current as-built condition, the 8SF has floodprotection features UP to an elevation 'of 803.5 ft msl.A separate external flood hazard is the postulated fair-weather failure of the Jocassee Dam."This is derived from a NRC Safety Evaluation (SE) dated January. 28, 2011, addressingcommitments made in regards to the June 22, 2010, Confirmatory Action Letter (CAL) toaddress external flooding concerns.The following description is a synopsis of the SE.In April 2006, the U.S. NRC staff questioned the flood protection barrier for the SSF. The NRC'identified that the licensee had incorrectly calculated the Jocassee Dam Failure frequency andhad not adequately addressed the potential consequences of flood heights predicted at ONS.Based on concerns raised by the NRC, by letter dated August 15, 2008, (ML081640244) theNRC requested information in a 10 CFR 50.54(f) letter. Duke Energy responded to thelicensee's request On September 26, 2008 (ML0827501 06).After further correspondence, the NRC staff issued a CAL to the licensee on June* 22, 2010,requesting the following: 1) submit to the NRC all documentation necessary to demonstrate thatthe inundation of the ONS site, from the postulated fair-weather failure of Jocassee Dam, hasbeen bounded; 2) by November 30, 20"10, submit a list of all modifications necessary to mitigatethe and 3) make all necessary modifications by November 30, 2011. Subsequentcorrespondence with the NRC has deferred these dates.The staff also requested that the compensatory measures (CMs) listed in the CAL remain inplace until they can be superseded by regulatory, action related to the Fukushimaresponses.The safety evaluation (SE) describes the methods and parameters chosen for the analysis. Itconcludes by.stating: "The unmitigated Case 2 dam breach parameters that were used in theflooding models, provided by* Duke 'Energy for ONS site, demonstrated that the licensee hasincluded conservatisms of the parameters utilized in the dam breach scenario. Theseconservatisms provide the staff with additional assurance that the above Case 2 scenario-willbound the inundation at ONS, therefore providing reasonable assurance for the overall floodingscenario at the site. This new flooding scenario is based on a random fair-weather failure of theJocassee Dam. This Case 2 scenario will be the new flooding, basis for the site"' (SE datedJanuary 28, 2011 ). The SE also states that the licensee has committed to keep the CMs inplace Until final resolution has been agreed upon between the licensee and the NRC staff.1.4 Watershed -and Local Area ChangesChanges to the local site topography and support~buildings have taken place since originalconstruction. Changes* in local area conditions have been captured in the modeling performedto support the flooding assessment due to LIP and dam failure 'inundation using recent aerial8 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 1 -Site Information Related to the Flood Hazardand ground survey data (2010) along with updated drainage, utility trench location and buildinggeometry.There has been Construction of housing and support facilities directly around Lake Keowee inthe watershed since 1971, but the overall percentage of land use has not significantly, changedsince the construction of the reservoirs and ONS. There is no significant change in land usearound Lake Jocassee. Most of the Lake Jocassee watershed is comprised of protected forestlands.1.5 Current Licensing Basis Flood Protection and MitigationFeaturesBased on the ONS flood hazards, a list of flood protection, mitigation, and earlywarningindicator features has been compiled. This list of features was created to fulfill the NRC-issuedinformation request on March 12, 2012, in accordance with 10 CFR 50.54(f). Enclosure 4. of the50.54(f) letter was directed toward addressing the NTTF Recommendation 2.3 for Flooding andrequested the results of a flooding design basis walkdown. Below is a high level description ofthe different features presented in the 2.3 Flooding Walkdown report. Many of the features areactually groups of smaller features and for convenience have been grouped together.The first group consists of Features I1 through 9. These features are included because of thePMP initiating flood as described above. They are all either at Yard elevation (-796 ft .msl) orbelow grade and are listed below:Flood Protection and Mitiqation Features:1. Auxiliary Building exterior subsurface walls and seals2. Radwaste trench covers and seals from Radwaste Facility to Turbine building3. Radwaste trench covers and Seals from Radwaste Facility to Auxiliary building4. Interim Radwaste trench covers and seals5. Manhole 7 Cover, Technical Support building vault and seals6. Borated Water Storage Tank (BWST) trench covers7. Yard drainage system8. CT-5 trench covers in Auxiliary building9. PMP rainfall event flood barrier sandbags and Gryffolyn coveringsA second group consists of Features 10 through 16. These features are included because theyare part of the Keowee Reservoir Retention items. Listed below are the seven features:Flood Protection and Mitigqation Features:10. Keowee River Dam11. ONS Intake Canal Dike12. Little River Dam13. Little River Dikes A, B, C, D14. Keowee Intake15. Keowee Hydro Powerhouse16. Keowee Spillway9 Duke Energy Carolinas, LLC J ONS FLOODING HAZARD REEVALUATION REPORTSection 1 -Site Information Related to the FlOOd HazardThe third group consists of Features 17 through 31. Their purpose is to mitigate floodconditions based on the January 28, 2011, SE postulated fair-weather failure of the JocasseeDam. This list was derived from the fifteen CAL CMs, and the actions taken by ONS in order tosatisfy the CAL. These features include plant flood protection procedures, early flood detectionwarning equipment housed at Jocassee Hydro, and emergency equipment housed at ONS andoperated under emergency procedures. The list of features is provided below:Flood Protection. Mitigation Features, and Measures:17. EM 5.3 Procedure (External Flood Procedure)18. APiO/AN1700/047 Procedure (External Flood Abnormal Procedure)19. Jocassee Flood mitigating plans and procedures20. Duke Energy Hydro generation guidance document21. Dam safety inspection program22. Maintained monitoring program23. Keowee Spillway enhancements24. Jocassee Forebay and tailrace alarms25. Jocassee storage building with backup spillway operating equipment26. Portable generator and electric drive motor near the spillway27. Documentation of table top exercises28. Instrumentation and alarm selected 'seepage mnonitoring locations29. Video monitoring of Jocassee Dam30. Second set of B.5.b-like equipment31. Jocassee Dam-ONS response drill documentationThe fourth group consists of Features 32 through 34. These features are included because theyare the exterior flood protectiOn features for the SSF. Listed below are the three features:Flood Protection and Mitiqation Features:"32. SSF flood barriers including exterior walls33. SSF steel plate with CO2 refill access34. SSF external wall penetrations35. Feature #35 is the last feature on the Flood Walkdown list and corresponds to the SiteElevation and ToPography.More info'rmation on these features and walkdown conclusions can be found in the FloodWalkdown Report (NRC 50.54 (f) NTTF Recommendation 2.3).10

,.onan oeuuyOfb.uUuu uiu., ,;,, ..=,, ~Ll. .i r .z~)1Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -- Flooding Hazard ReevaluationSection 2 -Flooding Hazard ReevaluationThe reevaluations in Section 2.0 are not part of the ONS licensing basis as documented in theUFSAR. The following sections describe additional reevaluation analysis for assessingappropriate external potential flooding hazard events including the effects from LIP on the site,PMF on reservoirs and dam failure that havebeen performed post-design basis to meet theHierarchical Hazard Assessment (HHA) procedure described in NUREG/CR-7046 forassessment of flooding hazard at safety-related SSCs.ONS is located on the Keowee reservoir which is a Federal Energy Regulatory Commission(FERC) regulated hydroelectric development that is impounded by two embankments adjacentto ONS and five additional embankments along the Little River Arm of the reservoir away fromthe site. As FERC-regulated dams, the structures have been designed and verified withand hydraulic analysis and dam stability analyses in accordance with "FERCEngineering Guidelines for the Evaluation of Hydropower Projects." These structures aremonitored and inspected on regular intervals by Duke Energy, FERCI, and independent damsafety experts.2.1 Local Intense PrecipitationThe flood water elevation due to a maximum LIP was reevaluated using current practiceHydrometeorological Report (HMR) PMP and state-of-the-practice engineering software. Theanalysis evaluated the maximum water surface elevation within the ONS power block arearesulting from the occurrence of the PMP and assuming three different site drainage scenarioswith an updated site topography and building layout. This reevaruation differs from the licensingbasis analysis in that it utilizes HMR 5.1 PMP and different rainfall distribution` patterns inaccordance with guidance in NUREG/CR-7046. The modeling software used in this evaluationexceeds procedures outlined in NUREG/CR-7046, !-D channelized flow using the USACE'sHydrologic Engineering Center's-River An~alysis System (HEC-RAS), as it analyzes overlandflow on relatively flat surfaces using 2-D flow equations. Due to the complex site geometryincluding building layout, roof drainage, subsurface drainage, and lack of defined 1-D flowchannel in the currently Configured Yard, a model using 2-D flow equations was employed asdescribed in the following sections. Figures and tables referenced in this section are presentedin Appendices A and C.This section presents a summary of the model developed to reView local flooding at the ONSyard due to an assumed rainfall event based on HMR 51 for a PMP rainfall event.This work consists of the ONS site flood inundation evaluation and is based on an expandedIWCS 2-D model based on updated site data from Duke Energy regarding the Yard drainageand building and roof drainage transmitted over the period of September 2011 to September2012. The roof drainage and Yard drainage performance was evaluated with the subsequentflow routing (sub-surface and overland flow) through the ONS site utilizing 1-D modeling for roofand sub-surface Yard drainage and 2-D modeling for Surface drainage (overland). This analysis11 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard Reevaluationincludes the maximum depths and durations for the Yard and roof inundation as well as the flowpatterns around the Yard. This section provides a summary of the IWOS model construction.The Beyond design basis case utilizes the HMR 51/52 methodology for an area less than 10square miles. The PMP event that produces the study case site flood event was determined bytrial procedures using the model to route the runoff. The Beyond design basis case analysiswas performed for three scenarios:* Scenario 1 is the complete system with fully functioning roof and Yard drainage.* Scenario 2 is the Yard and roof drainage considering the Yard drainage catch basins tobe blocked (not functioning).* Scenario 3 is the Yard drainage (surface) only considering both the roof inlets and Yarddrainage (sub-surface) catch basins to be blocked (not functioning).Rainfall precipitation for the Yard was determined using HMR 5 1/52 as they apply to the sitelocated in the U.S. east of the 105th Meridian. HMR 51 defines the depth in inches of PMP fordurations of 6, 12, 24, 48, and 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> for watersheds from 10 mi2 to 20,000 mi2.HMR 52defines the depth in inches of PMP for durations of 5, 15, 30, and 60 minutes for watershedsfrom 1 mi2 to 200 mi2.Both HMRs provide isohyetal charts to determine the PMP values basedon location. The location used for the site is approximated by Latitude 34.80 N and Longitude82.90 W. It should be noted that the PMP charts are not sensitive to a small deviation inLatitude and Longitude. Table 3 contains the PMP depths for the site using HMR 51 and 52.Table 3. Probable Maximum Precipitation Depths for the Site Using HMR 51 and 52Depth-Duration All-Seasonal PMP values, by Duration (hrs)1-mi2 Point Rainfall 10-mi2_____5-min I5-min 30-min 1-hr 6-hr 12-hr" 24-hr '48-hr. 72-hrPMP(Ice) 6.2 9.7 14.0 18.95 30 35.8 40.2 44.3 46.7As directed by procedures outlined in HMR 51 and 52, intermediate points are determined fromapplying a smooth curve through the derived points. Intermediate points were determined inthis manner for a duration interval of 5 minutes up to 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, and a duration interval of 1 hourbeyond 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. The complete PMP depth-duration curve is provided below inFigure 1.Taking the first portion of the curve, up to 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, the 5-minute interval duration depths areprovided below in Table 4. Bold values correspond to the values derived directly from HMR 51and 52 PMP charts.The process outlined in this report is based on NRC regulations for the next generation nuclearstations to be constructed in the U.S. (NRC Standard Review Plan, NUREG-0800, 2.4.2). ThePMP rainfall applied to the ONS watershed for this analysis was an all-season, 6-hour eventand a 72-hour event.12

£ ~ .::........Ll .i r. ..........Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard ReevaluationFigure 1. Probable Maximum Precipitation Depth Duration Curve50 ... .450 -- --I I ,05 6 ... .18....3.36.4.... ... 6 .. ... ..6 72,Durtin horsTable 4. 5-Minute Interval Duration Duration Cumulative PMP(minutes), Depth (inches)5 6.1810 8.0215 9.7220 11.2925 12.7230 14.0235 15.1440 16.0545 16.8450 17.5455 18.2360 18.9513

t. ...... ... ...... , ...... ... ........ ..... ! ... .. .. .. .. r ..... r i --- in ( (1 .OueEnergy Carolinas, LLC I ONS FLOOOING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard ReevaluationAs described in HMR 52, PMP estimates were obtained from HMR 51 for 6-, 12-, 24-, 48-. and72-hour storm durations (HMR 51 Figures 18 through 22) to estimate the largest volume PMPevent shown in Table 3. Additionally, a 6-hour local intense event was used for analysis basedon discussion found in NUREG7046, Section 3. The 6-hour PMP LIP was developed for 5-minute increments following prceures outlined in Setin 6 of HMR 52. After a review of the6-hour and 72-hour precipitation modeled results, it was determined that a longer duration eventcould have a significant impact on site flooding. The maximum 5-minute rainfall intensity for the6-hour event was 72 inches per hour while the maximum 5-minute rainfall intensity for the 72-hour event was 19 inches per hour. Therefore, the 72-hour precipitation was modified to includethe peak intensity indicated by using the 6-hour event based on the peak 1-hour distribution forthe 6-hour event shown in Table 4. The IWCS model was re-run for each storm duration usingsix temporal distributions applied to the rainfall: front, one-third, center, two-thirds, and end-loaded storm as well as the distribution recommended in HMR 52. Figures 2 and 3 compare thesix temporal distributions.The 72-hour PMP event was identified as the storm duration which produced the mostconservative flo Yard elevations through simulations using the IWCS model. This event wasdetermined to be the HMR 51, modified 72-hour event, with 46.6 inches of total rainfall, and two-thirds loaded distribution.The coupled 1-D and 2-1) hydraulic model was developed to be used for the basis of the study.The model encompasses the currently configured main Yard and extends to include the 230-kVswitchyard east of the main Yard and the ISFSI south of the main Yard. A separate model wascreated for the Keowee Hydro Powerhouse sub-basin (Figures A-4, A-S-A and A-5-B). Refer toSection 1.2 for an additional description of the model configuration and inputs in addition to thereevaluation of the PMP defined in this section.Figure 2. Incemntal precipitation during them 6-hour PMP for six different temporal distributions7.(003.00 Inrementi Precilpitation CrenteI .00

• II ncremental Preciptataion Ton-Thirds3.00 UIcrermental Precipetateon CeRterU Incremental IPrecipitation End0aq 0Minute14 Duke Energy Carolinas, LU.C I ONS HAZARD REEVALUATION REPORTSectbon 2 -Flooding Hazard ReevaluaonFigure 3. Incremental precipitation during the 72-hour PMP for six different temporal distribtion200014.00u ncremetld Precuptato Fron12.001aO0 U Incremental Preciuaron One-Thid8.00 U Incemnt~al Preapitaton C:ente3 .0IJ s incremental Precr~ation Two-Thrd-2.00 U I Incremental Predipitation End0.001 5 9 131721252933374145495357616569HourSeveral tests were simulated with the model using the 6-hr and 72-hr storms to select the stormthat produced the greatest flooding impact at critical areas around the ONS site. Both stormdurations were reviewed using the six different temporal distributions shown in Figures 2 and 3(six 6-hour cases plus six 72-hour cases : 12 trial cases). From this sensitvt analysis, thecritical temporal distribution was selected as the HMR 51152 72-hour, two-thirds loaded PMPevent.The results provided in Table C-i are based on model results using the HMR 51 /52 PMP withtwo-thirds loaded temporal distribution. Locations referenced in this section are based on FigureC-1.Figures C-2 through C-4 show the Beyond design basis case maximum flood depths in the Yardwith Yard drainage and roof drainage, with roof drainage and no Yard drainage, with no Yarddrainage or roof drainage, and specific locations of maximum flood depth in the Yard. Theslope and configuration of the Yard facilitate rapid removal of the intense rainfall of the HMRPMP event.Table C-i quantifies the inrese in flood dept around the Administrative, Turbine, Auxiliary,and Reactor buildings due to modeling the Yard by simulating the Yard drainage catch basinsbeing blocked. The average increase in flood depth due to the catch basins being blocked is0.19 ff, which is a 7 percent increase. The average increase in flood depth east of the turbinebuilding is 0. 1 if, a difference of 7 percent. The average increase in flood depth west of theAuxiliary and Reactor buildings is 0.29 ft, a difference of 8 percent.The Yard flood depths are the same for Scenarios 2 and 3 where only the Yard drains aremodeled as blocked and where the Yard drains and roof drains are both modeled as blocked.15 Duke Energy Carolinas, LLC j ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard ReevaluationThe maximum flood water surface elevations during the Beyond design basis case around theKeowee Hydro Powerhouse sub-basin structure are shown in Table C-1. There is effectively norise in water surface elevation around the Keowee Hydro Powerhouse due to the catch basinsbeing blocked. However, assuming the catch basins and the culvert under the roadway thatconveys-the hillside runoff are blocked increases the depth of water adjacent to the western sideof the powerhouse and produces a nominal increase on the northern side. The increase inmodeled depth of water is due to the flow that runs off the hillside and into the drainage ditchesconveying the flow to the culvert results in flow overtopping the culvert inlet, and the water thenflows over the roadway and up against the western side of the structure.The Yard drainage is surcharged in numerous locations when trying to handle the flowsassociated with the HMR PMP event and excess water flows onto the surface. From testingmodel response for just the roof connections to the Yard drainage, it was noted that the Yarddrains overflowed onto the surface in a number of locations with just the flows coming off theroof system. Both the east and west Yard drainage lines show heavy surcharging of thesystem. This produces flooding at the surface in some locations; and under the strain of theintense rainfall, the drain system fills to an extent that prevents additional flow from enteringfrom the surface.The roof drainage is undersized for the HMR PMP event. With the exception of the ReactorBuilding and the lower level roof of the central Auxiliary Building, the water does not overtop theroof parapets with the roof and Yard drainage functioning. Comparing the total inflow for theroof section to the maximum volume stored on the roof, the lower section of the central AuxiliaryBuilding, B8075-8078-8082-B1 (Figure C-12), has flow leaving the roof drainage system underpressure and up onto the roof. The other areas where flow appears to overtop the parapets arelikely due to the simplified way that they are modeled or the level of detail that was available tobuild the model. Most of the roof areas of the Reactor, Auxiliary, and Turbine buildings have alarge amount of available storage until the rainwater overflows the parapets.The Reactor Building roof was not fully developed in the model and would require additionalrefinement to allow the excess rainfall that cannot get into the roof drain system to overflow tothe appropriate areas. This refinement was not performed due to the small percentage ofcontribution of this water to the total site inundation flow and resulting ground level inundationestimates.The inundation of rainwater on the Turbine Building averages 4.06 ft in depth over the centralspan of the Turbine Building. The outer edges range from approximately 1.37 to 3.87 ft in depthand the lower roof on the eastern edge is 6.49 ft in depth. The rainwater in general stays on theroof for 30 minutes and for 1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> for the central span.The range of depths of inundated rainwater on the Auxiliary Building roof is between 0.33 and3.10 ft, correcting for parapet height. The average is less than 1 ft taking into account theexcessive depth on the lower central roof. The duration of inundation is generally 30 minutes to1 hour with the exception of the lower levels of the central and southern sections of the AuxiliaryBuilding that have durations closer to 2 to 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />. This is due to the heavy surcharging of the16 Duke Energy Carolinas, LLC [ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard Reevaluationsystem. This results in some extended pooling of water on the roofs which can be seen inTable C-2. Table C-2 lists a summary of the Beyond design basis case roof drainage.characteristics.The buildings with the greatest depth above the roof deck are those with the smallest surfacearea and corresponding small volumes with relation to the entire roofed area. The excessvolume on the central span of the Turbine Building will overflow onto the east and west sectionsof the roof where there is available volume. Whether the roof can hold this much weight ofwater is beyond the scope of this study.The modeled scenario with the Yard catch basins blocked off relieves the lower roof sectionssomewhat, but has no real effect on the upper roof sections, as can be seen in Table C-3.2.2 Flooding in ReservoirsSection 5.5.1 of American Nuclear Society (ANS) 2.8, under "Hydrologic Dam Failures," statesthat "critical dams should be subjected analytically to the probable maximum flood from theircontributing watershed. If a dam can sustain this flood, no further hydrologic analysis shall berequired." The two significant reservoirs upstream of ONS are Jocassee and Keowee; both arelicensed by Duke Energy and were constructed and are maintained in accordance with FERCguidelines. Dam-specific PMP and PMF documentation was reviewed, demonstrating that bothdams can safely pass their PMFs.Per ANS 2.8, Section 5.5.4, "if no overtopping is demonstrated, the evaluation may beterminated and the embankment may be declared safe from hydrologic failure." Overtoppingshould be investigated for either of these two conditions:,, PMF surcharge level plus maximum (1 percent) average height resulting from sustained2-year wind speed applied in the critical direction; or* Normal operating level plus maximum (1 percent) wave height based on the probablemaximum gradient wind.2.2.1 Probable Maximum Flood -KeoweeFlooding hazard reevaluation for a PMF on the Lake Keowee watershed was performed byreviewing the updated analysis developed for the FERC-Iicensed and regulated hydroelectricdevelopment (#2503). The peak reservoir elevation from that analysis is 808.9 ft msl based onhydrologic and hydraulic modeling performed in accordance with Chapters II and VIII of theFERO "Engineering Guidelines for the Evaluation of Hydropower Projects" using HMR 51/52 forthe PMP development and HEC-1 for the hydrologic and routing model (0.9 ft higher than theUFSAR study,). The spillway and dams at the Keowee development have been designed topass the PMF with adequate freeboard and structural stability factors to safely accommodatethe effects of the PMP. Table 5 summarizes the normal and PMF freeboard for the damstructures that impound Lake Keowee.17 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORT'Section 2 -Flooding Hazard ReevaluationTable 5. Keowee Dam -Normal and probable maximum flood freeboard (ft)~~Reservoir' Elevation(ft ms!)... .Top. of Dam Elevation' Full Pond. PMFDam Structure ..(ft msl) (800.0). (808,.9)Keowee Dam 815.0 15.0 6.1ONS Intake Canal Dike 815.0 15.0 6.1Saddle Dikes A, B, C, and D 815.0 15.0 6.1Little River Dam 815.0 15.0 6.1The PMP used in the evaluation of Lake Keowee was estimated from HMR No. 51, ProbableMaximum Precipitation Estimates, United States East of the 105th Meridian (HMR-51). TheProbable Maximum Storm (PMS) which generates the PMF was estimated using computertechniques outlined in HMR No. 52, Application of Probable Maximum Precipitation Estimates,United States East of the 105th Meridian.A set of depth-area-duration (DAD) curves (Figures 4 and 5) was prepared for the Keoweedrainage basin using the all-season PMP charts published in HMR-51 ,and the basin centroidlocation. The PMP depths in inches were for storm durations ranging from 6 to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and forstorms smaller and larger in area than the drainage basin.Figure 4. PMP DAD curves for Keowee watershed PMP depth vs. Duration450,40.0:35.0_ --o 2>00 mn12ont I1.000 mL.2~25.020.010.0-.---o 5,00O nil.,?10,000 fTiI2..---- 20,000 rnL20.0 I--00 12 18 24 30 3842Dura~tn (?u.)48 54 60 68 72 78 8418 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard ReevaluationFigure 5. PMP DAD curves for Keowee watershed PMP depth vs. Drainage AreaAO.0 q ..35.03. 0.025.0 ----0"N 01 o25.0 N. ho'010 100 1.o00 10.000 100,000Dwing. area (rrt.)The drainage basin for the Keowee Development covers approximately 435 square miles of thesoutheastern slope of the Blue Ridge escarpment. The drainage basin terrain transitions fromrounded mountains through foothills to Piedmont. The land is characterized by dense forests -some original growth, but most of the forest is mature second growth. Except for the tops ofridges, the vegetation is generally dense and the soils are permeable and absorbent. The smallamount of farming in the region is confined to the wider portions of valley floors and thePiedmont portion of the drainage basin. In the southern part of the basin, there is moredevelopment than in the rest of the basin. Development is generally characterized by scatteredrural housing and small towns.The Keowee drainage basin does not fulfill all of the terms of the definition of a gauged basin asdescribed in the FERC guidelines. To the extent that the basin does not meet the definition of agauged basin, it must be analyzed as an ungauged basin. For this reason, a regional study wasutilized to develop unit hydrographs for the sub-basins in the drainage area of the KeoweeDevelopment.The Jocassee Development is the largest upstream development with substantial storagecapacity. The PMF was routed through the Jocassee Development by level pool routing.Theoretically, the routing parameters at Jocassee could be set to help reduce the peak reservoirelevation at Keowee by holding back additional runoff to reduce the peak reservoir elevation atKeowee. However, Jocassee was modeled to operate as if it were experiencing a PMF.Therefore, to be conservative, the same model input parameters that were specified for the19 8,.,,J ;,I E,,,,,,;II.7- .. i..r"t .., I'fZ.... t;, ... .;......... ...~..., ... 0 ur ....... ...;....Duke Energy Carolinas, LLC I FLOODING HAZARD REEVALUATION REPORT .w,Section Flooding Hazard ReevaluationJocassee Development PMF were used in the Keowee model. During a PMF event in thevicinity of either of these adjacent developments, both Jocassee and Keowee would beoperated as if each of them were expecting a PMF event.There are a number of ponds and small lakes in the Keowee drainage basin. These arecharacterized by passive sp~illways and negligible storage capacity. These structures have verylittle effect on the stOrm hydrograph as it passes through their ponds, and the total storagevolumes are small so that even a breach would not have any measurable effect on reservoirelevations at the Keowee D evelopment.The SCS runoff CNs were used to model abstractions and compute excess rainfall. The CNmethod 'relates cumulative rainfall to cumulative excess rainfall based upon the singleparameter CN which ranges in value from 0 to 100 depending on the combination of soil typeand land cover/use. The CN 'method is widely used for PMF studies as it is incorporated directlyinto the HEC-1 Computer model. The Geographic Information Systems (GIS) facilitated thesecomputations.To determine the sCS curve number for a sub-basin, both land use and hydrologic soil groupmust be known. This information is combined using the published tables (SCS 1972) toestablish the curve number value for th~e sub-basin.Soil types were obtained from the soil surveys of Oconee, Pickens, Transylvania, and Jacksoncounties. Land use information was obtained from the U.S. Geological Survey (USGS) forNorth Carolina and the Land Resources Commission for South Carolina. The resolution on thisdata was 60 meters so that every 60-by-60 meter cell was characterized by one of the followingsix land use categories: urban, agricultural/grass, scrub/shrub, forest, water, andbarren/transitional land. A determination of the set of CNs for the "water" land use category isnot relevant because water is accounted for in the determination of percent impervious. SOSCNs for each combination of hydrologic soil group and landluse were then area-weighted todetermine the average CN for each sub-basin.The drainage basin was divided into 26 sub-basins as shown in Figure 6. Sub-basins I through25 were delineated on USGS quad Sheets (map scale 1:24,000) based on similarity oftopography, geology, and land use. In order to use sub-basin outlines in GIS, the outlineswere digitized from the quad sheets. As a matter of interest, the sub-basin outlines weredigitized into MicroStation files. The MicroStation files were then imported into the Arclnfo GISwhich produced an ASCII listing of the )(-Y coordinates for each of 25 sub-basins. For sub-basin 26 (Jocassee basin), coordinates from the Jocassee HMR-52 input bekw re ioughtinto GIS, transformed to the origin used for the Keowee sub-basins, converted to ASCii code,and added to the ASCII coordinate files.The PMP DAD curves (Figures 4 and 5) and digitized sub-basin coordinates were used asinputs into the USACE HMR-52 computer pr'ogram. The HMR-52 program computed the stormsize, location, and orientation that produced the maximum precipitation volume for the drainagebasin (PMS). A 700-square-mile storm with centroid at X=10.3 miles and Y=I13.0 miles and20 Duke Energy Carolinas, LLC IONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard Reevaluationorientation angle of 187° produced the greatest total rainfall volume for the drainage basin(Figure 7).The centroid of the PMS obtained from HMR-52 was moved in 2-mile in~crements to obtain thePMF which produces the maximum reservoir elevation. The reservoir elevation was calculatedusing the level pool routing option in HEC-1 (dated February 1, 1985) assuming an initialreservoir elevation at 800.0 ft msl (full pond). The results indicated that the PMS with centroidat X=1 0.3 miles and Y=9.0 miles is the PMF.It was not necerssary to perform a separate regional unit hydrograph analysis for the PMF studybecause of the availability of a state-wide study performed by the USGS (Bohman, 1989). ThePMF study utilized available hydrologic data from gauges in the vicinity of the study area andderived regional regression equations for unit hydrograph lag time. Dimensionless unithydrographs were developed for the two major physiographic regions in the study area (ie.,,Blue Ridge and Piedmont). An independent review of the unit hydrograph _analysis andverification study was performed by Clayton Engineering.In review of the existing FERC PMF analysis, the effectiveness of the gated spillway structureand two hydro turbines at discharging the estimated PMF inflow was considered. Lake Keoweehistorically has not experienced significant floating debris field problems over the 40+ yearssince impoundment. The shoreline is stable and~debris is managed to facilitate boating activityon the reservoir. Due to the layout of the spillway structure and the relatively low velocity profilein the two reservoir arms during a natural flood~event like the PMF, floating debris is notanticipated to become a problem that could significantly impact the effectiveness of the fourspillway gates.The PMF outflow hydrographs and corresponding reservoir levels are shown on Figure. 8. Theoutflow hydrograph is a product of the inflow hydrograph, reservoir storage, and dam operation.The PMF produced a peak inflow of approximately 332,721 cfs, The estimated PMF peakdischarge is 139,961 cfs. The PMF peak reservoir (headwater) is approximately 808.9 ft mslresulting in 6 ft of margin between the peak flood elevation and the top of dam at 81 5*ft msl.21 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard ReevaluationFigure 6. Keowee watershed sub-basins0 ___ £ I 6 60 IMkI22 Duke Energy Carolinas, LIC [ ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard ReevaluationFigure 7. Table 6.2 PMS from HMR 52 which generates PMFI-y~mesas 44010 9105 tOt 4001-2.mw~o 4145

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• f( #J (Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard ReevaluationFigure 8. Keowee PMF hydrographs24 3G 38 42 46 54 60 66 12 78 84 80 86Th~o 0u.)2.2.2 Probable Maximum Flood -JocasseeThe PMF has been evaluated in accordance with current engineering guidelines for Jocassee; aFERC-licensed and regulated hydroelectric development (#2503). The peak reservoir elevationfrom that analysis is 1 +122 ft msl based on hydrologic and hydraulic modeling performed inaccordance with Chapters II and VII! of the FERC guidelines using l-MR51i52 for the PMPdevelopment and HEC-1 for the hydrologic and routing model. The spillway, pump-turbines,and dams at the Jocassee Development have been designed to pass the PMF with adequatefreeboard and structural stability factors to safely accommodate the effects of the PMP. Table 6summarizes the normal and PMF freeboard for the dam structures that impound LakeJocassee.Table 6. Jocassee Dam -Normal and probable maximum flood freeboard (ft)Reservoir Elevation(ft ras!)Top of Dam Elevation ' ..Full Pond PMFDam Structure (ft msl) (1,110.0) -(1,122.0)Jocassee. Dam 1,125.0 15.0 3.0Dike 1 1,125.0 15.0 3.0Dike 2 1.,125.0 15.0 3.0Generalized all-season estimates of PMP for the Jocassee watershed were obtained from HMR51. Following procedures given in HMR 52, a set of DAD curves (Figure 9) was prepared for24 LNm roll Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTScin2 -Floodng Hazard Reevaluationthe Jocassee drainage basin using th all-season PMP charts published in HMR 51 and thebasin centroid location. The PMP depths in inches ware for storm durations ranging from 6 to72 hours and for storms smaller and larger in area than the drainage basin. The HMR 52computer program was used to calculate the PMS in each sub-basin in the watershed. Theaverage PMS depth over the entire watershed was 36.41 inches in 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Average sub-basin depths ranged from 38.32 inches near the centrold to 25.91 inches near the periphery.The USACE computer program HEC-1 was used to calculate the inflow hydrograph to Jocasseereservoir. For the computer model the Jocassee Lake watershed was conceptually subdividedinto 42 separate basins (Figure 10). The lag-times calculated for each sub-basin and the SCSdimensionless unit hydrograph were used in HEC-1 to compute synthetic unit hydrographs. Thedirect runoff hydrographs for each sub-basin were calculated by computing rainfall excessdepths at each time step using the SOS ON Method and then applying these depths through theunit hydrograph procedure. The series of hydrograph combinations and stream routings wascontinued until a total inflow hydrograph was computed for the Jocassee reservoir. Channelrouting was performed using the HEC-1 normal depth routing option. Stream channel cross-sections were obtained from 7.5-minute series USGS topographic maps for the watershed.Figure 9. Jocesses PMP DAD curves PMP depth vs. Area4a4aU1S I...- jI III ~w',,,,,,,,,, I*1 S I'0 st -1tUGSThe SOS runoff ON was used to estimate infiltration rates during design rainfall events. Thehydrologic soil group for the watershed was estimated based on studies of soil types usinggeneralized state soil maps for South Carolina and North Carolina. The soils in the watershedgenerally fall into the "B" hydrologic soil classification. The watershed soil cover is basicallyforest in good hydrologic condition. These factors lead to the selection of a runoff CN equal to55.25 Duke Energy Carolinas, ILLC ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard ReevaluationIn 1993, Duke Energy conducted a sensitivity analysis of the watershed by assuming anequivalent uniform infiltration rate of 0.093 inch/hour and back calculating a CN of 60 using theSCS CN formula. This parametric study indicated that varying the CN did not result in anysignificant changes in the peak stage.There are no continuous recording rainfall or stream gauges in the Jocassee watershed thatwould allow computation of a unit hydrograph for the basin. This fact required the use ofsynthetic unit hydrographs to model the watershed rainfall/runoff response. The Kirpich methodwas used to define the hydrograph lag-time in all of the Jocassee watershed sub-basins.26

..... .iu w u~.. .. ... ......... ..... u~uI~pwr1U I.#K 1-m,'Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard ReevaluationFigure 10. Jocass.. watershed sub-basinsThere are four reservoirs within the watershed upstream of Lake Jocassee: the Bad Creekpumped storage reservoir, Fairfield Lake reservoir, Sapphire Lake reservoir, and Lake Toxawayreservoir. The following setins describe the assumptions that were included in the HEC-1model for reservoirs upstream of Jocassee.Bad Creek Pumoed Storaoe ReservoirReservoir storage and elevation vary considerably over the course of a week. The iniJtialconditions assumed to apply to this lake at the time of occurrence of the design storm werebased upon an average storage of 16,565 acre-feet (ac-if) at a lake elevation of 2,269 ft msl.The surface area of the lake at this elevation is 0.29 square miles and the drainage into the27 Duke Energy Carolinas, lIC I oNs FLOODING REEV'ALUATION Section 2 -Flooding Hazard Reevaluationreservoir is very small at 1.39 square miles. The principal means of outflow from the reservoir isthrough four pump-turbines, which have a combined discharge capacity of 8,000 cfs. The EastDike was designed 2 ft lower than the Main and West Dams as an emergency spillway. Therock-fill design of the East Dike would provide protection from erosion due to overtopping. The2-ft design height difference, storage, and 4-pump-turbine discharge provide adequate marginfor a site PMP. The reservoir operation is-modeled by assuming no outflow up to an elevationof 2,310 ft msl at which point the four pump-turbines start discharging at a constant rate of 8.000cfs. The HEC-1 model also provides for dam overtopping using the East Dike if the watersurface elevation rises to the crest elevation of 2,313 ft msl; however, this elevation was notreached in the simulation. Bad Creek is capable of safely passing the sub.'basin specific inflowassociated with the Jocassee PMF by a combination of storage and discharge.Fairfield Lake ReservoirThe Fairfield Lake Dam was built in 1895. Under present state and federal criteria, theappropriate spillway design criteria are one-half PMF and full PMF, respectively. The USAGEPhase I inspection report indicates the dam will be overtopped for both the one-half and fullPMF (USAGE PMF= 14,800 cfs) by 3.4 ft and 5.2 ft, respectively. The normal pool and spillwayare both at an elevation of 3,155 ft msl. The dam crest is at an elevation of 3,159.6 ft msl. Theonly discharge from the dam is through a double arch culvert spillway with a pipe or box of 6-ftnominal radius. The total storage capacity of the reservoir at the top of the dam isapproximately 1,040 ac-ft. Breaching of this reservoir at 0.5 ft of overtopping was simulated inthe HEC-1 model.Sapphire Lake ReservoirThe normal pool elevation is 3,100 ft msl and the lake at this elevation covers 46 acres. Two36-inch-diameter concrete pipes are employed for discharging low flows. In the Jocasseewatershed model, the Sapphire Lake Reservoir is modeled with discharges through both thelow-flow concrete pipes and dam overtopping along the concrete masonry crest. No dambreach formation was assumed. Sapphire Lake Reservoir is capable of safely passing the sub-basin specific inflow associated with the Jocassee PMF by a combination of storage. anddischarge.Lake Toxawav ReservoirThe normal pool elevation is 3,000 ft msl with a lake covering 514 acres. The dam has a side-channel spillway that is 115 ft wide. One 48-inch-diameter gated pipe with a crest elevation of 5ft below normal pool is used for low flow discharging. The Lake Toxaway Reservoir wasmodeled by considering the discharge through the side-channel spillway only. Lake Toxaway iscapable of safely passing the sub-basin specific inflow associated with the Jocassee PMF by aCombination of storage and discharge.Lake Jocassee ReservoirThe normal pool elevation varies between 1,108 and 1,110 ft msl within the week, but themaximum power-pool during the hurricane season is 1 ,108 ft ms!. All four pump-turbines wereassumed to be available to pass flood flows during the PMF. The constant four pump-turbine28 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard Reevaluationdischarge is approximately 28,000 cfs. BOth Tainter gates were assumed to be fully functionalduring 'the PMF.The spillway rating curve for the ogee was computed using standard methods,, accounting forabutment and pier energy losses. These discharges were then combined to produce thereservoir outflow rating curve. The 1,110 ft msl initial water level elevation selected for modelingis somewhat higher than the maximum power pool level of 1,108 ft that historically occurs duringthe hurricane season. Storage-elevation values are calculated by HEC-1 using the conicmethod based upon the elevation versus water surface area relationship.In review of the existing FERC PMF analysis, .the effectiveness of the ability of the JocasseeDevelopment to pass the PMF was evaluated by reviewing the installed equipment to pass flow,lake level monitoring equipment, procedures to anticipate and respond to storm events, andmaintenance practices to ensure that equipment will be reliable.The H EC-1 model was used to test the sensitivity of availability of the two spillway gatescombined with four pump-turbines where different combinations of pump-turbine availabilitywere examined. These simulations show that adequate margin to pass the PMF is proVided bytwo gates' without pump-turbines. The two 30-ft by 38-ft-wide radial gates have a proven recordof reliability throughout the Duke Energy fleet due to the simple and effective design. There arefour different ways to operate the gates including: the normal installed electric motor, backup airdriven motor operation, backup electrical generator driven motor operation, and manualoperation with a hand wheel. All equipment for the four diverse methods of operation is locatedat the spillway gates. Personnel are trained and procedures are used to direct the requiredactions. Reliability is also assured through a comPrehensive periodic maintenance program asrequired by FERC including an annual test to open the gates and 5-year full open testing. Ampreadings for the motors provide readings to verify that the spillway gates are functioning asexpected.In addition to having reliable spillway gates, the four pump-turbines provide significant additionalmargin for protection against overtopping. A conservative assumption was made that based onmaintenance and operational procedures only two of the four hydro units will be available topass flow. This, in addition to the spillway gates, yields additional margin.Spillway gate operation and unit operation were evaluated for the impact of debris. LakeJocassee historically does not have significant floating debris due to the stable Shoreline, and adebris management program is in place to facilitate boating activity on the reservoir. Thespillways and intake structures are also protected by the submerged openings of the spillwayand intake structures. The PMF event in an impounded reservoir results in a low velocity profilein the reservoir during a natural flood event which limits the generation and transport ofsignificant debris.Monitoring and control of the reservoirs is assured by redundant level measurement in thereservoir and tailrace. Multiple video cameras provide redundant means to vedify and monitorlevels. All level monitoring including level alarms is provided to both the control room op siteand to a central hydro control station that is staffed 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> per day.29 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORT_Section 2 -Flooding Hazard Reevaluationinventory control for storm events is managed through a combination of 15 ft of minimumreserve freeboard and procedures to anticipate major rain events. Weekly rain forecasts areprepared by Duke Energy and system operations of Bad Creek, Jocassee, and Keowee arecoordinated based on the forecasted rainfall for thie basin. This planning provides additionaltime to manage reservoir levels to anticipate large precipitation events like the PMF. HydraFleet Central Operations Center procedures require consideration for lowering reservoir levelsin anticipation of significant storms. For normal operation, the weekly projection and dailylhourlyprecipitation monitoring has resulted in no precipitation-based spillway operations at Jocasseeover 40+ years of operation.The HEC-1 Jocassee watershed PMF modeling results were developed for each sub-basinincluding the five reservoirs. All reservoirs except Fairfield Lake were capable of safely passingthe sub-basin specific inflow associated with the Jocassee PMF by a combination of storageand discharge. The modeling showed Fairfield Dam overtopped during the PMF; but due to thelimited storage behind the dam (1,040 ac-ft at top of dam), breach inflow to Jocassee wasmanaged through storage and discharge.The PMF Outflow hydrographs and corresponding reservoir levels are shown on Figure 11. Theoutflow hydrograph is a product of the inflow hydrograph, reservoir storage, and dam operation.The PMF produced a peak, inflow of approximately 522,734 cfs. The estimated PMF peakdischarge is 85,405 cfs. The PMF peak reservoir (headwater) is approximately 1,122.0 ft msl.Overtopping of the Jocassee Dam is not considered a credible event due to the multiple anddiverse means of passing water and the large margin of storage capacity associated with thereservoir.!30 Duke Eneg C.anroinasm, LLC I ON FLOODING HAZARD REEVALUATION REPORTScon2 -Floodng Hazard ReevaluationFigure 11. Jocasseoo IPMF hyclrogrphs44004 II14,,* -m4-es.4*6166 -340004li o( 4%311111241110IlliI'.i'IDO ila4 qu .u'~ -"at'l2.3 Dam Failures2.3.1 Potential Dam FailureThe Keowee Hydroelectric Development is owned and operated by Duke Energy, and is part ofthe Keowee-Toxaway Project licensed by the FERC. The Keowee-Toxaway Project includesthe Jocassee Pumped Storage Development and the Keowee Development. The FERCregulates the Project and their role includes regulatory oversight of all water-retaining structuresat both developments. The ONS is located on Lake Keowee adjacent to the Keowee Dam andtailrace.Dam failures at the Jocassee and Keowee Developments have been examined for potentialimpact at ONS. The loss of Lake Keowee initiated by a failure of the Keowee Dam waspostulated as a design criteria event that was focused on cooling water supply and not on adam failure initiating event. Based on a review of the UFSAR, modeling performed between2008-2011 to respond to the August 15, 2008 10CFR 50.54(f) information request and theJanuary 28, 2011, NRC Staff Assessment of Duke's response to the Confirmatory Action Letterregarding Duke's commitment to address external flooding concerns, it was determined that ahypothtical fair-weather failure of the Jocassee Dam and a resulting cascading overtoppingfailure of Keowee Dam would be the enveloping critical dam failure event for ONS.31 n -"v ....... , ......... f.. .A ....; ..t ......>..... L1 -..... Z m ..Z. ZZ~v Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSrn~ian 2 -Flooding Hazard Reevaluation2.3.2 Dam Failure PermutationsFERC regulations require that dams for which failures pose a risk to human life be designed tosurvive a combination of loading conditions including forces from water and seismic eventswithout risk of failure. Both the Jocassee and Keowee Dams were designed, constructed, andare maintained to high standards and have performed in accordance with these stringentstandards for over 40 years.Consideration of upstream dam failure initiating events criteria as described in ANS 2.8 will bediscussed in the following sections including hydrologic event dam overtopping failure, potentialseismic loading induced dam and water-retaining appurtenances failure, fair-weather pipingdam failure, surge and seiche, ice-induced flooding, tsunami and channel diversion.2.3. 2. 1 Potential Hydrologqic OvertoppingAs a result of reviewing the dam structures at Jocassee and Keowee for criteria outlined in ANS2.8 for design basis floods and comparing to the design basis requirements required by theregulating agency, FERC, it was determined that the Jocassee Development and KeoweeDevelopment have adequate margin to meet the criteria for overtopping and stability as requiredby NTTF Recommendation 2.1. Both Jocassee and Keowee can safely pass their respectivePMFs without overtopping as described in Section 2.2.2.3.2.2 Potential Seismic FailureThe Jocassee Dam is a robust rock-fill dam that is designed to be stable under site-specificseismic loading. Deformation along the respective slip planes at the Maximum Section andAbutment Section is insignificant and would not result in a breach failure of the dam. Thepostulated seismic-induced failure of any of the water-retaining appurtenant structures at theJocassee Dam site was compared to the bounding case fair-weather failure of the JocasseeMain Dam presented in the Flood Hazard Reevaluation Report (FHRR). The appurtenantstructure peak discharge and reservoir volume release, due to the postulated seismic-inducedfailure, is significantly less than the fair-weather failure of Jocassee Dam. Therefore, theJocassee Dam fair-weather failure and resulting flood inundation at ONS presented in the ONS-2.1 FHRR is affirmed as the bounding case for external flooding at ONS.Duke Energy performed new seismic analyses for the Jocassee Dam as requested by a March20, 2014, Request for Additional Information to update the previous analysis initially submittedin the FH-RR. Duke Energy performed a new combination deterministic/probabilistic analysis perthe guidance provided in JLD-ISG-2013-01 to determine the dam factor of safety anddisplacements at the ground motion response spectrum (GMRS) level. A series of slope stabilityand dynamic response analyses were performed for representative slip surfaces (slidingmasses) of the maximum and abutment sections of Jocassee Main Dam. For the post-earthquake loading condition, the calculated downstream and upstream slope stability factors ofsafety are above 1.5 and 1.6, respectively for both sections. The calculated earthquake-induced displacements for representative sliding masses of both sections are insignificant (lessthan 0.1 cm or 0.04 inch). Since the calculated post-earthquake slope stability factors of safetyare well above 1.0 and the estimated earthquake induced displacements are relatively small,32 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard Reevaluationthe Jocassee Main Dam is expected to perform satisfactorily following the design earthquakeground motions considered. No fragility level was calculated.2.3. 2.3 Site Geoloqy CharacteristicsThe .Jocassee Dam site is underlain by gneiss bedrock. The weathering profile of the rockconsists of residual soil (saprolite) transitioning with depth to less weathered materials andfinally to the unweathered rock itself. The foundation of the maximum section of the dam wasexcavated to expose a zone (layer) of weathered rock overlying sound rock. The shear wavevelocity of these materials was estimated from field measurements in the gneissic rock at theOconee Nuclear site.Figure 12 shows the coordinates used to perform a site-specific probabilistic seismic hazardanalysis (PSHA) for Jocassee. Geologic information in this area is provided for two individualsoil profiles, "JD-I" and "JD-5". These profiles are combined into a single composite profile,"composite profile 1", for the site-specific PSHA that was performed. Figure 13 shows shearwave velocities of JD-1, JD-5, and composite profile 1 versus depth relative to the control pointelevation (CPE) of each profile. The CPE of JD-1 is 690 ft msl and JD-5 is 840 ft msl.33 Duke Energy Carollna.. LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard ReevaluationFigure 12. Map of Jocassee Main Dam location showing Latitude and Longitude. North is to the top of the figure.. ...t t ih il Om~.ONOCw~Un~34 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard ReevaluationFigure 13. Composite profile 1 representing geologic conditions below the control point elevationat .Jcse Dam (LCl, 2014). Profiles JD-1 and JD-5 are Individual profiles at Jocse fromAMEC (AMEC, 2014b) that are combined into composite 1. "Lower" and "Upper" profilescorrespond to the lower-range and upper-range cases, respectively, to capture epistemicuncertainty In mean shear wave velocity per the SPID (EPRI, 2013a).Vs (ft/sec0 2000 4000 60 8000 10000o II2060~ I~'80II1Q0IS160 1 pe18035 Duke Energy Carolinas, LLC IONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard Reevaluation2.3.2.4 Seismic Hazard Methodoloqy DescriptionThe methodology used to calculate site-specific probabilistic seismic hazard analysis (PSHA) atJocassee is documented in Lettis Consultants International (LCI) (LCI, 2014) and followsSeismic Evaluation Guidance: Screening Prioritization and Implementation Details (SPID; EPRI,2013a) and Regulatory Guide 1.208 (USNRC, 2007). The process involves:1. Perform PSHA for hard-rock conditions at Jocassee using:* Central and eastern United States (CEUS) seismic source characterization, CEUS-SSC (2012);* EPRI (2013b) CEUS ground motion prediction equations (GMPEs);* A revised seismicity catalog for select sources that removes several earthquakesidentified as reservoir-induced seismicity and aftershocks related to the Charlestonevent (Youngs, 2014);2. Determine the frequency- and amplitude-dependent site response (median values andstandard deviations) for all spectral frequencies of interest using the results of step 1;3. Perform PSHA for soil conditions at Jocassee using:* CEUS-SSC (2012);* EPRI (201 3b) CEUS GMPEs;* A revised seismicity catalog for select sources that removes several earthquakesidentified as reservoir-induced seismicity and aftershocks related to the Charlestonevent (Youngs, 2014);* Determine the site response.2.3.2. 5 Seismic Hazard for Hard-Rock ConditionsThe procedure to develop probabilistic site-specific control point hazard curves for hard-rockconditions follows the methodology described in Section 2 of the SPID (EPRI, 2013a). Thisprocedure computes the site-specific bedrock hazard curve for each of the seven spectralfrequencies for which ground motion equations are available.CEUS-SSC background seismic sources within a 400-mile (640 kin) radius of Jocassee wereincluded. This distance exceeds the 200-mile (320 kmn) recommendation of USNRC (2007) andwas chosen for completeness. Background sources included in this site analysis are thefollowing:* Atlantic Highly Extended Crust (AHEX)* Extended Continental Crust--Atlantic Margin (EGGAM)* Extended Continental Crust--Gulf Coast (ECCGO)* Illinois Basin Extended Basement (IBEB)* Mesozoic and younger extended prior -narrow (MESE-N)* Mesozoic and younger extended prior -wide (MESE-W)* Midcontinent-Craton alternative A (MIDCA)* Midcontinent-Craton alternative B (MIDCB)* Midcontinent-Craton alternative C (MIDCC)* Mldcontinent-Craton alternative D (MIDCD)36

...... .° ... ... .. .... ~.... ... .... .. ..FF .......~Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard Reevaluation* Non-Mesozoic and younger extended prior -narrow (NMESE-N)* Non-Mesozoic and younger extended prior -wide (NMESE-W)*] Paleozoic Extended Crust narrow (PEZN)[] Paleozoic Extended Crust wide (PEZW)[] Reelfoot Rift (RR)* Reelfoot Rift including the Rough Creek Graben (RR-RCG)*] Study region (STUDY R)For sources of large magnitude earthquakes, designated Repeated Large MagnitudeEarthquake (RLME) sources in CEUS-SSC (2012), the following sources lie within 1,000 km ofthe site and were included in the analysis:[] Charleston[] Commerce*] Eastern Rift Margin Fault northern segment (ERM-N)*] Eastern Rift Margin Fault southern segment (ERM-S)[] Marianna*] New Madrid Fault System (NMFS)*] Wabash ValleyFor each of the above background and RLME sources, the mid-continent versions of theupdated CEUS EPRI GMPEs were used as well as a lower-bound moment magnitude of 5.0.2.3.2.6 Site Response AnalysisSite effects are accounted for using 1-D equivalent-linear analysis of a Soil profile representativeof the geologic conditions at Jocassee Dam between bedrock and the CPE. Two borings atJocassee are combined into 'composite profile 1', (Figure 13). This profile is randomizedaccording to the recommendations of Appendix B of the SPID (EPRI, 2013a) to account foraleatory and epistemic variability as they relate to shear wave velocities, layer thicknesses,equivalent-linear material properties (shear modulus and damping), and depth to bedrock. Thedynamic response of each randomized profile is then determined using random vibration theory(RVTI) for a number of input control motions developed from the hard-rock hazard calculated instep 1 at a range of PGA amplitudes. The re'sults of this analysis yield site amplificationfunctions (median and standard deviation) for a range of frequencies and amplitudes which areincorporated into the following site-specific PSHA.2.3.2. 7 Seismic Hazard for Soil ConditionsThe procedure to develop probabilistic site-specific control point hazard curves used in thepresent analysis follows the methodology described in Section B-6.0 of the SPID (EPRI, 2013a).This procedure (referred to as Method 3) computes a site-specific control point hazard curve fora broad range of spectral accelerations given the site-specific bedrock hazard curve and site-specific estimates of soil, soft-rock, or firm-rock response and associated uncertainties. Thesame seismic sources (background and RLME) are incorporated as specified above for hard-rock hazard. This process is repeated for each of the seven spectral frequencies for whichground motion equations are available. The dynamic response of the materials below the37 m L iDuke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSedion 2 -Flooding Hazar Revuationcontrol point is represented by the amplification functions described above. The resulting controlpoint mean hazard curves for Jocassee are shown in Figure 14 and the corresponding uniformhazard response spectra (UHRS) are shown in Figure 15. Figure 14 (LCI. 2014) shows meanseismic hazard calculated for a range of spectral frequencies and amplitudes at the Jocasseedam site (Jocassee).Figure 14. Site-specifIc mean soil hazard curves for seven spectral frequencies at Jocassee (LCl,2014).1E-3Ii1E-41E-S-25 Hz-10 HzS5Hz-PGA-25 Hz-1 Hz,,,-0,5 Ha1E-61E-70.010.11Spectral acceleration (g)10Note: g -the acceleration due to Earth's gravity. feet per second squaredHz -counts per unit of time, the SI unit for frequency is hertzFigure 15 (LCI, 2014) shows horizontal mean UHRS for mean annual frequencies ofexceedance (MAFE) of 10.4, 105 and 104 at Jocassee using control point elevation (CPE)information provided in AMEC (AMEC, 201 4b).38 Duke Energy Carolinas. LLC I ONS FLOODING HAZARD REEVALUATION REPORTStoi2 -Flodng Hazard RevaluationFigure 15. Horizontal mean UHRS for MAFEI of 104, 10"', and 104 at Jocassee (CId, 2014).10.*iM(u.0.1-1E-6-IE-5-1E-40.01o01S0~100Frequency, Hz2.3.2.8 Seismic Performance EvaluationSeismic performance evaluations were completed on two representative sections of JocasseeMain Dam including the right abutment section (looking downstream) located at Station 8+00and a maximum section located at Station 12+00. Site-specific seismic ground motion timehistories were used to evaluate the selected representative cross sections. In accordance withthe combined events flood hazard evaluation guidelines in ANS 2.8 and NUREG7046, the site-specific SSE used for the analyses is consistent with the UHRS defined at a mean annualfrequency of exceedance of 10-4.This spectrum was calculated from a PSHA conducted by LCl(LCI, 2014), and further subdivided into high-frequency (HF) and low-frequency (LF)components based on hazard deaggregation per USNRC Regulatory Guide 1.208 andNUREG/CR-6769. Three sets of three-component time histories for the LF spectrum were usedto analyze the dam. In addition, the Jocassee appurtenant water-retaining structures (SaddleDikes 1 and 2. gated spillway, and intake tower/powerhouse water conveyance system) wereevaluated to determine their respective potential seismic-induced failure discharge and reservoirvolume release and associated inundation potential at ONS for comparison with the FHRRbounding case Jocassee Main Dam fair weather breach. The appurtenant stutres arelocated at various distances away from the Main Dam and their assumed failure dischargeswould not contribute to a failure of the Main Dam. The design of the appurtenant structuresconsidered seismic loadings; however for this evaluation, failure of the structures was assumed.The results and conclusions are summarized in the respective seismic performance andappurtenant structures sections.39

...........,S nut alnoru .. .:~ i. I. ... ,.. *z ~Duke Energy Carolinas, LIC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard Reevatuation2.3.2.9 Seismic PerformanceTwo specified rivers and stream combination loading-conditions: were considered in the seismicdam performance .evaluation consistent with ANSI/ANS-2.8-1 992, Section 9.2.1 .2 (Seismic Dam-Failures).. The two loading alternatives are defined as: ...Alternative 1 -Combination of, ., A 25-year flood* A flood caused by damnfailure resulting .from a safe shutdown earthquake (SSE), andCoincident with the peak Of the 25-year flood, and* Waves induced by 2-year wind speed applied along the critical direction.Alternative 2- Combination of* The lesser: ofone-half of the PMF or the 500-year flood* A flood caused by dam failure resulting from an operating basis earthquake (OBE), andcoincident with the peak of the flood selected above, where the OBE is defined as halfthe SSE defined above, and* Waves induced by 2-year wind speed applied along the critical direction.Alternatives 1 and 2 require the combination of a hydrologic event and a triggering seismicevent for the evaluation of the water-retaining structure. The hydrologic event is. assumed toincrease the loading on the structure. A hydrologic and hydraulic (H&H) evaluation wasperformed to determine the peak Jocassee reservoir elevation associated with a 25-year (24-hour) flood event, 500-year (24-hr) flood event, and one-half of the PMF. The results of theH&H evaluationwere added to the dam stability evaluation to support the SSE .and OBE seismicperformance review of JocasSee Dam. The results of the H&H evaluation indicate the 25-yrflood does not result in an increase in reservoir elevation and the 500-yr inflow is less than thehalf PMF inflow. The 25-year flood event Peak elevation is the-normal maximum reservoirelevation at 1,110.0 ft msl and the corresponding 500-year flood event peak elevation is 1,1-11 .5ft msl. These results assume operator action to control the level by running the Hydra units topass water downstream utilizing current Hydro procedures.Seismic performance for the respectiVe Jocassee: Dam sections (Maximum and Abutment) wasevaluated by performing a suite of geotechnical analyses that included a static stress, slopestability and dynamic stress/deformation analysis. These analyses represent currentgeotechnical practice for dam seismic stability evaluations and include:* The static stress, analyses were performed using SIlGMAIW, a finite element softwareprogram for stress ,and deformation analyses of earth structures,* The dynamic response analYSes were performed using QUAD4MU, a computer programfor evaluating the seismic response of soil structures using finite element procedures,* The slope stability analysis was performed using' software UTEXAS4, and* Deformation analysis is performed using s~ftware TNMN to calculate the displacementof potential sliding mass using the Newmark method. The Newmark method assumesthat the potential, sliding mass underlain by a well-defined slip .surface is rigid and theyield acceleration is constant. The Newmark method utilizes double-integration of the40 Cu.iiaiue, SIbiuvu-flIurmaUaf; wi~nno~u Tr-m pUDIC per iu v..;oJa~tJUiOJ(1Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORT', ~Section 2 -Flooding' Hazard Reevaluationdifference between the horizontal acceleration and the horizontal yield acceleration ofthe sliding mass.Eleven slip surfaces were identified for each section of Jocassee Dam, five slip surfaces for theupstream slope and Six slip surfaces for the downstream slope. The slip surfaces evaluatedinclude variable slip surface thickness (shallow, mid-depth, and deep) and heights of the dam,and were selected to represent various, sliding modes based .on engineering experience withsimilar structures. Acceleration time histories were developed specific to the Jocassee Damsite to match the 10-4 horizontal and :vertical low-frequency UHRS. The acceleration timehistories (design earthquake ground motions) correspond to the Safe Shutdown Earthquake(SSE). The dynamic response analyses are performed for six combinations, of horizontalcomponent (Hi, H2) and vertical (V) acceleration time histories. The resulting seismicperformance evalUation identified insignificant deformation (less than i ft)of the dam structurethat would not result in a condition that would lead to the breach of the dam.2.3.2.10O Appurtenant StructuresThe methodology employed to evaluate the combined effects flooding impacts at ONS due tothe seismic loading failure of a water-retaining appurtenance structure at the JocasseeDevelopment is based on estimates of the peak discharge and volume release for eachappurtenant structure. Four water-retaining appurtenances were identified by reviewing projectdrawings and the available FERC Supporting Technical Information Report including theregulating agency probable failure modes These appurtenant structures are allindependent structures from the main dam. The two saddle dikes, the gated spillway and thepower production water conveyance sYstem were identified for assumed failure and dischargeanalysis. Estimates of the peak discharge~and volume release were. developed and compared tothe fair-weather failure of the Jocassee Main Dam presented in the March 2013 FHRR. Reviewof the H&H analysis indicated there was not a significant difference between the 25- and 500-yrflood loading conditions and reservoir volume; therefore, the analysis focused on review of thepotential discharge from a postulated failure of each of the appurtenance structures. Acomparison of the size of the four appurtenant structures to the Jocassee Main Dam was madeand resulted in the estimation that the peak failure release from an appurtenance wasapproximately 6 percent of the fair-weather dam failure discharge presented in .the FHRR. Thepercentage of released Jocassee reservoir volume, following a potential seismic event for theindividual appurtenant structure failures is in the range of 6.5 percent to 39.1 percent of theJocassee reservoir and is dependent on the particular invert elevation of the appurtenantstructure. The-observance of an uncontrolled release from any of the appurtenant structureswould result in an operator declaration of a condition "B". This, is procedurally mitigated in thesame manner as a declaration of a Condition "B" for the main dam. Condition "B" is procedurallydefined as a situation where failure may develop, but preplanned actions taken during certainevents (i.e., major floods; earthquakes, etc.) may prevent or mitigate failure. The potentiallyhazardous situation may allow days or weeks for response and time to take remedial action.The following volumetric comparisons of the appurtenant structures and the Keowee Reservoir=provide additional assurance and conservatism that the structures are not thecontrolling case for external flooding at ONS. Each of the two spillway gates at Jocassee are 38ft wide and 33 ft high. The available area for release through these structures is less than that of41

~nta..... :lrit; v: :t:. l .*tiv .i~ pll~giJ r.,, I i ; V.I;NrDuke ,Energy Carolirnis, LLC I ONS FLOODING HAZARD REPORTSection 2 -Flooding Hazard Reevaluationthe four spiliway gates at Keowee which measure 38 ft wide and 35 ft high each. (ReferenceSTI No. 2503-JO-01 Jocassee Development and STI No. 2503-KW-01 Keowee Development)Additionally the uncontrolled flow that could potentially pass through the power production waterconveyance system at Jocassee, approximately 28,000 cfs, is significantly less than thecapacity of the four spillway gates at Keowee. At full pond Keowee reservoir elevation (800 ftmsl), the spillway discharge of a single gate fully open is nearly 28,000 cfs. The availablevolume of water that could potentially be released by a coincident failure of both saddle dikes atJocassee, assuming erosion scours down to the partially weathered rock (PWR) layer, isapproximately 282;063 ac-ft. This breach volume is less than the available storage volume ofLake Keowee between elevation 800 ft msl and top of dam elevation 815 ft msl, approximately303,738 ac-ft, taking no discharge capacity credit for the spillway gates or flow through theKeowee power prodUction Water conveyance system.2.3.3 Unsteady Flow Analysis of Potential Dam FailuresSince a seismic failure of the Jocassee Dam is not credible, a postulated non-seismic failure ofthe Jocassee Dam is assumed in order to demonstrate the corresponding flood hazardpostulated at the ONS site. This section summarizes the resulting flood wave andcorresponding flood elevations at the ONS site. To simulate a potential fair-weather failure ofthe Jocassee Dam, an unsteady flow model of the Jocassee/KeoweelHartwell reservoir systemwas developed using the USAGE HEC-RAS (Version 4.1) program. HEC-RAS is a 1-0dynamic flow model with unsteady flow model components used in estimating inundation due tohypothetical dam failures.The HEC-.RAS Jocassee-Keowee Dam Breach Model (ONS 1-D Model) was developed toinclude additional Lake Hartwell detail and cross-section refinement of Lake Keowee,. includingthe Keowee River, Little River,"and the connecting canal sections of the reservoir. The ONS 1-0 Model includes:* Reservoir storage volume;* Manning's n value sensitivity;* Routing of water flow at Keowee Dam (breach and overtopping) to the Keowee tailrace;* Tributary and storage area flood routing;* Additional dam failures (ONS Intake Canal Dike, Little River Dam); and.* River routing to tie the ONS Intake Canal Dike and Little River Dam outflow back intoKeowee River.HEC-GeoRAS Version 4.2.93 was used to develop model geometry independent of HEC-RASusing available GIS data from the State of South Carolina (with some overlap into Georgia) tocreate Digital Elevation .Model (DEM) electronic files for Jocassee, Keowee, and Haftwellreservoir~systems. A small portion of the lower southwestern corner Of Lake Hartwell wasmodeled using the USGS National Elevation Data Set (NED) to develop the storage volume.The completed electronic geometry files were then imported to HEC-RAS,The ONS 1-0 Model consists of the Jocassee, Keowee, .and Hartwell reservoir systems with. anapproximate length of 44 miles. The hydraulic responses of three, reservoirs comprising 1742

~. oi=u ou u.iy eauuv i,,.u,,,,ouur,, wi,,,uuiu ,,w,, =JUusI. i .m, ;,~£.g'FU~ISDuke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard Reevaluationriver/tributaries are incorporated in the ONS 1-0 Model. An independent peer review wasperformed on the geometry of the ONS 1-P Model, unsteady flow boundary and initialconditions, and results. The ONS 1'D Model's complexity and detail required numerous modelsensitivity runs in order to optimize the ONS 1 -D Model's performance and stability.Additionally, a TUFLOW FV 2-0 hydraulic model was developed to simulate the complex flowpaths moving between the Keowee and Little River arms of Lake Keowee including the ONSIntake Canal and Dike that abuts the ONS site at the south forming an island during damn breachsimulations. The 2-D analysis was performed to add detail the HEC-RAS analysis and modelthe potential inundation in critical areas identified around ONS. A 2-D computational model wasconstructed with a domain of the area immediately surrounding ONS with a 2-0 mesh. Themesh size'was selected to model the desired area while keeping the size of the computationalarray at a manageable size and facilitate the analysis within the time frame of the study andwithin the computing power of current, publically available micro-computers. Tables and graphsreferenced in this section can be found in Appendix 0.Using an uncoupled 1-D model to inform both the upstream and downstream boundaries of the2-D model requires that the results of the 2-D model at the boundaries be compared with the 1-D model and differences resolved. This process~was described .in the independent peer review(Wilson-201 3). The 1-D (or the 2-0) model cannot be independently calibrated and validated asthe modeled case is hypothetical and has an extremely low probability of occurring.Additionally, since the Jocassee and Keowee reservoirs were impounded in the early 1970s,Jocassee Damn has never discharged water through the gated spillway and Keowee has rarelyoperated the Spillway gates to discharge precipitation runoff. The maximum spillway dischargefrom Keowee occurred in August 1994 as 'a result of Tropical Storm Beryl. The total dischargefrom the spil!way was approximately 54,000 cfs which was contained within the downstreamriverbanks.The 2-0 software has been validated against several test cases including cases with unsteadyand complex hydraulic phenomena. The inputs into the current 2-0 model do not fall outside ofthe acceptable range, and the grid is considered fine enough ensuring losses are calculated asaccurately as the model will allow. The 2-0 model was used to inform user-defined coefficientswithin the 1-D mOdel in areas that the 1-0 model assumption "is stretched". This was done inareas with rapidly expanding or contracting flow. 'The 2-0 model does not have user-definedexpansion or contraction coefficients that are included in the calculation of :losses like the model does. The 2-0 equations rely more on solving flow physics and less on, user-definedcoefficients. As the model development process unfolded, the 1-D model was brought intoalignment with the 2-0 model at the boundaries by better informing user-defined coeffcients inareas where the 1-0 model assumption was ustretched".The flood wave associated with the fair-weather piping breach failure of Jocassee Dam has fourpotential routes to the Three of the routes are associated with high water surfaceelevations within Lake Keowee, while the fourth route is associated with the Keowee Riverbelow Keowee Dam. The first route is located at the ONS discharge outlet that adloins the right.abutment of Keowee Dam. Water could flow over the parking lot adjoining the ONS dischargestructure and through the road leading to the Yard. Thle second route is associated with the43 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection'2- Flooding Hazard ReevaluationEnergy Center swalethat adjoins the SC 130 bridge crossing of the Keowee Lake-ConnectingCanal. The third route is associated with the overtopping of the north face of the ONS intakeCanal Dike. The fourth route is, associated with the rising Keowee Dam-Keowee River tailwaterdue to a cascading failure of Keowee Dam.Unsteady flow requirements in HEC-RAS require detailed inputs that describe boundaryconditions and initial conditions at the first upstream cross-sections and ONS 1 -D Modelendpoint. In addition, boundary conditions are presented at internalmodel locations such asspillway'gates and hydroelectric turbines at the respective *hydrauliC.structures.The initial base flow conditions Utilized for the ONS 1-D Model are presented in Table D-1.These flows were developed to represent a "normal" (i.e., non-flood) condition that would allowthe ONS 1-0 Model to maintain normal conditi~ons at each of the modeled facilities, prior tO therouting Of the dam failure hydrographs.Total spillway discharge capacities for the Jocassee and Keowee Developments are provided inthe FERC Supporting Technical Information documents. The total spillway discharge capacityof the Hartwell Dam was provided by the USACE. The family of curves for various gateopenings and heads utilized in the model were developed by HDR based on the provided totalspillway discharge capacities for each development. The discharge from all hydro units utilizesrating curves at the respective developments with open/close operation based on reservoirelevation settings.The gated Spillway at Keowee Dam uses reservoir elevation settings for their respectiveoperations. The spillway gates at Jocassee Dam were included in the model setup; however,operation is not simulated during the ONS external flooding event (breach of JocaSsee MainDam) and the gates remain clOSed.Jocassee Development ONS 1-D ModelOperating rules for the two spillway Tainter gates are included in the model based on:* Open gates at a rate of 1 minute per foot; all gates fully opened in approximately 33minutes.* Maximum gate opening of 33 ft.Note: The gate operating rules were not initiated for the simulation of the fair-weatherJocassee* Main Dam breach.Keowee Development ONS 1-D ModelThe four spiliway Tainter gates are operated based on:* Flood operating procedure (non-preemptive operations) -initiate gate operations oncethe reservoir elevation reaches an elevation of 801 ftrnsl.* During Jocassee Development failure scenarios, gates start opening as soon as achange in reservoir elevation at the Keowee Dam is detected.* Open gates at a rate of 45 seconds per foot; all gates fully opened in approximately 23minutes, if needed.44¸ S. ..t ... .. ,.............. ; .i..... r.,1,,,, ; ,,,,,, .. 1; 77 ;.3rR Duke Energy. Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection Flooding Hazard Reevaluation* Maximum gate opening of 35 ft.Hartwell Development ONS 1-D ModelThe 12 spillway Tainter gates are' operated based on:* Flood operating procedure (non-preemptive operations) -initiate gate oPerations oncethe reservoir elevation reaches an elevation of '665 ft ins!,* During preemptive gate operations, gates begin opening 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after breach of the dam*of interest is initiated.* Open gates at a rateof 10 minutes per foot; all gates fully opened in approximately 6.5hours, if needed.* Maximum gate opening of 35.5 ft.The noted starting reservoir elevations at the Duke Energy and USACE developments(Jocassee, Keowee, and Hartwell) correspond to each facility's respective normal maximumpool elevation, and are provided in Table D-2.Based on prior Jocassee-Keowee Dam breach modeling, the hypothetical fair-weather failure, ofJocassee Dam produces a flood wave that creates conditions for a cascading failure of KeoweeDam and, potentially, the cascading failures of the ONS Intake Canal Dike and Little River Dam.Model Breach ParametersThe breach geometry and reservoir storage volume along with the type of breach failure are the primary parameters used to determine time-to-failure and peak breach discharge .values fromtypical embankment dam~breach r'egression methodologies. For the reevaluation of potentialinundation at~the ONS due to' dam failure, the assumed initiating mechanism is the uncontrolled .internal piping of embankmentrmaterials. Overtopping as the result ofa basin-specificprecipitation event is not considered credible due to the design .of the structures and theavailable hydrologic and hydraulic-information referenced in section-2.2.Section '7 of the NRC's Interim Dam failure Staff GUidance (JLD-ISG-1 300-01) documentreferences' several regression methodologies that have been developed to estimateembankment dam breach parameters' and potential peak discharge from the developed breach. iThe regression methodologies investigated to support-the development of breach parameters inanalyzing the downstream impacts at the Duke Energy ONS include: Froehlich 1 995a, 1 995b,2008; Waider and O'Connor 1997; MacDonald and Langridge-Monopolis 1984 and Von Thun and Gillette 1990.Dam breach' parameters are required-at a given dam structure to simulate flood routing from thereservOir into the downstream reach beloW the structure. The contributing outflow from thebreached structure is typically called the breach outflow hydrograph. The breach parameters foran earthen structure are typically defined by a trapezoidal~channel having a prescribed bottombase width and side slope. The breach development phase is'different~ for piping failures andovertopping failures. Piping failures are defined: by the establishment of flow patterns throughembankments, abutments, or foundations that create an orifice channel that continues tocollapse until the final crest portion of the embankment section collapses and forms .an openchannel. Overtopping'failures considered in the flood hazard reevaluation are attributed to Duke Energy Carolinas, LLC IONS FLOODING HAZARD REEVALUATION REPORT-. Section 2 -Flooding Hazard Reevaluationembankment crest, slope, or embankment toe Scouring due to high overtopping velocities basedon a cascading darn failure scenario where the downstream dam is overtopped from anupstream dam failure. Change in embankment slopes (intermediate bench or abrupt changes atthe toe of the slope) create ideal locations for relative energy dissipation that can result inscouring. Scouring leads to the phenomena called embankment head cutting. Sustainedovertopping from rapidly rdsing reservoir levels cap lead to further UPstream embankment head-Cutting migration until the crest and upstream embankment Slope are compromised and~an openchannel develops. Outflow from the overtopping of the dam continues to increase rapidly duringthe breach development phase. The breach development time ends When the breach reachesits final size,Breach parameter development for the Jocassee Dam andKeowee Dam structureS followedtwo different patterns due to dam design and construction. The zoned rock-fill construction andsize of the Jocassee Dam is :significantly different than the dams that were,,.used to develop thereferenced dam failure regression equations. The Keowee Dam. is a well-constructed,homogenous earth-fill dam that is more representative of the type of'dam referenced in thedevelopment of the referenced regreSsion equations. Duke Energy Performed dam breachparameter research specific for application at the Jocassee Dam and Keowee Dam andcommissioned independent assessments by dam engineering professionals to provide aprofessional opinion on the application of the PrOPOsed breach parameters for Jocassee andKeowee Dams. Due to the complex nature of these breach analyses, several modelingmethods (regression, physical, and hydraulic) were considered to arrive at a conservative, yetplausible, solution. The empirical methods used were compared to actual dam breaches that fallwithin the range of each dam's physical characteristics. Where needed, parameter constraintswere applied to the chosen regression parameters in Order to arrive at a reasonable estimate ofthe breach characteristics.. Considering regression and physical analyseS methodologies,plausible and conservative values for breach width and formation time were chosen..These/Values were used in HEC-RAS to develop the outflowhydrograph from the dams. Multiplebreach patterns were analyzed using HEC-RAS in order to determine the sensitivity of thebreach Outflow hYdrograph to the various breach parameters.Keowee Development Breach ParametersDuke Energy provided the Keowee Dam breach parameters to Ehasz and Bowles (2013) for aprofessional assessment and opinion on their applicability at Keowee Dam. The modeledbreach parameters and failure time were determined by Ehasz and Bowles (2013) to be,"realistic but conservative" for the cascading failure of Keowee Dam., An additional review of theKeowee Development breach parameters was conducted by an independent FERC board ofconsultants (BOC) (three geotechnical engineering experts and one hydraulics expert) to reviewgeotechnical, hydraulic aspectsof breach consequences, and flood mitigation modifications atthe ONS site. The BOO concluded the dam breach parameters Were conservative but realisticfor the overtopping event. The modeled Keowee breach parameters are presented in Table D-3.The Keowee Dam is approximately 3,500 ft long land is comprised of the Main Dam and WestSaddle Dam '(WSD). The WSD is approximately,2,100 ft long and varies in height from 20 ft tot55 ft with a minimum creSt elevation of 815 ft msl, The WSD is exposed to the Same48 Duke Energy Carolinas, LLCI ONS FLOODING HAZARD REEVALUATION REPORTSecton 2- Flooding Hazard Reevaluationovertopping characteristics and failure potential as the Keowee Main Dam. HEC-RAS is limitedto a single dam breach designation. Therefore, to overcome this model limitation, a breach ofthe WSD was simulated using a 1,880-foot by 20-foot crest gate in the Joc~assee-Keowee DamBreach Model. The ONS 1-D Model is assigned a full crest gate opening time frame of 30minutes to simulate the WSD breach development. The crest gate does not begin to open untilthe reservoir elevation exceeds 817 ft msl.The default sinusoidal wave breach progression provided in HEC-RAS, Figure D-l, wasdetermined to be reasonable by Ehasz and Bowles (2013) and approved for application at thethree Keowee Development dam structures by Duke Energy.The time varying topography feature of TUFLOW FV was used to implement the breaches ofthe Keowee Dam, West Saddle Dam, ONS intake dike, and the Little River Dam. A sinusoidalbreach progression which was Consistent with the HEC-RAS analysis was defined for thebreach geometry in Table D-3. The bottom width, bottom elevation, and the geometry of theright and left side slopes are defined every 5 percent of the breach time fraction (resulting in 21inflection points on the sinusoidal breach curve). Using the breach progression curve, a timeseries of modeled elevations for each cell within the breach was then defined. The breach eventis triggered when the water surface at a designated point for each embankment is exceeded.Then a new bed elevation is calculated by the model and updated. A linear interpolation isperformed between the 21 points of the sinusoidal breach curve.Jocassee Damn Breach ParametersThe breach parameter selection process for JocaSsee Darn is outlined in detail in AMEC'sJocassee Dam Breach Parameter Analysis report dated December 2014 (AMEC, 2014a) whichdeveloped a refined set of dam breach parameters applicable to Jocassee Darn using guidanceprovided in the JLD-ISG-201 3-01. A summary of the breach parameter development processfrom the AMEC analysis states the following:The Von Thun and Gillette breach equations were found to be most suited for thebreach parameter analysis Of Jocassee Dam based on a linear trendline ofaverage breach widths vs. reservoir Volume.Comparing the HEC-RAS Sensitivity analYsis to the empirical breach flowpredictors, direct use of the dam breach parameters produced by the Von Thunand Gillette equations resulted in an over-prediction of peak outflow leavingJocassee Dam during a failure. The sensitivity analysis and~ research shows thatthere are several justifiable ways to adjust the peak outflow produced by HEC-RAS for the particular breach event. The key to a realistic peak outflow lies inthe breach progressiOn pattern used in the ONS I1-D Model.The breach progression pattern developed uses the NWS BREACH progressionpattern as a base with different aspects of the pattern modified to account for thephysical characteristics of Jocassee Dam and Reservoir. Figure D-3 presentsthe original NWS BREACH progression and the modified progression.47t usauy oe,,siu.ve Inrormau:on; wimnoid from pulblic per 10 CFR 2.390(d)(1) :'Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard ReevaluationThe breach initiation phase was not altered from the NWS BREACH modelbecause this is a subjective area in the development. For a large volumereservoir such as Jocassee the pool level will not drop significantly duiqthebreach initiation phase. The breach development time was extended tID()FZZbased on the Von Thun an for failure time. The time toempty reservoir was extend]ed [o to account for the continuation ofbreach growth until the reservoir is fully drained. The rate of breach formationafter the development time is generally proportional to the depth of water in thereservoir at each time step in relation to the final pool level.Comparing the sensitivity runs to the outflows a breach formed to nearly 100percent during the development phase over-predicts outflows by as much as 200percent. Considering the size and low erodibility of, n..--Dam, the breach:b)(,)(F) .. ....................progression~owas-adjusted-.os o p re tat mark (after thebreach initiation and development phases). As a result of sntvianalysis onbreach development time, the breach development was limited tclijpercent-...................during the formation which allows the peak outflow to align with historical data.Because the breach is assumed to occur against one of the abutments (based ongeologic features) it was assumed that the breach growth would be limited by theabutment in one direction. As previously mentioned, in the case of Teton Damwhere the breach occurred against the abutment, the chosen regression methodover predicted the breach a minimum of 152 percent. For this analysis:t)(7)(F) ........-..... the breach widthi-was-~imited-tcJLlpercent of the total width predicted by the VonThun and Gillette equations which is considered conservative in this case.The final Jocassee Dam breach parameters utilized in the ONS 1-0 Model are presented inTable 7.Table 7. Final Jocassee Dam Breach ParametersFinal JOcassee barn Breach ParametersTop Width 959 ftBottom Width 634 ftSide Slopes 0.5H: 1VFinal Bottom Elevation 800 ftBreach Development Time to Peak Outflow io)(7)IF)Full Formation TimeTime to Empty ReservoirComputed Peak Outflow at Jocassee Dam _________The breach progression for the Jocassee Dam required the development of a site-specificmodified sine wave. Table 8 provides the recommended breach progression ordinates for theONS 1-D Model.48

.Gm.u, iy ;IiUIIIldLI~II, wiI.hIOuu 11,01,, puu~II pe iv AU I) ""Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORT Bll 1Section 2 -Flooding Hazard ReevaluationTable 8. Final Jocassee Dam Breach Formation Pattern (HEC-RAS Input)Time Breach Time; Time, Breach(h) Fraction Fractionl JJhr Fraction 'Fraction-(b)(7)(F) 0.0000 0.000o b(7(F 0.2236 0.79640.0028 0.0032 0.2486 0.81 330.0047 0.0063 0.2736 0.82890.0069 0.0102 0.2986 0.84330.0091 0.0144 0.3236 0.85680.01 16 0.0194 0.3486 0.86950.0139 0.0243 0.3736 0.88140.1234 0.7000 0.6036 0.99580.1256 0.7077 0.7599 0.99850.1486 0.7343 0.8816 0.99960.1736 0.7574 0.9536 0.99990.1986 0.7779 1.0000 1.0000The Jocassee Dam stage-discharge hydrographs, breach discharge, and modified sine wavebreach progression are shown in Figure D-2. The detailed site-specific, modified breachprogression and breach discharge are shown in Figure D-3.2-D ModelingThe 2-0 model domain includes the area immediately surrounding the station including the LittleRiver arm and the Little River Dam, shown in Figure 0-4. The results of the ONS 1-D Modelanalysis were extracted and utilized as boundary conditions for the 2-0 analysis. Version2014.01.007 of the computational hydraulic solver TUFLOW-FV was utilized to define theboundary conditions for the 2-D analysis based on the results of the ONS 1-0 Model analysis(BMT WBM 2014). TUFLOW FV solves the Non-linear Shallow Water Equations (NLSWE), alsoknown as the St. Venant equations, using a finite-volume numerical scheme. The code canprocess wetting and drying of mesh elements, steady and unsteady flows, and sub-critical andsuper-critical flows. It also includes hydraulic structures, time-varying bed elevations, and logiccontrols. It is parallelized to take advantage of running simulations on multiple centralprocessing unit (CPU) cores. User-defined logic controls allow for both time-varying bedelevations (i.e., breach development) and breach initiation to occur within the model.An explicit time discretization is used and an appropriate timestep is determined dynamicallybased on the Courant-Fredrichs-Lewy (CFL) condition, commonly known as the Courantnumber. A second-order, limited central-difference scheme was used for the spatialdiscretization for this analysis. Additionally, the code allows for a flexible, or "hybrid,"computational mesh, which may include both triangles and quadrilaterals. TUFLOW FV hasundergone extensive validation and benchmarking (BMT WBM 2013, N6elz and Pender 2013).The NLSWE are a system of equations describing the conservation of momentum and mass inan incompressible fluid under the hydrostatic pressure and Boussinesq assumptions. Thestandard form of the NLSWE is:49 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard Reevaluationau-+ v.F(u) = s(U)where F(U) represents the flux terms in the x and y directions and S(U) represents the sourceterms such as the gravitational force-and bed shear stress (BMT WBM 2013). The x and ycomponents of the inviscid flux (F') and viscous flux (F'> terms in the NLSWE are:hv [ -hK. o*where Kv is the horizontal eddy-viscosity term (BMT WBM 2013)., For this analysis, thteSrnagorinsky formula is used to calculate the eddy-viscosity. The Smagorinsky formula is:Ky .2 ,()2where C5 is the Smagordnsky coefficient and I! is the Smagorinsky length scale, which is relatedto the local mesh size (BMT WBM 2013).Boundary condition locations and types are shown in Figure D-4. A flow hydrograph taken fromthe Keowee River 3-38889 HEC-RAS cross-seCtion .was used ?for the 2-0 upstream boundarycondition. The boundary condition is approximately 1 .6 miles uPstream of, the Keowee Dam inLake Keowee. A stage .hydrograph taken from the Keowee River 6-23089 HEC-RAS cross-section was used for the Keowee River at the downstream boundary of the 2-0 model which isapproximately 6.6 miles downstream of the Keowee .Dam..The Keowee powerhouse andSpiliway discharges were imposed as internal boundary conditions to ensure consistency withthe 0NS 1-D Model which simulates gate flow and weir flow directly. Figure 0-5 shows the flow.hydrographs for the Upstream boundary and the internal powerhousetspillway boundary.Additional detail pertaining to the development of the internal Keowee powerhouse and spillwaydischarge boundary condition is provided below. Stage hydrographs for the downstream.boundary are shown in Figure D-6.The 2-D analysis was performed to add detail to the 1-D HEC-RAS analysis and simulatepotential :inundation in critical .areas identified, around ONS. The upstream flow boundary for the2-0 model was based on review of the 1-D Jocassee Darn breach flows routed from JocasseeDam to the Keowee Dam through the Keowee Arm of the Keowee Reservoir. The selection ofthe boundary, approximately 1.6 river miles upstream of the Keowee, was determined byexamination of the I1-D model output and through testing using the 2-D model and comparison*with 1-0 results. Using an uncoupled I1-D model to inform both the upstream and downstreamrboundaries of the 2-0 model requires the results of the 2-D model at the boundaries to be.compared with the 1-D model .and differences resolved. Grid refinement increases the ability ofthe. model to capture velocity gradients in the flow, and the grid Size was decreased to the levelthat was required to capture velocity gradients. The inflow boundary location Was selected50O

uu~nu..;u,.l, w;u;,;uuk; stu., pill.pu,, m.= u p)"Duke Energy Carolinas, LL.C !ONS FLOODING HAZARD REEVALUATION REPORT'Section 2 -Floodtng Hazard Reevaluationbased on a location that was far enough upstream to have a fully developed velocity distributionin the flow as it approached the Keowee Dam. The boundary lOcations and the grid size werealso selected based on balancing computational detail and reporting multiple cases within areasonable timeframe.Prior to beginning the unsteady simulation, the 2-0 model was run to a steady-state initialcondition consisting of a Keowee reservoir level of .800 ft msl and a discharge of 1,650 cfsflowing from the. Keowee Upstream inflow boundary to~the spillway outflow boundary. Below thedam, an inflow boundary, of 1,650 cfs at the sp~llway and a downstream water surface elevationof 660 ft msl at the downstream boundary, were used. The 800 ft msl represents the fullreservoir elevation of Lake Keowee and the 660 ft msl represents the full normal elevation of Hartwell Lake downstream of Lake Keowee..Time accurate conveyance of flow through Keowee Dam is important for the determination-ofproper headwater and. tailwater elevations prior to initiation of the dam breach,. The 2-D model isnot able to explicitly model the 1-0 flows through the ,powerhouse or sPillway gates in the sameway as .the ONS 1-D Model. As a result, a single discharge boundary was used to represent thepowerhouse flows, gated spillway flows, and the spillway overtopping flows (thatoccur whenwater elevations in the reservoir are generally higher than 815 ft msl). The initial overtoppingelevation at Keowee Dam is 815 ft msl. The powerhouse and gated spillway flows weredetermined from the time series data output by the ONS 1-D Model and the ,spillwayovertopping flows were calculated with the weir equation. Spillway flows in the 2-D model didnot include the ",gate flow"~ used to represent flows through the West Saddle Dam (WSD) breachin the ONS 1-0 Model. These flows were represented in the 2-D model using the samebreaching method as the main Keowee Dam breach.Flows through the spillway and .powerhouse were modeled by removing mesh cells from the.model domain at the outflow structure-location and assigning a subcritical outflow and inflowboundary-condition upstream and downstream of the outflow structure. The flow hydrograPh forthe Keowee Spillway boundary is included on Figure D-5. The TUFLOW FV software supports acontinuous update of the dam topography for simulating the breach of the Keowee Dam. Thisenhanced code feature facilitated a close breach formation simulation relationship between the2-0 and 1-D models that resulted ingood agreement of the dam breach hYdrographs betweenthe two models. .in order to improve model stability near the boundaries representing the spillway 'flow, theelevation of nodes approaching and adjoining the spillway were manually adjusted. Upstream ofthe spillwvay, mesh elevations, were lowered to 745 ft msl to increase the' cross-sectional area forthe outflow boundary ,upstream of the spillway. This prevented the flow upstream of the spillwayfrom becoming supercritical. Similarly, mesh node elevations immediately downstream of theinflow boundary representing flow entering the tailrace were adjusted to prevent, supercriticalflOW near the model boundary. These modifications had no effect on conditions near ONS.The channel bathymetry and land topography assigned to the computational mesh weregenerated Using a DEM created from digital data sources Using Geographic InformationSystems (GIS) software. Topographic data is from the USGS-NED and site survey data of the51

• oe~uriiy penszilve .nrormanion; wirnowo from puW~iG per 1u Id-K z.isuua,ll) " j'Duke Energy carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazai'd ReevialuationONS vicinity collected in 2010. Bathymetric data is from pre-impoundment 1 :24,000 contours forHartwell Lake and surveyed data collected, by Duke Energy in 2010 for Lake Keowee. Updatedbathymetric-survey information of the ONS intake canal gathered in 201.3 was used whereavailable. Topographic breaklines were enforced for the Keowee Dam, West Saddle Dam, ONSIntake Dike, and the Little River Dam. Additional breaklines were enforced for roadwayembankmnents and bridge approaches in the vicinity Of ONS.In the 2-0 model, Manning's roughness coefficients (Manning's n-values) were used torepresent the frictional resistance and energy loss in the flowing water. For this analysis, to theextent possible, the Manning~s n-values match the companion ONS 1 -D Model, whereManning's n-values were selected for the river cross-sections based on a review of topographicmaps and reference materials in Chow's "Open-Channel Hydraulics" (Chow 1988). Additionalsensitivity and assessment of Manning's n-values was performed and documented during theONS 1-0 Model development. Manning's n-values were primarily limited to two designations inthe model -floodplain and overbank (n = 0.08) and main channel (n = 0.025). The riprapinstalled for erosion protection along-the east side of the ONS yard was designated with aManning's n-value of 0.04. Figure D-7 depiCts the spatial extent of the Manning's n-values.Both the 1-0 and 2-D models were improved by utilizing appropriate results from one anotherthus bringing the models into close alignment. A series of model runs was performed to testperformance between the models; and adjustments were made that produced excellentcomparison and agreement and a high degree of confidence for using both models in thisevaluation. This is specifically true for the 2-0 model in areas of flow complexity and site-*specific details, such as the depth of inundation in and around QNS.2.3.4 Water Level at the plant SiteA comparison of model output results is presented in Table 9. The comparison details the highlevel of agreement between the 1-0 and 2%D models as well as the overall hydraulic impact onONS resulting from a poStulated fair-weather piping breach failure of Jocassee Dam coupled-with the cascading failure at Keowee Dam.As can be inferred from Table 9, the comparison of the 2-0 model results with the ONS 1 -DSModel results indicates that the timing of breach initiation (K~7(F oir reaching 817 ftmsl) occurs slightly earlier in the 2-D model wee DamJ Jafter the JocasseeDam breach, which can be compared to hou~i"' Ifor the ONS 1-D Model. The maximum waterin I peaks neal(x() , -in the 2-D model and(b)(7XF /in the oNs 1-0 Model. The ONS intake dike is not breached duringThe analysis as the intake canal water surface does, not overtop the structure. The maximum.water surfac eeainithitkeanal reache (fl)(7)(F) Iin the 2-0 modelcompared td(b)(7)(F La= Model. The maximum water sud, ......r." , bl(7(FI " i(b)(7)(F) ito in 'the Keowee tailrace area iq" ...un the 2-D model :compared tq, Jthe ONS 1-0 Model.' While this differece ofT. feet~is greater than th~e difference atother points, it is still a reasonable comparison considering the complex hydraulics;of theKeowee River south of ONS, location where the 1-0 and 2-D elevations were measured and52 OuuuIILy Illlaulnlmluull, Wiueuulu U ui.. Vuul;n,;aa ,, 1 .ZII.08vti 1)Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard Reevaluationmore specif ically the complex hydraulics that exist as the river channel meanders through theoxbow area known as Old Picken's Knob just east of the SCi 83 highway bridge.Dam breach inundation levels reached elevatior(b7')F) Iresulting in approximnately~F)!!Fof inundation above the nominal Yard elevation of 796 ft around the SSF.The comparison indicates that between the ONS 1-D Model results and the 2-D model resultsthere are no significant differences in the model results in terms of maximum stage reached andtiming in the reservoir. While the models do not produce the Same results, the trends in theresults between the models are generally, preserved. This agreement provides confidence inthe results of the simulations.Figures D-8A through D-10B illustrate the general flow patterns, depthadvlct~iesiaur' .-f~ ,,,f~e elevations (Figure B-Series) at time (t) =1brz)(F) .I,I~bX!)(! Iforthe modeled case over the 2-D model domain. The time (t) =1()(7)(F)nhasher breach is Keowee Reservoir reaches the peak elevationjust upstream of Keowee Dam, (t) .. Icusas the peak tailwater and ONS Yardinundation reaches the peak depth and (t) =1b()F Ioccurs after the breach and the peakfloWS have been conveyed through out the Study area and peak water surface elevations havereceded.The purpose of the 2-D model analysis was to provide estimates for the water depth and flow,velocity in the vicinity of ONS resulting from a postulated fair-weather failure at Jocassee Dam.Figure D-1 1 shows the location of monitoring locations that provide the basis for Figures D-12through D-16, which show the water depths and elevations upstream of Keowee Dam, Keowe&Dam tailwater, Visitor's Center Swale wall, ONS Intake Canal Dike, ~and the SSF, respectively.The Visitor's Center Swale wall is actually located Closer to the reservoir, since this area :is drymost of the time. The Yard. is potentially exposed to four inundation paths. The primary sourceas modeled is the Keowee Dam tailwater, while the Visitor's Center Swale wall, ONS dischargeoutlet and ONS Intake Canal Dike (because of their proximity to the Yard) could serve assecondary sources and are dependent on maximum post-Jocassee Dam breach reservoirelevations.Flooding at the ONS site is primarily caused b ib)(7X(F) Asathe predominant flow direction during initial inundation of the si (bx)(7F)I()7)(F) water surface elevations in Lake Koepaknear--~*in the simulation, asmall flood wave resulting.. in water ...depths of approximatel j1b(7(F) West SaddleDam (ONS discharge outlet path) and flows around the north side of the Administration building.The flood wave from this path does not reach the SSF. Likewise, there is no Yard inundationfrom the Visitor Center Swale wall and the ONS intake Canal Dike pathS because Keoweereservoir elevations do not overtop these structures.53 I-Y~oDuke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard ReevaluationTable 9. Comparison of 1-D and 2-D model results -time to breach and maximum water surfaceelevations (Elevation in ft msl and Time in hours)(b)(7)(F)* The ONS Intake Canal Dike crest is nominally at an elevation of 815 ft msl but has a wall builtalong the North End to provide protection from flood waters entering the Yard to an elevation of824 ft msl. Figure 0-14 and Table 9 indicate that the peak water surface elevation in the ONSIntake Canal Dike reacheL7°('F) imsl with a dike crest elevation oLEmsl.The Visitor's Center Swale wall is built to an elevation of 832 ft msl. Figure D-1 5 and Table 9indicate that the maximum water surface elevation reached at the Visitor's Center Swale wall is817.2 ft msl.The nominal elevation of the Yard is 796 ft msl. The Yard would be exposed to flooding viadownstream backwater from Keowee Dam (T0wtr.F~ue -13 and D-16 indicate that theYard would be approximately inundated to elevatior b)7)(F),iduring the modeleddam failure.54 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard Reevaluation2.4 Storm Surge and SeicheThe ONS site is located on an inland reservoir in the northwestern corner of South Carolina andis not subjected to storm surge or seiche flooding. surge and seiche flooding have beenreviewed in the FERC-required evaluation of the Keowee and Jocassee Developments and arenot considered credible events to produce maximum water levels at the site.A seiche caused by an earthquake or landslide is not considered credible based on thetopography and geology around the reservoirs.Storm surge events are not expected to affect the site. The maximum wave height and waverun-up have been calculated for Lake Keowee and Lake Jocassee using USBR 1981. The)results of wind-driven wave run-up using USBR Wind Velocity charts are as follows in Table 10:Table 10. Wind-driven wave run-up resultsLocation' Wave Height Maximum 'FetchKeowee Main Dam -Fair Weather 6.10 ft. 5.84 ft. 2.37 milesKeowee Main Damn -PMF 3.60 ft. 3.73 ft. 2.37 milesJocassee Main Dam -Fair Weather 6.48 ft. 7.09 ft. 3.04 milesJocassee Main Dam -PMF 3.80 ft. 4.47 ft. 3.04 milesThe results using ANS 2.8, 2-Yr Wind Velocity are as follows in Table 11:Table 11. 2-year wind velocity resultsLoc~ation .. Wave Height. .Wave Run-Up Maximum FetchKeowee Main Damn -Fair Weather 5.33 ft. 5.11 ft. 2.37 milesKeowee Main Damn -PMF 3.20 ft. 3.34 ft. 2.37 milesJocassee Main Dam -Fair Weather 6.10 ft. 6.66 ft. 3.04 milesJocassee Main Dam -PMF 3.80 ft. 4.43 ft. 3.04 milesThe wave height and wave run-up figures are vertical measurements above full pond or PMFelevations as tabulated above. The design normal freeboard at each damn is 15 ft which isadequate to prevent overtopping of wind-driven waves at both dam sites.The Keowee reservoir has not exceeded an elevation of 800.0 ft msl and the Jocassee reservoirhas not exceeded an elevation of 1,110 ft msl since construction was completed (approximately40 years).During combined events of a PMF and wind-driven waves, because of the time-lagcharacteristics of the runoff hydrograph after a storm, it is not considered credible that themaximum reservoir elevation due to PMF would occur simultaneously with winds causingmaximum wave heights and run-ups. Refer to Section 2.8 for an additional discussion ofcombined effects of a wind-driven wave impact combined with a PMF.55 Duke Energy Carolinas, LLC ONS FLOODING HAZARD REEVALUATION REPORTSection 2 -Flooding Hazard Reevaluation2.5 TsunamiSince the ONS site is not located on an open ocean coast or large body of water, tsunami-induced flooding will not produce the maximum water level at the site.2.6 Ice-Induced FloodingSince the ONS site is not located in an area of the U.S. subjected to periods of extreme coldweather that have been reported to produce surface water ice formations, ice-induced floodingwill not produce a credible maximum water level at the site and is not considered a realisticexternal flooding hazard to ONS.2.6.1 Ice EffectsLong-term air temperature records (1951-2011 ) available at the South Carolina StateClimatology Office were reviewed to assess historical extreme air temperature variations at theONS site. The analysis was also supported by onsite temperature data measured at the ONSsite.The climate at the ONS site is characterized by short, mild winters and long, humid summers.Local climatology data for Pickens County, South Carolina, for a period of 30 years show amean air temperature of 59.7O Fahrenheit.There has not been a recorded event of significant surface ice formation on Lake Jocassee orLake Keowee since filling in the early 1970's.2.6.2 Ice Jam EventsThere are no recorded ice jam events in the upper reach of the Savannah River based on asearch of the USACE's Ice Jam Database. Water temperatures in this area of the southeastU.S. consistently remain above freezing.2.7 Channel DiversionsDue to the location of ONS on the banks of Lake Keowee and the upstream topography of thereservoir, channel diversion is not a credible flooding event. The controlling external floodingevent is upstream dam failure.2.8 Combined EffectsSection 9 of ANS 2.8 outlines general criteria to be reviewed for addressing combined flood-causing events. Lake Jocassee and Lake Keowee are man-made impoundments located innorthwestern South Carolina protected from coastal events as well as extreme cold weatherevents. Both reservoirs are considered "enclosed bodies of water" as defined in ANS 2.8Section 7.3.3. Based on this definition and guidelines noted in ANS 2.8 Section 9.2.3.2 for thestreamside location of ONS, Alternative II was determined to be the most limiting case and wasused for reviewing the possible combinations producing maximum flood levels. This includes:56 Duke Energy Carolinas, LLC f ONS FLOODING HAZARD REEVALUATiON REPORTSection 2 -Flooding Hazard Reevaluation1. PMF.2. 25-year surge or seiche with wind wave activity.3. 100-year or maximum controlled level of water body, whichever is less.Damn failure as defined above in Section 2.3.1 was also reviewed.Combined flooding effects (PMP, PMF, dam failure and/or wind-driven waves) are concluded inTable 12. LIP was reviewed for the ONS site using a state-of-the-practice, coupled 1-D and 2-Dmodel, including reviewing water impounding on roofs of buildings, with and without sitedrainage features. Due to the detailed 2-D analysis, variable water surfaces were developed forthe entire Yard. The maximum elevation noted in Table 12 is for a single reporting point.Flooding in upstream reservoirs was reviewed using modern computer programs for hydrologyand hydraulics and the current HMR 51 rainfall. PMF flood elevations do not produceovertopping at Keowee or Jocassee. Dam failures were simulated for Jocassee and Keowee asdetailed in Section 2.3. The failure of Jocassee Dam the cascading failure ofKeowee Dam produced a flood inundation elevation ofb)(7)(") imsl. The breachinundation exceeds the Yard nominal elevation of 796 ~ft msl Stormsurge and seiche-generated waves were not considered a credible event for evaluation of anONS flood hazard. A combined event of the PMF plus wind-driven waves was reviewed forboth Keowee and Jocassee. As shown in Table 12, Keowee maintains approximately 2.8 ft offreeboard when combining the peak PMF elevation with wind-driven waves. A PMF forJocassee coupled with wind-driven waves (Section 2.4) would produce some lapping of wavesover the 20-ft-wide crest of the dam; however, due to the large riprap that comprises theupstream and downstream shell of the Jocassee rock-filled dam, the breaking of waves over thecrest of the dam is not expected to have any significant impact on slope stability.Table 12. Combined effects flood elevationsReevaluation C*ombinedReevaluation Combined Effects Effects Flood ElevationFlood Causing Mechanism Flood Elevation Keowee ~ JocasseelLocal Intense Precipitation 800.39 ft msl (Note 1) N/ARun-up______p__us___PMF__ ___ 12.2______t_____l__1126.4 ft mslTsunami _ __ __ _ __ _ _ __ _ _ N/A_ __ _ __ _N/AIce-Induced Flooding _____ /A__________N/AChannel Diversion N/A N/ANotes: 1 location of recorded maximum Yard elevation is based on location in Figure B-l, West 13.57 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 3 -Comparison of Current Licensing Basis and Reevaluated Flood-Causing MechanismsSection 3 -Comparison of Current LicensingBasis and Reevaluated Flood-CausingMechanismsTable 13 below summarizes the comparison of current licensing basis and reevaluated flood-causing mechanisms, which includes wind effect for flooding in reservoirs and dam failures.The table outlines a comparison for current licensing basis and reevaluated flood-causingmechanisms for the ONS site including the dam failure mechanism that considers thepostulated fair-weather piping breach failure of Jocassee Dam to be the enveloping dam failureevent.Table 13. Current licensing basis and reevaluation flood elevations'Curr ent Licensing, Reevaluation ReevaluationBasis Flood Flood Delta fromFlood-Causing MechaniSm Elevation, Elevation Lice nsing:'Basils800.39 ft mslLocal Intense Precipitation 798.17 ft msl (Note 1) +2.22 ft.Flooding in Reservoirs 808.0 ft msl 889ftml+.f.Dam Failures (Note 3) N/A (Note 4) __Note____ 2)_______Storm Surge and Seiche/Wind-WaveRun-up N/A N/A____N___ATsunami N/A N/A___NiA _Ice-Induced Flooding N/A N________/A _Channel Diversion N/A N/A N/ACombined effects N/A 812.2 ft msl N/ANotes:Location of recorded maximum Yard elevation is based on location in Figure B-i, West 132Location of recorded maximum inundation elevation is shown in Figure D-1 1, Keowee 1W3 Enveloping dam failure scenario is fair-weather Jocassee Damn and cascading Keowee Damn failure.SThere were no dam failures postulated in the original licensing/design case basis of the plant. On Jan 28, 2011 aSE was issued descr'ibing a new flooding hazard for the site. This is a Beyond design basis event. See Section 1.3for further discussion.3.1 Local Intense PrecipitationThe current licensing basis case ONS flood elevation from the LIP is 798.17 ft msl (Section 1.2).The Beyond design basis case reevaluated flood elevation is 800.39 ft mnsl, is 2.22 ft more thanthe current licensing basis flood elevation, and 3.89 ft above the elevation of safety-relatedSSCs of 796.5 ft msl. The elevation reported here is specific to the point near the Unit 1Reactor Building (West 13). Because of the detailed analysis using a 2-D model, waterelevations around the Yard vary significantly. Reference Table B-I for additional floodinundation elevations at selected points around the Yard.58 Duke Energy Carolinas, LLC I ONS FLOODINGHAZARD REEVALUATION REPORTsection.3 -Comparison of Current Ucensing Basis and Reevaluated Flood-Causi'ng Mechanisms-3.2 Probable Maximum FloodingThere is no current licensing or design basis ONS flood elevation from probable maximumflooding in upstream reservoirs with Coincident wave run-Up.'The reevaluated flood ,elevation is 808.9 ft msl or 812.2 ft ms! with coincidental wave run-up.The PMF elevation increased by 0.9 ft from the current flood elevation and does-not impactsafety-related SSCs.3.3 Dam FailuresThere are no current licensing or design basis ONS dam failure flood elevations.The reevaluated flood hazard elevation due to a combined Jocassee'and Keowee.amsflzaIilureassuming full reservoir elevations at the initiation of the Jocassee Dam breach i{j7~x) msl.This elevation is due to the initial failure by piping of the Jocassee Main Dam and thie Cascadingfailure of the Keowee Main Dam and West Saddle Dam due to overtopping. With the Yard at awnlelevation of 796 ft msl, this inundation Would produceaa depth of water approximatelyLZ) round the SSF .... .....3.4 Storm Surge and SeicheStorm surge and seiche are not expected to affect the site for the reasons listed above inSection 2.4.3.5 TsunamiTsunami-nduced flooding is not expected to affect the site for the reasons listed above inSection 2.5.3.6 Ice-Induced FloodingIce-induced flooding is not expected to affect the site for the reasons listed above in Section 2.6.3.7 Channel DiversionChannel diversions are not expected to affect the site for the reasons listed above in Section2.7.3.8 Combined EffectsTher~e are no current licensing or design basis combined site flood hazard ;effects. Combinedflooding effects are discussed in Section 2.8.59 Duke Energy Carolinas, LLC I ONS FLOODINGHAZARD REEVALUATION REPORT-Section 4 -Interim Evaluation and Actions Taken or PlannedSection 4- Interim Evaluation and .Actions Taken !or PlannedBased on the results listed above, only two of the flood-causing mechanisms produce floodwaters that could potentially impact the site; the LiP rainfall event and the combined Jocasseeand Keowee Dams failure.II.Actions have been taken for both the LIP event and the postulated fair-weather failure of theJocassee Dam. ONS was in the process of analyzing both of these flood hazards prior to therelease of the March 12, 2012, NRC 10 50.54(f) request for information.The reevaluated flood elevation for an HMR 51/52 generated LIP event is 800.39 ft msl. This is'2.22 ft more than the current licensing basis flood elevation, and 3.89 ft above the elevation ofsafety-related SSCso0f 796.5 ft msl.. The elevation repoi'ted here is specific to the point near theUnit 1 Reactor Building (West 13).The reevaluated flood hazard elevation due to a combined Jocassee and Keowee Dams failure,assuming full reservoir elevations at the initiation of the Jocassee Dam breach. in the Keowee tailrace and (b)7)( Imsl at the Standby Shutdown Facility (SSF.).The 2.1 Haztard Reevaluation has shown that the Beyond design basis flooding hazards for LIPexceeds the current licensing basis flooding levels. LIP maximum flooding levels are below theSSF flood walls and current'floodirng response procedures adequately address the floodingcaused by the new Beyond design basis event (BDBE). As such,-added interim actions are not !required to respond to the maximum LIP flooding levels.The flooding levels caused by an upstream dam failure are within the BOBE as defined'by"Oconee's Response to Confirmatory Action Letter (CAL) 2-10-003" issued to the NRC on'August 2, 2010 (ADAMS ML102170006). Compensatory actions that were completed inresponse to the June 22, 2010, Confirmatory Action Letter (CAL 2-10-003) will remain in placeUntil the CAL is super'seded by regulatory action related to the Fukushima response. Theexisting interim actions identified in CAL 2-.10;-003 are Sufficient in mitigating the effects offlooding as predicted in the FHRR.'60¸ Duke Energy Carolinas, LLC FLOODING H-AZARD REEVALUATION REPORTSection 5 -Additional ActionsSection 5- Additional ActionsEarly in 2012, a question arose about the LIP analysis for the Yard, which Was entered into theONS CAP. This led to a thorough investigation of the current status of various structures on siteand their ability to resist flood waters from an LIP event. A walkdown was performed for allClass 1 structures and other structures deemed critical to safe shutdown. The walkdownsurveyed the building envelope to identify weaknesses in flood protection. It was determinedthat ONS is in nonconformance with the Licensing Basis as described in UFSAR Section 3.4.1.1because water may exceed a 6-inch sill in a few areas surrounding the Class 1 structures. Allother areas surrounding the structures were determined to be acceptable. Interim actions weretaken in the form of adding Flood Barrier Sandbags and Gryff01yn coverings. These barrierlocations and heights are based on a preliminary analysis that was performed on local floodheights in the Yard. The LIP data discussed in Section 1.2.1 of this report finalizes andvalidates the concern from the preliminary analysis. The sandbag flood barriers continue toserve as an effective measure against the finalized current licensing basis LIP ONS submitted its Flood Hazard Reevaluation. Report to the NRC on March 12, 2013, pUrsuantto the NRC's 10 CFR 50.54 (f) letter. By letter dated March 20, 2014, the NRC submitted arequest for additional information regarding the FHRR consisting of 15 questions. Specifically,the last two questions were industry-wide requests. The revision and resubmission of theFHRR causes the need for ONS to revise the original response to PAI's 14 and 15. Theseresponses are presented below:5.1 RAI-14: Hazard input to the integrated assessment: Floodevent duration parameters

Background:

The March 12, 2012, 50.54(f) letter, Enclosure 2, requests the licensee toperform an integrated assessment of the plant's response to the reevaluated hazard if thereevaluated flood hazard is not bounded by the current design basis. Flood scenario parametersfrom the flood hazard reevaluation serve as the input to the integrated assessment. To supportefficient and effective evaluations under the integrated assessment, the NRC staff will reviewflood scenario parameters as part of the flood hazard reevaluation and document results of thereview as part of the staff assessment of the flood hazard reevaluation. The licensee hasprovided reevaluated 'flood hazards at the site including LIP flooding, probable maximumflooding on contributing watershed, flooding in streams and rivers, and flooding from breach ofdams. The LIP flooding is reported to exceed the current licensing basis and subsequently the*licensee has committed to perform integrated assessment.Request: The licensee is requested to provide the applicable flood event duration parameters(see definitiOn and Figure 6 of the Guidance for Performing an Integrated Assessment, JLDISG-201 2-05) associated with niechanisms that trigger an integrated assessment using the results ofthe flood hazard reevaluation. This includes (as applicable) the warning time the site will have toprepare for the event (e.g., the time between notification of an impending flood event and arrival61 Duke Energy Carolinas, LLCI ONS FLOODING HAZARD REEVALUATION REPORTSection 5 -Additional Actionsof floodwaters on site) and the period of time the site is inundated for the mechanisms that arenot bounded by the current design basis. The licensee is also requested to provide the basis orsource of information for the flood event duration, which may include a description of relevantforecasting methods (e.g., products from local, regional, or national weather forecasting centers)and/or timing information derived from the hazard analysis.5.1.1 Response to RAl-14RAI-14 is requesting flood event duration parameters including duration from the FHRR todefine key inputs to the Integrated Assessment. ONS has two external flooding events that areincluded in the FHRR that will be addressed in the IA. Below are the requested parameters foreach of the external flooding hazards:Upstream Dam ,Failure Flood Duration Parameters1. The warning time the 'site will have topeare for the event -Tewrigtime fora Sunny Day failure is assumed to be[l Ibased on a time after detection, an (b()(7)(F) Ibetween a significant pipe collapse in the JocasseeDam .(internal breach formation process) and downstream dam breach flood waters inthe Keowee Tailrace reaching the elevation of nominal site grade. 796 ft msl. Thisassumption is based on early warning due to an aggressive monitoring program for thedam and historical piping failures. The dam's early warning and monitoring programincludes seepage collection points that monitor flow volume and turbidity, regularlyscheduled visual walk-down inspections, forebay and talirace electronic level alarms,and 24-hour video surveillance of the dam and adjoining abutments that enhance earlydetection of unusual conditions including possible piping through the dam.2. The period of time the site Is inundated -The site grade at a nominal 796 ft msl isinundated by floodwaters from a fair-weather failure of the Jocassee dam forapproximatel (b)(7)(F) The period of time where the flood impacts the site belOwnominal site grade as defined by the overtopping of the Keowee dam until floodwatersrecede below the turbine building drain invert is aprxmtlF()F3.. The basis -or source of information for the flood event duration -The informationused to the duration includes the hydrograph for the breach and the HEC-RASmodel that routes the flood waters to the site and beyond.4. Relevant forecasting methods -FERC and NRC requirements for upstream dam1monitoring include video camera monitoring of the dam/abutments and at seepage leakoff points, forebay and tailrace alarms, 24-hour staffing at Jocassee and at HydroCentral, inspections immediately after receiving 2 inches or more rainfall, inspectionsfollowing any felt seismic event and weekly dam safety inspections. Monitoring and sitenotifications are included in Duke Energy Hydro and ONS procedureS.Local Intense Precipitation Flood Duration Parameters1. The warning time the site will have to prepare for the event -The major stormsthat have sufficient atmospheric moisture to deliver the 18.95 inches of rain can bereliably forecasted 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> in advance due to the size of the storms. The major, stormtypes that could contain sufficient moisture include Tropical Cyclones, Synoptic Storms,62 Ouke Energy Carolinas, LLCj ONS FLOODING HAZARD REEVALUATION REPORTSection 5 -Additional Actions;and. Mesoscale Convective Complexes. Isolated thunderstorms, do not have the abilityto approach LIP level rainfall events due to the location of ONS where no orographic liftis present.2. T[he period of time the site is inundated -The site Will start developing wateraccumulation in and around the power block early in the assumed 72-hour durationrainfall event as modeled using a two-thirds loaded distribution. Water levels areprojected to decline to nominal levels within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> after the rainfall has subsided.3. ,The basis or "source of information for the flood event duration -- The 72-hourevent was based on the event that Produced the most Conservative prec;ipitation for thesite drainage basin and the most conservative temporal distribution based on the resultsof the runoff model.4. Relevant forecasting methods -The forecasting for the LIP magnitude storms isbased on using the National Weather Service (NWS) Quantitative PrecipitationForecasts (QPF's) for medium range forecast and Probabilistic Quantitative PrecipitationForecasts (PQPF's) for shOrt- range forecast. A monitoring threshold Would be set basedon the appropriate level of extreme rainfall for the basin where the ONS is located. Sixinches in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is considered an extreme rainfall event With a return rate :of less thanI in 1000 years. This monitoring threshold would be applied to the medium forecastprior to the event. If this threshold is met based on medium range QPF forecaStS (3 to 7days prior to the event), the nuclear site would be notified by the fleet meteorologist(staffed 7 days a week) which would then initiate site monitoring once per shift asdirected by site, procedure. A mitigation action trigger would be established u~sing .the95th Percentile PQPF value of 6 inches in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> 'n the short-range forecast (Day 1).The action trigger is conservatively based on one-half the maximum historical 24-hourprecipitation event. When this trigger is met, the site would initiate flooding .responseactions 'including securing flood gates and doors. Using one-half of the 24-hour histOricprecipitation event provides a conservative trigger that will be activated well in advanceof a storm capable of delivering LiP rainfall of a more extreme value of 18.95 inches fora 1-hour/I-mi2precipitation event.The maximum historical precipitation event from 1973 to 2012 in North Carolina and UpstateSouth Carolina was 12.32 inches in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> occurred on August 27, 1995 (Tropical StormJerry) based on the highest recorded levels at Greenville, South Carolina: The highest 48-hourand 72-hour total for the same event was 14.47'inches. No consequential flooding resulted atthe ONS'site during this event.5.2 RAI 15: input to integrated assessment: Flood height andassociated effects

Background:

The March 12, 2012, 50.54(f) letter, Enclosure 2, requests the licensee to performan integrated assessment of the plant's response to the reevaluated hazard if the reevaluatedflood hazard is not bounded by the current design Flood: scenario parameters from theflood hazard reevaluation serve as the. input to the integrated assessment. To support effcientand effective evaluations under the integrated assessment, the NRC staff will review flood63 Duke Energy CarolinaS, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 5 -Adlditional Actionsscenario parameters as part of the flood hazard reevaluation and document results of the reviewas part of the staff assessment of the flood hazard reevaluation. The licensee has providedreevaluated flood hazards at the site including LIP flooding, probable maximum flooding oncontributing Watershed, flooding in streams and rivers, and flooding from breach of dams. TheLIP flooding is reported to eXceed the current licensing basis and subsequently the licensee hascommitted to perform integrated assessment.Request: The March 12, 2012, 50.54(f) letter, Enclosure 2, requests the licensee to perform anintegrated assessment of the Plant,'s response to the reevaluated hazard if the reevaluated floodhazard is not bounded by the current design basis. The licensee is requested to provide theflood height and associated effects (as defined in Section 9 of JLD-ISG-2012.-05) that are notdescribed in the flood hazar'd reevaluation report for mechanisms that trigger an IntegratedAssessment. This includes the following quantified information for each flooding mechanism (asapplicable):* Hydrodynamic loading, including debris;* .Effects caused by sediment deposition and erosion (e.g., flow velocities, scour):* .Concurrent site conditions, including adverse weather; and* Groundwater ingress.5.2.1 Response to RAI 15SThe mechanisms that exceeded the current licensing basis or design basis and triggered theintegrated assessment at ONS are the LIP event and the sunny-day failure of Jocassee Damand the cascading failure Of Keowee Dam.Local Intense PrecipitationHydrodynamic EffectsSection 2.1 and Appendix C of the FHRR provided detailed results (flood depths and durationsof inundation) at various locations throughout the site. Flow velocities from the 2-D model werereviewed at relevant door openings to safety-related structures to determine whether'hydrodynamic loading iS of concern at any of the critical locations. The results indicate thatmaximum velocities are generally below i ft/sec, With occasional exceedance at locations whereflow is constrained between twO buildings. Furthermore, the velocities reported by the model donot represent velocities at the maximum flood stage and the velocity'vectors are generally notorthogonal to the doors. Since hydrodynamic loads are a function of flow velocity and flooddepth, these toads are expected to be minimal and well within the margin of safety provided forthe respective flood protection features. ASCE/SEI 7-10 standard provides a recommended'approach for estimation of dynamic effects of moving water with flow velocities below 10 ft/sec.Based on this approach, dynamic effects of moving water can be converted into equivalenthydrostatic head by increasing the design flood elevation by an equivalent surcharge depth, dh,equal to dh Where V = average velocity of water in fl/sec, g = acceleratio~n due togravity, 32.2 ft/sec2, a = coefficient of drag The ayerage maximum velocity at ONS criticalstr~uctures is 1.13 ft/sec. Per F EMA 259, the most ConServatiVe coefficient of drag for building64 i.,onagns oecurity ,nrorinpUon; wImnno~u irom purnu pUr ,u £'.O3uIUd)i)FDuke Energy Carolinas,, LLC I ONS FLOODING .HAZARD REEVALUATION REPORT~~Section 5 -Additional Actionswidth/flood depth ratio is 2. Using these extremely conservative values, the equivalentsurcharge depth is equal only to 0.04 ft.Debris EffectsThe areas within the protected area that could potentially provide a source for debris are eitherpaved or covered with gravel or paved surfaces with little vegetation or loose materialsavailable. The protected area is also surrounded by vehicle barrier system and security fenceswhich would significantly minimize the potential for an~y debristo impact safety-relatedStructures. In addition, relatively low velocities would minimize the movement of debristhroughout the power block. Therefore, debris effects at ONS were considered negligible.Effects caused by sediment deposition and erosiOnAs described previously, the average maximum velocity throughout the power block is 1.13ftlsec, with a single highest velocitY' of 6 ft/sec. Since most areas within the power block arepaved, no erosion is expected. because maximum values of flow velocity that can be sustainedWithout Significant erosion are' an order of magnitude higher than the average maximumvelocity. The LIP event is a localized flOoding event, which is not expected to car'ry significantamount of sediment typical for riverine flooding. Therefore, sediment deposition at ONS wasconsidered negligible.Concurrent Site conditionsThe meteorological events that could potentially result in significant rainfall of the LIP magnitudeare squall lines, thunderstorms with .capping inversion, and mesoscale convective systems.These meteorological e~vents are typically accompanied by hail, strong winds, and eventornadoes.Groundwater IngqressThe LiP is a localized, short duration event, which is not expected to increase groundwaterlevels on site. Furthermore;, ONS is protected against groundwater ingress.-ySunny-day Failure of Jocassee DamI-Ivdrodynamic and Debris EffectsThe sunny-day failure of Jocassee Dam and the cascading failure of Keowee Dam results in.flooding hazard elevation of~b(;)F) n the tailrace. The flooding hazard elevation isabove the nominal elevation of the power block (796 if) and, therefore, safety-related structuresthroughout the power block will be affected by the associated effects Of the dam failure. Theresults of the 2-D modeling indicate that the. flow velocities in the Keowee tailrace immediatelydownstream Of the breach are approximately 40 ft/sec. TheSe high velocities are limited to areaswithin the immediate breach opening and dissipate to less than 30 ft/sec within 1,000 'ftdownstream of the main dambreach. These localized high velocities; will .result in significanthydrodynamic forces and debris Carried by the breach wave .and will result in impact forces onstructures located within the immediate breach inundation zone defined by the natural riversegment downstream of Keowee Dam leading into the upper reach of Lake, Hartwell, Becausethe exact flow paths for debris cannot be predicted, any structures located directly downstr'eamof the Keowee Dam breach, will be :considered lost due to hYdrodynamic and debris impact65 Duke Energy Carolinas. LLC J ONS FLOODING HIAZARD REEVALUATION REPORTSection 5 -Additional Actionsloads. Conversely, flow velocities adjacent to the Intake Canal dike and the east slope of thepower block are significantly lower (inundation due to backwater impacts) and do not exceed 4ft/sec.Concurrent Site ConditionsThe results of the FHRR indicate that all access routes from the southeast direction will beinundated during the event and existing infrastructure will likely be severely damaged due tohigh velocities and impacts from debris and mud flow.Groundwater InoqressGroundwater levels on site will not increase due to the sunny-day breach. Furthermore, ONS isprotected against groundwater ingress.66 Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORT,, ~Section 6 -ReferencesSection 6 -ReferencesAMEC Environment and Infrastructure, Inc. 201 4a.Jocassee Dam Breach Parameter AnalysisReport. Prepared for =Duke Energy Carolinas, LLC. November 24, 2014.*(2014b). Data for Site Amplifications-- Rev.i, Fukushima 2,1 Seismic ReevaluationProject, Oconee Nuclear Station, Sen~eca, SC, AMEC Project No. 6234-1t3-0075, Letterfrom J. Li and C. Sams to R. Keiser dated August 27, 2014.AmeriCan Nuclear Society (ANS). 1992. ANS-2.8-1992, "Deternmining Design Basis Flooding atPower Reactor Sites." 2.8 Hydrologic Dam Failures," Sections 5.1.3, 5.5.1, and 5.5.4.1992.BMT WBM. 2013. TUF!-OW FV Science Manual.BMT WBM. 2014. TU!FLOW FV User's Manual.Bohman, L.R. (USGS), Determination of Flood Hydrographs for Streams in~South Carolina:.Volume 1, Simulation of Flood Hydrographs for Rural Watersheds in South Carolina,Water Resources Investigations Report 89-4087, United States Geological Survey,SWater Resources Division, June 1989.CEUS-SSC Central and Eastern United States Seismic Source Characterization forNuclear Facilities, U.S. Nuclear Regulatory Commission Report, NUREG-21 15; EPRIReport 1021097, 6 Volumes; DOE Report#. DOE/NE-0140.Chow, Ven Te, Maidment, David R., Mays, Larry W., Applied Hydrology, McGraw Hill, I1988a.*1988b. Open-Channel Hydraulics. 3rd Edition. McGraw-Hill, Incorporated, New York,New York.Duke Energy, ONS Un~its 1, 2 & 3, Final Safety Analysis Report, Revision. 18, September 12,Units 1. 2 & 3, Updated Final Safety Analysis Report, Revision 1, June 25, 2012.Ehasz, P.E., Joseph L. and Bowles, P.E., Dr. David S., 2013. uJocassee and Keowee Dams,Breach Parameter Review." February 2013.EPRi. (2013a). Seismic Evaluation Guidance Screening, Prioritization and ImplementationDetails (SPID) for the Resolution of Fukushima Near-Term Task Force Recommendation2.1: Seismic, Elec. Power Res. inst. Rept 1025287, Feb..(201 3b). EPRI (2004, 2006) Ground-Motion Model (GMM) Review Project, Elec. Power'Res. lnst, Palo Alto, CA, Rept. 3002000717, June, 2 volumes.Federal Energy Regulatory Commission. 2007. Engineering Guidelines for the Evaluation ofHydropower Projects, Chapter VI, Emergency Action Plans, Office of HydropowerLicensing, Washington, D.C. October 2007.67 Duke Energy Carolinas, U.C I ONS FLOODING HAZARD REEVALUATION REIPORTSec~on 6 -References--1993. Engineering Guidelines for the Evaluation of Hydropower Projects, Chapter I!,Selecting and Accommodating Inflow Design Floods for Dams, Washington, D.C.October 1993.Froehlich, 2008. "Embankment Dam Breach Parameters and Their Uncertainties.' ASCEJournal of Hydraulic Engineering. December 2008. pp. 1708-1721.-- 995a. Dam Breach Parameters Revisited." Proceedings Of the 1995ASCE Conference on Water Resources Engineering, San Antonio, Texas. August. pp.887-891.-- 995b. "Peak Outflow from Breached Embankment Dam." Journal of Water ResourcesPlanning and Management, 121, no. 1, pp. 90-97.HDR. 2014. Oconee Nuclear Station, External Site Flooding Evaluation, Fukushimna *Study,Jocassee-Keowee Dam Failure Assessment, 1-D HEC-RAS Model. Report prepared forDuke Energy Carolinas, LLC. December 2014.LCI (2014). Project Report- Oconee Composite profile 1 (Jocassee Dam) seismic hazard usingthe CEUS seismic source model, Oconee Nuclear Station Hazard, OEP001-PR-03-Revi.MacDonald, T.C. and J.L. Langridge-Monopo!is. 1984. "Breaching Characteristics of DamFailures." Journal of Hydraulic Engineering, no. 110., p. 567-587.N~elz, S. and pender, G. 2013. Benchmarking the Latest Generation of 2D Hydraulic ModellingPackages, Report -SCi120002. UK Environment Agency. Horison House, DeaneryRoad, Bristol, BSI 9AH. August 2013.U.S. Department of Commerce, National Oceanic and Atmospheric Administration, U.S.Departmentof the ArmyNOAA Hydi'ometerologoical Reprot No. 52, Application ofProbable Maximum Precipitatio Estimates -United Steates Each of the i Otth Meridain.1982.U.S. Army Corps of Engineers. 2011. HEC-Ge0RAS GIS Tools for support of HEC-RAS usingArcGIS, Version 4.3.93. Hydrologic Engineering Center. U.S. Army Corps of Engineers,Institute for Water Resources Hydrologic Engineering Center, Davis, CA. February 2011.-.2010. "HEC-RAS, River Analysis System User's Manual, Version 4.1,;" HydrologicEngineering Center, January 2010...2010. HEC-1, Hydrologic Modeling System, Version 3.5.0, Hydrologic EngineeringCenter, August 20.10.-.Ice Jam Database, Total Number of Events Ranked by State,https:llrscqisias.crrel.usace.armv.millapex/f?p=2 73:39:1 4230682549501.68.

Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 6- -References1982- NOAA Hydrometeorological Report No. 52, Application of Probable MaximumPrecipitation Estimates -United States East of the 105th Meridian. U.S. Department ofcommerce, National Oceanic and Atmospheric Administration, August 1982..1978. NOAA Hydrometeorological Report No. 51, Application of Probable MaximumPrecipitation Estimates -Uni/ted States East of the 105th Meridian. U.S. Department ofCommerce, National Oceanic and Atmospheric Administration, June 1978.U.S., NUclear RegulatOry Commission. 2014. E-Mail, Request for Additional Information- OconeeFlooding Hazard Reevaluation Report (TAG NOS. MF1012, MFi013, AND MFi014),dated September 15, 2014, (ADAMS Accession No. ML142588222),,* Letter. 2014. Oconee Nuclear Station, Units 1, 2, and 3, Request for AdditiOnalInformation Regarding Fukushima Lessons Learned Flood HaZard ReevalUationReport (TAG Nos. MF1012, MFi01 3, and MF1014), dated March 20, 2014, (ADAMSAccession No. MLMLi 4064A59 1).*, 2013. "Japan Lessons-Learned Project Directorate .. .-....213 .1) Gudhc oAssessment of FlOoding Hazards Due to Dam Failure,. Interim Staff Guidance, Revision0. 2013.-. 2011i. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plantsin the United States of America, NUREG/CR-7046, Office Of Nuclear RegulatoryResearch, Richland, WA. NOvember 2011.*. 2011. Safety.Evaluation by the office, of Nuclear Reactor Regulation Related to DukeEnergy Carolinas, LLC, Confirmatory Action Letter -Commitments to Address ExternalFlooding Concerns, Closure of Inundation Site Results, Oconee Nuclear Station Units 1,2, and 3 (ONS), dated-January 28, 2011..2010. Letter From Luis A Reyes to Dave Baxter. "Confirmatory Action Letter -OconeeNuclear Station, Units 1, 2, and 3 Commitments to Address External!Flooding Concerns(TAC Nos. ME3065, ME3066 and ME3067)," dated June 22, 2010.*2008. Letter from Joseph G. Giitter to Dave Baxter, "Information Request Pursuant to10 CFR 50.54(f) Related to External Flooding, Including Failure of the Jocassee Dam,at Oconee Nuclear Station, Units 1, 2, and- 3, (TAC NOS. MD8224, MD8225,MD8226)", dated August 15, 2008.Office of NuclearoRegulator-Research,' Regulatory Gu~ide 1.208, A Performance-Based Approach To Define the Site-Specific Earthquake Ground Motion," (March 2007.Walder, J. and J. O'Connor. 1997. "Methods for Predicting Peak Discharge of Floods Caused byFailure of Natural and Constructed Earthen Dams." Water Resources Research, vol. 33,no. 1 0, p. October 1997.Wilson 'Engineering, 2013. "Independent Technical Review of HEC-RAS and SRH-2DModeling," Wilson Engineering Project WE 13002. March 2013.69

.......... :t,. c lw LH ..t :m , m a .lJrl..~ U~ .~*Duke Energy Carolinas, LLC I ONS FLOODING HAZARD REEVALUATION REPORTSection 6 -ReferencesYoungs, R.R. (2014). 'Review of EPRI 1021097 Earthquake Catalog for RIS Earthquakes inthe Southeastern US and Earthquakes in South Carolina Near the Time of the 1886Charleston Earthquake Sequence." Report transmitted by EPRI letter on March 6, Reference Calculations:* JOC-233493-03 Rev 0, Jocassee Dam-Seismic Dam Performance* ONS C-00392,192503-003-001 Rev 0 Hydraulic Analysis of External Flood Due to FairWeather Breach of Jocassee Dam .using TUFLOW FV* JOC-233493-02-01 Rev, 0, Keowee Reservoir Volume CapaCity -Combined Saddle.* Dike 1 and Saddle Dike 2 Appurtenant Structure Failure70