Text

Report, Enclosure Oconee Nuclear Station Flooding Hazard Reevaluation Report
	ML13240A016
Person / Time
Site:	Oconee
Issue date:	03/06/2013
From:	Christopher J; HDR Engineering
To:	; Duke Energy Carolinas, Office of Information Services
References
	FOIA/PA-2013-0249, FOIA/PA-2016-0071
	Download: ML13240A016 (152)
	v • d • e

ENCLOSURE -1 OCONEE NUCLEAR STATION (ONS)

UNITS 1, 2, AND 3 DOCKET NOS. 50-269, 50-270, and 50-287 FLOODING HADZARD REEVALUATION REPORT

a-ins ecu o.m.t*.-\Ar.th, df"" "under- I0C ONS FLOODING HAZARD REEVALUATION REPORT RESPONSE TO REQUEST FOR INFORMATION PURSUANT TO TITLE 10 OF THE CODE OF FEDERAL REGULATIONS 50.54 (F) REGARDING RECOMMENDATION 2.1: FLOODING OF THE NEAR-TERM TASK FORCE REVIEW OF INSIGHTS FROM THE FUKUSHIMA DAI-ICHI ACCIDENT Prepared for:

DUKE ENERGY CAROLINAS, LLC Charlotte, North Carolina Prepared by:

HDR ENGINEERING, INC. OF THE CAROLINAS Charlotte, North Carolina MARCH 2013

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REPORT VERIFICATION PROJECT: ONS FLOODING HAZARD REEVALUATION REPORT TITLE: RESPONSE TO REQUEST FOR INFORMATION PURSUANT TO TITLE 10 OF THE CODE OF FEDERAL REGULATIONS 50.54 (F)

REGARDING RECOMMENDATION 2.1: FLOODING OF THE NEAR-TERM TASK FORCE REVIEW OF INSIGHTS FROM THE FUKUSHIMA DAI-ICHI ACCIDENT This document has been reviewed for accuracy and quality commensurate with the intended application.

Prepared by: Date: 03/06/2013 Checked by: Date: 03/06/2013 Tim BanE Quality Review by: Date: 03/07/2013 Ty Ziegles P. E.

3 Christopher E , P.E.

Approved by: Date: 03/07/2013 Corporate Seal: Professional Engineer Seal:

HDR Engineering, Inc. of the Carolinas 440 S. Church Street, Suite 1000 Charlotte, NC 28202 South Carolina License No. C03 18

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ONS FLOODING HAZARD REEVALUATION REPORT TABLE OF CONTENTS Section Title Pane No.

EXECUTIVE

SUMMARY

.......................................................................................... ES-1 I SITE INFORMATION RELATED TO THE FLOOD HAZARD .................................. I 1.1 Detailed Site Information ............... ....................................................................... 1 1.2 Current Design Basis Flood Elevations ................................................................... 2 1.2.1 Local Intense Precipitation .......................................................................... 2 1.2.2 Flooding in Reservoirs ............................................................................... 8 1.2.3 Dam Failures .............................................................................................. 9 1.2.4 Storm Surge and Seiche ............................................................................... 9 1.2.5 Tsunam i ................................................................................................... . . 10 1.2.6 Ice Induced Flooding ................................................................................. 10 1.2.7 Channel Diversion .................................................................................... 10 1.2.8 Combined Effects ...................................................................................... 10 1.3 Licensing Basis Flood-Related and Flood Protection Changes .............. 10 1.4 Watershed and Local Area Changes ..................................................................... 13 1.5 Current Licensing Basis Flood Protection and Mitigation Features ...................... 13 2 FLOODING HAZARD REEVALUATION ........................................................... 17 2.1 Local Intense Precipitation .................................................................................... 17 2.2 Flooding in Reservoirs ......................................................................................... 25 2.2.1 Probable Maximum Flood - Keowee ...................................................... 26

TABLE OF CONTENTS (Continued)

Section Title Paue No.

2.2.2 Probable M axim um Flood - Jocassee ..................................................... 35 2.3 Dam Failures ............................................................................................................... 43 2.3.1 Potential Dam Failure ............................................................................... 43 2.3.2 Dam Failure Perm utations ........................................................................ 44 2.3.3 Unsteady Flow Analysis of Potential Dam Failures ................................. 46 2.3.4 W ater Level at the Plant Site ..................................................................... 54 2.4 Storm Surge and Seiche ........................................................................................ 58 2.5 Tsunam i ...................................................................................................................... 59 2.6 Ice Induced Flooding .................................................................................................. 59 2.6.1 Ice Effects ................................................................................................. 59 2.6.2 Ice Jam Events .......................................................................................... 60 2.7 Channel Diversions ............................................................................................... 60 2.8 Com bined Effects ................................................................................................ 60 3 COMPARISON OF CURRENT DESIGN BASIS AND REEVALUATED FLOOD CAUSING MECHAN ISM S............................................................................................... 63 3.1 Local Intense Precipitation ................................................................................... 64 3.2 Probable Maxim um Flooding ............................................................................... 64 3.3 Dam Failures ............................................................................................................... 64 3.4 Storm Surge and Seiche ........................................................................................ 65 3.5 Tsunam i ...................................................................................................................... 65 3.6 Ice Induced Flooding ............................................................................................ 65 ii

TABLE OF CONTENTS (Continued)

Section Title Page No.

3.7 C hannel D iversion ................................................................................................ 65 3.8 Com bined Effects ................................................................................................. 65 4 INTERIM EVALUATION AND ACTIONS TAKEN OR PLANNED .......................... 66 5 ADDITIONAL A CTIONS ................................................................................. 67 6 REFERENCES ................................................................................................. 69 APPENDICES APPENDIX A - FIGURES AND TABLES APPENDIX B - CURRENT LICENSE BASIS LIP MODEL ANALYSIS INUNDATION LEVELS APPENDIX C - FLOOD HAZARD RE-EVALUATION BEYOND LICENSE/DESIGN BASIS LIP MODEL ANALYSIS INUNDATION LEVELS APPENDIX D - DAM BREACH MODEL UNSTEADY FLOW MODELING DETAILS iii

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ONS FLOODING HAZARD REEVALUATION REPORT LIST OF FIGURES Fig-ure Title Page No.

1 PROBABLE MAXIMUM PRECIPITATION DEPTH-DURATION CURVE ............ 20 2 INCREMENTAL PRECIPITATION DURING THE 6-HOUR PMP FOR SIX DIFFERENT TEMPORAL DISTRIBUTIONS .............................................................. 22 3 INCREMENTAL PRECIPITATION DURING THE 72-HOUR PMP FOR SIX DIFFERENT TEMPORAL DISTRIBUTIONS .............................................................. 22 4 PMP DAD CURVES FOR KEOWEE WATERSHED ................................................. 28 5 PMP DAD CURVES FOR KEOWEE WATERSHED ................................................. 29 6 KEOW EE W ATERSHED SUB-BASINS ..................................................................... 32 7 TABLE 6.2 PMS FROM IJMR-52 WHICH GENERATES PMF ................................. 34 8 KEOW EE PM F HYDROGRAPHS ............................................................................... 35 9 JOCASSEE PM P DAD CURVES ................................................................................. 37 10 JOCASSEE W ATERSHED SUB-BASINS ................................................................... 38 11 JOCASSEE PM.F HYDROGRAPHS ............................................................................. 43 iv

ONS FLOODING HAZARD REEVALUATION REPORT LIST OF TABLES Table Title Page No.

1 RESERVOIR FLOODING RESULTS ............................................................................ 8 2 CALCULA TION RESULTS ............................................................................................ 9 3 PMP DEPTHS FOR THE SITE USING HMR 51 AND 52 .......................................... 19 4 INTERVAL DURATION DEPTHS ............................................................................... 20 5 NORMAL AND IDF (PMF) FREEBOARD (FT) ........................................................ 27 6 NORMAL AND IDF (PMF) FREEBOARD (FT) .......................................................... 36 7 COMPARISON OF I-D AND 2-D MODEL RESULTS - TIME TO BREACH AND MAXIMUM WATER SURFACE ELEVATIONS (Elevation in ft and Time in hours) ....56 8 WIND DRIVEN WAVE RUN-UP RESULTS ............................................................... 58 9 2-YEAR W IND VELOCITY RESULTS ....................................................................... 58 10 COMBINED EFFECTS FLOOD ELEVATIONS .......................................................... 62 11 CURRENT DESIGN BASIS AND REEVALUATION FLOOD ELEVATIONS ...... 63 V

Cr tisSuio ~1il~irrrao V[hI irip~i isisr fOi1 F .9(~i List of Acronyms BEP Best Exact Prediction BSP Best Simplified Prediction BWST Borated Water Storage Tank CAL Confirmatory Action Letter CAP Corrective Action Program CCW Condenser Cooling Water cfs cubic feet per second CM compensatory measures CN curve number DAD depth-area-duration DEM digital elevation model EAP emergency action plan FERC Federal Energy Regulatory Commission GIS Geographic Information Systems HCLPF high confidence of a low probability failure HEC-RAS Hydrologic Engineering Center's - River Analysis System HHA Hierarchical Hazard Assessment HMR Hydrometeorological Report IDF Inflow Design Flood ISFSI Independent Spent Fuel Storage Installation IWCS InfoWorks CS LE low erodibility LIP local intense precipitation msl mean sea level NED National Elevation Data Set NRC Nuclear Regulatory Commission NTTF Near-Term Task Force PGA peak ground acceleration PMF probable maximum flood vi

r7nr=-: TT: iromRublic PMP probable maximum precipitation PMS probable maximum storm SCS Soil Conservation Service SE Safety Evaluation SRM Staff Requirements Memorandum SSC systems, structures, and components SSF Standby Shutdown Facility STI Supporting Technical Information SWM4M storm water management model TIN triangulated irregular network UFSAR Updated Final Safety Analysis Report USACE United States Army Corps of Engineers USGS United States Geological Survey vii

C"pta'n~ ~~.irity Sensitiue Informati3n ~AIithholr1 from public dicclouur~ ur~J~i 13 CFR Executive Summary Following the accident at the Fukushima Dai-ichi nuclear power plant resulting from the 2011 Great Tohoku Earthquake and Tsunami, the Nuclear Regulatory Commission (NRC) established the Near-Term Task Force (NTTF) and tasked it with conducting a systematic and methodical review of NRC processes and regulations to determine whether improvements are necessary.

The resulting NTTF report concludes that continued United States (U.S.) nuclear plant operation does not pose an imminent risk to public health and safety and provides a set of recommendations to the NRC. The NRC directed its staff to determine which recommendations should be implemented without unnecessary delay (Staff Requirements Memorandum [SRM] on SECY- 11-0093).

The NRC issued its request for information pursuant to Title 10 of the Code of Federal Regulations, Section 50.54(f) (10 CFR 50.54[f]) on March 12, 2012, based on the following NTTF flood-related recommendations:

Recommendation 2.1: Flooding m Recommendation 2.3: Flooding Enclosure 2 to the NRC 50.54(D letter addresses Recommendation 2.1 and requests a written response from licensees to:

I. Gather information with respect to NTTF Recommendation 2.1, as amended by SRM on SECY-1 1-0124 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 are important to protect the updated hazards at operating reactor sites.

3. To collect information to address Generic Issue 204 regarding the flooding of nuclear power plant sites following upstream dam failures.

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eGuiwn's ecui;ty Sensitly÷ ',hfrnti," rth 1 .1 ;,ib',ic J~3C',iou,* undr 10 CFR 2.3,(Jn Oref i Executive Summary This report was prepared for the Oconee Nuclear Station (ONS) Generating Plant Units 1, 2 & 3 (ONS) in response to NTTF Recommendation 2.1 only.

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, frorn p'Jb!!" rliSur dr Section 1 Site Information Related to the Flood Hazard 1.1 Detailed Site Information Oconee 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. The United States Army Corps of Engineers' (USACE) Hartwell Reservoir is south of the 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 I and Chapter 2 include reference to figures showing the general arrangement, layout, and relevant elevations of the station. The original design of the ONS Yard (Yard) grade was nominally 796 ft mean sea level (msl) (all elevations referenced in this report are based on National Geodetic Vertical Datum [NGVD] 1929). The mezzanine floor elevation in the Turbine, Auxiliary, and Service Buildings is 796.5 ft msl. Exterior accesses to these buildings are at an elevation of 796.5 ft msl. Section 4.0 provides further discussion of modifications to the Yard grade.

All of the man-made dikes and dams forming the Keowee Reservoir rise to a minimum elevation of 815 ft msl including the ONS Intake Canal Dike.

The ONS site, as per the original licensing/design basis case, site is a "flood-dry site," which is not subject to flooding from the nearby streams and Lake Keowee River (excluding postulated dam break scenarios). The full pond water elevation of Lake Keowee is 800 ft msl.

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Section I Site Information Related to the Flood Hazard 1.2 Current Design Basis Flood Elevations 1.2.1 Local Intense Precipitation The flood water elevation due to a maximum local intense precipitation (LIP) (also known as the probable maximum precipitation [PMP]) was reevaluated by HDR Engineering, Inc. of the Carolinas (HDR) in the last quarter of 2012 using the Current licensing/design basis case PMP and state-of-the-practice engineering software. The analysis evaluated the maximum water surface elevation within the ONS power block area resulting from the occurrence of the PMP and assuming three different site drainage scenarios with an updated site topography and building layout. Figures and Tables referenced in this section are presented in, Appendices A and B.

Rainfall precipitation for the ONS site was based on the UFSAR 2.4.2.2 stated depth and duration of 26.6 inches in 48 hours5.555556e-4 days 0.0133 hours 7.936508e-5 weeks 1.8264e-5 months . As prescribed by the UFSAR 2.4.2.2, the temporal distribution applied to the rainfall was derived from the normalization of mass rainfall curves located at Clemson College from the historical precipitation event of mid-August 1940. Figures A-I and A-2 illustrate the cumulative and incremental precipitation, as well as rainfall mass curve used in the model analysis. The maximum 1-hour rainfall intensity for the normalized rainfall precipitation event was approximately 3.5 inches per hour. Figure A-3 is an output from the rainfall/runoff simulation model showing the rainfall distribution as input in the analysis.

The coupled one dimensional (l-D) and two dimensional (2-D) hydraulic model was used for the basis of this study. This model encompasses the main Yard and extends to include the 230 kilovolt (kV) switchyard east of the main Yard and the Independent Spent Fuel Storage Installation (ISFSI) south of the main Yard (Figures A-4 and A-5-A). A separate model was created 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 used as the basis for generating the modeling surface for the main Yard. The 3-inch topography data 2

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Section I Site Information Related to the Flood Hazard was extended using the 1-foot topography contours for areas outside the coverage of the 3-inch topography. 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 to the ISFSI area is mainly between the main Yard and ISFSI where there is no 3-inch topography coverage, 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 irregular network (TIN) file, which was imported into the InfoWorks CS, Version 11.5 software (IWCS).

The modeling of the Yard reflects the up to date configuration of the Yard, based on 2010 surveyed data. There were some locations in the terrain model that had to be modified due to temporary 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 the area locally or lower the area locally. The approach used was to raise an area by specifying a minimum elevation to use for that zone. If a terrain value was lower than this defined minimum elevation, 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 any value in the terrain data would be capped by this value for determining the 2-D mesh element elevation. The final mesh elevations used for the simulation are illustrated in Figures A-6-A and A-6-B.

Soil and terrain surface characteristics for the Yard and off-site sub-basins were used to develop the hydrology characteristics using the Soil Conservation Service (SCS) curve number (CN) method. Figure A-7-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 enter the Yard as shown in Figure A-7-B. In addition, model node IDs are shown in Figure A-7-B.

Flow hydrographs were calculated for the downstream location of these sub-basins and typically applied directly to the 2-D mesh at locations where it had been determined by contours that the flow would naturally concentrate. For off-site Basins 1, 2, and 5 shown in Figure A-7-A that are on the western side of the site, the calculated flows were routed along overland flow paths, 3

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Section I Site Information Related to the Flood Hazard through culverts, or over weirs that represent roadways to adjacent overland flow paths that connect to the 2-D mesh of the Yard. The flow coming off the sub-basins was further subdivided to be applied where it would enter the Yard.

The Keowee Hydro Powerhouse area has no additional modeled routed drainage. Rainfall is directly applied to the 2-D mesh. This assumption was used because the subject drainage area is fairly small (at less than 10 acres) and with the pervious areas being grassy and steep, initial and continual losses would be minimal and thus the approach taken would yield a more conservative result.

Physiographic characteristics were derived from the following resources:

m Soil Characteristics (UFSAR 2.5.4.2; 2.5.6.3) (Contractor determined) (Natural Resources Conservation Service)

Surface Characteristics (Contractor determined by aerial photos provided by Duke Energy)

The Yard drainage was created from drawings and walkdown information of the current site layout. This data was used to build the existing conditions model (Figure A-7-A) where color shading represents different sub-basins in the runoff model. The layout of the site, including the location of building and drainage information was taken from the Duke Energy-supplied MicroStation drawing files. These files were also used to input pipe size and elevation of the elements within the system along with the associated supplied spreadsheet of the catch basin data. Duke Energy catalogued the site drainage catch basins. This information is represented in 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 created from drawing and photograph files. Each roof section was modeled as a conceptual volume defined by an elevation-area relationship. An orifice was used to drain the roof area to the respective segments of the roof drainage system. Overflow of the roof gutter or parapet was 4

Section I Site Information Related to the Flood Hazard accounted for by use of a conceptual weir of appropriate elevation and length that discharges to a location based on determined flow paths. These locations are typically directly applied to the 2-D mesh, at downspout locations, where appropriate, or other roof sections depending on roof geometry. Details for parts of the Auxiliary Building and the other buildings on site were reviewed by the modeler; and where extensive detail was not deemed necessary (based on experience), a more simplified roof catchment and orifice drainage system was defined to simulate 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 were modeled by defining a catchment area for each roof area and connecting this to the 2-D Yard surface (Figure A-9). An orifice was used to represent each downspout to discharge to the Yard at the appropriate location. A weir was also used at each downspout location to allow overtopping of the gutter to add flow to the same location the downspouts discharge to. Roofs with a direct response to the Yard and overflow from gutters were represented by the use of a weir to direct the flow to the 2-D surface.

The modeling software used for this effort was IWCS with 2-D - a coupled I-D and 2-D simulation model produced by Innovyze (formerly Wallingford Software). This modeling package allows the hydrology and hydraulics for I-D pipe flow and 2-D overland flow to be modeled within one software environment. The hydrology was divided into three areas: off-site drainage, which is modeled as SCS basins and derived flows loaded onto the Yard 2-D mesh at appropriate locations; the Yard, which is the 2-D surface directly around the Reactor and Turbine buildings where the rainfall is applied directly to the mesh; and roof drainage. The roof surfaces use the storm water management model (SWMM) routing and direct flow to the roof drains, Yard drains, or directly to the Yard as appropriate. Two models were developed: one for the main Yard to the 230-kV switchyard and ISFSI area, and one for the Keowee Hydro Powerhouse sub-basin.

Figure A-10-A shows catch basins and other nodes located within the Yard study area. The link between the I-D and 2-D simulations can be an important factor in the model results along with 5

"ta Got~sn Wi- ne Section I Site Information Related to the Flood Hazard the simulation time step used. The 1-D and 2-D simulation engines are separate with a link between them which, in this IWCS model, represents the catch basin nodes. The simulation engines calculate depth and flow in the pipes and across the surface at every point simultaneously for each "major" time step. If a result cannot be determined at a particular time step, then the time step is halved to a "minor" time step and the simulation engines try to calculate again until a result is achieved. The interaction between the I-D and 2-D simulations takes place at the major time steps at the catch basins. Thus it is important to use an appropriate time step for the simulation to ensure proper exchange of flow between the I-D pipes and 2-D surface. A I-second time step has been used for these simulations to prevent excess flow from building up on the surface over the catch basins between major time steps, which would artificially increase the water surface elevations on the 2-D 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 size defined for simulation. If mesh triangles have an area less than the minimum mesh element size, then triangles are merged together to create a 2-D element greater than the minimum mesh element size. This is to maintain simulation stability. The main Yard has a maximum triangle size of 250 square ft and a minimum mesh element size of 30 square ft.

The average mesh element size in highly detailed areas around buildings is approximately 80 square ft with an average size of about 150 square ft across the open part of the Yard. This mesh is tighter around features of hydraulic significance such as buildings, swales, and catch basins and the mesh is looser in areas that are open and reasonably flat. The Keowee Hydro Powerhouse sub-basin mesh has a maximum triangle size of 90 square ft and a minimum mesh element 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 distribution modeled after the August I 1-14, 1940, storm event for the area.

6

-Section I Site Information Related to the Flood Hazard

Scenario 1: Complete system with fully functioning roof and Yard drainage.

Scenario 2: Yard and roof drainage considering the Yard drainage catch basins to be blocked (not functioning).

n Scenario 3: Yard drainage (surface) only considering both the roof inlets and Yard drainage (sub-surface) catch basins to be blocked (not functioning).

The simulations were run for a period of 50 hours5.787037e-4 days 0.0139 hours 8.267196e-5 weeks 1.9025e-5 months to allow enough time for all of the water from the rainfall event to flow off or out of the system. Site inundation elevations under current design basis PMP and existing site layout are provided in Appendix B.

Table B-1 quantifies the increase in flood depth around the Reactor, Auxiliary, Turbine, and Administrative buildings due to modeling the Yard by simulating the Yard drainage catch basins being blocked. The average increase in water depth due to the catch basins being blocked is 0.67 ft. The average increase in flood depth east of the Turbine Building is 0.77 ft. The average increase 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 drains are modeled as blocked and where the Yard drains and roof drains are both modeled as blocked.

Figures B-2 and B-4 show the location of maximum water surface elevations and durations for points in the Yard around the Standby Shutdown Facility (SSF), Protected Service Water (PSW),

and Essential Siphon Vacuum (ESV) structures and in the CT5 area when Yard drainage is effective.

The maximum depth of water for the Current licensing/design basis case basis around the Keowee Hydro Powerhouse sub-basin is shown in Figures B-3 and B-5. The 2-D terrain in this area is showing local low areas in paving next the powerhouse but the base map contours around the powerhouse are 1 foot while the modeled water depths are around 0.5 ft.

7

Co01.,ete _n5rIrn *oi:'e In.cm.tion "nnuSi Section I Site Information Related to the Flood Hazard The efficiency of the Yard drainage and roof drainage systems was evaluated using the IWCS model but for this review, the drainage systems were assumed to be blocked, producing a more conservative LIP inundation condition at the site.

1.2.2 Flooding in Reservoirs Since ONS is located near the ridgeline between the Keowee and Little River valleys, or more than 100 ft above the maximum known flood in either valley, the records of past floods are not directly applicable to siting considerations.

Original Project studies were conducted to evaluate effects on reservoirs and spillways of maximum hypothetical precipitation (PMP) occurring over the entire Lake Keowee drainage area. This rainfall was estimated to be 26.6 inches within a 48-hour period. Unit hydrographs were prepared based on a distribution in time of the storms of October 4-6, 1964, for Jocassee and August 13-15, 1940, for Keowee. Reservoir flooding results are summarized as follows:

TABLE 1 RESERVOIR FLOODING RESULTS Keowee Jocassee Maximum spillway discharge 147,800 cfs 70,500 cfs Maximum reservoir elevation 808.0 ft 1,114.6 ft Freeboard below top of dam 7.0 ft 10.4 ft Note: Data above from UFSAR.

While spillway capacities at Keowee and Jocassee have been designed to pass the inflow design flood (IDF) with no surcharge on full pond, the dams and other hydraulic structures have been designed with adequate freeboard and structural safety factors to safely accommodate the effects of PMP. Due to the time-lag characteristics of the runoff hydrograph after a storm, it is extremely unlikely the maximum reservoir elevation due to the PMP would occur simultaneously with winds causing maximum wave heights and run-ups.

8

Section I Site Information Related to the Flood Hazard Considering this assessment, the ONS site can be characterized as a "flood-dry site," as described in Section 5.1.3 of the American National Standard Report, Determining Design Basis Flooding at Power Reactor Sites, because the safety-related structures of the existing ONS are above spillway discharge flooding elevations. The Yard is nominally 796 ft msl and during 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 back up significantly over the river elevation of approximately 686 ft msl. This meets the intent of the definition of a "flood-dry site."

1.2.3 Dam Failures There were no dam failures postulated in the original licensing/design basis case basis of the plant. A dam failure event was postulated more recently and is described below in Section 1.3.

1.2.4 Storm Surge and Seiche Storm surge and seiche events were never postulated to affect the site, and no flood elevation is given in the original licensing basis of the plant. The maximum wave height and wave run-up were calculated for Lake Keowee and Lake Jocassee by the Sverdrup-Munk formulae. The results of these calculations are as follows:

TABLE 2 CALCULATION RESULTS Lake Wave Height Wave Run-Up Maximum Fetch Keowee (Keowee River Arm) 3.70 ft 7.85 ft 8 miles Jocassee 3.02 ft 6.42 ft 4 miles Keowee (Little River Arm) 3.02 ft 6.42 ft 4 miles Note: Data above from UFSAR 9

Section I Site Information Related to the Flood Hazard The wave height and wave run-up figures are vertical measurements above normal full pond elevations as tabulated above. The design freeboard at each dam is 15 ft which is adequate to prevent overtopping of wind-driven waves.

1.2.5 Tsunami Tsunamis were never postulated to affect the site, and no flood elevation is given in the original licensing/design basis case basis of the plant.

1.2.6 Ice Induced Flooding Ice induced flooding were never postulated to affect the site, and no flood elevation is given in the original licensing/design basis case basis of the plant.

1.2.7 Channel Diversion Channel diversions were never postulated to affect the site and no flood elevation is given in the original licensing/design basis case basis of the plant.

1.2.8 Combined Effects Combined flooding effects (PMP, PMF, dam failure and/or wind-driven waves) were never postulated to affect the site and no flood elevation is given in the original licensing/design basis case of the plant.

1.3 Licensing Basis Flood-Related and Flood Protection Changes ONS has made the following licensing basis flood-related and flood protection changes described below.

There is one exception to the Keowee Reservoir Retention dikes and dams minimum elevation of 815 ft msl. This exception is described as two reinforced concrete trenches extending through 10

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Section I Site Information Related to the Flood Hazard the ONS Intake Canal Dike with a minimum elevation of 810 ft msl. This exception only occurs during very rare occasions when the covers would be removed for maintenance. These trenches are protected from wave action by the Condenser Cooling Water (CCW) Intake Structure and the Causeway at the west end of the CCW Intake Structure. Therefore only the maximum reservoir elevation of 808 ft msl is applicable with regard to flooding through the reinforced concrete trenches.

An additional licensing feature 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 Jocassee are designed with 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" (UFSAR Section 9.6.3.1). In 1983, a Jocassee dam failure study was completed to determine the maximum water surface elevation around the SSF if a postulated fair-weather failure of the Jocassee Dam is considered. The results of the study estimated a peak flood elevation of 817.45 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 risk reduction measure. This was not part of the design basis. Based on ONS's September 26, 2008, response to a Title 10 of the Code of Federal Regulations, Section 50.54(f) (10 CFR 50.54[f]) request for information, ONS increased the height of the flood wall around the SSF by 2.5 ft as a risk reduction measure with a resulting elevation of 803.5 ft msl.

The UFSAR Section 9.6.3.1 was updated to say: "As a PRA enhancement the SSF is provided with a five foot external flood wall which is equipped with a water tight door near the south entrance of the SSF. A stairway over the wall provides access to 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-built configuration of the 5' flood wall provided at the north entrance and the flood wall at the south entrance to the SSF, SSF external flood protection is provided for flooding that does not 11

uri.y S"Sr-

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Section I Site Information Related to the Flood Hazard exceed 801 ft above mean sea level." In its current as-built condition, the SSF has flood protection features up to an elevation of 803 ft 6 inches msl.

A separate external flood licensing basis change is the postulated fair-weather failure of the Jocassee Dam. This change is derived from an NRC Safety Evaluation (SE) dated January 28, 2011, addressing commitments made in regards to the June 22, 2010, Confirmatory Action Letter (CAL) to address 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 and had 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) the NRC requested information in a 10 CFR 50.54(f) letter. Duke Energy responded to the licensee's request on September 26, 2008 (ML082750106).

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 that the inundation of the ONS site, from the postulated fair-weather failure of Jocassee Dam, has been bounded 2) by November 30, 2010, submit a list of all modifications necessary to mitigate the inundation, and 3) make all necessary modifications by November 30, 2011. Subsequent correspondence with the NRC has deferred these dates.

The staff also requested that the compensatory measures (CMs) listed in the CAL remain in place until they can be superseded by regulatory action related to the Fukushima responses.

The SE describes the methods and parameters chosen for the analysis. It concludes by stating:

"The unmitigated Case 2 dam breach parameters that were used in the flooding models, provided 12

Section I Site Information Related to the Flood Hazard by Duke Energy for ONS site, demonstrated that the licensee has included conservatisms of the parameters utilized in the dam breach scenario. These conservatisms provide the staff with additional assurance that the above Case 2 scenario will bound the inundation at ONS, therefore providing reasonable assurance for the overall flooding scenario at the site. This new flooding scenario is based on a random fair-weather failure of the Jocassee Dam. This Case 2 scenario will be the new flooding basis for the site" (SE dated January 28, 2011). The SE also states that the licensee has committed to keep the CMs in place until final resolution has been agreed upon between the licensee and the NRC staff.

1.4 Watershed and Local Area Changes Changes to the local site topography and support buildings have taken place since original construction. Changes in local area conditions have been captured in the modeling performed to support the flooding assessment due to LIP and dam failure inundation using recent aerial and ground survey data (2010) along with updated drainage, utility trench location and building geometry.

There has been construction of housing and support facilities directly around Lake Keowee in the watershed since 1971, but the overall percentage of land use has not significantly changed since the construction of the reservoirs and ONS. There is no significant change in land use around Lake Jocassee. Most of the Jocassee watershed is comprised of protected forest lands.

1.5 Current Licensing Basis Flood Protection and Mitigation Features Based on the ONS Current Licensing/design basis case, a list of flood protection, mitigation, and early warning indicator features has been compiled. This list of features was created to fulfill the NRC-issued information request on March 12, 2012, in accordance with 10 CFR 50.54(f). of the 50.54(f) letter was directed toward addressing the NTTF Recommendation 2.3 for Flooding and requested the results of a flooding design basis walkdown. Below is a high level description of the different features presented in the 2.3 Flooding Walkdown report. Many 13

Section I Site Information Related to the Flood Hazard of the features are actually groups of smaller features and for convenience have been grouped together.

The first group consists of Features I through 9. These features are included because of the PMP initiating flood as described above. They are all either at Yard elevation (-796 ft msl) or below grade and are listed below:

Flood Protection and Mitigation Features:

1. Auxiliary Building exterior subsurface walls and seals

2. Radwaste trench covers and seals from Radwaste Facility to Turbine building

3. Radwaste trench covers and seals from Radwaste Facility to Auxiliary building

4. Interim Radwaste trench covers and seals

5. Manhole 7 Cover, Technical Support building vault and seals

6. Borated Water Storage Tank (BWST) trench covers

7. Yard drainage system

8. CT-5 trench covers in Auxiliary building

9. PMP rainfall event flood barrier sandbags and Gryffolyn coverings A second group consists of Features 10 through 16. These features are included because they are part of the Keowee Reservoir Retention items. Listed below are the seven features:

Flood Protection and Mitigation Features:

10. Keowee River Dam

11. ONS Intake Canal Dike

12. Little River Dam

13. Little River Dikes A, B, C, D

14. Keowee Intake

15. Keowee Hydro Powerhouse

16. Keowee Spillway 14

s SUM ,,..i p,,i Section I Site Information Related to the Flood Hazard The third group consists of Features 17 through 31. Their purpose is to mitigate flood conditions based on the January 28, 2011 SE postulated fair-weather failure of the Jocassee Dam. This list was derived from the fifteen CAL CMs, and the actions taken by ONS in order to satisfy the CAL. These features include plant flood protection procedures, early flood detection warning equipment housed at Jocassee Hydro, and emergency equipment housed at ONS and operated 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. AP/0/A/I 700/047 Procedure (External Flood Abnormal Procedure)

19. Jocassee Flood mitigating plans and procedures

20. Duke Energy Hydro generation guidance document

21. Dam safety inspection program

22. Maintained monitoring program

23. Keowee Spillway enhancements

24. Jocassee Forebay and tailrace alarms

25. Jocassee storage building with backup spillway operating equipment

26. Portable generator and electric drive motor near the spillway

27. Documentation of table top exercises

28. Instrumentation and alarm selected seepage monitoring locations

29. Video monitoring of Jocassee Dam

30. Second set of B.5.b like equipment

31. Jocassee Dam-ONS response drill documentation The fourth group consists of Features 32 through 34. These features are included because they are the exterior flood protection features for the SSF. Listed below are the three features:

Flood Protection and Mitigation Features:

32. SSF flood barriers including exterior walls

33. SSF steel plate with C02 refill access 15

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. . . . ... , . ,* ....**, ,, *,,, , \*\w N

Section 1 Site Information Related to the Flood Hazard

34. SSF external wall penetrations

35. Feature #35 is the last feature on the Flood Walkdown list and corresponds to the Site Elevation and Topography.

More information on these features and walkdown conclusions can be found in the Flood Walkdown Report (NRC 50.54 (f) NTTF Recommendation 2.3).

16

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Section 2 Flooding Hazard Reevaluation The reevaluations in Section 2.0 are not part of the ONS licensing basis as documented in the UFSAR. The following sections describe additional reevaluation analysis for assessing appropriate external potential flooding hazard events including the effects from LIP on the site, PMF on reservoirs and dam failure that have been performed post-design basis to meet the Hierarchical Hazard Assessment (HHA) procedure described in NUREG/CR-7046 for assessment 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 adjacent to ONS and five additional embankments along the Little River Arm of the reservoir away from the site. As FERC-regulated dams, the structures have been designed and verified with hydrologic and hydraulic analysis and dam stability analyses in accordance with "FERC Engineering Guidelines for the Evaluation of Hydropower Projects." These structures are monitored and inspected on regular intervals by Duke Energy, FERC, and independent dam safety experts.

2.1 Local Intense Precipitation The flood water elevation due to a maximum LIP was reevaluated using current practice Hydrometeorological Report (HMR) PMP and state-of-the-practice engineering software. The analysis evaluated the maximum water surface elevation within the ONS power block area resulting from the occurrence of the PMP and assuming three different site drainage scenarios with an updated site topography and building layout. This reevaluation differs from the design basis analysis in that it utilizes HMR51 PMP and different rainfall distribution patterns in accordance with guidance in NUREG/CR-7046. The modeling software used in this evaluation exceeds procedures outlined in NUREG/CR-7046, I-D channelized flow using the USACE's Hydrologic Engineering Center's-River Analysis System HEC-RAS, as it analyzes overland flow on relatively flat surfaces using 2-D flow equations. Due to the complex site geometry including building layout, roof drainage, subsurface drainage, and lack of defined I-D flow 17

Section 2 Flooding Hazard Reevaluation channel in the currently configured Yard, a model using 2-D flow equations was employed as described in the following sections. Figures and tables referenced in this section are presented in Appendices A and C.

This section presents a summary of the model developed to review local flooding at the ONS Yard 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 expanded IWCS (Version 11.5) 2-D model based on updated site data from Duke Energy regarding the Yard drainage and building and roof drainage transmitted over the period of September 2011 to September 2012. The roof drainage and Yard drainage performance was evaluated with the subsequent flow routing (sub-surface and overland flow) through the ONS site utilizing I-D modeling for roof and sub-surface Yard drainage and 2-D modeling for surface drainage (overland). This analysis includes the maximum depths and durations for the Yard and roof inundation as well as the flow patterns around the Yard. This section provides a summary of the IWCS model construction.

The Beyond licensing/design basis case utilizes the HMR 51/52 methodology for an area less than 10 square miles. The PMP event that produces the study case site flood event was determined by trial procedures using the model to route the runoff. The Beyond licensing/design basis case analysis was performed for three scenarios:

Scenario I 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 to be blocked (not functioning).

a Scenario 3 is the Yard drainage (surface) only considering both the roof inlets and Yard drainage (sub-surface) catch basins to be blocked (not functioning).

Rainfall precipitation for the Yard was determined using HMR 51/52 as they apply to the site located in the U.S. east of the 10 5 th Meridian. HMR 51 defines the depth in inches of PMP for 18

M-3X-lflCi ~oui:0 -Tn8i!ýM!vo .1T403I. wIu~r~i_-FS1],[AI _1EII 0iiO Section 2 Flooding Hazard Reevaluation durations of 6, 12, 24, 48, and 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months for watersheds from 10 mi2 to 20,000 mi2. -HIMR 52 defines the depth in inches of PMP for durations of 5, 15, 30, and 60 minutes for watersheds from I mi 2 to 200 mi 2 . Both HMRs provide isohyetal charts to determine the PMP values based on location. The location used for the site is approximated by Latitude 34.8' N and Longitude 82.90 W. It should be noted that the PMP charts are not sensitive to a small deviation in Latitude 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 52 Depth-Duration All-Seasonal PMP values, by Duration (hrs) l-mi 2 Point Rainfall . 10-mi2 5-min 15-mmn 30-min l-hr 6-hr 12-hr 24-hr 48-hr 72-br PMP (in.) 6.2 9.7 14.0 18.95 30 I 35.8 40.2 44.3 1 46.7 As directed by procedures outlined in HMR 51 and 52, intermediate points are determined from applying a smooth curve through the derived points. Intermediate points were determined in this manner for a duration interval of 5 minutes up to 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months , and a duration interval of 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months beyond 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months up to 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months . The complete PMP depth-duration curve is provided below in Figure 1.

Taking the first portion of the curve, up to I hour, the 5-minute interval duration depths are provided below in Table 4. Bold values correspond to the values derived directly from HMR 51 and 52 PMP charts.

The process outlined in this report is based on NRC regulations for the next generation nuclear stations to be constructed in the U.S. (NRC Standard Review Plan, NUREG-0800, 2.4.2). The PMP rainfall applied to the ONS watershed for this analysis was an all-season, 6-hour event and a 72-hour event.

19

ri y en.i ye rc Section 2 Flooding Hazard Reevaluation FIGURE 1 PROBABLE MAXIMUM PRECIPITATION DEPTH-DURATION CURVE 50 45 40 35 c 30 S25 20 a..

-15 10 5

0 0 6 12 18 24 30 36 42 48 54 60 66 72 Duration (hours)

TABLE 4 5-MINUTE INTERVAL DURATION DEPTHS Cumulative Duration PMP (minutes) Depth (in.)

5 6.18 10 8.02 15 9.72 20 11.29 25 12.72 30 14.02 35 15.14 40 16.05 45 16.84 50 17.54 55 18.23 60 18.95 20

Section 2 Flooding Hazard Reevaluation As described in HMR 52, PMP estimates were obtained from HMR 51 for 6, 12, 24, 48, and 72-hour storm durations (HMR 51 Figures 18 through 22) to estimate the largest volume PMP event shown in Table 3. Additionally, a 6-hour local intense event was used for analysis based on discussion found in NUREG7046, Section 3. The 6-hour PMP LIP was developed for 5-minute increments following procedures outlined in Section 6 of HMR 52. After a review of the 6-hour and 72-hour precipitation modeled results, it was determined that a longer duration event could have a significant impact on site flooding. The maximum 5-minute rainfall intensity for the 6-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 include the peak intensity indicated by using the 6-hour event based on the peak 1-hour distribution for the 6-hour event shown in Table 4. The IWCS model was re-run for each storm duration using six 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 the six temporal distributions.

The 72-hour PMP event was identified as the storm duration which produced the most conservative flood Yard elevations through simulations using the IWCS model. This event was determined to be the HMR 51, modified 72-hour event, with 46.6 inches of total rainfall, and two-thirds loaded distribution.

The coupled I-D and 2-D 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-kV switchyard east of the main Yard and the ISFSI south of the main Yard. A separate model was created for the Keowee Hydro Powerhouse sub-basin (Figures A-4, A-5-A and A-5-B). Refer to Section 1.2 for an additional description of the model configuration and inputs in addition to the re-evaluation of the PMP defined in this section.

21

Ir- '-

Section 2 Flooding Hazard Reevaluation FIGURE 2 INCREMENTAL PRECIPITATION DURING THE 6-HOUR PMP FOR SIX DIFFERENT TEMPORAL DISTRIBUTIONS 7.00 6.00 r 5.00 Incremental Precipitation Front 4.00 a Incremental Precipitation One-Third U 3.00 a Incremental Precipitation Center Incremental Precipitation Two-Thirds

~2.00 2.00Incremental Precipitation HMR-52 S1.00 1 NIncremental Precipitation End U0.00

-I4 4.- .-4 -1 NNN NrVfl Minute FIGURE 3 INCREMENTAL PRECIPITATION DURING THE 72-HOUR PMP FOR SIX DIFFERENT TEMPORAL DISTRIBUTIONS 20.00 e- 18.00

. 16.00

- 14.00 A-, Incremental Precipitation Front g~12.00 n Incremental Precipitation One-Third R Incremental Precipitation Center S8.00 E 6.00 Incremental Precipitation Two-Thirds 4.00

Incremental Precipitation HMR-52 2.00 a Incremental Precipitation End 0.00 1 5 9 131721252933374145495357616569 Hour 22

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Section 2 Flooding Hazard Reevaluation Several tests were simulated with the model using the 6-hr and 72-hr storms to select the storm that produced the greatest flooding impact at critical areas around the ONS site. Both storm durations were reviewed using the six different temporal distributions shown in Figures 2 and 3 (six 6 hour6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months cases plus six 72 hour8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months cases = 12 trial cases). From this sensitivity analysis, the critical temporal distribution was selected as the HMR 51/52 72-hour two-thirds loaded PMP event.

The results provided in Table C-I are based on model results using the HMR 51/52 PMP with two-thirds loaded temporal distribution. Locations referenced in this section are based on Figure C-1.

Figures C-2 through C-4 show the Beyond licensing/design basis case maximum flood depths in the Yard with Yard drainage and roof drainage, with roof drainage and no Yard drainage, with no Yard drainage or roof drainage, and specific locations of maximum flood depth in the Yard.

The slope and configuration of the Yard facilitate rapid removal of the intense rainfall of the HMR PMP event.

Table C-I quantifies the increase in flood depth around the Administrative, Turbine, Auxiliary, and Reactor buildings due to modeling the Yard by simulating the Yard drainage catch basins being blocked. The average increase in flood depth due to the catch basins being blocked is 0.19 ft, which is a 7 percent increase. The average increase in flood depth east of the turbine building is 0.1 ft, a difference of 7 percent. The average increase in flood depth west of the Auxiliary and Reactor buildings is 0.29 ft, a difference of 8 percent.

The Yard flood depths are the same for Scenario 2 and Scenario 3 where only the Yard drains are modeled as blocked and where the Yard drains and roof drains are both modeled as blocked.

The maximum flood elevations of water during the Beyond licensing/design basis case around the Keowee Hydro Powerhouse sub-basin structure are shown in Table C-1. There is effectively no rise around the Keowee Hydro Powerhouse due to only the catch basins being blocked.

23

C*tains Se~rt-ihnt' Snciti.', lnk'rm*,i. 1 - wvitnnolca from puk" "~i LiJriUCR233()1 Section 2 Flooding Hazard Reevaluation Assuming the catch basins and the culvert under the roadway that conveys the hillside runoff are blocked increases the depth of water adjacent to the western side of the powerhouse and produces a nominal increase on the northern side. The increase in modeled depth is due to the flow that runs off the hillside and into the drainage ditches conveying the flow to the culvert overtops at the culvert inlet, and the water then flows 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 flows associated with this event and excess water flows onto the surface. From testing model response for just the roof connections to the Yard drainage, it was noted that the Yard drains overflowed onto the surface in a number of locations with just the flows coming off the roof system. Both the east and west Yard drainage lines show heavy surcharging of the system. This produces flooding at the surface in some locations; and under the strain of the intense rainfall, the drain system fills to an extent that prevents additional flow from entering from the surface.

The roof drainage is undersized for the HMR PMP event. With the exception of the Reactor Building and the lower level roof of the central Auxiliary Building, the water does not overtop the roof parapets with the roof and Yard drainage functioning. Comparing the total inflow for the roof section to the maximum volume stored on the roof, the lower section of the central Auxiliary Building, B8075-8078-8082-BI (Figure C-12), has flow leaving the roof drainage system under pressure and up onto the roof. The other areas where flow appears to overtop the parapets are likely due to the simplified way that they are modeled or the level of detail that was available to build the model. Most of the roof areas of the Reactor, Auxiliary, and Turbine buildings have a large amount of available storage until the rainwater overflows the parapets.

The Reactor Building roof was not fully developed in the model and would require additional refinement to allow the excess rainfall that cannot get into the roof drain system to overflow to the appropriate areas. This refinement was not performed due to the small percentage of contribution of this water to the total site inundation flow and resulting ground level inundation estimates.

24

G..nt.ins Su.it.y o...ti... Informatinn --Wthhold from public disclosure ,,,4,M 10 CFR _.390 i)

Section 2 Flooding Hazard Reevaluation The inundation of rainwater on the Turbine Building averages 4.06 ft in depth over the central span of the Turbine Building. The outer edges range from approximately 1.37 to 3.87 ft in depth and the lower roof on the eastern edge is 6.49 ft in depth. The rainwater in general stays on the roof for 30 minutes and for 1.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months for the central span.

The range of depths of inundated rainwater on the Auxiliary Building roof is between 0.33 and 3.10 ft , correcting for parapet height. The average is less than 1 foot taking into account the excessive depth on the lower central roof. The duration of inundation is generally 30 minutes to I hour with the exception of the lower levels of the central and southern sections of the Auxiliary Building that have durations closer to 2 to 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months . This is due to the heavy surcharging of the system. This results in some extended pooling of water on the roofs which can be seen in Table C-2. Table C-2 lists a summary of the Beyond licensing/design basis case roof drainage characteristics.

The areas with the greatest depth above the parapet are those with the smallest area and coresponding small volumes with relation to the entire roofed area. The excess volume on the central span of the Turbine Building will overflow onto the east and west sections of the roof where there is available volume. Whether the roof can hold this much weight of water is beyond the scope of this study.

The scenario to run the model with the Yard catch basins blocked off relieves the lower roof sections somewhat, but has no real effect on the upper roof sections, as can be seen in Table C-3.

2.2 Flooding in Reservoirs Section 5.5.1 of American Nuclear Society (ANS) 2.8, under "Hydrologic Dam Failures," states that "critical dams should be subjected analytically to the probable maximum flood from their contributing watershed. If a dam can sustain this flood, no further hydrologic analysis shall be required." The two significant upstream reservoirs are Jocassee and Keowee; both are licensed by Duke Energy and were constructed and are maintained in accordance with FERC guidelines.

25

Section 2 Flooding Hazard Reevaluation Dam specific PMP and PMF documentation was reviewed, demonstrating that both dams can safely pass the PMF.

Per ANS 2.8, Section 5.5.4, "if no overtopping is demonstrated, the evaluation may be terminated and the embankment may be declared safe from hydrologic failure." Overtopping should be investigated for either of these two conditions:

w PMF surcharge level plus maximum (1 percent) average height resulting from sustained 2-year wind speed applied in the critical direction; or v Normal operating level plus maximum (I percent) wave height based on the probable maximum gradient wind.

2.2.1 Probable Maximum Flood - Keowee Flooding hazard re-evaluation for a PMF on the Lake Keowee watershed was performed by reviewing the updated analysis developed for the FERC-licensed and regulated hydroelectric development (#2503). The peak reservoir elevation from that analysis is 808.9 ft msl based on hydrologic and hydraulic modeling performed in accordance with Chapters II and VIII of the FERC Engineering Guidelines for the Evaluation of Hydropower Projects using HMR51/52 for the PMP development and HEC-l for the hydrologic and routing model. The spillway and dams at the Keowee development have been designed to pass the PMF with adequate freeboard and structural stability factors to safely accommodate the effects of the PMP. Table 5 summarizes the normal and PMF freeboard for the dam structures that impound Lake Keowee.

26

Section 2 Flooding Hazard Reevaluation TABLE 5 NORMAL AND PROBABLE MAXIMUM FLOOD FREEBOARD (FT)

Reservoir Elevation Top of Dam (ft sI)

Dam Structure Elevation Full (ft msl) Pond PMF (800.0) (808.9)

Keowee Dam 815.0 15.0 6.1 ONS Intake Canal Dike 815.0 15.0 6.1 Saddle Dikes A, B, C, and D 815.0 15.0 6.1 Little River Dam 815.0 15.0 6.1 The PMP used in the evaluation of Lake Keowee was estimated from HMR 51, Probable Maximum PrecipitationEstimates, United States East of the 1051h Meridian (HMR-51). The Probable Maximum Storm (PMS) which generates the PMF was estimated using computer techniques outlined in HMR 52, Application of Probable Maximum PrecipitationEstimates, United States East of the 10 5 1h Meridian (HMR-52).

A set of depth-area-duration (DAD) curves (Figures 4 and 5) was prepared for the Keowee drainage basin using the all-season PMP charts published in HMR-51 and the basin centroid location. The PMP depths in inches were for storm durations ranging from 6 to 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months and for storms smaller and larger in area than the drainage basin.

27

-*,4ntain* S;ecurity. ,,*nutivc In;f,.."atiuii - Vvitnnoid rrom public di u.idiuiG ufRd9 iO d,(*)

Section 2 Flooding Hazard Reevaluation FIGURE 4 PMP DAD CURVES FOR KEOWEE WATERSHED 50.0 o10 m.2 45.0 40.0 200 ml.2 35.0 30.0- 1,000 ml.2 1 25.0

,, . 5,000 m1.2 n 20.0- 10,000 ml.2 20,000 ml.2 15.0 10.0 5.0 0.0 I I I I 0 0 12 18 24 30 36 42 48 54 60 66 72 78 84 Duration (hr.)

28

Conains t er'uriwy ensitiv=,Ii,, ,u..... . tl,,iid from pubic aisciosure under 10 CFR 2L.3(J)(1.).

Section 2 Flooding Hazard Reevaluation FIGURE 5 PMP DAD CURVES FOR KEOWEE WATERSHED 10 1,000 10,000 100,000 Drainage area (mid.2)

The drainage basin for the Keowee Development covers approximately 435 square miles of the southeastern slope of the Blue Ridge escarpment. The drainage basin terrain transitions from rounded 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 of ridges, the vegetation is generally dense and the soils are permeable and absorbent. The small amount of farming in the region is confined to the wider portions of valley floors and the Piedmont portion of the drainage basin. In the southern part of the basin there is more development than in the rest of the basin. Development is generally characterized by scattered rural housing and small towns.

The Keowee drainage basin does not fulfill all of the terms of the definition of a gaged basin as described in the FERC guidelines. To the extent that the basin does not meet the definition of a gaged basin, it must be analyzed as an ungaged basin. For this reason, a regional study was 29

Section 2 Flooding Hazard Reevaluation utilized to develop unit hydrographs for the sub-basins in the drainage area of the Keowee Development.

The Jocassee Development is the largest upstream development with substantial storage capacity. 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 reservoir elevation at Keowee by holding back additional runoff to reduce the peak reservoir elevation at Keowee. 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 the Jocassee Development PMF were used in the Keowee model. During a PMF event in the vicinity of either of these adjacent developments, both Jocassee and Keowee would be operated 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 are characterized by passive spillways and negligible storage capacity. These structures have very little effect on the storm hydrograph as it passes through their ponds, and the total storage volumes are small so that even a breach would not have any measurable effect on reservoir elevations at the Keowee Development.

The SCS runoff CNs were used to model abstractions and compute excess rainfall. The CN method relates cumulative rainfall to cumulative excess rainfall based upon the single parameter CN which ranges in value from 0 to 100 depending on the combination of soil type and land cover/use. The CN method is widely used for PMF studies as it is incorporated directly into the HEC-I computer model. The Geographic Information Systems (GIS) facilitated these computations.

To determine the SCS curve number for a sub-basin, both land use and hydrologic soil group must be known. This information is combined using the published tables (SCS 1972) to establish the curve number value for the sub-basin.

30

Indor s 'h" di;. _'cure 10 CFR ' 39.1J',(1*

Section 2 Flooding Hazard Reevaluation Soil types were obtained from the soil surveys of Oconee, Pickens, Transylvania, and Jackson counties. Land use information was obtained from the U.S. Geological Survey (USGS) for North Carolina and the Land Resources Commission for South Carolina. The resolution on this data was 60 meters so that every 60-by-60 meter cell was characterized by one of the following six land use categories: urban, agricultural/grass, scrub/shrub, forest, water, and barren/transitional land. A determination of the set of CNs for the "water" land use category is not relevant because water is accounted for in the determination of percent impervious. SCS CNs for each combination of hydrologic soil group and land use were then area-weighted to determine the average CN for each sub-basin.

The drainage basin was divided into 26 sub-basins as shown in Figure 6. Sub-basins 1 through 25 were delineated on USGS quad sheets (map scale 1:24,000) based on similarity of topography, geology, and land use. In order to use the sub-basin outlines in GIS, the outlines were digitized from the quad sheets. As a matter of interest, the sub-basin outlines were digitized into MicroStation files. The MicroStation files were then imported into the ArcInfo GIS which produced an ASCII listing of the X-Y coordinates for each of the 25 sub-basins. For sub-basin 26 (Jocassee basin), coordinates from the Jocassee HMR-52 input deck were brought into 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 as inputs into the USACE HMR-52 computer program. The HMR-52 program computed the storm size, location, and orientation that produce the maximum precipitation volume for the drainage basin (PMS). A 700-square-mile storm with centroid at X=10.3 miles and Y=13.0 miles and orientation angle of 1870 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 increments to obtain the PMF which produces the maximum reservoir elevation. The reservoir elevation was calculated using the level pool routing option in HEC-I (dated February 1, 1985) assuming an initial 31

~nteno ~3~i~lii~

iiurrwuoi - rinola ornpubllici! dIiscu uuv e 1 CR2.90d)1 Section 2 Flooding Hazard Reevaluation reservoir elevation at 800.0 ft msl (full pond). The results indicated that the PMS with centroid at X=10.3 miles and Y=9.0 miles is the PMF.

FIGURE 6 KEOWEE WATERSHED SUB-BASINS 2 0 42 so ~ manI 32

Section 2 Flooding Hazard Reevaluation It was not necessary to perform a separate regional unit hydrograph analysis for the PMF study because of the availability of a state-wide study performed by the USGS (Bohman, 1989). The PMF study utilized available hydrologic data from gages in the vicinity of the study area and derived regional regression equations for unit hydrograph lag time. Dimensionless unit hydrographs were developed for the two major physiographic regions in the study area (i.e., Blue Ridge and Piedmont). An independent review of the unit hydrograph analysis and verification study was performed by Clayton Engineering.

In review of the existing FERC PMF analysis, the effectiveness of the gated spillway structure and two hydro turbines at discharging the estimated PMF inflow was considered. Lake Keowee historically has not experienced significant floating debris field problems over the 40+ years since impoundment. The shoreline is stable and debris is managed to facilitate boating activity on the reservoir. Due to the layout of the spillway structure and the relatively low velocity profile in the two reservoir arms during a natural flood event like the PMF, floating debris is not anticipated to become a problem that could significantly impact the effectiveness of the four spillway gates.

The PMF outflow hydrographs and corresponding reservoir levels are shown on Figure 8. The outflow 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 peak discharge is 139,961 cfs. The PMF peak reservoir (headwater) is approximately 808.9 ft msl resulting in 6 ft of margin between the peak flood elevation and the top of dam at 815 ft msl.

33

- tcons Setuinty .... If.... ti..

. ,+ -, fm pubolidundgr 10 CFReealaton r

Section 2 Flooding Hazard Reevaluation FIGURE 7 TABLE 6.2 PMS FROM HMR-52 WHICH GENERATES PMF n.003.

04M - US )al 070

70. 03*7. II.. 001073

37.. 050004 11301TAT300003l.

0140C11retIcommm.a I . .0 903 00710 01=411211Too 6-131 000.00=711 OF0M a s 4 0 4 1 00 00 12 3.00 0.30 0.07 3.00 0.,3 0.00 0.40 0.03 0.14

b0. $0.

3.04 0.TO 0.04 0.37 0.30 2.30 0.04 4.40 0.04 9.40 0.0' 0.53 3.30 2.32 3.30 0.70 0.00 0.00 0.09 i 800. 141. 3.S3 3.00 0.13 0.74 0.40 0.57 0.33 0.30 0.07 0.00 0. 0 4.33 0,43 0.01 4.00 0.20 3.01 0.04 0.70 0.00 0.01 to . 04. 30 .0) 0.07 0.00 0.37 0.04 4.100 3.03 0.00

100. ,

00s4). 00 007. 4.70 0.12 0.30 0.T0 0.40 0.07 0.47 0.00 0.03

. 30. 373. .10.4 3..' 0.33 3.04 0.7G 0.40 0.3A 0.30 3.30 0.)0 0.00 0.100 t.o) 3.00 0.00 0.40 0.00 0.00 a 700. 430. 3S.70 3.07 0.0'0 0.03 0.041 0.03 0.00 0,20 0.30

.00 0.20 33 1040.

5000. 0309 40,0 . 0,40P 2.10 0.63 0.02 0.03 0.20 0.33 0.07 0.30 3.30 II "21004 430. 0.00? 3.00 0.07 0.00* 0.7G 0.37 0.30

o. 2004. 400. 3.0 0.30 0.30 0.30 0.00 0.07 0.00o 0.30 0.30 0.30 o0 4000*. 420. 0.00 6.00 0.00 0.00 0.44 0.012 0.43 0.00 0.00 0.1G 0.3g 0.00 0.07 0.00 o3000. 430. 0.00 0.00 0.00 0.00 0.O4 0.33 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.34 0.00 0.10 0.00 0.00 0.00 0.00 0.00 0.02 0.00 0.00 0.00 0 060000. 0.*00 0.00 0.34 0.00 404. 3.o4 0.o4 0.00 0.00 0.40 0.00 0.00 0.00 0.00 0 44000. 434. 0.00 0.o4 o.o0 4.00 07.07 0.00 0.O4 0.O4 ovo* togpTo 4,00 3.,32 0.07 0.43 Tuff I0010A0. 0 40. 0IM3011 1-00 T0 60.00 0lo I00 07L07 AA 00900 30. 01. ý0.203 000707 0.00 3.70 0.10 4.00 0.00 I30.0 I3..0 60.30 30.01 2 0.03 03701 04.006 .131 30.00 37.22 07.00 0.236 20.44 00.30 0 0.0 3.00 3,07 7.03 33.03 33.,3 03.77 21.31 20.00 030 23.27 .4.00 3 0.00 3"0.3710'.023.30 07.S0 C 0.75 0.40 2.23 4.27 7.0 3.00 10.04 03.13 1 1 0i.04 00.31 ).72 .0061)30.30 30.00 20.04 3 33.01.13 0103.00 0 0.60 0.,4 1.37 3.27 3.04 3.00 3.00

)0.3 6.70 30.30 00. 10.00 20.

0.00 0.04 33.47 30.41 30.40 312".300.00 0.0 00.03 03.07 33.0 0.00 00.0 23.0 04.0 00.70107.03 00.43 00.00 00.33 20.0,Ili 33.00 0 3.00 02.0 0.7 0.00 3.3 0.0 0.23 0.47 0.73 33.07 3l) 0.00 23.04 30.20 20.00 20.70 07.70 20.47 00.33 07.00 20.20 20.00 33.07 0.04 3.00 3.00 2.00 0.00 0.30 30.0, 10 0.0 10.02 3.0 20.03 00.00 20.07 0li 1.00 27.00 310.0 )00.4 20.03 00.00 0.40 0.00 3.03 0.00 0.00 7.40 0.07 30.00 30.30 00.40 3203.0 00.30 10.0, 0.0 00.40 37.00 07.07 20.07 2I0.00,4 0 0.30 0.30 0.00 3.30

14. 3.24 0.00 30. 3 10.0 30.70 I3.00 30,: 1:730. 10 7. , 1,4:.01 23.10 03.1 2, 1,1:1.

0.30 0.00 0.13 4.0 3.00 3.&S 0.4 I4. 0 33.00 3 3.00 1.20 0.0 S. 30. 3,.01 .00 37.02 37.70 30.00 0.33 0.2 0.93 0 0.4 0 3.00 0.4 3 0.231. 1 00 0.1I3.30 4 33.0 0 33.0 30.70 0 32, 0 aI 130.S270 30.00 26.30 0.04 0.1 0 4.2 2 0.4 0.03.02 2. 0.14 0.,4 1.00 0.4 0.30 0.03 0.07 30.37 30.04 1 0.10 3I.0 3h.3 30,0 4.30 0.30 0.03 0.03 3.70 3.73 3.30 0.44 0.00 4.33 1..0 4.00 4.01 7.34 7.00 7.43 7.I0 0.33 0 0.01 0.00 0.00 0.31 0.02 0.00 0.20 3.70 100

3. 00 3.07 3.04 .04 0 0.30 4.:9 10 .0U 0.030 .0 0.0" 0.03 0.40 0.00 0.07 0.3 0.G4 0.70 0.00 1.34 1 3.0: 0.1 13.1 3.0 0.00 2.00 2.34 0.33 20,* 2.01 0 0.00 0.00 0,00 0.00 0.00 0.00 0.00 0.00 0.00 0.10 0.00 0.00 0.00 0.00 .0 0.00 0,00 0.00 0.00 0.00 0.00 U 4.00 0.00 0.00 0 . 0.00 0.00 0. 0. 0 .0 0 0.0 0 0.00 0.00 0.00 0.00 0

0.00 0.00 0.00 0.00 0.00 0.0" 0.00 0.00 0.00 3.00 0.00 0.00 0.00 0.00 0.00 0.00 0.o0 0.0 0.00 0.00 0.00 0.00 0.00 0.00 0.O4 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 47=400 0.' 3031 1.13 0.70 4.04 0.731i2 ,T.32 31.07 20.0 3 24.1,0 37.14 )@.0IIt."0 30.20 30.43 03.33 33.74 32.13 P1104014 041 3700 rim Fall M0 meT I TIM0 000i343707ll0 704 0.14=1131,0.

0340 0.O4 270.O4 0300 0.07 0.07 0034 0.07 0.00 0700 0.00 0.00 a30 0.33 3.0 3000 0.33 3.73 0000 0.00 0.00 2000 0.30 3.07 33004.03t 3.70 3000 0.00 0.70 3300 0.33 0.02 o000 0.01 0.3. 3000 0.00 0.00 3200 0.30 3.3' 0000 0.07 ..30 2000 0.33 0.03 0000TO 0.07 00 0.7

w0 0.0O 0.00 04047 ,0 e&

7300P0 T3O30734, TlIM lwillllll-m TIMl NICK IATION TIM2 powlptrl.Ti?0 00We7300 I30 1X 300 U003077 7300 0000707T70U 0=o0 0700 0.07 3..0 3004 0.00 07.00 0200 3400 0.44 GI0 0.7 6.0. 07.00 0l000 0*000 3300 0030 0.200.20 20.30 20.04 0.130 * .0 0000 0.77 0.03 05003 3.00 0.73 Base 1.11 6,11 1307.17 000 3200 0.03 00.00 06000 0.30 "0.00 3000 2.20 30.00c 0-00 M0AL. 1,5 3004 T.0 o3.0 0314033 0.00ld 0303 0.03 00.37 340 .03 230 7300 100,0i 37,07 3000 0.33 03TI.3 3000 0.00 03.00 303 0:00 G GASio 0.30 ,.14 20.00 0430 0.30 00.17 3000 0.00 33.00 0000 0.7 0.30 Tor ll00.7 3200 0.04 23.07 0400 0.19 00.02 3000 0.30 300. 30.70

.000 0 IO0.40,0 l 6-0N70713. 3.30 34

. . .. ,scTosure

...... . ... -...... un d Section 2 Flooding Hazard Reevaluation FIGURE 8.

KEOWEE PMF HYDROGRAPHS 400,000 805.0 70.0 7M0.0 2W,000' 785.0 M7.0 778.0 2100.000' 770.0 Z; 76.0 760.0 75&0 750.0 745.0 740,0 24 30 3W 42 48 54 60 6N 72 79 94 90 96 Thw (hr.)

2.2.2 Probable Maximum Flood - Jocassee The PMF has been evaluated in accordance with current engineering guidelines for Jocassee; a FERC-licensed and regulated hydroelectric development (#2503). The peak reservoir elevation from that analysis is 1122 ft msl based on hydrologic and hydraulic modeling performed in accordance with Chapters II and VIII of the FERC guidelines using HMR51/52 for the PMP development and HEC-1 for the hydrologic and routing model. The spillway, turbines, and dams at the Jocassee Development have been designed to pass the PMF with adequate freeboard and structural stability factors to safely accommodate the effects of the PMP. Table 6 summarizes the normal and PMF freeboard for the dam structures that impound Lake Jocassee.

35

Section 2 Flooding Hazard Reevaluation TABLE 6 NORMAL AND PROBABLE MAXIMUM FLOOD FREEBOARD (FT)

Reservoir Elevation Dam Structure Top of Dam Elevation (ft sl)

(ft msl) Full Pond PNF (1,110.0) (1,122.0)

Jocassee Dam 1,125.0 15.0 3.0 Dike i 1,125.0 15.0 3.0 Dike 2 1,125.0 15.0 3.0 Generalized all-season estimates of PMP for the Jocassee watershed were obtained from HMR 51. Following procedures given in HMR 52, a set of DAD curves (Figure 9) was prepared for the Jocassee drainage basin using the all-season PMP charts published in HMR 51 and the basin centroid location. The PMP depths in inches were for storm durations ranging from 6 to 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months and for storms smaller and larger in area than the drainage basin. The HMR 52 computer program was used to calculate the PMS in each sub-basin in the watershed. The average PMS depth over the entire watershed was 36.41 inches in 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months . Average sub-basin depths ranged from 38.32 inches near the centroid to 25.91 inches near the periphery.

The USACE computer program HEC-l was used to calculate the inflow hydrograph to Jocassee reservoir. For the computer model the Jocassee Lake watershed was conceptually subdivided into 42 separate basins (Figure 10). The lag-times calculated for each sub-basin and the SCS dimensionless unit hydrograph were used in HEC-I to compute synthetic unit hydrographs. The direct runoff hydrographs for each sub-basin were calculated by computing rainfall excess depths at each time step using the SCS CN Method and then applying these depths through the unit hydrograph procedure. The series of hydrograph combinations and stream routings was continued until a total inflow hydrograph was computed for the Jocassee reservoir. Channel routing 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.

36

eml Ita iiiatkii VyiLliliulo [rpm

- PUUIIC aIscIobu~ ~~do; 10 CER 2.390(d)(17 Section 2 Flooding Hazard Reevaluation FIGURE 9 JOCASSEE PMP DAD CURVES 50 45 40 35 30 12 Hour DqXh (in.) 48 Hour 25

-72 Hcour 20

.15 10 5 i-10 100 1000 10000 100000 Area (sq. rwO.)

The SCS runoff CN was used to estimate infiltration rates during design rainfall events. The hydrologic soil group for the watershed was estimated based on studies of soil types using generalized state soil maps for South Carolina and North Carolina. The soils in the watershed generally fall into the "B" hydrologic soil classification. The watershed soil cover is basically forest in good hydrologic condition. These factors lead to the selection of a runoff CN equal to 55.

In 1993, Duke Energy conducted a sensitivity analysis of the watershed by assuming an equivalent uniform infiltration rate of 0.093 inch/hour and back calculating a CN of 60 using the SCS CN formula. This parametric study indicated that varying the CN did not result in any significant changes in the peak stage.

37

. . ~Czui~jSnsv

.. .nform~tion- Wi*.thhold from public disdcos,_re undcr1 F .9* )1 Section 2 Flooding Hazard Reevaluation There are no continuous recording rainfall or stream gauges in the Jocassee watershed that would allow computation of a unit hydrograph for the basin. This fact required the use of synthetic unit hydrographs to model the watershed rainfall/runoff response. The Kirpich method was used to define the hydrograph lag-time in all of the Jocassee watershed sub-basins.

FIGURE 10 JOCASSEE WATERSHED SUB-BASINS I

38

Section 2 Flooding Hazard Reevaluation There are four reservoirs within the watershed upstream of Lake Jocassee: the Bad Creek pumped storage reservoir, Fairfield Lake reservoir, Sapphire Lake reservoir and Lake Toxaway reservoir. The following sections describe the assumptions that were included in the HEC-I model for reservoirs upstream of Jocassee.

Bad Creek Pumped Storage Reservoir Reservoir storage and elevation vary considerably over the course of a week. The initial conditions assumed to apply to this lake at the time of occurrence of the design storm were based upon an average storage of 16,565 acre-feet (ac-ft) 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 the reservoir is very small at 1.39 square miles. The principal means of outflow from the reservoir is through four turbines, which have a combined discharge capacity of 8,000 cfs. The East Dike was designed 2-ft lower than the Main and West Dams as an emergency spillway. The rock-fill design of the East Dike would provide protection from erosion due to overtopping. The 2-ft design height difference, storage, and 4-turbine discharge provide adequate margin for a site PMP. The reservoir operation is modeled by assuming no outflow up to an elevation of 2,310 ft msl at which point the four turbines start discharging at a constant rate of 8,000 cfs. The HEC-I model also provides for dam overtopping using the East Dike if the water surface elevation rises to the crest elevation of 2,313 ft msl; however, this elevation was not reached in the simulation.

Bad Creek is capable of safely passing the sub-basin specific inflow associated with the Jocassee PMF by a combination of storage and discharge.

FairfieldLake Reservoir The Fairfield Lake Dam was built in 1895. Under present state and federal criteria, the appropriate spillway design criteria are one-half PMF and full PMF, respectively. The USACE Phase I Inspection report indicates the dam will be overtopped for both the one-half and full PMF (USACE PMF= 14,800 cfs) by 3.4 ft and 5.2 ft, respectively. The normal pool and spillway are both at an elevation of 3,155 ft msl. The dam crest is at an elevation of 3,159.6 ft msl. The only discharge from the dam is through a double arch culvert spillway with a pipe or box of 6 ft nominal radius. The total storage capacity of the reservoir at the top of the dam is 39

Cv *,an ~"ri" C*,,*iiiv* iniu, ,',,&*t*n Wit*hhold fr*_ p~jblin disclosure under 0O" 3O ")f Section 2 Flooding Hazard Reevaluation approximately 1040 ac-ft. Breaching of this reservoir at 0.5 ft of overtopping was simulated in the HEC-1 model.

Sapphire Lake Reservoir The normal pool elevation is 3,100 ft msl and the lake at this elevation covers 46 acres. Two concrete pipes of 36 inches diameter each are employed for discharging low flows. In the Jocassee watershed model, the Sapphire Lake Reservoir is modeled with discharges through both the low-flow concrete pipes and dam overtopping along the concrete masonry crest. No dam breach 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 and discharge.

Lake Toxaway Reservoir The 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 5 ft below normal pool is used for low flow discharging. The Lake Toxaway Reservoir was modeled by considering the discharge through the side-channel spillway only. Lake Toxaway is capable of safely passing the sub-basin specific inflow associated with the Jocassee PMF by a combination of storage and discharge.

Lake Jocassee Reservoir The normal pool elevation varies between 1,108 and 1,110 (maximum) ft msl within the week, but the maximum power-pool during the hurricane season is 1,1 08 ft msl. All four turbines were assumed to be available to pass flood flows during the PMF. The constant four pump-turbine discharge is approximately 28,000 cfs. Both Tainter gates were assumed to be fully functional during the PMF.

The spillway rating curve for the ogee was computed using standard methods, accounting for abutment and pier energy losses. These discharges were then combined to produce the reservoir outflow rating curve. The 1,I10 ft msi initial water level elevation selected for modeling is 40

Cur S-'l3.,'*"

e-/a!ririty ie ;,*u iatL,,f ';.r.thhold from~ puJblip dicclos:rc ~dr0CR .390(d)(1)

Section 2 Flooding Hazard Reevaluation somewhat higher than the maximum power pool level of 1,108 ft that historically occurs during the hurricane season. Storage-elevation values are calculated by HEC-1 using the conic method based upon the elevation versus water surface area relationship.

In review of the existing FERC PMF analysis, the effectiveness of the ability of the Jocassee Development 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, and maintenance practices to ensure that equipment will be reliable.

The HEC-I model was used to test the sensitivity of availability of the two spillway gates combined with 4 turbines where different combinations of turbine availability were examined.

These simulations show that adequate margin to pass the PMF is provided by 2 gates without turbines. The two 30 ft by 38 ft wide radial gates have a proven record of reliability throughout the Duke Energy fleet due to the simple and effective design. There are four different ways to operate the gates including: the normal installed electric motor, backup air driven motor operation, backup electrical generator driven motor operation, and manual operation with a hand wheel. All equipment for the four diverse methods of operation is located at the spillway gates.

Personnel are trained and procedures are used to direct the required actions. Reliability is also assured through a comprehensive periodic maintenance program as required by FERC including an annual test to open the gates and 5-year full open testing. Amp readings for the motors provide readings to verify that the spillway gates are functioning as expected.

In addition to having reliable spillway gates, the 4 turbines provide significant additional margin for protection against overtopping. A conservative assumption was made that based on maintenance and operational procedures only 2 of the 4 hydro units will be available to pass flow. This, in addition to the spillway gates, yields additional margin.

Spillway gate operation and unit operation was evaluated for the impact of debris. Lake Jocassee historically does not have significant floating debris due to the stable shoreline, and a debris management program is in place to facilitate boating activity on the reservoir. The spillways and 41

Section 2 Flooding Hazard Reevaluation intake structures are also protected by the submerged openings of the spillway and intake structures. The PMF event in an impounded reservoir results in a low velocity profile in the reservoir during a natural flood event which limits the generation and transport of significant debris.

Monitoring and control of the reservoirs is assured by redundant level measurement in the reservoir and tailrace. Multiple video cameras provide redundant means to verify and monitor levels. All level monitoring including level alarms is provided to both the control room on site and to a central hydro control station that is staffed 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months per day.

Inventory control for storm events is managed through a combination of 15 ft of minimum reserve freeboard and procedures to anticipate major rain events. Weekly rain forecasts are prepared by Duke Energy and system operations of Bad Creek, Jocassee, and Keowee are coordinated based on the forecasted rainfall for the basin. This planning provides additional time to manage reservoir levels to anticipate large precipitation events like the PMF. Hydro Fleet Central Operations Center procedures require consideration for lowering reservoir levels in anticipation of significant storms. For normal operation, the weekly projection and daily/hourly precipitation monitoring has resulted in no precipitation based spillway operations at Jocassee over 40+ years of operation.

The HEC-I Jocassee watershed PMF modeling results were developed for each sub-basin including the 5 reservoirs. All reservoirs except Fairfield Lake were capable of safely passing the sub-basin specific inflow associated with the Jocassee PMF by a combination of storage and discharge. The modeling showed Fairfield Dam overtopped during the PMF, but due to the limited storage behind the dam (1040 ac-ft at top of dam), breach inflow to Jocassee was managed through storage and discharge.

The PMF outflow hydrographs and corresponding reservoir levels are shown on Figure 11. The outflow 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 peak 42

Cuddilib Q~u;ty 3 &3t;v~ liiiUIIIIdUUfl - vv;t~hcld frcm public diccio~ur~ nr,~e 10 CFR 2.330(dX1~.

Section 2 Flooding Hazard Reevaluation discharge is 85,405 cfs. The PMF peak reservoir (headwater) is approximately 1122.0 ft msl.

Overtopping of the Jocassee Dam is not considered a credible event due to the multiple and diverse means of passing water and the large margin of storage capacity associated with the reservoir.

FIGURE II JOCASSEE PMF HYDROGRAPHS 000,000 1124 540.000 1122 410.000 11K6 300.000 *1 CI 0 240,000 1112 180.000 1110 0 lo 0 500 1000 1500 2000 2500 o000 e500 4000 4500 5000 Time Iminuietl

-- . Inlog, -OhilTo,. Sta~e 2.3 Dam Failures 2.3.1 Potential Dam Failure The Keowee Hydroelectric Development is owned and operated by Duke Energy, and is part of the Keowee-Toxaway Project licensed by the FERC. The Keowee-Toxaway Project includes the Jocassee Pumped Storage Development and the Keowee Development. The FERC regulates the Project and their role includes regulatory oversight of all water retaining structures at both developments. The ONS is located on Lake Keowee adjacent to the Keowee Dam and tailrace.

43

"" nfnrrnnt'p - WAeithhold from .ubie-dlsdosut undu, i, ,,I( .3,IO)("l)

Section 2 Flooding Hazard Reevaluation Dam failures at the Jocassee and Keowee developments have been examined for potential impact at ONS. The loss of Lake Keowee initiated by a failure of the Keowee Dam was postulated as a design criteria event that was focused on cooling water supply and not on a dam failure initiating event. Based on a review of the UFSAR, modeling performed between 2009-2011 and existing dam failure studies performed to prepare FERC required emergency action plans (EAP) for the Project, it was determined that a hypothetical fair-weather failure of the Jocassee Dam and a resulting cascading overtopping failure of Keowee Dam would be the enveloping critical dam failure event for ONS.

2.3.2 Dam Failure Permutations FERC regulations require that dams for which failures pose a risk to human life be designed to survive a combination of loading conditions including forces from water and seismic events without risk of failure. Both the Jocassee and Keowee dams were designed, constructed, and are maintained to high standards and have performed in accordance with these stringent standards for over 40 years.

As a result of reviewing the dam structures at Jocassee and Keowee for criteria outlined in ANS 2.8 for design basis floods and comparing to the design basis requirements required by the regulating agency, FERC, it was determined that the Jocassee Development and Keowee Development have adequate margin to meet the criteria for overtopping and stability as required by NTTF Recommendation 2.1. Both Jocassee and Keowee can safely pass the PMF without overtopping as described in Section 2.2.

A seismic evaluation of Jocassee dam was performed based on current FERC seismic requirements, and on a 2007 updated fragility analysis based on seismic inputs from the 1989 EPRI uniform hazard study. Both seismic evaluations support a conclusion that a seismic failure of the Jocassee dam is not a credible event.

44

-ontaln C*'*u.it. Sc^'"tivo ,f..,,,-,.. Wi....... from pubki di~ciosui* under 11o CFR 2.3*U*c).1)

Section 2 Flooding Hazard Reevaluation The Jocassee Development was designed constructed and is maintained to meet FERC regulations. Both the Jocassee and Keowee dams were designed and constructed to conservative seismic criteria.

Jocassee Pumped Storage Project FERC 2503-SC Supporting Technical Information (STI),

No. 2503-JO-01, 12-3-09 REV. 0, Section 8.2.3 of the STI includes the minimum factors of safety computed by the 1990 analysis and the 1993 supplemental analysis as required by FERC.

For the three different loading scenarios: Earthquake - Normal Pool El I110 (upstream),

Earthquake - Normal Pool El 1110 (downstream), Earthquake and Rapid Drawdown- Pool El 1077 (upstream), the factors of safety are 1.24, 1.13, and 1.22, respectively. The required factor of safety for all three cases, as directed by FERC requirements, is 1.0. The factors of safety listed above are based on an earthquake acceleration of. 12g horizontal at the base of the dam.

Section 8.3 of the STI addresses the earthquake loading for the Jocassee Spillway which is computed using Chopra's "Simplified Analysis of Earthquake Resistance Concrete Gravity Dams," and is incorporated in the CGDAMS program. The spectra utilized are from ONS.

Section 8.3.1 indicates the calculated earthquake factor of safety is 1.8, which exceeds the conservative required FERC factor of safety of 1.0.

In addition to the deterministic evaluation shown above, an updated probabilistic assessment regarding seismically-induced dam failure was completed in 2007. This was needed to update the seismic fragility estimated for Jocassee Dam using state-of-the-art methods in order to reflect the increased knowledge of embankment dam behavior during an earthquake and the increased understanding of seismic hazard in the eastern U.S. The updated seismic fragility for the Jocassee Dam was used in the probabilistic risk assessment of ONS. The fragility is presented as the median peak ground acceleration (PGA) of a scaled uniform hazard motion, which represents the median hard rock hazard motion of the ONS site as given in the 1989 EPRI uniform hazard study.

45

Section 2 Flooding Hazard Reevaluation The fragility of the dam was characterized by the fragility of the downstream embankment slope. Given that the sliding criterion for fragility determination was chosen as 2 inches, the median fragility level of the dam was 1.64 g. The randomness, characterized by the lognormal standard deviation, 3 r, was found to be approximately 0.35. The overall uncertainty, characterized by the lognormal standard deviation, j3 u, was found to be 0.67. Thus, the HCLPF (high confidence of a low probability failure), value was 0.305g.

The above information represents two separate approaches for the seismic assessment of Jocassee Dam, deterministic and probabilistic. Both approaches employ current accepted methodologies. Based on these assessments presented above, a seismic failure of Jocassee is not considered a credible failure..

2.3.3 Unsteady Flow Analysis of Potential Dam Failures Since a seismic failure of the Jocassee dam is not credible, a postulated non-seismic failure of the Jocassee Dam is assumed in order to demonstrate the corresponding flood hazard postulated at the ONS site. This section summarizes the resulting flood wave and corresponding flood elevations at the ONS site. To simulate a potential fair-weather failure of the Jocassee Dam an unsteady flow model of the Jocassee/Keowee/Hartwell reservoir system was developed using the USACE HEC-RAS (Version 4.1) program. The HEC-RAS model is a 1-D dynamic flow model with unsteady flow model components used in estimating inundation due to hypothetical dam failures.

The HEC-RAS Jocassee-Keowee Dam Breach Model (1-D Model) was developed to include additional Lake Hartwell detail and cross-section refinement of Lake Keowee, including the Keowee River, Little River, and the connecting canal sections of the reservoir. The I-D Model capabilities include:

Reservoir storage volume;

Manning's n value sensitivity; 46

Section 2 Flooding Hazard Reevaluation

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 into Keowee River.

HEC-GeoRAS Version 4.2.93 was used to develop model geometry independent of HEC-RAS using available GIS data from the State of South Carolina (with some overlap into Georgia) to create Digital Elevation Model (DEM) electronic files for Jocassee, Keowee, and Hartwell reservoir systems. A small portion of the lower southwestern comer of Lake Hartwell was modeled 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 1-D Model consists of the Jocassee, Keowee, and Hartwell reservoir systems with an approximate length of 44 miles. The hydraulic responses of three reservoirs comprising 17 river/tributaries are incorporated in the I-D Model. An independent peer review was performed on the geometry of the 1-D Model, unsteady flow boundary and initial conditions, and results.

The 1-D Model's complexity and detail required numerous model sensitivity runs in order to optimize the 1-D Model's performance and stability.

Additionally, a 2-D hydraulic model was developed to simulate the complex flow paths moving between the Keowee and Little River arms of Lake Keowee including the ONS Intake Canal and Dike that abuts the ONS site at the south forming an island during dam breach simulations. The 2-D analysis was performed to add detail to the HEC-RAS analysis and model the potential inundation in critical areas identified around ONS. A 2-D computational model was constructed with a domain of the area immediately surrounding the station with a 2-D mesh. The mesh size was selected to model the desired area while keeping the size of the computational array at a manageable size and facilitate the analysis within the time frame of the study and within the computing power of current, publically available micro-computers. Tables and graphs referenced in this section can be found in Appendix D.

47

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l,;'u1*..ata*,, - Wvihhoia orn public ,)

Section 2 Flooding Hazard Reevaluation The flood wave associated with the fair-weather piping breach failure of Jocassee Dam has four potential routes to the Yard. Three of the routes are associated with high water surface elevations within Lake Keowee, while the fourth route is associated with the Keowee River below Keowee Dam. The first route is located at the ONS discharge outlet that adjoins the right abutment of Keowee Dam. Water could flow over the parking lot adjoining the ONS discharge structure and through the road leading to the Yard. The second route is associated with the Energy Center swale that adjoins the SC 130 bridge crossing of the Keowee Lake-Connecting Canal. The third route is associated with the overtopping of the north face of the ONS Intake Canal Dike. The fourth route is associated with the rising Keowee Dam-Keowee River tailwater due to a cascading failure of Keowee Dam.

Unsteady flow requirements in HEC-RAS require detailed inputs that describe boundary conditions and initial conditions at the first upstream cross-sections and I-D Model endpoint. In addition, boundary conditions are presented at internal model locations such as spillway gates and hydroelectric turbines at the respective hydraulic structures.

The initial base flow conditions utilized for the 2013 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 allow the HEC-RAS model to maintain normal conditions at each of the modeled facilities, prior to the routing of the dam failure hydrographs.

Total spillway discharge capacities for the Jocassee and Keowee Developments are provided in the FERC STI documents. The total spillway discharge capacity of the Hartwell Dam was provided by the USACE. The family of curves for various gate openings and heads utilized in the model were developed by HDR based on the provided total spillway discharge capacities for each development. The discharge from all hydro units utilizes rating curves at the respective developments with open/close operation based on reservoir elevation settings.

48

.Conbrt3:ri*, Sor.:,nitc I,,fom..... v, '^.Nihhol from., p,,%"-lt~asclosure unaer -iu CFR 2.33.)1 Section 2 Flooding Hazard Reevaluation The gated spillway at Keowee Dam uses reservoir elevation settings for their respective operations. The spillway gates at Jocassee Dam do not require operation to support the ONS external flooding event and remain closed.

Jocassee Development I-D Model The two spillway Tainter gates are operated based on:

" Open gates at a rate of 1 minute per foot; all gates fully opened in approximately 33 minutes.

" Maximum gate opening of 33 ft.

Keowee Development 1-D Model The four spillway Tainter gates are operated based on:

" Flood operating procedure (non-preemptive operations) - initiate gate operations once the reservoir elevation reaches an elevation of 801 ft msl.

" During Jocassee Development failure scenarios, gates start opening as soon as a change 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 23 minutes, if needed.

" Maximum gate opening of 35 ft.

Hartwell Development I-D Model The 12 spillway Tainter gates are operated based on:

" Flood operating procedure (non-preemptive operations) - initiate gate operations once the reservoir elevation reaches an elevation of 665 ft msl.

" During preemptive gate operations, gates begin opening 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months after breach of the dam of interest is initiated.

Open gates at a rate of 10 minutes per foot; all gates fully opened in approximately 6.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months , if needed.

" Maximum gate opening of 35.5 ft.

49

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......... F""9(d,1 Section 2 Flooding Hazard Reevaluation The noted starting reservoir elevations at the Duke Energy and USACE developments (Jocassee, Keowee, and Hartwell) correspond to each facility's respective normal maximum pool elevation and are provided in Table D-2.

Based on prior Jocassee-Keowee dam breach modeling, the hypothetical fair-weather failure of Jocassee Dam produces a flood wave that creates conditions for a cascading failure of Keowee Dam and, potentially, the cascading failures of the ONS Intake Canal Dike and Little River Dam.

Model Breach Parameters Duke Energy and HDR performed dam breach parameter research specific for application at the Jocassee Dam and found a publication (Xu and Zhang 2009) that applied regression methodology to calculate breach parameters that included a dam erodibility factor in the calculation. Prior regression-based methodology (Froehlich 1995a, 1995b, 2008; Walder and O'Connor 1997; MacDonald and Langridge-Monopolis 1984), used by HDR in previous dam breach modeling, utilized similar dam and reservoir control variables adapted by Xu and Zhang (2009) but did not include dam erodibility. Duke Energy retained the services of Joseph Ehasz, P.E., and Dr. David Bowles, P.E. (Ehasz and Bowles 2013) to perform an independent assessment and to provide a peer review on the application of the proposed breach parameters for Jocassee and Keowee Dams.

Keowee Development Breach Parameters Duke Energy provided the Keowee Dam breach parameters to Ehasz and Bowles (2013) for a professional assessment and opinion on their applicability at Keowee Dam. The modeled breach parameters and failure time were determined by Ehasz and Bowles (2013) to be "realistic but conservative" for the cascading failure of Keowee Dam. The modeled Keowee breach parameters are presented in Table D-3.

The Keowee Dam is approximately 3,500 ft long and is comprised of the Main Dam and West Saddle Dam (WSD). The WSD is approximately 2,100 ft long and varies in height from 20 ft to 55 ft with a minimum crest elevation of 815 ft msl. The WSD is exposed to the same overtopping characteristics and failure potential as the Keowee Main Dam. HEC-RAS is limited 50

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Section 2 Flooding Hazard Reevaluation to a single dam breach designation. Therefore, to overcome this model limitation, a breach of the WSD was simulated using a 1,880-foot by 20-foot crest gate in the Jocassee-Keowee Dam Breach Model. The HEC-RAS model is assigned a full crest gate opening time frame of 30 minutes to simulate the WSD breach development. The crest gate does not begin to open until the reservoir elevation exceeds 817 ft msl.

The default sinusoidal wave breach progression provided in HEC-RAS was determined to be reasonable by Ehasz and Bowles (2013) and approved for application at the three Keowee Development dam structures by Duke Energy.

In the 2-D model, the breaching of Keowee Dam and the WSD, and if necessary, the ONS Intake Canal Dike was implemented by updating the elevations assigned to the computational mesh during the simulation, according to the breach parameters. Each structure was updated five times during its failure. The stepped breach approach in the 2-D model is different than the sine wave breach progression used in the HEC-RAS model. Dam failure occurs continuously over the breach interval in HEC-RAS, while the 2-D model breach occurs in five stepped increments over the failure interval. The use of five increments in the 2-D model represents a balance between modeling efficiency and representing the breach accurately. Figure D-1 shows a comparison between the sine wave breach progression approach used in the HEC-RAS modeling and the incremental approach utilized in the 2-D model analysis. Comparing the two approaches, it is evident that the incremental approach used in the 2-D model is an appropriate approximation.

Jocassee Dam Breach Parameters The breach parameter selection process for Jocassee Dam is based on nonlinear regression methodology developed by Y. Xu and L. M. Zhang (Xu and Zhang 2009). Other breach parameter methods were evaluated for sensitivity purposes. Empirical relationships were developed between multi-breach parameters and dam/reservoir control variables. The breach parameters are identified as breach depth, top width of breach, average breach width, peak breach discharge, and failure time. The dam and reservoir control variables include dam height, 51

Section 2 Flooding Hazard Reevaluation reservoir shape coefficient (reservoir volume and depth), type of dam, failure mode (overtopping or piping), and dam erodibility. There are three levels of dam erodibility and they include high, medium, and low erodibility (LE). Dam erodibility is based on the material composition of the dam structure, compaction conditions, cross-sectional geometry of the dam, and construction time. The Jocassee Dam is a 385-foot-high rock-fill embankment with an impervious core. Xu and Zhang (2009) identified erodibility as the most important control variable in the calculation of mean breach parameters and Ehasz and Bowles (2013) concurred, noting that "Our interpretation, based on the rock-fill materials, compaction and density, places the rock-fill at Jocassee Dam between the very low and LE category." Xu and Zhang employ two forms of regression analysis to establish empirical relationships in the determination of mean values for the five breach parameters. The additive form of regression provides linear relationships with Xu and Zhang identifying this approach as Best Simplified Prediction (BSP). The multiplicative form of regression provides non-linear relationships and Xu and Zhang identify this approach as "Best Exact Prediction" (BEP). The two regression forms of breach parameter calculations for Jocassee Dam are presented in Table D-4.

The independent breach parameter assessment performed by Ehasz and Bowles (2013) noted that the Xu and Zhang (2009) mean breach parameter methodology provides the best prediction among similar regression methods, with an emphasis on the LE conditions exhibited by Jocassee Dam. In addition, the calculation is considered to be a "state-of-the-practice" for estimating piping dam breach parameters. Ehasz and Bowles (2013) recommended that the breach parameters reflect the mean values calculated by the BEP regression equations for the LE case.

The Jocassee Dam breach parameters are presented in Table D-5 Appendix D.

The breach progression for the Jocassee Dam required the development of a site-specific hybrid sine wave. Multiple evaluations were developed to optimize the peak breach discharge with the Xu and Zhang peak discharge, such that the timing of the peak discharge coincided with the peak tailwater elevation. The peak stage-discharge timing criteria are based on recommendations from Ehasz and Bowles (2013). The evaluation involved adjustments to the piping flow coefficient and the breach weir coefficient. The Jocassee-Dam stage-discharge hydrographs and 52

Cor.,i.3uri.,' Sen"*"t""; lh~furmauion - vvitnhoia irurri ,uu,,k d*;.o!_'ro un'cr

,10*^ Z,*F'R"i.3O0)(1 Section 2 Flooding Hazard Reevaluation breach progression analysis for the BEP LE case is shown in Figure D-2. The approved Jocassee Dam hybrid breach progression sine wave is shown in Figure D-3.

2-D Modeling The 2-D model domain includes the area immediately surrounding the station, shown in Figure D-4. The results of the 1-D model analysis were extracted and utilized as boundary conditions for the 2-D analysis. Version 2.2 of the computational hydraulic model SRH-2D (the 2-D model) (Lai 2008) was utilized for this analysis. Version 2.2 was released in August 2012. This model allows for analysis of open channel flows on unstructured hybrid meshes. The 2-D model supports the use of a "hybrid" mesh which utilizes both triangles and quadrilaterals. The use of a hybrid mesh allows for better computational efficiency without loss of accuracy compared to a fully triangular mesh. The 2-D model applies a finite-volume discretization to the 2-D, depth-averaged St. Venant equations, and conserves mass both locally and globally. The code can process wetting and drying of elements, steady and unsteady flows, sub-critical and super-critical flows, and complex channel geometries. The 2-D model has been extensively tested and validated (Lai 2008).

In the 2-D model, Manning's roughness coefficients (Manning's n-values) were used to represent the frictional resistance and energy loss in the flowing water. For this analysis, to the extent possible, the Manning's n-values match the companion I-D model, where, Manning's n-values were selected for the river cross-sections based on a review of topographic maps and reference materials in Chow's "Open-Channel Hydraulics" (Chow 1988). Manning's n-values were limited to two designations in the model - floodplain and overbank (n = 0.08) and main channel (n = 0.025). Figure D-5 depicts the spatial extent of the Manning's n-values. It is important to note the absence of main channel Manning's n-values just downstream of Keowee Dam in Figure D-5. The coefficient utilized in this area of the model is the same as the floodplain and overbank value. A higher Manning's n-value in this area models the additional turbulence and energy losses in this area during the breaching scenario.

Both models were improved by utilizing appropriate results from one another. These modifications improved both models and brought the results into closer alignment. A series of 53

Go.... So................. ,, - vvthn ,d from p i10 Section 2 Flooding Hazard Reevaluation model runs was performed to test performance between the models and adjustments were made that produced excellent comparison and agreement and a high degree of confidence for using both models in this evaluation and, specifically for the 2-D model, in areas of flow complexity and site-specific details, such as the depth of inundation in and around ONS.

2.3.4 Water Level at the Plant Site A comparison of model output results is presented in Table 7. The comparison details the high level of agreement between the I-D and 2-D models as well as the overall hydraulic impact on ONS 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 7, the comparison of the 2-D model results with the I-D model results indicates that the timing of breach initiation (Keowee Pool reaching 817 ft msl) occurs slightly earlier in the 2-D model at Keowee Dam, 0.04 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months (-2.5 minutes). The ONS Intake Canal Dike does not breach, as the water surface does not overtop the structure.

The maximum upstream water surface elevation estimated by the 2-D model at Keowee Dam occurred slightly later than in the I-D model by 0.05 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months (3 minutes) and was 1.7 ft higher.

The maximum upstream water surface elevation estimated by the 2-D model at the ONS Intake Canal Dike occurred later than in the I -D model by 0.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months (30 minutes) and was 2.8 ft lower.

The maximum upstream water surface elevation estimated by the 2-D model at the Visitor's Center Swale occurred earlier than in the I-D model by 0.02 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months (-1 minute) and was 2.0 ft lower.

The maximum upstream water surface elevation estimated by the 2-D model in the Tailwater near ONS occurred later than in the I -D model by 0.9 hours1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months (-55 minutes) and was 3.0 ft higher.

54

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Section 2 Flooding Hazard Reevaluation Dam breach inundation levels did not exceed elevation 790.4 ft resulting in approximately 5.6 ft of inundation margin between the nominal Yard elevation of 796 ft and the maximum inundation level. The SSF located in the Yard was not inundated by dam breach flood waters.

The comparison indicates that between the I-D model results and the 2-D model results there are no significant differences in the model results in terms of maximum stage reached and timing in the reservoir. While the models do not produce the same results, the trends in the results between the models are generally preserved. This agreement provides confidence in the results of the simulations.

55

I .. I I

~~curiiv ~ ~ U ~ i ~ ~ ~~ziz~ur~. u ~2f U UI I -t-ý(d)(ý Section 2 Flooding Hazard Reevaluation TABLE 7 COMPARISON OF I-D AND 2-D MODEL RESULTS - TIME TO BREACH AND MAXIMUM WATER SURFACE ELEVATIONS (Elevation in ft msl and Time in hours)

Breaching Keowee Dam Intake Dike HEC-RAS 2-D HEC-RAS 2-D Elevation Decimal Time Elevation Decimal Time Elevation Decimal Time E im 817 16.28 817 16.24 n/a n/a n/a n/a Maximum Water Surfaces Keowee Dam Intake Dike HEC-RAS 2-D HEC-RAS 2-D Elevation IDecimal Time Elevation Oecimal Time Elevation IDecimal Time Elevation Decimal Time 818.4 16.53 820.1 16.58 8101 17.17 807.2 17.67 Maximum Water Surfaces Swal e Tall water HEC-RAS 2-D HEC-RAS 2-D Elevation DecimalTime Elevation DecimalTime Elevation Dedmal Time Elevation ]Decimal Time 817.5 16.55 815.5 16.53 787.4 17.52 790.41 18.41 Maximum Water Surfaces SSF SSF HEC-RAS 2-D HEC-RAS 2-D1 Elevation [Dedmal Time Elevation Decimal Time Depth iDdmal Time Depth Dedmal Time al l/a n[ /a n/a 0 n/a 0 n/a Figures D-6A through D-9B illustrate the general flow patterns, depths, and velocities (Figure A-Series), and water surface elevations (Figure B-Series) at time (t) = 15.0, 17.0, 18.4 (Peak Tailwater), and 20.0 hours0 days 0 hours 0 weeks 0 months for the modeled case over the 2-D model domain. The time (t)= 15.0 hours0 days 0 hours 0 weeks 0 months occurs before the main Keowee Dam is breached, (t)=17.0 hours0 days 0 hours 0 weeks 0 months occurs right as the Keowee Dam has completed breaching, and (t)=20.0 hours0 days 0 hours 0 weeks 0 months occurs after the breach and the peak flows and peak water surface elevations have occurred in Keowee Dam headwater area.

As stated previously, 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 56

CGnt:a.n5 &.eew*rit-Emn*,,t;N;¢h, yTi~,at~an -wilnnola trom puff~ als-TrM . 'Jdrý0 FP Section 2 Flooding Hazard Reevaluation failure at Jocassee Dam. Figure D-I 0 shows the location of monitoring locations that provide the basis for Figures D-l I through D-15, which show the water depths and elevations upstream of Keowee Dam, Keowee 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 dry most of the time. Recall that the Yard is potentially exposed to three potential inundation paths. The primary source could be the ONS Intake Canal Dike because of its proximity to the Yard, while the Visitor's Center Swale wall and Keowee Dam tailwater could serve as secondary sources, and which is dependent on event timing.

With respect to the three different inundation paths, the 2-D model results indicate that the peak water surface elevations stay well below the critical elevation for each path.

The ONS Intake Canal Dike crest is nominally at an elevation of 815 ft msl, but has a wall built along the North End to provide protection from flood waters entering the Yard to an elevation of 824 ft msl. Figure D-12 indicates that the peak water surface elevation in the ONS Intake Canal Dike reaches 807.2 ft msl.

The Visitor's Center Swale wall is built to an elevation of 832 ft msl. Figure D-14 indicates that the maximum water surface elevation reached below the Visitor's Center Swale wall is 815.5 ft msl.

The nominal elevation of the Yard is 796 ft msl. The Yard is potentially exposed to flooding via water flowing over the Keowee Dam (the west end of the WSD) or to downstream backwater from Keowee Dam (Tailwater). Figures D-12 and D-15 indicate that the Yard stays dry during the modeled dam failure. Figure 12 indicates that the maximum water surface elevation in the Keowee Dam tailwater area is 790.4 ft msl, which is approximately 5.6 ft less than the Yard elevation. Furthermore, Figures D-6A through D-9B show no velocity and water surface elevation in the Yard at peak tailwater elevation time (t) = 18.4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months .

57

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Section 2 Flooding Hazard Reevaluation 2.4 Storm Surge and Seiche The ONS site is located on an inland reservoir in the northwestern corner of South Carolina and is not subjected to storm surge or seiche flooding. Storm surge and seiche flooding have been reviewed in the FERC-required evaluation of the Keowee and Jocassee Developments and are not 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 the topography and geology around the reservoirs.

Storm surge events are not expected to affect the site. The maximum wave height and wave run-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:

TABLE 8 WIND-DRIVEN WAVE RUN-UP RESULTS Location Wave Height Wave Run- Maximum Fetch Up Keowee Main Dam - Fair Weather 6.10 ft. 5.84 ft. 2.37 miles Keowee Main Dam - PMF 3.60 ft. 3.73 ft. 2.37 miles Jocassee Main Dam - Fair Weather 6.48 ft. 7.09 ft. 3.04 miles Jocassee Main Dam - PMF 3.80 ft. 4.47 ft. 3.04 miles The results using ANS 2.8, 2-Yr Wind Velocity are as follows:

TABLE 9 2-YEAR WIND VELOCITY RESULTS Location Wave Height Wave Run-Up Maximum Fetch Keowee Main Dam - Fair Weather 5.33 ft. 5.11 ft. 2.37 miles Keowee Main Dam - PMF 3.20 ft. 3.34 ft. 2.37 miles Jocassee Main Dam - Fair Weather 6.10 ft. 6.66 ft. 3.04 miles Jocassee Main Dam - PMF 3.80 ft. 4.43 ft. 3.04 miles 58

Section 2 Flooding Hazard Reevaluation The wave height and wave run-up figures are vertical measurements above full pond or PMF elevations as tabulated above. The design normal freeboard at each dam is 15 ft which is adequate 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 reservoir has not exceeded an elevation of 1110 ft msl since construction was completed (approximately 40 years).

During combined events of a PMF and wind-driven waves, because of the time-lag characteristics of the runoff hydrograph after a storm, it is not considered credible that the maximum reservoir elevation due to PMF would occur simultaneously with winds causing maximum wave heights and run-ups. Refer to Section 2.8 for an additional discussion of combined effects of a wind-driven wave impact combined with a PMF.

2.5 Tsunami Since 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 Flooding Since the ONS site is not located in an area of the U.S. subjected to periods of extreme cold weather that have been reported to produce surface water ice formations, ice induced flooding will not produce a credible maximum water level at the site and is not considered a realistic external flooding hazard to ONS.

2.6.1 Ice Effects Long-term air temperature records (1951-2011) available at the South Carolina State Climatology Office were reviewed to assess historical extreme air temperature variations at the ONS site. The analysis was also supported by onsite temperature data measured at the ONS site.

59

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Section 2 Flooding Hazard Reevaluation 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 a mean air temperature of 59.7' Fahrenheit.

There has not been a recorded event of significant surface ice formation on Lake Jocassee or Lake Keowee since filling in the early 1970's.

2.6.2 Ice Jam Events There are no recorded ice jam events in the upper reach of the Savannah River based on a search of the USACE's Ice Jam Database. Water temperatures in this area of the southeast U.S.

consistently remain above freezing.

2.7 Channel Diversions Due to the location of ONS on the banks of Lake Keowee and the upstream topography of the reservoir, channel diversion is not a credible flooding event. The controlling external flooding event is upstream dam failure.

2.8 Combined Effects Section 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 in northwestern South Carolina protected from coastal events as well as extreme cold weather events. Both reservoirs are considered "enclosed bodies of water" as defined in ANS 2.8 Section 7.3.3. Based on this definition and guidelines noted in ANS 2.8 Section 9.2.3.2 for the streamside location of ONS, Alternative II was determined to be the most limiting case and was used for reviewing the possible combinations producing maximum flood levels. This includes:

I. PMF.

2. 25-year surge or seiche with wind wave activity.

60

Section 2 Flooding Hazard Reevaluation

3. 100-year or maximum controlled level of water body, whichever is less.

Dam failure as defined above in Section 2.3.1 was also reviewed.

Combined flooding effects (PMF, dam failure and/or wind-driven waves) are concluded in Table 10. Flooding in upstream reservoirs was reviewed using modem computer programs for hydrology and hydraulics and the current HMR 51 rainfall. PMF flood elevations do not produce overtopping at Keowee or Jocassee. Dam failures were simulated for Jocassee and Keowee as detailed in Section 2.3. The failure of Jocassee dam combined with the cascading failure of Keowee Dam produced a flood inundation elevation of 790.4 ft msl. The dam failure breach inundation does not reach the Yard nominal elevation of 796 ft msl. Storm surge and seiche generated waves were not considered a credible event for evaluation of an ONS flood hazard. A combined event of the PMF plus wind-driven waves was reviewed for both Keowee and Jocassee. As shown in Table 10, Keowee maintains approximately 2.8 ft of freeboard when combining the peak PMF elevation with wind driven waves. A PMF for Jocassee coupled with wind driven waves (Section 2.4) would produce some lapping of waves over the 20 ft wide crest of the dam, however, due to the large riprap that comprises the upstream and downstream shell of the Jocassee rock-filled dam, the breaking of waves over the crest of the dam is not expected to have any significant impact on slope stability.

61

Ce.ldn 3~I tyS 1 0 ;~ I~mzitaten kAithhotd from Mpulid G loweu under 10 CFRI2-390(d~(1 Section 2 Flooding Hazard Reevaluation TABLE 10 COMBINED EFFECTS FLOOD ELEVATIONS Reevaluation Reevaluation Combined Combined Effects Flood Causing Mechanism Effects -Flood Flood Elevation Elevation Jocassee Keowee Flooding in Reservoirs 808.9 ft ms] 1122.0 ft msl Combined with 790.4 ft msl Dam Failures Dam __Failures_ Jocassee failure Storm Surge and Seiche/Wind-Wave Run-up 812.2 ftms] 1]26.4 fi msl plus PMF Tsunami N/A N/A Ice Induced Flooding N/A N/A Channel Diversion N/A N/A 62

Cent3ir.~ ~uiLy C~. 1~ti~o Inforrnntizn WiLhnoia Tram public aisciosure undt. 13 GFR 2.39O(d',(~)

Section 3 Comparison of Current Design Basis and Reevaluated Flood Causing Mechanisms Table II below summarizes the comparison of current design basis and reevaluated flood causing mechanisms, which includes wind effect for flooding in reservoirs and dam failures.

The table outlines a comparison for current design basis and reevaluated flood causing mechanisms for the ONS site including the dam failure mechanism that considers the postulated fair-weather piping breach failure of Jocassee dam to be the enveloping dam failure event. As summarized in Section 2.8, dam failure at Jocassee is the single external event that is considered creditable for producing flood hazard impacts at ONS.

TABLE 11 CURRENT DESIGN BASIS AND REEVALUATION FLOOD ELEVATIONS Current Reevaluation Flood Causing Design Basis Reevaluation Flood Delta Mechanism Flood Flood Elevation From Design Elevation Basis Local Intense 798.17 ftmsl 800.39 ft msl +2.22 f.

Precipitation (Note 1)

Flooding in 808.0 ft msl 808.9 ft msi +0.9 ft.

Reservoirs Dam N/A 790.4 ft msl N/A Failures (Note 3) (Note 2)

Storm Surge and Seiche/Wind-Wave N/A N/A N/A Run-up Tsunami N/A N/A N/A IceInduced N/A N/A N/A Flooding Channel Diver N/A N/A N/A Diversion Combined effects N/A 812.2 ft msl N/A Notes:

1 Location of recorded maximum Yard elevation isbased on location in Figure B-i , West 13 2 Location of recorded maximum inundation elevation is shown in Figure D-10, Keowee TW 3 Enveloping dam failure scenario is fair-weather Jocassee Dam and cascading Keowee dam failure.

63

Section 3 Comparison of Current Design Basis and Reevaluated Flood Causing Mechanisms 3.1 Local Intense Precipitation The current licensing/design basis case ONS flood elevation from the LIP is 798.17 ft msl (Section 1.2).

The Beyond licensing/design basis case reevaluated flood elevation is 800.39 ft msl, is 2.22 ft more than the current design basis flood elevation, and 3.89 ft above the elevation of safety-related SSCs of 796.5 ft msl. The elevation reported here is specific to the point near the Unit 1 Reactor Building (West 13). Because of the detailed analysis using a 2-D model, water elevations around the Yard vary significantly. Reference Table C-i for additional flood inundation elevations at selected points around the Yard.

3.2 Probable Maximum Flooding There is no current design basis ONS flood elevation from probable maximum flooding in upstream reservoirs with coincident wave run-up.

The reevaluated flood elevation is 808.9 ft msl or 812.2 ft msl with coincidental wave run-up.

The PMF elevation increased by 0.9 ft from the current flood elevation and does not impact safety-related SSCs.

3.3 Dam Failures There are no current design basis ONS dam failure flood elevations.

The reevaluated flood hazard elevation due to a combined Jocassee and Keowee dam failure assuming full reservoir elevations at the initiation of the Jocassee dam breach is 790.4 ft msl.

This elevation is due to the initial failure by piping of the Jocassee main dam and the cascading failure of the Keowee main dam and West Saddle dam due to overtopping. With the Yard at a nominal elevation of 796 ft msl, this provides approximately 5.6 ft of margin. The Keowee Hydro Powerhouse and 230Kv switchyard would be inundated by this flooding.

64

"~ntc~i.~ y ""rz I~(marion Withhl, frzm

- UldlObuu1 Section 3 Comparison of Current Design Basis and Reevaluated Flood Causing Mechanisms 3.4 Storm Surge and Seiche Storm surge and seiche are not expected to affect the site for the reasons listed above in Section 2.4.

3.5 Tsunami Tsunami induced flooding is not expected to affect the site for the reasons listed above in Section 2.5.

3.6 Ice Induced Flooding Ice induced flooding is not expected to affect the site for the reasons listed above in Section 2.6.

3.7 Channel Diversion Channel diversions are not expected to affect the site for the reasons listed above in Section 2.7.

3.8 Combined Effects There are no current licensing/design basis case combined site flood hazard effects. Combined flooding effects are discussed in Section 2.8.

65

curi iscosure under 10 CF )

Section 4 Interim Actions Taken or Planned Based on the results listed above, only two of the flood causing mechanisms produce flood waters that could potentially impact the site, the LIP rainfall event and the combined Jocassee and Keowee dam failure.

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 design basis flood elevation, and 3.89 ft above the elevation of safety-related SSCs of 796.5 ft msi. The elevation reported here is specific to the point near the Unit I Reactor Building (West 13).

The reevaluated flood hazard elevation due to a combined Jocassee and Keowee dam failure, assuming full reservoir elevations at the initiation of the Jocassee dam breach, is 790.4 ft msl in the Keowee tailrace.

The 2.1 Hazard Reevaluation has shown that ONS meets the original licensing/design basis and there were no errors discovered in the analysis that led to this determination. The 2.1 Hazard Reevaluation has also shown that ONS exceeds the current licensing/design basis case flooding levels for the new beyond design basis hazards for an upstream dam failure and for LIP. As a result, an Integrated Assessment will be required for the site and will be performed as directed by JLD-ISG-2012-05. Based on the flooding levels determined by the 2.1 Hazard Reevaluation, ONS will be developing modifications to provide additional levels of protection for the site for the new hazards. The final designs will be based on the outcome of the Integrated Assessment and associated regulatory action to update the site's licensing basis. Additionally, this issue has been entered into the ONS Corrective Action Program (CAP) for further analysis, and any required interim actions will be determined.

66

S~ecurity

~enbiuv~. Information - Withhr'Id from ~ubiio aisciosure urid~1 10 CFR 2.33~d)( l~.

Section 5 Additional Actions Additional actions have been taken for both the LIP event and the postulated fair-weather failure of the Jocassee Dam. ONS was in the process of analyzing both of these flood hazards prior to the release of the March 12, 2012, NRC 10 50.54(0 request for information.

Early in 2012, a question arose about the LIP analysis for the Yard, which was entered into the ONS CAP. This led to a thorough investigation of the current status of various structures on site and their ability to resist flood waters from an LIP event. A walkdown was performed for all Class 1 structures and other structures deemed critical to safe shutdown. The walkdown surveyed the building envelope to identify weaknesses in flood protection. It was determined that ONS is in nonconformance with the Licensing Basis as described in UFSAR Section 3.4.1.1 because water may exceed a 6-inch sill in a few areas surrounding the Class I structures. All other areas surrounding the structures were determined to be acceptable. Interim actions were taken in the form of adding Flood Barrier Sandbags and Gryffolyn coverings. These barrier locations and heights are based on a preliminary analysis that was performed on local flood heights in the Yard. The LIP data discussed in Section 1.2.1 of this report finalizes and validates the concern from the preliminary analysis. The sandbag flood barriers continue to serve as an effective measure against the finalized current licensing basis LIP event.

Based on concerns raised by the NRC, by letter dated August 15, 2008, (ML081640244) the NRC requested information in a 10 CFR 50.54(f) letter. Duke Energy responded on September 26, 2008 (ML082750106) to the licensee's request. The NRC staff reviewed the information and after further correspondence, the NRC staff issued a CAL to the licensee on June 22, 2010, which included fifteen CMs to mitigate against the postulated fair-weather failure of Jocassee Dam. Those fifteen interim actions are listed above in Section 1.5 of this report.

The staff also requested that the CMs listed in the CAL remain in place until they can be superseded by regulatory action related to the Fukushima responses.

67

,,acins.; Se 3a,,o;i;, ;ifu, ,,st;,. 'X.thh.ld puTblic disclosure unde . . )

Section 5 Additional Actions ONS has installed two other interim actions to help protect against the hypothetical fair-weather failure of the Jocassee dam as it was described in the January 28, 2011, SE. These two features are the temporary ONS Intake Canal Dike Flood Barrier and the permanent swale wall located above CTP-1. ONS does not take credit for these two features in the CLB. These two items decrease flooding levels from the postulated fair-weather failure of Jocassee Dam as described in the January 28, 2011, SE. The swale wall, which is located north of CTP-1, keeps CTP-I from being damaged during the event. The ONS Intake Canal Dike flood barrier wall significantly lowers the water level in the Yard from the first peak of flood waters.

68

Ccntoin3 3e~.ur" Sensl~lve ffIIdi -Vrioi rmpbcasiueunei CR230J' Section 6 References Bohman, L.R. (USGS), Determination of Flood Hydrographsfor 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, Water Resources Division, June 1989.

Chow, Ven Te, Maidment, David R., Mays, Larry W., Applied Hydrology, McGraw Hill, 1988.

. , Open-ChannelHydraulics,McGraw Hill, 1959.

Duke Energy, ONS Units 1, 2 & 3, Final Safety Analysis Report, Revision 18, September 12, 2012.

. ONS Units 1, 2 & 3, UpdatedFinalSafetyAnalysis Report, Revision 1, June 25, 2012.

Ehasz, P.E., Joseph L. and Bowles, P.E., Dr. David S., 2013. "Jocassee and Keowee Dams, Breach Parameter Review." February 2013.

Federal Emergency Management Agency. 1982. City of Augusta, Georgia, Flood Insurance Study. April 1982.

Federal Energy Regulatory Commission. 2007. Engineering Guidelines for the Evaluation of Hydropower Projects, Chapter VI, Emergency Action Plans, Office of Hydropower Licensing, Washington, D.C. October 2007.

1993. Engineering Guidelines for the Evaluation of Hydropower Projects, Chapter II, Selecting and Accommodating Inflow Design Floods for Dams, Washington, D.C.

October 1993.

Froehlich, D.C. 2008. "Embankment Dam Breach Parameters and Their Uncertainties." ASCE Journal of Hydraulic Engineering. December 2008. pp. 1708-1721.

69

Section 6 References 1995a. "Embankment Dam Breach Parameters Revisited." Proceedings of the 1995 ASCE Conference on Water Resources Engineering, San Antonio, Texas. August. pp.

887-891.

1995b. "Peak Outflow from Breached Embankment Dam." Journal of Water Resources Planning and Management, vol. 121, no. 1, pp. 90-97.

Hager, Willi H., "Discharge Measurement Structures," Hydraulic Structures Design Manual #8, Discharge Characteristics,Chapter 2, D.S. Miller, Editor, International Association of Hydraulic Research (LAHR), 1994.

Kolkman, P.A., "Discharge Relationships and Component Head Losses for Hydraulic Structures," Hydraulic Structures Design Manual #8, DischargeCharacteristics,Chapter 3, D.S. Miller, Editor, International Association of Hydraulic Research (IAHR), 1994.

MacDonald, T.C. and J.L. Langridge-Monopolis. 1984. "Breaching Characteristics of Dam Failures." Journal of Hydraulic Engineering, no. 110., p. 567-587.

U.S. Army Corps of Engineers. 2011. HEC-GeoRAS GIS Tools for support of HEC-RAS using ArcGIS, 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," Hydrologic Engineering Center, January 2010.

U.S. Army Corps of Engineers, HEC-I, Hydrologic Modeling System, Version 3.5.0, Hydrologic Engineering Center, August 2010.

USACE Ice Jam Database, Total Number of Events Ranked by State, https://rsgisias.crrel.usace.army.mil/apex/f?.p=273:39:144230682549501.

U.S. Army Corps of Engineers, HEC-RAS, River Analysis System, Version 4.0.0, Hydrologic Engineering Center, March 2008.

70

Section 6 References U.SNRC. 2011. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, NUREG/CR-7046, Office of Nuclear Regulatory Research, Richland, WA. November 2011.

Walder, J. and J. O'Connor. 1997. "Methods for Predicting Peak Discharge of Floods Caused by Failure of Natural and Constructed Earthen Dams." Water Resources Research, vol. 33, no. 10, p. 2337-2348, October 1997.

Wilson Engineering, 2013. "Independent Technical Review of HEC-RAS and SR.H-2D Modeling", Wilson Engineering Project WE 13002. March 2013.

Xu, Y. and Zhang, L.M., 2009. "Breaching Parameters for Earth and Rock-fill Dams. Journal of Geotechnical and Geoenvironmental Engineering, 135(12): 1957-1970." December 2009.

71

GoRtagms spalrotv S Ccntair~

Vviiiinoiu rrom 5~g~ujritu pUDlIC OISCIObUi~ ~

c~rIuiti~:9 10 CFR 2.390(d)(1)

APPENDICES

,^ ^p* ^ ^^^, .,#*.,

tJ~~r~tnJnv

. j . . . . . . . .

Icurr

-I. -N w.nZ.~ ffrom -.. ai1Z.W1r

-;-; L-; iz iu iiI-ZMi APPENDIX A FIGURES AND TABLES

FIGURE A-1 CUMULATIVE AND INCREMENTAL PRECIPITATION DURING THE 48-HOUR PMP FOR A RAINFALL DEPTH OF 26.6 INCHES 30 4.00 3.50 25 3.00 20 2 2.50 15 2.00 '

0. 1.0 "5

E_ 100 0.50 0.00 Hours CCumulI ,re Precip.Iltuon ,. Incrempntal Precip.TalmOn A-1

FIGURE A-2 MID-AUGUST 1940 RAINFALL MASS CURVE

.MASS RAINFALL CURVES

, .: . . . .. * . ..... .... I , - 2 * .

r7 - '.. . ' T i- I." ... . .,- , - -... .. t-" -

. 71¶- .1 ----T

4

~fc~

-- E-T-.

7jTT 8 "i'-

(I, ~-144 7.. 7 7 tj L z7 4-t :17 I-ROCK HOUSE 6 2i 2-CAESARS H4EAD

.4-~ 3 -WALI4ALLA

-J

'4 T-1j 7 J7 4~4.

t_

~ t.4 T-r .....

7 h i/

7-10

I/SR 12.2-2.l~:t INDICATES OBEVDDArA

.4.

AUJGUST 19440 Source: U.S. Geological Survey, 1949, Floods of August 1940 in the southeastern States: U.S. Geological Survey Water-Supply Paper 1066.

A-2

FIGURE A-3 AUGUST 111-14, 1940, PRECIPITATION Rainfall intensity* (in/hr) 0.0 1,0 r--ýT 2,0 3.0 4.0 i I .' l I 1 i Moo0 06!00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 Day 0 Day I Day 2 A-3

... . *..~ .

FIGURE A-4 ONS SITE INCLUDING KEOWEE HYDRO POWERHOUSE A-4

FIGURE A-5-A MODEL EXTENTS OF ONS YARD Offsite hydrology area

_ 2-D simulation area A-5

FIGURE A-5-B MODEL EXTENTS OF KEOWEE HYDRO POWERHOUSE SUB-BASIN A-6

FIGURE A-6-A 2-D ONS YARD MESH ELEMENT ELEVATIONS

~4A Admin Bldg

U-*

U*-- le Reactor, Auxiliary &

°,U Turbine buildings

.7 Area raised minimum elevation capped at 795.89 ft msl

\,,: * .1.

Area raised minimum elevation capped at 796.00 ft msl

- ,~l* ~ - -

/

A-7

FIGURE A-6-B 2-D ONS ISFSI MESH ELEMENT ELEVATIONS

,* ,'*>= 850, 1

'*. i_*I '.--" >= 84&

>= 840.

, ¢+.,:L.'" >= 844.

' m~jm =*>= B42.

!'i , i ,'>= 840,

>= 839.

>= 838,

>= 837.

I>= 835.

I ('>= Y, I*, 834,

~I II I * >= 8329,

lJ*ImI>= 831.

I>- 829,

>=:328.

S>= 827.

' * , :,I%II>=

,." I i>= 826.825.

>= 824.

- 0 >- 823.

1

8 I'l 1* II lIl >= 822.

4fi >= 820.

>= 819, II I )* i * >= 817.

lip* ,* , >=8 3,

>* 807.

__,>*, *!:: I>= 812.

>* 805.

.. . * >= 8105 AL* >= 804.

>= 803

>= 808.

-> 801.

>= 800,

- m>= 799, A-8

FIGURE A-7-A COMPLETE HYDROLOGY OF THE ONS YARD Flo, pathor-c~rflo.

A-9

FIGURE A-7-B SUB-BASIN HYDROLOGY OF THE ONS YARD A-10

% ý, ý,,r!ta t173 FIGURE A-8 ROOF DRAINAGE CON NECTIONS TO ONS YARD DRAINAGE

-a.

0 -

Nw, On

--- 1 4---. -

.%*~ \.~* ..

I./ -

A-Il

II I - 's, 11 t-'. ý'. ý- . , ,, , I Ij I FIGURE A-9 ROOF CONNECTION TO ONS YARD VIA DIRECT CONNECTION OR DOWNSPOUTS to C

-El-lb T\ lurbineI*A 4

-4*

Reactor R dlo 4

A-12

FIGURE A-10-A CATCH BASINS AND OTHER NODES U

Attivo

Blocked Lhidvr Building

ýuncuon or Manhole 4 -i--

~*~*~\*~g* q~

\ ~

0a

-U.

y 4

4 1t\i.-~

I -. S

-U a.. a a U' a

-~ 4

.~'< ~-..

\.

A A-a-

~a.

I A-13

APPENDIX B CURRENT LICENSE BASIS LIP MODEL ANALYSIS INUNDATION LEVELS

C-' C5~j~*'~I ~. './\IIihiLj!'j rJJ>.i~~~~JU ~

FIGURE B-I LOCATION IDS OF REPORTED WATER ELEVATION AROUND REACTOR, AUXILIARY, TURBINE, AND ADMINISTRATION BUILDINGS B-I

FIGURE B-2 LOCATIONS OF MAXIMUM DEPTH IN ISFSI YARD AND RELAY HOUSE IN 230-KV SWITCHYARD B-2

FIGURE B-3 LOCATIONS OF MAXIMUM DEPTH AT KEOWEE POWERHOUSE B-3

~c~o~ti'~ .~K( IiG~-V~2 2DO~d~1~~

TABLE B-I CURRENT LICENSING BASIS COMPARISON OF DEPTHS AND ELEVATIONS AROUND THE REACTOR, AUXILIARY, TURBINE, AND ADMINISTRATION BUILDINGS Administration, Turbine, Ground Yard No Yard Yard No Yard Auxiliary, and SC Grid X SC Grid Y Elevation Drainage Drainage Drainage Drainage Difference Reactor (ft.) (ft.) (flt.) WSEL WSEL* Depth Depth (ft.)

Buildings (ft.) (ft.) (ft.) (ft.)

Point North 1 1429776 1082989 796.86 797.75 798.18 0.89 1.32 0.43 North2 1429836 1083071 797.94 798.05 798.18 0.11 0.24 0.13 North 3 1429872 1083082 797.39 797.66 797.80 0.27 0.41 0.14 North 4 142994 i 1083099 797.26 797.66 797.80 0.40 0.54 0.14 North5 1430110 1083158 797.27 797.53 797.70 0.26 0.43 0.17 East 1 1430169 1083131 796.53 797.53 797.69 1.00 1.16 0,16 East 2 1430186 1083083 796.91 797.53 797.69 0.62 0.78 0.16 East 3 1430205 1083025 796.54 797.53 797.69 0.99 1.15 0.16 East 4 1430169 1082934 796.75 797.18 797.30 0.43 0.55 0,12 East 5 1430195 1082862 797.17 797.18 797.26 0.01 0.09 0,08 East 6 1430220 1082791 795.89 796.27 797.21 0.38 1.32 0.94 East 7 1430261 1082689 796.04 796.15 797.21 0.11 1.17 1.06 East 8 1430289 1082586 795.88 796.16 797.21 0.28 1.33 1.05 East9 1430324 1082501 796.15 796.16 797.21 0,01 1.06 1.05 East 10 1430357 1082398 795.87 796.16 797.21 0.29 1.34 105 East II 1430398 1082275 796.34 796.35 797.22 0.01 0.88 0.87 South I 1430372 1082205 796.38 79639 797.23 0.01 0.85 0.84 South 2 1430331 1082194 796.60 796.60 797,23 0.00 0.63 0.63 South 3 1430303 1082184 796,41 796.42 797.22 0.01 0,81 0.80 West 1 1430125 1082179 795.84 797.09 79750 1.25 1.66 0.41 B3-4

Administration, Turbine, Ground Yard No Yard Yard No Yard Auxiliary, and SC Grid X SC Grid Y Elevation Drainage Drainage Drainage Drainage Difference Reactor (ft.) (ft.) Eetio WSEL WSEL* Depth Depth (ft.)

Buildings (ft.) (ft.) (ft.) (ft.)

Point West 2 1430035 1082177 796.67 796.79 797.50 0.12 0.83 0.71 West 3 1429982 1082225 796.88 796.90 797.43 0.02 0.55 0.53 West 4 1429933 1082256 795.38 796.96 797.74 1.58 2,36 0.78 West 5 1429960 1082287 795.62 797.02 798.10 1.40 2.48 1.08 West 6 1429994 J1082328 796.35 797.02 798.10 0.67 1.75 1.08 West 7 1430040 1082431 796.00 797.37 798.12 1.37 2.12 0.75 Wes 8 !429948 1082445 70 641 7 "* f 066 1,7 1.05 West 9 1429913 1082479 79631 797.07 798.12 0.76 1.81 1.05 West 10 1429846 1082497 795.44 797.08 798.13 1,64 2.69 1.05 West !1 1429859 1082613 796.62 797.12 798.16 0,50 1.54 1.04 West 12 1429803 1082635 795.53 797.11 798.16 158 2-63 1.05 West 13 1429837 1082694 796.79 797.44 798.17 0.65 1.38 0.73 West 14 1429919 1082807 796.57 797.46 798.17 0.89 1.60 0.71 West IS 1429956 1082883 796.62 797,46 798.17 0,84 1.55 0.71 West 16 1429958 1082930 796.00 797.44 798.17 1.44 2.17 0.73 West 17 1429838 1082903 797.01 797.45 798.17 (.44 1.16 0.72 West 18 1429748 1082883 796.55 797.46 798.17 0.91 1.62 0,71 West 19 1429735 1082983 796.78 797.63 798.19 0.85 1.41 0.56

WSLL -Water Surface hlevalion Level B-5

FIGURE B-4 CURRENT LICENSING BASIS MAXIMUM DEPTH AND DURATION FOR SSF, PSW, ESV AND CT5 INYARD WITH FUNCTIONING DRAINS

.1

- . . . .- . d. ,~..*.

'7;Afl - ................

11 1....

I, 4 I nr i 1 171lrf 1?lt i I ~

17B I*

B a .~4C Elevatlon (iljUlI Min Max POint 55F! 3*7.102 Point SSF2 796.509 797.076 Point CIS 796.750 798.186 Point PSW2 795.341 795.934 Point PSWl 796.000 796.191 Point ESVI 797.124 797.128 Point ESV? 796.700 796.703 13-6

FIGURE B-5 CURRENT LICENSING BASIS MAXIMUM ELEVATION AND DURATION INKEOWEE HYDRO POWERHOUSE SUB-BASIN WITH FUNCTIONING DRAINS 7;02 201 70210-J-)

A C\J ~ (2 702.00 /

70 ',9o 4 00.00. i 8 I :2C I80 0600o :2C, 18:rjr! 00CGo 0, oc:

8:.1 S.I Z.1195C E:3194C.

Elevation (ft ,,ul.

Min Max Point KI 701.725 702.137 Point K2 701.900 702.044 13-7

I'-urlaiis )ý!

FIGURE B-6 CURRENT LICENSING BASIS MAXIMUM DEPTH AND DURATION INISFSI YARD Point ISFSI I Oevaborn (f AMS'.1 325.30'-1 I5C' Ir.-

824.90 ' I

,S v v r114

,:'Q i',", P,.',

'.'V,;t; 8!12,/194:' ', l~q 19:

Elevaticii Min Pint ISiSi- I wilh Funclioning Yard Drainage 824.945 Po'il ISFSI- I with No iffective Yard Drainage 824.945 K25.-240 B-8

i~ *WAA~ I ~O~~.~;t~'v nI:t12iI:n ~ f.~;:r. ~ ~~ ~r'd~r C2 p~j;~:t~i' FIGURE B-7 CURRENT LICENSING BASIS MAXIMUM DEPTH AND DURATION INISFSI YARD Point ISFSI 2 Elevator,~E A!MS,

24 5

I --

r" ..... I 824 30 1

I ' I

,':6:*'C S I~:'

rJ*:¢lU, i R00~0 Si1z'1294: 19 4C,

'i.:: 13..ý Elevation Min PointISFSI-2 wilh Functioning Yard Drainage 8245,2"0 824.332 824,5' ISFSI-2 with No Eflivcie Yard Drainage Poirr ...

824.332 B-9

APPENDIX C FLOOD HAZARD RE-EVALUATION BEYOND LICENSE/DESIGN BASIS LIP MODEL ANALYSIS INUNDATION LEVELS

FIGURE C-I BEYOND LICENSING/DESIGN BASIS CASE LOCATIONS OF MAXIMUM FLOOD ELEVATION IN ONS YARD FIGURE C-2 C-I

BEYOND LICENSING/DESIGN BASIS CASE MAXIMUM DEPTHS IN ONS YARD WITH YARD DRAINAGE AND ROOF DRAINAGE k

0 U

Depth (ft)

- >= 4.00

>= 3.50

>= 3.00

>= 2.50 S>-=2.00

>= 1.50

\\

SI, >= 1.00

>= 0.50 V£,

>= 0.25

>= 0.10 C-2

FIGURE C-3 BEYOND LICENSING/DESIGN BASIS CASE MAXIMUM DEPTHS IN ONS YARD WITH ROOF DRAI[NAGE AND NO YARD DRAINAGE I-I.-

U

01

0 S

9

.1 0

if-,-,-I 0 WIV j

Depth (ft)

>= 4.00

>= 3.50 i*>= 3.00

>= 2.50

>= 2.00 m >= 1.50

>= 1.00

>=0.50

>= 0.25

>= 0.10 C-3

FIGURE C-4 BEYOND LICENSING/DESIGN BASIS CASE MAXIMUM DEPTHS IN ONS YARD WITH NO YARD DRAINAGE OR ROOF DRAINAGE ols,

,,'*--,Depth (ft)

>2 .50

i>--2.50

\""'.'::-. **.*. . .. *0 >= 2.00

, *.=......*,* ,.-->= 1.00

>= 0.25

>= 0.10 C-4

FIGURE C-5 BEYOND LICENSING/DESIGN BASIS MAXIMUM FLOOD ELEVATION INONS YARD NEXT TO ADMINISTRATIVE BUILDINGS (NORTH 1.5) WITH FUNCTIONING DRAINS EI,.'..ation if A."S-&

801,0 800,0 797,0!

796.0 ' I ' I ' I ' I ' I ' I ' I ' ' I ' I O0000 0600 1200C 8 00 0000 0600 2.'.20018.00 0000 0600 :12.00 c 800 0000 Day 0 '1 D y 42 Day 3 Elevation (ft msl)

Min Max Point North 1 796.858 800.254 Point Morth 2 797,942 800,025 Point Nortil 3 797,385 799.493 Point North 4 797.260 799.654 Point North 5 797.267 799.123 C-5

2< , .;K..;t~... ........ ,- Wii'* r I. i;o*.....r*Hl~

,*:,.. " ~2 Q.].C.

FIGURE C-6 BEYOND LICENSING/DESIGN BASIS MAXIMUM FLOOD ELEVATION INONS YARD BELOW TURBINE BUILDING (SOUTH 1-3) WITH FUNCTIONING DRAINS Elevoati.r, i.h ".mil,

'97,~00 I

I I I I I I I I ' I 0000 06WO 12-00 18:00 00:00 0600 G 2.00 1800 00,00 06.CC 1200 :800 C 0O0 Sa,. 0 Da,. 1. Da.,.Z Da" 3 Elevation (fi msl)

Min Max Point South 1 796,382 797.580 Point South 2 796.600 797,557 Point South 3 796,413 797,517 C-6

FIGURE C.7 BEYOND LICENSING/DESIGN BASIS MAXIMUM FLOOD ELEVATION INONS YARD NEXT TO ADMINISTRATIVE AND TURBINE BUILDINGS (EAST 1-5) WITH FUNCTIONING DRAINS Elevation 'ft A 5,L."

799,.C0 -I 798,50 -

798.00 797,50 II 797,00 796.50 -- i 796,00$ I I ' I I I I I I I I I I 0000 0600 1200 1i00 0000 06,00 121 00 18.00 00:00 0600 2:0, 18,00 00.;a Day0 DalI Da2, Day 3 Elevation(ft msl)

Min Max Point East 1 796.469 798,617 Point East 2 796.911 798,626 Point East 3 796.539 798,695 Point East 4 796,748 797,605 Point East 5 796.836 797.607 C-7

FIGURE C-8 BEYOND LICENSING/DESIGN BASIS MAXIMUM FLOOD ELEVATION INONS YARD NEXT TO TURBINE BUILDING (EAST 6.11) WITH FUNCTIONING DRAINS Elevation kAMISL' CC9.O 797 51 797 00 79650 796,00 I _ _---.

795-5CtI 00.00 06.00 120 0C 1800 OC00 06 00 12:00 18,C 00.00 0600 12 00 18 00 00 00 Da. 0 Ca., Da. 2 Day )

Elevation (ftmsl)

Min Max Point East 6 795.888 797.601 Point East 7 796.039 797.508 Point East 8 795.880 797,507 Point East 9 796.002 797.518 Point East 10 795.870 797.505 Point East 11 796.017 797.548 C-8

FIGURE C-9 BEYOND LICENSING/DESIGN BASIS MAXIMUM FLOOD ELEVATION INONS YARD NEXT TO AUXILIARY, UNIT 3 REACTOR, AND UNIT 3 BORATED WATER STORAGE TANK BUILDINGS (WEST 1.6)

WITH FUNCTIONING DRAINS EIe'-.ation (I';'h LI 801,0 800.0

?99,0 798.0 Li 797,0 .. . . . . . . . . . . . . . . . . . . . . . . -* .* . * . . . . . . .

-.. - ;.*-~-,-*-----

9 ,0 .. . . . . .

9 ,0 ' I ' I ' I ' I I ' I 0000 06.00 1200 18H00 00.00 0600 1200 1800 00:00 06.00 12:00 !8,00 00,00 E:ay 0 Day 1 0a-,2 Day 3 Elevation(ftmsl)

Min Max Point West 1 795,842 798.697 Point West 2 796.967 798.669 Point West 3 796.978 798.344 Point West 4 795.375 798,970 Point West 5 795.619 800.041 Point West 6 796.345 800.048 C-9

FIGURE C-10 BEYOND LICENSING/DESIGN BASIS MAXIMUM FLOOD ELEVATION INONS YARD NEXT TO AUXILIARY, UNITS 1&2REACTOR, UNITS 1&2BORATED WATER STORAGE TANK, AND HOT MACHINE SHOP BUILDINGS (WEST 7-13) WITH FUNCTIONING DRAINS Elevacirn 'ftMSL-11r 801,0-1 800.0 799,0 798.0 797 C 796,0 795.0 . 'iI I ' I I I I '

00 CO 06ý00 I2d0 1800 00:00 06:00 12.00 18.00 00:00 060c, 12:00 18:00 0000 cav. 0 Da,*,, Day3 Elevation (ftmsl)

Min Max Point West 7 796.358 800.057 pu . .Lsý 796.464 800,056 Point West 9 796,312 800.054 Point West 10 796.317 800.069 Point West 11 796.621 800.107 Point West 12 795.892 800.111 Point West 13 796.787 800,128 C-IO

FIGURE C-1 I BEYOND LICENSING/DESIGN BASIS MAXIMUM FLOOD ELEVATION INONS YARD NEXT TO AUXILIARY, TURBINE, AND ADMINISTRATIVE BUILDINGS (WEST 14-19) WITH FUNCTIONING DRAINS 8 .- .

?g .... ......

. ....... . . . . -...-.. ..... ..- , ..,'1. .

..... ........................ . .... . ..... ..... .. . .. .. . .. .. ... : : iz!

','. C: " : "0 :ECO :ccc :2 27 :~2 72C 2162 1:2 : [. C, Elevaton (r msl)

Min MaK PointWest14 796.570 800.131 PointWest 15 796.707 800.132 Poil West16 796.321 800.132 PointWest17 796.905 800.131 vOlns West16 796.692 800.125 Pont Wee!19 796.981 8900,146 C-I I

7~ .**...rr~~iIon VC.17 c~78c;osurc LvceI FIGURE C-12 BEYOND LICENSING/DESIGN BASIS CASE ROOF DRAINAGE PERFORMANCE B8076-8079-8083- ..N B8076-8079-8083-C *N Note: The auxiliary building roof area node identifications have been shortened to the last part (e.g.. B8075-8078-8082-A2 = A2). A = the northern auxiliary iuilding: B = the middle auxiliary building: and C -- the southern auxiliary building.

C-12

Cotis*~ ~~i~ Informtion WAitiho.,l from -,b.i-i:-uner1 CFR2- 0d)1)\4 TABLE C-1 BEYOND LICENSING/DESIGN BASIS CASE COMPARISON OF FLOOD DEPTHS AROUND ADMINISTRATIVE, TURBINE, AUXILIARY, AND REACTOR BUILDINGS Yard No Yard Yard No Yard SC Grid X SC Grid Y Elevation Drainage Drainage Drainage Drainage Difference (ft) (ft) (ft) WSEL WSEL* Depth Depth (ft)

(ft) (ft) (ft) (fl)

North 1 1429776 1082989 796.86 800.25 800.52 3,39 3.66 0.26 North 2 1429836 1083071 797.94 800.03 800,27 2.09 2.33 0.25 North 3 1429872 1083082 797.39 799.49 799,48 2.10 2.09 -0.02 North 4 1429941 1083099 797.26 799.65 799.78 2.39 2.52 0.12 North 5 1430110 1083158 797.27 799,12 799.21 1.85 1.94 0.08 East 1 1430169 1083131 796.53 798.62 798.61 2.09 2,08 0.00 East 2 1430186 1083083 796.91 798.63 798.63 1.72 1.72 0.00 East 3 1430205 1083025 796.54 798.69 798,71 2.15 2.17 0.01 East 4 1430169 1082934 796.75 797.61 797.69 0.86 0.94 0.09 East 5 1430195 1082862 797.17 797.61 797.70 0.44 0.53 0.08 East6 1430220 1082791 795.89 797.60 797.69 1.71 1.80 0.08 East 7 1430261 1082689 796.04 797.51 797.62 1.47 1.58 0,11 East 8 1430289 1082586 795.88 797.51 797.62 1.63 1.74 0.11 East 9 1430324 1082501 796.00 797.52 797,62 1.36 1,47 0.11 East 10 1430357 1082398 795.87 797.51 797.61 1.63 1374 0.11 East II 1430398 1082275 796,02 797.55 797.64 1.21 1.31 0.09 South I 1430372 1082205 796.38 797.58 797.68 1.20 1.30 0.10 South 2 1430331 1082194 796.60 797.56 797.66 0.96 1.06 0.10 C-13

. . .. d rom puii dicosur Yard No Yard Yard No Yard SC Grid X SC Grid Y Elevation Drainage Drainage Drainage Drainage Difference (ft) (ft) (ft) WSEL WSEL* Depth Depth (ft)

I (fl) (ft) (ft) (ft)

South 3 1430303 1082184 796.41 797.52 797.60 1.11 1.19 0.08 West I 1430125 1082179 795.84 798.70 799.07 2.86 3.23 0.38 West 2 1430035 1082177 796.67 798.67 798.92 2.00 2.25 0.25 West 3 1429982 1082225 796.88 798.34 798.92 1.45 2.04 0.58 West 4 1429933 1082256 795.38 798.97 799.23 3.59 3.85 0.26 West 5 1429960 1082287 795.62 800.04 800.32 4.42 4.70 0.27 West 6 1429994 1082328 796.35 800.05 800.32 3.70 3.97 0.27 West 7 1430040 1082432 796.00 800.06 800.33 4.06 4.33 0.27 West 8 1429948 1082445 796.41 800,06 800.33 3.65 3.92 0.28 West 9 1429913 1082479 796.31 800.05 800.33 3.74 4.02 0.28 West 10 1429846 1082497 795.44 800.06 800.34 4.62 4.90 0.28 West 11 1429859 1082613 796,62 800.11 800.38 3.49 3.76 0.27 West 12 1429803 1082635 795.53 800.11 800.38 4.58 4.85 0.27 West 13 1429837 1082694 796.79 800.13 800.39 3.34 3.60 0.26 West 14 1429919 1082807 796.57 800.13 800.39 3.56 3.82 0.26 West 15 1429956 1082883 796.62 800.13 800.39 3.51 3.77 0.26 West 16 1429958 1082930 796.00 800.13 800.39 4.13 4.39 0.26 West 17 1429838 1082903 797.01 800.13 800.39 3,12 3.38 0.26 West 18 1429748 1082883 796.55 800.13 800.39 3.58 3.84 0.26 West 19 1429735 1082983 796.78 800.15 800.42 3.37 3.64 0.27 C-14

C-FitAmi8S~rty eiitvýIormation -R 6~h~ trom puWic isclosure unaer iOCR239()1 Yard No Yard Yard No Yard SC Grid X SC Grid Y Elevation Drainage Drainage Drainage Drainage Difference P(t) (It) (It) WSEL WSEL* Depth Depth (It)

I (It) (It) (ft) (It)

Other Points inYard RH W 1430655 1082853 770.29 771.93 772.10 1.64 1.81 0.17 RH N 1430663 1082892 771,00 771.87 772.05 0.87 1.05 0.18 RH E 1430693 1082864 771.05 771.83 772.06 0.78 1.01 0.23 RH S 1430687 1082828 771.09 771.83 772,04 0.74 0.95 0.21 ESV I 1430067 1081874 797.12 798.99 799,31 1.87 2.19 0.32 ESV 2 1430122 1081891 796.70 798.74 799.11 2.04 2.41 0.37 PSW I 1430295 1082080 796.00 797.76 797.92 1.76 1.92 0.16 PSW 2 1430352 1081986 795.34 797.33 797.43 1.99 2.09 0.10 SSF1 1429764 1082541 796.52 800.11 800.38 3.59 3.86 0.27 SSF 2 1429834 1082400 796.51 800,07 800.34 3.56 3.83 0.27 CT5 1429250 1082240 796.75 800.15 800.42 3.40 3.67 0.27 ISFSI 1 1429523 1081261 824.33 825.20 825.25 0.87 0.92 0.05 ISFSI 2 1429667 1081237 824.93 825,43 825.48 0.50 0.55 0.05 Keowee PH with just calch-basins blocked KI 1433450 1084003 701.73 702.93 702.94 1.20 1.21 0.01 K2 1433340 1084012 701.90 702.45 702.45 0.55 0.55 0,00 Keowee PH with catch-basins and culverts blocked KI 1433450 1084003 701.73 702.93 702.99 1.20 1.26 0.06 K2 1433340 1084012 701.90 702.45 702.69 0.55 0.79 0.24 C-15

TABLE C-2 BEYOND LICENSING/DESIGN BASIS CASE ROOF DRAINAGE

SUMMARY

Max MaxAvailabi NdlRofevlParapet Mal Mal VlmTotal Depth WE e Total Roof Level Depth WSEL* Volume Volum WSEL Volume Rainfall Node ID Level eof to (ft.) (ft.) (f) on Roof on Roof Parapet (ft.) f Roof Pae(ft.)

(t.) (ftfte parapet B8075.8078-8082-RB-Mid

. . . I. . ...

-nb-, . . .f.)-

970.67 973.25 2.65 973.32 11,332 10,916 -0.07 .417 46,918 B8075M8078.8082-RB-Nth' 970.67 973.25 2.65 973.32 11,325 10,913 -0.07 -413 46,899 B8075-8078-8082-RB-Sth 970.67 973.25 2.74 973.41 11,842 10,916 -0.16 -926 48,611 B8075-8078-8082-A2 813.50 816.63 0.95 814.45 3,028 10,019 2.18 6991 15,507 B8075-8078-8082-A3 838.00 841.13 1.02 839.02 2,319 7,079 2.10 4759 10,961 B8075-8078-8082-A4 853.00 853.25 0.25 853.25 52 52 0.00 I 1,056 B8075-8078-8082-A6 868.00 871.13 0.65 868.65 317 1,525 2.48 1208 2,415 B8075-8078-8082-la 862.00 865.00 0.06 862.06 130 6,524 2.94 6394 13,230 B8075-8078-8082-lb 858.00 861,13 1.46 859.46 13,815 29,621 1.67 15806 57,706 B8075-8078-8082-BI3 826.00 829.13 0.98 826.98 1,827 5,853 2.15 4027 7,368 B8075-8078-8082-B14 844.00 847.13 0.36 844.36 108 953 2.77 845 1,105 B8075-8078-8082-B15 858.00 861.13 0.86 858.86 1,308 4,764 2.27 3457 5,851 B8075-8078-8082-BI6 882.75 885.75 0.98 883.73 1,918 5,881 2.02 3962 7,584 B8075-8078-8082-B17 826.50 828.00 1.37 827.87 6,091 6,665 0.13 573 17,335 B8075-8078-8082-B18 860.79 861.13 2.22 863.01 1,164 558 -1.88 -606 5,844 B8075-8078-8082-BI 813.50 816.63 3.10 816.60 13,489 13,613 0.03 123 21,162 B8075-8078-8082-B2 838.00 841.13 0.77 838.77 1,748 7,079 2.35 5331 10,947 B8075-8078-8082-B3 853.00 853.25 0.39 853.39 74 52 .0.14 -22 1,053 B8075-8078-8082-B4 908.42 911.13 0.68 909.10 354 1,416 2.03 1061 2,612 B8075-8078-8082-CIO 853.00 856.13 0.33 853.33 87 817 2.79 730 967 C-16

~~~~~~S~ewsitive Itnformiation -VVthh~ol ...... .,d1 FR2f Total Depth Avallabi Parapet Max Max Tol Dep e Total Roof Level Depth WSEL* Volume Volume Rainfall Node ID (f ( (ft) on Roof on Roof to Volume (f) ...... . (ft.)t,. ,3(ft.) ) ,f.

.f....... ...

............. ._ .......... (Roof a et (ft)

Parapet B8075-8078-8082-CIl 882.75 883.00 2.33 885.08 1,140 490 -2.08 -650 7,692 B8075-8078-8082-C12 862.00 865.00 0.72 862.72 1,510 6,273 2.28 4762 8,104 B8075-8078-8082-C13 858.00 861.13 0.59 858.59 792 4,220 2.54 3428 5,228 B8075-8078-8082-C2 813.50 816.63 2.62 816.12 8,210 9,801 0.51 1591 15,296 B8075-8078-8082-C3 813.50 816.63 2.94 816.44 1,152 1,225 0.19 73 1,524 B8075-8078-8082-C4 838.00 841.13 0.83 838.83 1,887 7,079 2.29 5192 11,212 B8075-8078-8082-C5 853.00 861.13 0.36 853.36 76 1,699 7.76 1623 1,020 B8076-8079-8083-C-M 879.00 884.50 4.16 883.16 15,850 27,867 1.34 12016 93,143 B8076-8079-8083-C-N 879.00 884.50 3.66 882.66 11,270 27,026 1.84 15756 90,628 B8076-8079-8083-C-S 879.00 884.50 4.36 883.36 15,460 24,478 1.14 9018 82,782 B8076-8079-8083-EL-N 840.59 845.50 3.96 844.55 3,350 4,638 0.95 1288 35,638 B8076-8079-8083-EL-M 840.59 845.50 5.70 846.29 5,499 4,469 -0.79 -1030 35,848 B8076-8079-8083-EL-S 840.59 845.50 9.81 850.40 10,014 4,132 -4.90 -5882 31,839 B8076-8079-8083-ET-N 879.11 884.50 3.84 882.95 4,833 10,926 1.55 6093 61,009 B8076-8079-8083-ET-M 879.11 884.50 3.95 883.06 5,362 11,263 1.44 5902 60,179 B8076-8079-8083-ET-S 879.11 884.50 3.81 882.92 4,406 10,179 1.58 5773 52,696 B8076-8079-8083-W-N 879.07 884.50 1.27 880.34 3,067 82,433 4.16 79366 33,024 B8076-8079-8083-W-11 879.07 884.50 1.55 8 880.62 4,725 8 "", .88 0 B8076-8079-8083-W-S 879.07 884.50 1.29 J880.36 3,191 82,433 4.14 79241 31,761 Notes:

Negative depths =distance over parapet level Negative volumes ý volume above parapet level

WSEL =water surface elevation level

Roof has defined parapet overflow to Yard or other roof segment as appropriate C-17

TABLE C-3 ROOF PERFORMANCE WITH BLOCKED ROOF DRAINS AND YARD CATCH BASINS Available Max Max Total Depth Volume Total Roof Parapet WSEL* Volume Volume WSEL to to Rainfall Level Level Depth on Roof on Roof of Roof Parapet Parapet Volume Node ID (ft.) (ft.) (ft.) (ft.) (ft.) (ft.") (ft.) 1 00.)

B8075-8078-8082-RB-Mid' 970.67 973.25 2.63 973.30 11,204 10,916 -0.05 -289 46,912 B8075-8078-8082-RB-Nih 970.67 973.25 2.63 973.30 11,199 10,913 .0.05 -286 46,892 B8075-8078-8082-RB-Sth 970.67 973.25 2.65 973.32 11,317 10,916 -0.07 -402 48,604 B8075-8078-8082-A2 813.50 816.63 11.11 824.61 15,505 10,019 -7.99 -5,486 15,505 B8075-8078-8082-A3 838.00 841.13 14.72 852.72 14,148 7,079 -11.59 .7,069 10,960 B8075-8078-8082-A4 853.00 853.25 16.65 869.65 1,056 52 -16.40 .1.004 1,056 B8075-8078-8082-A6 868.00 871.13 11.33 879.33 2,415 1,525 -8.20 .890 2,415 B8075-8078-8082-1a 862.00 865.00 11.43 873.43 11,599 6,524 .8.43 -5,076 13,228 B8075-8078-8082-lb 858.00 861.13 15.43 873.43 70,865 29,621 -12.31 -41,244 57,699 B8075-8078-8082-BI3 826.00 829.13 8.63 834.63 7,367 5,853 -5.50 -1,514 7,367 B8075-8078-8082-BI4 844.00 847.13 7.20 851.20 1,104 953 -4.08 -152 1,104 B8075-8078-8082-B15 858.00 861.13 20.17 878.17 12,311 4,764 -17.05 -7,547 5,850 B8075-8078-8082-B16 882.75 885.75 8.87 891.62 7,583 5,881 -5.87 -1,702 7,583 B8075-8078-8082-B17 826.50 828.00 13.49 839.99 17,332 6,665 .11.99 .10,667 17,333 B8075-8078-8082-B!8 860.79 861.13 10.37 871.16 15,913 608 .10.04 .15,305 5,844 B8075-8078-8082-BI 813.50 816.63 4.51 818.01 14,419 13,613 -1.39 -806 21,159 B8075-8078-8082-B2 838.00 841.13 14.75 852.75 14,176 7,079 .11.63 .7,097 10,945 B8075-8078-8082-B3 853.00 853.25 16.65 869.65 1.053 52 .16.40 -1,001 1,053 B8075-8078-8082-B4 908.42 911.13 12.04 920.46 2,612 1,416 -9.33 -1,196 2,612 B8075-8078-8082-C1O 853.00 856.13 7.61 860.61 967 817 -4.49 -151 967 B8075-8078-8082-C 11 882.75 883.00 16.46 899.21 7,691 490 -16.21 -7,201 7,691 B8075-8078-8082-C12 862.00 865.00 16.82 878.82 13.345 6,273 -13.82 -7.073 8,103 B8075-8078-8082-C13 858.00 861.13 115.33 973.33 135,837 4,220 -112.21 -131,617 5,227 C-18

en~~~~sIwelntormatio - wtnhft, ulcdcs~ :d* 0CR230d*'"

Available Max Max Total Depth Volume Total Roof Parapet WSEL* Volume Volume WSEL to to ainfall Level Level Depth on Roof on Roof of Roof Parapet Parapt Volume Node ID (ft.) () (ft.) (ft.) (f) -Z(ff) )

B8075-8078-8082-C2 813.50 816.63 11.19 824.69 15,294 9,801 -8.07 -5,493 15,294 B8075-8078-8082-C3 813.50 816.63 8.44 821.94 1,523 1,225 -5.32 -298 1,523 B8075-8078-8082-C4 838.00 841.13 16.59 854.59 16,453 7,079 .13.46 -9,375 11,211 B8075-8078-8082-C5 853.00 861.13 4.88 857.88 1,020 1,699 3.25 679 1,020 B8076-8079-8083-C-N 879.00 884.50 12.79 891.79 90,617 27,026 -7.29 -63,591 90,616 B8076-8079-8083-C-M 879.00 884.50 12.75 891.75 93,132 27,867 -7.25 -65,265 93,131 B8076-8079-8083-C-S 879.00 884.50 12.88 891.88 82,772 24,478 -7.38 -58,294 82,772 B8076-8079-8083-EL-N 840.59 845.50 27.87 868.46 35,633 4,638 .22,96 -30,996 35,633 B8076-8079-8083-EL-M 840.59 845.50 29.04 869.63 35,843 4,469 -24.13 -31,374 35,843 B8076-8079-8083-EL-S 840.59 845.50 28.00 868.59 31,835 4,132 -23.09 -27,703 31,835 B8076-8079-8083-ET-N 879.11 884.50 17.69 896.80 61,002 10,926 .12.30 .50,075 61,002 B8076-8079-8083-ET.M 879.11 884.50 17.04 896.15 60,172 11,263 -11.65 -48,909 60,172 B8076-8079-8083-ET.S 879.11 884.50 16.58 895.69 52,689 10,179 -11.19 -42,510 52,689 B8076-8079-8083-W-N 879.07 884.50 3.46 882.54 33,021 82,433 1.97 49,412 33,020 B8076-8079-8083-W-M 879.07 884.50 3.59 882.66 36,213 82,433 1.84 46,220 36,214 B8076-8079-8083-W-S 879.07 884.50 3.41 882.48 31,759 82,433 2.02 50,674 31,757 Notes:

Negative depths =distance over parapet level Negative volumes =volume above parapet level WSEL =water surface elevation level

Roof has defined parapet overflow to Yard or other roof segment as appropriate, C-19

C~z;t3~z

,fcm~cn Scu~.y 3fis1Iv

-A~t~.cl f~i poucdiscosue uder1U u 2.3O~~ )

APPENDIX D DAM BREACH MODEL UNSTEADY FLOW MODELING DETAILS

UUILdIIi~ ~2curity ~ hfc~rn~tu VV~dhuiu fig ~Wi~ d~chsnrs undpr 10 CFR 239u(d~1)

TABLE D-I UNSTEADY FLOW INITIAL CONDITIONS No. Location Description Jocassee Dam Fair-Weather Failure (cfs) 5 Canal 1 550 6 Cane Creek 1 400 8 Conneross Creek 1 650 9 Crooked Creek 1 300 10 Crow Creek 1 150 11 Deep Creek 1 500 12 Eastatoe Creek 1 150 15 Keowee River 1 600 16 Keowee River 2 750 17 Keowee River 3 900 18 Keowee River 4 1,450 19 Keowee River 5 1,600 20 Keowee River 6 1,750 21 Keowee Spill 1 150 23 Little Creek N 1 150 24 Little Creek S 1 250 25 Little Creek S 2 550 26 Little Creek S 3 400 32 Martin Creek 1 500 36 Powerhouse 1 150 38 Savannah River 1 5,100 53 Seneca River 1 2,250 54 Seneca River 2 2,750 55 Seneca River 3 3,400 56 Seneca River 4 3,900 59 Tugaloo River 1 1,200 60 Twelvemile Creek 1 500 TABLE D-2 INITIAL RESERVOIR ELEVATIONS Development Initial Elevation (ft msl)

Jocassee 1,110 Keowee 800 Hartwel. 660 D- I

cil

ctis~~~'cif *,matb,* - Wvhhliold fiui'i public discluiu~ under i0CFP 2.39*)(.

TABLE D-3 KEOWEE DEVELOPMENT BREACH PARAMETERS KEOWEE DEVELOPMENT STRUCTURES- BREACH PARAMETERS Crest e oir Boltom Breach Bottom Average Time to Topof Breach Starling Failure Mode Elevation (f Breach 11idthl Breach Right Side Left Side Failure Breach Breach Initiation Structure Elevation (11ml) Elevation (1t msl) (f) Width (f0) Slope (Za)Slope (ZI) (alr)e idlh(f) ProgressioB Elavaion(Ih nsl) ml)

Keowee Dam 815 800 O'rloppmg 670 500 8973 345 2.03 0.75 1,295 Sine Wave 817 Keow'ee WcstI~he Simulated Saddle Des 815 800 Owertopping 795 1880 1880 0 0 0.5 1880 Gate 817 Saddle Dam Opening Oconee Intake Canal 815 800 Overlopping 742 450 596 2 2 0.75 742 SineWave 817 Dike ittle Roer 815 800 Overtopping 670 290 435 1 0.75 580 SineWave 817 Dam D-2

FIGURE D-I COMPARISON OF THE HEC-RAS SINE WAVE BREACH WITH THE INCREMENTAL APPROACH OF THE 2-D MODEL 1

0.9 0.8

.20.7 0.5

"*0.4 S0.3 ir

--o-West Saddle Dam Sine Wave Breach (HEC-RAS) 0.2 ;--West Saddle Dam 2-D Breach 0.1 Keowee Dam Sine Wave Breach (HEC-RAS) i-Keowee Dam 2-D Breach 0

16.2 16.3 16.4 16.5 16.6 16.7 16.8 16.9 17 Time (hr)

D-3

~ar~t~ire S~~cu;;t~' ~erI~ziuv~ hfcrma~ior' - \AI~lhhrlri from ~ dizc~osurc. LJIChI U '1k L.JYU(CJ)(1)

Section I Introduction and Background TABLE D-4 XU AND ZHANG BREACH PARAMETER CALCULATIONS FOR JOCASSEE DAM Best Additive Function I Height of breach m ft Erodibility of Dam High Cl 1.072 103 337 Medium C1 0.986 93 304 Low C1 0.858 78 255 Xu Zhong Equation 11 Best-Simplified Prediction Best-Exact Prediction Failure time T1 Zone-filled Dams b3 -0.189 Tf hrs Piping b4 -0.611 hrs Erodibility of Dam Erodibility of Dam High C5 0.038 3.0 High b5 -1.205 3.5 Medium C5 0.066 6.0 Medium b5 -0.564 7.6 Low C5 0.205 23.2 Low b5 0.579 29.2 Xu Zhong Equation 21 Xu Zhang Equation 17 Breach top width Bt Zone-filled Dams b3 -0.089 B, Piping b4 -0.262 m ft Piping b4 -0.239 m ft Erodibility of Dam Erodibilityof Dam High b5 0.377 448 1,470 High b5 0.411 495 1,624 Medium bS -0.092 268 879 Medium bS -0.062 293: 962 Low b5 -0.288 203 666 Low b5 -0.289 214 701 Xu Zhong Equation 18 Xu Zhang Equation 14 Average breach width Bave Zone-filled Dams b3 -0,226 Bae Piping b4 -1.747 m ft Piping b4 -0.389 m ft Erodibilityof Dam Erodibility of Dam High b5 -0.613 326 1,071 High b5 0.291 377 1,238 Medium b5 -1.073 201 658 Medium b5 -0.14 237 777 Low b5 -1.268 157 515 Low bS -0.391 173 566 Xu Zhong Equation 19 Xu Zhang Equation 15 Peak outflow QP Zone-filled Dams b3 -0.649 Of 3 3 3 Piping b4 -1.232 m /s ftW/s Piping b4 -1.039 m /s ft /s Erodibilityof Dam Erodibility of Dam High b5 -0.089 210,544 7,435,022 High b5 -0.007 288,407 10,184,627 Medium b5 -0.498 121,241 4,281,419 Medium b5 -0.375 173,065 6,111,495 Low b5 -1.433 36,801 1,299,565 Low b5 -1.362 49,887 1,761,665 Xu Zhang Equation 20 Fu Zhong Equation 16 D-4

", s Securfty Sens ~ato - ubidscosure Ihod Cu under 1FfR230d()

TABLE D-5 JOCASSEE DAM BREACH PARAMETERS D-5

Contains Seci 1 formaticn- vvithh from , uopic disclosure ,Isd )(

FIGURE D-2 BEST EXACT PREDICTION LOW ERODIBILITY FAILURE SCENARIO BREACH PROGRESSION AND STAGE-DISCHARGE HYDROGRAPHS 1 20 3,000,000 100 2.500000 0 s0 2.000,021

~060 1,500,020

~040 1,000,030 500,000 0 00 0 1l/1/2.0083001 1111/2028 60C 11t1/2/092 0C I 11/2008 190OD 11/2(200p "/60 1/2/,20086 ro 11122,70081i TomI

-Headwater -- Tailwaer -Breach Frcrmsoion Bec Diszharge

- -- Breal0. In liatnon Plpe 20ola/se &reach Formation Cownlate D-6

" .tSesi * - ,,Tnldrom public disclosure undelE10 CFR 2.3S Section I Introduction and Background FIGURE D-3 JOCASSEE DAM SINE WAVE BREACH PROGRESSION 09 08 07 v 06 g05 04 03 02 01 0 01 0.2 03 04 05 06 07 0f: 09 Melnti-ye T pln Iog1Sl-lal D-7

Section I Introduction and Background Section I I ntrocluction and Background FIGURE D-4 STUDY AREA OVERVIEW 2-D MODEL 0 2.5005,000 Feet Aea Overview Oconee Nuclear Station IExternal Site Flooding Evaluation 2.D Model D-8

Section 4 Resuhls FIGURE D-5 MANNING*S ROUGHNESS COEFFICIENTS 0.080 UI I

W Manning's Roughness Coefficients I-4al " IIOconee Nuclear Station I External Site Flooding Evaluation 2.- Model D)-9

.Section I Intro( uction and Background FIGURE I)-6A WATER VELOCITIES AND FLOW PATTERNS AT T = 15.0 HOURS 0 2 4 6 8 10121416182022242628303234363840

Section I Introcuction and Background FIGURE D-6B WATER SURFACE ELEVATIONS AT T = 15.0 HOURS (b)(7)(F)

D-1 I

Section I Introduction and Background FIGURE D-7A WATER VELOCITIES AND FLOW PATTERNS AT T = 17.0 HOURS 0 2 4 6 8 1012141618202224262830323436:3840 D-12

Section I Introcuction and Background FIGURE D-7B WATER SURFACE ELEVATIONS AT T = 17.0 HOURS (b)(7)(F)

D-13

Section I Introduction and IBackground FIGURE D-8A WATER VELOCITIES AND FLOW PATTERNS AT T = 18.4 HOURS 0 2 4 6 8 1012141618 20 22 24 26 28 30 32 34 36 38 40 D)-14

Section I IntroL uction and Background FIGURE D-8B WATER SURFACE ELEVATIONS AT T = 18.4 HOUIRS (b)(7)(F)

D-15

! . , ... . , , i ,

Section 1 Intro('uction and Background FIGURE D-9A WATER VELOCITIES AND FLOW PATTERNS AT T = 20.0 HOURS I = zu.U Velocity Mamnitude (flos) 0 2 4 6 8 10121416182022242628303234363840 D-16

Section I Introduction and Background FIGURE D-9B WATER SURFACE ELEVATIONS AT T = 20.0 I-TII1D (b)(7)(F)

D-17

Section 1 Introduction and Background FIGURE D-10 MONITORING POINT LOCATIONS Oconee Nuclear Station External Site Flooding Evaluation II Monitong Point Locations 2-D ModelI D-18

Cuid~F~ S~uri[y 3~ns~t;vc Irf~dbu - vvitliiiulu irorn pUDIIC d~du~~ ud~ 10 CFP 2.390(d)(1~

Section 4 Results FIGURE D-l I KEOWEE DAM HEADWATER ELEVATION 840 830 820 I

.1A E

810 / I- Dam Breach Initiation

/, !- Dam Overtopped C800 Headwater Elevation Monitoring Location Dry

~790 780 770 760 0 4 8 12 16 20 24 28 32 36 Time (hr)

D-19

Section I Introduction and Background FIGURE D-12 KEOWEE DAM TAILWATER ELEVATION NEAR ONS 840 830 -SSF Ground Elevation

-Tailwater Elevation 820 - - Monitoring Location Dry

'810 E

r.1

~790 780 770 760 0 4 8 12 16 20 24 28 32 36 Time (hr)

D-20

Section I Introduction and Background FIGURE D-13 WATER SURFACE ELEVATION INONS INTAKE CANAL DIKE 840 830 820 810 E -North Wall Elev.

C800 C 800 . -Dike Overtopped

-WSE inIntake Canal 790 780 770 760 0 4 8 12 16 20 24 28 32 36 Time (hr)

D-21

Section I Introduction and Background FIGURE D-14 WATER SURFACE ELEVATION NEAR VISITOR'S CENTER SWALE WALL 840 830 820 E

~810 c800 A

-Swale Wall Elevation

-Swale Elevation

~790

-WSE near Swale

- - Monitoring Location Dry 780 770 760 0 4 8 12 16 20 24 28 32 36 Time (hr)

D-22

Section I Introduction and Background FIGURE D-15 WATER SURFACE ELEVATION AT SAFE SHUTDOWN FACILITY 840 830 820 . Monitoring Location Dry

-810 E

00800

-790 780 770 760 0 4 8 12 16 20 24 28 32 36 Time (hr)

D-23

ML13240A016

Text

SUMMARY

SUMMARY

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