ML20366A009
| ML20366A009 | |
| Person / Time | |
|---|---|
| Issue date: | 12/29/2020 |
| From: | NRC/OCIO |
| To: | |
| Shared Package | |
| ML20366A007 | List: |
| References | |
| FOIA, FOIA/PA-2017-0690, NRC-2017-000688 | |
| Download: ML20366A009 (171) | |
Text
Kelvin Henderson J_~ DUKE Vice President
~ ENERGY Catawba Nuclear Station Duke Energy CN01VP I 4800 Concord Road York, SC 29745 0 . 803 701.4251 I. 803.701 .3221 10 CFR 50.54(f)
CNS-1 4-028 March 12, 2014 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555 Duke Energy Carolina, LLC (Duke Energy)
Catawba Nuclear Station, Units 1 and 2 Docket Numbers 50-413 and 50-414 Renewed License Numbers NPF-35 and NPF-52
Subject:
Flood Hazard Reevaluation Report, Response to NRC 10 CFR 50.54(f) Request for Additional Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) regarding Recommendations 2.1, 2.3 and 9.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, Dated March 12, 2012
References:
- 1. NRC Letter, Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(a Regarding Recommendations 2.1, 2.3, and 9.3, of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated March 12, 2012 (Agencywide Document and Management System (ADAMS) Accession No. ML12053A340)
- 2. NRC Letter, Prioritization of Response Due Dates for Request For Information Pursuant to Title 10 of the Code of Federal Regulations 50. 54({) Regarding Flooding Hazard Reevaluation for Recommendation 2. 1 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated May 11 ,
2012, (ADAMS Accession No. ML12097A509)
- 3. NRC Letter, Trigger Conditions for Performing an Integrated Assessment and Due Date Response, Dated December 3, 2012, (ADAMS Accession No. ML12326A912)
- 4. Duke Energy Letter, Catawba Nuclear Station Flooding Walkdown Information Requested by NRG Letter, Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50. 54({) Regarding Recommendations 2. 3, Flooding Walkdowns, of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated March 12, 2012, dated November 27, 2012 (ADAMS Accession No. ML12334A444)
United States Nuclear Regulatory Commission Page 2 March 12, 2014 Ladies and Gentlemen:
On March 12, 2012, the NRG issued Reference 1 to all power reactor licensees and holders of construction permits in active or deferred status. Enclosure 2 of Reference 1 requested that each licensee perform a reevaluation of external flooding sources and report the results in accordance with the NRC's prioritization plan (Reference 2). The due date established for Catawba was March 12, 2014. Attachment 1 to this letter contains the required Flooding Hazard Reevaluation Report for Catawba.
The attached flood hazard reevaluation report describes the approach, methods and results from the reevaluation of flood hazards at Catawba. The eight (8) flood-causing mechanisms, and a combined effect flood identified in Attachment 1 to Enclosure 2 of Reference 1 are described in the report along with the potential effects on Catawba.
The flood hazard reevaluation report shows that some flood levels exceed the Current Licensing Basis (CLB) levels. The increased levels are the results of newer methodologies and guidance which are applicable to new reactor reviews and typically exceed the methodologies and guidance used to establish the CLB for existing plants. As such, these differences are not the results of errors within the CLB flood evaluations.
In accordance with Reference 3, an Integrated Assessment {IA) is required if flood levels determined during the f lood hazard reevaluation are not bounded by the CLB flood levels. of reference 1 specifies that the IA be completed and a report submitted within two years of submitting the Flooding Hazard Reevaluation Report. An IA will be completed and a report submitted no later than March 12, 2016.
As discussed within Reference 1, NRG acknowledged that the current regulatory approach and the resultant plant capabilities, an accident with consequences similar to the Fukushima event is unlikely with nuclear power plants located in the United States. The NRG concluded that the continued plant operation do not pose an imminent risk to the public health and safety. The flooding walkdowns of Catawba CLB flood protection features have been performed and the results were provided by Reference 4. In general, the flood walkdowns verified that the flood protection systems for Catawba are available, functional and implementable and if necessary, any degraded, nonconforming flood protection features were entered in Catawba Corrective Action Program. of attachment 1 provides a discussion of the interim evaluation and actions taken to address the higher flooding levels relative to the CLB flood levels. These actions will enhance the current capability to maintain the plant in a safe condition during the beyond-design-basis external flooding events that exceed the CLB flood levels and as a result, continued plant operation does not impose an imminent risk to the public health and safety while completing the Integrated Assessment.
This letter contains regulatory commitments as listed in the table provided by Enclosure 1 of attachment 1. The table provides a list of the interim actions taken along with the dates these actions were implemented. Duke Energy commits to not modify any of these interim actions or completion dates without notifying the NRG Project Manager, Jason Paige, in advance.
United States Nuclear Regulatory Commission Page 3 March 12, 2014 Should you have any questions concerning this letter or requ ire additional information, please contact Phil Barrett at (803) 701-4138.
I declare under penalty of perjury that the foregoing is true and correct. Executed on March 12, 2014.
Sincerely, Kelvin Henderson Vice President, Catawba Nuclear Station - Catawba Flood ing Hazard Reevaluation Report to Attachment 1 - Interim Actions Taken
United States Nuclear Regulatory Commission Page 4 March 12, 2014 xc:
V.M. Mccree, Regional Administrator U. S. Nuclear Regulatory Commission, Region II Marquis One Tower 245 Peachtree Center Avenue NE, Suite 1200 Atlanta, GA 30303-1257 Eric J. Leeds, Director, Office of Nuclear Reactor Regulation US. Nuclear Regulatory Commission One White Flint North, Mailstop 13-Hl6M 11555 Rockville Pike Rockville, MD 20852-2738 J.C Paige U.S. Nuclear Regulatory Commission One White Flint North, Mailstop 8 G9A 11555 Rockville Pike Rockville, MD 20852-2738 G.A. Hutto NRC Senior Resident Catawba Nuclear Station Justin Folkwein American Nuclear Insurers 95 Glastonbury Blvd., Suite 300 Glastonbury, CT 06033-4453
United States Nuclear Regulatory Commission Page 5 March 12, 2014 bxc:
R.J. Duncan (EC07H)
B.C. Waldrep (EC07H)
C.J. Thomas (EC05P)
M.C. Nolan (EC05P)
K. Henderson (CN0 1VP)
R.T. Simril (CN01 SM)
C.S. Kamilaris (CN01SA)
R.N. Pryce (CN04MD)
R.D. Hart (CN01 RC)
P.W . Barrett (CN01 RC)
CNS Master File (CN04DM, File CN 801 .01 )
RGC Date File (CN01 RC)
NCMPA-1 PMPA NCEMC ELL (EC2ZF)
United States Nuclear Regulatory Commission to Letter CNS-14-028 Page 1 of 1 Attachment 1 FLOODING HAZARD REEVALUATION REPORT FOR Catawba Nuclear Station, Units 1 and 2 Docket Numbers 50-413 and 50-414 Renew ed License Numbers NPF-35 and NPF-52
CATAWBA NUCLEAR STATION 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:
RDR ENGINEERING, INC. OF THE CAROLINAS Charlotte, North Carolina February 17, 2014
REPORT VERIFICATION PROJECT: CNS FLOODING HAZARD REEVALUATION REPORT TlTLE: 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: February 1. 2014 Checked by: Date: February 17, 2014 Reviewed by: Date February 17, 2014 Approved by: Date: February 17, 2014 Corporate Seal: Professional Engineer Seal:
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HOR Engineering, Inc. of the Carolinas 440 South Church St., Suite 1000 Charlotte, NC 28202 South Carolina License No. C03 l 8
CNS 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 TABLE OF CONTENTS Section Title Page No.
LIST OF A CRONYMS ................................................................................................ xiii EXECUTIVE
SUMMARY
.......................................................................................... ES-I SITE INFORMATION RELATED TO THE FLOOD HAZARD ................ ....................... I 1.1 Detailed Site Information ............................................................................................. l 1.2 C u1Tent Design Basis Flood Elevations ........................................................................ 2 1.2. l Local Intense Precipitation ...............................................................................2 1.2.2 Flooding in Reservoirs ......................................................................................9 1.2.2.1 Catawba River Reservoirs ..................................................................9 1.2.2.2 Standby Nuclear Service Water Pond .............................................. 15 1.2.3 Dam Failures ................................................................................................... 19 1.2.4 Storm Surge and Seiche ..................................................................................2 1 l.2.5 Tsunami .......................................................................................................... 23 1.2.6 Ice-Induced Flooding ...................................................................................... 23 1.2.7 Channel Diversion .......................................................................................... 23 1.2.8 Combined Effects ...........................................................................................24 1.3 L icensing Basis Flood-Related and Flood Protection Changes .................................. 25 I .4 Watershed and Local Area Changes ...........................................................................27
TABLE OF CONTENTS (Continued)
Section Title Page No.
1.5 Current Licensing Basis Flood Protection and Mitigation Features ........................... 31 2 FLOODING HAZARD REEVALUATION ......................... ....................................... 36 2.1 Local Intense Precipitation ......................................................................................... 36 2.1.1 Probable Maximum Precipitation ................................................................... 3 7 2.1.2 Site PMP Model Setup................................................................................... .41 2.1.3 Security Barrier Model Features .................................................................... .49
- 2. 1.4 CNS ICM Model Results ................................................................................ 52 2.2 Flooding in Reservoirs ................................................................................................60 2.2. 1 Probable Maximum Flood - Lake Norrnan .................................................... 75 2.2.2 Probable Maximum Flood - Lake Wylie ....................................................... 79 2.3 Dan1 Failures ............................................................................................................... 83 2.3.1 Potential Dam Failure ..................................................................................... 83 2.3.2 Dam Failure Perrnutations .............................................................................. 88 2.4 Storm Surge and Seiche .............................................................................................. 98 2.4.1 Seiching Analysis ........................................................................................... 98 2.4.2 Wind-Driven Waves Analysis - Lake Wylie Source ................................... 100 2.4.3 Wind-Driven Waves Analysis - SNSWP Source ......................................... I 02 2.5 Tsunan1i .................................................................................................................... 105 2.6 lee-Induced Flooding ................................................................................................ I 05 2.6. 1 Ice Effects ..................................................................................................... 105 2.6.2 Ice Jam Events .............................................................................................. 105 2.7 Channel Diversions ................................................................................................... 106 II
TABLE O F CONTENTS (Continued)
Section Title Page No.
2.8 Combined Effects ..................................................................................................... 106 2.8. 1 CNS Yard Combined Effects ........................................................................ I 08 2 .8.2 SNSWP Dam Combined Effects .................................................................. 119 2.8.3 Cooling Towers Combined Effects .............................................................. 120 3 COMPARISON OF CURRENT D ESIGN B ASIS AND REEVALUATED FLOOD CAUSING M ECHANISMS .................................................................................................. 127 3.1 SNSWP Dain ............................................................................................................ 128 3.2 Cooling Tower Breach .............................................................................................. 130 3.3 Riverine Flooding on Lake Wylie ............................................................................ 130 3.4 Local Intense Precipitation ....................................................................................... 132 3.5 Dam Failures ............................................................................................................. 133 3.6 Storm Surge and Seic he ............................................................................................ 134 3.7 Tsunami .................................................................................................................... 134 3.8 Ice-Induced Flooding ................................................................................................ 134 3.9 Channel Diversion .................................................................................................... 1-34
- 3. 10 Combined Effects ..................................................................................................... 135 4 INTERIM A CTIONS TAKEN OR PLANNED ......................................... ................. 136 4.1 LIP Actions ............................................................................................................... 136 4.2 Combined Effects PMF Flooding ............................................................................. 136 5 REFERENCES********** ********************************************* ......... ............................ ....... l 37 lll
TABLE OF CONTENTS (Continued)
Section Title Page No.
ENCLOSURE 1 Catawba Nuclear Station, Units I and 2 - Flood Hazard Reevaluation Report Interim Actions.
iv
CNS FLOODING HAZARD REEVALUATION REPORT RESPONS E 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 LIST OF FIGURES Figure Title Page No.
l .2.2.2- 1 SNSWP PMF HYDROGRAPHS ............................................................................... 18 l.4-1 AERlAL PHOTOGRAPH OF CNS SITE IDENTIFYING AREAS OF SITE SECURITY CHANGES OBSERVED DURING SITE WALKDOWN FOR THE FUKUSHIMA 2.1 FLOOD HAZARD REVIEW (REFERENCE 26) ............. 30
- 2. 1.1-1 TYPICAL EXAMPLE OF HMR NO. 52 FIGURE USED IN THE PMP ANALYSIS ................................................................................................................ 38 2.1.1-2 CNS PMP HYETOGRAPH .......................................................................................40 2.l.2-1 CNS DIGITAL TERRAIN MODEL 3-DIMENSIONAL PERSPECTIVE LOOKING NORTH NO BUILDINGS SHOWN ..................................................... .43 2.1.2-2 CNS DIGITAL TERRAIN MODEL EXTENTS SHOWN BY RED LINE ............ .44
- 2. 1.2-3 CNS DIGITAL TERRAIN ROOF DRAINAGE CONNECTIVITY ....................... .46 2.1.2-4 CNS ICM MODEL YARD ROUGHNESS ZONE BOUNDARIES ........................ .48 2.1 .3-1 CNS ICM MODELED SECURITY BARRIERS ...................................................... 51
LIST OF FIGURES (Continued)
Figure Title Page No.
2.1.4-2 CNS ICM MODEL PMP RESULT NODE LOCATIONS AT DOORS TO BUILDINGS WITH IDENTIFIED SSCs .................................................................. 56 2.1.4-3 CNS ICM MODEL LIP RESULT MAXIMUM WATER ELEVATIONS AROUND THE MAIN POWER BLOCK STRUCTURES ...................................... 57 2.2- l OVERVIEW AND PROFILE OF CATAWBA WATEREE RIVER DAMS ...........61 2.2-2 WYLIE DEVELOPMENT HYDROLOGIC SUB-BASIN FROM 1992 FERC PMF STUDY .............................................................................................................. 63 2.2-3 CATA WBA-WATEREE BASIN INCLUDING SUB-BASIN DELINEATION AND DESIGNATED SUB-BASIN NUMBER. THE CNS 2.1 FUKUSHIMA STUDY IS LIMITED TO TWENTY TWO SUB-BASINS, NUMBERS 0-21 ........64 2.2-4 CATAWBA RIVER MODEL, AUGUST 1940 FLOOD PROFILE ALONG CATAWBA RIVER...................................................................................................70 2.2. 1- 1 SUB-BASIN INFLOW HYDROGRAPHS FOR : {7 F) r (J1fo0:::,1.., SB24o- lrd) W)(4/ I SCENARIO CF_ ACS_PMF_ 1B2 ..............................................................................76 2.2.1-2 WYLIE RESERVOIR STAGE NEAR CNS SITE (REFERENCE 18) .................... 78 2.2.2-1 SUB-BASlN INFLOW HYDROGRAPHS FOR WYLIE PMF SCENARIO WYLIE- PMF- 2A .......................................................................................... ............ 81 2.2.2-2 WYLIE RESERVOIR STAGE NEAR CNS SITE (REFERENCE 18) .................... 82 2.3.2-1 WYLIE RESERVOIR STAGE NEAR CNS SITE INTAKE STRUCTURE (REF.- - - .CE 18), LAKE WYLIE WATER LEVEL ABOVE !rbJ)l 1 FT MSL (bi . r, FO ~ls~ HOURS ....................................................................... ~~~ ..................94
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LIST OF FIGURES (Continued)
Figure Title Page No.
2.3.2-2 WYLIE RESERVOIR STAGE NEAR CNS SITE SNSWP DAM (b)(3) 11, USC (RE::o E 18), LAKE WYLIE WATER LEVEL ABOVE T_~S.h *****-*§*8246'1(d) (b)(3)16US' ihl
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§ c\24o l(dr(b) * ...£ ___ OURS........................................................................ ................95 I t ,I 1 ' *~
2.3.2-3 WYLI E RESERVOIR STAGE NEAR CNS SITE COMPARISON BETWEEN UPSTREAM CROSS SECTION NEAR INTAKE AND ALLlSON CREEK DISCHARGE STRUCTURE (REFERENCE 18) .....................................................96 2.3.2-4 CATAWBA RIVER WATER SURFACE PROFILE COMPARISON BETWEEN NORMAL POOL, II* lfi US - Iii i'.l24o-l di Ill 4) lD ft REFERENCE 18) ................. 97 2.8. 1-1 STAGE HYDROGRAPH - HEC-RAS MODEL RUN CF ACS PMF 8J4 (REFERENCE 18) ................................................................................................... 110 2.8.1-2 2-D BOUNDARY CONDITION LOCAT1ON (REFERENCE 17) ........................ 111 2.8. 1-3 CNS ICM MODEL PMP RESULT NODE LOCATIONS...................................... 11 3 2.8.1-4 CNS ICM MODEL PMP RESULT NODE LOCATIONS AT DOORS TO BUILDINGS WITH IDENTIFlED SSCs ................................................................ 114 2.8. 1-5 MAXIMUM WATER LEVELS IN CNS YARD DURING THE COMBINED EFFECTS PMF FLOOD EVENT (REFERENCE 17) ............................................ 11 7 2.8.3- 1 COOLING TOWER BREACH WIDTH SENSITIVITY DEPTH HYDROGRAPHS (NORTH CAROLINA ST ATE PLANE NAD83 vii
LIST OF FIGURES (Continued)
Figure Title Page No.
COORDINATE SYSTEM EASTING AND NORTHING: 138 127 1 US FT, 479869 US FT) (REFERENCE 17) ......................................................................... 122 2.8.3-2 CNS COOLING TOWER 2A BREACH SIMULATION (REFERENCE 17) ....... 123 2.8.3-3 CNS COOLING TOWER AREA REPRESENTATIVE ELEVATION AND DEPT H HYDROGRAPH DURING HYPOTHETICAL FAILURE OF COOLING TOWER 2A - NORTH CAROLINA STATE PLANE NAD83 COORDINATE SYSTEM EASTING AND NORTHING: 138 127 1 US FT, 479869 US FT (REFERENCE 17) ........................................................................... 124 2.8.3-4 CNS COOLlNG TOWER AREA REPRESENTATIVE VELOCITY HYDROGRAPH DURING HYPOTHETICAL FAILURE OF COOLING TOWER 2A - NORTH CAROLINA STATE PLANE NAD83 COORDfNATE SYST EM EAST ING AN D NORTHING : 138127 1 US FT, 479869 US FT (REFERENCE 17) ................................................................................................... 125 2.8.3-5 MAXIMUM INUNDATION IN COOLING TOWER AREA DURING A HYPOTHETICAL FAILURE OF COOLfNG TOWER 2A (REFERENCE 17) .... 126 viii
CNS FLOODING HAZARD REEVALUATION REPORT RESPONSE TO REQUEST FOR INFORMATION PURSUANT TO TITLE 10 OF THE CODE OF FEDERAL REGULATIONS SO.S4 (F) REGARDING RECOMMENDATION 2.1: FLOODING OF THE NEAR-TERM TASK FORCE REVIEW OF INSIGHTS FROM THE FUKUSHIMA DAI-ICHI ACCIDENT LIST OFTABLES Table Title Page No.
l.2. l-1 MAXIMUM POWERHOUSE YARD INUNDATION LEVELS ..............................3 l.2. 1-2 5-MINUTE TTME SERIES FOR PEAK I-HOUR RAINFALL FOR HYDROMETEOROLOGICAL REPORT 33 (HMRJJ) ............................................ .4 1.2. 1-3 MAXIMUM POWERHOUSE YARD INUNDATION LEVELS COMPARISON............................................................................................................7 1.2.1-4 5-MINUTE TIME SERIES FOR PEAK I-HOUR RA INFALL FOR HMRS I/52 .....8 1.2.2-1 LAKE WYLIE PROBABLE MAXIMUM FLOOD FLOODING RESULTS .......... 15 l .2.2.2- 1 SNSWP DESIGN INFORMATION .......................................................................... 16 l .2.2.2-2 SNS WP DRAINAGE BASIN HOURLY INCREMENTAL RUNOFF .................... 17 1.2.3- 1 DUKE ENERGY FERC LICENSED DEVELOPMENTS ON THE CATAWBA RIVER UPSTREAM OF CNS ...................................................................................19 1.2.3-2 COMBINED EFFECTS SPF PLUS DAM FAILURE SIMULATJON SCENARJO RESULTS ..............................................................................................20 16 92 O 1.2.3-3 COMBINED EFFECTS SPF PLUS I':, ::, *- sr § ~e--l \OJl.!f l:J rNFI SIMULATION SCENARIO RESULTS ....................................................................2 1 ix
LIST OF TABLES (Continued)
Table Title Page No.
1.2.4-1 SURGE AND SEICHE WA VE CALCULATION RESULTS ................................. 22 J.2.8- 1 COMBINED EFFECTS MAX IMUM RESERVOIR ELEVATION WITH WIND-DRNEN WAVES ......................................................................................... 25 2.1.1-1 PMP RATIOS AND ESTIJ\.1ATES (INCHES) FOR DURATIONS LESS THAN I HOUR.......................................................................................................... 37 2.1.1-2 5-MINUTE INCREMENTAL CNS PMP .................................................................. 39 2.1.2-1 ROOF RUNOFF ROUTING VALUES .................................................................... .45 2.1.2-2 ROUGHNESS ZONE MANNING' S n VALUES .................................................... 47 2.1.4-1 CNS ICM MODEL LlP RESULT NODES ............................................................... 58 2.1.4-2 CNS ICM MODEL LIP RESULT LOCATIONS AT DOORS TO BUILDINGS WITH IDENTIFIED SSCs NODES ..........................................................................59 2.2-1 CATAWBA-WATEREE PMF ANALYSIS SUB-BASINS ..................................... 65 2.2-2 MODEL VERJFICATION SUB-BASIN PREC IPITATION COMPARISON .........68 2.2-3 CATAWBA RlVER MODEL RESULTS COMPARJSON WITH 1916 FOOD EVENT .......................................................................................................................69 2.2.1-1 CATAWBA RNER MODEL RUN CF- ACS- PMF- 1B2 RESULTS (REFERENCE 18) ..................................................................................................... 77 2.2.2-1 CATAWBA RNER MODEL RUN RESULTS FOR WYLIE_PMF_2A SCENARIO (REFERENCE 18) ................................................................................ 80 X
LIST OFTABLES (Continued)
Table Title Page No.
2.3. 1-1 FINAL DAM BREACH PARAMETERS FOR PIPING AND OYERTOPPTNG MODE FAILURES AT DUKE ENERGY HYDROELECTRIC DAMS (REFERENCE 18) ..................................................................................................... 87 2.3.2-1 HEC-RAS MODEL FINAL RUN MATR1X (REFERENCE 18) ............................. 89 2.3.2-2 HALF PMF PLUS I~ ,JJtfi ll s C ~ ~t..!.O- J) \O !J lO)lr i:;)
MODEL RESULTS, INC LUDING RESERVOIR STAGE NEAR CNS SITE (REFERENCE 18) .....................................................................................................90
- 2. 3.2-3 HALF PMF PLUS WYLIE DAM CATAWBA RIVER FAILURE MODEL RESULTS, INCLUDING RESERVOIR STAGE NEAR CNS SITE (REFERENCE 18) .....................................................................................................91 2.3.2-4 PMF PLus .... u s_ § a_L-O--
lllJ_3_' i_6_ .l)-lu_il_'_IJ_x,_111:_, _ _ _ _ _ _ _ _ _IMODEL RESULTS, INCLUDING RESERVOIR STAGE NEAR CNS SITE (REFERENCE 18) .....................................................................................................93 2.4. l -l SEICHING WIND-DRIVEN WAVE RESULTS .................................................... 100 2.4.2- 1 WATER SURFACE ELEVAT IONS USED TN CALCULATIONS ....................... 10 1 2.4.2-2
SUMMARY
OF WIND-DRIVEN WAVE ANALYSIS - LAKE WYLIE WATER LEVELS .................................................................................................... 104 2.4.3-1 SU!\.1MAR.Y OF WIND-DRIVEN WAVE ANALYSIS - SNSWP DAM UPSTREAM SLOPE ............................................................................................... 104 2.8.1- l COMBINED EFFECTS 2-D MODEL INUNDATION RESULTS AT NODES IDENTIFIED IN FIGURE 2.8.1-3 ........................................................................... 115 XI
LIST OF TABLES (Continued)
Tab1e Title Page No.
2.8.1-2 COMBINED EFFECTS 2-0 MODEL INUNDATION RESULTS AT DOORWAY NODES IDENTIFIED IN FIGURE 2.8. l -4 ....................................... 116 3- 1 CURRENT DESIGN BASIS AND REEVALUATION FLOOD ELEVATIONS .128 XII
List of Acronyms 1-D, 2-D one d imensional, two dimensional, etc.
CAP Corrective Action Program CFR Code of Federal Regulations cfs cubic feet per second CMH Conduit Manholes CN curve number CNS Catawba Nuclear Station DTM Digital Terrain Model ECR Engineering Change Request ft foot/feet FERC Federal Energy Regulatory Commission GIS Geographic lnfotm ation Systems HEC-RAS Hydrologic Engineering Center's - River Analysis System HHA Hierarchical Hazard Assessment HMR Hydrometeorological Report I and E Instrumentation and Electrical ICM Integrated Catchment Model in/hr inch(es) p er hour L lag time LIP local intense precipitation LPSW Low Pressure Service Water mph miles per hour m1 miles msl mean sea level NEI Nuclear Energy Institute NGVD National Geodetic Vertical Datum NRC Nuclear Regulatory Commission NSW Nuclear Service Water NTTF Near-Term Task Force Xlll
List of Acronyms NUREG N uclear Regulation PMF probable maximum flood PMP probable maximum precipitation PMS probable maximum storm scs Soil Conservation Service SNSW Standby Nuclear Service Water SNSWP Standby Nuclear Service Water Pond SOF Statement of Fact SPF Standard Project Flood sq ft square feet sqmi square miles SRM Staff Requirements Memorandum SSC systems, structures, and components UFSAR Updated Final Safety Analysis Report U.S. United States USACE United States Army Corps of Engineers USGS United States Geological Survey Yard CNS Yard XIV
Executive Summary Following the accident at the Fukushima Dai-ichi nuclear power plant resulting from the 2011 Great Tohoku Ea1thquake and Tsunami , the Nuclear Regulatory Commission (NRC) established the Near-Tenn Task Force (NTTF) and tasked it with conducting a systematic and methodical review ofNRC processes and regulations to detennine 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 prov ides 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 IO of the Code of Federal Regulations, Section 50.54(f) (IO CFR 50.54[£]) on March 12, 2012, based on the following NTIF flood-related recommendations:
- Recommendation 2. 1: Flooding
- Recommendation 2.3: Flooding to the NRC 50.54(f) letter addresses Recommendation 2.1 and requests a wrinen response from licensees to:
- 1. Gather information with respect to NTTF Recommendation 2.1, as amended by SRM on SECY- 1 I -0124 and SECY- 11-0137, and the Consolidated Appropriations Act for 20 l 2, Section 402, to reevaluate seismic and flooding hazards at operating reactor sites.
- 2. Collect information to faci litate NRC's detem1ination of the need to update the safety-related design basis and systems, strnctures, 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.
ES- 1
Executive Summary This report was prepared for the Catawba Nuclear Station (CNS) Generating Plant Units l and 2 in response to NITF Recommendation 2.1 only.
Section 1 Site Information Related to the Flood Hazard 1.1 Detailed Site Information Catawba Nuclear Station (CNS) is located m northeastern York County, South Carolina, approximately 6 miles north of Rock Hill, South Carolina. The site is located on a peninsula bounded by Beaver Dam Creek to the north, Big Allison Creek to the south, Duke Energy Carolinas, LLC's (Duke Energy) Lake Wylie to the east, and private property to the west. Duke Energy's Wylie Dam and Hydroelectric Station are located approximately 4.8 river miles southeast of the site. Rock Hill, South Carolina; Gastonia, North Carolina; and Charlotte, North Carolina; are the nearest large cities.
The location and description of CNS presented in the Updated Final Safety Analysis Repo1t (UFSAR) Chapter 2 include reference to figures showing the general arrangement, layout, and relevant elevations of the station. The original design of the CNS Yard (Yard) grade was nominally 593.50 feet (ft) (SOF 1.1.1-01) mean sea level (ms)) (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 594.00 ft msl. Exterior accesses to these buildings are at an elevation of 594.00 ft msl (SOF 1.1.1-02). Section 1.4 provides further discussion of modifications to the Yard grade.
The j(tl(1 l 10 O's c s82~"Cd) 1b 1ft msl, and the Nuclear Service Water (NSW) and Standby Nuclear Service Water (SNSW) pumps are located in a concrete structure on the south abutment to the dam at elevation 599.50 ft msl and are not subject to flooding or wave effects based on the existing licensing basis (SOF 1. 1.1-03).
Section I Sile Information Related to the Flood Hazard 1.2 Current Design Basis Flood Elevations 1.2.1 Local Intense Precipitation The fl ood water elevation due to a maximum local intense precipitation (LIP) (also known as the point probable maximum precipitation [PMP]) has been evaluated for producing local inundation throughout the Cooling Tower Yard, Switchyard, Construction Yard, and the Powerhouse Yard over the life of the generating facility. The inundation analysis is documented in calculation CNC-l 114.00-00-0040, Rev 29. The analyses have been perfonned using a variety of hydraulic routing tools, including the United States Anny Corps of Engineers (USACE), HEC-1 model, traditional hand calculation methods combined with computer automated Microsoft Excel spreadsheets to facilitate the performance of the routing calculations. The routing analysis is based on the "Modified Puls" method available in the HEC-1 model. CNC-1114.00-00-0040 has been revised 29 times to incorporate the review of hydrology and hydraulic assumptions and physical changes in Yard areas that have occurred since the calculations were 01iginated in 1978.
The latest calculation, Revision 29, addresses the Vehicle Barrier System enhancement project, subterranean barrier modifications, and items noted in the 2.3 Fukushima Near-Tem1 Task Force (NTTF) Flood Walkdown Inspection report (October 2012).
The licensing basis PMP for the CNS site is sununarized in Section 2.4.2.3 of the UFSAR and in Section 5 of the 2.3 Fukushima NTIF Flood Walkdown Inspection report. The CNS licensing basis PMP is based on U.S . Weather Bureau Hydrometeorological Report (HMR) 33. A 6-hour (hr) duration PMP, producing 24. 1 inches (adjusted period total) and a peak 1-hr rainfall of 9.2 inches, was used to analyze potential inundation in the Yard areas (SOF 1.2. 1-01 ). The HEC-1 model, using the Soil Conservation Service (SCS) dimensionless unit hydrograph method, was used to estimate the precipitation/runoff relationship for each sub-area in the model and routed using the "Modified Puls" method. Revision 22 of the calculation documents that an Excel spreadsheet was developed to facilitate the routing for updating the analysis (SOF 1.2.1 -02). The resulting maximum inundation levels in the Powerhouse Yard using the HMR33 PMP are shown in Table 1.2. 1- 1.
2
Section I Site Information Related to the Flood Hazard TABLE 1.2.1-1 MAXIMUM POWERHOUSE YARD INUNDATION LEVELS PMP Input to Model HMR33 Analysis Basis (with 0.80 Reduction Factor)
Previous Maximum Yard Inundation Level CNC 1114.00-00-0040 Rev 22 593.94 ft msl (SOF 1.2.1-03)
CNC 1114.00-00-0040 Rev 28-29 using 20 IO Survey and catch basin network 594.00 ft msl Unit 1 Yard Inundation Level (SOF 1.2.1-04)
CNC 1114.00-00-0040 Rev 28-29 using 20 IO Survey and catch basin network 594.80 ft ms!
Unit 2 Yard Inundation Level (SOF 1.2.1-05)
Note: The elevations shown in Table 1.2. 1-1 include the effectiveness of the yard drainage system as documented in the UFSAR Section 2.4.2.3.3.
The description of the routing assumptions used in the existing PMP calculations is found in Section 2.4.2.3. l of the UFSAR and repeated below.
The plant site is provided with a surface water drainage system that is designed and constructed to protect all safety-related facilities from flooding during a local PMP. The drainage system consists of (I) catch basin inlets which are coM ected by corrugated metal pipes to fonn several networks and (2) graded areas which permit free surface outflow to Lake Wylie when ponding in the powerhouse yard reaches Elevation 593.50 ft msl. All pipe networks and graded areas discharge at elevations which are higher than Lake Wylie full surface elevation (Elevation 569.40).
To obtain time dependent inflow for the PMP, the site is divided into sub-areas. Inflow to the power block area is due to precipitation which falls on 129 acres, which include the powerhouse yard, buildings, and the construction yard. The switchyard and cooling tower yard sub-areas have been bermed/curbed to route water away from the power block area. Elevations of these benns/curbs are conservatively set by neglecting outflow from the switchyard and cooling tower yard storm drainage systems. Inflow to the switchyard and cooling tower yard sub-areas is due 3
Section I Site Information Related to the Flood Hazard to precipitation which falls directly on the yards and structures, excluding the cooling towers.
The inflow hydrograph for the power block area is determined by combining the inflow hydrograph for the construction yard and powerhouse yard sub-areas. Each hydrograph is based on a SCS dimensionless unit hydrograph. The HEC-1 computer program was used to develop a total hydrograph for a given Jag time with lag time (L) being defined as the time in hours from the center of mass of rainfall excess to the peak discharge.
For the construction yard, a hydraulic length of 1,81 5 ft and an average slope of 1.18 percent was obtained from site topography. The maximum retention is based on the SCS Curve Number 98.
Lag time for the construction yard sub-area is 13.4 minutes. The time of concentration for the construction yard is 22.4 minutes. Lag time for the powerhouse yard sub-area was assumed to be zero to approximate an instantaneous time of concentration. Since the time of concentration used to develop the inflow hydrograph is s mall, the peak I-hour precipitation (9.2 in.) was distributed according to the USACE procedure for 5-minute durations as shown in Table 1.2.1-2.
TABLE 1.2.1-2 S-MJNUTE TIME SERIES FOR PEAK I-HOUR RAINFALL FOR HYDROMETEOROLOGICAL REPORT 33 (HMR33)
Time I Incremental PMP Cumulative PMP (minutes) , (inches) (inches) s 0.28 0.28 10 0.37 0.65 15 0.46 I. 11 20 0.55 1..66 25 0.83 2.49 30 1.56 4.05 35 2.3 6.35 40 IO. I 7.36 45 0.74 8. 1 50 0.46 8.56 55 0.37 8.93 60 0.27 9.2 During a local intense PMP, water will pond in the power block area and on the roof of the service building. With the exception of the reactor building, the roofs of safety-related structures are designed so that water flows directly off roofs with no accumulation. A gutter drain system 4
Section I Site Information Related to the Flood Hazard catches the water and routes it to collection points which discharge directly into the yard drainage system. The reactor building roof drainage system is designed for a rainfall intensity of 5.0 inches per hour (in/hr). Intensities in excess of 5.0 in/hr result in ponding; however, once the water level reaches Elevation 711.34 ft msl, the water flows directly off the roof. The reactor building roof is designed to safely carry live loading due to ponding. In detennining the effect of a local intense PMP on the powerhouse yard, it is assumed that water flows directly off the reactor building and service building without ponding or discharging through the roof drainage system. Water which ponds in the power house yard will discharge into catch basins and over the northeast and south ends of the yard that discharge into Lake Wylie. Two types of catch basin inlets are credited for the site. Type 11 inlets consist of slotted catch basin covers with an effective opening of 0.69 square feet (sq ft}. Type I inlets have no slotted cover, but are protected by steel grating on four sides and top. The total effective opening in the grating on any one side is at least equal to the effective opening of the pipe inlet ( 1.48 sq ft}, but may be as much as 3.9 times the effective pipe opening. The open area provided by all four sides of the Type I inlet varies from 4 to 15.6 times the pipe opening as margin for not considering complete blockage by debris accumulation. There are 89 Type I inlets provided in the power block area, but only 80 are required to be operable at any given time. All inlets are connected to corrugated metal pipes which are fully coated with a paved invert. The yard drainage p ipes, individually and with.in a network, are designed using Manning's equation for pipe flowing full.
Accumulative totals are used throughout the networks to determine pipe sizes. All pipe gradients are 0.5 percent or greater. Water in the power block area is assumed to rise and fall as a "level pool."
The PMP flood event is routed through the CNS switchyard using the Modified Puls method for an instantaneous time of concentration. The switchyard catch-basin drainage system was considered blocked with no outflow. A curb (Elevation 632.67 ft ms!) is provided on the north, south, and east ends of the switchyard to block water from flowing onto the powerhouse yard. In addition, trench plugs are provided at the curb location in all trenches that connect between the switchyard and the powerhouse yard. The flood routing was performed with the HEC-1 computer program using storage and discharge data which are based on the switchyard topography. Storage in the switchyard was estimated by characterizing the yard as an inverted 5
Section I Site Information Related to the Flood Hazard pyramid with a top area of 16.5 acres and a correspondi ng apex depth of 1.00 fi below Elevation 632.00 ft msl. When ponding in the switchyard reaches elevation 632.00 ft, sheet outflow over the west side of the yard is routed using a standard weir equation. The natural topography below the overflow area conveys the discharge away from the s ite.
Similarly to the switchyard runoff calculation, the PMP flood event is routed through the cooling tower yard using the Modified Puls method for an instantaneous time of concentration. T he cooling tower yard catch-basin drainage system was considered blocked with no outflow. The area occupied by the cooling towers was neglected for the inflow and storage calculations since all precipitation which fa lls on the towers was assumed to be contained within the system. An earth berm (Elevation 620.50 ft msl) is provided on the northwest end of the cooling tower yard to route water away from the powerhouse yard. In addition, trench plugs are provided at the berm location in all trenches that connect between the cooling tower yard and the powerhouse yard . The flood routing was performed with the HEC- 1 computer program using storage and discharge data which are based on the cooling tower yard topography. Storage in the cooling tower yard is determined by characterizing the yard as an inverted pyramid with a top area of 32.4 acres (ac) and a corresponding apex depth of 1.50 ft below elevation 620.00 ft ms!. When ponding in the cooling tower yard reaches elevation 620.35 ft msl, sheet outflow over the southwest side of the yard is routed using a standard weir equation. The natural topography below the overflow area conveys the discharge away from the site.
In 1984, the N RC requested that CNS perform PMP calculations using HMR5 J/52 (SOF 1.2.1-06). A 6-hr duration PMP producing 30.1 inches (non-adjusted period total) (SOF 1.2.1-07) and a peak I-hr rainfall of 19.0 inches was used to analyze potential inundation in the Yard areas using the same hydraulic model incorporating the HMR33 PMP. The resulting maximum inundation levels in the Powerhouse Yard using the HMR5 l/52 PMP are shown in Table 1.2. 1-3.
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Section I Site Information Related to the Flood Hazard TABLE 1.2.1-3 MAXIMUM POWERHOUSE YARD INUNDATION LEVELS COMPARISON PMP Input to Model PMP Input to Model Analysis Basis HMR 33 HMR51/52 (with 0.80 Reduction Factor)
Previous Maximum Yard Inundation Level CNC 1114.00-00-0040 Rev 22 593.94 ft msl 594.74 ft msl (SOF 1.2.1-03)
CNC l 114.00-00-0040 Rev 28-29 using 20 l OSurvey and catch basin network 594.0 ft msl 594.9 ft msl Unit I Yard Inundation Level (SOF 1.2.1-04)
CNC 1114.00-00-0040 Rev 28-29 using 20 10 Survey and catch basin network 594.8 ft msl 595.9 ft msl Unit 2 Yard Inundation Level (SOF 1.2. 1-05)
Note: The elevations shown in Table 1.2.1-1 include the effectiveness of the yard drainage system as documented 111 the UFSAR Section 2.4.2.3.3.
As a difference in assumption for the application of the PMP using HMRS l /52, no reduction in PMP values was applied to account for the imperfect fit of isohyetal patterns to the basin shape (SOF 1.2. 1-08). Rainfall percentages given in HMR No. 52 for the 5-, 15-, 30-, and 60-minute intervals were used to estimate rainfall for each 5-minute interval during the peak one hour with the resulting rainfall distributed according to the USACE procedure as shown in Table 1.2. 1-4.
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Section 1 Site Information Related to the Flood Hazard TABLE 1.2.1-4 5-MINUTE TIME SERIES FOR PEAK I-HOUR RAINFALL FOR HMRSJ/52 Incremental Cumulative Time (minutes)
PMP (inches) PMP (inches) 5 0.35 0.35 10 0.80 1.15 15 1.05 2.20 20 I.I 6 3.36 25 1.6 1 4.97 30 2.02 6.99 35 6.18 13.77 40 1.49 14.66 45 1.60 16.26 50 l.14 17.40 55 0.95 18.35 60 0.65 19.0 Inflow hydrographs fo r the powerhouse yard, switchyard, and cooling tower yard were developed in the same manner as the HMR33 calculations using the SCS method and routed using the Modified Puls method. Benns around the switchyard and cooling tower yard are high enough to prevent water from flowing from these yards onto the powerhouse yard (SOF 1.2.1-09). Calculations (CNC-1 114.00-00-0040 Rev 29) (Reference 8) based on the I-hour PMP distribution in Table 1.2.1-4 indicate that water will pond onsite to a maximum elevation of 594.90 ft ms! for Unit l and 595.90 ft msl for Unit 2 (SOF 1.2.1-10). These values are 0. 16 ft and 1.16 ft higher than values shown in the UFSAR for the HMR5 l /52 PMP.
Section 5 of the 2.3 Fukushima NTTF Flood Walkdown report notes for the HMRS 1/52 PMP crediting 80 Type I catch basins, associated piping network, and sheet outflow areas the resultant pending water level is 594.59 ft msl ( elevation determined prior to CNC- 1114.00-00-0040 Rev 22), which is higher than the entrance elevation to safety-related structures. The higher yard inundation elevation was evaluated by Duke Energy. Ponding of water remains above 594.0 ft msl elevation for approximately 35 minutes. Water was routed through doors into the Auxiliary Building, Auxiliary Service Building, Exterior Doghouses, fom1er UHl Buildings, and Turbine Buildings. Water entering the Turbine Buildings, would eventually be routed down to the Turbine and Service building basement (568.0 ft ms!) which is separated from any structures, 8
Section I Site Information Related 10 the Flood Hazard systems, and components important to safety by a I 2-ft-high concrete flood wall. In other buildings, the water would spread across the floor areas and be intercepted by the floor drain system (WL system). The floor drain system routes the volume of water to four floor drain sumps and a floor drain tank, all located at elevation 543.00 ft ms! in the Auxilia1y Building.
The evaluation concluded that no safety-related equipment is affected by this water inflow (SOF 1.2. 1-11 ).
The flood levels presented in the 2.3 Fukushima NTTF Flood Walkdown repott evaluating the site's flood protection features and procedures were 594.90 ft msl for Unit land 595.90 ft for Unit 2 (Reference 6). The current revision to the Yard Flooding Analysis is based on an aerial topographic survey performed in March 20 I 0. This survey allowed a more accurate model of the storage volumes and location and elevation of outflow weirs. The analysis showed that water will overtop the switchyard curb. The calculation concluded that it was appropriate to include the Switchyard drainage area in the Powerhouse drainage area. The west Switchyard outflow area is neglected in the current analysis (SOF 1.2.1-12).
CwTent design basis recognizes that external flood water will flow through gaps under exterior doors. This flow is evaluated in calculation CNC-1206.03-00-0142 (Flooding of Safety-Related Structures Due to Excessive Rainfall) (SOF 1.2.1-13).
1.2.2 Flooding in Reservoirs 1.2.2.1 Catawba River Reservoirs The main hydrologic/hydraulic features influencing the CNS plant site are the Catawba River and the series of seven reservoirs that regulate the river upstream and along the shores where the CNS site is located (Lake Wylie). The headwaters of the Catawba are at the Blue Ridge Divide (Eastern Continental Divide) near O ld Fort, North Carolina. The river flows generally east and then south where it joins the Wateree luver at Lake Wateree near Camden, South Carolina. The Catawba River is approximately 240 miles (mi) long and has a drainage area of approximately 4,750 square miles (sq mi) above Wateree Dam.
9
Section I Sile Information Related lo the Flood Hazard Lake Wylie, originally created in 1904 with the construction of a small low head dam on the Catawba River for hydroelectric power production, was rebuilt to its current size in 1925 with the construction of Wylie Dam at the same site near Rock Hill, South Carolina. The lake extends north from Wylie Dam up the Catawba River 28 mi to Mountain Island Dam. The impoundment also extends approximately 5 miles up the South Fork, a western tributary that runs parallel to the Catawba River.
.________________________________ _. There are l l hydroelectric reservoirs and l 3 Federal Energy Regulatory Commission (FERC)-regulated hydroelectric powerhouses along the Catawba River.
regulate flows on the Catawba River upstream from CNS and Lake Wylie. They
- h-a-ve- a -co
_m bined usable storage of approximatel~ 13 31 .;; - s.:; § a:t~&- 0 ' 0 '< * " 11F 1
___ I reservoirs are regulated by the FERC and are operated by Duke Energy under FERC License No.
2232. The reservoirs are managed to maintain seasonal reservoir levels using available hydro turbines and spillway st1uctures, and all dam structures have been remediated to meet cu.n-ent FERC engineering guidelines for stability and discharge of the probable maximum flood (PMF).
The maximum flow recorded for the Catawba River at United States Geological Survey (USGS) gage number 1460 near Rock Hill, South Carolina Uust downstream of the Wylie Dam) is 15 I ,000 cubic feet per second (cfs) on May 23, 1901. The period of record for this gage is 1895 to 1903 and 1942 to the present. Two major floods not recorded by the USGS Rock Hill gage are the flood of July 191 6, with an estimated flow at Wylie Dam of299,400 cfs, and the flood of August 1940, with an estimated now of 169, I 60 cfs. The July 191 6 flood is considered the flood of record fo r the Catawba River upstream of Lake Wy
- te that USGS gage records for the
_ ~ hydropower reservoirs upstream of 1942 to present period are highly regulated through the ... .:,,_
the gage.
Original Project studies were conducted prior to the release of HMRS 1/52 using a regional hydrologic study to evaluate effects on reservoirs and spillways of PMP occurring over the entire 10
Section I Site Information Related to the Flood Hazard Catawba River basin. The following paragraphs summarize the hydrologic and hydraulic methodology employed to determine the PMF. Additional details including figures are found in Section 2.4 of the CNS UFSAR.
The greatest stom1 recorded over the Wylie drainage area occurred from July 13 to 17, 1916.
However, greater amounts of precipitation occurred regionally in Elba, Alabama; and Bonitoy and Yankeetown, Florida. It is of note that the later storms all occu1Ted immediately along the coastal area and are expected to produce diminishing amounts of precipitation by transposing these stom1s inland some 200 mi to the Wylie watershed. To arrive at the PMP over the Catawba River basin, the July 13 to 17, 1916, stom1 was selected based upon meteorological and physiographic considerations as a guide to the determination of time and area rainfall distribution pattern. The following adjustments were made to this storm to increase its magnitude and intensity to such values considered to be equal to the PMP over the Catawba River basin.
- 1. Rainfall depth-duration values were distributed m accordance with that of the 1916 storm.
- 2. Storm position was transposed over a limited distance within the Catawba River basin to produce a maximum concentration of precipitation over a selected area.
- 3. Precipitation amounts are increased 40 percent.
ln the area of the Wylie watershed, snow melt is not a consideration because of its southern location. Hourly incremental rainfall and rainfall excess for the 54-hour period of the PMP are available for inspection in the Regulatory Compliance Licensing Files as fonner FSAR Figures 2-35 and 2-36.
The topography of the Catawba River basin is gentle to moderate, sloping toward the river in a southeasterly direction. The soil designated according to the National Cooperative Soil Survey Classification of 1967 is Ultisoil U5-3. Initial loss for conditions, usually preceding major floods in humid regions, normally range from about 0.2 to 0.5 inch and is relatively small in comparison with the flood runoff volume. A value of 0.5 inch was used for initial loss in the study. Infiltration rates vary throughout the storm period from a high rate at the beginning to a relatively low and uniform rate as the precipitation continues. Model infiltration rates were 11
Section I Site Information Related lo the Flood Hazard estimated based on comparison of regional studies which were judged to be comparative to the Catawba River. The topography, soil groups, and climate of the regional basins were judged to be very similar. For the design basis study, an infiltration rate of 0.10 inch per hour was selected (SOF 1.2.2.1-03).
To obtain time dependent inflow to the Catawba River from the PMP, each reservoir's drainage area was divided into subareas depending on the number of larger tributary streams flowing into each reservoir. Synthetic unit hydrographs were used. Synthetic unit hydrograph coefficients were derived from the historic stom1 of September 29 to 30, 1958 (Hurricane Gracie) for nine tributaty streams from which gaging records were available. The lag time was reduced so that it more closely represented assumed conditions during a large flood runoff. The subdivision of any reservoir into principle subareas was necessary for the purpose of reflecting more accurately the non-uniformity and varying-intensity of rainfall over large reservoir drainage areas. Hourly precipitation amounts were distributed to existing precipitation stations by the Thiessen polygon method. The area of each polygon falling within a subarea was expressed as a percentage of the total subarea. These percentages were the rainfall-subarea coefficients assigned to each precipitation station rainfall.
The steps used to synthesize flood flow into reservoirs are summarized below:
I . The applicable portion of each rainfall station's precipitation was converted directly into inflow for that portion of the polygon covered by reservoir water surface.
- 2. The runoff (rainfall less losses) from each rainfall station was applied to the percentage which the precipitation station Thiessen polygon bounded. These values for each precipitation station are summed for each subarea, resulting in the average hourly rainfall excess for the subareas. The average hourly rainfall excess in inches is then applied to each subarea unit hydrograph, resulting in a storm hydrograph of local inflow for each subarea for each hour of runoff.
- 3. The total inflow to each reservoir consists of local inflow from each subarea of the reservoir local drainage area, plus local inflow due to reservoir surface rainfall, plus upstream flow, plus base flow.
12
Section I Site Information Related to the Flood Hazard The flood resulting from the PMP is routed through the Catawba River system to Wylie Dam by means of a flood routing program developed by C. T . Main (November 1968) (Reference 42).
Local reservoir inflow for each hour of the stom1 and for each reservoir was calculated.
Reservoir elevations were computed from reservoir inflows and with the discharges con-esponding to these elevations. The method of computing reservoir elevations and discharges used successive a roximations to satisf the relation that
- storage.
II) 3 16 U 5 C ~ C:2-.v-l a 10 ftJ 71/Fl
,.._ ____________________ ___. The discharge from the first reservoir allowing for lag time, where applicable, was added to the local inflow for the next reservoir, and the routing procedure was repeated for aJl reservoirs for each hour of the stonn plus any additional hours needed to cover the complete runoff.
I I l,b 7 F)
These initial reservoir levels were based on historical water level records for late summer and early fall. Discharges were then limited to gate capacities at given elevations and the reservoirs begin to rise if inflow continues to exceed gate capabilities. When reservoir elevations start to fall, which occurs when inflows become less than outflows, discharges are continued at the capacity of the gates until such time as the reservoirs reach their predetermined control elevations. Subsequently, the reservoir levels are held constant for the remaining period of the flood; outflow becomes equal to inflow during this period. Discharges from generation of power were assumed to continue throughout all gate operation procedures unless reservoir levels overtop bulkheads protecting powerhouses or switchyards, at which time the discharge through the powerhouse was stopped for the remainder of the stonn period. The effect of not having any power generatjon releases was also calculated.
0 eration of all flood ates is perfonned at the direction of personnel from the Duke Energy (bl(3, 16 *.1::. * ~ :1.:.40- a t (t>>l*H~ The decision to operate the floodgates is based on water elevations, rainfall, power plant operations, and weather forecasts over the entire eleven-reservoir, Duke Energy-operated Catawba River system. The spillway gates are opened as necessary to maintain the reservoirs at or close to the normal operating level. The reservoir levels are monitored 13
Section I Site Information Related to the Flood Hazard hourly. The operation of the Catawba ruver system modeled in the C.T. Main computer program is consistent w ith Duke Energy hydro operations practice (Reference 42).
(b)(3):16 U ~ C ~ 824o-1(d). (b)\4I tDJ\*/lFl (b)(3l 16 USC ~ 824o-1{d) fb)(.!J IOt'*llr:ct (b)(3) 16 IJ Sr*
§ 8240-f(dT (bl
, ,1 IL- ,,,,r, I . .
system*,esu ts,n-a-m axnnum-m ow-o
. fl Dec. _ . G e-.
Using the methodology summarized in this section, routing the PMF through the Catawba River 1s with a maximum discharge of (1.J)(,l) 16 USC
- ** * * * *****
- i:s: §8246~1(d) lb\
I. IL n11r-1 Several trial positions of the Storm Center were made to detem1ine the most critical position for producing the maximum flood over Lake Wylie. The storm center was positioned over each of the reservoir drainage areas in tum and then routed th.rough the Catawba River system into Lake Wylie. This methodology is standard practice to maximize the PMP rainfall isohyetals over the drainage to produce the most runoff impacts. T he location whic h produced the highest reservoir 1
e Ievat10n a t w y11*e Dam o f u s c § ft ms! results from 11011~116 ,J s c !I 8240-11d1 (b)(4/. ,b)tll, t l
\b)(;;,
8240-1 (Table 1.2.2- 1 td) (b (4 14
Section I Site Information Related to the Flood Hazard TABLE 1.2.2-1 The maximum reservoir elevation calculated for Lake Wylie assumes that all gates are available for operation. All of the flood gates at Wylie Dam are inspected and physically operated yearly in accordance with FERC regulation. In addition, each gate is fully opened every 5 years. These Based on the above 1scuss1on 1.2.2.2 Standby Nuclear Service Water Pond The Standby Nuclear Service Water Pond (SNSWP) is a nuclear safety-related impoundment constructed by placing a dam across a small tributary of Lake Wylie to the north of the CNS Yard. Table 1.2.2.2- 1 (SOF 1.2.2.2-0 I) provides pertinent information about the pond and dam.
15
Section I Site Information Related to the Flood Hazard TABLE 1.2.2.2-1 SNSWP D ESIGN INFORMATION The SNSWP was analyzed for a PMP centered critically over the SNSWP drainage basin using the procedure outlined in the Bureau of Reclamation publication titled, Design of Small Dams (Reference 56). Due to the small drainage area, the PMP (30. 1 inches) (SOF 1.2.2.2-02) for a 16
Section I Site Information Related to the Flood Hazard I 0-sq-mi area and a 6-hr duration was used. The 6-hr PMP was divided into an hourly temporal sequence which produced the greatest PMF for the basin. The incremental runoff values are presented in Table 1.2.2.2-2 (SOF 1.2.2.2-03).
TABLE 1.2.2.2-2 SNSWP DRAINAGE BASIN HOURLY INCREMENTAL RUNOFF Hour Runoff (inches) Inflows (cfs)
I 2.4 70 2 2.7 450 3 3.3 750 4 14.9 3650 5 4.6 2800 6 2.5 900 Detemtination of the runoff for a period of longer duration was not considered due to the size of the basin. The time of concentration, 40 minutes (SOF 1.2.2.2-04), was calculated using the hydraulic length and slope of the basin and formula Tc= (( I J.9*L3)1H)°-38 .
Figure 1.2.2.2-1 gives the PMF inflow, outflow, and water surfac.e elevation hydrographs for the SNSWP (SOF 1.2.2.2-05).
17
Section I Site Information Related to the Flood Hazard FIG URE 1.2.2.2-1 SNSWP PMF HYDROGRAPHS 0
0 I~
585
~ 5 - --5 X
vi :;
{
~
/
EL ,u;.,
-- ~-- 584-58~ er>>
~ 4 -t ...
I *
- RA !'N 5&l. ~
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ci J C) 0
- -~- ---
I
- 1 :! '
... " s:'11' .. . I I
~
,l J
'\ -- ......... ,l~
-- ~ ~- - ~
581 ~
580 ~
571 i
~ ... : :: I If-..
\ (' / I ' \
" OUl LI If H' DR* iiAj PH 2 4 578 -~
- I: ~
.., - .I i/1 ~
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577 w
~ . .u /J / \
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= I ' ......
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~ t:> ~*"' :...-* ::;..- ... _
575 0 I
- - - 574 0 1 2 3 6 7 8 9 TIME.HRS.
s (PX3) 16 USC § 824t>-ICO! [D)(~ l b){- Fl j The wave run-up was calculated using a maximum 1==-----------------1 w ind velocity of 40 miles per hour (mph) and a fetch length of 0.42 mi. The maxim um height of the wave on the slop e including the run-up is 1.0 ft The SNSWP dam is protected from wave action by riprap.
18
Section I Sile Information Related 10 lhe Flood Hazard l .2.3 Dam Failures Other small fann ponds and dams are scattered throughout the drainage basin but none were reported to have significant storage to be considered in an evaluation of impacts due to dam failures. This section addresses the consideration of a dam failure at one ofthe l(t.,iJ, ,;,, ' * "
3
~" !All the dams above Wylie are composed of part earth embankment and part concrete gravity-type structures. Table 1.2.3-1 provides a list of the upstream dams and drainage areas in sq-mi for each reservoir (SOF 1.2.3-0 I).
TABLE 1.2.3-1 DUKE ENERGY FERC LICENSED DEVELOPMENTS ON THE CATAWBA RIVER Flood design considerations for the licens ing basis at the CNS site included two dam failure scenarios.
I. A 25-year frequency flood passing through Lake Wylie combined with a seismic failure of an upstream dam.
19
Section I Site Information Rdated to the Flood Hazard
- 2. A Standard Project Flood (SPF) passing through Lake Wylie combined with the fa ilure of an upstream dam due to an Operating Basis Earthquake (OBE). The SPF is considered equal to one-half of the PMF.
The seismic fa ilure for each upstream dam was timed to coincide with the Standard Project Stonn centered over its drainage area. At the hour which the reservoir reaches its maximum level, it was assumed that seismic failure of the dam occurs. The flood routing was computed for hourly intervals by means of a flood routing program with the procedure described in UFSAR Section 2.4.3. The results of the test scenarios showing maximum reservoir elevations al each upstream reservoir are shown in Table 1.2.3-2 (SOF I .2.3-02).
TABLE 1.2.3-2 COMBINED EFFECTS SPF PLUS DAM FAILURE SIMULATJON SCENARJO RESULTS The bounding dam failure scenario for the CNS site was concluded to result from the /
I This combined effects fa ilure event resulted m a 20
Section I Site Information Related 10 the Flood Hazard maximum static water elevation o -* ft lower than the Yard elevation of 593.50 ft msl.
ls1MULATroN Assuming a l'tilt'.111 6 t ~ C § "24o-Hd) th 41 'b 7
== jDam, the normal source of cooling water for CNS is lost between elevation 569.40 and 550.00 ft msl. Elevation 550.00 ft msl is the approximate top of rock for that section of the Wyl ie Dam (SOF 1.2.3-04). If this occurs, the plant would be aligned to the SNSWP as a cooling water source. The SNSWP dam was designed to withstand rapid drawdown on the Lake Wylie slope of the dam.
Local flooding effects from a PMP centered over the SNSWP were considered in the licensing basis. However the south rim of the SNSWP is higher than the top of the SNSWP dam (crest (b)nl 1 USG
$ B24o !(a) (br --elevationD n msl) and a fa ilure o f the dam would resuh in flood -breach discharge entering
' l ,.... r Lake Wylie in lieu of the CNS Yard.
1.2.4 Storm Surge and Seiche Storm surge and seiche events were postulated to affect the site using the Probable Maximum Hurricane winds, as defined by the Weather Bureau report HUR 7-97. The description of analyses performed to address surge and seiche impacts on Yard flooding is substantially 21
Section I Site Information Related to the Flood J-la1,ard repeated from the CNS UFSAR Section 2.4.5. Surge and seiche waler levels generated by various wind mechanisms (as described in Weather Bureau Report HUR 7-97 and "Shore Protection Manual", Department of the Army Corps of Engineers, 1973) are described in Table 1.2.4- 1 (Reference 52.)
Two hurricane tracks were considered possible occurrences and were included in studies perfonned by Duke Energy to max imize the surge and wave effects at the plant site. Case A assumes a hurricane track wherein the storm center moves shoreward in a northwesterly direction, crosses the coastline near Savannah, Georgia, and then gradually re-curves toward the northeast to pass to the east or Lake Wylie. This u*ack was hypothesized to place the radius of maximum wind coincident with the effective fetch at the plant site. Case 8 is patterned after the track of Hurricane "Ginger" of the 197 1 season. This stonn follows a generally northwesterl y course from the Atlantic Ocean, and goes ashore on the North Carolina coast between Wilmington and Cape Hatteras. It then follows a westerly course to a point between Charlotte and Raleigh where it curves northeast into Virginia. This track is also modified to put the radius of maximum wind coincident with the effective fetch at the plant. The maximum wind speeds calculated were 101.5 mph for Hurricane A and 116.0 mph for Hurricane 8 . (SOF 1.2.4-0 I.)
TABLE 1.2.4-1 SURGE AND SEICHE WAVE CALCULATION RESULTS Wind Wave Total Velocity Wind Tide Height Run-up lleight1 Assumed Hurricane Path (mph) (ft) (ft) (ft) (ft)
A IOI.SO 0.33 7.40 4.00 6.60" 0.33 12.40 5.50 8, )Qb B 11 6.00 0.44 8.60 5. 10 7.70" 0.44 14.40 5.80 8.40b Note: Data above from UFSAR Secuon 2.4.5.1 1
Total Heights for Hurricanes A and B include the component due to differential pressures.
- significant wave: the average height of the one third highest waves of a given wave group.
- b. = one percent wave: the average of the highest one percent of all wa,*es in the group 1.67 times the height of the significant wave.
22
Section I Site Information Related to the Flood Hazard It should be noted that the hypothetical I -in- I 00-year flood could be passed by the Wylie Dam with no significant increase in water surface elevation (SOF 1.2.4-02). Therefore, combining surge or seiche wave height with I00-year flood elevations is not the bounding site flood causing event (combined effect flood elevation 592.2 - 569.4 = 22.8 ft>> 8.4 ft).
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. CNS is located inland (more than 150 miles from the Atlantic coast) (SOF 1.2.5-0 I) and not on a waterway that would be subject to effects of a Tsunami.
1.2.6 lee-Induced Flooding Ice-induced flooding was never postulated to affect the site, and no flood elevation is given in the original licensing/design basis case basis of the plant. The climate in the Catawba River basin is moderate (minimum monthly mean water temperature for Lake Wylie is in the low 40's)
(SOF 1.2.6-0 I) and there has not been any recorded ice formation on reservoirs in the river system.
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. The Catawba River is highly regulated by a series of dams. Reservoirs are back-to-back and backwater effects of each dam mitigate reservoir velocities that would be necessary to produce channel diversion. In the event of the loss of Lake Wylie, the Catawba Nuclear Station could be safely shut down using the SNSWP.
The SNSWP was constructed in a small tributary to the main channel of Lake Wylie and is protected from scour by topographic features and rip rap placement on dam slopes.
23
Section I Site Information Related to the Flood Hazard 1.2.8 Combined Effects Combined flooding effects ( PMP, PMF, dam failure and/or wind-driven waves) were reviewed for impacts at the CNS site. Maximum water level elevation at the station occurs with the simultaneous fai lure o lb ~ 161JSC §BUo.1 OJ {n Several stonn locations were used to
J find the highest flood level. The maximum water surface elevations when combined with a 40-mph wind are shown in Table 1.2.8-l (SOF 1.2.8-0 I).
desc<ibed in the USACE Sho,e Pmteclion Manual (1973) (Refere~ce 52 perfom1ed assuming deep water waves, a lake surface elevation o
+
Procedures used in the licensing basis evaluation for calcuJating wind set-up and waves are The calculation was (li)(3) 16 LI S C t-msl,--and-a-40-mph §8240:::1(d) (b)
. ,. . ,. , . ., . ., .~ . . .f
- L ,i fr overland wind (SOF 1.2.8-02). The run-up was calculated fo r three locations, the plant yard at the end of the intake canal, the discharge structure, and the SNS WP dam. The results presented m Table 1.2.8-1 assume a stauc water elevaUon o t msl, con-espoT ng (b)(1) 16 LIS C the SPF and ;82'6lid). (b) 1t,~3 ,r I_ $ ~ ~ (bl(3Hfi H-6 C fai lure of 82Jc-1 ~ 1 - , am, indicate there would e mmor wave run-up o - ft-aHhenorth- §"82401(d) (b)
L - r end plant yard, which is below openings for Class I structures (SOF 1.2.8-03).
24
Section I Site Information Related to the Flood Hazard TABLE 1.2.8-J COMBINED EFFECTS MAXll\ifUM RESERVOIR ELEVATION WITH WIND-DRIVEN 4o-1 ( ), (b)(4 , (b)( )(
1.3 Licensing Basis Flood-Related and Flood Protection Changes CNS staff conducted a station flood walkdown in conj unction with I0CFRS0.54 (t)
(Reference 6.) in late 2012 as documented in CNC-1 11 4.00-00-0065. (Reference 9.) A total of 18 flood protection featu res were evaluated per the guidelines in Nuclear Energy Institute (NE!)
12-07.
The report noted the following licensing basis flood-related and flood protection changes from the UFSAR as described below.
25
Section I Site Information Related to the Flood 'Hazard I. The modification (EC 108015),~o i e height of the Unit l ZD vents at the Diesel (t1)( ) 11) 1J ':, '*
§ fl24o- r(ar(b)_ _ _ _G., . eneramrl:rutlding
\. ,.,. ,..
roof (El-eva
- ft msl) was completed after the flood feature walkdown. The modified height of the ZD vents opens at Elevation 598.00 ft ms! (lA)
(IJ)(3) 16 LI SC (b)( ) us, E and J 598.04 fi ms! (1B). The openiJ ace ai lea bo~e.Jhe_Jjood .l***I of '.'"'~'~-'~ tb) 3 11
~.B-2~o~{~(b) .... ... *-2. -*~ ood b:r:::~ for the Unit I and Unit 2 ~~1 .i ft msl Electrical Penetration Room doors have been identified and placed in the orrec11ve Action Program (CAP). Other exterior designated doors with low margin are also identified in CAP and are being evaluated.
- 3. The site topographic survey is an input into the CNS PMP analysis to determine site flood levels. Any major changes to the topography are controlled by the mod ification process. The last site topography survey was in March 20 LO, and there have been no 1 16 major activities implemented since the survey was performed. : ._3
£. ! d
- 4. A potential deficiency with the Unit 2 Auxiliary Building t * , fl msl Electrical IF Penetration Room door was identified. Due to th.e recently rev1seo ponding levels described in the design basis section of this report, the water flow rate through the gap under the door will increase. The water entering through the gap under this door routes to the Unit 2 CA Pump Room. A review of the calculation for flooding of safety-related structures due to external flooding identified that this may resu lt in the water level in the CA Pump Room rising and then overflowing into the Turbine Driven CA Pump pit.
Preliminary results show that the water level in the Turbine Driven CA Pump pi1 may rise to a level that would be above the bottom of the turbine driven pump shaft.
- 5. As a conservative measure, an interim action has been incmporated to reduce the water input to the CA Pump Room from the Waste Solidification Building sump in the event of an external flooding event. The Waste Solidification Building Sump Pump discharge vaJve is normally closed. Operation of this sump pump is directed per the annunciator response procedure for a high level in this sump. This procedure has been revised to include a step to contact Operations to ensure an external flooding event is not occurring or expected prior to placing the Waste Solidification Building sump pump in service. An additional interim action has been incorporated into AP/0/ A/5500/030 (Plant Flooding) to
. . . . . . . ~ (b){3\16USC provide a bamer to reduce the water flow under the Urut 2 Auxiliary Buildmg~ )11§;s2~~2.r.~ (hl msl Electrical Penetration Room door. These actions wi ll prevent the water level in the 26
Section I Site Information Related to the Flood Hazard Turbine Driven CA Pump pit from reaching a level which would threaten the Turbine Driven CA Pump.
- 6. An ECR (engineering change request) has been created to install a flood gate (barrier) to block the Unit 2 Electrical Penetration Room door during an external flooding event.
- 7. During the procedure walkthro ugh for AP/0/A/5500/030 and RP/0/A/5000/007, it was observed that for the two Auxiliary Service Building doors (ARS and ARG) required to be closed or have the opening blocked, there is no guidance on how to manually close the doors. Also, no equipment or supplies are staged to block the door opening if the door cannot be closed. An action was entered into the CAP to add steps to the procedure for closing the doors manually. Another action was entered in CAP to have an appropriate temporary barrier available to block the door openings, if the doors cannot be closed.
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 PMP and dam failure inundation using recent aerial and ground survey data (2010) along with updated drainage, utility trench location, and building geometry. Calculation CNC-0114.00-00-0040 Rev 29 (Reference 8) documents local area changes and the impact on PMP inundation modeling. Changes to local area runofli'drainage conditions can generally be grouped by modifications within the secure area and outside of the secured area. Figure 1.4-1 (Reference #26) identifies areas where site changes have been made that could impact site drainage. The changes within the secure area include:
- The four domed storage tanks, two of which are to the south of Reactor No. 1 and two of which are to the north of Reactor No. 2.
- All surface types (asphalt, concrete, and crushed stone).
- Installed (or being installed) security shield/walls attached along the top of the buildings allow water from the roofs to drain between the security wall and face of the building.
- Diesel generator vents were raised following the completion of the 2011 site fl ood analysis.
27
Section I Site Information Related to the Flood Hazard
- Security barrier and fencing:
/t>t("J 1*> I :- - : -:2'c 1 [JJ it" I tr* -~F
- Doublewide trailers secured with hurricane strap tie downs (e.g., Craft Offices Buildings 7757, 7768, and 7769).
- The concrete pad containing portable storage container boxes and the Paint Mix Storage Building (Building 7722) east o f Lhe Craft Offices.
- Building 7767.
- The pennanent arched tent structure to the west of Building 7767 with both the east and west ends open to the Yard.
- Building 7772 (Scaffold Storage Building with no siding on th e lower 25 inches of the walls).
- A potential for flow obstruct-ion during the LIP may form during debris buildup on grating placed over the cable trench located at the southeast comer of Turbine Building No. 1 and the Standby Shutdown Facility.
JExterior Secure Area
- An 8-inch curb in Transformer Yard.
28
Section I Site Information Related to the Flood Hazard
- There are two sections of paved parking lots located generally west of the Transfom1er Yard. The eastern lot generally drains to the east/southeast (toward the Powerhouse Yard) while the western parking lot generally drains to the southwest (away from the plant site).
- Construction Yard plateau to the west/no11hwest of the vendor parking lot. Repairs included stone and riprap placement in the gully and maintenance work of the Construction Yard plateau edge to fonn an eastern-edge benn and adjoining drainage swale with spaced stone be1m s within the swale and peIJ>endicular to the plateau benn for energy dissipation.
- Fukushima Flex Construction:
- Proposed diesel pump ramp modifications to the land adjoining the SNSWP.
- Proposed building and laydown area located on the Cooling Tower Plateau and located north of the cooling towers does not appear to pose any flow path disruption to the Powerhouse Yard.
- The chlorine pre-treatment building (Building 7773a) adjoining the Low Pressure Service Water (LPSW) intake Structure (Building 7773) and the temporary trailer adjoining the intake. Both buildings show visible evidence of flow passage through/under the buildings.
- The Cooling Tower Yard berm running along the western edge of the plateau.
- Additional roof structure is being added to Building 7714 (Water Chemistry Building) that adjoins the Allison Creek-CNS Discharge.
- New Building 7752.
- Buildings 7714 and 7752.
29
Section I Site Information Related to the Flood Hazard FIGURE J.4-1 AERIAL PHOTOGRAPH OF CNS SITE IDENTIFYING AREAS OF SITE SECURJTY CHANGES OBSERVED DURING SITE WALKDOWN FOR THE FUKUSHJMA 2.1 FLOOD HAZARD REVIEW (REFERENCE 26)
(b)(3):16 U S.C § 824o-1(d) (b)(4), (b)(7)(F)
Changes in the approximately 3,020-sq-mi drainage basin have occurred since initial licens ing bas is analyses were performed. T he largest change would be in the Charlotte, North Carolina, 30
Section I Site Information Related to the Flood Hazard area and in the areas immediately surrounding the reservoirs where populations have increased.
The impacts of these changes while looking at the entire 3,020-sq-mi drainage basin are considered small percentages of the total drainage area. Section 2 hydrology summaries are based on studies perfonned in the 1990' s and consider changes in the watershed since the initial licensing basis hydrology was perfom1ed in the I 970's.
1.5 Current Licensing Basis Flood Protection and Mitigation Features Based on the CNS licensing/design basis case, a list of flood protection, mitigation, and early warning indicator features has been compiled in specification CNS 1465.00-00-0011.
Appendix A of I 0CFR50, General Design Criterion (GDC) 2 requires that nuclear power plant structures, systems, and components important to safety be designed to withstand the effects of natural phenomena such as flood, tsunami, and seiche without loss of capability to perfonn their safety function. In accordance with Regulatory Guide 1.59, Design Basis Floods for Nuclear Power Plants, Rev. 2, 8/77 (Reference 61), Nuclear Power Plants are required to be designed to prevent the loss of capability for cold shutdown and maintenance thereof resulting from the most severe flood conditions that can reasonably be predicted to occur at the site as a result of severe hydro-meteorological conditions, seismic activity, or both.
CNS has developed a list of features created to fulfill the NRC-issued infonnation request on March 12, 2012, in accordance with 10 CFR 50.54(t). Enclosure 4 of the 50.54(f) letter was directed toward addressing the NTIF Recommendation 2.3 for Flooding and requested the results of a flooding design basis walkdown. Below is a description of the different features presented in the 2.3 Flooding Walkdown report (CNC-1114.00-00-0065 Rev I).
The following are protection features that are credited in the licensing basis to protect safety-related systems, structures, and components against external sources of flooding.
31
Section I Site Information Related to the Flood Hazard Site Flood Protection and Mitigation Features:
- 1. Yard drainage and catch basins Surface water drainage is accomplished th.rough the yard drainage catch basin inlets and piping networks. Type I catch basins do not have a slotted cover, but are protected by steel grating on four sides and top to prevent blockage. The total effective opening in the grating on any one side is at least equal to the effective opening of the pipe inlet. There are 89 Type I catch basins provided in the power block area, and only 80 are required to be operable.
- 2. Sheet outflow areas The Powerhouse yard has two sheet outflow areas, one on the south side of the Powerhouse yard and one on the North east side of the powerhouse yard near the LPSW intake area. Additionally, a sheet outflow area is provided on the west side of the Switchyard.
- 3. Cooling tower protective betm The Cooling Tower Yard is at a higher elevation than the Powerhouse Yard. An earth berm on the north and west perimeter with minimum top elevation 620.50 ft ms! 1s provided to divert water away from the Powerhouse Yard area.
- 4. Switchyard protective concrete and asphalt curbs The Switchyard is at a higher elevation than the Powerhouse Yard. A concrete and asphalt curb on the north, south, and east perimeter with minimum top elevation 632.67 ft ms! diverts water from flowing onto the Powerhouse Yard area.
32
Section I Site Information Related to the Flood Hazard
- 5. Flood barriers in cable trenches between cooling tower and switchyard Flood Barriers are installed in below-grade trenches at benn and curb locations. The flood baniers stop water flow between the Cooling Tower Yard and Switchyard, and the Powerhouse Yard.
- 6. Designated pressure rated (3.00 psi) flood banier doors in the auxiliary building, auxiliary service building, exterior doghouses, UHi buildings, fuel receiving buildings, and diesel generator buildings.
For the time period during the local intense PMP when the yard inundation level is estimated to be above elevation 594.00 ft msl, designated doors are credited to remain closed to minimize water inflow. The designated doors are:
- Auxiliary Building (Electrical Pen Rooms): AX658A, AX6568
- Exterior Doghouses: ~"<661, AX660
- UHI Buildings: AX30 I A, AX300A
- Fuel Receiving Building: AX600, AX600B, AX627, AX629, AX629B
- Diesel Generator Buildings: AX302B, AX304B, AX306B, AX308B Entrances for these doors have flood barriers with top elevation 597.00 ft msl (AX302B and AX304B) and 597.13 ft msl (AX306B and AX308B) that are credited to minimize inflow.
All doors entering safety-related buildings are pressure doors (designed for 3.00 psi). All regularly used exterior doors are equipped with automatic closures, except for equipment access doors, AR6 and AR5. These doors are controlled from inside the Auxiliary Service Building, and cannot be opened from the outside. Station Security, by procedure, ensures that the Auxiliary Building and Auxiliary Service Building exterior doors are closed in the event of severe weather.
33
Section I Site Information Related to the Flood Hazard
- 7. Designated Below Grade Conduit Seals Electrical conduits in Conduit Manholes (CMH) 2, 3, 18A, 18B, and 21 are sealed to prevent water intrusion into safety-related buildings. Electrical conduits which communicate between safety-related structures and miscellaneous yard areas are sealed or enclosed to prevent water intrusion.
- 8. Trench Cover Seals Trench covers in the Refueling Water Storage Tanl< Pipe trenches and the Monitor Tanl<
Building Pipe trench. which conununicate with the Auxiliary Building area, are sealed to prevent water intrusion.
- 9. Access Hatch Seals in Diesel Generator Building Roofs Roof hatches at grade (Elevation 594.00 ft ms!) and penetration sleeves in the Diesel Generator building roofs are sealed to prevent water intrusion.
I 0. Turbine/Service Building Flood Wall A 12-ft-high concrete wall (top Elevation 577.50 ft msl) along column line 34 in the Turbine/Service Building retains water entering the Turbine/Service Building preventing water from entering safety-related areas. Estimates of water infiltration depth behind the flood wall yield a maximum elevation of 568.50 ft msl in the Turbine Building basement (Elevation 568.00 ft ms!).
- 11. Groundwater Drainage A permanent Category I groundwater drainage system is installed to maintain a normal groundwater level at or near the base of the foundation mat and basement walls, eliminating the uplift and hydrostatic forces on the Auxiliary and Reactor Buildings. The groundwater drainage system consists of foundation underdrains and continuous exterior wall drains. Testing and inspection of the ground drainage system are performed in accordance with SLC 16.7-8.
34
Section I Site Information Related to the Flood Hazard
- 12. Auxiliary building roof - sealing of penetrations Roofs of safety-related structures are designed with no obstructions so that water will flow direM roofs with minimal accumulation. The Auxiliary Building Roof at (b/(l) 16 IJ S C
~ 8240 1(d) /bT **-Elevaticmt=__J
- t msl is at ground elevation. PMP flood levels will accumulate on roof.
. '-.~
All roof penetrations should be sealed to prevent water intrusion.
35
Section 2 Flooding Hazard Reevaluation The reevaluations in Section 2.0 are not part of the CNS 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 PMP on the site, PMF on reservoirs, and dam failures that have been perfonned post-licensing basis to meet the Hierarchical Hazard Assessment (HHA) procedure described in NUREG/CR-7046 for assessment of flooding hazard at safety-related SSCs. (Reference 60)
CNS is located on the shoreline of Lake Wylie which is a FERC-regulated hydroelectric development that is impounded by a concrete gravity dam and powerhouse, gated and ogee spillway, and an embankment on the west abutment approximately 4.8 river miles downstream of CNS. As a FERC-regulated dam, the structures have been designed and verified w ith hydrologic and hydraulic analysis and dam stability analyses in accordance with "FERC Engineering Guidelines for the Evaluation of Hydropower Projects." (Reference 13) These structures are monitored and inspected on regular intervals by Duke Energy, FERC, and independent dam safety consulting engineers.
2.1 Local Intense Precipitation The flood water elevation due to a maximum PMP 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 CNS power block area resulting from the occurrence of the PMP and updated site topography and structure layout. This reevaluation utilizes HMRS l PMP and rainfall distribution patterns in accordance with guidance in NUREG/CR-7046. The modeling software selected for this evaluation generally exceeds guidance outlined in NUREG/CR-7046, 1-D channelized tlow using the USACE' s Hydrologic Engineering Center's-River Analysis System HEC-RAS software. The selected model is capable of combining both 1-D analysis methods for roof drainage simulations and more appropriate 2-D flow equations for surface flow on relatively flat CNS Yard surfaces 36
Section 2 Flooding Hazard Reevaluation
- 2. 1. l Probable Maximum Precipitation In accordance with guidelines from Section 3.2 of N RC NUREG/CR-7046, the LIP was estimated for the CNS site using point PMP. Point rainfall (l-mi2) PMP values for durations of I hour and less are detennined using the procedures as described in HMR No. 52 (Reference 45).
Since the CNS site is less than l-mi 2 , a I -hour PMP was used to evaluate the effects of local intense precipitation in the immediate vicinity of the site. This methodology is current industry practice.
Generally, for smaller drainage areas like CNS. shorter durations are critical. HMR No. 52 contains guidance to detennine PMP estimates for durations less than 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
PMP charts (HMR No. 52 Figures 24, 36, 37, and 38) were used to detem1ine PMP estimates for durations of I hour and less based on the location and size of the drainage basin. The site location was approximated on each HMR52 figure as shown in Figure 2.1. 1-1 . Using the PMP chart and the site location, the I-hour, 1-mi2 PMP estimate was detennined to be I 8.9 inches per hour (in/hr) as illustrated in Figure 2. 1.1-1 (SOF 2.1.1-01).
For areas less than 200 mi2, ratios were used to detennine the 5-, 15-, and 30-min duration PMP estimates. The ratios were found using PMP charts (HMR No. 52 Figures 36, 37, and 38).
Using the PMP charts and the site location, the ratios and PMP estimates for durations less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> were detennined as shown in Table 2.1.1-1 . The ratios were applied to the I-hour, l -mi2 PMP estimate of 18.9 in/hr (SOF 2 .1.1-02).
TABLE 2.1.1-1 PMP RATIOS AND ESTIMATES (INCHES) FOR DURATIONS LESS THAN l HOUR 1-mi2 Point Rainfall 5-min 15-min 30-min 1-hr PMP (in.) 6.2 9.7 14.0 18.9 Ratio to 1-/ir PMP 0.326 0.512 0. 740 -
37
Section 2 Flooding Hazard Reevaluation FIGURE 2.1.1-1 TYPICAL EXAMPLE OF HMR NO. 52 FIGURE USED IN THE PMP ANALYSIS
- 67' I
.f -
T 29' l 17.0
.l 103° 1
l'igure 24.-1-br l-c 2 BtP aoalysia ..... ...a
....... -- figure 23 aod 6-br 10-.S.
prec1p1t'at10D fToa llt'R No, Sl, The PMP was evaluated based on a front-end loaded, I-hour maximum temporal distribution.
The PMP duration was chosen based on guidance provided in NRC NUREG/CR-7046, Section 2.4.3 (Reference 60). The front-end loading temporal distribution applies the most intense rainfall at the beginning of the storm and decreases in intensity over time as shown in Table 2.1.1-2 and Figure 2.1. 1-2 (SOF 2. 1. 1-03).
38
Section 2 Flooding Hazard Reevaluation TABLE 2.1.1-2 5-MINUTE INCREMENTAL CNS PMP Incremental Time Precipitation (minutes)
(inches) 0 0 5 6.16 10 1.82 15 l.69 20 1.57 25 1.44 30 1.30 35 l.l I 40 0.92 45 0.78 50 0.72 55 0.70 60 0.68 Total 18.9 39
Section 2 Flooding Hazard Reevaluation FIGURE 2.1.1-2 CNS PMP HYETOGRAPH 6.5 6.0 5.5 50 4.5 Cl
- 5 4.0 C
~
- a. 3 5 Cl 0
C:
2 3.0
~
Q,
~ 2.5 0.
2.0 1.5 10 05 0.0 5 10 15 20 25 30 35 40 45 so 55 60 n me (mint ues) 40
Section 2 Flooding Hazard Reevaluation
- 2. 1.2 Site PMP Model Setup lnnovyze Infoworks ICM (Integrated Catchment Model), Version 3.0 software 2012 (ICM)
(Reference 35) was used to evaluate the effects of the point PMP at CNS. ICM is a full y integrated I-Dimensional (1-0) and 2-Dimensional (2-0) hydrodynamic model which allows for a more appropriate hydraulic simulation (vs. a channelized 1-D approximation model) of the relatively flat topography found on the CNS site. 1-0 model simulation options are used to model runoff from building roofs, while 2-D simulation is used to model overland site hydraulics enabling the hydraulics and hydrology to be incorporated into a single model.
Overland flow for the entire CNS site including the SNS WP and Yard is modeled with ICM's 2-0 surface floo ding module. This portion of the modeling extent is known as the 2-D Zone. The buildings within the 2-D Zone and their associated hydraulic features are modeled as 1-0 sub-catchments that connect and link to the 2-D Zone using the weir and sluice gate model options to simulate roof drainage from edges/parapet walls and scuppers, respectively. Roof drains (flat roofs) were conservatively assumed 100 percent blocked during the simulation to route additional water to the yard ground surfaces. Blocking roof drains allow more water to spill over the roof edge or scuppers adding more water to the ground surface.
The required 2-D model mesh Digital Ten-ain Model (DTM), Figure 2.1.2-1, was developed using CNS site-specific aerial photography and LiDAR survey data dated 201 0. (References 46 and 47) This survey was also used to determine the location and footprint dimensions of buildings and permanent features (i.e., security barriers) in the yard. Building drainage (e.g.,
parapet elevations, scuppers, etc.) for all buildings within the security perimeter of CNS was developed using engineering drawings provided by Duke Energy. Site conditions were observed by the modeling team through conducting a CNS Yard walkdown which was documented by report dated November 2013 (Reference 26).
Model boundary conditions were assigned to locations that would not impact flow calculations in areas of the CNS Yard near critical equipment and buildings. This was accomplished by reviewing the site topography and the 2-0 Zone extents which were chosen by the modeler to 41
Section 2 Flooding Hazard Reevaluation end on or near the watershed delineation features surrounding the s ite, Figures 2.1.2-1 and 2. 1.2-2.
All buildings within the 2-0 Zone, including but not limited to the reactor, auxiliary, and turbine buildings, were created as 1-0 sub-catchments and modeled using the Storm Water Management Model (SWMM) rainfall-runoff and routing simulation options within ICM. Each roof section was modeled as a conceptual volume defined by an elevation-area relationship. The roof surfaces use a Curve Number (CN) of 98. SWMM runoff routing values (Manning's n values) were selected based on roof material types. Roughness values for each material type are provided in Table 2.1.2- 1 (SOF 2. 1.2-0 I).
42
Section 2 Flooding Hazard Reevaluation FIGURE 2.1.2-1 CNS DIGIT AL TERRAIN MODEL 3-DIMENSIONAL PERSPECTIVE LOOKING ORTH NO BUILDINGS SHOWN 43
Section 2 Flooding Hazard Reevaluation FIGURE 2.1.2-2 CNS DIGITAL TERRAIN MODEL EXTENTS SHOWN BY RED LINE Catawba Nuclear Station: 20 Model Extent Calculation CNS-194292-009 (LIP and LIP 2-0 Model Results) lnfoworks ICM: Base Case Hydrology: LIP 44
Section 2 Flooding Hazard Reevaluation TABLE 2.1.2-1 ROOF RUNOFF ROUTING VALVES Surface Material Manning's II value Steel 0.01 I Asphalt 0.030 Concrete 0.016 Tent 0.010 Overflow of the roof gutter or parapet system was accounted for by use of a conceptual weir that discharges to a location based on assigned flow paths (e.g., discharges onto ground or another root). All conceptual weirs were modeled with a discharge coefficient of approximately 2.6 (ICM model input of 1.43 in metric), a typical minimum discharge coefficient for broad crested weirs per the United States Department of The Interiors Geological Survey C ircular 397, Discharge Characteristics of Broad-Crested Weirs (Reference 57), and a modular limit of 0.9.
These locations are directly applied to the 2-D Zone, at downspout locations where appropriate, or other roof sections depending on roof geometry. Figure 2. 1.2-3 shows the ICM model building roof connectivity, including 1-D sub-catchment connections (i.e., weirs) and sluice gates (i.e., scuppers) (SOF 2. 1.2-02).
45
Section 2 Flooding l lazard Reevaluation FIGURE 2.1.2-3 CNS DIGITAL TERRAIN ROOF DRAINAGE CONNECTIVITY Catawba Nuclear Station: Complete ICM Model Connectivity Calculation CNS-194292-009 (LIP and LIP 2-0 Model Results) lnfoworks ICM: Base Case Hydrology: LIP Note: Building IDs were not added to this figure to preserve clarity of the roof connectivity links.
46
Section 2 Flooding Hazard Reevaluation Overland flow surface roughnesses for the 2-D Zone were classified as grass, gravel, riprap, or concrete/asphalt. Table 2.1.2-2 provides the associated Manning's II values used for each roughness zone (SOF 2. 1.2-03). Figure 2. 1.2-4 shows the model boundaries of each roughness zone (SOF 2 .1.2-04).
TABLE 2.1.2-2 ROUGHNESS ZONE MANNING'S n VALUES Surface Material Manning's II value Grass 0.030 Gravel 0.023 Rip Rap 0.036 Concrete/Asphalt 0.013 Trees 0.100 Shrubs 0.070 All areas in the 2-D model mesh, including contributing watersheds outside of the main CNS Yard, assume I 00% nmoff maximizing the inundation of the site for the LIP reevaluation of flood hazard potential following guidance in NUREG/CR 7046.
47
Section 1 Floodan,g 1'bz.ard Rec\alu.,11on FIGURE 2.1.24 CNS IC~I MODEL YARD ROUGHNESS ZONE BOUNDARIES C.1:IWt>a NucMat station:- RougMea Zones OYW 20 Mod.el &ant Calculation CN&.1M~.Q09 (UP .aftd LIP1.0 Mmtal RMll.b)
Inf-ICM. BKeCne Hydrology: LIP 48
Section 2 Flooding Hazard Reevaluation 2.1.3 Security Ban-ier Model Features Changes to the local site topography and support buildings have taken place since original construction and have been captured in calculation CNC-1114.00-00-0040 Rev 29 (Reference 8).
Changes to local area runoffi'drainage conditions can generally be grouped by modifications within the secure area and outside of the secured area. Figure I .4-\ (Section \.4) identifies site landscape/structure change areas that have been added to the ICM-site model.
,.____ __. During the PMP event, these security barriers act to redirect surface flow patterns.
They are modeled as permanent porous polygons with a porosity of O percent (i.e., fully obstructed) that raise the ground elevation 2.66 feet (32 inches),
provided by Duke Energy and visual observations made during HDR' s October 8, 2013, Fukushima NTTF 2.1: Catawba Nuclear Station Flood Hazard Reevaluation Sire Walkdown in Support of 2-D Terrain Model (Reference 26). Figure 2. 1.3-1 shows the location of the modeled security batTiers.
ro J) t6 1J s c § ~2.!o-1 di (b 4) ., i71(f
\ Th.is security barrier was observed to be comprised!
o 31 16 1J s C .§ :l2~o-1 di ('0)(41 ['ti 7) FJ i_,__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___, I The sections comprised of the fencing were modeled at a height of 7 feet and a calculated porosity of 82 percent (i.e., 18% of the cross-sectional area blocked by a 17-gauge cyclone fence and steel grating). The gate sections were modeled at a height of 3.66-feet (44 inches) and a porosity of O percent (i.e., fully obstructed). Due to the difficulty in estimating the percent blockage of the fencing security batTier, a sensitivity analysis was performed on the porosity of the fenced security barrier during 49
Section 2 Flooding Hazard Reevaluation the LIP event. This analysis assumed twice the cross-sectional area was blocked by the cyclone fencing and steel grate material resulting in a porosity of 64 percent (i.e., 36 percent blocked).
This sensitivity analysis indicated that the modeled peak water surface elevation and general flow paths are not significantly affected by realistic but conservative changes to the porosity.
For this reason, the calculated porosity of 82 percent was utilized in the final model setup. (SOF
- 2. 1.3-0 I) Figure 2.1.3- 1 shows the location of the modeled northern security batTier and is identified as Vehicle baiTier-fence" in the figure legend.
In addition to the user inputs outlined above, the breaklines utilized in the DTM development were applied and the building polygons within the 2-D Zone were modeled as voids when creating the mesh. The resulting mesh contains 297,977 triangles and 136,634 elements. The approximate minimum, maximum, and average element areas are 1 ft:\ 1,371.8 ft\ and 194.9 ft2, respectively.
50
Section 2 Flooding I lazard Reevaluation FIGURE 2.1.3-1 CNS ICM MODELED SECURITY BARRIERS (b)(3):16 U.S.C. § 8240-1 (d), (b)(4), (b)(7)(F) 51
Section 2 Flooding Hazard Reevaluation 2.1.4 CNS ICM Model Results The evaluation of potential flooding on the CNS site was performed by applying the point PMP to the ICM model as 5-minute interval rainfall intensities (in/hr) as shown in Section 2.1.1, Figure 2. 1.1 -4. This rainfall profile was applied to both the 2-D Zone and the 1-D sub-catchments (roofs). The ICM model was used to create a 6-hour simulation to evaluate the PMP maximum flooding effects within the CNS Yard and SNSWP under existing modeled site characteristics. PMP mnoff to the SNSWP and responding storage in the pond was conservatively modeled assuming no outflow from the existing pipe outlet spillway.
Results of the LIP modeling for inundation locations and levels are shown in figures included in Appendix B of calculation CNS-294292-009, Rev. 0. (Reference 16). The model output included in Reference 16 includes figures related to the location of the site, development of the PMP, flow patterns and the LIP maximum flood depths and elevations in the CNS Yard with no Yard catch basin and roof drains active. Runoff from the roofs of building was directly added to the 2-D mesh as noted in Section 2.1.2. Flood inundation level versus time hydrographs in Reference 16 show residual water remaining at the model output node points beyond the initial falling limb of the hydrograph and extending to hour 6 of the LIP simulation . The remaining water shown at these nodes is the result of the relatively flat CNS Yard surface and the non-active catch basins. This is expected as CNS Yard catch basins are typically the lowest elevation points in the CNS Yard by design and surrounding areas are sloped to drain to these points. The catch basin blockage is a conservative modeling assumption recommended by guidance provided in NRC NUREG/CR 7046 (Reference 60). It should be noted that higher maximum water surface elevations characteristically correspond to higher ground surface elevations and not necessarily a greater depth of water.
The effects of the LIP result in variable water surface elevations modeled across the entire CNS Yard. Three primary locations have been identified for reporting typical summary results:
52
Section 2 Flooding Hazard Reevaluation I. the perimeter around the main complex buildings and the diesel generator area, A representative maximum water surface elevation level in the CNS Yard around the main complex (i.e., Auxiliary, Reactor, and Turbine Buildings) ranges from approximately 594.9 ft msl to 595.6 ft ms!. (SOF 2.1.4-01) Previous ly, the maximum water surface elevation levels in the North (Unit #2) and South Yard (Unit # 1) po1tions of the CNS Yard were 595.9 ft msl and 594.9 ft msl (Reference 8), respectively. A representative maximum water surface elevation level in the CNS Yard around Diesel Generator Building Unit # I and Unit #2 are approximately 594.9 ft msl and 595.5 ft msl, respectively (SOF 2. 1.4-02). Previously, the maximum water surface elevation levels for Diesel Generator Building Unit # I and Unit #2 were 594.9 ft msl and 595.9 ft msl (Reference 8), respectively.
- 2. the Cask Storage area in the northern portion of the CNS Yard A representative average maximum water surface elevation level of flow in the CNS Yard around the Cask Storage area is approximately 602. 1 ft ms!. (SOF 2.1.4-03)
- 3. the SNSWP A representative maximum water surface elevation level for the SNWSP
- is approximately 583.0 ft ms! (SOF 2. 1.4-04). Previously, the maximum SNSWP elevation was determined to be 583.S ft msl (Reference 8).
ICM model results for the UP indicate that the protective berms/curbs around the switchyard and cooling tower sub-areas are overtopped and a portion of the sub-basin runoff does contribute to flooding on the CNS Yard. It should be noted that previous analyses indicated that the protective bemllcurb in the switchyard and cooling tower areas were not overtopped.
Twenty-one (2 1) result nodes defining CNS Yard areas of interest are presented in Figure 2. 1.4- l and Table 2. 1.4-1. Figure 2.1.4-2 shows the location of twenty-two (22) safety building doors 53
Section 2 Flooding Hazard Reevaluation related to SSCs result nodes and Table 2.1.4-2 provides the peak depth, elevation, and maximum velocity modeled at the nodes during the 6-hour simulation. Additionally, both tables provide the North Carolina State Plane NAD83 Coordinate System Northing and Easting in US survey feet along with a brief description of the location and the duration of inundation (SOF 2. 1.4-05).
Inundation durations were approximated for each location assuming a flood arrival time defined by a flood depth of O. l ft. The end of inundation was determined when the flood depth was within 0.1 ft of the end of simulation depth (e.g., if the depth at the end of the simulation is 0.1 ft the inundation is a_ssumed to end of the time when flood depths fall below 0.2 ft). This provides a consistent method of inundation duration calculation between all locations.
For comparison, Table 2.1.4- 1 includes peak LIP design basis 1-0 water surface elevations from calculation CNC-1114.00-00-0040 Rev 29. Due to the limits of the 1-D model used in the design basis analysis, a node-by-node comparison is not possible and some locations lack suitable infom1ation for comparison. Maximum ICM LIP model inundation elevations in the CNS Yard area are shown in Figure 2.1.4-3. Areas outside the CNS Yard area have been clipped from this figure as they are at higher ground elevations than covered by the color scale used in the figure and do not impact SSCs identified in the 2.3 Walkdown report (Reference 9). Water surface elevation and depth hydrographs as well as velocity hydrographs at each node location for the LIP simulation are provided in CNS-194292-009, Rev 0. (Reference 16).
54
Sec11c,.n .2 Floodmg 11:izard RC<\aluo11on FIGURE 2.1.4-1 CNS IC\1 MODEL PM P RESULT ODE LOCATIONS Catawba Nuclear Station: 20 Result Node Locations Calculation CNS-194292-009 (LIP and LIP 2-0 Model Results) lnfoworks ICM: Base Case Hydrology: LIP 55
Flooding Hazard Rffi*1luat1on FIGURE 2. 1.4-2 CNS ICM MODEL PMP RESULT NODE LOCATIONS AT DOORS TO BUILDINGS WITH IDENTIFIEDSSCs (b)(3):16 U.S.C. § 8240-1 (d), (b)(4), (b)(7)(F) 56
Sccuon 2 Hooding Haurd Rc-e\'ilUdllOn FIGURE 2.1.4-3 CNS ICM MODEL LIP RESULT MAXIMU'\1 WATER ELEVATIONS AROUND T II E MA IN POWER BLOCK STRUCruRES C . - Nuclear Station: Maxim""' Wale, Surfau Elevabon Main Compln C.lculatlon CNS.19'292.cot ILIP and LIP 2.0 Model RHUl11) lnfoworks tcM: Base Can Hydrology* LIP Nole tl1a1 areas 0111Side lhe CNS Yard anea have been clipped fonn this figure for purposes of prcsen1a1ion of color levels.
57
Section.! Flooding H.az.lrd Recvaluauon TABLE 2.1.4-1 CNS ICM MODEL LIP RESULT NODES 1\ta,.imum Maximum Eltv::.tion~ ~l 3ximum Velocity, lnuntfotion Duration, Design Basis l\1a:Umum \\'ater Nod< 0..cription Northior; Eosting 1 Depth, ft f t msl ft per second Hrs:min Surface Ele,*a:rion. ft mls I SNSWPond 482984.:!3 1380827.67 9.1 583.0 2.5 1:35 583 5 2 Cask Storage Pad I 481583.85 1380801.9.l 0.3 60:!. I 07 0.40 NA 3 Cask Storage Pad 2 481510.18 t:\80789.01 0 .3 602.0 0 .8 0.50 NA 4 Turbine Building Unit #2
- Sourhw!!SI Comer 480254.85 1380198.79 I.S 505.6 09 3:50 595 9 5 Turbine Buildin~ Unit 111
- Northwe,1 Comer 480493.57 1380204.65 1.S 595.6 1.3 4*20 595.9 6 Turbine Building Unit #2
- Nonheast Com<r ~80486.25 1380603.01 1.7 595.5 I.I 4*00 595.9 7 Turbine Building Unit #2
- Southeast Comer 480247. 16 1380618.02 2.l 595.5 02 4.3S 595 .9 8 Diesel Generator Building Unit #2 48050S.66 1380694.1S 1.3 595.S 0.5 1:45 595.9 9 Reactor Building Unit #1 480442.68 1380739.21 1.9 5954 05 5.US 595.9 10 Au.*uliary Build.in~* North Comer 480336.13 1381 037.15 14 595.3 I.I 2:35 595.9 II Auxiliary Building 480160 38 1381065 81 1.8 595.2 1.9 3:30 5<l4.<l- 595.9 12 Au,ihary Bmlding
- South Comer 479998.55 1381031.76 1.5 595.l 1.6 J :~O 594.9 13 Reactor Build111g Unit # I 479907.01 1380730 06 12 594.9 03 .l:55 594.9 14 Diesel Generator Building Unit # I 479846.60 1380680.27 0.9 594.9 O.J 1:40 594 9 15 Turbine Building Unit Iii* Nonheast Comer 480107.66 1380615.09 1.4 594.9 0.0 2:20 594.9 16 Turbine Building Unit # I* Southeast Comer 479872.13 1380588.00 I.I 594.9 1.1 2.15 594.9 17 Turbine Building Unit # I . Southwesc Comer 479880 6 S 1380194. 76 2. 1 505.4 2.6 3.25 594.9 18 Turbine Building Unit# I
- Northwest Ct,mer 4801 I0.96 1380196.96 1.8 595.5 00 4:20 594.9 19 Sw11chyatd 4802S3 SO 1379222.00 0.7 632.8 0 .5 4:35 NA 20 WC Pond Berm 479254.00 1381117.10 0.6 620.6 0.7 .1 :15 NA 21 Cooling Tower Semi 479726.00 1381156.10 0.4 610.7 2.~ I.SO NA Notes:
1 Reference fib"'" 2. I .4-1 for yard node locations.
'faisting CNS design basis m:i.,inmm woter elevations are from CNC-1114.00-00-0040 Rev 29.
58
Se,ciion .:! Flooding ~ d Rccvalu:,tion TABLE 2. 1.4-2 CNS ICM MODEL LIP R ESULT LOCATIONS AT DOORS TO BUILDINGS WITH JDEJ'l,'TIFIED SSCs NODES l\1;aximum 1\1.aximum £te,r:ation, Maximum Velocity, Inundation Dur:ition . Design B:isis Maximum \Vater Door No. Bldg. Destin:ation D,suiplioo Northine Easting Depth , fl ft ms l ft per sttond Hrs:min Surface Elevation, fl mis:
AX300A U2UHI Sump8 54Jt0 Common Area !Room 214) 1380796.997 480449.787 1.9 595.4 07 5:15 595.9 AX30 18 UI UHi Sump A 543t-O CNnmon Arc* (Roon, 216) 1380786.9 479904.6 1.2 594.9 I.I 4:00 594.9 AX660 U2 Ext DH SumpC U2 CA Pump Rm tRoom 260) 1380 739 157 480437.66 I9 595.4 0.5 5:05 595.9 AX661 U I Est DH SumpD UI CA Pump Rm tRoom 150) 13S07J0.97 479912.27 I.I 59H 0.3 2:15 594 .9 AX6568 U2 El Pen Rm SumpC Ul CA Pump Rm I Room 160) 1380659.<>97 480346 on 1.9 595.5 0.4 3:55 595 .9 AX658A UI El Pen Mr. Sump D Ul CA Puonp Rm (Room 250) 1380651.8 480007.3 1.0 594 9 04 2:00 594.9 A X600 UI FB FDT 54Jt0 Common Area (Room 255) 1381012.77 480005.45 1.6 595.3 0.3 3*05 594.9 AX627 U2FB FDT 543t 0 Common Area (Room 255) 1381008.6 ~8026'1.7 0.9 595.2 1.3 1:30 59 5.9 AX629 U2FB FDT 54Jt 0 Common Arca (Room 2 55 ) 1381 020.2 480.l33.5 2.0 595.:' 0.4 :uo 595.9 AX600B U IFB FDT 54Jt 0 Common Area (Roon, 255J 1380987 .7 479986.4 1.3 595.3 0. 1 2:05 594.9 AX6298 U2FB FDT 543-tQ Common Ar** 1Roon1 255 ) 1381 0023 480352 9 0.8 595. 1 0.9 1-25 59 5.9 AX664D AS8 FDT 543t0 Common Arta ( Room 255) 1381032.1 480091.9 1.3 595 .J 0.5 1:55 594,9- 595.9 AX605D ASB FDT 543+0 Common Area (Room 2 55 ) 1381032 .2 48010 1.3 I5 595.2 0.2 5:00 594.9- 595.9 AX6 17 ASB FDT 543+0 Common Area (Room 255) 1381024 .3 480207.5 LS 595.2 0.2 5:00 594.9- 595.9 AX671 ASB FDT 543+0 CCHnmon Arca (Room 255 ) 1381 036 .3 48021 5.0 1.4 595.J 0.2 2:30 594.9- 595.9 AX666A AS8 FDT 54.l+O Common Area (Room 2 55) 1381 0 17.2 480265.2 !.9 595 3 0.3 :us 594.9- 595,9 AR5 ASB FDT 543+0 C<Hnmon Arca I Roon, 2 55) 1381 024 .4 4801 98.9 1.6 595.3 0.3 3:05 594.9- 595.9 AR6 ASB FDT 543+0 Common Area ( Room 2 55 ) 1381 0 15 4801 19.0 1.6 595 2 0.0 4 :10 594.9- 595.9 AX3028 DIG IA DIG Sump I A DIG Room (Room 302i 1380724.154 479799,405 I7 594 ,9 1.2 3:30 594,9 AX304B DIG 18 DIG Sump I B DIG Roo m IR,,om 304) 1380630.07 47980 1.22 :!3 594.9 0.5 4 :35 594 .9 AX306B DiG2A DIG Sump lA DIG Room ! Room 306) 1380751.4 48051 7.6 2.1 595 4 0,8 3:35 595.9 AX308B DIG28 DIG Swnp 28 DIG Room 1Room 308) 1380633.6 480519.62 2.0 595.5 0.6 4 :25 595.9 Notes:
' Re ference Figure 2 1.4-2 for door node locolions.
' Existing CNS design basis maximum water tle\'ations are from CNC-1114.00-00-0040 Rev 29 59
Section 2 Flooding Hazard Reevaluation 2.2 Flooding in Reservoirs T he Duke Energy dams and reservoirs on the Catawba River are regulated by the FERC under Catawba-Wateree FERC Project No. 2232 and are maintafoed to standards required by 18 CFR Subpart 12. The flood standard imposed by the FERC on the Duke Energy dams is the PMF.
T he NRC requires the estimation of the design-basis flood that would cause adverse effects to the CNS site. By NRC definition, ..a design-basis flood is a nood caused b y one or an appropriate combination of several hydrometeorologjcal, geoseimic, or structural-failure phenomena, which results in the most severe hazards to SSCs important to the safety of a nuclear power plant. The CNS site adjoins Lake Wylie which is formed by the Catawba River and Duke Energy' s Wylie Dam. As shown in Figure 2.2-1 , the)
L 3 t '-' S G § 82 lo- IU O !* 0 '1 i=
L,..-_ _ _ _ _ _... IT he hydrometeorologicaJ flood standard imposed on the CNS s ite is the PMf associated with one or the Duke Energy dams/reservoirs adjoining or located upstream of the CNS site.
60
Section 2 Flooding Hazard Reev3'u:moa FIGURE 2.2-1 OVER\'lEW (b)(3):16 U .S.C. § 8240-1 (d), (b)(4). (b)(7)(F) 61
Section 2 Flooding Hazard Reevaluation 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 fu rther hydrologic analysis shall be required." There are All are licensed y L,..,....._ _ _ _.....,..-
a-re_m
_ a.,...
in"".'ta~i,...n-ed-;--:-in_ a_cc_o_r-:
d-an_c_e_w it;-
h-::F:--;E:::-;R::-:C
- -g---
- -
uid-;-e-;-h:-
.n-e-s.-::D:---
am-specifie PM P and PMF documentation was reviewed, demonstrating that each of the dams can safely pass the FERC-approved PMF. A description of the upstream dams, including FERC Exhibit F drawings showing layout and sections of dam structures, is provided in Appendix 0 .
The Duke Energy Catawba-Wateree Developments underwent a PMF evaluation in I992 (References 28 through 34) to determine each dam and reservo ir hydrologic (PMP) and hydraulic (PMF) performance to maintain compliance with FERC regulations. Law Environmental Inc., Kennesaw, Georgia, developed PMF evaluations (Reference 37) for the Catawba-Wateree FERC projects using the USACE HEC-1 software to develop rainfall-runoff hydrographs from the sub-basins that comprise the Catawba River basin. The National Weather Service's DAMBRK model was used to route the PMF flood waters through the respective Developments. The Catawba River PMP values for the respective Duke Energy Developments are based on Hydrometeorological Reports 51/52 and use elliptical-shaped isohyetal patterns to maximize the PMP rainfall over a given Catawba-Wateree development' s basin. The hydrologic and hydraulic analysis for the FERC C.atawba-Wateree developments was the basis for the CNS-
- 2. 1 Fukushima Study for flooding from reservoirs. The FERC-approved Catawba-Wateree Legacy HEC-1 model (Reference 37) was adapted to develop the 2013 Fukushima 2.1 PMF inflow hydrographs for the various Catawba-Wateree Developments. The 201 3 Fukushima 2.1 PMF is based on a 2 I6-hour rainfall event comprised of three 72-hour precipitation sub-events including the 40 percent PMP, 0-rainfall, and the HMR5 l PMP.
The Legacy HEC- 1 model was used to develop two sets of inflow hydrographs (2 16-hour event) for Cowans Ford Dam and Wylie Dam consistent with the respective sub-basins designated for each Development during the 1992 and 1998 FERC PMF studies (References 37, 38, 39, and 62
Section 2 Flooding Hazard Reevaluation 12). The 22 sub-basins that compJisc the Wylie Dam drainage basin arc shown in Figure 2.2-2 and 2.2-3.
FIGURE 2.2-2 WYLIE DEVELOPMENT HYDROLOGIC SUB-BASIN FROM 1992 FERC PMF STUDY T
63
Section 2 Flooding Hazard Reevaluation FIGURE 2.2-3 CATAWBA-WATEREE BASlN INCLUDING SUB-BASIN DELINEATION AND DESIGNATED SUB-BASIN NUMBER. THE CNS 2.1 FUKUSHIMA STUDY IS LIMITED TO TWENTY TWO SUB-BASINS, NUMBERS 0-21 64
Section 2 flooding Hazard Reevaluation T able 2.2- 1 provides a list of the s ub-basins associated with each of the respective Duke Energy dams.
TABLE2.2-1 CATAWBA-WATEREE PMF ANALYSIS SUB-BASINS (b1(3l 16 U.S C § 82.!o-1\0I fb 4 1. bJ - Fi 65
Section 2 Flooding Hazard Reevaluation The 1992 Catawba-Wateree DAMBRK PMF routing model used 93 cross sections to describe (b)i3) I6U S 1_
§ B241) I1t11 i~*t (41 (t>H7)IFI in- F-igure--2.2~1-,- including- lhe D
the 225-mile profile length and reservoir geometry of the Catawba-Wateree River system shown reservoirs. For the Fukushima 2.1 reservoir fl ooding evaluation, the DAMBRK routing model was replaced to provide current state-of-practice software using the USACE, Hydrologic Engineering Center - River Analysis System (HEC-RAS) version 4.1. HEC-RAS was incorporated for its options of a Geographic lnfo1mation Systems (GIS) inte1face. multiple river branch/tributary interface, dam spillway and breaching options, interactive user interface and greater cross-section detail than the previous one-branch DAMBRK model capabilities. The hydraulic model was identified as Catawba River System HEC-RAS Model (Catawba River Model). The Catawba River Model incorporates the area
,..., 1t ~ 7" 1 bounded by the headwaters of j ,;
through the Catawba River tailrace -~ _ Dam, including significant tributaries lo the Catawba River/Duke Energy Development reservoirs. The main stem Catawba River Model length is approximately 165 miles. The 20 13 Catawba River Model accounts for significant G
jOl(3)it)IJ"-f' tdbutaries off the main stem of the Catawba River and within th spective-f)ukeEnergy §8~~"'* 11 Ll1 (b)
,4) m,,7)1n Development reservoirs. The respective rese.rvoir-tributary reaches and their geo-referenced cross sections are used to account for reservoir volume in the HEC-RAS model. The 2013 Catawba River Model identified 47 main stem and tributary reaches that required lateral/direct inflow hydrographs versus the 22 main stem tributary sub-basins employed in the HEC-1 model and 16 lateral inflows in the DAMBRK model. The additional lateral and direct inflow hydrographs for the 20l3 HEC-RAS model were developed by applying a drainage area weighting method to distribute the inflow between the original HEC- I inflow hydrographs and the additional lateral/direct inflow hydrographs in the 2013 HEC-RAS model.
Verification of Catawba River Model was previously conducted during development work for supporting FERC-required analyses (Reference 37, 1992 Law Engineering Catawba-Wateree PMF Study). The l 992 model verification was based on using available rainfall and runoff data from across the entire 4,750-square-mile drainage basin (Lake James to Waterce). Review of the storms used for J 992 model calibration and verification indicated they were generally moderate to low in return frequency; therefore, the storms selected for the Fukushima 2 .1 HHR HEC-RAS analysis model verification were based on the l argest stOITilS of record available.
66
Section 2 Flooding Hazard Reevaluation The FERC-approved Catawba-Wateree PMF model hydrology was based on development of synthetic unit hydrographs for each of the 22 sub-basins, numbered Oto 21, shown in Table 2.2-1 (Reference 18). To respond to guidelines presented in NUREG/CR-7046 addressing application of linear unit hydrograph theory in PMF analysis, the largest historic floods of record for the Catawba River were used to test the models ability to simulate historic flood elevations along the 3 6 5 3240 101 4 upper segments of the Catawba R.ive~*b
- c § *1 b> *:J i:: ~ he Catawba River Model (HEC-1 and HEC-RAS) was used to verify the ability of the model unit hydrographs and routing paramete rs (cross sections and roughness) to reproduce historic flood levels of record.
Floods of record for 191 6 and 1940 that occurred over the drainage basin represented in Figure 2.2-2 were reconstructed from historic precipitation and runoff records (SOF-2.2-0 I). The 1916 and 1940 events were not used in the 1992 Catawba-Wateree PMP/PMF Study (Reference 37) development of the synthetic regional unit hydrograph; therefore, they were judged to be a valid verification record for the hydro logic and hydraulic river model. The July 19 16 hunicane precipitation event is identified as the " Flood of Record for the Catawba River. The Duke Energy hydro dams in existence at that tim e and within the 2 .1 Fukushima Study areas are Ill<, F Dam experienced a peak discharge of 19 16 event representing 66 percent of the 1.992
§ 824o-1(dr(6) ...... (b)(4l (ba('),F) cfs (Reference 3 1). The August 1940 event is described as the largest flood of record for th
_l 6_
(b-)(-.3>_1_ _s_..:._§_e_2_
.:0_-*- d- l
_ _ _ _ _ _ _ _ _ _ _ _ The August 1940 rainfall over the
- o_,_,. _ r: _,_ ~
upper third of the Catawba River basin varied between l 00-year and 400-year return periods
( Reference 27).
1b1 \lblJSG '§t!Z o 1 The Catawba River sub-basin precipitation comparison between the ta to1\4} IOlt7J(F} uly 19 16, and August 1940 events are shown in Table 2.2-2.
67
Section 2 Flooding Hazard Reevaluation TABLE 2.2-2 MODEL VERIFICATION SUB-BASIN PRECIPITATION COMPARISON (b)(3):16 U.S.C. § 824o-1(d), (b)(4), (b)(?)(F)
The basin average rainfall for the three events shown in Table 2.2-2 are:
- Cowans Ford PMP (FERC-1992) - 33.25 inches
- July 1916 - 19.94 inches, or 60 percent of the Cowans Ford PMP 68
Section 2 Flooding Hazard Reevaluation
- August 1940 - 13. 17 inches, or 39.6 percent of the Cowans Ford PMP.
,,,..,.,~;:;::;::;:;::::;::;;::::::::::::::::::=~~ Dam experienced anj' :s, 16 u !o \; § bl'41.J-t a, 10 41
'°11 "F
!~~~1;~ ~~~~~ (, ~ ~,Ao-. 0 10
!and the Catawba River Model was modified to reflect physical site parameters (embankment and spillway crest elevation) al the time of the event. Catawba River Model verification results are presented for both non-failure and failure of the Lookout Shoals structure in Table 2.2-3.
TABLE 2.2-3 CATAWBA RIVER MODEL RESULTS COMPARISON WITH 1916 FOOD EVENT 1916 Observations and Calculations I 20JJ HEC-RAS " fo Breach I 2013 HEC-RAS ,\t'Breach The Catawba River Model dam discharge parameters were modified to reflect physical site parameters that existed at the time of the August 1940 flood event. This was a required step in the verification process to replicate "as-existed" conditions in 1940. Catawba River Model results for the 1940 event are presented in Figure 2.2-4.
The modeled results reflect good correlation with the observed conditions for both the July 1916 and August 1940 fl ood events. The results support the use of SCS synthetic unit hydrographs developed in l 992 for the FERC-approved Catawba-Wateree HEC-1 Model. The use of these
. . . . bH'l1fll'-( §.~-lo urnt hydrographs 1s appropnate to account for the hydraulic performance of the .11dJ ib/14 1 itia7H~l (bo(,}l 16 LS"
§ 8240-11d 1b events used for the Fukushima 2. 1 HHR. Additional details regarding the model verification are presented in Appendix E, '*FERC-Approved Cowans Ford PMF and its Application to Lhe Catawba River in Compliance with NUREG/CR-7046 - Appendix I".
69
Section 2 Flooding Hazard Reevaluation FIGURE 2.2-4 CATAWBA RIVER MODEL, AUGUST 1940 FLOOD PROFILE ALONG CATAWBA RIVER.
(b)(3)*16 U.S.C § 824o-1(d). (b)(4), (b)(7)(F) 70
Section 2 Flooding Hazard Reevaluation The following sections summarize use of the Catawba River Model to perfon11 reservoir flooding evaluation for the CNS site.
Baseline Model Runs:
Initial non-failure model runs for both the fai r-weather and PMF events were performed to establish baseline hydraulic model performance results for comparison with future modeling scenarios in determining relative impacts at CNS. The non-failure model runs were used to test applicable hydro plant and spillway operations criteria including available hydro units, starting reservoir elevation, spillway capacity constraints, and design sto1m event. The fair-weather design storm is the base flow for the Catawba River and its modeled tributaries within the 2013 Catawba River Model.
The Duke Energy Developments on the Catawba River are regulated by the FERC under Catawba-Wateree FERC Project No. 2232. The Catawba-Wateree relicense application was submitted to the FERC in 2006 including the Comprehensive Relicensing Agreement, Appendix A: Proposed License Articles, A-l.0 Reservoir Elevation Articles (Reference 11). The FERC license establishes reservoir target elevations that are below nom1al full pond elevations for each of the Developments. External flooding evaluations for the CNS 2.1 Fuk'l.lshima Study use the FERC reservoir target elevations as initial reservoir elevations. This assumption is consistent with CNS design basis analysis as shown in UFSAR Table: 2-59 and is supported by historic rcsr oir or ra1 ing levels. Calcularion CNS- I94292-010, Rev Oprovides supporri ng detai Is for (b)13) 16 U 2 C
§ s24o 1 io)-,bl the - reservoir operating levels established during the FERC relicensing of the hydro (4) ("117)(F) projects in 2006.
All Duke Energy FERC Developments have debris management programs established in follow up to their Catawba-Wateree License with the FERC. However, in fo llow up to NRC-ISG, Section 4.2.2.4 (Reference 59), the 2013 Catawba River Model includes a 5-percent spillway n" 31 t - s - ~ *:,:e,l.r- . 1t, ,.,
capacity reduction a and a 5-1 percent spillway capacity reduction at The two spillway capacity reductions are implemented to address the uncertainty of debris on the 71
Section 2 Flooding Hazard Reevaluation
. , b,.Jl1b Uncontrolled spillways at _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __
are not subject to flow restriction from gate piers; therefore, debris can flow over these structures.
No significant reservoir storage reduction has been included i_n FERC-licensed reservoir capacity due to sedimentation. The Duke Energy Developments reservoir storage was verified during
. . fi o - " 5 ~ !I t*.
. re11censmg or ,c.1 ll , t 7 i:: servoirs using bathymetry surveys ( 1996-2005) in support of the 2006 Hy ro e 1cense Application (Reference 11) with the exception of Oxford Development. Based on the relicensing bathymetric survey!> at the six reservoirs and review of shoreline management conducted during FERC relicensing, there has been no significant storage reduction in Lake Hickory (Oxford Dam).
Develop Design-Basis Flood Scenarios: (fair-weather, seismic.flooding)
Fair-weather scenarios involve a piping failure at an upstream dam and allow the Catawba River Model simulation to determine if downstream Development dams achieve sufficient overtopping to warrant potential fai lure. If no downstream dams indicate potential for ove1topping, then the fair-weather external flood is routed through each downstream reservoir using storage and spillway capacity similar to a precipitation flood event. Each upstream reservoir was tested for fair-weather failure impacts and the elevations at the Lake Wylie cross sections near the CNS were reviewed for comparison to the CNS Intake Dike and SNSWP Dam crest elevations to detem1ine site impacts. Wave impacts are considered to detem1ine if adequate freeboard is provided at the site under these flooding scenarios.
Fair-weather models were simulated using average annual median inflows to each reservoir based on daily hydrology developed during the FERC relicensing (Reference 11 ). Fair-weather dam failures of upstream dams were simulated using the Catawba River Model. Storage and spillway capacity at each dam is adequate to discharge the upstream dam breach flow without causing overtopping at the downstream dams (Reference 18) (SOF 2.2-02).
72
Section 2 Flooding Hazard Reevaluation ln similar fashion to the fair-weather scenarios, the combined effects scenarios involve a piping failure at an upstream dam triggered by a seismic event during a half PMF event (ANS 2.8 Section 9.2 (Reference I)) and allow the Catawba River Model simulation to determine if downstream Development dams achieve sufficient overtopping to trigger potential failure during a half PMF event. All Catawba River Developments are able to store and discharge the FERC-required PMF; therefore, the half PMF event does not produce an overtopping at any dam.
\.
Test model simulations were performed starting at the upstream dam o _ _ _ _ _ during a half PMF event with a triggered piping dam failure at the peak half PMF reservoir elevation.
Each dam located downstream of the assumed seismic-induced failure site was evaluated for possible cascading failure due to ove1topping from the combined half PMF and upstream breach failure. For all half PMF plus dam failure combined effects run cases, no downstream dams experienced ove11opping. Each run case included routing of the half PMF plus a seismic-induced fail ure where the PMF runoff plus breach discharge floodwater was routed through each of the seven modeled reservoirs. ln addition, the combined effects external peak fl ood elevation at the Lake Wylie cross section near the CNS Intake Dike and the CNS-SNSWP Dam were reviewed for comparison to the CNS Intake Dike and SNSWP Dam crest elevations to determine the level of freeboard margin available prior to considering wind-driven wave site impact. Wave impacts were added to determine if adequate freeboard is provided at the CNS site.
The design-basis flood scenarios are developed consistent with NUREG/CR-7046 Section 3.3, 3.4, and 3.9 and Appendices D and H (Reference 60).
HOR used the National Inventory of Dams (NID) for the states of No11h Carolina and South Carolina to identify dams within the Catawba River system upstream of Wylie Dam that have potential to impact both the Duke Energy hydroelectric dams and the CNS site. Calculation CNS-194292-0 14 (Ref. 22) provides details about the NID search, which focused on reservoir 73
Section 2 Flooding Hazard Reevaluation storage capacity and hazard classi fication as the key screening parameters for detennining potential downstream impacts.
Experience with exjsting FERC Catawba-Wateree PMF models (Reference 12) was used in the HHA evaluation of flooding from upstream reservoirs through evaluation of the insignificant (b1(3) I6USC r7
§8240-l\*j}*{bi oontribution-of--thec_Jplus small dams in the Wylie drainage basin and constrnction of PMF
!~l11~¥6it.f
!l 8240 11 k \,
_ dHb* m odel..inputs-for the - EJ reservoirs and dams (Reference 22) (SOF 2.2-04). Modeling using (4) (b}(71(F l(.>) ti l, a2 40 _1 d) tt-H 4 , b pstream basin PMFs was identified as the bounding reservoir flooding events through a series of model scenarios including the fair-weather and seismic failure plus lialf PMP model runs. The selection of the ~ using the HHA process is consistent with the existing licensing basis PMF analysis. b"j/lt> u ~ ~ 40- u 0 ~ 4 lbJC/ *l~ 1s El J
the largest storage reservoir on the Catawba-Wateree at approximatelJ - lac~ftofstorage (§~~i~ci6,(~)~(~)
(b)(3)1GUSC JI *
§ 824o-1(d}(til atnormal-maximum-pool-elevafion msl. The storage and discharge associated with the * .,,.,.,,-
,., 1.... n11r1 Cowans Ford Dam is consistent w it t e modeled capability to manage upper Catawba River flood events and regulate discharges to downstream reservoirs. Duke Energy's operation of all reservoirs in the Catawba River chain provides for a well-managed water system that is operated to support all uses of the reservoirs including hydropower, recreation, municipal water systems, and steam power generation at plants located along the river managed by Duke Energy.
Each of the Duke Energy Developments underwent a PMF evaluation in 1992 to re-analyze the hydrologic (PMP) and hydraulic (PMF) performance to maintain compliance with the FERC dam safety regulations. The Catawba River PMP values for the respective Duke Energy Developments are based on Hydrometeorological Reports 51 /52 and uses elliptical-shaped isohyetal patterns to maximize the rainfall over a given Duke Energy Development' s basin. The CNS-2.1 Fukushima Study employs the FERC-approved Catawba-Wateree Legacy HMR52-HEC- l model (Reference 37) to reevaluate the CNS site for flooding from rivers and streams (external flood event).
74
Section 2 Flooding Hazard Reevaluation 2.2. I Probable Maximum Flood - Lake Norman A s s hown m. f'1gure 221
. _ - 1, tbe 2013,__
, io_)(7 IE_~_F_::.1,,
i _§_ i~_
-_ 1*
_ _ 1s base d on a 216h J OJ
- our ram. 1*a
- 11 event comprised of:
- 40 percent HMRS I PMP (centered over the centroid of the Cowans Ford Dam drainage basin) (Reference 38)
- 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of zero precipitation
- 72-hour fu ll PMP Fo1ty (40) percent of the PMP was used versus the 500-yr rainfall based on compa1ison of NOAA Atlas 14 point precipitation rainfall 72-hour totals at each of the seven dam locations and the 40 percent values for each dam sub-basin. ln several locations, the 500-yr precipitation total was approximately equal to the 40 percent PMP total (Reference 24).
Table 2.2. 1- 1 shows maximum reservoir elevation and discharge at each upstream dam for the hydraulic model simulation for thel~ *o> - i: s ~-
1
!shown in Figure 2.2. 1- 1. Figure assume a failure at any upstream dam.
75
Section:? Flooding Huard Rce\'alu:1.t1on FlGl' RE 2.2. 1-1 St:B-BASI~ L'IIFLO" HYDROGRAPHS FOR (b)(3) 16 U.S.C. § PMF SCD/ARJO CF_A CS_PMF_ I 82 21~.000 8240-1 (d), (b1(4),
b F L'l(),000 +- --r-22~.000 100,000 175,000
~ 150,000
- i
"' 115,000 100,000 75.000 50,000 15,000 0
0 96 110 llour
- BRIK':\\ry-R F'l.O\\ - M l' DD\' FLCl\\ - RIIOOOIR Fl OW - "ARRfOR fl...O\\' - JOIJlL'!0-1(0), b)(4) (Dl(l)(t-)
77
Section 2 Flooding Hazard Reevaluation FIGURE 2.2.1-2 WYLIE RESERVOIR STAGE NEAR CNS SITE (REFERE CE 18)
-CF ACS PMF 162 78
Section 2 Flooding Hazard Reevaluation 2.2.2 Probable Maximum Flood - Lake Wylie As shown in Figure 2.2.2- 1, the 20 13 Wylie Dam PMF is based on a 216 hour0.0025 days <br />0.06 hours <br />3.571429e-4 weeks <br />8.2188e-5 months <br /> rainfall event comprised of:
- 40 percent HMR5 J P MP (centered over the centroid of the Wylie Dam drainage basin)
(Reference 39)
- 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of zero precipitation
- 72-hour full PMP Table 2.2.2-1 shows maximum reservoir elevation and discharge at each upstream dam for the hydraulic model simulation for the Wyl ie Dam PMF for model run Wylie_ PMF_2A with no assumed dam failu res. Figure 2.2.2-1 shows the corresponding Wylie reservoir stage hydrograph with peak elevation (approximately 590.7 ft msl) less than the CNS Yard elevation. These modeling results do not assume a fai lure at any upstream dam. In this model scenario, there is approximately 0.8 ft of reservoir elevation difference between the peak elevation at Wylie Dam and the upstream cross section results shown in Figure 2.2.2-2.
79
Sed11Jn1 Aoodrng, H:u.:ud Rtt,'"3.lu:il11Jn TABLE 2.2.2-1 CATAWBA RIVER MODEL RUN RESULTS FOR W YLI E. PMF 2A SCENARIO ' REFERENCE 18*
1Dl(3) 16 USC § 824o-1(<l). (t,)(41, (b)(7)1f I so
S<<11on 1 Flooding Hllard Reevaluation FIGURE 2.2.2-1 Sl' B-BASIN INFLOW IIYOROGRAPIIS FOR WVLI.E PMF SCENARIO WYLIE_ P:'11F_2A 350,000 125,000 J00.008 275.000 2!-0.000 225,000 200.000
-e
'i 175.000
~
150,000 125.000 ,.
100.000 50,000 25,000 1,2 21,
" 120 Hour 163 240 164
- BRDGWTR FLO\\ -'1UDD\1 FLOW - RIIODDIR FLOW - \\'ARRJOR FLOW - JOIJNSFLOW - lOWF.R !'LOW
- GUNPWDR l'l OW -OXULTfl[ FLOW - M LITfl[ t' LOW - LLITTLE FLO\\ - LOOKDIR FLO\\ - L\"LEFL OW CO\\A..'IDlR FLOW - MTI.SL.DUl 1-"L()\V - DUTCULNC Fl,..O\\ $1-"CWYUE J.'LOW 81
Section 2 Flooding Hazard Reevaluation FIGURE 2.2.2-2 WYLIE RESERVOIR STAGE NEAR CNS SITE (REFERENCE 18) b)(3) 16 U S .C § t:lL40-1(d), (b)(4), (b)(7j(F)
- Wylie PMF 2a 82
Section 2 Flooding Hazard Reevaluation 2.3 Dam Failures 2.3. 1 Potential Dam Failure Per ANS 2.8, Section 5.5.4, "if no ove11opping is demonstrated, the evaluation may be terminated and the embankment may be declared safe from hydrologic fa ilure** (Reference I ) .
Overtopping should be investigated for either of these two conditions:
- PMF surcharge level plus maximum (l percent) average height resulting from sustained 2-year wind speed applied in the critical direction; or
- Normal operating level plus maximum ( I percent) wave height based on the probable maximum gradient wind.
Consistent with NUREG/CR-7046 and considering the detailed hydrologic and hydraulic analyses performed for this reevaluation, a hierarchical hazard assessment (HHA) was performed on the Catawba River basin upstream of Wylie Dam to determine if other non-Duke Energy hydroelectric dams have the potential to impact both the Duke Energy hydroelectric dams and the CNS site. HOR utilized the National Inventory of Dams (NID) to develop a list of dams in the Catawba River basin with focus on reservoir storage capacity and hazard classification as the key parameters of interest. For the screening analysis, HOR removed the inconsequential dams (Low Hazard and Not Classified dams) from consideration per the ISG, Section 3 dam failure guideline (Reference 59). The remaining small dams (non-critical dams) were evaluated for additional failure flood impact based on location and calculated cumulative volumes upstream of each Duke Energy Development along the Catawba River from Lake James to Lake Wylie.
These small dam volumes were used to estimate the maximum possible increases in reservoir water surface elevations for normal operating reservoir levels and at FERC-approved Cowans Ford PMF reservoir levels assuming the entire volume was instantaneously added to each reservoir (Reference 22). The small relative increases in elevation projected using this simple screening analysis do not produce a flood hazard to the Duke Energy Catawba River dams or the CNS site. Taking into account the variable timing of potential individual failures, the flood-wave travel times and attenuation and failure of the small tributary dams can be removed from 83
Section 2 Flooding Hazard Reevaluation consideration in detennining the flood hazard reevaluation design-basis tlood at CNS (Reference 22).
Breach Parameters:
Dam failures are typically identified as overtopping or piping failure modes and can occur at either concrete gravity or earthen embankment sections of dams. In addition, the type of failure mode (overtopping versus piping) also has a bearing on the hydraulic performance of the affected structure. Piping failw-es are generally limited to sunny day or fair-weather dam failures while overtopping failures are attributed with a hydrological event or upstream cascading dam fai lures. Seismic-induced dam failures could use piping failure mode breach parameters to simulate the failure of a dam structure.
Overtopping and piping fai lure breach parameters were developed for the Duke Energy Developments. The Duke Energy reservoirs on the Catawba River arr--e"""'r""e""""-"-'-a..;a;....;;..o.~~-=.a~-.
and are maintained to standards required by 18 CFR Subpart 12.
Regression equations are available that utilize dam features and reservoir storage volume to estimate dam breach parameters. The dam breach parameters of interest typically used to determine the structures hydraulic perfonnance include:
- Bottom breach elevation,
- Breach side slopes,
- Bottom breach wid1h,
- Average breach width, and 84
Section 2 Flooding Hazard Reevaluation
- Reservoir storage volume.
The regression methodologies chosen to support the development o f breach parameters m analyzing the downstream impacts of Duke Energy Catawba River dam failures include:
- Froehlich,
- Walder and O 'Connor
- MacDonald-Langridge Monopolis, and
- Wahl.
The regression methodologies above are consistent with Section 7 of the ISG document (Reference 59). The breach parameter development details and results are presented in Calculation CNS-193049-016 (Reference 66). Geometric-based breach parameters (bottom and average breach width, bottom breach elevation, side slopes) that are developed from regression methodologies are compared with the Duke Energy Developments' physical site geometry (prepared valley abutments and slopes, bottom valley width and elevation, and documented rock and PWR layers) to determine potential site constraints that limit final breach development.
Dam breach parameters are used in the HEC-RAS model to describe the shape, size, and progression rate of the breach. Developed dam breach parameters are inserted in the Catawba River Model through H EC-RAS Geometry file, lnline or Lateral Structure, Breach Plan Data module. The required dam breach parameters include:
- Final bottom breach w idth (ft)
- Final bottom breach elevation (ft msl)
- Left and right side slopes of the breach (horizontal slope component)
- Full formation time (hours - defined as failure time)
- Failure mode (overtopping or piping) o For piping failure, define elevation at which piping occurs within the embankment.
o For overtopping failure, define the trigger for failure which is typically a reservoir elevation at which the breach is initiated.
85
Section 2 Flooding Hazard Reevaluation
- Breach progression (I : I scale of time fraction versus breach development fraction) o There are two progressions, linear (HEC-RAS default) and sine wave.
o Sine wave progression is typically chosen to reflect the physical erosion process of breach development from initially slow to rapid growth and then slower growth near the end (earth embankments).
86
TABLE 2.3.1-1 FI NAL DAM BREACH PARAMETERS FOR PI PIN G AN D OVERTOPPING l'IIODE FAILU RES AT D Ut-:E ENERGY HYDROELECTRIC DAMS (REFERENCE 18)
(b)(;,\);1-:,U~C s,B24o-1(dl,(bl(4\ (b)(1){r1 87
Section 2 Flooding Hazard Reevaluation 2.3.2 Dam Failure Permutations T he Catawba River Model unsteady flow dam failure s imulations are based on I-hour time increments for inflow hydrographs, computation intervals of I minute, hydrograph output intervals of I minute. with total simulation time of 11 days.
T he suppot1ing calculation CNS- 194292-0 IO Rev O (Reference 18) includes modeling details for sensitivity model runs developed to test dam failure outcomes at the CNS Site relative to changes in Manning's 11-values, number of upstream dams involved in cascading failures breach size, and failure time. The final scenario matrix developed to support the detennination of the Fukushima
- 2. 1 flood hazard reevaluation for the CNS Site is shown in Table 2.3.2-1.
The Catawba River Model Combined Effects half PMF plus dam fai lure event results for the Fukushima 2. 1 fl ood hazards reevaluation (without wind-driven wave impacts) are presented in Tables 2.3.2-2 and 2.3.2-3. Table 2.3.2-2 results are based on th 40 4(0 tJ)(i IJt{ F 88
Flooding H.1.zard Rec,*aiu.a11on TABLE 2.J.2-1 H EC-RAS MODEL FL~AL RUN MATRL~ (REFERENCE 18) 89
Sie..."tion.:! Fl~.hnE f-bz:ard Recvalu;u1on TABLE 2.3.2-2 HALFPMFPUJ~ (b)(3) 16U.S C.§824o-1(d). (b)(4). (b)l)(Fl !r.moEt. RESULTS I NCLUDING RESERVOIR STAGE NEAR CNS SITE (REFERENCE 18>
90
SK1fon.2 TAHU.: 2.3.2-3 HALF PMF PLUS WYLIE DAM CATAWBA RIVER FAILURE MODEL RESULTS INCLUDING RESERVOIR !)TAGE l'iEAR CNS SITE (REFERENCE 181 91
Section 2 Flooding Hazard Reevaluation The Catawba River Model Combined Effects Precipitation Flood event plus dam failure (CNS site flood bounding event) results for the Fukushima 2. 1 flood hazards reevaluation (without wind-driven wave impacts) are presented in Table 2.3.2-4 and Figures 2.3.2-1, -2, and -3 showing hourly stage hydrographs at three CNS Site boundary locations and Figure 2.3.2-4 showing a Catawba River flood stage profile. Table 2.3.2-4 results are based on the 92
Section 2 Flooding Hazard Reevaluation TABLE 2.3.2-4 PMF PLUS! (b)(3):16 us c § 824o-1(d), (b)(4), (b'(7)(F) !MODEL RESULTS INCLUDING RESERVOIR ST AGE NEAR CNS SITE (REFERENCE 18)
(b)t3):16 U.S C § 824o-1(d), (b)(4). (bl, l )(f--
93
Section 2 Flooding Hazard Reevaluation FIGURE 2.3.2-1 WYLIE RESERVOIR STAGE NEAR CNS SITE INT AKE STRUCTURE (REFERE CE 18)
(b)@):16 U.S.C. § LAKE WYLIE WATER LEVEL ABOVEI ~ FT-MS-L-FORJ *- - -lfH-01--N-1-U-KRS-- -- - 824o-1(d). (bl(4). (bl (b)f3) 1 ti U ~ .c.; § 824o- 1(d), (b)(4), (b)( l)(t- )
CF ACS PMF 1b4 - - - CF ACS PMF 8j4 94
Section 2 Flooding Hazard Reevaluation FIGURE 2.3.2-2 WYLIE RESERVOIR STAGE NEAR CNS SIT SNSWP DAM~i<.L..li' LAKE WYLIE WATER LEVEL ABO ... '-MSLFO - -IH-ffifRS.--- - - -- -- ~b~l :.15.~.s.c. § 824o-1(d), (bl(4). (bl CF ACS PMF 1b4 - - - CF ACS PMF 8j4 95
Section 2 Flooding Haz.ard Reevaluation FJGURE 2.3.2-3 WYLIE RESERVOIR STAGE EAR CNS SJTE COMPARJSON BETWEEN UPSTREAM CROSS SECTION NEAR INTAKE AND ALLISON CREEK DISCHARGE STRUCTURE (REFERENCE 18)
(b)(3) 16 USC.§ t:l24o-1(d), (b)(4, (b)(i )(t-)
- - - CF ACS PMF 8j4 - CNS Yard Intake I ********* CF ACS PMF 8j4 - CNS Yard Discharge I 96
Flood.mg Hazard Rttvafu311on CATAWBA RIVER WATER SURFACE PROFILE COMPARISON BEnVEEN NOR~L.\L POO 824o-1(d), (b)(4) (b)( )( l (b)(3) 16 U.S.C § 824o-1(d), (b)(4) (b)(7)(F) REFERENCE 18)
Section 2 Flooding Hazard Reevaluation 2.4 Storm Surge and Seiche The CNS site is located on an inland reservoir over 150 miles from the Atlantic coastline of No,th and South Carolina and is not subjected to stonn surge or seiche flooding communicated from ocean wave-driven effects. The spatial scale of a strong storm system that would significantly drop atmospheric pressure would typically be very large compared to the size of Lake Wylie or other reservoirs in the Catawba River Bas in, so the pressure differential across the lake would not be large enough to result in significant water surface variations. Standard guidance for flooding analysis in reservoirs, such as USACE Engineering Manual 1110-2-1420 "Hydro logic Engineering Requirements for Reservoirs" ( 1997), do not typically recommend consideration of water level increases caused by atmospheric pressure gradients; consideration of water level is typically limited to wave analysis (through forcing by sustained winds) and water set-up (again from sustained winds). Standard guidance does not state a need to assess atmospheric pressure extrema on the potential that low pressure would have to raise water levels.
Because the influence of atmospheric pressure gradients on water levels is negligible, such analysis is not needed for dete rmining freeboard requirements. ln addition, stom1 surge and seiche flooding have been reviewed in the FERC-required evaluation of the Catawba River hydropower developments and are not considered credible events to produce maximum water levels near the sites. A seiche caused by landslide is not considered credible based on the topography and geology around the reservoirs. However, storm surge and seiche wave impacts were evaluated for maximum hurricane wind-driven wave formation using a similar analysis to guidance provided in the NRC NUREG/CR 7046 Appendix F (Reference 60).
2.4. 1 Seiching Analysis The seiching calculations were perfom1ed assuming a seiche with one mode of oscillation in a rectangular-shaped basin of constant depth. Increasing modes of oscillation are less common and less threatening because the energy in these modes is dampened more rapidly (Dean and Dalrymple, 1984) (Reference 2). The length of the representative rectangular basin was chosen using engineering experience to consider the shape of the reservoir and potential seiches that may occur.
98
Section 2 Flooding Hazard Reevaluation Oscillation Period: The oscillation period of the seiche was dete1mined using the fo llowing equation from Dean and Dalrymple {I 984, Refere nce 2):
2L T=-
fih where L is the length of the basin, g is the acceleration due to gravity, and h is the depth of the basin.
Seicl1ing Amplitude: The amplitude of the seiche was detem1ined using the following formula from the U.S. Bureau of Reclamation (198 1, Reference 55) for calculating wind setup:
U2 F S = 1400D where U is the wind velocity in mph, F is the fetch length in miles, and D is the average water depth in feet. The period of the seiche was used as the duration of the wind speed in the calculation of the wind setup. This wind duration is considered conservative because it would take longer for the wind setup to develop which would decrease the wind speed for the fetch calculation. The wind speeds were converted to the duration of the seic he using the following methodology from the Shore Protection Manual (USACE 1984) (Reference 51):
ut
-U- = 1.277 + 0.296 tanh(0.9 log10 - )
45 3 ,600 t where U, is the wind speed at the duration t, U3,600 is the one hour wind speed, and t is the duration of interest.
Table 2.4. l - l provides a summary of the seiche analysis results from CNS-194292-01 7 Rev I (Reference 63).
99
Section 2 Flooding Hazard Reevaluation TABLE 2.4.1-1 SEICHJNG WIND-DRIVEN WAVE RES ULTS Wind Speed Maximum for Wind Water Fetch Avg. Seiche Setup Surface Site Length Water Period, T Calculation U, Wind Setup S Elevation Location (ft) Condition DeDth (ft) (min) (mph) (ft) (ft, msl) 13.730 Normal 40 13 96.8 0.44 569.84 SNSWP Dam CF ACS 13,730 PMF 8i4 73 10 35.1 0.03 602.23 CNS 20,270 Normal 40 19 95.6 0.63 570.03 Intake CF ACS Area-I 20,270 PMF 8i4 73 14 34.6 0.04 602.24 CNS 4,140 Normal 40 4 103.2 0.15 569.55 Intake CF ACS Area 2 4,140 PMF 8i4 73 3 37.8 0.01 602.21 (SOF 2.4.\-01) CNS-194292-017 Rev. l The maximum water surface values shown in Table 2.4.1-1 are not bounding. Bounding maximum water surface elevations for the CNS site considering combined effects is produced by wind-driven waves. Report Section 2.8 summarizes the bounding wind-driven wave heights combined with notmal and maximum flood inundation reservoir levels.
2.4.2 Wind-Driven Waves Analysis - Lake Wylie Source Wind-driven wave heights were developed using the Coastal Engineering Design and Analysis System (CEDAS) Automated Coastal Engineering Software (ACES) at four locations around the CNS site based on proximity to water bodies and topography. These locations are similar to site areas previously studied and reported in the CNS UFSAR. The four locations are:
I . Lake Wylie face of the SNSW Service Pond Dam
- 2. CNS Pump House
- 3. CNS Yard/Intake
- 4. CNS Discharge Structure 100
Section 2 Flooding Hazard Reevaluation The analyses were developed using water surface elevations for Lake Wylie presented in Table
!l 2.4.2-1. There was a slightly lower peak water surface elevation at the .__ (b1(4________,
'. )\.i b -., *
(bl(7\(F1
- 140- I
- ~
- f1 msl) from the HEC-RAS model results; but for this reevaluation, a single peak value of 16 IJ S C § :'t msl was used.
B24o-1 (d) (IJ) t4) (b)
(7)(F) TABLE 2.4.2-1 WATER SURFACE ELEVATIONS USED IN CALCULATIONS Normal CF ACS PMF 8j4 Location fft md\ m msl r .1):ol:::i * ::;i.; I (b (4)
I. Wylie-SNSW Service Pond Dam t '7 C
- 2. CNS Pump House 569.4 (b)(3)16IJSC
--- ......... *****--***********§S24o-l(d) (b)
- 3. CNS Yard 569.4 14) (b)(7HFl
- 4. CNS Discharge Structure 569.4 599.8 (SOF 2.4.2-01) CNS- I 94292-013-01 Rev 2 Wind Speed for the Normal Reservoir Condition: The 11 6-mph wind speed associated with the hurricane analysis in the UFSAR Section 2.4.5.1 was used for the wave analysis during normal reservoir elevation. This wind speed was the licensing basis of the riprap design for the SNSWP Dam per Duke Energy calculation CNC- I 150.02-00-0002, Rev 02 (Reference 4). The duration of this wind speed was assumed to be a I-minute average in accordance with the U.S. Weather Service methodology for reporting hurricane wind speeds (SOF 2.4.2-02) CNS-194292-013-0 I Rev 2 (Reference 19).
Wind Speed for PMF Condition: A 40-mph overland wind speed was used for the PMF wave analysis. This was consistent with the wind speed assumed in licensing basis as reported in UFSAR Section 2.4.3.6 (SOF 2.4.2-03) (CNS-194292-01 3-01 Rev l ). The American National Standard ANSI/ANS-2.8- I 992 shows the 2-yr wind speed at this location to be between 40 mph and 50 mph, although no indication of further precision is provided. An analysis performed on a SO-year wind record from Charlotte Douglas International Airport (Reference 43) yielded a 2-yr fastest mile, 10 m elevation wind speed of 32.9 mph (Reference 19: CNS-194292-013-0l Rev 2). The site-specific frequency distribution was developed using the Fisher-Tippett Type I distribution which was developed by G umbel (1 958) (Reference 14). This distribution is used by
Section 2 Flooding Hazard Reevaluation the National Weather Service (NWS) to derive frequency distribution for multiple meteorological parameters. The 40-mph fastest mile wind speed was selected for the Fukushima
- 2. 1 reevaluation considering the data record and the wind speed provided by ANSI/ANS-2.8-1992 with a reduction factor in accordance with the Bureau of Land Reclamation ( 198 1, Reference 55).
Fetch: The fetch lengths were developed using currently available aerial photography and GIS tools. Note: The CNS Yard location has a significantly longer fetch associated with the flood condition because the higher water elevation submerges low-lying areas of land.
Average Water Depth: The average water depth for the fetch associated with each location was approximated using cut-lines through Lake Wylie developed from GIS digital terrain files Results for the wind-driven wave analysis for Lake Wylie source are provided in Table 2.4.2-2 (Reference 18). The reevaluation of the CNS site for potential flooding impacts from wind-driven waves was based on a bounding site flooding event that potentially inundates the CNS Yard by approximately 8 ft. At this level of inundation, there would be no additional wave shoreline run-up. Combined effects flooding including wind-driven water levels influencing CNS Yard inundation is discussed in Section 2.8.
2.4.3 Wind-Driven Waves Analysis - SNSWP Source A separate analysis was performed to review the impact fro m wind-driven wave heights for the SNSWP under PMP flooding conditions without impacts from flooding on Lake Wylie. The analysis was based on methodology outlined in "Freeboard Criteria and Guidelines for Computing Freeboard A llowances for Storage Dams", ACET Technical Memorandum No. 2.
United States Bureau of Reclamation, December 198 1 (Reference 55). Wind speed used in this analysis was based on ANS 2.8 Section 9.2, Figure I . An unmodified wind speed of 50 mph was assumed for PMF pond level analysis and is more conservative than the wind speed used in the analysis outlined in Section 2.4.2. A hurricane wind of 116 mph was used to evaluate available freeboard based on combined effects guidelines defined in ANS 2.8 Section 9.2.2. Due to the 102
Section 2 Flooding Hazard Reevaluation short fetch distances the wind-driven waves were small and the analysis showed adequate freeboard for norn1al reservoir level plus hurricane wind and PMF plus 2-year winds, therefore, no additional refinement of the wind speeds used for this structure was perfom,ed (Reference 64). Table 2.4.3- 1 provides a summary of inputs and outputs. Wave run-up plus setup were compared to available freeboard for norrnal and LIP Flood Pool elevations by simple addition of the peak static pool elevations and the wave effects heights based on no overtopping of the SNSWP Dam. Adequate freeboard is available during both events.
Licensing design basis for wind-driven riprap sizing and freeboard (Reference 4) assumed a hunicane wind of 116 mph. Section 2.8 discusses the adequacy of the riprap based on overtopping due to combined effects flooding.
103
Section 2 Flooding Hazard Reevaluation TABLE 2.4.2-2
SUMMARY
OF WIND-DRIVEN WAVE ANALYSIS - LAKE WYLIE WATER LEVELS ACES Outout Wind Spectral Duration for Wind Speed Time for Significant Peak Avg. Water , vave for Wave Wave Wave to Wave Wave Location Condition Fetch Depth Generatio11 Generation Celerity Travel Fetch Height, Period, (ft) (ft) (min) (mph} (ft/s) (min) Hmo {ft} Tp (s)
I . Wylie-SNSW Normal 6.330 40 s 102* 15 7 4.3 3.0 Service Pond Dam CF ACS PMF 8i4 6,330 73 10 35* IO II 1.4 2.0 Normal 6,330 40 5 102* 15 7 43 3.0
- The wind speeds shown in Table 2.4.2-2 are adjusted to the duration used in the analysis as described in Reference 19).
TABLE 2.4.3-1
SUMMARY
OF WIND-DRIVEN WA VE ANALYSIS - SNSWP DAM UPSTREAM SLOPE Wind Speed Wave Avg. Water for Wave Run-up Peak Fetch Depth Generation W ave Height + Setup Elevation Freeboard Location Condition (ft) {ft) (mp h) (ft) (ft) ( ft) (ft)
(bl(3) Hl u SC § 8240-1 Normal 984 20 52 1.28 1.05 (d), (bi(4) (b)(i)(F\
CNS-SNSW Pond Dam LIP Flood 1168 29 42 0.89 0.79 583.79 11.21 Hurricane 984 20 116 2.20 1.91 575.91 I9.Q9 (SOF 2.4.3-0 1) CNS-194292-021 Rev 0 104
Section 2 Flooding Hazard Reevaluation 2.5 Tsunami Since the CNS 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 CNS 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 fom1ations, ice-induced flooding will not produce a credible maximum water level at the site and is not considered a realistic external flooding hazard to CNS.
2.6. 1 Ice Effects Long-term air temperature records (l 951 to 2011 ) available at the South Carolina State Climatology Office were reviewed to assess historical extreme air temperature variations at the CNS site. The analysis was also supported by onsite temperature data measured at the CNS site.
The climate at the CNS site is characterized by short, mild winters and long, humid summers.
Local climatology data for Winthrop College near Rock Hill, South Carolina, for a period of December 1899 through March IO12 show an average armual minimum air temperature of 50. 7° Fahrenheit (Reference 49: http://www.sercc.corn/cgi-bin/sercc/cliMA IN. pl?sc93 50).
There has not been a recorded event of significant surface ice fomrntion on Lake Wylie or any of the 11 FERC-regulated Catawba River Developments FERC #2232 in the last I 00 years.
2.6.2 Ice Jam Events There are no recorded ice jam events in the upper reach of the Catawba River based on a search of the USACE's Ice Jam Database (SOF 2.6.2-01). Water temperatures in this area of the southeast U.S. consistently remain above freezing (Reference 50).
Section 2 Flooding Hazard Riievaluation
- 2. 7 Channel Diversions Due to the location of CNS on 1he banks of Lake Wylie and the upstream topography of the reservoir, channel diversion is not considered a credible flooding event. The Catawba River is highly regulated by a series of dams. Reservoirs are back-to-back and backwater effects of each dam mitigale reservoir velocities that would be necessary to produce cha1mel diversion. Over a period of hundred plus years of regulation, the section of the Catawba River where CNS is located has not exhibited any tendency to meander toward or migrate away from the CNS site.
2.8 Combined Effects Section 9 of ANS 2.8 outlines general criteria to b e reviewed for addressing combined flood-causing events (Reference I). As discussed in Sections 2 .2 and 2 .3, the evaluation of precipitation events was performed for inflows up to the PMF. Due to the magnitude of the jb)i3) 16 U ~ C
'§ 8240- l lfJl*tOI .... s.t orage and-discharge capacity at the QRc dam sites upstream of CNS, rainfall events (4\ itJl(ftiFl less than the PMF did not produce the bounding flooding levels at Lake Wylie Dam and CNS.
ANS 2.8 Section 9.2.1.1 provides three alternatives with combinations for precipitation events to be evaluated. A lternative I was fully developed for the flood hazard reevaluation. Alternatives II and Ill are not applicable to the Catawba River basin based on the climate and topography.
Snowpack is not a meteorological event that occurs in the Piedmont Region of North Carolina.
PMP is produced by hurricane events during July to October. ANS 2 .8 Section 9 .2. l .2 provides two alternatives to review seismic dam failures with precipitation events. As discussed in Section 2.3, Alternative ll was identified as the applicable case for further evaluation since the potential breach volume in the upstream reservoirs during a half PMF would be larger than the 25-year flood.
Lake Wylie is a man-made impoundment located in the Piedmont Region of North Carolina protected from coastal events as well as extreme cold weather events. Lake Wylie is considered an "enclosed body of water" as defined in ANS 2 .8 Section 7.3.3 for consideration of storm surge combined effects flooding. Based on this definition and guidelines noted in ANS 2.8 Section 9 .2.3 .2 for the streamside location of CNS, Alternative II was determined to be the most limiting case and was used for reviewing the possible combinations producing maximum flood 106
Section 2 Flooding Hazard Reevaluation levels. Alternative II includes the consideration of a 25-year-retum-period surge or seiche. The Catawba River reservoirs are not known to be subject to surges or seiches, and there was no available source for validating a return period for this analysis. As discussed in Section 2.4, stonn surge- and seiche-generated waves were evaluated for Lake Wylie and found to produce a lower wave potential on Lake Norman than a simple wind-driven wave.
Combined effects for seismic dam failures, ANS 2.8, 9.2.1.2 and surge and seiche, ANS 2.8, 9.2.2 were considered but are bounded by ANS 9.2. 1.1 based on 1-D Catawba River Model trial simulations. Upstream FERC-regulated Catawba River dam sites are all designed for PMF flooding, seismic loadings specified by FERC requ irements, and have adequate spi llway discharge capacity for flood events up to the PMF (Section 2.2). Surge and Seiche phenomena do not produce significant fl ooding at any of the reservoir sites based on available freeboard and physical limitations of topography and location discussed in Section 2.4. HOR calculations CNS-194292-010 Rev O (Reference 18) and CNS-1 94292-0 l l Rev O (Reference 17) provide additional info1mation on the development of the combined effects flood.
U stream dam fai lure as defined above in Section 2.3. I was also reviewed.
"J 3 lo, a This conclusion was reac through experience with previous FERC emergency action plan model dam breach simulations in addition to the series of Catawba River Model (HEC-RAS) runs performed for this reevaluation (Reference 18). No additional upstream dam failure was found through modeling releases of volumes of water that exceed the bounding ANS 9.2. l . l-event outlined above.
( xtemalflooding combined eff: :.:~:::efound conservative but realisticwere theresult ofl 107
Section 2 Flooding Hazard Reevaluation 2.8.1 CNS Yard Combined Effects ANS 2.8 Section 9.2.1.1, Alternative l was used for evaluation of precipitation flood combined effects as described in rep011 Section 2.2. This included the combination of mean monthly inflow to each upstream reservoir, median soil moisture conditions, antecedent rainfall event of 40 percent of the PMP over 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> fo llowed by 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of no rainfall, the full 72-hour PMP and 2-year wind speed applied in the critical direction. This evaluation was performed for the critical combination of the PMP applied over the D 31 Iii U ~ - 2A I
.,___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___J eak Wylie reservoir elevations near the CNS site were determined using the Catawba River Model (HEC-RAS 1-D unsteady breach simulation). Water s urface elevation hydrographs at cross sections located near the SNS WP Dam and CNS Intake structure along with the CNS Discharge structure were used in the ICM 2-D model for the CNS site (Section 2. 1). Combined Effects wind-driven wave run-up was applied to the upstream 2-0 Boundary Condition since it is associated with the longest fetch length and higher base flooding elevation, resulting in a more conservative combined effects assessment. HOR did not evaluate wind-driven wave run-up to the Allison Creek cove, CNS Discharge, due to the simultaneous opposite wind direction required to produce waves toward the CNS site.
The 2-0 Zone boundary condition used in modeling the UP described in Section 2.1 was modified along the SNSWP Dam and CNS Intake by inserting a Lake Wylie stage hydrograph
_, Dam fai lure HEC-RAS model Run CF ACS PMF 8j4 described in Section 2.3. A second boundary condition was modified along Allison Creek Cove using a second downstream Lake Wylie stage hydrograph from HEC-RAS Model Run CF ACS PMF 8j4 (Reference 18). A modeling period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> was selected for review of the Catawba River Model output for cross sections near the CNS site. The length of the modeling period was selected to minimize the 2-0 model run time whi le allowing adequate time for the complete routing cycle of inundation on the CNS site. Figure 2.8.1-1 shows the upstream boundary 108
Section 2 Flooding Hazard Reevaluation condition stage hydrogTaph from the Catawba River Model using Plan CF ACS PMF 8j4 (SOF 2.8. i -02).
T he 24-hour period was selected to capture the peak Combined Effects base fl ood (i.e., no wind-driven wave run-up contribution) peak stage, approximate!
ms~, as* well as the ris ing . 9:~7~-0~.(~,
(b)(3)16LISC 1b\
and falling limbs of the hydrograph. Outing the mod ation, JCM calculates the overtopping flows (broad crested weir relationship) resulting from the stage hydrograph.
Figure 2.8. 1-2 provides the location of the 2-D boundary condition inputs along the 2-D Zone boundary.
109
Section 2 Flooding Hazard Reevaluation FIGURE 2.8.1-1 H- HEC-RAS MODEL RUN CF ACS PMF 8J4 REFERENCE 18 110
Stct1C'n 2 flood11111 llawd Reevalu,11on l'I GURE 2.8.1-2 2-D BOUNDARY CONDITION LOCATIO (Rf.FERENCE 17)
(b)(3) 16 USC § 824o-1(d), (b)(4), (b)(7)(F)
Ill
Section 2 Flooding Hazard Reevaluation The 2-D boundary condition stage hydrographs and model network were used to create the 24-hour simulation to determine the base fl ood (i.e., no wind-driven wave run-up contributions) of Combined Effects scenario within the CNS Yard and SNSWP. The additional flooding contribution from wind-driven wave run-up was detennined using a wave numerical model, (COULWA YE) (Reference 41 ). In order to evaluate the inundation potential due to the waves a methodology cons istent with the Federal Emergency Management Agency's (FEMA) fl ood mapping (FEMA 2003) (Reference 68) was adopted to determine the maximum water surface elevation above the still water elevation that would be reached as result of the incident waves.
COULWA VE was used to calculate the transformation of open-water waves from Lake Wylie propagating over the upstream model boundaty (SNSWP Dam and CNS Intake structure)
(Reference I 7).
The model results, nodes were generated at an offset distance surrounding the perimeter of the main complex, near the Cask Storage area on the no,them portion of the CNS Yard, and in the SNSWP to define locations of interest. T wenty-one (21) result nodes defining CNS Yard areas of interest are presented in Figure 2.8.1-3 and Table 2 .8. 1- 1. Figure 2.8. 1-4 shows the location of twenty-two (22) safety building doors related to SSCs result nodes and Table 2.8.1-2 provides the peak depth, elevation, and maximum velocity modeled at the nodes during the 24-hour simulation. The maximum ICM Combined Effects model inundation elevations with simulated wave impacts in the CNS Yard area are shown in Figure 2.8.1-5. Areas outside the CNS Yard area have been clipped from this figure as they are at higher ground elevations than covered by the color scale used in the figure and do not impact SSCs. Water surface elevation and depth hydrographs as well as velocity hydrographs at each node location for the Combined Effects simulation are provided in CNS-194292-011, RevO (Reference 17).
112
Floodu1g ltaz.ud Ree\'alua11011 FIGURE 2.8.1-3 CNS ICI\I MODEL PMP RESULT NOOE LOCATIONS (b)(J) 1ti U ~ C § 8240-1 (d) (b)(4) 1.b)(f)(r)
I 13
Secuc,,n:? Flooding 11.u.ard Rcnaluauon FIGURE 2.8.1-4 CNS I CM I\IOOEL PI\IP RESULr NOOE LOCATIONS AT oooru; *10 BUI LDINGS WITII IOE l W I ED SSCs (bJ(3J 16 USC § 8240 1(d), (b)(4) (b)tf)(FJ 114
Flooding H.nard Rccv..luilt+on TABLE 1.8.1-1 COMBINED EFFECTS 2-0 MODEL INUNDATION RESULTS AT NODES IDENTIFIED IN F IGURE 2.8.1-3 (b) _,) 16 U to L SI o.<<10-1 ld1, ib)(4), (b/1 I l(t-1 115
Section!. Flood1pg Hazard Rccv:1lu:111on T ABL£ 2.8. 1-2 ib)(
116
Scc11on 1 Flooding Hu.ard Retvalua11on FIGURE 2.8.1-5 l\lAXI I\IUM WATER LEVELS I N CNS YARD DURI NG TH E COMBINED EFFECTS PMF FLOOD EVENT (b)(3) 16 U SC § 8240-1 (d) (b)(4) (b)(7)(F) 117
Section 2 Flooding Hazard Reevaluation Combined Effects for seismic dam failures, ANS 9.2. l.2 and 9 .2 .2 were considered but are bounded by ANS 9.2. 1.1 based on 1-0 Catawba River Model trial simulations. Section 2.3 discussed the series of HEC-RAS dam fai lure model runs that were used lo simulate combinations of fair-weather, half PMF plus seism ic, and PMF plus failure impacts at CNS.
1 ' ,, t;, - ~ , !l O
- I \ J Modeli11g results indicate that with the exception of the 141 (b* _, Fl plus dam failure, no other combined effects cases produced reservoir levels on Lake Wylie that exceeded L . . .
l(t.il(:'J l) .JS C ; 1t;blo-* ,J b b 7 11F
µt msl. The maximum Lake Wylie reservoir I
elevations near the CNS site due to c
- 111:1" ~ ~ 02.ir " 1" 1 ~
- F Iinduced by a
. . . h k f th h If MF r: h ....,\b-,(-JJ-, -n_. -u -_., ....
c;_,§..,..
B...,4- o--
se1sm 1c event occumng at t e pea o e a P event 1or a storm centered overt e l\di (b1i4J (bi(7)(F)
(6)(3 *lo Lis ' ~ s:.to-. Id V .( 61 I . r--=i were approximately equal at l...=i ft msl. The.se-two combmed §.821161 (d)._(b)
. J ' C 1(7)(F, e ffiects evaIuatton
- cases resu Ited m
- approxnnate
- I y~ : --O,i-HeelA}ar re_ L - d- mar-gm-al-tt~e- * *L CNS
- --s1tean* d. ~j(J~~-ulf6
~ 824o:::1\'J) (b) C is significantly lower than the bounding CNS Yar ood case Lake Wyl ie elevation ofG fr *§~:1~~,(d)s(~
ms l. Therefore, no other combined hydrologic flood scenario was found to produce water levels
- L , . ,,,.
lt.~,, '
1 0 u5 ~ eu:40- 1101 0 1
> t)I "~ !HOR calculations CNS-I 94292-0 IO Rev 0 (Reference I 8) and CNS- 194292-01 l Rev O (Reference 17) provide additional information on the development of the Combined Effects flood.
Upstream FERG-regulated Catawba River dam sites are all designed for PMF flooding and seismic loadings specified by FERC requirements and have adequate spillway discharge capacity for flood events up lo the PMf (Section 2.2). Surge and Seiche phenomena are not expected to control at any of the reservoir sites based on available freeboard and physical limitations of topography and location discussed in Section 2.4.
Upstream dam fai lure as defined above in Section 2.3. 1 was also reviewed.
This conclusion was reached n
addition to the series of Catawba River Model (HEC-RAS) runs performed for this reevaluation (SOF 2.8. 1-03). No additional upstream dam failure was found through modeling to releases a volume of water that exceeds the bounding ANS 9.2. 1. 1 event outlined above.
118
Section 2 Flooding Hazard Reevaluation 2.8.2 SNSWP Dam Combined Effects Combined effects for precipitation floods were cons idered for the SNSWP Dam. There is significant freeboard provided at the SNSWP Dam for combi1ned effects resulting from upstream precipitation floods. There are no upstream reservoirs that contribute to fl ooding. The SNSWP Dam is designed for seismic conditions; and if a slope failure occurred, the release of water th.rough a potential breach would flow into Lake Wylie and not on the site.
The reevaluation included a 2-D model simulation of th t,j 3 1605 § St:4G-I o b ,I a 17 F)
T he SNSWP Dam was also reviewed for rapid drawdown from the reevaluated bounding (b)(:J) 1tj I , C _ ,ft
§ R24o-1(d)(bl ****** :flooding-event elevation-orc..._Jft msl (Reference 65). Rapid drawdown slope factors of safety
' ,-, r exceed current standard of practice (SOF 2.8.2-02). Table 2.8.1-1 shows the duration of the combined effects flooding wave is approximately 16.7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />.
11 9
Section 2 Flooding Hazard Reevaluation 2.8.3 Cooling Towers Combined Effects The NRC Standard Review Plan Section 2.4.4 requires the review of any onsite water control or storage structures that exist above site grade be evaluated for potential flooding of SSC impm1ant to safety. The CNS site includes six cooling towers at the south east end of the site adjacent to Allison Creek. These six towers are above grade. To comply with the Standard Review Plan requirement, modeling of a breach of one of the cooling towers was perfo1med using the ICM CNS combined effects model. The modeled event was based on the assumption of a full cooling tower reservoir. A maximum water volume associated with Cooling Tower 2A of 119,210.26 ft 3 (approximately 2.74 acre-feet) is documented in Duke Energy calculation CNC-l l 15.00 0001, Rev 11 CNS Cooling Towers: Basin, Cable T ray Suppo11s, Gates & Screens Amertap Ball Screens dated May 2013 (Reference 3). A failure of Cooling Tower 2A was simulated in the ICM 2-D model to evaluate flooding on the site since the cooling towers are at a higher elevation than the CNS Yard. A sensitivity analysis was perfom1ed on the assumed breach width of the concrete structure. This analysis assumed three breach w idths, approximately 92 ft, 184 ft, and 263 ft. These three breach widths correspond to approximately 11 percent, 22 percent, and 31 percent of the total circumference of Cooling Tower 2A per Duke Energy drawing 73-42352, Rev D Schematic Views C lass 700 Round Mech. Draft Tower. Each of the breaches was assumed on the perimeter of Cooling Tower 2A in order to maximize the potential flooding toward the CNS Yard and is assumed to fully form the breach instantaneously at the beginning of the simulation. This sensitivity analysis indicated that the modeled peak water surface elevation and general flow paths are not significantly affected by breach sizes w ithin this range. Figure 2.8.3-1 provides a comparison of stage hydrographs at the top of the access road for the Cooling Tower area (North Carolina State Plane NAD83 Coordinate System Easting and Northing:
1381271 US ft, 479869 US ft). The maximum inundation depth difference between the three breach assumptions is less than one inch; and based on a review of model results, none of the three breach width assumptions significantly impact the CNS Yard due to the small volume in the Cooling Tower reservoirs. The 184-foot (22 percent) breach width was utilized in the final model setup. Figure 2.8.3-2 indicates the location of the final modeled breach.
120
Section 2 Flooding Hazard Reevaluation The ICM model results show an assumed breach of a Cooling Tower reservoir produces isolated flooding with variable water surface elevations across the Cooling Tower yard area and does not significantly impact the CNS Yard when compared to the LIP or PMF combined effects events.
Breached flood waters are shown to overtop the protective curb/berm at the upper rim of the Cooling Tower yard area; however, the maximum depth on the CNS yard is isolated to a small area within the security fenc ing and is less than I inch in average depth. Figures 2.8.3-3 and 2.8.3-4 provide representative stage, elevation, and velocity hydrographs.
This volume of water was not sufficient to bound the licensing basis LIP event discussed in Section 2.1 (SOF 2.8.3-0 l ).
Figure 2.8.3-1 depicts the maximum inundation elevations m the Cooling Tower area.
Additional details are provided in CNS-1 94292-011 Rev. 0.
121
Section 2 Flooding Hazard Reevaluation FIGURE 2.8.3-1 COOLING TOWER BREACH WIDTH SENSITIVITY DEPTH HYDROGRAPHS (NORTH CAROLINA STATE PLANE NAD83 COORDINATE SYSTEM EASTING AND NORTHING: 1381271 US FT, 479869 US FT) (REFERE CE 17) 0 50 ~
0 -15 0 -IO 0.35 0.30
°[ 0.25 Q
t- +
0.15 +-
0.10 ..
0.05 0.00 .,...J.._ _ _ _ ~---------,-======,,....,,,,,,,,,,.-----------===
0:00 0*06 0: 12 0: 18 0:24 0:30 0:36 0 42 0 48 0:5-1 1:00 Simula tion T imt, Hr::\1in
- CTF foot Breach Depth 1ft) - CTF - 184-foot Breach Depth (ft) - CTF - 262-foot Breach Depth (fl) 122
Flooding JldZilid RCC\ alualtun FIGURE 2.8.3-2 C 'S COOLING TOWER 2A BREACH SIMULATION (REFERENCE 17)
Catawba Nuclear Station: 20 Boundary Condition Calculation CNS-194292--011 (Combined Effects Model Results) lnfoworks ICM: Base Case Hydrology: Combined Effects 123
Section 2 Flooding Hazard Reevaluation FIGURE 2.8.3-3 CNS COOLING TOWER AREA REPRESENTATIVE ELEVATION AND DEPTH HYDROGRAPH DURING HYPOTHETICAL FAILURE OF COOLING TOWER 2A- NORTH CAROLINA STATE PLANE NAD83 COORDINATE SYSTEM EASTING AND NORTHING: 1381271 US Ff, 479869 US Ff (REFERENCE 17) 621.0 0.20 620.9 0. 18 l,
620.8 0. 16 I I I I 620.7 0. 14 I I
~ 620.6 1
- 0. 12 e I I J 620.5 :/\. I 0.10 i..
- t j ~ Q
.;j 620.4 u, ' I f
I I '
0.08 I
620.3 I
'I 0.06 I I I I 620.2 0.04 I I I I I I 620. 1 0.02 I I I \
620.0 I
- - ~-- -- ----- ---- ------ -- ---~---- 0.00 0:00 0:15 0:30 0:45 Sim ulation Tim~. Hr:Min
- Elevation. ft msl - - Depth. ft 124
Section 2 Flooding Hazard Reevaluation FIGURE 2.8.3-4 CNS COOLING TOWER AREA REPRESENTATIVE VELOCITY HYDROGRAPH DURING HYPOTHETICAL FAILURE OF COOLING TOWER 2A - NORTH CAROLINA STATE PLANE NAD83 COORDINATE SYSTEM EASTING AND NORTHING:
1381271 US FT, 479869 US FT (REFERENCE 17) 0.2.5 0.20 V\
6
~ 0. 10
\
~
0 .05 0.00 0:00
\ 0: 15 0 :30 Simulation Time, Hr:Min 0:45
- Velocity. ft per second 125
Scc11on .2 Flood,ni l lazard Rffi alua11on FIGURE 2.8.3-5 I\IAXIMUI\I INUNDATION I COOLING TOWER AREA DURING A II YPOTII ETICAL FA ILURE OF COOLING 1 OWEll 2A (REFERENCE 17)
- e1975 e2000 - &1125.52110 e2000 52025 - 62150,621 JS e,01', &2oso - ~,, 1~ enriri eio so eio H - s22 oo e,o oo 0 - 61075 82100
- 62100*62125 Feet Catawba Nuclear Station: Maximum Water Surface Elevation over Cooling Tower Calculation CNS-194292-011 (Combined Effects Model Results) lnfoworks ICM: Base Case Hydrology: Combined Effects 126
Section 3 Comparison of Current Design Basis and Reevaluated Flood Causing Mechanisms Comparison of current design basis and reevaluated flood causing mechanisms is provided in this section through use of tables and text. Items discussed include SNS WP Dam and CNS Yard impacts related to flooding from, Cooling Tower breach, flood ing on Lake Wylie, PMF, LIP, and combined effects. It should be noted that due to the different methods used to estimate flood hazard impacts at the CNS site between the current design basis and the reevaluated flood causing mechanisms a direct comparison is not always possible. Th.is can be seen in the LIP analysis where new 2-D modeling methods provide s ignificantly more simulation results at thousands of points where the current design basis is based on a simple 1-D cross section average approximation of water levels in the CNS Yard. This can also be see in comparison of combined effects stream routing modeling results where the reevaluation analysis used a combination of I-D dynamic routing model to simulate the large Catawba River PMF routing and used a 2-D model to provide a more refined focus on the local CNS site impacts. The current design basis did not find an overall precipitation-based flooding event with or without assumed dam failures that exceeded the nominal CNS Yard elevation of 593.5 fl ms!. The reevaluation flood hazard analysis CD JI lb US. C 6 c<.t40 01 r0>:.i1 10 1l ft Table 3-1 provides a general summary of the flood causing mechanisms reviewed for the current design basis (Section I) and the reevaluation (Section 2). The values provided in the table representing the reevaluation elevations are approximated from the different models used for the analysis and do not represent an absolute maximum inundation level at the s ite but in general were selected to match the location referenced in the current design basis.
127
Section 3 Comparison of Current Design Basis and Reevaluated Flood Causing Mechanisms TABLE 3-J CURRENT DESIGN BASIS AND REEV ALUATJON FLOOD ELEVATIONS Current Reevaluation Design Basis Reevaluation Flood Delta Flood Flood From D esign Flood Causin2 Mechanism E levation Elevation Basis Local Intense Preci12itation Unit 1 side of the Yard 594.9 ft msl 595.5 ft msl +0.6ft Unit 2 side of the Yard 595.9 ft msl 595.6 ft ms! -0.3 ft Flooding in Reservoirs ,-,:., 0 1b)(3) 16
.: 3 C * $£ § USC§ Lake Wylie CNS Intake
- 3 C. § ft msl 8240-msl 1 8240-l(d) 2 SNSWP Dam ,.4!>-1 ft msl Dam Failures t !
,-~, r msl*
rr! (b I I 71(r msl msl 3 (bl(4 \ ib)
I 1(1 I -
Storm Surge and Seiche/Wind-Wave Run-up Lake Wylie 577.8 fl msl 569.55 ft msl -8.25 ft Tsunami NIA NIA NIA lee induced Flooding NIA NIA NIA Channel Diversion NIA NIA NIA Combined effects Lake Wylie CNS Intake 593.7 ft msl 603.2 ft ms1 5 +9.5 ft SNSWP Dam 594.4 ft msl 603.2ft msl 5 +8.8 fl Allison Creek CNS Discharge 593.4 ft msl 599.8 ft ms16 +6.4 ft Notes:
1 Catawba River Model Run Case Wylie PMF 2A 1
4 atcree centere a or an a e
- 1...
1b->(_'J_
) ,_o_u_"__**________________a_,j '"'
3.1 128
Section 3 Comparison of Current Design Basis and Reevaluated Flood Causing Mechanisms One a rea of s ignificant difference between the design basis and the reevaluation is with the determination of the Catawba River PMF and combined effects flooding. The design basis hydraulic model appears to have been based on a "level pool" model that did not consider unsteady flow between dams. Experience w ith flood modeling of the Catawba River Dams through review of FERC-required PMF evaluations and modeling experience performing emergency action pla n (EAP) analyses was considered for the reevaluation. Existing FERC compliance models have been developed using unsteady models and show a difference between rhe simple assumption of level pool routing and more detailed unsteady flow routing using the St Venant equations. Additionally, the hydrology applied for the design basis used a historic hu1Ticane event plus a multiplier rather than current practice of applying HMR51/52. These modeling differences, coupled with the application of antecedent rainfall events preceding the ID t, PMF, lead to some differences in routing elevations at th ~.:; r ~ dams upstream of the CNS
~ , 1,0 site. ,e> ~ lD 1 Fl 129
Section 3 Comparison of Current Design Basis and Reevaluated Flood Causing Mechanisms 3.2 Cooling Tower Breach A failure of a Cooling Tower by breach of the reinforced concrete water reservoir was not documented in the UFSAR. The reevaluation perfonned to support this report determined that for an assumed breach of the concrete reservoir, there are no s ignificant flooding impacts to the CNS Yard (SOF 3.2-01 ). The amount of water stored in tbe cooling tower reservoirs and the topography of the foundation plateau to the southeast of the CNS Yard do not produce a signi ficant source of flooding to effect the CNS Yard.
3.3 Riverine Flooding on Lake Wylie Flooding 011 Lake Wylie As outlined in Section 3 . l , there was a difference in modeling performed for the design basis compared to the reevaluation. There are a number of reasons for this including the lack of computer models that could adequately simulate the complex hydraulic process of rainfall and runoff in the early I 970s. The reevaluation used different hydrology and hydraulic methods that produced different results for the PMF. Smaller events evaluated including upstream dam (bl(3)18USG
"~ 82 qQ
_,, ,L 1 11 r111r1
- * ***1(,-*Ii*-I '~c,
, .*..((1)....., .I ............ e_:-k *-*
!I t Dam and D failures and the half PMF show better correlation between modeled reservoir elevations at
,u,,11 am. T his is likely due to the similarity in the volume and discharge parameters used in the models for flooding simulations where the spillway discharge capacities were not significantly exceeded. For the design basis PMF analysis, a historic hurricane event was modified using a real storm pattern to distribute the rainfall over the basin.
ln the reevaluation, HMR5 l/52 was used incorporating the elliptical storm pattern produced using these recommended methodologies. PMP estimates from HMR5 l are based on the analysis of many historic storms which occurred over a significantly large portion of the United States producing a regional maximization of possible rainfall. The difference in the stom1 shape used for each evaluation resulted in various differences in storm centering and results from the PMF modeling along with the unsteady flow model used for the reevaluation. The reevaluation 130
Section 3 Comparison ofCurrent Design Basis and Reevaluated Flood Causing Mechanisms generally yielded slightly higher reservoir levels at the dams. This should be expected since the rainfall distribution was fit to the basin using guidance from HMR52. Overall, the design basis flooding analysis was not significantly lower than the reevaluation considering all inputs and modeling capabil ities. It is observed that applying backwat er analysis methods to the design basis flows and stage would probably yield better agreement between the flooding results at the CNS site.
PMF Bounding Event The bounding reevaluation flooding event was found to be j ll ' 3116 'J s C § B.2-tc-1to11b1*~1 <t,,, 111-,
l'b)(J> rn u'* ~ V' * " * *:I " " " '111 j(ANS 2,8 9.2.2.1, Alternative I). The design basis bounding event was the half PMF p lus a ! 0 ,; 16 uS cs 5240- 110 * ~ 4 t> ~ F j the design basis modeling fo r the PMF did not result in 11 1 li> US - Dam overtopping and fa iling.
ti n24o-1(d) b
~. It! (7 F The reevaluation analysis detennined the bounding case through a series of model runs following a similar methodology as used for the original design basis. However, the revaluation analysis found that I I
Probable Max imum Flooding The reservoir routing method described in the CNS UFSAR appears to be based on "level pool,
storage assumptions including analysis o f Lake Wylie reservoir levels. This method of hydraulic 13 I
Section 3 Comparison of Current Design Basis and Reevaluated Flood Causing Mechanisms analysis was common standard-of-practice at the time when the modeling was perfonned.
Maximum reservoir levels reported in UFSAR Section 2.4.3.S appear to be captured at the Wylie Dam. Because Lake Wylie is a river-shaped reservoir w ith storage tributaries, "fingers," located along the length of the reservoir, consideration of backwater impacts along the reservoir length from the dam to the CNS site (approximately 4 .8 river miles) would likely result in higher water levels than recorded at the Wylie Dam in the licens ing basis analysis for the extreme flood events evaluated. The reevaluation PMF analysis, summarized in Section 2, uses a *'state of the practice" hydraulic dynamic routing model that considers backwater impacts in the routing of the flood flows in each reservoir and a comparison of water levels at Wylie Dam with water levels near the CNS site on the main reservoir channel confirms that water levels would likely be higher at CNS than model estimates using level pool routing.
NUREG 7046 recommends application of HMR5 J/52 (HMR applicable to the CNS site) to develop the PMP for the evaluation of the PMF (Reference 60). Previous licensing basis PMP-PMF analyses used a regional storm bas is with adjustment for conse1vatism. A direct compa,ison of PMP values between previous studies and the analysis used for this review was not made; however, a comparison of the results of the licensing basis PMF routing and the updated HMRS 1/52 and HEC-RAS routing was reviewed and shows higher.,.................,_=----........
(b)(3) 1G U S CJ b 'll ' **1 S J
- I.
':i 8240-l(d}Tb)
I., r,"'! r am. The combined effects PMP event for th ~~*1-i
"~F b11-'J !bl am
!l'(3} 16 LIS C I§ 82.tr.-t di tJ)(4) (OJ(7)(F 3.4 Local Intense Precipitation The 01i ginal design basis LIP was based on PMP from HMR33 and a 6-hour duration. The 6-hour event included a peak I-hour rajnfall of 9.2 inches. In 1984, revised LIP calculations were performed using HMR5 1/52 resulting in a 6-inch increase in a total of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> of rainfall and a I 0-inch increase in the peak I -hour rainfall. The licensing design LIP was applied to the site using a 1-D model whic h is clifficult to use when no defined c hannel exjsts. Site topographlc 132
Section 3 Comparison of Current Design Basis and Reevaluated Flood Causing Mechanisms geometry approximations were used to create flow channels for the simulation and the existing catch basins were also included in the analysis to help remove the intense rainfall from the CNS Yard.
When comparing the 2-D modeling results analysis to the CNS licensing basis 1-D channelized analysis documented in the UFSAR, there are many differences that can be attributed to methodology, models, site drainage, and base hydrology assumptions. ln many cases, several of these factors may be involved simultaneously, which makes it difficult to isolate individual sources of difference. The two primary factors identified by HOR as the largest contributors of deviations from the previous licensing basis analyses are the varying modeling methodologies (i.e., software used) and the total LIP rainfall amount (i.e., I-hr LIP versus 6-hr LIP). The 2-D model is also capable of simulating water spilling from the building roofs and focusing this runoff at distinct areas of the CNS Yard more appropriately than the simple 1-D model. The maximum depths at specific nodes were not reviewed due to the differences in the output format (l-D cross section vs. 2-D mesh elements) but the overall maximum depth of inundation in the CNS Yard near critical structures was comparable as illustrated in Tables 1.2.1-3 and 2.1 .4-1.
3.5 Dam Failures Upstream dam failures were assumed in the licensing desigrn basis flooding analyses and in the reevaluation analyses. Each upstream dam was evaluated for fair-weather fai lure and for cascading fail ures at sequential downstream dams.
Both analyses considered combined effects flooding assuming a seismic failure of an upstream 1b""'
~3""'
). 1..,,..
dam during a half PMP event. The licensing design basis arnalyses found the fai lure of ~2 u_,
- aa
~ """
t:_.,,. ; . § ....;;
'1;_);~~ ctH /1
,.....,__""i:_ _4_....,
8240-lld1 1n HI Dam during a half PMP event to be the CNS site bounding flooding event. fie tllt7) F reevaluation analyses using the HEC-RAS unsteady flow model did not find any combination of seismic dam failures plus half PMP flooding to bound the flood ing at CNS.
133
Section 3 Comparison of Current Design Basis and Reevaluated Flood Causing Mechanisms As noted in Sections 2.2 and 2.3 the reevaluation analysis following guidelines in ANS 2.8 9.2.2.1 , Alternative 1 to be the bounding CNS Site floodin event roducin a maximum o of in undation on the CNS Yard and water levels ,t 7 1F (t,, )) ' S
~ (. 21 !JI I; I G ft msl for periods (b)(3) tf:ill SG
§8240::l(a), (ti\
- ,,,,-.,,r, (b)(3) 1'> USC
§ ~24ci- l(or(t1r ..between _
hours as shown in Table 2.8.1-1 .
, ..
- t.. 17 'r 3.6 Storm Surge and Seiche Storm surge and seiche were addressed in the licensing design basis assuming hurricane-driven winds produced a seiche and the setup from the wave calculation was the surge component that was added to the wave height. The reevaluation did not find that storm surge and seiche was a probable physical flood ing event for the CNS site as described in Section 2.4. The location of the Cataw ba River combined with the highly regulated river reaches, dams, isolates the river from storm surge associated with large bodies of water and tidal effects. Seicl1ing calculations using methodology included in NRC/CR 7046 were used for Lake Wylie and found to produce small wave impacts less than derived us ing wind-driven waves outlined in Section 2.4.2 3.7 Tsunami Tsunami-induced flooding 1s not expected to affect the site for the reasons listed above in Section 2.5.
3.8 Ice-Induced Flooding Ice-induced flooding is not expected to affect the site for the reasons listed above in Section 2.6.
3.9 Channel Diversion Channel diversion s are not expected to affect the site for the reasons listed above in Section 2.7.
134
Section 3 Comparison of Current Design Basis and Reevaluated Flood Causing Mechanisms 3.10 Combined Effects Combined effects floodjng reviewed in the licensing design basis and reevaluation includes applicable sections of ANS 2.8 Section 9.2. The licensing design basis identified the combined Cowans Ford Dam failure plus half PMP flood and 2-year mean wind speed waves as the bounding CNS Site flooding event (Section 1.2.8). The reevaluation identified I to J) 16 U S-C § 32.!o-1 l1J lb)(~J {b 'i)(F}
ITbe stage hydrographs were used with L.------------------
the CNS Site 2-D model and 2-yr mean wind speed waves to simulate flooding at the CNS Site and inundation (Section 2.8). The licensing design basis analysis did not fi nd a river flooding event that resulted in inundation of the CNS Yard. The reevaluation found the CNS Yard would (b)(3) 113 U S C __n
~824o-r~aroµ, *be inundated by-as much ~LJ.ft (not considering the SNS WP), and the inundation duration
§~~!~~,(~~lb) *
- l- 1ft msl would be for approximately I 3 eurs-at varfous- looations-onthesite ~~~~~~~(~s(~
as shown in Table 2.8. 1-1 . Inundation durations at the 22 door locations identified in the cu1Tent design basis are shown in Table 2.8.1-2 with the inundation durations rangino from I I .25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br />
~X:li 16 us C to 18.6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. Water elevation in the SNSWl' is expected to reach elevationG !l mslo, - -~i~~I~
§324o-l(d)(h) ******** ftabove-normal pond Ievel-andE Jft above the design crest of the dam. Water levels m the
'" 11 *H11r SNSWP are contained within the natural topography around the pond and do not drain toward the CNS powerblock buildings. A failure of the SNSWP Dam would release water back into Lake Wylie and not flood the site.
135
Section 4 Interim Actions Taken or Planned 4.1 LIP Actions Flooding from t he LIP event is managed with available Type I catch basins, procedures for securing doors in critical Safe shutdown facilities, sump areas, sump pumps, and sand bags.
Strategies to address specific water ingress areas are included in detail in Enclosure 1.
4.2 Combined Effects PMF Flooding Flooding from the Combined Effects event is managed using strategies to protect the core, spent fuel, and containment in the event that severe site flooding does occur.
These strategies are addressed in detail in Enclosure 1.
136
Section S References
- l. American Nuclear Society (ANS). 1992. ANS-2.8-1992, Determining Design Basis Flooding at Power Reactor Sites. 1992.
- 2. Dean, R. G. and R. A. Dalrymple. 1984. Water Wave Mechanics for Engineers and Scientists, Prentice-Hall, New Jersey, 353 p.
- 3. Duke Energy. 2013. Calculation CNC- 11 15.00-00-000 I, Rev 11 CNS Cooling Towers:
Basin, Cable Tray Supports, Gates & Screens Amertap Ball Screens dated May 2013.
- 4. Duke Energy. Calculation CNC- l l 50.02-00-0002, Rev 02, R.ipRap Design for the SNSW Pond Dam.
- 5. Duke Energy. Calculation CNC- l 150.02-00-0001, Rev 09, SNSW Pond Outlet Discharge Pipe.
- 6. Duke Energy. 2012. 2.3 Fukushima Near-Tenn Task Force (NTTF) Flood Walkdown Inspection report (October 2012).
- 7. Duke Energy. CN- 1003-15, Rev 10, Master Site Plan.
- 8. Duke Energy. CNC- l 114.00-00-0040 Rev 29.
- 9. Duke Energy. CNC-1 114.00-00-0065 Rev l. Fukushima 2.3 NTTF Flood Walkdown Inspection .
- 10. Duke Energy. 2012. Catawba N uclear Station Unit I and Unit 2, UFSAR Chapter 2, April 2012.
11 . Duke Energy. 2006. Duke Energy Comprehensive Relicensing Agreement , Appendix A, Reservoir Elevation Articles (Page A-1 ), 07-18-06 http://www.duke-energy.com/pd fs/relicensing/comp_relicensing_agreement. pd f.
- 13. FERC. " Engineering Guidelines fo r the Evaluation of Hydro Power Projects."
- 14. Gumbel, E.J. 1958. Statistics of Extremes," Columbia University Press, New York, 1958, 375 pp.
137
Section 5 References
- 15. HOR Engineering, Inc. 2013. CNS-194292-006, Rev. 0, Cowans Ford Dam East Bulkhead Stability
- 16. HOR Engineering, Inc. 2013. CNS-194292-009, Rev . 0, LIP
- 17. HDR Engineering, Inc. 2013. CNS-194292-011, Rev. 0, Combined Effects
- 18. HDR Engineering, Inc. 2013. CNS-194292-0 I 0, Rev. 0, External Flooding And Dam Failure
- 19. HDR Engineering, Inc. 20 13. CNS-194292-013.01 , Rev, 2, Wave Analysis (Pait 1 of 3):
Wave Height Calculations,
- 20. HDR Engineering, Inc. 20 13. CNS-194292-0 13.02, Rev, 2, Wave Analysis (Part 2 of 3):
Wave Overtopping Calculations, and 2 1. HOR Engineering, Inc. 2013. CNS-194292-01 3.03, Rev 2, Wave Analysis (Pait 3 of 3):
Stone Stability Calculations
- 22. HOR Engineering, Inc. 2013. CNS-194292-014, Rev. 0, HHA-N ID Volume Screening for Non-Duke Energy Dam Failures.
- 23. HDR Engineering, Inc. 2013. CNS-194292-015, Rev. 0, Wylie Dam Bulk.head Stability
- 24. HOR Engineering, Inc. 2013. CNS-194292-020, Rev 0, (Cowans Ford Antecedent Stom1 Hydrograph Development
- 25. HOR Engineering, Inc. 2013 . CNS-194292-019, Rev 0, Reservoir Volume Calculation -
Dam Breach Parameters.
- 26. HOR Engineering, Inc. 2013. Fukushima NITF 2.1 CNS Flood Hazard Reevaluation Site Wa/kdown in Support of2D Terrain Model 011 October 8, 2013, 194292-DocOO l-Rev02.
138
Section 5 References
December 2010, Rev. I.
February 2008.
September 201 1, Rev. 2.
- 36. IntraSearch Inc. 2103. Astrium Services/Spot Image - Pleiades Satellite Imagery, 0.5 Meter Multispectral Resolution, Acquisition Date 02-18-2013. Prepared by IntraSearch Inc., MapMart.
- 37. Law Environmental, Inc. 1992. Catawba/ Wateree PMF Study, Hydrologic/Hydraulic Model, April 1992.
- 38. Law Environmental, Inc. 1992. Final Report, Catawba/ Wateree PMF Study, Cowans Ford Hydropower Facility, September 1992.
- 39. Law Environmental, Inc. 1992. Final Report, Catawba/Wateree PMF Study, Wylie Hydropower Facility, October 1992.
- 40. Leenknecht, D.A. , Szuwalski, A. and Sherlock, A.R. (1992). Automated Coastal Engineering System: User's Guide. U.S. Army Corps of Engineers, Coastal Engineering Research Center, Waterways Experiment Station, Vicksburg, MS.
- 41. Lynett, P. J., Wu, Y.-R., and Liu, P. L.-F. (2002). Modeling Wave Runup with Depth-Integrated Equations, COULWAVE. Coastal Engineering, 46(2), 89- 107.
139
Section 5 References
- 43. National Climatic Data Center. 2013. Asheville, NC. Website:
http://gis.ncdc.noaa.gov/map/viewer/#app=cdo
- 44. National Oceanic and Atmospheric Administration. 1978. National Weather Service, Hydrometeorological Report No. 51, Probable Maximum Precipitation Estimates, United States East of the I05th Meridian, June 1978.
- 45. National Oceanic and Atmospheric Administrat10n. 1982. National Weather Service, Hydrometeorological Report No. 52, Application of Probable Maximum Precipitation Estimates - United States East of the I05th Meridian, August 1982.
- 46. Sanborn. 2010. Aerial Survey Catawba_DTM_6-2 l-2010 drawing. March 2010.
- 47. Sanborn. 2010. Aerial Survey MrSID 20 to I Mosaic. March 2010.
- 48. Saville. McClendon. Cochran. 1963. Freehoard Allowances for Waves in Inland Reservoirs. Paper #3465, ASCE Transactions, Vol. 128, 1963, Part IV.
- 49. Southeast Regional Climate Center, Winthrop College, SC, 289350, http://www.scrcc.com/cgi-bin/sercc/cliMA TN .pl?sc9350.
- 50. U.S. Anny Corps of Engineers. lee Jam Database. \VWw.1ce1ams.crrcl.usace.army.mil/
(https://rsgisias.crrel.usace.anny.mi l/apex/f?p=273 :39:470753 87243 l OI).
- 51. U.S. Army Corps of Engineers. 1984. Shore Protection Manual, 4th edition, Coastal Engineering Research Center, Washington, D.C. 1984.
- 52. U.S. Army Corps of Engineers. 1973. Weather Bureau Report HUR 7-97 and Shore Protection Manual, Department of the Army Corps of Engineers, 1973.
- 53. U.S. Anny Corps of Engineers. 1966. Engineering Technical Letter 1110-2-8, Computation of Freehoard Allowances for Waves in Reservoirs. Co1ps of Engineers, August, 1966.
- 54. U.S. Army Corps of Engineers. 1966. Technical Report No. 3, Shore Protection, Planning cmd Design. Third Edition, Corps of Engineers, 1966.
- 55. U. S. Bureau of Reclamation. 1981. Freeboard Criteria and Guidelines for Computing Freehoard Allowances.for Storage Dams. ACET Technical Memorandum No. 2, 63 p.
- 56. U. S. Department of the lnterior, Bureau of Reclamation. I 987. Design o_( Small Dams, A Water Resources Technical P11blicatio11. Third Edition.
- 57. United States Department of The Interiors Geological Survey Circular 397, Discharge Characteristics of Broad-Crested Weirs.
140
Section 5 References
- 58. U.S. Geological Survey. 2009. National Map - York County, South Carolina, Ortho-lmagery, 0.5 ft. Natural Color Resolution, Acquisition Date 02-2009.
- 59. United States Nuclear Regulatory Commission. 2013. Japan Lessons-Learned Project Directorate, JLD-ISG-2013-0 1, Guidance for Assessment of Flooding Hazard Due to Dam Failure, Interim Staff Guidance, Revision 0, July 2013.
- 60. United States Nuclear Regulatory Commission. 2011. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United State of America, NUREG/CR-7046, November 2011 .
- 61. United States Nuclear Regulatory Comrnission.1977. Regulatory Guide 1.59, Design Basis Floods/or Nuclear Power Plants, Rev. 2, August 1977.
- 62. United States Nuclear Regulatory Commission. Appendix A to Part SO - General Design Criteria for Nuclear Power Plants. ( l 0CFRS0).
- 63. HOR Engineering, Inc. 2013. CNS-194292-017, Rev 1, Seiche Analysis.
- 64. HOR Engineering, Inc. 2013. CNS- l 94292-021, Rev 0, SNSW Pond Wave Run-up.
- 65. HOR Engineering, Inc. 2013. CNS-194292-012, Rev 0, SNSWP Dam Rapid Drawdown.
- 66. HOR Engineering, Inc. 2013. CNS- I 94292-016, Rev 0, Mountain Island and Wylie Dam Breach Parameters.
- 67. Federal Highway Administration. 2009. FHWA-NHl-09-11 2, Hydraulic Engineer Circular No. 23, Volume 2, Chapter 5, 2009.
- 68. FEMA. 2003. Guidelines and Specifications for flood mapping partners. Washington D.C. Misc. paginated.
141
United States Nuclear Regulatory Commission to Letter CNS-14-028 Page 1 of 6 Enclosure 1 FLOODING INTERIM ACTIONS FOR Catawba Nuclear Station, Units 1 and 2 Docket Numbers 50-413 and 50-414 Renewed License Numbers NPF-35 and NPF-52
United States Nuclear Regulatory Commission to Letter CNS-14-028 Page 2 of 6 1 Evaluated Site Flooding Scenarios This enclosure describes the interim actions taken at the Catawba Nuclear Station (CNS) in response to reevaluated flood elevations that exceed the Current Licensing Bases (CLB) flood elevations. The results of the Hazard Reevaluation Report (HRR) are summarized in Table 3-1 of Attachment 1 and the two flood event scenarios under which the Current Licensing Basis is exceeded are the Local Intense Precipitation (LIP) event and the Probable Maximum Flood (PMF) event due to a Combined Effect event. This condition has been entered in the CNS Corrective Action Program (CAP) (C-14-1940).
Impacts associated with the increased flood elevations and durations and the associated interim actions taken in response to the reevaluated LIP flood event are described in Section 2, and for the reevaluated PMF event are described in Section 3 of this enclosure.
2 Local Intense Precipitation (LIP) Event 2.1 LIP Event Overview The Hazard Reevaluation Report identifies the Local Intense Precipitation (LIP) event as a flood event that exceeds the CLB of the plant. The LIP evaluation is described in Section 2.1 and the results summarized in Table 3-1 of Attachment 1.
The plant nominal grade is 593.5 ft msl (mean sea level), and the CLB credits existing flood protection features to provide protection from an external flooding event for an elevation up to 594.9 feet msl for Unit 1 and 595.9 ft ms1 for Unit 2.
The reevaluated LIP event for the Unit 1 side of the yard results in a water surface elevation of 595.5 ft msl, which exceeds the current design bases value of 594.9 ft msl by 0.6 feet. The Unit 2 side of the yard flood reevaluation results in a water surface elevation of 595.6 ft msl, which is lower than the current design bases value of 595.9 ft msl by 0.3 feet.
A comparison of the CLB and the HRR methodology and analysis is provided in Attachment 1, Section 3.
2.2 LIP Impacts The results of the reevaluated LIP flood hydrographs show that flood levels exceed the current design bases flood protection elevation for a short and limited duration at critical water ingress locations. Debris impact is negligible due to lack of a credible debris field, low flow velocities and shallow flow depths during the reevaluated LIP event.
Based on the limited duration and a minor increase in flooding elevation compared to the current design bases values, the impact of the reevaluated LIP flooding to SSCs does not present a significant hazard to the safe operation of the plant. In addition, as part of the NTTF Recommendation 2.3 Flooding Walkdowns, credited flood protection features were inspected, and potential deficiencies entered and addressed in the plant CAP system. Impacts to Systems, Structures and Components (SSC) will be assessed as part of the Integrated Assessment.
Interim actions implemented to address the minor increase in flooding elevations and durations due to the reevaluated LIP are discussed in Section 2.3, LIP Interim Actions.
2.3 LIP Interim Actions CNS procedure AP/0/A/5500/030 (Plant Flooding) includes severe weather warning notification from the Duke Meteorological department for forecasted severe weather and an initiating criterion for a projected rainfall event of 7 inches or more in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. This communication is provided to site personnel and provides adequate warning time for site preparation.
United States Nuclear Regulatory Commission to Letter CNS-14-028 Page 3 of 6 The HRR analysis conservatively assumed that all storm drains are blocked. However, the CLB credits the CNS site drainage system to remain functional during the LIP event. This functionality is assured through the implementation of a quarterly Preventive Maintenance (PM) program by CNS Site Services and an annual PM inspection program by CNS Design Engineering. In addition, NSD 104 (Material Condition, Housekeeping, Foreign Material Exclusion and Seismic Concerns) dictates general housekeeping policies that decrease the likelihood of significant debris inventory available to challenge the capacity of the site drainage system. A full time site services team routinely maintains the general site areas in an orderly fashion.
An interim action has been implemented to provide additional assurance of the storm drain system functionality by revising the plant flooding procedure AP/0/N5500/030 (Plant Flooding) to perform a walk down inspection of the site drainage system catch basins when warning of a significant rain event is received. This walk down will visually inspect the storm drain system to confirm that the storm drain inlets are clear of debris. The inspection is expected to take approximately 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> for the actual inspection, which is well within the severe weather warning timeframe.
Training requirements were assessed for the revision to AP/0/N5500/030 (Plant Flooding) during the walkthrough validation. It was determined no formal classroom training for the procedure revisions is required because the procedure steps consist of simple tasks.
Reasonable simulations were performed for the additional steps added to plant procedure AP/0/N5500/030 (Plant Flooding) and the credited activities can be performed concurrent with environmental conditions that are expected to simultaneously occur.
The combination of the existing and revised procedures provides reasonable assurance that the storm drains will remain functional during the LIP event, providing mitigation for the postulated increased water elevations due to the reevaluated LIP events. Any additional leakage into critical areas of the plant can be handled by the credited site flood protection features, including internal drains and sump pumps.
The interim action strategies implemented have been evaluated for all plant operating modes and reasonable concurrent environmental and site conditions. The implementation of the interim actions will not reduce the effectiveness of site security requirements.
3 Probable Maximum Flood (PMF) Event 3.1 PMF Event Overview The Hazard Reevaluation Report identifies the PMF due to a Combined Effect event as a flood event that exceeds the CLB values of the plant. The Combined Effect evaluation is described in Section 2.8 and the results summarized in Table 3-1 of Attachment 1.
The reevaluated PMF storm event isr ' t- I) I:, £ 0- b nd consists of an antecedent storm equivalent to 40% bt me probable maximum preb pitation (PMP) event that lasts for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, followed by a dry period of 72 hour~~UJJs..u..Q..l-',;l:..u.Ll,~= U,1.<:u..c=UJ..IC1.1.--,
100% PMP. The resultant water surface elevations at lJ 21 c JS_ ~814':.._ lr:J* t ______________
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A comparison of the CLB and the HRR methodology and analysis is provided in Attachment 1, Section 3.
United States Nuclear Regulatory Commission Enclosure 1 to Letter CNS-14-028 Page 4 of 6 3.2 PMF Impacts Durin the PMF event, flood water fro b :, t LI :;; C § II.24-o-l[dl t,l(-t) ti)(, FJ Based on a review of orthoimagery, debris that could impact the site is expected to consist of generally large, woody floating debris such as fallen trees or floating docks. This debris is expected to reach the CNS site at the CNS intake, which is located in a protective cove that is not directly aligned with the main channel flow of Lake Wylie. Due to the topography of the cove and the adjacent area, the flow velocities are lower than the r1ow velocities in the main channel, limiting larger and heavier debris from reaching the site. Debris conveyance across the CNS site from Lake Wylie would be the result of relatively shallow overland flow velocities.
l(b)(3) 10 IJ::::, ~ ti 4 ,l 0~ I Interim actions implemented to address the increase in flooding elevations and durations due to the reevaluated PMF are discussed in Section 3.3, PMF Interim Actions.
3.3 PMF Interim Actions which is one of the dams by t> 3 An eva uatron was pe orme an a
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inaicate when an antecedent storm event has occurred when conditions indicatin a PMP event are likely, I t> J 16 l; s ... ~ t-.:4J- 11r.1 1 (bJt41 tt.l\7l(FI (D)(3J 16 us c § 240-* *d 'b .i c -llF he triggers are based on a combination of the overall Catawba River basin performance, water elevations along the basin, the meteorological forecast. and the gate positions and discharge volumes through multiple dams along the basin, which are monitored and controlled by) - -- jr.he.J[iggeuioinJ§ ___(1 ~~~l~~ ~5 ~
1 established are at 144 hours0.00167 days <br />0.04 hours <br />2.380952e-4 weeks <br />5.4792e-5 months <br />, 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> and 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> nor to a potential flooding event §4 ) ~1; 1m ~ ( )
11 at t~e CNS sit~. These trigg~rs a~e documente~ in~ ,...,,.,,.,,.,,.,~;;,.,,.,,..,..,Procedure...'.'..Catawl2a:W~l~J~~ ~~2 l!~(~/(tit Project CNS Hrgh-Water Notifications Process'. C proce ure P/0/B/5000/030 (Severe {4 1 toJ(71(F*
Weather Preparations) has been revised to include CNS site preparation and responses to these trigger points for entry to site procedures and implementation of interim actions.
Strategies have been implemented at the CNS site to prevent flood waters from reaching the site yard. The reevaluated PMF analysis shows that elevated water levels in Lake Wylie inundate the site from the north and as the flood progresses, from the south side due to backwater effects.
The two primary components of the interim actions are the irnstallation of portable dams on the north and south side of the plant to prevent flooding from inoreased water elevations on Lake Wylie, and the installation of storm drain plugs to prevent water from back-flowing through the storm drain system due to elevated tailwater conditions in Lake Wylie.
Engineering evaluations were performed to support the interim actions taken. The evaluations included conservative case analyses on the portable dams and the intake slope for stability, scouring, debris impacts, overturning, sliding, and surcharge loading. An assessment was also performed for flooding from localized precipitation on site associated with the PMF on the watershed, and development of timing and sequence of depl:oyment of interim action features.
United States Nuclear Regulatory Commission Enclosure 1 to l etter CNS-14-028 Page 5 of 6 The existing plant Emergency Response flooding procedure RP/0/8/5000/030 (Severe Weather Preparations) has been e ised to include operator actions that correspond to the triggers (b)(3) 113 US I recei\l_edJ!O.m - Three new Extensive Damage Mitigation Guidelines (EDMG) have
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been implemen e o guI e e installation and deployment of the portable dams, the storm drain plugs and sealing cable trenches, and associated equipment operation.
The need for training for revisions to the existing plant procedure RP/0/B/5000/030 (Severe Weather Preparations) and the new EOMG's was assessed through the Systematic Approach to Training (SAT ) process and has been completed and formal 1raining is not required. Equipment and material required to implement the interim actions associated with the PMF event has been acquired, and is being controlled through a Periodic Test (PT) procedure, PT/0/N4400/002E (Flex Equipment Inspection). T his procedure provides assurance that the equipment is available to perform the interim actions.
Reasonable simulations were performed for the steps added to plant procedure RP/0/B/5000/030 (Severe Weather Preparations) and for new EDMG's, and the credited activities can be performed concurrent with environmental conditions that are expected to simultaneously occur. The equipment identified in the procedures is available for use and is controlled through plant procedures.
T he interim action strategies implemented have been evaluated for all plant operating modes, and reasonable concurrent environmental and site conditions. All required interim flood protection features have been acquired, pre-staged, and maintained to provide flood hazard protection. The implementation of the interim actions will not reduce the effectiveness of site security requirements as alternate site security measures wilJ be implemented when needed.
The combination of existing, revised and new procedures provides reasonable assurance for providing protection from the postulated PMF Combined Effects event.
4 Summary of Interim Action Commitments The following table summarizes interim actions taken or planned and their respective completion dates.
Catawba Nuclear Station - Flood Hazard Interim Action Commitments Item Initiating Trigger Interim Actions Taken or Implementation Number Event Planned Date 1 Localized Flood Warning received 1. Revise AP/0/A/5500/030 March 12, 2014 Intense from Duke (Plant Flooding) to include Precipitation Meteorological operator actions to clear or (LIP) Event department per secure potential debris prior AP/0/A/5500/030 (Plant to event and during event.
Flooding).
Item Initiating Trigger Interim Actions Taken or Implementation Number Event Planned Date 6 LI"',
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Probable Flood Warnings received
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- 1. Add i I procedures with appropriate
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Flood (PMF)
- 2. Revise RP/0/B/ 5000/030 to March 12, 2014
United States Nuclear Regulatory Commission Enclosure 1 to Letter CNS-14-028 Page 6 of 6
- Event include notifications from I .................... Jand . ___ (b)( B) 16 USC.
d:S:SUl.;l dlt:U vuerator actions.
- 1s**40:1 (d), (b)
- 3. Approve EDMG for portable March 12, 2014
- dam installation.
- 4. Approve EDMG for storm March 12, 2014 drain oluo installation.
- 5. Approve EDMG for pump March 12, 2014 operation.
- 6. Approve inventory Periodic March 12, 2014 Test procedure to control equipment and material
- 7. Acquire and stage required March 12, 2014 equipment and materials.
- 8. Acquire and stage storm March 12, 2014 drain plugs.
- 9. Training needs have been March 12, 2014 assessed and completed.
- 10. Required site work has been March 12, 2014 completed.
- 11. Engineering evaluations March 12, 2014 have been completed Item ADDITIONAL COMMITMENTS Number
- 3. A Flooding Integrated Assessment will be completed and report submitted to March 12, 2016.
the NRC on or before March 12, 2016 (Letter CNS-14-028, Reference 1)