Latest revision as of 19:13, 7 March 2021

Text

NRC-2017-000688 (Formerly FOIA/PA-2017-0690) - Resp 5 - Final, Agency Records Subject to the Request Are Enclosed, Part 3 of 15
	ML20366A011
Person / Time
Issue date:	12/29/2020
From:	; NRC/OCIO
To:	;
Shared Package
ML20366A007	List: ML20366A008; ML20366A009; ML20366A010; ML20366A011; ML20366A012; ML20366A013; ML20366A014; ML20366A015; ML20366A016; ML20366A017; ML20366A018; ML20366A019; ML20366A020; ML20366A021; ML20366A022; ML20366A023;
References
	FOIA, FOIA/PA-2017-0690, NRC-2017-000688
	Download: ML20366A011 (262)
	v • d • e

seeURIW=R!LA1'1!e INP'OltMM'ION - Ylii:1'1111eu, UNBER 18 erR :!.398 NLS2016049 ENCLOSURE 1 Cooper Nuclear Station Flood Hazard Reevaluation Report, Revision 1

(~KuGilf Related Version~

I s1:euR1T'l"=REL.MEB lt4FORMMteN WITHHoti, tJNt,I!"- u, e""- 2.s!o

SEeURIT't'-ftELATEt, INFORMATION - Wll't II IOLE) UNDEft 16 CFR 2.S96 H

Nebraska Public Power District Alwnys there when )'011 necJ t,s Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 1 Project No.: 11784-017 September 2016

~ Safety-Related D Non-Safety-Related 55 East Monroe Street* Chicago, IL 60603 USA* 312-269-2000 www.sargentlundy.com SECURIT¥-REb\TEf) INFORMATION - WITltttete UNf>ER 10 Cfifit 2.~90

SECURIT¥=RELATEB 1Nf-ORM>%TION - Y't'ITHHOLB UNBER 18 Cf-R 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 LEGAL NOTICE This report was prepared by Sargent & Lundy, L.L.C. ("S&L"), expressly for the sole use of Nebraska Public Power District

("Client") in accordance with the agreement between S&L and Client. This Deliverable was prepared using the degree of skill and care ordinarily exercised by engineers practicing under similar circumstances. Client acknowledges: (1) S&L prepared this Deliverable subject to the particular scope limitations, budgetary and time constraints, and business objectives of the Client; (2) information and data provided by others may not have been independently verified by S&L; and (3) the information and data contained in this Deliverable are time-sensitive and changes in the data, applicable codes, standards, and acceptable engineering practices may invalidate the findings of this Deliverable. Any use or reliance upon this Deliverable by third parties shall be at their sole risk.

Legal Notice ii SECURIT'f-RELATEB INf-ORMt<TION - 1t'VITHHOLB UNBER 18 Cf-R 2.398

SECURITY-RELATEB INl'-Oft.MATION - WITHHOLB UNBEft. 10 Cf-ft. 2.390 Nebras ka Public Power Dis trict SL-012450 Cooper Nuclear Station Revision 1 F LOOD H AZARD R EEVALUATION R EPORT Project No,: 1178-017 SIGNATURES Preparer :

Section I f.;~4fM~ Date Reviewer:

Section I

~L~

M. Kaiseruddin Date 21 \ 4- I ' 6

sa(J l; .9 I \. 4 ,11 C

)

Preparer: , 1 ~

Sections 2 and '3 M. Salehi Date (except Section 2.3)

Reviewer: .9/ 1 4 /l 6 Sections 2 and 3 N. M. Patel Date (except Section 2.3)

Prepar er:

Section 2.3 N. M. Patel Date

'Reviewer:

Section 2.3 Date Preparer: qbttlL/2 Sections 4 and 5 M. Nienaber Date Approver:

B. E. Jelke Date Signatures Hf ,,.. ,,

s.,.,.genof,s.. Lundy ***

t*

SECUfUTY-RELATEB INl'-Oft.MATION - WITI-IHOLB UNBER 10 CFft. 2.390

SECURIT*RELATEB INFORMATION - WlfHHOLB UNBEff 16 Cfff 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION Rl!PORT Project No.: 11784*017 TABLE OF CONTENTS LEGAL NOTICE ....................................................................................................................................... 11 SIGNATURES ................................................:........................................................................................ 111 TABLE OF CONTENTS ......................................................................................................................... IV LIST OF TABLES ................................................................................................................................... IX LIST OF FIGURES ................................................................................................................................. XI LIST OF ACRONYMS AND ABBREVIATIONS.................................................................................... xv INTRODUCTION/ PURPOSE ............................~................................................................................. XIX

1. SITE INFORMATION RELATED TO THE FLOOD HAZARD .......................................................1-1 1.1 Detalled Site Information ......................................................................................................1-1 1.1.1 Sitelayout ..................................................................................................................... 1-1 1.1.2 Spatial Data Sets............................................................................................................1-2 1.1.3 Elevation of Structures, Systems, and Components (SSCs) .........................................1-2 1.1.4 Topography ....................................................................................................................1-2 1.1.5 Missouri River and Tributaries ........................................................................................1-2 1.2 Current Design Basis Flood Elevatlons ..............................................................................1-4 1.2.1 Summary of CNS External Flood Design and Licensing Basis ......................................1-4 1.2.2 CLB Local Intense Precipitation (LIP) ............................................................................1-6 1.2.3 CLB Flooding in Streams and Rivers .............................................................................1-6 1.2.4 CLB Dam Breaches and Failures ...................................................................................1-7 1.2.5 CLB Storm Surge ........................................................................................................... 1-7 1.2.6 CLBSeiche ....................................................................................................................1-7 1.2.7 CLB Tsunami. .................................................................................................................1-7 1.2.8 CLB Ice-Induced Flooding ..............................................................................................1-7 1.2.9 CLB Channel Migration or Diversion ..............................................................................1-7 Table of Contents

(

- (\

iv Sorge~'; Lundy *

)/

SECURlf'f-RELAfEB INf-ORMAflON - WlfHHOLB UNE>ER 16 CFR 2.396

SECURIT'f-RELA'fED INI-ORMA'ffON - 1t'VITI II IOLB UNDER 16 CFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 1.2.10 CLB Combined Effects ...................................................................................................1-8 1.2.11 CLB Associated Effects ..................................................................................................1-8 1.3 Flood-Related Changes and Flood Protection Changes .................................................1-10 1.4 Changes to the Watershed or to the Local Area .............................................................. 1-11 1.5 Current Design Basis Flood Protection and Mitigation Fe;atures ...................................1-12 1.6 Additional Site Detail...........................................................................................................1-16 1.7 References ...........................................................................................................................1-17 1.8 Tables ...................................................................................................................................1-19 1.9 Fig ures..................................................................................................................................1-22

2. FLOOD HAZARD REEVALUATION .............................................................................................2-1 2.1 Local Intense Precipitation (LIP) ..........................................................................................2-1 2.1.1 Probable Maximum Precipitation Depths .......................................................................2- 1 2.1.2 Drainage Areas and Local Drainage Parameters ...........................................................2-2 2.1.3 Peak Discharges ..,.........................................................................................................2-3 2.1.4 Hydraulic Model Setup ...................................................................................................2-3 2.1.5 Effect of LIP .................................................................................................................... 2-6 2.1.6 References ............................,........................................................................................2-6 2.1.7 Tables.............................................................................................................................2-8 2.1.8 Figures .........................................................................................................................2-15 2.2 Flooding in Streams and Rivers (PMF)..............................................................................2-32 2.2.1 Probable Maximum Precipitation (PMP) ......................................................................2-33 2.2.2 PMP Runoff Hydrographs ............................................................................................2-35 2.2.3 Water Level Determinations .........................................................................................2-37 2.2.4 Combined Effects .........................................................................................................2-44 2.2.5 Associated Flooding Impacts .......................................................................................2-46 2.2.6 References ...................................................................................................................2-48 Table of Contents _ ( ..

.*' \

V I

Sorg1oJnt & Lun cty' 1"

,..,\,,.,~

)

9ECURIT¥-RELATEB INFORM>\TION - Wl'fHHOLD UN BER 16 e1-R 2.998

SECURITY-RELATED INFORMATION - WITtlllOLD UNDER 16 CFR 2.396 Nebraska Public Power District SL--01 2450 Cooper Nuclear Station Revision 1 FLOOD HAZARD Rl!l!VALUATION REPORT Project No.: 11784-017 2.2.7 Tables ...........................................................................................................................2-52 2.2.8 Figures ......................................................,.................................................................. 2-63 2.3 Dam Breaches and Fallures ...............................................................................................2-92 2.3.1 Flood Protection Level at the CNS Site ........................................................................2-94 2.3.2 Hydrologic Evaluation ...................................................................................................2-94 2.3.3 Hydraulic Evaluation .....................................................................................................2-98 2.3.4 Combined Effects .......................................................................................................2-104 2.3.5 Associated Flooding Impacts .....................................................................................2-105 2.3.6 References .................................................................................................................2-109 2.3.7 Tables.........................................................................................................................2-111 2.3.8 Figures .......................................................................................................................2-133 2.4 Storm Surge .......................................................................................................................2-168 2.4.1 References .................................................................................................................2-168 2.5 Seiche .................................................................................................................................2-169 2.5.1 References .................................................................................................................2-169 2.6 Tsunaml ..............................................................................................................................2-170 2.6 .1 References .................................................................................................................2-170 2.7 Ice-Induced Flooding ........................................................................................................2-171 2.7.1 Methodology ...............................................................................................................2-171 2.7.2 Most Severe Historical Ice Jam Event.. ......................................................................2-171 2.7.3 Upstream Breach ofan Ice Dam ................................................................................2-172 2.7.4 Downstream Ice Jam and Resulting Backwater .........................................................2-172 2.7.5 Effect of Ice-Induced Flooding ....................................................................................2-172 2.7 .6 References .................................................................................................................2-173 2.7.7 Figure .........................................................................................................................2-174 2.8 Channel Migration or Diversion .......................................................................................2-176 2.8.1 Historical Channel Migration or Diversion ..................................................................2-176 2.8.2 Regional Topographic Evidence ................................................................................2-177 2.8.3 Ice Causes .................................................................................................................2-179 Table of Contents vi Sa.1r9ant: &, Lundy

SECUfflTY-M'ELATEE> INFOffMATION - V't~ITHHOLE> UNflEff 16 CFff ! .~96

SECUR:IT¥-RELATEB INFOR:MATl6N - VtlTI ltl6LE> UN BER 16 CFR 2.396 Nebraska Public Power District SL.012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT 2.8.4 Flooding of Site Due to Channel Migration or Diversion .............................................2-179 I

2.8.5 Human-Induced Changes of Channel Diversion ........................................................2-180 2.8.6 Conclusions ................................................................................................................2-180 2.8.7 References .................................................................................................................2-181 2.8.8 Figures .......................................................................................................................2-184 2.9 Combined Effects ..............................................................................................................2-199 2.9.1 References .................................................................................................................2-199

3. COMPARISON OF CURRENT AND REEVALUATED FLOOD-CAUSING MECHANISMS ........3-1 3.1 Local Intense Precipitation ...................................................................................................3-1 3.2 Flooding in Streams and Rivers...........................................................................................3-1 3.3 Dam Breaches and Failures ........................................................................................... '......3*2 3.4 Storm Surge ...........................................................................................................................3-3 3.5 Seiche .....................................................................................................................................3-3 3.6 Tsunami ..................................................................................................................................3-3 3.7 Ice-Induced Flooding ............................................................................................................3-3 3.8 Channel Migration or Diversion ...........................................................................................3-4 3.9 Combined Effects ..................................................................................................................3-4 3.10 Associated Effects ................................................................................................................3-4 3.10.1 Hydrostatic and Hydrodynamic Loads............................................................................3-4 3.10.2 Debris Loads ..................................................................................................................3-5 3.10.3 Erosion and Sedimentation ............................................................................................3-5 3.11 Other Pertinent Factors ................................................................................,........................3-5 3.11.1 Flood Duration ................................................................................................................3-5 3.11.2 Overtopping ....................................................................................................................3-5 3.1 1.3 Inundation .......................................................................................................................3-6 3.12 Conclusions .......................................................................... "................................................3-6 Table of Contents /*!"

vii ( \

So.rgi0~- ~ Lundy* l,

).,*

/

SECURIT'f-RELATEE> INFORrMTl6N - WITHH6LE> UNE>ER 16 CFft 2.396

8ECURIT¥-RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT 3.13 References .............................................................................................................................3-6 3.14 Tables .....................................................................................................................................3-7

4. INTERIM EVALUATION AND ACTIONS TAKEN OR PLANNED ................................................4-1 4, 1 Regulatory Background ................ .,,........ ,.. ,......................,............ ,............................... ,,., ..4-1 4.2 Evaluation of the Impact of the Reevaluated Flood Levels on Structures, Systems, and Components (SSCs) ........................................................ ,....................................................4-1 4.3 Interim Evaluatlon and Actions Taken or Planned for CNS ..............................................4-2 4.3.1 Dam Failure_.................................................................................................................. .4~2 4.3.2 Channel Migration or Diversion ..................................................................................... .4-3 4.4 Reference ........................................................................................................................... ,...4-3

5. ADDITIONAL ACTJONS ... ,................. ,................................ ,......................................................... 5-1 Table of Contents .,,,..,--*

(' '-.

viii Sargon~.&1 Lu"dyl1C

\ ,.I

./

SECURIT¥=~ELATED INFORMATION - VtlTHHOLD UNE>ER 16 CFR ! .S90

SECURIT-RELAfEB INFORMATION - WITHHOLB UND!R 16 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 LIST OF TABLES Table 1.8-1: Missouri River Dams ...........................................................................................................................................1-20 Table 1.8-2: Design Evaluation Summary ...............................................................................................................................1-20 Table 1.8-3: Missouri River Drainage Area .............................................................................................................................1-21 Table 2.1-1: PMP Values and Intensities at the CNS Site .........................................................................................................2-9 Table 2.1-2: Peak Discharge .....................................................................................................................................................2-9 Table 2.1-3: Drainage Area and Peak Flow at each Cross Section-Zone A .........................................................................2-1 0 Table 2.1-4: Drainage Area and Peak Flow at each Cross Section - Zone B .........................................................................2-11 Table 2.1-5: Drainage Area and Peak Flow at each Cross Section- Zone C .........................................................................2-12 Table 2.1-6: Drainage Area and Peak Flow at each Cross Section -Zone D .........................................................................2-13 Table 2.1-7: PMP Water Levels ..............................................................................................................................................2-14 Table 2.2-1: Point 3 (shown in Figure 2.2-4) AdjuS1ed Precipitation Depths Based on HMR 52 .............................................2-53 Table 2.2-2: Model Input Parameter Definitions and References ............................................................................................ 2-54 Table 2.2-3: Summary of Unsteady Computational Parameters .............................................................................................2-56 Table 2.2-4: Location of Inflow Hydrographs........................................................................................................................... 2-56 Table 2.2-5: Comparison of Manning's Roughness Coefficients used in the Model to Standard Values ................................ 2-57 Table 2.2-6: NSE Coefficient S1Jmmary and Peak Discharge Comparison for 2011 Validation Simulation ............................. 2-57 Table 2.2-7: Inflow Hydrograph Location Summary for PMF Simulations ...............................................................................2-58 Table 2.2-8: PMF Simulations Peak Magnitude and Time at RM 556.16 ................................................................................2-60 Table 2.2-9: Monitoring Point Summary ..................................................................................................................................2-60 Table 2.2-10: Calculation of Wind-Driven Waves and Wind Setup Approaching CNS ............................................................2-61 Table 2.2-11: Submerged Embankment Results.....................................................................................................................2-61 Table 2.2-12: Wave Runup Approaching CNS Main BuHding Complex ..................................................................................2-61 Table 2.2-13: Forces on Intake Structure ................................................................................................................................ 2-62 Table 2.2-14: Debris Impact Loads ......................................................................................................................................... 2-62 Table 2.3-1: Salient Features of Missouri River Mainstem Dams..........................................................................................2-112 Table 2.3-2: Dam Break Parameters for Hypothetical Dams.................................................................................................2-113 Table 2.3-3: HEC-HMS Model Input Parameters and Definitions.......................................................................................... 2-116 List of Tables ix SECURITY-RELATED INFORMATION - WITHHOLB UNBER 16 CFR 2.396

SECURIT'f-RELATEf> INFORMATION - WITHHOLf) UNf>ER 16 CFR ! .396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.3-4: Hypothetical Dam Outflow Summary from HEC-HMS Model ............................................................................ 2-1 18 Table 2.3-5: 500-Year Flow on Missouri River at Drainage Locations .................................................................................. 2-121 Table 2.3-6: Peak Flow at HEl>RAS Inflow Locations ..........................................................................................................2-122 Table 2.3-7: Land Use Types and Manning's Roughness Coefficients ................................................................................. 2-124 Table 2.3-8: Non-System Dam Failure Peak Stage at CNS and Plant Flood Protection Level ............................................. 2-124 Table 2.3-9: Peak Stage/Flow at CNS for Combined System and Non-System Dam Failure ............................................... 2-125 Table 2.3-10: Model Boundaries for TUFLOW ...................................................................................................................... 2-126 Table 2.3-11 : Maximum Channel and Right Overbank Discharge end WSEL at CNS for Upstream Boundary Sensitivity Analysis ............................................................:.....................................................................................................2-126 Table 2.3-12: Monitoring Point Summary for Fort Peck Hydrologic Dem Failure .........................................:........................ 2-127 Table 2.3-13: Monitoring Point Summary for Oahe Sunny-Day Dam Failure ........................................................................ 2-127 T"ble 2.3-14: Calculation of Wind-Driven Waves and Wind Setup Approaching CNS ..........................................................2-128 Table 2.3-15: Summary of Wind Setup, Wave Runup, and Total Water Levels at SSCs ......................................................2-128 Table 2.3-16: Summary of Water Depth above Roof at Important Plant Structures .............................................................. 2-129 Table 2.3-17: Summary of Water Depth above Bridge Deck at Important Bridges ...............................................................2-130 Table 2.3-18: Resultant Forces and Elevations on Main Building Complex Structures ......................................................... 2-131 Table 2.3-19: Resultant Forces and Elevations on Intake Structure .....................................................................................2-131 Table 2.3-20: Debris Impact Loads ....................................................................................................................................... 2-132 Table 3.14-1: Current Licensing Flood Elevations and Reevaluated Flood-Causing Mechanisms ...........................................3-8 Table 3.14-2: Debris Impact Loads Summary ..............................................................................................., ........................... 3-9 List of Tables X

SECURIT11'=RELATEf> INFORMATION - 't'VITI IHOLf> UNf>ER 16 CFR 2.996

s~eURITY-RELATEB INFORMATION - WITtftlOLB UNDER 18 eFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784*017 LIST OF FIGURES Figure 1.9*1 : Site Location ......................................................................................................................................................1-23 Figure 1.9-2: Missouri River Tributaries .................................................................................................................................. 1-24 Figure 1.9-3: Overhead View of CNS 1 ................................................................................................................................... 1-25 Figure 1.9-4: Overhead View of CNS 2 ................................................................................................................................... 1-26 ,

Figure 1.9-5: Missouri River Reservoir System .......................................................................................................................1-27 Figure 1.9-6: Missouri River Path in 1879 at the Site of CNS.................................................................................................. 1-28 Figure 1.9-7: Aerial Photograph of the Plant Site in 1971 ....................................................................................................... 1-29 Figure 1.9-8: Aerial Photograph of CNS Showing Flooding .................................................................................................... 1.30 Figure 2.1-1: Locatlon of Security Barriers ..............................................................................................................................2-16 Figure 2.1-2: Drainage Areas for LIP Evaluation .....................................................................................................................2-17 Figure 2.1-3: Offsite Drainage Area behind USACE levee ..................................................................................................... 2- 18 Figure 2.1-4: Cross Sections for LIP Evaluation - Zone A ....................................................................................................... 2-19 Figure 2.1-5: _C ross Sections for LIP Evaluation - Zone B .......................................................................................................2-20 Figure 2.1-6: Cross Sections for LIP Evaluation - Zone C ....................................................................................................... 2-21 Figure 2.1-7: Cross Sections for LIP Evaluation - Zone D ....................................................................................................... 2-22 Figure 2.1-8: HEC-RAS Cross Sections for Zone A ................................................................................................................2-23 Figure 2.1*9: HEC-RAS Cross Sections for Zone B (sheet 1 of 2) ..................................................................................._.......2-24 Figure 2.1-10: H EC-RAS Cross Sections for Zone C (sheet 1 of 2) ........................................................................................2-26 Figure 2.1-11: HEC-RAS Cross Sections for Zone D (sheet 1 of 4) ........................................................................................ 2-28 Figure 2.2- 1: location Map .....................................................................................................................................................2-64 Figure 2.2-2: PMP Position 1 - Sheet a (see subsequent Sheets b, c, and d for PMP Positions 2 to 4) .................................2-65 Figure 2.2-3: Geographic Distribution of Basins o f Influence for Missouri River Drainage above CNS ................................... 2-69 Figure 2.2-4: PMP Spatial Distribution over Platte River Basin (P3 Centroid; 41 .35N, 96.20W) ............................................. 2-70 Figure 2.2-5: Antecedent Final Model PMF Hydrographs for P1, P2, P3, and P4 ................................................................... 2-71 Figure 2.2-6: Subsequent Storm Final Model PMF Hydrographs for P1 , P2, P3, and P4 ....................................................... 2-72 Figure 2.2-7: Missouri River Junctions ....................................................................................................................................2-73 Figure 2.2-8: Full Floodplain PMF Hydrographs for Gavins Point Release of 160,000 cfs ...................................................... 2-74 List of Figures xi SECURIT¥-RELATEB INFORMATION 'VITttHOLD UNBER 16 CFR 2.996

SEOURIT¥*REU<f!B INl-6RMJ!ltfl6N - WITHHOLB UNB!ff 16 CI-R 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.2-9: PMF Hydrographs for 2-0 Model Upstream Boundary RM 556.16 .................................................................... 2-75 Figure 2.2-10: PMF Downstream Boundary Condition Rating Curve RM 510.03....................................................................2-76 Figure 2.2-11: Study Area Overview for the 2-0 Model........................................................................................................... 2-77 Figure 2.2-12: Spatial Distribution of Land Use Classes to Determine Manning's Roughness Coefficients ............................ 2-78 Figure 2.2-13: Computational Mesh Overview ..................................................................................*..................................... 2-79 Figure 2.2-14: Computational Mesh Near CNS....................................................................................................................... 2-80 Figure 2.2-15: 2-0 Model Inflow Hydrographs......................................................................................................................... 2-81 Figure 2.2-16: Comparison of Discharge Hydrographs through the Study Reach...................................................................2-82 Figure 2.2-17: Contours of Maximum Water Surface Elevation for PMF Event - Large Scale................................................ 2-83 Figure 2.2-18: Contours of Maximum Water Surface Elevation for PMF Event- Small Scale ................................................ 2-84 Figure ~*2:.19: Contours of Maximum Depth for PMF Event- Overview.......................:***********...............................................2-85 Figure Z:2-20: Contours of Maximum Depth for PMF Event- Small Scale.............................................................................2-86 Figure 2.2-21: Contours of Maximum Velocity for PMF Event- Small Scale ..........................................................................2-87 Figure 2.2-22: Fetches from Embankment Points of Interest .................................................................................................. 2-88 Figure 2.2-23: Labeled Points of Interest ................................................................................................................................2-89 (bJ(3) 1 U '> C. § 8240 Figure 2.2-24: -1(d) (b)(4) (b)(7)(F) and Locations of Interior Runup Calculations ...*.........................................................2-90 Figure 2.2-25: Expected Maximum Extent of Wave Runup at Representative Locations........................................................ 2-91 Figure 2.3-1 : Non-System Dams Downstream of Gavins Point Dam ............................*....................................*.................. 2-134 Figure 2.3-2: Remaining Non-System Dams Downstream of Gavins Point after Screening Inconsequential Dams ............. 2-135 t~~E~/fJ;(~} Figure2:3-3:HEt>HMS*Plan*for*MissourrRiverbet~ to Omaha, l',IE....................................................2-136 Figure 2.3-4: HEC-HMS Plan for Missouri River from Omaha, NE to CNS ...........................................................................2-137 (b)(3) 16 Figure 2.3-5: Dam Failure Hydrographs at u s c § Dam due to System Hydrologic Dam Failure ................................ 2-138 824o-1(d)

Figure 2.3-6: Dam Failure Hydrographs at (b)t4) (b,i7J Dam due to System Sunny-Day Dam Failure ...............................2-139

~b~(il~~ (~}~{~)*~.ig~r1:1 ?}:?: §t:!!~cted pam Fail1Lr.eJ:iY-dtographs am due to System Dam Failure ...................................2-140 (4) (b)(7)(F) Figure 2.3-8: Land Use Classes Used for Manning's Roughness Coefficient ....................................................................... 2-141 Figure 2.3-9: Estimated Peak Stage at CNS due to Non-System Dam Failure ..................................................................... 2-142 Figure 2.3-10: Estimated Peak Stage at CNS due to System and Non-System Dam Failure ..*............................................2-143 Figure 2.3-11 : Estimated Peak Discharge at CNS due to System and Non-System Dam Failure ........................................2-144 Figure 2.3-12: Study Area Overview .....................................................................................................................................2-145 Figure 2.3-13: Computational Mesh Overview ......................................................................................................................2-146 List of Figures , .../

xii ( \

Sorgont jLundy ' 1 c

);

seeURIT¥-REU<TEB INF6RM1'Tl6N - Vrlfl l~IOLD UNBER 18 CFR 2.998

S!CUfflT'(-ftl!LATl!O INfiOftMATION - WITHHOLE> UNE>Eff 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD Rl!l!VALUATION REPORT Project No.: 11784*017 Figure 2.3-14: Computational Mesh Near CNS ..................................................................................................................... 2-147 Figure 2.3-15: Building Roof Elevations Included in Model (ft NAVD88) ............................................................................... 2-148 Figure 2.3-16: Model Boundary Condition Location and Type ..............................................................................................2-149 Figure 2.3-17: Discharge Hydrographs for Upstream Boundary and Stage Hydrograph for Downstream Boundary J * *1-~~~~l~~~(~)~(~)

Hydrologic Failure ..................... ..............................................................................................................................2-150(4) (b)(7)(F)

Figure 2.3*18: Discharge Hydrographs for Upstream Boundary and Stage Hydrograph for Downstream Boundary J . . . . j ~b~~~~~~)s(~)

Sunny-Day Failure ..................................................................................................................................................2-151 (4) (b)(7)(F)

Figure 2.3-19: Site Monitoring Points forWSEL Depth and Velocity During Dam Failure Events .........................................2-152 31 6

Figure 2.3-20:l\~)~ ~ I Hyd. Failure - Overview of Velocity Magnitude at 1/10/3000 20:30 (time of maximum velocity with WSEL above plant flood protection elevation at Point 11) ......................................................................................2-153 (b)(3)16USC

§ 824o.1(d}(b} Figure2;3"2t

I I Hyd. Failure- Mid-Level View of Velocity Magnitude at 1/10/3000 20:30 (time of maximum velocity (4), (b)(7)(F) with WSEL above plant flood protection elevation at Point 11) ...............................................................................2-154

~b~~l~~{~)~(;} Figure.2.,a.22{ *** * ... ! Hyd. Failure - Site-Level View of Velocity Magnitude at 1/10/3000 20:30 (time of maximum velocity (4) (b)(l)(F) with WSEL above plant flood protection elevation at Point 11) ................................................:..............................2-155 Figure 2.3-23 CT)~3b1; Hyd. Failure - WSEL Overview at 1/11/3000 20:20 (time of max. WSEL at Site) ..........................2-156 l24o-1 (d)

Flgure 2.3*24.J(b)(

4) (b) Hyd. Failure - WSEL Mid*Level View at 1/11/3000 20:20 (time of max. WSEL at Site) .................2-157 Figure 2.3-25: (l)(F) Hyd. Failure - WSEL Site-Level View at 1/11/3000 20:20 (time of max. WSEL at Site).................2-158 Figure 2.3-26: WSEL with Fetch Overlay ..............................................................................................................................2-159 Figure 2.3-27: Fetch Directions for Waves Approaching Plant East and Plant West ............................................................2-160 Figure 2.3-28: Fetch Directions for Waves Approaching Plant North and Plant South .......................................................... 2-161 Figure 2.3-29: Plan View of Pressure Calculation Surfaces for j~l( (ii,4) (b)(l)(F) 40* 1 ....................................................2-162 Figure 2.3-30: Groundi::over in Vicini of CNS......................................................................................................................2-163 (b)(3) 1 Figure 2.3*31 : Inundation Map for u Sc § Hydrologic Dam Failure Scenario (Large-Scale Map) ..................................... 2-164 82401 Figure 2.3-32: Inundation Map for (d) (b) Hydrologic Dam Failure Scenario (Medium-Scale Map) .................................2-165 (4) (b)(7)

Figure 2.3*33: Inundation Map for (F) Hydrologic Dam Failure Scenario (Small-Scale Map) ..................................... 2-166 Figure 2.3-34: Bridge Location Map ...................................................................................................................................... 2-167 Figure 2. 7-1 : Hydrologic Unit Code (HUC) for Different Watersheds Upstream and Downstream of the Site ....................... 2-175 Figure 2.8-1: 1879 Land Cover .............................................................................................................................................2-185 Figure 2.8*2: 1940 Aerial Photography.................................................................................................................................. 2-186 Figure 2.8-3: 1965 Aerial Photography..................................................................................................................................2-187 Figure 2.8-4: 1993 Aerial Photography..................................................................................................................................2-188 Figure 2.8-5: 1999 Aerial Photography.................................................................................................................................. 2-189 List of Figures ,.,,/,'

xiii \ \.

Sargent &;Lundy 1 ~c

),,

SECURIT¥-RELATEE> INFORMATION - WITHHOLE> UNE>Eft 16 CFff 2.396

9ECUR:IT¥-R:ELATED INFORMATION - WITtt~tOLD UNDER: 18 CFR: 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784*017 FLOOD HAZAR.D REEVALUATION REPORT Figure 2.8-6: 2003 Aerial Photography..................................................................................................................................2-190 Figure 2.8-7: 2005 Aerial Photography..................................................................................................................................2-191 Figure 2.8*8: 2010 Aerial Photography..................................................................................................................................2-192 Figure 2.8-9: Hydric Soils ......................................................................................................................................................2-193 Figure 2.8-10: Geomorphic Soil Description ..........................................................................................................................2-194 Figure 2.8-11: Soil Textures ..................................................................................................................................................2-195 Figure 2.8-12: 2011 Landsat Thematic Mapper Surface Reflectance On-demand ...............................................................2-196 Figure 2.8-13: 2012 Aerial Photography................................................................................................................................ 2-197 Figure 2.8-14: 2011 Flood Breach Locations ........................................................................................................................2-198 List of Figures xiv .. \

SurgcM~ & ! Luncty 1 ,.:

SECURIT'f-R:ELATED INFORMATION - 'NITliHOLD UNDER 18 CFR: 2.998

SECURIT'1'*RELATEO INfiORMATION - WITHHOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION Rl!PORT Project No.: 11784-017 LIST OF ACRONYMS AND ABBREVIATIONS Acronym or Abbreviation Explanation 1-, 2-, 3-D one-dimensional, two-dimensional, three-dimensional ac acre ac-ft acre-feet ACES Automated Coastal Engineering System AEC U.S. Atomic Energy Commission AEP annual exceedance probability ANS American Nuclear Society ANSI American National Standards Institute ASCIE American Society of Civil Engineers BSNP bank stabilization and navigation project BWR boiling water reactor CFR Code of Federal Regulations CEDAS Coastal Engineering Design & Analysis System CEM Coastal Engineering Manual cfs cubic feet per second CLB Current Licensing Basis CNS Cooper Nuclear Station COL combined operating license CRREL Cold Regions Research and Engineering Laboratory DEM digital elevation model ERP Elevated Release Point ESP early site permit ESPA early site permit application ESRI Environmental Systems Research Institute FEMA Federal Emergency Management Agency FHR flood hazard reevaluation List of Acronyms and Abbreviations ,,,.:-;'

xv Sorge~~ Lundy '

) -*

SECURIT¥-RELATED INFORMATION - WITHHOLD UNDER 16 CI-R 2.996

SECURIT¥*RELATEC, INFORMATION - 'NITHHOLB UNBER 16 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Acronym or Abbreviation Explanation FIS flood insurance study ft feet fps feet per second FSAR Final Safety Analysis Report GI Generic Issue GIS geographical information system HEC-HMS Hydrologlc Engineering Center Hydrologic Modeling System HEC-RAS Hydrolog!c Engineering Center River Analysis System HHA Hierarchical Hazard Assessment spectral significant wave height HMR Hydrometeorological Report hr hour HTab Hydraulic Table HU hydrologic unit HWM high-water mark in Inch in/hr inch per hour IPEEE Individual Plant Examination for External Events ISFSI Independent Spent Fuel Storage Installation ISG Interim Staff Guidance kips 1,000-pound force lb pound LiDAR Light Detection and Ranging LIP Local Intense Precipitation LOB Left Overbank m meter mi mile min minute List of Acronyms and Abbreviations I \

xvi S.argor\~ ~ j Lundy I l c SECURIT¥-RELATED INFORMATION - WITHHOLB UNBER 16 CFR 2.996

SECURIT¥-REUcfED INl'OptMATION - WITI II IOLB UNBER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Acronym or Abbreviation Explanation mph mile per hour MPF Multi-Purpose Facility MSL mean sea level MWe megawatt electric MWt megawatt thermal NAVD88 North American Vertical Datum of 1988 NCDC National Climatic Data Center NCHRP National Cooperative Highway Research Program NDNR Nebraska Department of Natural Resources N°EmbE north embankment east NGVD29 National Geodetic Vertical Datum of 1929 NID National Inventory of Dams NLSWE Non-linear Shallow Water Equation NOAA National Oceanic and Atmospheric Administration NPPD Nebraska Public Power District NRC U.S. Nuclear Regulatory Commission NRCS Natural Resources Conservation Service NSE Nash-Sutcliffe efficiency coefficient NTTF Near-Term Task Force NWS National Weather Service PA Protected Area PBL planetary boundary layer PMF Probable Maximum Flood PMP Probable Maximum Precipitation PMT Probable Maximum Tsunami psf pound per square foot RCIC Reactor Core Isolation Cooling RHR Residual Heat Removal List of Acronyms and Abbreviations xvii ' .

Sargo~ fi;,.) Lundy 11 a:

J, SECURIT¥-RELATEB INFORMATION - \VITI II IOLB UNBER 18 CFR 2.998

SE6URIT¥-REt:Al'eo INfiORM>\l'ION - rtfll'HHOLE> UNE>ER 16 eFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT Acronym or Abbreviation Explanation RG Regulatory Guide RM River Mile ROB Right Overbank scs Soil Conservation Services SER Safety Evaluation Report SGTS Standby Gas Treatment System SSC structure, system, and component Tp peak wave period tpd tons per day UMRSFFS Upper Mississippi River System Flow Frequency Study USAGE U.S. Army Corps of Engineers USAGE-OD USACE Omaha District USAR Updated Safety Analysis Report USBR United States Bureau of Reclamation USCG United States Coast Guard USDA United States Department of Agriculture USGS United States Geological Survey VBS vehicle barrier system WEmbN west embankment north WEmbS west embankment south WEmbW west embankment west WRF width reduction factor WSEL water surface elevation List of Acronyms and Abbreviations xviii Sorg0_;t,& Lundy 11 Q

', I SE6UfUT'f -RELATED INFORM1'TION - WITI II IOLD UNDER 18 CFR 2.998

8ECURl'fY-REUlc'fEB INfiORMA'flON - Wl'fHHOLB UNBER 16 CfiR 2.996 Nebraska Plllblic Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 INTRODUCTION / PURPOSE Following the accident at the Fukushima Dai-ichi nuclear power plant resulting from the March 11 ,

2011 , Great Tohoku Earthquake and subsequent tsunami, the U.S. Nuclear Regulatory Commission (NRC) established the Near-Term Task Force (NTTF). The NTTF Charter tasked the NTTF with conducting a systematic and methodical review of NRC processes and regulations to determine if the agency should make additional improvements to its regulatory system. Ultimately, a comprehensive set of recommendations was developed.

In response to the NTTF recommendations and pursuant to Sections 161.c, 103.b, and 182.a of the Atomic Energy Act of 1954, as amended, and Title 10 of the Code of Federal Regulations (10 CFR),

Section 50.54(f), the NRC has requested information from all operating power plant licensees. The purpose of the request is to gather information to:

Reevaluate seismic and flooding hazards at U.S. operating reactor sites.

Eacilitate the U.S. Nuclear Regulatory Commission's (NRC) determination if there is a need to update the design basis and structures, systems, and components (SSCs) important to safety to protect against the updated hazards at operating reactor sites.

Address Generic Issue (GI) 204 regarding flooding of nuclear power plant sites following upstream dam failures.

The information request relating to flooding hazards requires licensees to reevaluate their sites applying present-day regulatory guidance and methodologies being used for early site permit (ESP) and combined operating license (COL) reviews, including current techniques, software, and methods used in present-day standard engineering practice to perform the flood hazard studies. The results are compared against the site's current licensing basis (CLB) for protectiotn and mitigation from external flood events.

This report describes the flooding reevaluation performed for Cooper Nuclear Station (CNS). This report satisfies the information requested by Enclosure 2 (Recommendation 2.1: Flooding) of U.S. NRC letter, Request For Information Pursuant To Title 10 Of The Code Of Federal Regulations 50.54(()

Regarding Recommendations 2.1, 2.3, And 9.3, Of The Near-Term Task Force Review Oflnsights From The Fukushima Dai-Ichi Accident, dated March 12, 2012 (Reference 1.7-1 ).

Introduction I Purpose __,,.

xix Sarge'\ ~\ Lundy' "

,,v*

8EOURIT¥*RELATED INFORMATION - Wl'fHHOLB UNDER 16 CfiR 2.996

9ECURIT¥-RELATEE> INFORMATION - WITHHOLE> UNE>ER 16 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZA'RD REl!VALUATION REPoRT

1. SITE INFORMATION RELATED TO THE FLOOD HAZARD 1.1 DETAILED SITE INFORMATION Cooper Nuclear Station (CNS) is located on the Nebraska portion of a 1,090-acre (ac) site (Reference 1.7-2, Section 1.1) in Nemaha County, Nebraska and Atchison County, Missouri.

The plant, located approximately 55 miles (mi) south-southeast of Omaha, Nebraska and 100 mi north-northwest of Kansas City, Kansas, is on the west bank of the Missouri River at River Mile (RM) 532.5 located midway between the villages of Brownville and Nemaha, Nebraska. ArcMap was used to show the location of the plant (see Figure 1.9-1 ). This portion of the Missouri River is referred to as the Lower Brownville Bend. The U.S. Army Corps of Engineers (USACE) has stabilized the channel near the plant using pile dikes and bank protection. This control prevents meandering of the river within the alluvial flood plain (Reference 1.7-3, Section 4.1).

The Missouri River flows past the site in a southeaster1y direction under open-river conditions, there being no downstream dams to control the stage of the river. In the vicinity of CNS, levees with crest elevations of approximately 902 feet (ft) mean sea level (MSL) control the river section during flood stages. River flow is controlled by a series of flood control dams on the upper Missouri River, which are operated by the USACE for a number of authorized purposes, including flood control, navigation, irrigation, power, water supply, water quality control, recreation, and fish and wildlife. The Platte River (see Figure 1.9-2) is a major source of flow and joins the Missouri River south of Omaha, Nebraska.

Maximum water surface elevation (WSEL) at the CNS site, as reported by the USACE, was 899 ft MSL in 1952 prior to the installation of the upstream control dams. Peak flood flow In 1952 was 414,000 cubic feet per second (cfs), which would have been reduced to approximately 100,000 cfs if today's controls had been in place at that time.

The site coordinates are approximately 40° 21' north latitude and 95° 38' west longitude (Reference 1.7-4, Chapter II, Section 2.1). See Figure 1.9-1, Figure 1.9-3, and Figure 1.9-4 for various views of the plant.

1.1.1 Site Layout CNS consists of a single boiling water reactor (BWR) with a capacity of 835.5 megawatt electric (MWe) / 2,419 megawatt thermal (M\/Vt) and first went into service on July 1, 1974 (Reference 1.7-4, Chapter I, Section 1.0).

The principal! structures of the station consist of the Reactor Building, Turbine Building (including service area appendages), Control Building, Radwaste Building, Augmented Radwaste Building, Intake Structure, Diesel Generator Building, Drywall and Suppression Chamber, Miscellaneous Circulating Water System Structures (e.g., circulating water conduits, seal well, etc.). (See Reference 1.7-4,Section XII.) Aside from the Intake Structure, the nearest building to the river channel edge is approximateliy 200 ft away (Reference 1.7-5, Section 2.1).

Site lnformatio*n Related to the Flood Hazard 1-1 9ECURIT¥-RELATEE> INFORMATION - WITHHOLE> UNf>ER 16 CFR 2.996

SECUR:IT¥-R:ELATEI:> INFOR:MATION - W1ITHHOLD UNDER: 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-01 7 1.1.2 Spatial Data Sets Elevations in Section 1 are referenced to MSL for consistency with the CNS Updated Safety Analysis Report (USAR}. In this context, MSL is equated to Plant Datum and Is distinct from other geodetic vertical datums. Reference 1.7-3 notes that Plant Datum is the same datum used in the USAR.

1.1.3 Elevation of Structures, Systems, and Components (SSCs)

The station site grade level of 903 ft MSL has been raised 13 ft above the natural grade level of 890 ft MSL, In order to bring final grade 1 ft above the existing 902 ft MSL levee constructed by the USACE (Reference 1.7-4, Chapter II, Section 4.2.2.2).

The levee is situated at a nominal elevation of 902 ft MSL. The finished floor elevation is given as 903.5 ft MSL for all Class I structures (Reactor Building, Turbine Building, Diesel Generator Building, Control Building, Radwaste Building, Intake Structure and Controlled Corridor). The Z-Sump is at 890 ft MSL, and the Elevated Release Point (ERP) tower foundations are at 891 ft MSL (Reference 1.7-3, Section 4.0).

1.1.4 Topography Prior to the construction of CNS, the site was nearly flat with only one or two feet of relief over the majority of the area. General grade elevation was approximately 890 ft MSL. A bluff, approximately 150 ft above the floodplain, running north-south, is located about one mile west of the river near the plant area. An earthen levee parallels the west (right) river bank at a distance of approximately 500 ft.

Surface drainage of the site was poor because of the lack of natural relief. The levee also inhibits surface runoff from the area behind the levee to the river (Reference 1.7-6, Section 2.2).

Federal Levee R548 is adjacent to the CNS main plant area. The top elevation of the levee near the site is approximately 902 ft MSL, 1 ft below the nominal plant grade of 903 ft MSL. The levee extends north of the plant, where it terminates at the higher ground near the bluffs. South of CNS, the levee follows the right bank of the Missouri River, curving around to the west and running parallel to the left bank of the Nemaha River, which is a tributary to the Missouri River, and turning north where it meets the higher ground near the town of Nemaha. The top elevation of the levee varies from approximately 902 ft MSL near CNS to approximately 897 ft MSL on the southern end, with top elevations of the levee as low as 894 ft MSL locally, The area enclosed by the levee and the higher bluffs to the west Is 4000 ac (Reference 1.7-7, Section 5.1.8).

1.1 .5 Missouri River and Tributaries The Missouri River Basin drains 529,000 square miles (mi2), including about 9,700 mi2 located in Canada. The Basin spans 10 states, including all of Nebraska, most of Montana, Wyoming, North Dakota, and South Dakota; about half of Kansas and Missouri; and smaller parts of Iowa, Colorado, and Minnesota. The Missouri River is fed from several major tributaries, including the Yellowstone, Platte, Kansas, Grand, and Osage Rivers. The Missouri River extends 2,619 mi from its uppermost source at Browers Spring on Hell Roaring Creek and 2,321 mi from Three Forks, Montana, where the Site Information Related to the Flood Hazard 1-2 SECUR:ITY:-RELATED INFORM1'TION - WITI-IHOLD UNl:>ER 16 CF~ 2.996

SECURITY-RELATEB INI-ORMATION - 'filTI UIOLB UN BER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Jefferson, Madison , and Gallatin Rivers converge. The Missouri River is the longest river in the United States, draining one-sixth of the country. The Missouri River Mainstem System (System) consists of six dams and reservoirs on the Missouri River located in Montana, North Dakota, South Dakota, and Nebraska. The six System dams are Fort Peck Dam in Montana; Garrison Dam in North Dakota; Oahe Dam, Big Bend Dam, and Fort Randall Dam in South Dakota; and Gavins Point Dam in South Dakota and Nebraska. The System has a capacity to store 73.1 million acre-feet (ac-ft) of water, which makes it the largest reservoir system in North America. Runoff from upstream of the System is stored in the six reservoirs. Water is released from the System as needed for downstream flow support. Released water from the most downstream dam in the System, G1;1vins Point Dam, flows down the Missouri River, which includes the Bank Stabilization and Navigation Project (BSNP) from Sioux City, Iowa to the mouth near St. Louis, Missouri (Reference 1.7-8 and Figure 1.9-5).

The location of six System dams is noted in Table 1.8-1. There are no dams or similar structures on the Missouri River downstream of the plant site. (See Figure 1.9-2 and Figure 1.9-5 and Reference 1.7-4, Chapter II, Section 4.2.2.1.)

Site Information Related to the Flood Hazard ,.,,

i' ... \\

1-3 Smr gor\~, Sa; Lundy

1 *

~ ***

SECURIT¥-RELATEB INI-ORMATION - WITI II IOLB UNBER 18 CPR ! .398

SECURIT'a'*RELATED INFORMJfcTION - 1t'VITHHOLE> UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT 1.2 CURRENT DESIGN BASIS FLOOD ELEVATIONS This section summarizes key flood and plant information found in the CNS USAR.

1.2.1 Summary of CNS External Flood Design and Licensing Basis The flooding Design Basis of CNS consists of the Final Safety Analysis Report (FSAR) and FSAR questions, which used USACE studies. The CNS flooding Licensing Basis consists of the Safety Evaluation of the Cooper f-:Juclear Station (SER).

1.2.1.1 Flood Levels (FSAR/USAR)

Information on riverine flooding in the CNS USAR is based on independent studies performed by the USACE and by the U.S. Atomic Energy Commission (AEC). Information from the USAGE study is summ13rized in the USAR and its predecessor, the FSAR. The AEC study is summarized in the CNS SER. These studies are discussed in subsequent sections of this report.

The projected upper limit of elevation for a.1,000-year flood discharge is 900 ft MSL and for a 10,000-year flood discharge is 902 ft MSL. The Probable Maximum Flood (PMF) is established at 903 ft MSL with a projected return frequency estimated to be in excess of 1,000,000 years. The PMF is derived by centering a probable maximum rainstorm critically over the drainage a,rea above Brownville. The USACE has estimated that the peak discharge for the PMF is 600,000 cfs (Reference 1.7-4, Chapter II, Section 4.2.2.1). This estimate is based on a qualitative judgment that the peak of a PMF event should be between two to three times the peak of a standard project flood. Preliminary estimates of standard project conditions on the Missouri and Platte Rivers were used in estimating the PMF peak of 600,000 cfs at CNS (Reference 1.7-4, Chapter II, Section 4.2.2.1 and Reference 1.7-9). Table 1.8-3 summarizes the approximate drainage area (mi2) for locations of interest along the Missouri River.

The effects of a sustained wind in conjunction with a PMF were evaluated by USACE using the procedures described in the U.S. Army Coastal Engineering Research Technical Report 4. Assuming a 45-mile per hour (mph) overwater wind speed and a 903 ft MSL PMF WSEL, the significant shallow-water wave height was computed to be 4.0 ft. The 1% wave height was computed to be 6.7 ft. The runup was computed to be 6. 7 ft on a smooth vertical wail located in shallow water and 4.8 ft on a one-on-three riprapped slope. The fetches are of sufficient length that the above waves could be generated with winds from the north through east through south. It should be noted, however, that these wave height values are based on relationships derived from studies made 011 lakes and oceans, and it is believed that the same parameters would not produce waves as high as those computed above in highly turbulent, fast-flowing river flood waters (Reference 1.7-4, Chapter 11, Section 4.2.2.1 and Reference 1.7-18).

The wave action, as mentioned above, will not affect the plant proper since the nearest building is located about 200 ft from the river edge and is surrounded by grade to elevation 903 ft MSL. Wave energy would be dissipated before reaching any of the main buildings. Wave action at the Intake Structure will not affect the safe shutdown of the plant since the service water pumps and controls are Site Information Related to the Flood Hazard ,*/

1-4 Sorgont I '

' &' l.Ltncty1,ci

,,.\ J SECURIT¥-RELATED INFORMJfcTION - WITHHOLD UNDER 16 CFR 2.996

9ECURIT¥-RELATEB INFORMATION

WITI II IOLB UN BER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION R90RT Project No.: 11784-017 protected by massive reinforced concrete walls and slab up to elevation 919 ft MSL (Reference 1.7-4, Chapter II, Section 4.2.2.2 and Reference 1.7-18).

Flooding caused by ice blockage is considered credible only at river levels significantly lower than the PMF. Flooding caused by ice blockage would cause water surface elevations below those of the PMF.

(Reference 1.7-4, Chapter II, Section 4.2.2.1.)

The failure of a large upstream dam is not considered probable. These dams are massive earthen structures with impervious core walls, large freeboard for wave action, and adequate spillways. The dams are located in a zone of low seismic activity. The Gavins Point Dam, closest dam to the site, is over 275 mi upstream (Reference 1.7-4, Chapter 11, Section 4.2.2.1).

These dams are under constant inspection by local USACE personnel and are inspected once a year by a team of professionals. If seismic failure occurred in spite of these circumstances, the failure would most probably be caused by other than instantaneous failure of a major portion of the dam. Under these circumstances, overtopping of Gavins Point Dam, although conceivable, is not likely to occur (Reference 1.7-4, Chapter 11, Section 4.2.2.1).

1.2.1.2 USACE Study The USACE estimated a PMF elevation between 902 ft MSL and 903 ft MSL at CNS. This is based on a Probable Maximum Precipitation (PMP) event occurring upstream of Brownville, Nebraska and a resulting flow rate in the Missouri River of 600,000 cfs. The rainfall event producing this flow rate is described in FSAR Question 2.1 as originating over the Platte River Basin (Reference 1.7-9).

1.2.1.3 AEC Study Safety Evaluation Report The AEC performed an independent PMF study for CNS, which is summarized in the CNS SER. Based on detailed PMF estimates in the general region of the site, AEC staff conservatively estimated the peak PMF discharge to be about 1,000,000 cfs. This estimate was conservatively considered to reflect the total runoff potential represented by the large drainage area downstream of the USACE dams, plus the relatively minor component that could be contributed by releases from these dams. AEC staff concluded that the dams should remain intact during a PMF. Additionally, AEC staff constructed an analytical water surface profile model of the Missouri River from below CNS to the Brownville Bridge a few miles upstream and estimated the PMF still WSEL at the site would be 901 .2 ft MSL. The model was verified by reproducing historical flood high-water marks using estimates of floodplain geometry and flood runoff rates. Coincident wave action induced by an assumed 45-mph wind was estimated to produce a maximum WSEL of 909.2 ft MSL at the Intake Structure and 905 ft MSL on the other exposed safety-related structures. AEC staff did not consider seismically induced dam failure coincident with PMF credible but considered the effects of a seismically induced.failure of one of the largest upstream dams concurrent with flood levels of one half of the PMF and concluded that the water level that could result at CNS is less than the AEC staffs estimated PMF (Reference 1.7-2, Section 2.4.3).

This information has been incorporated into the USAR. (See Section 1.2.1.1 of this report)

Site Information Related to the Flood Hazard 1-5 SECURIT't'-RELATEB INFORMATION - WITI II IOLB UNBER 16 CFR 2.998

SECURITY-RELATED INFORMATION - WITtlHOLD UNDER 16 CFR 2.998 Nebrask.a Public Power District SL-012450 Cooper Nuclear Station

Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 1.2.1 .4 Conclusions The immediate station area grade is at elevation 903 ft Mean Sea Level (MSL). This is 1 ft above the existing levee, and equal to the highest projected level of the maximum probable natural flood.

Therefore, because 903 ft MSL was used in the design of the plant with wave energy dissipating before reaching any of the main buildings, the design basis still WSEL due to Missouri River Flooding is 903 ft MSL (Reference 1.7-4, Chapter 11, Section 4.2.2.1). Wave action at the Intake Structure is possible, but no value is given, as waves will not affect the safe shutdown of the plant since the Service Water pumps and controls are protected by concrete walls up to 919 ft MSL (Reference 1.7-4, Chapter II, Section 4.2.2.2).

In the 1973 SER for CNS, the Atomic Energy Commission (AEC) found that dam failure was less than the calculated value for PMF. The United States Army Corps of Engineers later stated that though failure of an upstream dam is considered improbable, the resulting stage of the river at CNS (assuming the most critical combinations of timing) would be approximately elevation 905-906 ft MSL (Reference 1.7-4, Chapter II, Section 4.2.2.2). This value was determined after the $ite had been designed, and after the SER had confirmed that the dams remain intact after a PMF, and that a seismic event does not exceed the staff estimated PMF. Therefore, 906 ft MSL is the Current Licensing Basis (CLB) for dam break.

1.2.2 CLB Local Intense Precipitation (LIP)

From Hydrometeorologlcal Report No. 33 (HMR-33) dated April, 1956 by the U.S. Department of Commerce-Weather Bureau and the USACE (Reference 1.7-10), it was determined that the PMP for the CNS site area is 23.5 inches (in) total rainfall for a 24-hour period. This bounding PMP value was obtained from HMR-33 Figure 17 (August). (See Reference 1.7-4, Chapter 11, Section 3.1.3). An independent evaluation by the AEC determined that the PMP 1-hour rainfall rate was 9.7 in per hour (Reference 1.7-2, Section 3.4).

Class I and Class II buildings are protected from the effects of precipitation through the use of roof drains and overflow scuppers. The Reactor Building, Diesel Generator Building, and Control Building use 4-in roof drains and 6-in scuppers. The remaining local site drainage is designed such that any excess rainfall not immediately absorbed into the ground will flow away from the buildings to be discharged into drywells or low lying areas adjacent to the plant site. Therefore, this configuration can safely remove the accumulated water from the PMP rate described in the USAR, Chapter II, Section 3.1.3, and can also accommodate the 9.7 in per hour (Reference 1.7-11 and Reference 1.7-4, Chapter 11, Section 3.2.3) rate estimated by the AEC without adverse effects on the safety-related systems necessary for safe shutdown (Reference 1.7-4, Chapter II, Section 3.2.3).

1.2.3 CLB Flooding In Streams and Rivers Refer to Section 1.2.1.

Site Information Related to the Flood Hazard ,,

(*"{

1-6 ' ~\ Lundy c S org ant:

)

SECURITY-RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.396

SECURITY-RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT 1.2.4 CLB Dam Breaches and Failures The USAR (Reference 1.7-4, Chapter II-, Section 4.2.2.1) notes that a dam failure was not considered a credible event. The maximum expected still water level at the site associated with a postulated dam failure was 906 ft MSL, with a minimum warning time of three days (Reference 1.7-4, Chapter II, Section 4.2.2.2). No associated effects (wind-wave, debris, etc.) were considered in the dam failure scenario.

1.2.5 CLB Storm Surge The CLB is silent on flooding effects from storm surge. However, due to its location, the storm surge flooding mechanism can be scree,ned out for CNS.

1.2.6 CLB Seiche The CLB is silent on flooding effects from seiche. However, due to its location, the seiche flooding mechanism can be screened out for CNS.

1.2.7 CLB Tsunami The CLB is silent on flooding effects from tsunami. However, due to its location, the tsunami flooding mechanism can be screened out for CNS.

1.2.8 CLB Ice-Induced Flooding Flooding caused by ice blockage is considered credible only at river levels significantly lower than the PMF. Flooding caused by ice blockage would produce WSELs below those of the PMF (Reference 1.7-4, Chapter II, Section 4.2.2.1). Thus, the CLB does not include quantitative parameters for ice-induced flooding, but the ice-induced flooding effects are bounded by the PMF.

1.2.9 CLB Channel Migration or Diversion The CLB discusses this mechanism only with respect to channel migration away from the site due to levee failure on the opposite river bank and the potential loss of the heat sink. Channel migration toward the site was not considered credible.

Changes in river alignment have occurred in the past as a result of meteorological events. The river channel at present is stabilized as a result of permanent revetments constructed under the supervision of the USAGE over a number of years; thereby, making It extremely unlikely that the river would be diverted at Brownville Bend. If, however, in spite of these controls, the river should be diverted, it would most likely occur as a result of the failure of a major upstream dam - either Oahe Dam or Fort Randall Dam, although dam failure is not considered credible in the CLB. The closer of the two dams, Fort Randall Dam, is almost 350 mi upstream from the plant site and there would be a three-day warning before the river reached a peak flood stage at CNS. While the river is at peak flood stage at the site, the postulated diversion of the Missouri River might occur upstream. During peak flood stage, reactor shutdown procedures could begin and continue as the flood water slowly receded. With the river Site Information Related to the Flood Hazard ,...,,,*

1-7 S u r"ga;,~ &4 Lundy 1 lc SECURIT¥-RELATEE> INFORMATION - WITf*ltlOLE> UNE>ER 18 CFR 2.998

SECUR:l'TY-R:El:Al'ED INFOR:MA:l'ION - 1'Vll'~IHOLD UNDER: 16 CPR: 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No,: 11784*017 diverted and the flood waters fully receded, what might remain in front of the Intake Structure would be a large body of still water cut off from the upstream flow and possibly cut off at a point downstream.

After the river diversion occurs, the resulting isolated body of water in the vicinity of the site, fed by groundwater inflow, would retain essentially the same stage characteristics that apply to the current open river as long as the main channel were retained in the existing valley. It was concluded that there would be an adequate supply of water to affect a safe shutdown of the plant (Reference 1.7-4, Chapter II, Sections 4.2.3.1 and 4.2.3.2). The AEC concurred with these findings in the CNS SER, which states that it was considered unlikely that major channel diversions would occur (Reference 1.7-2, Section 2.4.5).

1.2.10 CLB Combined Effects Combined effects of different flood-causing mechanisms are discussed in Section 1.2.1 through 1.2.8, where applicable.

1.2.11 CLB Associat_ e d Effects Section 9 of Reference 1.7-12 defines "Flood height and associated effects" as:

The maximum still WSEL plus the following factors:

Wind waves and runup effects.

Hydrodynamic loading, including debris.

Effects caused by sediment deposition and erosion.

Concurrent site conditions, including adverse weather conditions.

Groundwater ingress.

Other pertinent factors.

1.2.11.1 Wind Waves and Runup Effects The CLB values for wind waves and runup is 909.2 ft MSL at the Intake Structure and 905 ft MSL for other exposed safety-related structures (Reference 1.7-4, Chapter II, Section 4.2.2.2).

1.2.11.2 Hydrostatic and Hydrodynamic Loads The principal structures are designed to withstand hydrostatic loads up to the flood protection level of 906 ft MSL with margin (Reference 1.7-4, Chapter II. Section 4.2.2.2).

The CLB is silent on hydrodynamic loads.

1.2.11.3 Debris Loads The CLB is silent on flooding debris loads (Reference 1.7-4); however, the CLB does discuss a runaway barge (Reference 1.7-4, Chapter II, Section 4.3).

Site Information Related to the Flood Hazard 1-8 SECURIT¥-RELATED INFORM>\TION - WITHHOLB UNEJER: 16 CFft 2.996

SECURIT¥*RELATEB INFORMA'flON - WITltHOLB UNBER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 In summary, the Intake Structure and Class I equipment located inside are qualified to withstand a barge impact. Additionally, a barge that impacts the Intake Structure guide wall will, therefore, have little if any effect on plant operations.

1.2.11.4 Erosion and Sedimentation Effects of erosion and sedimentation during extreme flooding events are not analyzed in the CLB.

1.2.11.5 Concurrent Site Conditions The CNS CLB (Reference 1.7-4) does not specifically discuss evaluation of concurrent site conditions.

1.2.11.6 Groundwater Ingress The CNS CLB does not specifically address or quantify groundwater in-leakage from the site subsurface water table. Groundwater level Is monitored/logged once per shift based on level indicators located wi'.hin site well(s) providing plant water supply. According to CNS personnel, site groundwater level normally fluctuates between 875 ft MSL to 885 ft MSL with the highest recorded level of 900.8 ft MSL during the May 2011 Missouri River flood event (Reference 1.7-5, Section 3.7).

1.2.11.7 Other Pertinent Factors The Maintenance Procedure directs the CNS maintenance personnel in the installation of temporary flood control barriers and features. The procedure provides a system of primary barriers at the openings of the outside walls of the Main Building Complex to seal the buildings up to elevation 906 ft MSL. Secondary barriers are provided strategically inside the buildings to control any minor leakage past the primary barriers and to segregate the building complex into small areas that can be more easily protected (Reference 1.7-5, Section 3.5.)

Site Information Related to the Flood Hazard

.-* \

1-9 Sargo4 ~ Lun.-... ... c

~) - Y

/

SECUR:ITY-RELATEB INFORM:1'%l'ION - 'lt1ll'ttl IOLB UNBER: 16 CPR 2.396

SECURIT¥-RELATEE> INFORMATION - 1VITHHOLE> UNE>ER 16 Cf-ff 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 1.3 FLOOD-RELATED CHANGES AND FLOOD PROTECTION CHANGES The plant design features and their functional requirements that provide protection against the design basis external flood mechanisms are provided in the USAR (Reference 1.7-4). The credited flood protection related attributes of the overall plant configuration that support the design for mitigation against external flooding have not changed from the time of initial lieensing. Enhancements to procedural guidance supporting tlhe implementation of protective actions against external flooding have been made over time. The temporary barriers deployed in Procedure 7.0.11 (Reference 1.7-13) now consist of engineered flood barriers. The use of these barriers, instead of the original sandbag barriers, has resulted in a significant reduction of the barrier deployment time and effort.

Changes to the hydrosphere around the CNS site and physical changes to the CNS site (e.g., security changes, buildings, etc.) are discussed in Section 1.4 of this report.

Site Information Related to the Flood Hazard ,*<'

1-10 ( \

Sargent & , Lunctyt tO

.,.}..*,/

SECURIT¥-RELATEE> l~Nf-ORMATION - 'NITHHOLE> UNE>ER 16 CPR 2.396

SECURIT'f-RELATEE> INFORMATION - VIITHHOLD UNDER 16 CFR 2.396 Nebraska Publlc Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project Na.: 11784-017 1.4 CHANGES TO THE WATERSHED OR TO THE LOCAL AREA As shown in Figure 1.9-6, the river was much wider and further to the east than it is today, as also illustrated in Figure 1.9-7 and Figure 1.9-8. (Reference 1.7-14).

The CNS site is located in the floodplain of the Missouri River at approximate Missouri River Mile 532.5.

As a result of the location, the site is subjected to hydrometeorological events relevant to inland sites.

The Missouri River Basin upstream of CNS and downstream of Gavins Point Dam combined with Platte River Basin, as discussed in Section 2.2 of this report, encompasses approximately 132,657 mi2.

Changes in watershed properties particularly affect the estimation of the PMF and upstream dam failure flooding. It Is expected that watershed characteristics do change through the years, with the expansion of urban areas and change in land use and land cover. However, all of the changes that may have occurred in the past were captured in the current flooding hazard reevaluation. The reevaluation took into account the existing watershed conditions, which were incorporated through the hydrologic and hydraulic model calibration efforts. It should be noted that since the construction and operation of CNS, there has been no major upstream dam or impoundment on the Missouri River or tributaries constructed or proposed.

Any changes in local area that may have occurred in the past, including the vehicle barrier installed for a security measure, were Incorporated in the LIP analysis of the current flooding hazard reevaluation.

(See Section 2.1 of this report.)

Site Information Related to the Flood Hazard 1-11 SECURIT¥-RELATED INFORMATION - WITHHOLD UNl:lER 16 CFR 2.396

SECURIT¥*RELATED INFORM1'TION - 'NlfHHOLB UNBER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-01 7 FLOOD HAZARD REEVALUATION REPORT 1.5 CURRENT DESIGN BASIS FLOOD PROTECTION AND MITIGATION FEATURES The general ground elevation surrounding CNS Class I structures, which corresponds to the PMF event elevation, is elevated 13 ft above the natural floodplain to 903 ft MSL (Reference 1.7-4, Chapter 11, Section 4.2.2.2). The finished floor elevation of all Class I structures is placed at elevation 903.5 ft MSL, or 0.5 ft above the PMF event. These structures were designed for a hydraulic load equivalent to a groundwater elevation of 903 ft MSL and reviewed for integrity for a river elevation up to 906 ft MSL.

Grade level openings on exterior walls of the buildings (except for the Intake Structure) are protected from wave effects and WSELs up to 906 ft MSL with flood barriers erected per CNS Procedures 7.0.11 (Reference 1.7-13) and 5.1, Flood (Reference 1.7-15), as previously discussed in Section 1.2.11 .7 of this report.

The CNS Flood Protection Feature Inspections, in accordance with the request from the U.S. Nuclear Regulatory Commission (NRC) as defined in the Recommendation 2.3, Flooding, Enclosure 4 of the 50.54(f} letter dated March 12, 2012 (Reference 1.7-5) found that the CNS flood protection active and passive feahires, e.g., walls, floors, roofs, penetration seals, doors, check valves, etc., were confirmed to be installed per design, functional, in good material condition, and appropriately controlled procedurally to ensure continued functionality.

The following CNS safety-related plant structures and procedures have been identified as protected from flooding as noted:

Intake Structure The maximum water level on the outside of the Intake Structure of 909.2 ft MSL (PMF plus wave effects) will not affect safe operation of the Service Water pump motors. The Intake Structure is built with a floor elevation of 903.5 ft MSL. The Service Water pump motors are positioned approximately 4.5 ft above the floor and are protected by 24-inch-thick concrete walls to an elevation of 919 ft MSL. Therefore, direct wave action will be dissipated and the water level in the room would be below the elevation of the Service Water pump motors (Reference 1.7-4, Chapter 11, Section 4.2.2.2).

Reactor Building The Reactor Building is protected from wave effects and flood water by grade level building walls and by temporary flood barriers to elevation 906 ft MSL.

Emergency Diesel Generator Building The Emergency Diesel Generator Building is protected from wave effects and flood water by grade level building walls and by temporary flood barriers to elevation 906 ft MSL.

Radwaste Building The Radwaste Building is protected from wave effects and flood water by grade level building walls and by temporary flood barriers to elevation 906 ft MSL.

Site Information Related to the Flood Hazard .. ,,

1-12 t '.

Sar g e ~ & il..J..Jndy \ ,c SECURIT¥=RELATED INFORMATION - WITI IIIOLD UNDER 16 CFR 2.996

SECURIT¥-RELATEE> INFORMATION - WITHHOLf) UNDER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD Rl!l!VALUATION REPORT Control Building The Control Building is protected from wave effects and flood water by grade level building walls and by temporary flood barriers to elevation 906 ft MSL.

Controlled Corridor The Controlled Corridor is protected from flood water by grade level Reactor and Turbine Building walls to elevation 906 ft MSL.

Turbine Building The Turbine Building is protected from wave effects and flood water by grade level building walls and by temporary flood barriers to elevation 906 ft MSL.

Z-Sump {Below ERP Tower)

As noted in the USAR (Reference 1.7-4, Chapter II, Section 4.2.2.2), the top of floor drain Z-Sump, at the base of the ERP tower, is located at elevation 891 ft MSL and, therefore, is within postulated flood levels. The Z-Sump contains equipment essential to the operation of the Standby Gas Treatment System (SGTS) and, therefore, the sump must remain functional whenever Secondary Containment is required. Although the ground elevation at the sump is only 890 ft MSL, the Z-Sump will not be affected by flooding since the sump penetrations are sealed and the proper functioning of the sump is monitored when flood levels reach 890 ft MSL.

Diesel Fuel Storage Tanks As noted in the USAR (Reference 1.7-4, Chapter II, Section 4.2.2.2); there is sufficient fuel in the Diesel Oil Storage Tanks to ensure seven days of operation of a single diesel generator powering a single critical division of safe shutdown loads. This time duration is sufficient to obtain more fuel, if needed. The two storage tanks are buried and their appendages are protected by a substantial cover. The manholes providing access to the Diesel Oil Transfer Pumps, the capped fill connections, and the tank vents are all located above 906 ft MSL. The design and installation of the tanks ensure flotation does not occur when empty during the PMF.

The following CNS plant structures have been identified as important to the protection of the various safety-related structures and equipment and are also protected from flooding as noted:

Augmented Radwaste Building The Augmented Radwaste Building is protected from wave effects and flood water by grade level building walls and by temporary flood barriers to elevation 906 ft MSL.

Boner Room The Boiler Room is protected from wave effects and flood water by grade level building foundation walls and by temporary flood barriers to elevation 906 ft MSL.

Site Information Related to the Flood Hazard ,,

,\

1-13 I '

Sorgcn~ & i Lundy "~

SECURIT¥-RELATED INFORMATION - WITHHOLD UNDER 16 CfiR 2.396

SECURITY-RELATEf) INFORMATION - VilTI IHOLD UNDER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD Rl!l!VALUATION REPORT Project No.: 11784-017 Fan Room The Fan Room is protected from wave effects and flood water by grade level building foundation walls and by temporary flood barriers to elevation 906 ft MSL.

Water Treatment Plant The Water Treatment Plant is protected from wave effects and flood water by grade level building foundation walls and by temporary flood barriers to elevation 906 ft MSL.

Tool Crib The Tool Crib is protected from wave effects and flood water by grade level building foundation walls and by temporary flood barriers to elevation 906 ft MSL.

Machine Shop The machine shop is protected from wave effects and flood water by grade level building foundation walls and by temporary flood barriers to the elevation of 906 ft MSL.

Multi-Purpose Facility (MPF) Building The MPF Building is protected from wave effects and flood water by grade level building foundation walls and by temporary flood barriers to the elevation of 906 ft MSL.

Other Site Structures Various site out-buildings and structures classified as not important to safe operation and shutdown of the plant are located at base elevations lower than the PMF elevation of 903 ft MSL. Per CNS Procedure 5.1 , Flood (Reference 1.7-15), evaluation of the protection of these assets is determined by NPPD plant management by implementing actions based oo various parameters, including plant safety, asset value, importance to overall long-term power generation, etc.

Procedures Upon reaching an actual river level of 895 ft MSL or receiving a river level forecast of 902 ft MSL within the next 36 hours4.166667e-4 days 0.01 hours 5.952381e-5 weeks 1.3698e-5 months , the site flooding procedure is implemented. Apart from implementing temporary protection up to 906 ft MSL as previously discussed, the procedure directs the discharge of liquid radwaste as required to provide room for handling flood leakage. The floor and equipment drains and portable gasoline pumps are used to control leakage past the primary and secondary barriers.

Site Information Related to the Flood Hazard 1-14 SECURITY-RELATED INFORrMTION

WITIIHOLD UNDER 18 CFR 2.996

SECURITY-RELATED INFORMATION =VIITI II IOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 A plant shutdown is initiated under any of the following conditions:

Floodwaters either reach 902 ft MSL, or are forecast to reach 902 ft MSL within the next 36 hours4.166667e-4 days 0.01 hours 5.952381e-5 weeks 1.3698e-5 months (as from the 10,000 year flood or an upstream dam failure).

Floodwater accumulates in either Diesel Generator Room, any of the four Reactor Building Quads, or the Control Building basement.

Plant conditions warrant reactor to be shut down.

(Reference 1.7-4, Chapter 11, Section 4.2.2.2.)

Site Information Related to the Flood Hazard 1-15 SECURIT'f-RELATED INFORMATION

WITI ltiOLD UNDER 16 CFR 2.996

SECURITY-FtELATED INFOFtMATION - WITHHOLB UNDEFt 16 CFFt :2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT 1.6 ADDITIONAL SITE DETAIL All available s ite details have been noted.

Site Information Related to the Flood Hazard 1-16

SECURITY-RELATED INFORMATION - WITHHOLD UNDEFt 18 CFR 2.998

SECUFtlT'f -FtELATED INfiOFtMA:l'ION - Wl'fHHOLD UNDER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178~-017

1. 7 REFERENCES 1.7-1. U.S. Nuclear Regulatory Commission, Request for 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, March 12, 2012.

1.7-2. Safety Evaluation of the Cooper Nudlear Station. Docket 50-298. 02-14-73.

1.7-3. NPPD Engineering Evaluation Number 12-035, Revision 0, "Review of 2012 Topographic Survey of CNS," March 2013.

1.7-4. Cooper Nuclear Station USAR, Revision xxvi1.

1.7-5. Nebraska Public Power District, Flooding Walkdown Submittal Report for Resolution of Fukushima Near-Term Task Force 10 CFR 50-54 (f) Section 2.3 Flooding Response.

1.7-6. Nebraska Public Power District, Columbus, Nebraska, Engineering Criteria Document for Cooper Nuclear Station. June, 3, 1970.

1.7-7. Calculation 2012-12283, Revision 0, Evaluation of Local Probable Maximum Precipitation (PMP).

1.7-8. United States Coast Guard, Mississippi River and Tributaries Waterways Action Plan Missouri River Annex 2011 .

1.7-9. Cooper Nuclear Station, FSAR Question Number 2.1, Amendment Number 9.

1.7-10. Hydrometeorological Report No. 33, Dated April 1956.

1.7-11. Cooper Nuclear Station, FSAR Ques1ion Number 2.3.6, Amendment 17.

1.7-12. U.S. Nuclear Regulatory Commission, "Interim Staff Guidance far Performing the Integrated Assessment for External Flooding," JLD-ISG-2012-05, November 30, 2012.

1.7-13. CNS Operations Manual, Maintenance Procedure 7.0.11 , Flood Control Barriers, Revision 29, Dated 02-19-14.

1.7-14. Calculation 2014-00225, Revision 0, Task 810-Missouri River Channel Geomorphic Evaluation at CNS.

1.7-15. CNS Emergency Procedure 5.1 Flood, Revision 13.

1.7-16. Hydrodynamic Computer Modeling to Predict Missouri River Probable Maximum Flood Elevations and Flow Velocities at Cooper Nuclear Station, NEDC 11-076, Revision 1, Dated August 08, 2011 .

Site Information Related to the Flood Hazard , ....;*

1-17 ( \

S.:,rgcni: & Lun~'

i:;

\ }

_}..,"'

SECURIT¥-RELATEB INFORMATION - WITI It IOLB UNBER 16 CfiR 2.996

secURITY-RELATED INFORMATION - '1/ITHHOLB UNDeR: 18 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION RfiltORT Project No.: 11784-017 1.7-17.ArcMap Version 9.3.1 (Build 3000). ESRI, Redlands, CA 1.7-1 B. Cooper Nuclear Station, FSAR Question Number 2.2, Amendment Number 9.

1.7-19. Cooper Nuclear Station, FSAR Question Number 2.4, Amendment Number 11.

Site Information Related to the Flood Hazard 1-18 SECURIT'f-RELATEE> INFORMATION -WITHHOLD UNDER 10 CFR 2.390

SEeURIT¥-RELATEE> INFORMATION

WITI II IOLE> UNE>ER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 1.8 TABLES The tables associated with Section 1 are presented on the following pages.

Site Information Related to the Flood Hazard .*,

1-19 ' .

Sar-gon~ & Lundy t ~c 1

SEeURIT't'-RELATEE> INFORMATION - WITHHOLE> UNE>ER 16 eFR ! .396

SEeURl'f¥-RELA'fEO INI-ORMA'flON - \\'Ill ll'iOLI) UNOER 16 eFR 2.396 Nebraska Public Power District Sl-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 1.8-1 : Missouri River Dams Name Location Near River Mile Gavins Point Yankton, South Dakota 811 Fort Randall Lake Andes, South Dakota 880 Big Bend Chamberlain, South Dakota 987 Oahe Pierre, South Dakota 1072 Garrison Bismarck, North Dakota 1389 Fort Peck Glasgow, Montana 1771 Note:

1. Plant location: River Mile 532.5 Table 1.8-2: Design Evaluation Summa1ry CNS Condition Comment Evaluation PMF Peak Flow Rate 11> 600,000cfs PMP Event centered above Brownville, NE.

Plant site elevated +/-903 ft MSL. First floor of all Class I PMF Still Water Surface E_levation 903 ft MSL C2l buildings at 903.5 ft MSL.

Flood barriers not needed at intake since critical PMF + Wave Runup at Intake Structure equipment is elevated above 906 ft MSL and protected 909.2 ft MSL from wave impacts.

Class I buildings' grade level openings at 903.5 ft MSL PMF + Wave Action Main Plant Complex No impact protected by flood barriers from standing water up to 906 ft MSL.

Notes:

1. The USACE estimated a higher river stage during the PMF than the AEC, despite the fact it used a lower now rate (600,000 cfs versus 1,000,000 cfs). Details of the methodology utHized by the AEC to develop its stage flow relationship were not described, except for a statement in the SER text that the AEC constructed an *Analytical Model." The analysis conducted by CNS in 2011 is consistent with the USACE stage discharge estimates (Reference 1.7*16).

2. This elevation Is based on a steady flow rate of 600,000 els. See Reference 1 .7, Chapter II, Section 4.2.2.1.

3. See Reference 1.7-5, Section 2.7, Site Information Related to the Flood Hazard 1-20 SECURIT¥~RELATED INFORMATION - WITHHOLB UNOER: 16 CFft 2.S96

SECURIT¥*RELATEf> INFORMATION - WITHHOLE> UNE>ER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION Rl!PORT Project No.: 11784-017 Table 1.8-3: Missouri River Drainage Area Drainage Area Location (Approximate (Missouri River)

(Square Miles)

Above Fort Peck Dam 57,500 Above Garrison Dam 181,400 Above Oahe Dam 243,490 Above Fort Randall Dam 263,480 Above Gavins Point Dam 279,480 Above Mouth of Platte River 323,530 Platte River at Mouth 90,200 At Cooper Nuclear Station 4 14,600 Reference 1.7-4, Chapter II, Section 4.2.2.1 Site Information Related to the Flood Hazard 1-21

/(

\

Sargent &,Lundy* *c

\ .,

)-'

SECURIT¥-RELATEB INFORMATION - WITHHOLE> UNE>Eft 16 CfR 2.996

SECURITY-ftELATEE> IN~OftlVIATION - WITIIIIOLD UNDER 18 CPR 2.396 Nebraska Public Power District SL,01245O Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 1.9 FIGURES The figures associated with Section 1 are presented on the following pages.

Site Information Related to the Flood Hazard 1-22 SECUftlTY-RELATEf> INFORMATION - WITttttOLD UNElER 16 CFft 2.390

SEOURIT'i'*RELATEB INFORM>\TION - WITI II IOLB UNBER 18 OFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVAt.UATION REPORT Project No.: 11784-017 Figure 1.9-1 : Site Location Reference 1.7-17 Site Information Related to the Flood Hazard 1-23 Snrgnnt: & Lundy SEOURIT¥*RELATEB INFORMATION - WITttttOLB UNBER 18 CFR 2.998

SECURIT¥*RELATED INFORMATION - Vt11TI II IOLD UNDER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 1.9-2: Missouri River Tributaries Reference 1.7-4. Figure 11-4-1 Site Information Related to the Flood Hazard 1-24 S...-gant: & Lundy SECURITY-RELATED INFORMATION

WITI II IOLD UNDER 18 CFR 2.998

SECURITY-RELATED INFORMATION - WITtttfOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 1.9-.3: Overhead View of CNS 1 Site Information Related to the Flood Hazard 1-25 S.,rgono: & Lundy SECURIT¥-RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.996

9ECURIT¥*RELATEB INFORMATION - WITHHOLD UNDER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revi sion 1 Project No.: 1178-4--017 FLOOD HAZARD REEVALUATION REPORT Figure 1.9-4: Overhead View of CNS 2 Site Information Related to the Flood Hazard 1-26 SECURITY-RELATED INFORMATION - WITl-l~tOLB UNDER 18 CFR 2.998

SECURIT¥*RELATEB INFORMATION - Wl'fHHOLB UNBER 16 CFR 2.S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 1.9-5: Missouri River Reservoir System tissouri River ~lainstem Reservoir System

Site Information Related to the Flood Hazard 1-27 S..rgc,no:. & Lundy SECURIT¥-RELA'fEB INFORMATION - V/l'fHHOLB UNBER 16 CFR 2 .S96

SECURITY*RELATED INFORMATION - WITIHIOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 1.9-6: Missouni River Path in 1879 at the Site of CNS 0

Reference 1.7- 14 (Note: Current river path Is overlaid and is in faded blue.)

Site fnformation Related to the Flood Hazard 1-28 SECURITY-RELATED INFORMATION - WITI II IOLD UNDER 16 CFR 2.996

SECURITY*RELATED INFORMATION - WITHHOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11764-017 Figure 1.9-7: Aerial Photograph of the Plant Site in 1971 0 zooo f .. ..

Reference 1.7-14 (This photograph was taken after construction of CNS began In 1968, but prior to CNS officially opening In 1974. The river channel and banks looked much like they do today.)

Site Information Related to the Flood Hazard 1-29 Snrgnnc & Lundy SECURIT¥ -RELATED INFORMATION - WITI II IOLD UN BER 16 CFR 2.996

SECURIT¥-RELATES INFORMATION - WITHI-IOLS UNSER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Pro1ect No.: 1178-4-017 Figure 1.9-8: Aerial Photograph of CNS Showing Flooding t

- -~ I u

.. * ** Jllf l .....,. ~ * *

Reference 1.7-14 (This Figure shows a uten,te Image of the Missouri River taken on July 9, 2011 ancl the effect of the maximum releases from Gavlns Point Dam cluring the 2011 ftoocl. Flood waters hacl Inundated the ftoodplain In many of the areas where the Missouri River hacl once meandered within the bounclaries of the levees. There was visible ftoocling east of the eastem levee due to the upstream levee breaches. There was also visible stancling water on the west side of the river, west of the levee, likely due to Interior drainage. There Is no evidence that a new channel was beginning to form. The resolution of the image Is such that it Is not possible to discern the status of the bank stablliiaUon structures.)

Site Information Related to the Flood Hazard 1-30 SECURIT'f-RELATES INFORMATION - WITHHOLS UNSER 16 CFR 2.996

SECURITY-RELATEB INFORMATION

WITHHOLf> UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT

2. FLOOD HAZARD REEVALUATION 2.1 LOCAL INTENSE PRECIPITATION (LIP)

Probable Maximum Precipitation (PMP), also known as local Intense Precipitation (LIP), is the measure of the extreme precipitation (high intensity/short duration) at a given location. Evaluation of the flooding hazards to the safety-related Systems, Structures, and Components (SSCs) at Cooper Nuclear Station (CNS) due to LIP is presented in this section of the report. U.S. Nuclear Regulatory Commission (NRC) guidelines NUREG/CR-7046 (Reference 2.1-1), NRC Regulatory Guide 1.59 (Reference 2.1-2), and ANSI/ANS-2.8-1992 (Reference 2.1-3) fom, the basis for the approach and methodology used in this evaluation. The analysis was performed with the conservative assumption that the local storm drainage system (culverts, ditches, storm sewers, dry wells, etc.) would not be functional during the LIP event.

The LIP flood effects on CNS were detem,ined by performing site-specific hydrologic and hydraulic analyses. The rational method (Reference 2.1-4) with conservative runoff coefficients (i.e.,1.0) was used for computation of peak PMP runoff from different drainage areas of the plant site. The U.S. Army Corps of Engineers (USACE) Hydrologic Engineering Center River Analysis System (HEC-RAS) computer program (Reference 2.1-5) was used to determine the maximum water surface elevation and flow velocity. Due to the relatively short duration of the flooding event and the shallow depth of inundation, the effects of wind-waves were not considered. Reference 2.1-6 defines Plant Datum the same as Datum used in the USAR (which is MSL).

The vertical datum used for this section (i.e., Section 2.1) was the CNS Plant Datum. The National Geodetic Vertical Datum of 1929 elevation (NGVD29) is equal to Plant Datum elevation plus 0.11 feet [ft] (Reference 2.1-6). The North American Vertical Datum of 1988 elevation (NAVD88) is equal to NGVD29 elevation plus 0.26 ft (Reference 2.1-6). The NAVD88 elevation is equal to Plant Datum elevation plus 0.37 ft. All directions are with respect to the Plant North direction, which is oriented to the west of the true north direction.

The effect of LIP on CNS was not evaluated previously in the Updated Safety Analysis Report (USAR, Reference 2.1-7). As presented in Section 4.2.2.2 of the USAR, the finished floor elevation of Principle Class 1 Structures (SSCs) is at 903.5 ft Plant Datum (903.87 ft NAVD88) and the general site grade elevation is at 903.0 ft Plant Datum (903.37 ft NAVD88).

2.1.1 Probable Maximum Precipitation Depths As prescribed in NUREG/CR-7046 (Reference 2.1-1 ), the LIP used in the analysis is the 1-hour, 1-square mile PMP at the CNS site. Parameters to estimate the LIP were obtained from the U.S.

National Weather Service (NWS) Hydrometeorological Reports HMR 51 and HMR 52 (see References 2.1-8 and 2.1-9).The estimated depths from HMR 51 are for precipitation durations 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and longer and drainage areas from 10 to 20,000 square miles. These estimates were used with procedures outlined in HMR 52 to determine PMP depths of various durations less than 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months and Local Intense Precipitation (LIP) 2-1 SECURIT¥-ftELATEB INFORMATION - WITHHOLB UNBER 16 CFR 2.996

SECURIT¥*RELATEE> INFORMJ!<TION - WITHHOLB UNE>ER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 drainage are*as up to 1 square mile for the site. Table 2.1-1 presents the PMP depths and intensities for various durations at the CNS site.

2.1.2 Drainage Areas and local Drainage Parameters The CNS site is located on the west (right) bank of the Missouri River near Brownville, Nebraska, at approximate River Mile (RM) 532.5. The latest available topographic survey (Reference 2.1-6) for the plant site area was used for delineation of drainage areas (zones). The main plant area is relatively flat without well-defined flow paths, and is delineated into drainage areas considering drainage away from the Central Building Complex in all directions. The majority of the plant area perimeter is bounded by 9 to 10 rows of jersey barriers (Figure 2.1-1) with variable longitudinal spacing (1 inch to 36 inches). A portion of the security barrier south of the plant is formed by Kontek concrete block barriers. The jersey barriers are 12.5 ft long and 32 inches (in) high and the Kontek blocks are 10 ft long and 3 ft high. Due to the variability in opening size, potential for barrier relocation, and potential for staggered openings between barrier rows; conservatively, openings between barriers were not considered flow paths for thi~ analysis.

Figure 2.1-2 shows the four drainage areas considered in the main plant area, identified as Zones A, B, c,.and D. All safety-related facilities at CNS are located within these four zones. Peripheral portions of the main plant area that are not directly connected to, or that do not affect the safety-related facilities, were not included in the PMP zones. These small areas located along the periphery of the main plant area would generate a relatively small amount of runoff that would drain away from these areas without affecting the runoff draining away from the safety-related facilities.

Zone A is located on the east side of the plant, near the Missouri River. The Intake Structure is located along the downstream (eastern) boundary of Zone A. The grade elevation in this zone varies from 902 ft (902.37 ft NAVD88) to 903.5 ft (903.87 ft NAVD88). Although runoff could flow to the south where the grade slopes down toward the area of the discharge canal and sludge pond, all runoff from Zone A is considered to flow over the eastern boundary to the river on the south side of the Intake Structure, resulting in conservative estimates for the maximum water level in Zone A.

Zone B is located on the north side of the main plant area. Security bar riers are located along the northern edg1e of the zone at the downstream boundary, with relatively high elevations on the west side and lower elevations on the east side toward the river. The grade elevations at the downstream boundary of Zone B range from 902.5 ft (902.87 ft NAVD88) on the west side, to 897 ft (897.37 ft NAVD88) and below on the east side. Due to multiple obstructions on the western side of Zone B (i.e.,

tanks, buildirngs, etc.), the flow paths on the west side of some cross sections were considered blocked and not used for conveyance. Additionally, due to the relatively high grade elevation and security

barriers downstream of the tanks, the areas between the tanks were designated as ineffective flow areas within the HEC-RAS model. All runoff from Zone B was considered to drain away from the main plant through the area between the Condensate Storage Tank and the Fabrication Shop, and discharge over the top of the security barriers on the east side of the northern boundary. Overtopping of the barriers was considered at the downstream boundary of Zone B.

Local Intense Precipitation (LIP) /

.,.:- ~

2-2 Sorga~ ' Lunc:ty* **

,)

SECURIT¥ -RELATEE> INFORMJ!<TION - WITHHOLB UNE>ER 16 CFR 2.396

SECURITY-RELATED INl-0RMATl0N - WITHHOLD UNDER 16 CI-R 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAzARD REEVALUATION REPORT Project No.: 11784*017 Zone C is located on the south side of the main plant area. Runoff from this zone drains over the southern periphery of the main plant area to the low elevation area near the discharge canal, where it can flow unobstructed to the Missouri River. The grade elevations at the downstream boundary of Zone C range from 904 ft (904.37 ft NAVD88) to 902 ft (902.37 ft NAVD88), and all runoff from Zone C was considered to exit the zone on the west side of the storage tanks and buildings located near the downstream (southern) boundary.

Zone D is located on the west side of the main plant area. The security barriers (32 inches high) are located at the western edge of this zone and act as an obstruction. As runoff accumulates behind the barriers and causes ponding in Zone D, runoff will flow to the south. Overtopping of the barriers along the western boundary of Zone D was not considered in this analysis due to the relatively high elevations of the top of barriers. Although the flow path along the west side of the East Warehouse between the security barriers and the building has the capacity to convey the entire peak flow from Zone D, it is expected that some runoff will flow into Zones B and C. Flow-balancing calculations were performed to determine the quantities of runoff flowing to these zones.

The offsite drainage area was delineated (Figure 2.1-3) considering Federal Levee R548 that is adjacent to CNS with a top elevation of approximately 902 ft (902.37 ft NAVD88). The levee extends north of the plant, where it terminates at the higher ground near the bluffs. South of CNS, the levee follows the right bank of the Missouri River, curving around to the west, running parallel to the left bank of the Nemaha River, and turning north where it meets the higher ground near the town of Nemaha.

The area enclosed by the levee and the higher bluffs to the west measures 4000 acres (ac). The effect of runoff from the offsite drainage area on PMP water levels near CNS is discussed in Section 2.1.4.

2.1.3 Peak Discharges To compute the peak runoff, time of concentration for each zone was estimated using the Kerby Equation (Reference 2.1-10). For each zone, flow length, average slope, and roughness coefficient were estimated and used as input for the Kerby Equation. The surfacing in the main plant area is mostly gravel and concrete or asphalt-paved, and the roughness coefficient was considered to be 0.02 (Reference 2.1-4).The estimated times of concentration are presented in Table 2.1-2. Using the PMP values corresponding to the time of concentration, the applicable PMP intensity for each zone was estimated. Employing the rational method (Reference 2.1-4), peak runoff for each of the zones was estimated. A conservative runoff factor value of 1.0 (indicating 100% runoff without any infiltration or other losses) was used in the rational method.

2.1 .4 Hydraulic Model Setup For computations of water levels, the HEC-RAS Version 4.1 computer program (Reference 2.1-5) was used. Separate HEC-RAS runs for each zone were performed. The site features and flow obstructions in each drainage area are characterized by cross sections (Figure 2.1-4 through Figure 2.1-7) and used in the hydraulic analysis.

Local Intense Precipitation (LIP) 2-3 SECURIT't'*RELATED INFORl\~TION - WITHHOLD UNDER 16 CFR 2.998

SECURITY-RELATEE> INFORMATION - WITHHOLE> UNE>ER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 The surfacfng in the main plant area is primarily gravel and concrete or asphalt-paved. Reference 2.1-4 recommends Manning's roughness coefficients ranging from 0.011 to 0.025 for such surfaces.

Conservatively, a Manning's roughness coefficient of 0.030 was used to account for minor obstructions.

The flow at each cross section was computed by prorating the peak discharge of the entire zone based on the drainage area upstream of that cross section. Table 2.1-3 through Table 2.1-6 present the peak flow at each cross section for Zones A through D, respectively.

For Zones A, C, and D, the critical depth was considered as the downstream boundary condition to account for the flow transition from the relatively flat main plant area, over the peripheral boundary and down a steep slope. Critical depth was considered for the downstream boundary condition in Zone B to account for the flow over the security barriers, which were considered to act as a weir. The present-day regulatory guidance (References 2.1-1 and 2.1-11) does not provide combined-events criteria governing the coincident water level in an adjacent river during the LIP event. The normal river water level at CNS is well below elevation 890 ft (880.37 ft NAVD88), and the CNS USAR defines the normal summer water level as 880 ft (890.37 ft NAVD88 [Reference 2.1-7]).The 25-year water level in the Missouri River at CNS is 898.04 ft (898.41 ft NAVD88 [Reference 2.1-12]).The 25-year water level is well below the lowest elevation of any cross section considered in the evaluation and will not affect drainage from the site during an LIP event. Therefore, there is no backwater effect from the Missouri River at the downstream boundary for Zones A, B, and C. Zone D discharges to the floodplain behind the USACE levee, and is not affected by water levels in the Missouri River or the offsite area.

Runoff from the offsite drainage area will pond on the floodplain behind the USACE levee. Comparing the total PMP runoff volume with t he storage volume available behind the levee showed that the maximum surface elevation of the ponded water level will be less than 892 ft (892.37 ft NAVD88).Therefore, water levels at the boundary of the main plant area, during an LIP event, will not be affected by runoff from the offsite drainage area.

Several temporary trailers are installed in the main plant area at CNS. The trailers are accounted for in the analysis as complete obstructions. Sensitivity runs with and without the trailers performed using HEC-RAS indicated that these trailers have a negligible effect on the PMP water levels estimated for this analysis. '

Initially, the maximum water levels for each zone were computed without considering the cross flow between the adjacent zones. Subsequently, a trial-and-error flow-balancing exercise was performed to determine the cross flows that result in matching water levels at the interface between zones.

2.1.4.1 LIP Runoff Water Levels without Cross Flow between Zones The resulting maximum water level in each zone during an LIP event, without consideration of cross flow between zones, is summarized below:

Local Intense Precipitation (LIP) .,,,

,.. \

2-4 S a rgo;,t& Lundy'

),)

SECURIT¥*RELATEE> INFORMATION - WITI IHOLD UNDER 16 CFR 2.996

SE6URIT¥-RELATEB INFORMATION - WITHHOLB UNBER 16 6FR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017

Zone A maximum water level= 903.05 ft (903.42 ft NAVD88)

Zone B maximum water level= 903.35 ft (903.72 ft NAVD88)

Zone C maximum water level= 903.59 fl (903.96 ft NAVD88)

Zone D maximum water level = 903.80 ft (904.17 ft NAVD88) 2.1.4.2 Water Levels with Cross Flow between Zones Preliminary water level estimates without consideration of cross flow showed the water levels in Zones Band D differ by nearly 6 inches. Through a process of trial-and-error, a cross flow of 63 cubic feet per second (cfs) is considered to flow from Zone D to Zone B (Figure 2.1-5). A cross flow of 63 cfs was chosen because It represents all of the peak flow at the upstream-most cross section of Zone D and provides closely matching (less than a 1-lnch difference) final water surface elevations between Zones B and D.

Cross flow can occur from Zone D to Zone C upstream of the East Warehouse, and from Zone C to Zone D downstream of the East Warehouse (Figure 2.1-6). Cross flow from Zone D into Zone B was deducted from Zone D before the cross flow balancing between Zones C and D was performed. Cross flow from Zone C into Zone A (Figure 2.1-7) was estimated following the cross flow balancing between Zones C and D.

The maximum water level in Zone B is approximately 5 inches higher than the maximum water level In Zone A. The broad-crested weir equation (Reference 2.1-13) was used to estimate the cross flow from Zone B to Zone A The potential for submerged weir flow was checked using Figure 5-15 of Reference 2.1-14. A total cross flow of 108 cfs enters Zone A at the upstream boundary and was applied to every cross section In the zone. Conservatively, the flows at cross sections in Zone Band Zone C were not reduced to account for this flow out of the zone. Figure 2.1-8 through Figure 2.1-11 present the results of the hydraulic analysis for all HEC-RAS cross sections considering cross flow between two adjacent zones. The resulting maximum water level in each zone during an LIP event, considering cross flow between zones, is summarized below.

Zone A maximum water level= 903.19 ft (903.56 ft NAVD88)

Zone B maximum water level= 903.47 ft (903.84 ft NAVD88)

Zone C maximum water level= 903.50 ft (903.87 ft NAVD88)

Zone D maximum water level= 903.50 ft (903.87 ft NAVD88) 2.1.4.3 Velocity The maximum velocity obtained from the HEC-RAS output for each zone is summarized below.

Zone A maximum velocity = 3.64 feet per second (fps)

Zone B maximum velocity= 4.49 fps

Zone C maximum velocity = 2.87 fps

Zone D maximum velocity = 5.02 fps Local Intense Precipitation (LIP) 2-5 SECURIT't'-RELATEB INfiORMATION - WITHHOLB UNBEfit 16 Cfiift: 2.996

SECURIT¥*RELATED INFORMATION - \VITHHOLI:> UNDEfit: 16 CFfit: 2.396 Nebraska Public Power District SL-01245O Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 The HEC-RAS simulations were performed under subcritical flow conditions; however, the results indicated that there could be supercritical flow conditions in Zones B and D. Additional HEC-RAS test runs using a mixed-flow regime resulted in no change to the maximum water levels estimated for these zones. Since the subcritical flow dominates in the upstream areas, upstream water levels are controlled by water levels downstream, not the upstream boundary condition. However, the velocities at some cross sections are affected when a mixed-flow regime is employed.

In Zone D, supercritical flow occurs in the area located between the Warehouse and the security barriers at Cross Section D500, with a maximum velocity of 5.12 fps. T he model indicated that a hydraulic jump occurs between Cross Sections 0500 and D400. The Froude number is close to 1.0, indicating that the hydraulic jump is weak; howe'l(er, the potential for erosion exists due to turbulence at the location of the jump. In Zone B, supercritical flow occurs on the steep slope at the periphery of the main plant area at Cross Section B200. The velocity at this location is 9.34 fps; hence, there is a potential for erosion of the sloped surface. Both of the locations that have potential for site erosion are located around the periphery of the plant, away from safety-related SSCs, and would not affect any CNS safety-related facilities.

2.1.5 Effect of LIP Table 2.1-7 presents a summary of the Maximum Water Levels in all zones at different cross sections.

These water levels consider cross flow between zones for steady-state, subcritical flow conditions. The maximum estimated water level due to LIP at CNS is 903.50 ft (903.87 ft NAVD88), which is equal to the finished floor elevations for Principal Class 1 Structures. While significant inundation above the

. finished floor elevations is not expected, the potential for minor flooding at the entrances of these structures may exist during the peak of the event.

Reference 2.1-14 recomme,nds a maximum permissible flow velocity of 6.0 fps to prevent erosion of channels with fine-gravel surfacing. The potential for erosion in the main plant area is low, as the velocities do not exceed 6 fps and are generally less than 3 fps. Velocities on the steep slope at the periphery of the main plant area may cause local erosion of the sloped surface, but there would be no effect on safety-related facilities.

Due to the relatively short duration of the flooding event and the shallow depth of inundation, the effects of wind-waves were not considered. Additionally, debris loading and transportation were not considered in the analysis due to the relatively low velocity and shallow depth of LIP flood waters near CNS safety-related facilities, and due to the lack of debris sources in the CNS main plant area.

2.1.6 References 2.1-1. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, NUREG/CR-7046, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, November 2011.

2.1-2. Regulatory Guide 1.59, Design Basis Floods for Nuclear Power Plants, Revision 2, Office of Standards and Development, U.S. Nuclear Regulatory Commission, August 1977.

Local Intense Precipitation (LIP) ,,*'{

,. .\

2-6 S u r g e ~ & Lundy*~-:

1

,.,)..*~**

SECURIT¥ -RELATEB INFORMATION - WIT HHOLD UNf>ER 16 CFft: 2.S96

SECURIT¥ -RELATEB INFORMATION -WITHHOLD UNDER 10 CFR 2.390 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-017 2.1-3. American Nuclear Society, ANSI/ANS-2.8-1992, Determining Design Basis Flooding at Power Reactor Sites, July 1992.

2.1-4. Handbook of Applied Hydrology, VenTe Chow, McGraw- Hill Inc., 1964.

2.1-5. Hydrologic Engineering Center's River Analysis System {HEC-RAS) Version 4.1 for Windows.

U.S. Army Corps of Engineers, 2010.

2.1-6. NPPD Engineering Evaluation Number 12-035, Revision 0, "Review of 2012 Topographic Survey of CNS," March 2013.

2.1-7. Updated Safety Analysis Report (USAR - 2.7), Cooper Nuclear Station, Site and Environs, Hydrology, Site Flooding Protection, Dated 01 /16/01.

2.1-8. Hydrometeorological Report No. 51 (HMR 51), Probable Maximum Precipitation estimates, United States East of the 105th Meridian, National Weather Service, National Oceanic and Atmospheric Administration (NOAA), June 1978.

2.1-9. Hydrometeorological Report No. 52 {HMR 52), Application of Probable Maximum Precipitation Estimates - United States East of the 105th Meridian, National Weather Service, National Oceanic and Atmospheric Administration {NOAA), August 1982.

2.1-10. Hydrology and Hydraulic Systems, Ram S. Gupta, Second Edition, Waveland Press, Inc.,

2001.

2.1-11 . Standard Review Plan, Revision 4, NUREG-0800, Section 2.4.2 Floods, United States Nuclear Regulatory Commission (USNRC), March 2007.

2.1-1 2. Upper Mississippi River System Flow Frequency Study, Hydrology and Hydraulics, Appendix F, Missouri River, U.S. Army Corps of Engineers, Omaha District, November 2003.

2.1-13. Handbook of Hydraulics, Ernest F. Brater, Horace W. King, Sixth Edition, McGraw-Hill, Inc.,

1976.

2.1-14. Engineering Manual EM 1110-2-1601 , "Engineering and Design - Hydraulic Design of Flood Control Channels," Table 2-5, p 2-16, U.S. Army Corps of Engineers, 1991 .

Local Intense Precipitation (LIP) ~,..

2-7 /' '

' &;L.undy*

So.r gant: \ \c

).--

SECURIT¥ -RELATEB INFORMATION =WITI II IOLB UNBER 18 CFR 2.998

SECURIT¥-RELATED 1Nf-ORM)8[TION - \VITIIIIOLE> UNDER 16 Cf-R %.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.1.7 Tables Tables associated with Section 2.1 are presented on the following pages.

Local Intense Precipitation (LIP) 2-8 (\

Sorga r1/4:; & Lunc:ty, ,a 1

,.,';/

SECURIT'f -RELATEB INf-ORMATION - WITI ti IOLB UN BER 16 Cf-R %.396

SECURIT¥-RELATI!" INP'OfitMATION - WITHHOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.1-1: PMP Values and Intensities at the CNS Site 1 hr, Point PMP PMP Depth PMP Duration and Area Location Source Intensity (in)

Ratio (In/hr) 24 hr, 10 mi 2

- HMR 51 - Figure 20 33.3 -

1 hr, point location - HMR 52 - Figure 24 18.2 18.2 30 min, point 0.765 HMR 52 - Figure 38 13.9 27.8 15 min, point 0.534 HMR 52 - Figure 37 9.7 38.8 5 min, point 0.338 HMR 52 - Figure 36 6.2 74.4 Table 2.1-2: Peak Discharge Drainage Time of Rainfall Peak Flow Slope Zone Area Concentration Intensity Discharge Length (ft) (ft/ft)

(acres) (min) (in/hr) (cfs)

A 2.61 130 0.0077 4.0 74.4 194 B 5.30 280 0.0036 6.9 59.7 316 C 4.00 285 0.0035 7.0 59.1 236 D 6.29 650 0.0031 10.6 46.2 291 Note:

1. A 5-minute time of concentration is appl led to any drainage area In which the estimated time of concentration Is less than 5 minutes.

Local Intense Precipitation (LIP) 2-9

,* -(

Snrgor\t~ Lundy ' 1 '

\ I J;**'

SECURIT'f-RELATEB INFORM>\TION - WITHHOLB UNBER 16 CFR 2.996

SEOURIT¥-RELATED INFORM>9cTION - "ft'ITHHOLD UNDER 16 Cl-ff 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.1-3: Drainage Area and Peak Flow at each Cross Section - Zone A Col umn: (1) (2) (3) (4)

Peak Flow (cfs) Peak Flow (cfs)

Cross Section Upstream Ratio Upstream Flow Profile: Flow Profile:

Area (ac) Area to Total Area Initial (Without Final (With Cross Flow) Cross Flow)

A800 1.04 0.398 77 185 A700 1.22 0.467 91 199 A600 1.47 0.563 109 217 ASO0 1.73 0.663 129 237 A400 1.98 0.759 147 255 A300 2.23 0.854 166 274 A200 2.46 0.943 183 291 A100 2.61 1.000 194 302 Notes:

1. Column (2) = Column (1) /Total Area; Total Area= 2.61 ac

2. Column (3) = Column (2) x Peak Flow; Peak Flow" 194 cfs

3. Column (4) = Column (3) + 108 cfs from Zone B and Zone C (Cross Flow)

Local Intense Precipitation (LIP) 2-10 Sargc.-'.ti~ &1Lundy' '~

SEOURIT¥-RELATED INFORMATION - WITHHOLD UNDER 18 CFff 2.996

SEetJRIT'l'-RELATEB INPORMATION - WITHHOLB tJNBER 16 ei-R 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION Rl!PORT Project No.: 11784-017 Table 2.1-4: Drainage Area and Peak Flow at each Cross Section - Zona B Column: (1) (2) (3) (4)

Peak Flow (cfs) Peak Flow (cfs)

Upstream Ratio Upstream Flow Profile: Flow Profile:

Cross Section Area (ac) Area to Total Area lnltlal (Without Final (With Cross Flow) Cross Flow)

B1200 0.75 0.142 45 108 B11 00 1.16 0.219 69 132 B1000 1.49 0.281 89 152 B900 2.13 0.402 127 190 B800 2.38 0.449 142 205 B700 2.81 0.530 168 231 B600 3.41 0.643 203 266 B500 3.65 0.689 218 281 8400 4.10 0.774 244 307 B300 4 .65 0.877 277 340 B200 4.95 0.934 295 358 B100 5.30 1.000 316 379 Notes:

1. Column (2) = Column (1) I Total Area; Total Area= 5.30 ac

2. Column (3) = Column (2) x Peak Flow; Peak Flow

316 cfs

3. Column (4) = Column (3) + 63 cfs from Zone D (Cross Flow)

Local Intense Precipitation (LIP) 2-11 SEetJRIT','*RELATEB INFORMATION - WITHHOLB tJNBER 16 CFR 2.998

SECURFf"f-RELATEe INFORMATION - Vt'ITlftlOLD UNDER 16 eFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: ! 1784-017 Table 2.1-5: Drainage Area and Peak Flow at each Cross Section - Zone C Column: (1) I (2) (3) (4)

Peak Flow (cfs) Peak Flow (cfs)

Upstream Ratio Upstream Flow Profile: Flow Profile:

Cross Section Area (ac) Area to Total Area Initial (Without Final {With I Cross Flow) Cross Flow)

C1200 1.08 0.270 64 65 C11 00 1.19 0.298 70 72 I

C1000 1.37 0.343 81 84 csoo 1.74 0.435 103 109 C800 2.1 1 0.528 124 130 C700 2.50 0.625 148 154 C600 2.69 0.673 159 165 C500 2.95 0.738 174 180 C400 3.26 0.815 192 170 C3D0 3 .48 0.870 205 154

\

C200 3.82 0.955 225 145 156 C1D0 4.00 I 1.000 236 Notes:

1. Column (2) = Column (1) / Total Area; T otal Area = 4.00 ac

2. Column (3)

Column (2) x Peak Flow; Peak Flow" 236 cfs

3. Column (4) = final profile resulting from cross flow balancing with Zone D Local Intense Precipitation (LIP) -~*;J*

2-12 / \

Snrga~ & Lunr1y 110

\ .J

~

/

SECURIT¥-RELATED INFORMATION - 'NITHHOLD UNBER 16 CFR 2.396

SECURIT¥-RELATED INFORMATION - WITHHOLE> UNDER 16 CFR ! .S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No,: 11784-017 Table 2.1-6: Drainage Area and Peak Flow at each Cross Section - Zone D Column: (1) (2) (3) (4)

Peak Flow (cfs) Peak Flow (cfs)

Upstream Ratio Upstream Flow Profile: Flow Profile:

Cross Section Area (ac) Area to Total Area Initial (Wrthout Final (With Cross Flow) Cross flow)

D2000 1.36 0.216 63 0 D1900 1.66 0.264 77 14 D1800 1.81 0.288 84 21 D1700 2.18 0.347 101 38 D1600 2.38 0.378 110 47 D1500 2.82 0.448 130 67 D1450 2.99 0.475 138 75 D1400 3.42 0.544 158 95 D1300 3.96 0.630 183 120 D1200 4 .12 0.655 191 126 D1100 4.23 0.672 196 131 D1000 4.40 0.700 204 137 D900 4.78 0.760 221 152 D800 4.94 0.785 229 160 D700 5.19 0.825 240 171 D600 5.30 0.843 245 176 D500 5.46 0.868 253 184 D400 5.66 0.900 262 222 D300 5.82 0.925 269 258 D200 6.08 0.967 281 298 D100 6.29 1.000 291 308 Notes:

1. Column (2)

Column (1) /Total Area; Total Area* 6.29 ac

2. Column (3) = Column (2) x Peak Flow; Peak Flow= 291 els

3. Column (4) - Final profile resulting from cross flow balancing with Zone C Local fntense Precipitation (LIP) 2-13 Sargent S..,L.uridy 1

0:

' I SECURIT¥-RELATeD INFORMATION - WITHHOLD UNf>ER 1e Cf'R 2.396

SECURIT¥*RELATED INFORM3'TION - WITHHOLB UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD Rl!l!VALUATION Rl!PORT Project No.: 11784-017 Table 2.1-7: PMP Water Levels Zone A ZoneB ZoneC ZoneD Water Water Water Water Cross Cross Cross Cross Level (ft) Level (ft) Level (ft) Level (ft)

Section Section Section Section A800 903.19 81200 903.47 C1200 903.50 D2000 903.50 A700 903.17 6 1100 903.46 C1100 903.48 D1900 903.50 A600 903.16 81000 903.45 C1000 903.49 D1800 903.50 A500 903.14 8900 903.40 C900 903.47 D1700 903.50 A400 903.07 8800 903.39 C800 903.45 D1600 903.50 A300 903.02 8700 903.35 C700 903.44 D1500 903.50 A200 902.84 6600 903.33 C600 903.43 D1450 903.5 A1001 902.55 6500 903.32 csoo 903.4:f D1400 903.50

- - 6400 903.17 C400 903.42 01300 903.49

- - 8300 902.54 C300 903.38 D1200 903.49

- - 8200 900.51 C200 903.15 01100 903.49

. - 8100 899.79 C100 902.30 01000 903.47

- - - - - - 0900 903.15

. - . . - - 0800 903.06

- - - - - - 0700 902.85

- . - . - - 0600 902.51

- - - - - - D500 902.16

- - - - - - 0400 902.02

. - . - . - D300 902.01

. . - - . - 0200 901.76

- - . - . - 0100 901 .51 Note:

1. water levels are all in Plant Datum; add 0.37 to convert to ft NAVD88.

Local Intense Precipitation (LIP} ,,,-r 2-14 ' \

Sargent& Lundy 1 ,c:

\ )

/ .. ~

SECURIT¥-REL3'TED INFORMATION - WITHHOLD UNDER 16 CFR 2.996

SECURIT¥-RELATED INFORMATION - YtlTHHOLl:l UNl:lER 16 CFR Z.S90 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-D17 2.1.8 Figures Figures associated with Section 2.1 are presented on the following pages.

Local Intense Precipitation (LfP) 2-15 SECURIT'f-RELATEl:l INFORMATION - *tllTlllfOLD UNDER 16 CFR 2.996

SECURITY-RELATEB INFORMATION - WITllltOLB UNBER 18 0FR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.1-1: Location of Sec urity Barriers Local Intense Precipitation (LIP) 2-16 S..rgBn t &Lunc:ty SECURITY-RELATED INFORMATION

WITI II IOLD UNDER 18 0FR 2.998

SECURIT¥-RELATED INFORMATION - WITI II IOLD UNDER 18 OFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT Figure 2.1-2 : Drainage Areas for LIP Evaluation I

i i

I II I

I II

,~

I ZONEC 4.00AC I

8 I I B I

I I

I 93 I

Local Intense Precipitation (LIP}

2-17 Snrgenc & Lur>dy

SECURIT¥-RELATED INFORMATION - WITI II IOLD UNDER 18 OFR 2.398

SECURIT¥-RELATEB INFORMATION - 1t't11THHOLB UNDER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178'1-017 Figure 2.1-3: Offsite Drainage Area behind USACE Levee

--- O' 3000' GRAPHIC SCALE 6000' Local Intense Precipitation (LIP) 2-18 S a r g - & Lundy SECURIT¥-RELATEB INFORMATION - WITHHOLD UNBER 16 CFR 2.396

SECURITY-RELAl'EB INf-OfitMAl'ION - Wll'tttiOLB UNBER 18 Cf-R 2.998 Nebraska Public Power District SL--012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178~17 Figure 2.1-4: Cross Sections for LIP Evaluation - Zone A

,,_. ,,_.,,. ..,".'-. ,~,..-

120" I

L ocal Intense Precipitation (UP) 2-19 S.,rganc, & Lundy SECURl1'¥-RELA1'EB 1Nf-ORM3'1'10N - 't't111't II IOLB UN BER 18 Cf-fit 2.998

SEOURIT¥-RELATED INFORM3'TION - WITttttOLD UNDER 16 OFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 1178--017 FLOOD HAZARD REEVALUATION REPORT Figure 2.1-5: Cross Sections for LIP Evaluation - Zone B

tZl ND-Are,a No FIOlf Area - Tarc,cny Trar

-/-:*___ .

0

"'~~ ...

----~---------_?

r----

--~----4-- -

I Local Intense Precipitation (UP) 2-20 68.-ga""' &. Lundy SEOURIT¥-RELATED INFORM3'TION - WITI II IOLD UNDER 16 CFR 2.398

SECURIT¥-RELATEB INFORMATION - WITI II IOLD UNDER 18 OFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.1-6: Cross Sections for LIP Evaluation* Zone C

_______________________________. . . .lr-----iiia I @

Local Intense Precipitation (UP}

2*21 Serge nt: & l.undy SECURIT¥-RELATEB INFORMATION - '.VITI II IOLB UNDER 18 CPR 2.398

A

LATED INPORMATI

~HRffl"=Riet:Jrcfl~tNf~tMJ!rffonON SECURITY-RE - \'VITt II IOLD UNDER 18 OFR 2.398 k Public Power District SL-012450 Nebras a Station Revision 1 Cooper Nuclear REPORT FLOOD HAZARD REEVALUATION _,_,..No..* 11784-017 P,"""',

1 1

o ...F,.__ .,.,r_

I

Moflow-

T-I I

Local Intense PreeIPnation (UP) 2-22 5arge nc& L.u"d\f

A SEOURIT'r-

RELATED INF

~HRIT¥"=Rt~ffi=&iNFORRNM1<b!t'TTttlOmN - WITHHOLD UNBER 16 CFR 2.996

SECURIT¥-RELATEB INFORMATION - WITHHOLB UNBER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 117~.-017 Figure 2.1-8: HEC-RAS Cross Sections for Zone A i- I-

~

I- i- i-Local Intense Precipitation (UP) 2-23 5-*"" &. Lundy SECURIT¥-RELATEB INFORMATION - WITI II IOLD UNDER 18 OFR 2.398

SECUfflT'f-ffELATEB INFORMATION - WITI II IOLD UNDER 18 OFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.1-9: HEC-RAS Cross Sections for Zone B (sheet 1 of 2)

- "'-' Pl.an 02 311°"'3>10 Zore8 Plan:PlonQ2 3/l inOIO II ICII IIQQC

...~ iii-iiin9

~-.-.

i i

,, 1-----01----

~;.;iii-ii l

,m:maa*6CIII 0 MI0:!1111-GIDla

_ 111, Local Intense Precipitation (UP) 2-24 SEOURIT¥-ffELATEB INFOffMATION - 'li1ITI II IOLB UNDER 18 Offf 2.998

SECURITY-RELATED INFORMJl<TION - WITHHOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL--01 2450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No .: 11784--017 Figure 2.1-9: HEC-RAS Cross Sections for Zone B (sheet 2 of 2)

- - ---IDCD---___,i 1--- - - - 0 l - - - -....i

~~

Zono8 Pion. Pbn 02 311Dt'20l5 we;--

w....-....

6 J

- l'\orc P\an02

.. lo-----.c:,-- - - i lllDO JrlQQIIIS Zorw8 -

Pion Pion 02

~- - - -.r.i-----li 112111 S/IQQIII ~

_,__ _ . .,_____t e tGO m__

e,,-~

m,.,.._

ICII JIIO

- 300 .,C, SOO 600 0 100 :00

- le>> 40Q 9QD- 100 tc:D200lDDGD G Local Intense Precipffation (UP) 2-25 &org-,nc & Lundy c SECURIT¥-RELATED INFORMJl<TION - WITHHOLD UNDER 16 CFR 2.996

SECURIT'f -RELATEB INFORMATION - 'tVITHHOLD UNDER 16 CFR 2.396 Nebraska Public Power District SL~12450 Cooper Nuclear Station Revision 1 FLOOD HAzARD REEVALUATIO N R EPORT Project No.: 1178-017 Figure 2.1-10: HEC-RAS Cross Sections for Zone C (sheet 1 of 2) z....c

-*-~

ZoNC z....c i ....... _

WSf"_,.......

l'Qf'~ . . . . . .

ws,.... ~

i j l'

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

ZonoC ZoNC z....c mr.....~

~

t i .: j Local Intense Precipitation (LIP) 2-26 SECURIT¥-RELATED INFORMATION - WITI II IOLD UNDER 18 CFR 2.398

SECURIT"*RELATEB INFORMATION - 't\11TI II IOLB UN BER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAzARD REEVALUATION REPORT Project No.: 11784.017 Figure 2.1-1 O: HEC-RAS Cross Sections for Zone C (sheet 2 of 2)

.. - -..- TF.~

-.--~ -----------

-,r-~

j' ...

.,-ao, i F-;-§ §;;J j----c---,--,----:-a - - - - - - - ;

,.. __ l - -- - - ..

Zon4C

- - ---4!

o,-

11 a;.f"l!UI( - - - .

,. ~

. .:. II a...--~

~~

ar--~

~

I. I -. I Local Intense Precipitation (UP) 2-27 S..rganc & Lundy ,.

SEOURIW-RELATED INFORMATION - WITI II IOLB UNBER 18 CFR 2.998

SECUfUTV-RELATEB INFORMATION - WITHHOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 1178-017 FLOOD HAZARD REEVALUATION REPORT Figure 2.1 -11 : HEC-RAS Cross Sections for Zone D (sheet 1 of 4)

J i Z.,.,.O -*-

,.,,. "'-0$ lt 10iJIUt

.I '

J I

Local Intense Precip itation (LIP) 2-28 Sarg'""" & Lundy SECURITY-RELATED INFORMATION - 1ttITttt1OLB UNBER 16 CFR 2.996

SECURITY-RELATEB INFORMl!tTION - VIITI It IOLB UNBER 18 CFR 2.398 Nebraska Public Power District SL.()12450 Cooper Nuclear Station Revision 1 Project No.: 1178-4--017 FLOOD HAZARD REEVALUATION REPORT Figure 2.1-11: HEC-RAS Cross Sections for Zone D (sheet 2 of 4 )

li l

-- ~-- .-

........... s .... . . . . ~

~ .,_

Local Intense Precipitatio n (UP) 2-29 Sftrg..nc & Lundy

SECURITY-RELATEB INFORMl!tTION - WITtlttOLB UNBER 18 CFR 2.398

9EOURIT¥-RELATED INFORMATION - WITI II IOLD UNDER 18 CFR 2.998 Nebraska Public Power District Sl-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178~17 Figure 2.1-11 : HEC-RAS Cross Sections for Zone D (sheet 3 of 4) m,_.....,.

eo,.,.......

. ~--.

' r l f

J:ll!tl//0

-111

"-,,,,_Ol VW2010

~

~- -

111""9,.....

,...~

..r.

. .r*

Local Inten se Precipitation (UP) 2-30 S...rg*nt; C. L..uncty

9EOURIT¥-RELATED INFORMATION = VIITI II IOLD UNDER 18 OFR 2.398

SECURITY-RELATEB INFORMATION - WITHHOLB UNBER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.1-11: HEC-RAS Cross Sections for Zone D (sheet 4 of 4)

~!!!:::I Z..-0

- -~

~,....01 1/lGr.11..

- ~~

i::::::::!!!!!!::::::JI Local Intense Precipitation (UP) 2-31 Ser-gene & Lundy SECURIT¥-RELATEB INFORMATION - WITI II IOLB UNBER 18 CFR 2.398

SECURIT¥*RELATED INFORMA1'16N - 'NITHHOLE> UNE>E" 16 CPR ! .S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION Rl!PORT Project No.: 11784-017 2.2 FLOODING IN STREAMS AND RIVERS (PMF)

The Cooper Nuclear station (CNS) is located on the west (right) bank of the Missouri River in Nemaha County near Brownville, Nebraska at approximate Missouri River Mile (RM) 532.5 (see Figure 2.2-1 ).

In this section of the report, the Probable Maximum Flood (PMF} in the Missouri River was evaluated to assess the flooding hazard on the safety-related facilities at CNS. The PMF is the hypothetical flood (peak discharge, volume, and hydrograph shape) that is considered to be the most severe reasonably possible, based on comprehensive hydrometeorological application of the Probable Maximum Precipitation (PMP} and other hydrologic factors favorable for maximum flood runoff, such as sequential storms and snowmelt (Reference 2.2-1 ).

The hydrologic conditions in the Missouri River at CNS are complex due to size of the contributing Missouri River watershed (414,900 square mlles above Rulo, Nebraska near CNS, United States Geological Survey [USGS] gage number 06813500 [Reference 2.2-21) and the six System dams (Fort Peck, Garrison, Oahe, Big Bend, Fort Randall, and Gavins Point) located on the mainstem of the Missouri River upstream of CNS (Figure 2.2-2 sheet a). The Missouri River is the longest river in the United States, draining one-sixth of the country (Reference 2. 2-3). The U.S. Army Corps of Engineers (USACE) regulates all of the System dams. They are regulated as a hydraulically and electrically integrated system. Runoff from upstream of the System dams is stored in the six reservoirs. USAGE controls the water release from the System dams. Released water from the most downstream dam in the System, Gavins Point Dam, flows down the Missouri River toward CNS. In addition, there are also a large number of other dams (referred to as "Non-System" dams) in the drainage basins contributing to the Missouri River downstream of the "System" dams and upstream of CNS (see Figure 2.3-1 ).

The U.S. Nuclear Regulatory Commission (NRC), in Section 5.3 of NUREG/CR-7046 (Reference 2.2-1), suggests use of flood simulation models developed by federal agencies, such as USAGE. Following such recommendations, the Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS, Reference 2.2-4} and the Hydrologic Engineering Center River Analysis System (HEC-RAS, Reference 2.2-6) were used to perform the hydrologic (Section 2.2.2) and hydraulic (Section 2.2.3) analyses, respectively.

The PMF value for CNS was developed using the following steps:

Determine probable maximum precipitation (PMP) over the basins that drain into the Missouri River below Gavins Point Dam and upstream of CNS.

Develop the PMF hydrographs by applying the PMP over the basin.

Route the PMP runoff using one-dimensional (1-D) unsteady basin-scale hydraulic model and generate boundary conditions for a reach-scale two-dimensional (2-D) hydraulic model.

Determine depth and velocity of the fiow at CNS during PMF using a reach-scale 2-D hydraulic model.

Flooding in Streams and Rivers (PMF) ,.,~*

2-32 ( * ..

Sorgc "t- &JLunc1y1 1c:

\ .

,,Jr '

SECURIT¥-"ELATED INFORMATION - WITHHOLE> UNBER 16 CF" 2.998

SECURIT't' -RELATEt, INP.ORMATION =WITHHOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-01 7

Calculate wind setup, wind-wave runup, and hydrostatic and hydrodynamic forces on systems, structures, and components (SSCs) and other buildings at CNS due to the PMF.

Calculate debris impact forces and evaluate the erosion and sedimentation at the site.

Details of each step of the analysis are provided in the following sections.

2.2.1 Probable Maximum Precipitation (PMP)

In this section of the report, estimation of a realistic, yet conservative, PMP over the Platte River Basin and the adjoining reaches of the Missouri River identified as the Lower Basin (Fort Calhoun) and the Lower Basin (Cooper) is discussed (see Figure 2.2-3). This PMP was used to determine the maximum water level at CNS at Missouri RM 532.5 resulting from the PMF in the Missouri River.

2.2.1.1 Basin Delineation The applicable basin was delineated using the United States Department of Agriculture (USDA)

Watershed Boundary Dataset (Reference 2.2-7). Watershed boundaries define the aerial extent of surface water draining to a particular point, which is CNS. The watershed boundaries were defined through the use of hydrologic units (HUs) to establish a baseline rain gage boundary framework, accounting for all land and surface areas. Geographical Information System (GIS) software, specifically Environmental Systems Research Institute (ESRI) ArcGIS (Reference 2.2-8), was used to delineate the basin. The delineated basin outline is shown in Figure 2.2-3.

2.2.1.2 PMP Alternatives Section 9.2.1.1 of ANSI/ANS-2.8-1992 (Reference 2.2-9) and Appendix Hof NUREG/CR-7046 (Reference 2.2-1) specify three different alternatives for a flood reevaluation analysis. The alternatives comprise a combination of:

Alternative 1 - mean monthly (base) flow, median soil moisture, antecedent or subsequent rain (the lesser of rainfall equal to 40% of the PMP and a 500-year rainfall),

PMP, and waves induced by the 2-year wind speed applied along the critical direction.

Alternative 2- mean monthly (base) flow, probable maximum snowpack, a 100-year, snow-season rainfall, and waves induced by the 2-year wind speed applied along the critical direction.

Alternative 3- mean monthly (base) flow, a 100-year snowpack, snow-season PMP, and waves induced by the 2-year wind speed applied along the critical direction.

An evaluation of these alternatives showed that Alternatives 2 and 3 do not create an extreme peak in a short time period as Alternative 1 does. Therefore, Alternative 1 was used in this analysis as it was the most conservative approach.

The 500-year, 72-hour rainfall value for a point at the centroid of the PMP analyses for the basin was obtained from National Oceanic and Atmospheric Administration (NOAA) Atlas 14 (Reference 2.2-10).

Flooding in Streams and Rivers (PMF) 2-33 ((

S :::n"g B n \ ~ Lundy 11c

)-/

SECURIT¥*RELATEB INFORMATION - Vt,ITHHOLB UNBER 16 CP.R 2.996

SEOURIT¥*RELA1'Ef} INFORMATION - VilTHHOLf> UNE>ER 16 OFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Analysis showed that applying a 40% PMP over the basin results in approximately one half the rainfall volume that a 72-hour 500-year storm event would create. Therefore, the 40% PMP was considered as the antecedent rain. The 40% PMP storm event will precede the PMP storm event by 3 days (3 to 5 days allowable in ANSI/ANS-2.8-1992, Reference 2.2-9) as this period of transition is meteorologically reasonable for this region of the United States.

2.2.1.3 PMP Development PMP storm depth, spatial distribution, centering, and orientation pattern for a 72-hour storm period adopted for the drainage basins upstream of CNS and downstream of Gavins Point Dam were derived following the procedures described in the National Weather Service (NWS) Hydrometeorological Reports 51 and 52 (HMRs 51 and 52, References 2.2- 11 and 2.2-12, respectively). The PMP estimates obtained from these HMR procedures are location-specific and have accounted for orographic and seasonal effects.

The Jo~er portion of the Basin (38,672 square miles), including the Platte River watershed below Lake Mcconaughy and the portion of the Missouri River watershed between Gavins Point Dam and CNS, was chosen as the watershed area of interest for this PMP analysis. Centering the PMP event over the lower portion of the Basin produces the most hydrologically conservative result. ANSI/ANS-2.8-1992 (Reference 2.2-9) recommends that enough storm center positions be considered to ensure that the most critical condition has been determined. In this study, four storm centers (centroids) and orientations (Figure 2.2-4) were used so that the hydrologic sensitivity and resultant flows from the analyses of the PMP could identify through hydrologic modeling (Section 2.2.2) which location would produce the highest water elevation at CNS. The following steps were performed in establishing the PMP resulting in the highest water elevation at CNS:

Obtain the all-season precipitation values from HMR 51 at all four storm centers for basins ranging from 10 to 20,000 square miles for the 6-, 12-, 24-, 48-, and 72-hour durations.

Because the maximum basin size available from HMR 51 data is 20,000 square miles, only four basin sizes less than the 20,000 square miles were analyzed, in order to develop an envelope that generates the maximum precipitation volume. Basin sizes of 20,000-, 15,000-, 10,000-, and 6,500-square miles were chosen to develop the envelopment curves.

The incremental differences between Oto 6-hour, 6 to 12-hour, and 12 to 18-hour precipitation values were then calculated and the digitized isohyet pattern was centered on the basin centers and oriented along the long axis of each basin (Figure 2.2-4) using GIS software.

Determine the cumulative rainfall volume for each of the four enveloping basin sizes to determine which size has the highest volume and, therefore, the highest PMP value.

The 20,000 square miles of watershed yielded the highest precipitation volume with the exception of the fourth center (P4 in Figure 2.2-4) analysis in which the 15,000-square mile watershed yielded the highest precipitation volume.

Flooding in Streams and Rivers (PMF) 2-34 SEOURIT¥-RELATED INFORMATION - WITHHOLE> UNE>ER 16 OFR 2.996

SECURIT'f-REl:Al'EEJ INPO"MAl'ION - WITI lliOLEJ UNEJER 16 CFR 2.996 Nebraska Public Power District SL-01245O Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017

Distribute the storm-area-averaged PMP over the drainage basin and develop precipitation depths for each storm area and 6-hour temporal distribution period (see Table 2.2-1 ). The 40% PMP storm event was then determined by multiplying the data in Table 2.2-1 by 0.4.

2.2.2 PMP Runoff Hydrographs A hydrologic model of the Missouri River extending from downstream of Gavins Point Dam to Kansas City, Missouri was originally developed by USAGE Omaha District (USAGE-OD, Reference 2.2-13) using HEC-HMS Version 3.5. This existing model was obtained and modified for this study to generate hydrographs from the basins upstream of CNS and downstream of Gavins Point Dam that contribute to the Missouri River PMF at CNS. The process used to develop the PMF hydrographs for the watersheds upstream of CNS includes the following:

Review basin model configurations and parameterizations.

Validate the reasonableness of the model at key locations for each basin.

Determine the highest-computed PMF hydrograph at CNS based on hydrologic modeling.

2.2.2.1 Hydrologic Model Development The eight HEC-HMS models (one for each river basin depicted in Figure 2.2-2) received from USACE-OD used the following methods: Deficit and Constant loss, ModClark transform, Recession baseflow, and Muskingum-Cunge channel routing. A summary of model input parameter definitions and references are provided in Table 2.2-2. The analysis incorporated the Hierarchical Hazard Assessment (HHA) approach outlined in Section 2 of NUREG/CR-7046 (Reference 2.2-1 ). Consistent with the HHA approach, any adjustments to model input parameters were made globally conservative to the extent possible without increasing the level of detail of the model.

The USACE-OD basin model inputs were reviewed and verified by comparing the values with the corresponding range of values available in standard literature. The spatial distribution of the initial deficit, constant loss rate, and maximum deficit values were evaluated by creating a map of the basin and examining the variation in values across the basin model as compared to hydrologic soil group. In addition, the loss and transform parameters were verified for a typical subbasin within each basin or major tributary using values and equations found in the standard literature.

The United States Geological Survey (USGS) indicates that a small portion of each drainage area is non-contributing area; however, conservatively all areas were considered as contributing in the model.

The PMF is such an extreme event that normal drainage patterns may be altered; therefore, inclusion of the non-contributing drainage area would produce a conseNative estimate of the PMF hydrograph for CNS.

Flooding in Streams and Rivers (PMF) .*(

/ \

2-35 Sarg0~ ' '

~ t Lundy 1 *,

_;/

8ECUftlT¥-RELATEEJ INFORMATION - WITH HOLE> UNf>ER 1e CFR 2.996

SECURIT'f-R:ELATED INI-OR:MATION - WITI II IOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD RHVALUATION Rl!PORT Project No.: 11784-01 7 2.2.2.2 Hydrologic Model Validation Daily stream flow data were used for upstream boundary conditions to validate model performance at key locations within the basin. Such data were obtained from the USGS and Nebraska Department of Natural Resources (NDNR} Websites (References 2.2-2 and 2.2-13, respectively).

To examine the reasonableness of the magnitude and timing of the peak flow and the volume of the hydrographs, the models were executed for the largest historic storm for which data were available and computed hydrographs were compared to stream gage values at the key locations within the basin. The selected storm was a 1984 storm for all basins except the Platte River basin, which used a 2010 storm.

The model hydrographs were compared to measured hydrographs by computing the Nash-Sutcliffe model efficiency coefficient (NSE). The NSE generally is used to assess the predictive power of a model's ability to reproduce observed data. NSE ranges between negative infinity and 1.0 (1 inclusive),

with NSE = 1 being the optimal value. Essentially, the closer the model efficiency is to 1, the more accurate the model. In addition to NSE, the Pearson correlation coefficient (r) was determined. The coefficient provides a measure of the linear relationship between two variables, in this case, measured and computed discharge. The models were considered validated when the modeled versus measured hydrograph NSE was greater than 0 and/or r was greater than 0.7, unless otherwise justified.

If required, model parameters were adjusted to obtain an acceptable fit to USGS hydrographs. Analysis showed that the basin response was most sensitive to the constant loss rate. Therefore, the constant loss rate was reduced in all models and other parameters were adjusted until a reasonable match to gage records was realized. An attempt was made to globally reduce all constant loss rates in the basin; however, it was found that reducing the constant loss rate variably within the basin provided the best fit for each gage location. Some of the reduced constant loss rates were lower than the recommended range listed in Table 11 of HEC-HMS Technical Reference Manual (Reference 2.2-4), but the modified rates are considered acceptable and produced more conservative model results. To match the baseflow and recession limb of the hydrograph, the recession constant and initial discharges were further adjusted. The computed hydrographs provided a relatively good fit to the measured values in terms of peak discharge, volume, and timing, especially for the magnitude of the historic storm used and the size and relative coarseness of the model.

2.2.2.3 PMF Hydrograph Determination The PMF hydrograph is a result of applying a PMP over a specific area and routing the resulting hydrographs to a point of interest, which is CNS. PMP positions (as discussed in Section 2.2.1, Figure 2.2-4) were executed using the validated model for the watersheds upstream of CNS and downstream of Gavins Point Dam. As discussed in Section 2.2.1.2, the 40% PMP value was considered as the antecedent or subsequent storm. According to ANSI/ANS-2.8-1992 (Reference 2.2-9}, a preceding storm usually is the more critical, but an alternative subsequent timing should also be investigated.

Therefore, in addition to the antecedent storm with the PMP, another simulation was performed with the PMP and the subsequent storm. This was done only for the position that resulted in the highest PMF at CNS to compare whether the antecedent or subsequent condition resulted in a higher peak. The sequential timing (3-day lag) was the same as the antecedent condition.

Flooding in Streams and Rivers (PMF) 2-36 ,.,,,r*\

Sargent:& Luncty 1

11:

\ ,i

,Y SECURITY-RELATED INFORMATION - VtlTHHOLB UNBER: 16 CFR: 2.996

SECURIT't'-RELATEE> INFORMATION * 'NITHHOLE> UNE>ER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION Rl!PORT Project No.: 11784-017 NUREG/CR-7046 (Reference 2.2-1), recommends increasing the unit hydrograph peak discharge by 5% to 20% and reducing the unit hydrograph Jag time by 33% to account for non-linearity effects during an extreme event such as the PMF. The HEC-HMS modeling framework in this analysis used the ModClark transform, which does not produce a unit hydrograph. Therefore, instead of increasing the peak discharge or reducing the lag time of a unit hydrograph, the time of concentration in all subbasins was reduced by 33% as a surrogate for reducing unit hydrograph lag time and the constant loss rate was reduced so that the peak discharge was increased from 5% to 20%.

ANSI/ANS-2.8-1992 (Reference 2.2-9) recommends mean monthly flow during the month of occurrence of the PMF to be used as the baseflow at the beginning of an antecedent storm. Where USGS gage data were available, the initial baseflow values of the subbasins draining to the gage locations were adjusted to match the maximum mean monthly flow during the months when the PMP will most likely occur. The initial baseflow values in subbasins for which no USGS gage data were available were not changed. The four PMP positions in this Midwestern part of the country will likely occur in the warmer months of the year. Typically, the highest mean monthly flows at the USGS gages used for this study occur in May, June, and July.

PMF hydrographs at Brownville, Nebraska for all four PMP positions with 40% antecedent storm are presented in Figure 2.2-5. Similarly, hydrographs with 40% subsequent PMP are shown in Figure 2.2-6.

Analysis results (Figure 2.2-5 and Figure 2.2-6) showed that the 40% PMP Position 3 (Figure 2.2-2, sheet c) followed by 3 days of no precipitation, followed by the PMP Position 3 (Figure 2.2-2, sheet c) resulted in the highest peak flow at CNS, which was considered as the controlling PMF hydrograph and was routed through the Missouri River using dynamic hydraulic modeling (as discussed in Section 2.2.3).

Position 1, centered over the Platte Basin and Loup River Basin (Figure 2.2-2, sheet a), resulted in the lowest peak PMF at CNS. This is due to the presence of sandy soils in the Loup Basin and the associated relative high constant loss rates compared to adjacent basins. Position 4 (Figure 2.2-2, sheet d), centered near CNS, resulted in the second lowest peak PMF at CNS. This is due to the storm being centered over the lower portion of the contributing basin at CNS, and thus not having the runoff volume necessary to produce a relatively large PMF. Position 2 (Figure 2.2-2, sheet b) generated the second highest peak PMF at CNS. The Platte River and Elkhorn River contributed most of the peak discharge.

Figure 2.2-5 shows that the PMP Position 3 hydrographs have a peak discharge of approximately 832,250 cubic feet per second (cf:S) at CNS. Figure 2.2-7 shows the location and RM of each junction that their outflow hydrographs from the hydrologic model were used as an input to the hydraulic simulation described in Section 2.2.3.

2.2.3 Water Level Determinations The hydraulic conditions in the Missouri River between Gavins Point Dam (approximate RM 810) and CNS during flood flows are complex due to the presence of revetment, river training structures, levees, roadway embankments, river meanders, and bridges. To evaluate this complexity, a multi-leveled modeling approach was adopted in this flood hazard reevaluation study. A 310-mile basin-scale one-Flooding in Streams and Rivers (PMF) 2-37 SECURIT'f-RELATEE> INFORMATION - WITHHOLE> UNE>ER 16 CFR 2.996

SECURITY-RELATEB INFORMATION - WITHHOLE> UNBER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION Rl!PORT Project No.: 11784-017 dimensional (1-D) HEC-RAS unsteady model was used to predict the PMP hydrograph (as discussed in detail in Section 2.2.2) translation and attenuation in the Missouri River from Gavins Point Dam to CNS.

The results from the 1-D basin-scale routing model were then used as upstream boundary conditions for a reach-scale two-dimensional (2-D) hydraulic model. This reach-scale model, approximately 46 miles in length, was further used to predict the complicated interaction between the river channel and overbank areas that provides an estimate of flow distributions near CNS. The results from this 2-D reach-scale model were used to predict water surface elevations and velocities at CNS for the PMF.

2.2.3.1 One-Dimensional Steady-State Hydraulic Model In 2003, an unsteady model was developed and calibrated by the USACE-0O for the Upper Mississippi River System Flow Frequency Study {UMRSFFS), Reference 2.2-14. The Federal Emergency Management Agency (FEMA) regulatory model was developed in HEC-RAS by converting the UMRSFFS unsteady model to a steady-state model and then calibrated to the unsteady model 100-year flood event results (Reference 2.2-15). This model was obtained from FEMA and used for evaluatiqn of PMF at CNS. The model had undergone rigorous review prior to acceptance by FEMA.

The regulatory FEMA HEC-RAS steady-state model of the Missouri River was used to develop a 1-D HEC-RAS steady-state hydraulic model of the Missouri River for CNS PMF analysis that became the basis for the 1-D HEC-RAS unsteady model of the Missouri River (as discussed in Section 2.2.3.2).

The process used to develop the 1-0 steady-state hydraulic model from the regulatory FEMA model included:

The hydraulic model cross sections were modified and updated with post 2011 flood bathymetric and Light Detection and Ranging (UDAR) survey data.

Manning's roughness coefficients varied both horizontally and from cross section to cross section, but remained within the range of published values. In certain instances, Manning's roughness coefficients outside of the published ranges for overbank land uses were used to describe flow resistance from buildings or other overbank structures.

The sensitivity of steady-state hydraulic results at the Missouri River near CNS (RM 532.35) was assessed with a discharge of 290,000 cfs by increasing and decreasing the Manning's roughness coefficients in the model domain by 10% and 20%. Analysis demonstrated that the model results were sensitive to Manning's roughness coefficients, which is consistent with guidance in NUREG/CR-7046, Section 5.4 (Reference 2.2-1 ). However, the majority of stage-discharge comparisons from this sensitivity analysis are within the 95% prediction interval.

The sensitivity of steady-state hydraulic results for the Missouri River near CNS (RM 532.35) was assessed with a discharge of 290,000 cfs by increasing and decreasing the normal depth slope of the downstream boundary from 0.0001 to 0.0002 and 0.00005. The mean channel velocity and water surface elevation WSEL were identical between the three runs at this location. This indicates that the downstream boundary condition is located at an adequate distance downstream of CNS.

The model was calibrated for 100-, 200-, 500-year, and 2011 flood events (Reference 2.2-14) to better replicate published stage-discharge relationships. The NRC, in NUREG/CR-7046, Section 5.5 (Reference 2.1 -1), prescribes validation of the Flooding in Streams and Rivers (PMF) , f'

/*

2-38 Sorge~ ~ Luncty1*c 1

)/

SECURIT¥-RELATEB INfilORMATION - WITHHOLB UNE>ER 16 CFR 2.396

SECURIT¥-RELATED INFORMATION - Vt1ITlltt0LB UNDER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Pmjecl No.: 11784-017 simulation models using the largest historical flood near the site. The 2011 flood event on the Missouri River resulted in the highest peaks within the modeled reach since 1952 (i.e., prior to construction of the five lower mainstem dams). Therefore, the measured data at USGS stream gages were considered the best available information because the data were collected during the 2011 flood event. The computed WSELs compared favorably to measured gage data and published flood insurance study (FIS) values for the 100-, 200-, and 500-year discharges within the modeled reach. In addition, the computed WSELs compared reasonably to measured values within the reach for the 2011 flood flows. Therefore, the model was considered cali brated for flows between the 100- and 500-year events (including the 2011 flood event) and, in accordance with NUREG/CR-7046, Section 5.5 (Reference 2.1-1 ). provides some assurance that the estimated design-basis floods will not be underestimated. In the calibrated HEC-RAS steady-state model, the channel Manning's roughness coefficients varied from 0.025 to 0.029 in the channel and generally from 0.020 to 0.120 in overbank areas.

2.2.3.2 , One-Dimensional Unsteady Hydraulic Model The 1-D steady-state hydraulic model of the Missouri River, as discussed in the previous section, was the primary data source for the HEC-RAS unsteady model. With the exception of modifications to the Manning's roughness coefficients, levee locations, and ineffective flow areas, the geometry from the steady-state model was used in the unsteady flow analysis. Figure 2.2-1 shows the extent of the modeled reach. The model was used to generate boundary conditions, including an upstream inflow hydrograph, upstream flow distributions, and a downstream stage hydrograph for a reach-scale unsteady 2-0 model of the Missouri River valley in the proximity of CNS. Specifically, this model predicted translation and attenuation of hydrographs that contribute to the PMF at CNS, considering inflows at Gavins Point Dam and tributaries throughout the modeled reach. The process used to develop the unsteady model included:

Validate the HEC-RAS unsteady model with input and gage data from the 2011 flood event, making the necessary changes to replicate observed discharges, stages, and timing.

Analyze PMF flaw scenarios using the HEC-RAS unsteady model.

Establish inflow discharge hydrographs at RM 556.16 and outflow rating curve(s) at RM 510.03 to be used as boundary conditions for the unsteady 2-D model.

2.2.3.2.1 HEC-RAS Unsteady Model Development There are approximately 133.5 total miles of federal levees along the M issouri River. To address the uncertainty associated with predicting event routing through the modeled reach, some simplifying assumptions were made in order to develop a conservative estimate of flood translation and attenuation. Only federal levees were included in the model, which is consistent with the approach used by USAGE in the UMRSFFS (Reference 2.2-14). It is d ifficult to predict when, where, and how levee overtopping or breaching wiU occur over approximately 133.5 miles of levee using a 1-D unsteady model. Overtopping of the levee can be modeled considering levees as lateral weirs, but the assumption was made that the inclusion of lateral weirs was unnecessary to calculate a conservative Flooding in Streams and Rivers (PMF) 2-39 SECUR.I T¥-RELATED INFORMATION - WITHHOLD UNBER 18 efiR ! .996

SEOURIT¥-RELATED INFORM:ATION - 't'ilTHHOLD UNDER 16 CI-R 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-01 7 estimate of the hydrograph translation and attenuation throughout the system. Detailed hydraulic analysis in the vicinity of the site was performed using the reach-scale 2-D model. Therefore, two levee scenarios were evaluated for the unsteady analysis to "bookend" the boundary condition: complete levee failure (full floodplain) and the levees remain in place (levee-constrained).

Sensitivity of both upstream and downstream boundary locations of the 2-D model was tested by changing the Manning's roughness coefficient within a range of 20%. Analysis showed that PMF timing and magnitude at RM 556.16 (2-D model upstream boundary location) were not significantly sensitive to changes in Manning's roughness coefficient. The results demonstrated that the downstream boundary (at RM 510.03) of the 2-D model was sensitive to changes in Manning's roughness coefficient. This highlighted the importance of using Manning's roughness coefficients that had been validated.

In an unsteady simulation, non-conveyed volume would be temporarily stored in the overbank until the bank elevation is exceeded. Therefore, levee features were assigned to prevent water from being stored in the overbank until the channel bank elevation was exceeded. Aerial photography (Reference 2.2-16) was used to determine locations where flow was cut off by natural or man-made blockages.

A summary of the HEC-RAS unsteady computational model parameters are presented in Table 2.2-3.

2.2.3.2.2 HEC-RAS Unsteady Model Validation Several USGS stream gages are located within the modeled reach (Figure 2.2-1 ). Stage and discharge measurements recorded by USGS at these gage sites during the 2011 flood event were used to generate the inflow boundary conditions of 14 tributaries between RM 810 and RM 498. USAGE-reported daily discharges (Reference 2.2-17) at Gavins Point Dam were used to generate the inflow hydrograph at Gavins Point Dam for the validation event and to identify a discharge to be considered as a coincident flow with the PMF. The location of all inflow hydrographs pertaining to this evaluation are presented in Table 2.2-4.

The NSE was evaluated for the predicted stage and discharge hydrographs within the modeled reach (Reference 2.2-18). The HEC-RAS unsteady model was considered validated provided that:

NSE for each flow hydrograph was greater than 0.90 of the value reported at the gage locations.

Computed 2011 peak water surface elevations were within +/-1 foot of observed WSELs at gage locations.

Any locations and/or instances that do not meet the above two criteria were justified based on levee breach location and chronology (Reference 2.2-19).

The model was executed using the same roughness coefficients used for the steady-state hydraulic model (Section 2.2.3.2). The flow hydrograph matched reasonably well; however, the stage hydrographs were systemically 1 to 2 ft low. Therefore, in an effort to produce a model that achieves better validation criteria, a simulation with a 10% global increase of Manning's roughness coefficient for Flooding in Streams and Rivers (PMF)

..*{*.

2-40 (

Sarga~&.J Lundyc y

SECUfUTY-ftELATEB INI-ORMATION - Wilt lttOLD UNDER 18 01-R 2.396

SECURIT'l'-RELATEB INFORMATION - WITHHOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEV~LUATION REPORT Project No.: 11784-017 both the channel and overbank was executed. Table 2.2-5 shows the minimum and maximum roughness coefficients.

Graphical comparisons of observed and computed discharge hydrographs and stage measurements at

the gage locations were evaluated. The timing and magnitude of predicted flow hydrographs for the 2011 event compared well with the recorded flow hydrograph. The summary of the NSE coefficient along with peak discharge and stage comparisons are shown in Table 2.2-6.

2.2.3.2.3 PMF Hydraulic Simulations The resultant tributary discharges from the final model using PMP Position 3, preceded by the 40%

PMP antecedent condition simulation (as discussed in Section 2.2.2) were used in the HEC-RAS unsteady model as lateral inflow discharges at tributary locations throughout the model. For smaller tributaries, contributing flows were aggregated and incorporated at a RM corresponding to the approximate inflow location, and were referred to as Missouri Basin Inflow. Table 2.2-7 summarizes the location of inflow hydrographs used in the model. Additionally, the downstream boundary condition of a normal-depth boundary with a slope of 0.0001 *was specified in the model based on sensitivity to validation results.

Two different releases from Gavins Point Dam were considered: the mean monthly average flow of 35,000 cfs and the release of the record flow (from the 2011 flood event, Reference 2.2-17) of 160,000 cfs. Additionally, as discussed in Section 2.2 .3.2.1, for each flow condition, two simplifying assumptions were made to provide conservative approximations of PMF translation and attenuation through leveed reaches: full floodplain and levee constrained.

The HEC-RAS unsteady model cross section at RM 556.16 was chosen as the upstream boundary condition of the 2-D model because it is located at a sufficient distance upstream of the point of interest (i.e., CNS) and a tie-back levee, as well as a major confluence (the Nishnabotna River).The downstream boundary condition of the reach-scale 2-D model was located at RM 510.03. This location is approximately 5 miles downstream of federal levee alignments and is in a relatively straight river reach 20 miles downstream of CNS. Analysis of results showed that the full-floodplain condition with 160,000 cfs at Gavins Point Dam results in the highest peak discharge and includes the most conservative Gavins Point Dam release. Therefore, this condition was used for the upstream inflow hydrograph for the 2-D model. The hydrographs, as they translate and attenuate throughout the modeled reach, are shown in Figure 2.2-8. The hydrographs at RM 556.16 are shown in Figure 2.2-9, and the peak magnitude and date are summarized in Table 2.2-8. The rating curves created from the HEC-RAS unsteady model results from both levee conditions were nearly identical, as shown in Figure 2 .2-10.

2.2.3.3 Two-Dimensional Reach-Scale Hydraulic Model The purpose of conducting a detailed 2-D hydraulic model of the Missouri River near CNS was to determine spatially and temporally varying information about water surface elevations, depths, and velocities at CNS during the PMF. Evaluation of site-specific erosion, sedimentation, and debris effects was also performed based on information available from the 2-D model. The modeled (i.e., 2-D) reach Flooding in Streams and Rivers (PMF) /

,* \

2-41 S orge~& Luncty**11

\ }

)

9ECURIT¥-FtELATEB INFORM>\TION

WITtil IOLB UN BER 16 CFR 2.998

SECURlf>f=RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11764-017 FLOOD HAZARD REEVALUATION Rl!PORT of the Missouri River extended from north of Hamburg, Iowa (approximate RM 556), to north of Craig, Missouri (approximate RM 510). An overview of the modeled reach is shown in Figure 2.2-11 . The process used to develop the 2-D model included:

Developing the digital elevation model (DEM) surface roughness characteristics, appropriate computational mesh and description of levee crests, and boundary conditions from the 1-0 unsteady model, as discussed in Section 2 .2.3.2.1 .

Validating the 2-D unsteady model with gage data and high-water marks (HWMs) from the 2011 flood event and making any changes necessary to replicate observed stages, as discussed in Section 2.2.3.2.2.

Analyzing PMF flow scenarios using the 2-D numerical model TUFLOW FV, as discussed in Section 2.2.3.2.3.

2.2.3.3.1 2-0 Model Development TUFLOW FV, version 2013.02.056_dev (Reference 2.2-20), was used in this analysis to perform the 2-D hydraulic simulation. The model solves the Non-linear Shallow Water Equations (NLSWE) on a flexible mesh using a finite-volume numerical scheme. The model was not extended away from the Missouri River valley. Specifically, it did not include the Nishnabotna River valley in the model geometry. This eliminates potential storage for floodwaters during _ t he PMF, but the effect on peak WSELs at CNS is insignificant because the capacity of the Missouri River valley is large in comparison with the area extending north along the Nishnabotna River. Near the confluence of the Little Nemaha River and the Missouri River, the study area was extended west of the Missouri River valley approximately four miles. By extending the computational domain, the model was able to better calculate the flow distribution across the levees near the Little Nemaha, which is important for inundation at CNS. Major model inputs included digital elevation data, land cover/land use data, a computational mesh, levee crests, and boundary conditions, as described in the following paragraphs:

Elevation Data: The elevation source for the model was based on the combination of the DEM used for the 1 D HEC-RAS steady-state model {Section 2.2.3.1), USGS LiDAR data, USAGE bathymetry data, USGS 10-m DEMs (Reference 2.2-21), and a site-specific survey.

Surface Roughness: A combination of land cover/land use data {Figure 2.2-12) from three states, Iowa (Reference 2.2-22), Missouri (Reference 2.2-21 ), and Nebraska (Reference 2.2-23), were used to assign the appropriate Manning's roughness coefficient representing the surface roughness in the 2-D model.

Computational Mesh: The study area was represented by a computational mesh (Figure 2.2-13 and Figure 2.2-14) containing 410,314 unstructured elements. The mesh was coarser in areas that were farther away from CNS and finer in areas where more detail is required. Buildings at the CNS site were represented by a void space in the computational mesh. The mesh sensitivity analysis demonstrated that changes in mesh size do not cause a large enough change in WSELs to warrant changes from the original mesh size chosen. Most variations were within 0.1 foot at CNS.

Flooding In Streams and Rivers (PMF) ./ 1

/

,' \

2-42 Sor-ga~t;:~ Luncty'1 c

).7 SECURIT'f-RELATEB INFORMATION - VIITI II IOLD UNDER 18 OFR 2.998

SECUftl'f't' -R.ELATEB INFOftMATION - ...t11THHOLB UNBEft 16 CFR. ! .396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 fLDDD HAZARD REEVALUATION REPORT Project No.: 11784-01 7

Levee Crests: Levee crests and roadway embankment elevations from the DEM were incorporated into the model. It was assumed that no levees, railroad embankments, or roadway embankments would be compromised during the PMF. The autoweir function of TU FLOW FV was used, which automatically applies the standard weir equation to embankments and other high points in the model topography. The weir coefficient was estimated to be on the order of 2.5 using Hager's equation (Reference 2.2-24). A sensitivity analysis was performed and as a result, a weir coefficient of 1.6 was used globally. This represents a conservative WSEL at CNS.

Boundary Conditions: The location and type of the boundary conditions are shown in Figure 2.2-11. The 1-D unsteady HEC-RAS model (as described in Section 2.2.3.2.3) was used to establish the Missouri River boundary condition. The PMF hydrograph (Figure 2.2-9) was divided between within levee (referred to as main channel) and outside of levee discharges east of the main channel (referred to as left overbank).

La1eral inflows to the HEC-RAS model at RM 542.10 (Nishnabotna River), RM 535.30 (Honey Creek), and RM 527.8 (Little Nemaha River) were also included. The lateral inflows at RM 535.30 were included with the Missouri River overbank discharge because they represent a basin east of the Missouri River. The inflow hydrographs for each of the four boundaries are shown in Figure 2.2-1 5.

A normal-dep1h condition with a friction slope of 0.00022 was used at the downstream end of the model domain based on the geometry in the HEC-RAS unsteady model, which allowed for different main channel and overbank water surface elevations.

Sensitivity analyses were performed for both upstream and downstream boundary conditions. Results showed that WSEls at CNS were not sensitive to the upstream and downstream boundary condition.

2.2.3.3.2 2..() Model Validation The model was validated for the 2011 Missouri River flood event using the available <lischarge and water level data recorded at USGS gage sites as well as HWMs reported by USAGE after action report (Reference 2.2-19). Since several levee breaches were reported during the 2011 flood event, two different steady-state discharge and levee condition combinations were considered in the validation.

The first geometry considered levee breaches fully developed for L575 (RM 551 and RM 544) and L550 (RM 539 and RM 523), while the second geometry included only levee breaches fully developed for L575 and not L550. The simulation was conducted using steady-state discharge of 257,000 cfs and 207,000 cfs on the Missouri River for the first and second geometric conditions, respectively. The first case provided the highest discharge on the protected or land side of the levee, while the second case generated the highest discharge on the river side of the levee between RM 544 and RM 523.

Simulated WSELs in the channel and interior were on average 0.1 foot and 0.8 foot lower, respectively, than measured HWMs. Within the context of this validation, the model calculated 36,000 cfs Jess discharge in the left overbank than was measured on one day during the 2011 flood event, and discharge in the channel is overestimated. Overall, the model simulated flow distribution across the river valley reasonably well for a reach scale model.

Flooding in Streams and Rivers (PMF) .,.

/\

2-43 \ '

Sargent:. & Lundy

1 o:

\ ,I

.,1-'

SECURIT'f~RELA'fEB IN FORMATION - WITt1HOLB UNBER 16 CFR 2.986

SECURIT¥-RELATEB INFORMATION - 't'YITHHOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.2.3.3.3 2-D Model Hydraulic Simulations The inflow hydrograph used for the Missouri River was the full floodplain routing of the PMF event with a coincident discharge of 160,000 cfs from Gavins Point Dam, as discussed in detail in Sections 2.2.3.2.3 and 2.2.3.3.1. Figure 2.2-16 shows hydrographs at four locations within the modeled reach. From the upstream end of the model to Hamburg, peak discharges increased due to lateral inflows from the Nishnabotna River. Between the Nishnabotna River and CNS, the peak discharge was attenuated due to storage in the left overbank. Downstream of CNS, peak discharges increased again due to lateral inflows from the Little Nemaha River. The peak PMF discharge at CNS was 797,600 cfs.

Most of the CNS main plant areas were not inundated during the PMF event. Figure 2.2-17 and Figure 2.2-18 present contour plots of the maximum WSEL. Model results showed that the peak WSEL In the main channel near the intake structure was 902.8 ft NAVD88. The peak WSEL at CNS, which occurs at the upstream side of the plant on the main channel side of the levee (see Point Bon Figure 2.2-18),

was 903.3 ft NAVD88. When WSELs in the right overbank peak, the model indicated shallow flooding with depths of 0.5 foot or less near the Security Building (see Point 3 in Figure 2.2-18).

Maximum water depths are shown in Figure 2.2-19 and Figure 2.2-20 and contours of maximum velocity magnitude are shown in Figure 2.2-21. Peak velocities were less than 0.5 fps across much of the site, with the highest velocities seen where the federal levees north of the site are overtopped.

Model results indicated that velocities in that area peak between 5 and 6 fps.

Water depths and velocities are further investigated at three critical locations, including the Intake Structure, Switchyard, and the Elevated Release Point (ERP). A summary of grade elevation, maximum WSEL, maximum velocity, and maximum depth are provided in Table 2.2-9.

2.2.4 Combined Effects Determination of the total water level at the CNS site with the consideration of wind and wave effects based on the predicted maximum still water level from the PMF (Section 2.2.3.3.3) at the Missouri River is described in the following sections.

2.2.4.1 Water Level at CNS with Wind Setup In accordance with the guidelines in ANSI/ANS-2.8-1992 (Reference 2.2-9), the maximum PMF level at the plant site needs to consider the wind setup and wave runup effect from the coincidental occurrence of a 2-year design wind event. The 2-year fastest annual mile wind speed at the site is 55 miles per hour (mph) at 30 ft above the ground based on Reference 2.2-9. The methodology outlined In Coastal Engineering Manual (Reference 2.2-25) was followed to convert the annual extreme-mile wind speed to a 1-hour duration wind speed and then to 10-, 15-, and 20-minute wind speed durations.

Wind-driven waves were calculated using the "Windspeed Adjustment and Wave Growth" module of the Automated Coastal Engineering System (ACES) in the Coastal Engineering Design & Analysis System (CEDAS) Version 4.03 (Reference 2.2-26). The ACES uses the wind fetch option, elevation of observed wind, observed wind speed, duration of observed wind, duration of final wind, latitude of Flooding In Streams and RiVers (PMF)

..,,,,,(

\

2-44 \ ._

Sorgcnt:. & Lundy

l c

\ )

/ ,./

SECURIT1f*RELATEB INFORMATION - WITHHOLB UNBER 16 CFR 2.996

SECURIT't'*RELA'fEB INp;QRMJ!!c'flON - Wl'fHHOLB UNBER 16 ep;R 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 observation, restricted fetch geometry, and average fetch depth as input The shallow restricted option was chosen because the waves are not expected to propagate under a deep-water condition for a significant duration and the fetch is not unlimited for wave formation. The fetch geometry was determined by extending lines at directional (radial angle) increments of 22.5 degrees from a representative point at the CNS site to the extent of the river cross sections in all directions as shown in Figure 2.2-22. The ACES analysis was completed for each fetch. ACES outputs were spectral significant wave height (Hmo) and peak wave period (Tp). Wave characteristics were calculated using equations provided in Reference 2.2-27. Wind approaching along the longest and deepest fetch for each point of interest (Figure 2.2-23) was modeled in ACES to determine the controlling (maximum) significant wave height at each point In the case that the longest fetch was not the deepest, both the longest fetch and the deepest fetch were checked. The fetch with the larger wave height was then considered to be the controlling fetch.

Wind setup was calculated along the controlling fetch for each point of interest using Equation 4 of U.S.

Bureau of Reclamation ACER Technical Memorandum No. 2 (Reference 2.2-28). The calculated value was added to the PMF WSEL (described in Section 2.2.3.3.3) and the new WSEL was used for .

subsequent wave runup and associated effects calculations. Wind setup was not added to the PMF WSEL on the interior of the perimeter embankments because setup is not significant at these locations.

Equation 2-2 of EM 1110-2-1614 (Reference 2.2-29) was used to convert the spectral significant wave height (Hmo) to 1% wave height (H1%, the average of the highest 1% of waves). In accordance with ANSI/ANS-2 .8-1992 (Reference 2.2-9), H1-. was used as a design wave height for subsequent analyses.

A summary of ACES input and outputs along with wind setup and 1% wave height at six points of Interest are presented in Table 2.2-10. The largest wave height was calculated at point of interest West Embankment North (WEmbN, see Figure 2.2-23), with an H, 04 of 4.56 ft. Wave heights tended to be largest on the southern and western edges of the site due to the relatively longer and deeper fetches for waves to propagate to those points, whereas waves from the east are blocked by the federal levee.

2.2.4.2 Wave Runup lrbt3)~tilJSC §824o-1(d) ~

Locations of runup calculations for waves approaching the ,*,1141 1h1rl1t[) rom different directions are shown in Figure 2.2-24. Combinations of Coastal Engineering Manual (CEM) Chapter 6 (Reference 2.2-25) and FEMA guidelines (Reference 2.2-30) were used for wave run up calculations.

For conservatism, all reduction factors as well as the factor for influence of angle of incidence were set to 1, meaning no reduction. Design wave height (H,%) was used as wave input. For embankments located north and south of the Intake Structure, runup calculations showed that these embankments are overtopped. Therefore, Reference 2.2-30 was used to estimate the horizontal extent of runup. The extent of inundation is shown in Figure 2.2-25.

For WEmbN and North Embankment East (NEmbE) embankments (see Figure 2.2-23), the transmitted wave height was calculated using Equation Vl-5-54 of CEM (Reference 2.2-25). This was done because the wave is passing over other embankments to reach these two points of interest. Inputs included transmission coefficient (0.75), design wave height (H1%), median rock size, freeboard Flooding In Streams and Rivers (PMF) /

2-45 ( \

Sorgont. & Luncty 110

\ )

,.Y SECURl'f¥=RELATEB INp;QRMJ!!cTION

Yt11'fHHOLB UNBER 16 ep;R 2.996

SE6URIT'f-RELATEB INFORMATION - 1't1ITllltOLB UNDER 16 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 (negative for submerged embankment), and width of embankment crest. The minimum of transmitted wave height and breaker wave height (equal to 0.78 times design wave height [Hl'/41) was used for runup calculations of these two points. The results are summarized in Table 2.2-11.

Wave runup results are presented in Table 2.2-12. The wave runup from the west was calculated to be 1.4 ft, contributing to a maximum water level of 902.9 ft NAVD88. The runup produced from the plant west is not expected to reach the main critical building complex, as shown in the Figure 2.2-25. Runup from the plant north was calculated to be 0.5 foot, resulting in a maximum water level of 904.1 ft NAVD88. Topography indicates that CNS grounds in this area are below 904.1 ft NAVD88, further indicating that the buildings in this area would be exposed to runup from interior waves. Any interior protection provided to prevent exposure to wave runup from the north should extend to an elevation of at least 904.1 ft NAVD88 to provide protection to the Main Building Complex. While the farthest extent of the run up is expected to reach the Main Building Complex, it is expected to be minimal (on the order of inches). Reference 2.2-31 indicates that plant flood barriers extend to an elevation of 906 ft Plant Datum (906.37 ft NAVD88), which is high enough to provide adequate protection from the run up.

The vertical extent of runup on the Intake Structure was calculated to be 908.4 ft NAVD88, which is equivalent to a PMF WSEL of 903.0 ft NAVD88 plus 5.4 ft runup.

2.2.5 Associated Flooding Impacts 2.2.5.1 Overtopping Equation 11-4-28 of GEM (Reference 2.2-25) was used to estimate a theoretical wave runup at an unsubmerged embankment, identified as point of interest West Embankment South (WEmbS) in Figure 2.2-23. Inputs included design wave height (H 1%) at the embankment toe, peak wave period, embankment slope, embankment freeboard, and surface roughness reduction factor. Analysis showed that the theoretical runup is higher than the embankment height, confirming that the embankment is overtopped. Equation Vl-5-22 of CEM (Reference 2.2-25) was used to calculate the overtopping discharge at point of interest WEmbS. An overtopping discharge of 45 gallons per minute per linear foot was calculated at this location.

2.2.5.2 Erosion and Sedimentation The potential for erosion of the embankments due to wave action was assessed using erosion threshold guidance from the USAGE EROC/CHL TR-10-7 (Reference 2.2- 32). Inputs included a safety coefficient, grass quality factor, design wave height (H1-.), embankment slope, and duration of waves.

The potential maximum erosion depth was calculated to be 0.26 foot. This erosion depth was based on the wave exposure at WEmbN, which is the largest (most conservative) wave height as shown in Table 2.2-10.

2.2.5.3 Hydrodynamic Forces Hydrostatic and wave-induced hydrodynamic pressures and forces were calculated on the Intake Structure in accordance with the Goda pressure formula as described in GEM Table Vl-5-53 Flooding in Streams and Rivers (PMF) 2-46 SE6URITY-RELATEB INFORMATION - WITHHOLB UNt>Eft 16 efift 2.396

SECURITY-RELATED INfiOft:MAflON - 't'tlTHHOLD UNDEft: 16 CfiR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD Rlll!V.ALUATION REPORT Project No.: 11784-017 (Reference 2.2-25). Inputs included design wave height, wave length , water depth, and structure geometry. The largest wave heights are expected to impact the east face of the Intake Structure. For conservatism, pressure and force calculations were computed on the east face and treated as applicable on the north and south faces.

The Morison equation (Reference 2.2-27) was used to calculate the forces on the north wall of the Intake Structure due to a river current. Inputs included a drag coefficient, still water elevation, bottom elevation, water density, and current velocity. Outputs included the force per unit width of the north face wall of the Intake Structure.

Values for hydrostatic, wave-induced hydrodynamic, and current-induced hydrodynamic forces are listed in Table 2.2-13.

2.2.5.4 Debris and Impact Loads Review of possible flood debris items was undertaken to develop a spectra of flood debris sources. The following items were considered to represent a range of debris sources available upstream of CNS.

Two debris sources and masses were based on ASCE 7-10 {Reference 2.2-33) recommendations and the barge mass was based on typical barge sizes on the Missouri River. Additional vehicle and marine vessel masses were based on manufacturer data available on the Internet.

ASCE 7-10 miscellaneous debris - 1 kip

Large natural debris (ice, trees) - 4 kips

Large vehicles and boats (tug boat, bus, mobile home) - 40 kips

Tank-type debris (train cars, chemical tanks, semi trailers) - 100 kips

Barge - 5,100 kips Flood debris impact loads were calculated for the first two debris objects using the methodology presented in Chapter CS of ASCE 7-10 (Reference 2.2-33), with the following considerations:

Duration of impact load of 0.03 seconds was recommended based on Reference 2.2-33, Section C5.4.4, with the pulse shape taken as a half sine wave.

Velocity of the debris was considered to be equal to the water velocity, which may differ for each debris type, depending on the expected debris path.

Importance factor value of 1.3 for Risk Category IV was used (Reference 2.2-34, Section 4.2.8).

Depth coefficient was selected from Table CS-2 of Reference 2.2-33.

Orientation coefficient value of 0.80 was used, as recommended in Equation C-5 of Reference 2.2-33.

Flooding in Streams and Rivers (PMF) 2-47 SECURITV-"ELATED INFORM>\TION - WITIHIOLD UNDER 16 CFR 2.996

SECURITY-RELATEB INfiORMATION

WITI IHOLB UNBER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017

Blockage coefficient from Table C5-3 of Reference 2.2-33, considering sheltering within 100 ft upstream was used.

Dynamic load factor depends on the fundamental vibration period of the impacted structure, and the maximum value from Table C5-4 of Reference 2.2-33 was conservatively used.

Flood debris impact loads were calculated for the other larger size debris objects using the methodology presented in Section 3.14.8 of AASHTO (Reference 2.2-35). Equation 3.14.8-1 of Reference 2.2-35 is calibrated for impacts of large vessels, so its results for the Large Vehicles and Boats, Tank-Type Debris, and Barge sources are considered more applicable than the ASCE 7-10 (Reference 2.2-33) method.

Estimated debris impact loads due to PMF for different debris were determined using the methodologies identified above and based on channel and overbank velocities. A summary of impact load values is presented in Table 2.2-14. As shown in the table, a barge with the maximum channel velocityi(8.5 fps) will result in a maximum impact load of 3,332 kips.

2.2.6 References 2.2-1. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, NUREG/CR-7046, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, November 2011 .

2.2-2. United States Geological Survey (USGS), 2013, USGS National Water Information System (NWIS), Washington, D.C., accessed June 1, 2013, http://waterdata.usgs.gov/nwis/.

2.2-3. Missouri River Annex, 2011 , Mississippi River and Tributaries Waterways Action Plan.

2.2-4. U.S. Army Corps of Engineers (USACE). March 2000. Hydrologic Modeling System HEC-HMS Technical Reference Manual. U.S. Army Corps of Engineers, Hydrologic Engineering Center:

Davis, California.

2.2-5. U.S. Army Corps of Engineers (USACE). August 2010. Hydrologic Modeling System HEC-HMS Version 3.5. U.S. Army Corps of Engineers, Hydrologic Engineering Center: Davis, California.

2.2-6. U.S. Army Corps of Engineers (USACE). January 2010. River Analysis System HEC-RAS Version 4.1. USACE, Hydrologic Engineering Center, Davis, California.

2.2-7. United States Department of Agriculture, 2012. Geospatial Data Gateway. Website:

http://datagateway.nrcs.usda.gov/, accessed 12/14/2012. Washington, D.C.

2.2-8. ArcMap Version 10.2 (2013). ESRI, Redlands, CA.

2.2-9. American Nuclear Society, 1992, ANSI/ANS-2.8-1992: Determining Design Basis Flooding at Power Reactor Sites, American Nuclear Society Publishing, La Grange Park, IL.

Flooding in Streams and Rivers (PMF) ./

2-48 ( \.

Snrgo~~Lundy* ~*

j/

/

SECURITY-RELATEB INfiORMATION - WITI II IOLB UNBER 18 erR 2.996

SECURITY-ftELATEE> INFORMATION - 'tVITHHOLf> UNDER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARI> REEVALUATION REPORT 2.2-1 0. National Oceanic and Atmospheric Administration (NOAA). Atlas 14 Volume 8 Version 2, Precipitation-Frequency Atlas of the United States, Midwestern States, NOAA, National Weather Service, Silver Spring, MD.

2.2-11. NOAA, 1978. Hydrometeorological Report No. 51, Probable Maximum Precipitation Estimates, United States East of the 105th Meridian, U.S. Department of Commerce, NOAA, USACE, Washington, D.C.

2.2-12. NOAA, 1982, Hydrometeorological Report No. 52, Probable Maximum Precipitation Estimates, United States East of the 105th Meridian, U.S. Department of Commerce, NOAA, USAGE, Washington, D.C.

2.2-13. Nebraska Department of Natural Resources (NDNR), 2013, Department of Natural Resources Stream Gaging, accessed June 1, 2013. http://dnr.ne,gov/docs/hydrologic201 3.htmL 2.2-14. U.S. Army Corps of Engineers (USACE), November 2003, Upper Mississippi River System Flow Frequency Study: Hydraulics and Hydrology Appendix F, Missouri River, USAGE, Omaha District, Omaha, NE.

2.2-15. Federal Emergency Management Agency (FEMA). May 3, 2010. Flood Insurance Study; Douglas County, Nebraska and Incorporated Areas. Flood Insurance Study Number 31055CVOOOC. U.S. Department of Homeland Security, Washington, DC.

2.2-16. United States Geological Survey (USGS), 2013, USGS LandsatLook Viewer, Washington, o.c., accessed October 1, 2013. http://landsatlook,usgs.goyt.

2.2-17. U.S. Army Corps of Engineers (USACE), 2013, USAGE Northwestern Division MRR Daily River Bulletin, accessed September 1, 2013. http://www.nwd-mr.usace.armv.mil/rcc/.

2.2-18. Moriasi, D.N., J.G. Arnold, M.W. Van Liew, R.L. Bingner, R.D. Harmel, and T.L. Veith, 2007, "Model Evaluation Guidelines for Systematic Quantification of Accuracy in Watershed Simulations," Transactions of the ASABE 50(3): 885- 900, http:/fddr.nal.usda.gov/dspace/bitstream/10113/9298/1 /I ND44003774. pdf.

2.2-19. U.S. Army Corps of Engineers (USAGE), undated, After Action Report: Missouri River and Tributaries Flood of 2011, Received from John Remus, USACE, via e-mail on October 1, 2013.

2.2-20. BMT WBM, 2013, TUFLOW FV User Manual. Flexible Mesh Modeling, Version 2013.02.056_dev.

2.2-21 . University of Missouri, Columbia, 2013, Missouri Spatial Data Information Service, accessed October 10, 2013. ftp://www.cares.mlssouri.edu/pub/dem/.

2.2-22. Iowa Department of Natural Resources, 2013, Natural Resources Geographic Information Systems Library, accessed November 4, 2013. http://www.igsb.uiowa.edu/nrgislib:x/.

2.2-23. Multi-Resolution Land Characteristics Consortium, 2013, National Land Cover Database, accessed May 17, 2013. http://www.mrlc.gov/index.php.

Flooding in Streams and Rivers (PMF) .,~*,

2-49 Sar-g o ~ ~ Lundy 1 ,t-1

\

/

SECURIT¥-RELATEf> INFORMATION - WITtil IOLD UNDER 16 CFR 2.996

SECURITY-RELATED INFORMATION - Vt'ITHHOLD UNDER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD Rl!EVALUATION REPORT Protect No.: 11784-017 2.2-24. Hager, W.H., 1987. "Lateral Outflow Over Side Weirs." Journal of Hydraulic Engineering, ASCE, Vol. 113, No. 4, PP 491 -504.

2.2-25. U.S. Army Corps of Engineers (USAGE), 2008, Coastal Engineering Manual, EM 1110-2-1100, Washington, D.C. (in 6 volumes).

2.2-26. CEDAS-ACES Version 4.03 (2014), Veri-Tech, Vicksburg, MS.

2.2-27. Dean, R. and R. Dalrymple, 1991 , Water Wave Mechanics for Engineers and Scientists. World Scientific, Hackensack, NJ.

2.2-28. United States Bureau of Reclamation, 1981, Freeboard Criteria and Guidelines for Computing Freeboard Allowances for Storage Dams, ACER Technical Memorandum No. 2.

2.2-29. U.S. Army Corps of Engineers (USACE), 1995, Engineer Manual 1110-2-1614, Design of Coastal Revetments, Seawalls, and Bulkheads.

2.2-30. Federal Emergency Management Agency, 2007, Guidelines and Specifications for Flood Hazard Mapping Partners, Atlantic Ocean and Gulf of Mexico Coastal Guidelines Update, 360 p.

2.2-31. Nebraska Public Power District CNS Operations Manual, Maintenance Procedure 7.0.11, Rev. 29, "Flood Control Barriers."

2.2-32. U.S. Army Corps of Engineers (USACE), 2010, ERDC/CHL TR-10-7, Flood-Side Wave Erosion of Earthen Levees: Present State of Knowledge and Assessment of Armoring Necessity.

2.2-33. ASCE 7-10, "Minimum Design Loads for Buildings and Other Structures."

2.2-34. United States Nuclear Regulatory Commission (NRC), July 29, 2013, Guidance for Assessment of Flooding Hazards Due to Dam Failure, Japan Lessons-Learned Project Directorate JLD-ISG-2013-01.

2.2-35. AASHTO, "LRFD Bridge Design Specifications, "7th Edition.

2.2-36. U.S. Army Corps of Engineers (USACE), August 1994, EM 1110-2-1417 Flood Runoff Analysis, U.S. Army Corps of Engineers: Washington, D.C.

2.2-37. Natural Resources Conservation Service (NRCS) and United States Department of Agriculture (USDA), 2013, Soil Survey Geographic (SSURGO) Databases for Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, and South Dakota, accessed April 30, 2013.

http://soildatamart.nrcs.usda.gov.

Flooding in Streams and Rivers (PMF) 2-50 SECURITY-RELATED l,NFORMATION - Vt'ITI II tOLD UNDER 18 erR 2.998

SECURIT¥-RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.~S6 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No,: 11784-017 2.2-38. U.S. Department of Agriculture (USDA), June 1986, Technical Release 55.Urban Hydrology for Small Watersheds.

2.2-39. Natural Resources Conservation Service (NRCS), May 2010, National Engineering Handbook, Part 630 Hydrology.

2.2-40. Chow, V.T ., 1959, Open Channel Hydraulics, McGraw Hill.

~ ote: Reference 2,2-36 through Reference 2.2-40 are cited lo the tables that follow, Flooding in Streams and Rivers (PMF) 2-51 S~rgont &, Lundy~

SECURli"t'-RELATED INFORMATION - WITHHOLD UNDER 16 CF" 2.396

SECURITY-RELATEE> INFORMATION - WITltttOLE> UNE>ER 16 CFR 2.S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.2.7 Tables Tables associated with Section 2.2 are presented on the following pages.

Flooding in Streams and Rivers (PMFJ 2-52 SECURITY-ftELATEE> INFORMATION - WITltttOLD UNDER 18 CPR 2.S96

SECUR:IT'f-"ELATEE> INFORMATION - V'-tlTHHOLfl UNE>ER 16 CF~ 2.996 Nebraska Public Power District SL,01245O Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.2-1: Point 3 (shown in Figure 2.2-4) Adjusted Precipitation Depths Based on HMR 52 6-ht Increment 12 11 10 9 7 6 5 3 1 2 4 a Number 6-ht Time I 72 66 60 54 42 36 30 18 6 12 24 48 Period Time Period 0--6hr 6-12ht 12-18hr 18-24hr 24-30hr 30..J6hr 36--42hr 42-4Bhr 48-54hr 54-60hr 60-66hr 66*72hr lsohyet. (in)

A(10) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.69 12.52 2.18 0.65 0.64 B (25) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.69 11 .67 2.13 0.65 0,64 C (50) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.68 10.87 2.08 0.65 0.64 D (100) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.66 9.95 2.05 0.65 0.64 E (175) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.67 ; 9.19 2.01 0.65 0.64 F (300) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.67 8.43 1.88 0.65 0.64 G (450) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.66 7.90 1.94 0.65 0.64 H (700) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.66 7.26 1.91 0.65 0.64 I (1000) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.66 6.74 1.88 0.65 0.64 J (1500) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.66 6.18 1.86 0.65 0.64 K (2150) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.65 5.70 1.82 0.65 0.64 L (3000) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.65 5.26 1.80 0.65 0.64 M (4500) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.65 4.69 1.77 0.65 0.64 N (6500) !l.30 0.30 0.3 0 0.30 D.64 0.64 0.64 0.64 4.17 1.73 0.65 0.64 0 (10000) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.64 3.57 1.70 0.65 0.64 P (15000) 0.30 0.30 0.30 0.30 0.64 O.M 0.64 0.63 2.97 1.68 0.65 0.64 a (2soooJ 0.20 0.20 0.20 0.20 0.42 0.42 0.42 0.43 1.44 0.95 I 0.43 0.42 R (40000) 0.04 0.04 0.04 0.04 0.08 0.08 0.08 0.08 0.32 0.12 0.06 0.08 Flooding in Streams and Rivers (PMF) 2-53 SECU~IT,' -RELATEE> INFORMATION - V'flTHHOLB UNl:>E~ 16 CFP( 2.996

SECURIT¥*RELATEB INFORMATION - WITHHOLB UNBER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 F LOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.2-2: Model Input Parameter Definitions and References Hydrologlc Parameter Definition Reference Drainage area Area that contributes to runoff. USGS gages and GIS tools Deficit and Constant Loss Parameters Initial deficit The amount of precipitation lost due to Table 6-1 of EM 1110-2-1417 interception and depression storage. (Reference 2.2-36), as referenced in HEC-HMS Technical Reference Manual (Reference 2.2-4)

Constant loss rate The* loss rate Is based on the maximum Table 11 of HEC-HMS Technical infiltration capacity of the soil. Reference Manual (Reference 2.2-4)

Maximum deficit The maximum amount of water that can be SSURGO GIS soil data available stored in the soil profile. water holding capacity (Reference 2.2-37)

Impervious surface The*percentage of the basin from which all Aerial photographs precipitation runs off.

ModClark Transform Parameters Time of concentration The time it takes flow to travel from the TR-55 method (Reference 2.2-38).

hydraulically most distant point to the watershed Slope was calculated using elevation outlet. and flowpath length values *taken from USGS topographic map; velocity for shallow concentrated flow was estimated using NEH-4 (Reference 2.2-39).

Storage coefficient An index of the temporary storage of runoff In HEC-HMS Technical Reference the watershed as it drains to the outlet point. Manual (Reference 2.2-4). lit is This parameter typically is based on gage data assumed that this value was adjusted and is adjusted during the calibration process. through calibration by USAGE.

Flooding in Streams and Rivers (PMF) , ,*

2-54 ,: \

Sorga n~ ~ 1Lundy 1

r.

.,,I./

SECURIT¥-RELATEB INFORMATION - WITHHOLB UNBER 16 CFR 2.396

SECUff:ITY-ff:ELATEB INFOff:MATION - 'l'ilTHHOLB UNBEff: 16 CPff: 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD R.EEVALUATION REPORT Project No.: 11784-017 Table 2.2-2: Model Input Parameter Definitions and References, continued Hydrologic Parameter Definition Reference Recession Baseflow Parameters Initial discharge Discharge at the start of the simulation. These USGS and NDNR gages values may be adjusted based on antecedent (Reference 2.2-2 and conditions. If gage data warrant. this is adjusted Reference 2.2-13,)

for historic storms. ANSI/ANS-2.8-1992 suggests use of mean monthly baseflow at the beginning of an antecedent storm, during the month of occurrence, for the PMF hydrograph analysis.

Baseflow recession Represents the decay of the baseflow. This Table 16 of HEC-HMS Technical constant parameter may be adjusted during the Reference Manual (Reference 2.2-4) calibration process.

Threshold type (ratio to User~efined threshold flow that defines the time HEC-HMS Technical Reference peak or threshold at which the recession model of HEC-HMS Manual (Reference 2.2-4) discharge) defines the total flow, expressed as either a flow rate or ratio to the computed peak. It was assumed that this value was adjusted through calibration by USACE.

Reservoir Parameters Stage-Discharge Function Stage-discharge relationship for the reservoir Provided by USACE outlet works.

Elevation-Storage Function Elevation-storage relationship of the reservoir. Provided by USACE Initial Elevation Initial elevation in the reservoir at the start of the Provided by USACE simulation.

Flooding in Streams and Rivers (PMF)

..**(

2-55 S o r g e ~ ~ Lundy u*

\ ,I V

/

SECUff:ITY-ff:ELATED INFORMATION - WITtllfOLB UNDER 18 CPR 2.998

SECURITY-RELATEB INf-ORMATION - WITI II IOLD UN BER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.2-3: Summary of Unsteady Computational Parameters Parameter Value nme step (minutes) 5 Theta (implicit weighting factor) 1.0 Water surface calculation tolerance (ft) 0.02 Maximum number of iterations 20 DSS messaging level 4 Maximum error in water surface solution (abort tolerance, ft) 100 Table 2.2-4: Location of Inflow Hydrographs Inflow Hydrograph (USGS Gage) lniflow River Mile <11 Gavins Point Dam 810.87 James River near Scotland, SD (06478500) 797.73 Vermillion River near Vermillion, SD (0647901 0) TT1 .90 Big Sioux River at Akron, IA (06485500) 734.00 Floyd River at James, IA (06600500) 730.95 Omaha Creek at Homer, NE (06601000) 719.62 Little Sioux River near Turin, IA (06607500) 669.23 Soldier River at Pisgah, IA (06608500) 664.00 Boyer River at Logan, IA (06609500) 635.22 Platte River at Louisville, NE (06805500) 594.82 Weeping Water Creek at Union, NE (06806500) 568.67 East Nishnabotna River at Riverton, IA (06809900) and 542.10 West Nishnabotna River near Riverton, IA (06808820)

Little Nemaha River at Auburn, NE (0681 1500) 527.80 Tarkio River at Fairfax, MO (06813000) 507.50 Note:

1. River Mile corresponding to location in HEC-RAS model.

Flooding In Streams and Rivers (PMF) 2-56 SECURIT¥-RELATEB INFORMATION - WITI II IOLD UNBER 18 CFR 2.998

SEeURPl"t' -R:ELATED INFORM>9cTION

WITHHOLB UNBER 16 e1-R 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.2-5: Comparison of Manning's Roughness Coefficients used in the Model to Standard Values Channel Overbank Parameter Minimum Maximum Minimum Muimum Values from steady-state model 0.025 O.D29 0.020 0.120 Global 10% roughness increase 0.028 0.032 0.022 0.132 Values from Reference 2.2-40 0.016 0.060 0.011 I 0.160 Table 2.2-6: NSE Coefficient Summary and Peak Discharge Comparison for 2011 Validation Simulation Nash* Observed Predicted Observed Predicted Sutcliffe 2011 Peak Peak 2011 Peak Peak Stage Location Efficiency Discharge Discharge Stage (ft NAVD88)

Coofflclent (cfs) (cf11) (ft NAVD88)

USGS gage 06486000, Missouri River 1092.01 0.993 192,000 185,484 1092.74 at Sioux City, IA (RM 732.2)

USGS gage 06601200, Missouri River 0.993 191,000 186,390 1050.40 1049.78 at Decatur, NE (RM 691.0)

USGS gage 06610000, Missouri River 0.987 217,000 199,408 984.53 984.29 al Omaha, NE (RM 615.9)

USGS gage 06807000, Missouri Ri11er 933.14 0.981 229,000 227,608 933.B6 at Nebraska City, NE (RM 562.6)

USGS gage 06810070, Missouri Ri11er 272,000 904.82 903.51 0.941 233,089 at Brownville, NE (RM 535.3)

USGS gage 06813500, Missouri Ri11er 863.94 0943 328,000 234,043 863.87 at Ruic, NE (RM 498.0)

Flooding in Streams and Rivers (PMF) 2-57 sceUR:IT't'=RELATED INFORMATION - Yt'FfHHOLE> UNE>ER 16 eFfit 2.996

8ECURIT1f-RELATED INI-ORMATION - WITHHOLD UNDER 16 Cl-fit ! .396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.2-7: Inflow Hydrograph Location Summary for PMF Simulations Inflow Name Lateral Flow River Mile 11 >

Missouri Basin Tributary (21 808.26 Missouri Basin Tributary (21 807.02 James River 797.73 2

Missouri Ba~in Tributary ( J 796 30 Bow Creek <2l 787.75 Missouri Basin Tributary (2J 775.27 Vem,illion River 771.90 2

Missouri Basin Tributary < > 751.61 Aowa Creek C2> 745.19 2

Elk Creek < > 737.40 Big SiouX' River 734.00 Perry Creek 731 .76 Floyd River 730.95 Omaha Creek 719.62 12 Blackbird Creek > 697.41 Missouri Basin Tributary <2> 808.26 Missouri Basin Tributary 12> 807.02 James River 797.73 21 Missouri Basin Tributary ( 796.30 2

Bow Creek ( ) 787.75 Missouri Basin Tributary (21 775.27 Vermillion River 771 .90 Missouri Basin Tributary 12> 751 .61 Aowa Creek 121 745.19 Flooding in Streams and Rivers (PMF) 2-58 SECURITY-RELATED INFORMATION - WITIIIIOLD UNDER 18 CFR 2.998

SECURITY-RELATED INFORMATION - VtlTHHOLD UNDER 16 CFR 2.396 Nebraska Public Power District SL-01245O Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.2-7: Inflow Hydrograph Location Summary for PMF Simulations, continued Inflow Name Lateral Flow River Mile 111 Elk Creek IZl 737.40 Big Sioux River 734.00 Perry Creek 731.76 Floyd River 730.95 Omaha Creek 719.62 Blackbird Creek <2l 697.41 Missouri Basin Tributary l2) 691 .35 Little Sioux River 669.23 Tekamah Ditch <2> 664.16 Lower Soldier River 664.00 2

Missouri Basin Tributary < > 648.78 Boyer River 635.22 Pigeon Creek 12> 622.16 Missouri Basin Tributary 12> 616.48 Mosquito Creek 121 605.87 Platte River 594.82 Pony Creek and Keg Creek <2l 587.06 Plum Creek and Ervine Creek 12l 572.05 Missouri Basin Tributary 121 561.93 South Branch Weeping Water Creek 568.67 Nishnabotna River 542.10 Honey Creek <21 535.30 Little Nemaha River 527.S0 Tarkio River 507.50 Notes:

1. River Mile corresponding to location in HEC-RAS model.

2. These tributaries are not ~sled in Table 2.2-4 because they are subbasins within the Missouri River basin HMS model that do not have USGS stream gages.

Flooding In Streams and Rivers (PMF) __.,.,-('

2-59 *,' ' ...

S a r g e ~ iS."i Luncty* ~c

\ I

)/

SECURIT't'-RELATEB INFORMATION - Wll'tltlOLD UNE>ER 16 CFR 2.396

SECURITY-RELATED INFORMATION

WITI II IOLD UNDER 18 eFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION R .l !PORT Project No.: 11784-017 Table 2.2-8: PMF Simulations Peak Magnitude and Time at RM 556.16 Peak Time-Peak Simulation Event Begins on 1/1 00:00 Discharge (cfs)

(date, hours : minutes)

PMF + 35,000 cfs at Gavins Point, full floodplain 522,400 1/1 0 22:00 PMF + 35,000 cfs at Gavins Point, levee constrained 546,700 1/10 15:00 PMF + 160,000 cfs at Gavins Point, full floodplain 731 ,200 1/1015:00 PMF + 160,000 cfs at Gavins Point, levee constrained 712,700 1/1011:00 Table 2.2-9: Monitoring Point Summary Maximum Maximum Grade Maximum Maximum Overland Channel Monitoring Point Elevation WSEL Depth Velocity Velocity (ft NAVD88) (ft NAVD88) (ft)

(fps) (fps)

1. Intake structure (north) 894.0 902.8 0.4 8.5 8.8

2. Intake structure (east) 880.0 902.8 2.0 8.5 22.8

3. Switchyard 896.6 901.5 0.5 N/A 4.9

4. ERP 892.6 902.8 0.2 N/A 10.2 Flooding In Streams and Rivers (PMF) 2-60 (\

y Surgc,nt & Lundy , , c SEeURITY-RELATEB INFORMATION - WITl-11 IOLB UNBER 18 eFR 2.396

SECURITY-RELATED INFORMATION - WITIIHOLB UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.2-10: Calculat ion of Wi nd-Driven Waves and Wind Setup Approaching CNS Controlling Average Design Wind Point of Fetch Depth Fetch Length W ind Speed H,.o r. Wavelength Wind Setup H,,.

Interest Angle Along Speed Duration (ft) (s) (ft) (ft)

(ft)

(mph) (ft)

(deg) Fetch (ft) (min)

Intake 0 15.09 10466 46.8 10 2.16 2.68 36.4 0.21 3.61 structure NEmbE 0 14.33 12665 46.1 15 2.23 2.74 37.8 0.25 3.72 NEmbW 337.5 12.55 6220 -46.8 10 1.66 2.32 27.-4 0.15 2.77 SEmb 180 16.09 19525 45.6 20 2.72 3.07 -47.0 0.34 4 .5" WEmbN 180 16.23 19948 45.6 20 2.73 3.08 47.3 0.35 4.56 WEmbS 180 16.50 19311 45.6 20 2.71 3.06 46.8 0.33 4.53 Table 2.2-11 : Submerged Embankment Results Point of Freeboard, Including Transmission Transmitted Wave Maximum Interest Setup (ft) Coefficient Height (ft) Depth-Limited Wave (ft) 5.77 WEmbN -7.4 0.75 3.42 transmitted wave height acceptable 1.48 NEmbE -2.2 0.08 0.30 transmitted wave height acceptable Table 2.2-12: Wave Runup Approaching CNS Main Building Complex Point of Wave PMFWSEL Runup Vertlcal Runup Horizontal 1

Interest Runup (ft) (ft NAVD88) Extent (ft NAVD88) Extent (ft)

WEmbN 1.4 901.5 902.9 N/A NEmbE 0.5 903.6 904.1 N/A N of IS 4.9 903.0 N/A 103 S of IS 6.0 902.7 NIA 128 Note:

1. Wind setup is included in the PMF values listed for N of IS and S of IS. Wind setup was not Included In the PMF values listed for WEmbN and NEmbE due to the wave calculations being applied to a location that ls within the perimeter embankments where wind setup would be negligible.

Flooding In Streams and Rivers (PMF) 2-61 Sorga n ,: &,Lundy *'"

.~~*.

SECURIT11'*RELATED INFORMATION - W't11TI !HOLD UNDER 18 CFR 2.998

SECURIT¥=RELATED INFORMATION - WITI II IOLD UNDER 16 CFR 2.996 Nebras ka Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.2-13: Forces on Intake Structure Resultant Force Elevation Force Type (ft NAVD88) (lb per linear foot of wall)

Hydrostatic 869.6 78,312 Wave-induced 888.1 3,752 Current-induced 878.0 25 Table 2 .2-14: Debris Impact Loads Maximum Velocity Debris Source PMF (kip) 1000 lb miscellaneous debris 15.54 4000 lb large natural debris 62.15 Channel (8.5 fps) Large vehicles and boats 295.08 Tank-type debris 466.56 Barge 3332 1000 lb miscellaneous debris 3.66 4000 lb large natural debris 14.62 Overland (2.0 fps) Large vehicles and boats 69.43 Tank-type debris 109.78 Barge 784 Flooding in Streams and Rivers (PMF) 2-62 SECURIT't'-RELATED INFORMATION - WITI II IOLD UNDER 16 CFR 2.996

SECURIT¥-RELATEB INFORMA'flON - 'tVITI II IOLD UNBER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11764-017 2.2.8 Figures Figures associated with Section 2.2 are presented on the following pages.

Flooding in Streams and Rivers (PMF) 2-63 SECUR:IT'f-RELATEB INFORMATION - WITI II IOLD UNDER 16 CFR 2.396

SECURIT¥*RELATEB INF6RMAT16N - WITHH6LB UNBER 16 CFft 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT Figure 2.2*1 : Location Map e Rt.1800

+

+'° OlieOU)OO OmaNC,Nt<

AlllolNfNE RM700

+

OGGOl200 MeeounRNtt AIOec&MNE oa,oo,oo

~ R , ,..

Al LOOI" IA 06805500 Plane A,.,..

AHOUllv... NE 4'RM57' 0Geoe500

\"'-'OWlltWC,...,

AIU.-NE 0 USGS Gage 08807000 06810070 IMl,oon R,,,r A1 IMIIO<JIIRY111

+ Missouri River Mlle (1960) Ntbl-C<t,NE Al-~*~* NE Model Extent 06011500 L,m.-.R,vt1 Al ....llurn NE 06813000 FIS Counties T""'°Ri,tr N.Faoi!.. MO 0 25

°:'~, 1,. ,.,.,

C1td*h bo urce, E.r1 0.'1.,.'11 111 1 N -l J f..,

f '" ..,o RM500 1'1'f' lij ui,t** *"t P c.1,, U[ICO uaoa , ~o N PI " "CA N G ** *

u 1(1~ "I OIU H,l o,an1nc, ita, Wt '(

[1 11 J ec,111 M[TI E 1 t1 C t!I"* Hont Ko.-9 1 , _.1nt OpO l l"ld '"' 0 . . Wt'tr COfflf'"'" W' Flooding In Streams and Rivers (PMF) 2-64 SECURIT¥*RELATEO INF6RMil<TION - 1t'IITHH6LB UNBER 16 CFft 2.996

SECURITY-RELATEE> INFORMATION - WITI II IOLB UNBER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178--4-017 Figure 2.2-2: PMP Position 1

Sheet a (see subsequent Sheets b, c, and d for PMP Positions 2 to 4)

MINN!SO A G R E P L A Vermillion

.., River Basin

-- Missouri River Basin from Gav1ns Point to Sioux City I I\

Missouri River Basin from Omaha to Nebraska City

~ PMPStorm E l) M1ssour1 River Basin

~ Extent from Nebraska Ctty ,. **

to Kansas Cny T, f

1

0

---==:: :J*----

65 130

~,,,* :.

1 ti.:,. *

~------~

'l i*~ .~~~* C.t ar.90' o,,e,nic.* ~ ...... I , , .. , ...

C*"'ll!!llfl , ,

sc.: "r'-8"'~-,;;*

.. . c,un.,_:t:!'~*

Ul 11 ; *Ut l1-f :1,

!*: '!\c*;**:~,::

- - nt -""°"* ...,. ....... IS ttr .. l u .,

Flooding in Streams and Rivers (PMF) 2-65 S..rgant: & Lundy

SECURITY-RELATEE> INFORMATION - 't'IITI II IOLB UN BER 18 CFR 2.998

SECU"ITY-fitELATEO IN~OfitMATION - WITI II IOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784--017 Figure 2.2-2: PMP Position 2 (sheet b)

G p l R

A E

-* ,.w*r-~ 1

.., River Basin Missouri Basin from Point to s*

I ii\

A Missouri River Basin from Omaha to Nebraska C ity

,-,-,, PMP Storm [: D Missouri River Basin

~ Extent from Nebraska City to Kansas City 0 65 130 1

s.,!... '?'., ** c, d. '\**, .... ( * ""' ,. ... vu'b , ** , ... '"'*"****

Mies ltC*****t P . , , ca 0 US.t.'S f&O ilr,jp, '-IICAlll c. ........ tC. N .... 11 .. , . , Jf l o,.,. ... ,. 'SM v, ,~,, J*p,*tt *1111, l I '""II* H*f\11" flQI .,.. tr .. Cl'§. Uull Ce1111r1u ,1; Flooding In Str:eams and Rivers (PMF) 2-66 Sargnnt; &. Lundy SECURIT¥ -RELATED INFORM~TION - WITI II IOLD UNDER 16 CFR 2.996

SEeURITY*RELATEB INFORMATION - WITHHOLB UNBER 16 eFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4.017 Figure 2.2-2: PMP Position 3 (sheet c)

G R E P L A

-- Missouri River Basin from Gavins

. ~

Point to Sioux City Missouri River Basin from Sioux City to Omaha A

Platte River Basin Missouri River Basin rrom Omaha to Nebraska City

~ PMPStorm E n Missouri River Basin from Nebraska City ., .,

L.....11 Extent to Kansas City 0 65 130 s.,!: ... 't., *. Ct*if,I s... ,

t,, ~J~ .. ' A.l\tf(O ,,,.., * .., In.,...,.

MIies * , *

11 P .,,.

O,ll,. ft * ~**v ,

Ct acu U\C9 t AO l~o **,** M[,1 l ul lltiPS JIIQ~** c *

e .. - IC"'t .,; .... ~ .., 'fl l!*n* t*fooc l.1Jn11 ,utd '"* C.I~ U**r c ** m ... ,,,

Flooding in Streams and Rivers (PMF) 2-67 Snro*ne& Luncfv SEeURITY-RELATEB INFORMATION - WITllltOLB UNBER 16 eFR 2.396

SEC! IRITY RELli\TliQ INPORMATION - WITI II IOLD UNDER 16 CFR 2.396 Nebraska Public Power District SL-01 2450 Cooper Nuclear Station Revision 1 FLOOD HAZARD R£EVALUATION REPORT Project No.: 117~-017 fi gure 2.2-2: PMP Position 4 (sheet d)

G R E P L A Vermillion River Basin

,\ti Missouri River J

Basin from Gavms Point to Sioux City M1ssoun River Basin from Sioux City to Omaha I I\

A I Platte River Basin I Mi Basi 10

,.,..,, PMP Storm [ 1) Missouri River Basin

~ Extent from Nebraska City to Kansas City 0 65 130 "

Lt , tttt it!

~,,,,t,11, tJ1ty.,, ~t*41*1* ~owr t t ~ll('h l f""1* NAVlfG f .tt11110M l1t1*rl'l'lar,,

,., "", ,., P ro,11 n ra ca u-._c.c; rAn HP NR CA ~, r., a.,,_ 1r. N ti; ..... ,,., Nt Otdf\U'I. '""~" l " ' ' ' ' " " Ml 1 l. I I r.,-, .... IH0nQ K* ,.QI met nu* (,I\ Uu11 Cenmunltl' .,.

Flooding in Streams and Rivers (PMF) 2-68 Sargon,: & Lundy

S!CU"IT't'-ftELATED INFORMATION - WITI ltfOLD UNDER 16 CFR 2.996

SECURIT¥-RELATEB INF6RMAT16N - WITHH6LB UNBER 16 CFR 2.S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT Figure 2.2-3: Geographic Distribution of Basins of Influence for Missouri River Drainage above CNS M1nouri Rlwr above Fon Ped<

t>,1631q ml Y1llo-loM 70,0211q ml.

Mldclle Buln (Miuounl ~

'"**1*,q.m, l Lower 8a1ln (Fon Calhoun)- - ---1

~0.148-<<i, ml Gn,na Po,nl ~

Lo_, Buln (Cooper) 1,117 lq ml.

Flooding in Streams and Rivers (PMF) 2-69 SECURIT¥-RELATEB INF6RMATl6N - WITHH6LB UNBER 16 CFR 2.S96

SECURITY-RELATED INFORMATION - rt'rlTtfttOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.2-4: PMP Spatial Distribution over Platte River Basin (P3 Centroid; 41 .35N, 96.20W)

w ott.

s 0

H L

p Q

~

R H IA

,.!!e-clt, Jl ,q $S u Flooding in Streams and Rivers (PMF) 2-70 SECURITY-RELATED INFORMATION

WITI II IOLD UNDER 16 CFR 2.998

SECURITY-RELATEB INFORMATION - WITHHOLB UNBER 18 CFR ! .998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11764-017 Figure 2.2-5: Antecedent Final Model PMF Hydrographs for P1 , P2, P3, and P4 800000 I 02 700,000 ~

04 600,000 S00,000 ---------ti 300,000 1-----------H 200,000 I2 100,000 0

1/1/3000 o,oo I /6/3000 0 00 1/11/3000 OcOO I/16/3000 0;()0 1/21/3000 000 1/26/3000 0.00 1/31/3000 0 00 Date

- ruwl M ~ POitllQn 1 - r1N1Moc:t.ffto\1ll<Wll hn,11 Model POl,lt,on J - F""'I Model Po,,i,on 4

- PMI' "°"°" I t**I - P,_.P Pos,i,on 21.,) PMP Po,,1- l ton) -PMP Po\,l,on

t**I M15soun River at Brownv1llt, N E Flooding In Strums

nd Rivers (PMF}

2-71 SECURITY-RELATEB INFORMATION - 't't'ITI II IOLB UNBER 18 CFR 2.398

9ECURIT¥-RELATEB INFORMATION - WITHHOLB UN BER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4--017 Figure 2.2-6 : Subsequent Storm Final Model PMF Hydrographs for P1, P2, PJ, and P4 0 .2 700.000 t---ttt--+--....-----tt---------------------------....--i 04 600.000 06 500.000 t - - -f f

' ?i i

~ 400.000

_______________________! ! 0.8 3"

.,: n

~ 300.000 I -------________,-t * ~

200.000 12 100,000 14 0

1/1/3000 0:00 1/6/3000 0 00 1/ 11/3000 0-00 1/16/3000 0'.00 1/21/3000 0-00 1/26/3000 0:00 1/31/3000 0;00 Date Missoun River at Brownville. NE Flooding In Streams and Rivers (PMF) 2-72 S..rga ne,.&Lundy

SECURITV-RELATEB INFORMATION - 'NITI II IOLB UNBER 18 CFR 2.398

SECUftlTY-ftELATEB INFOftMATION * 't't,ITI It IOLB UNBEft 16 CFft 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017 Figure 2.2-7: Missouri River Junctions Flooding In Streams and Rivers (PMF) 2-73 SEOURIT,' -RELATED INFORM1'cTION - WITl-11-IOLD UNDER 16 CFft 2.996

SEOURITY-RELATEB INFORMATION - **'YITtttlOLB UNBER 18 OFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11764~17 Figure 2.2-8: Full Floodplain PMF Hydrographs for Gavins Point Release of 160,000 cfs 900000 160,000 ds at Gavins Point Full Floodplain

- ~xC,ty 100000 - Deutur

- ~*~

-Pt.;1l brnouth

- Nl>br**lt.tClty

- llrownvlll~

- RulO 200000 100000 L,,~...-----------------

l /l;/00000 l/ll/00 01)0 1/16/00 0-00 1/21/00 0.00 1/ 16/00 0 .00 I /31/00 0-00 2/5/00000 Flooding in Streams and Rivers (PMF) 2-74 Sarge"" & Lundy

SECURITY-RELATEB INFORMATION - *t'YITtlllOLB UNBER 18 OFR 2.398

SECURIT¥-RELATED INFORMiltTION - WITt II IOLD UNDER 18 OFR 2.398 Nebraska Public Power District SL--012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT Figure 2.2-9: PMF Hydrographs for 2-0 Model Upstream Boundary RM 556.16 800000 000 er, full Floodpl~., ~

000 ch l ~f> (Of\jltJlnN:i 700000 000 fSf ull floodpl~I~

- OOOcf~ lf'Vff Con\lrJ!Md 600000 sooooo i..

t" 400000 2

j

.300000 100000 l(X)()O()

0 1/1/lOOO 1/&/3000 1/ ll/3000 1/16/'JOOO 1/21/3000 1/16/1000 1/31/3000 Flooding In Streams and Rivers (PMF) 2-75 S..rguno: & Lundy SECURIT¥-RELATED INFORMiltTION - WITI II IOLD UNDER 18 CFR 2.998

SECURITY-RELATED INFORM]!(TION - WITI II IOLD UNDER 18 OFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No .: 1178--017 Figure 2.2-10: PMF Downstream Boundary Condition Rating Curve RM 510.03 River Missouri Reach 1 RS* 51003 seo--------------

RC

CH~= 100 inlt 1 RC

CHS_PMF. l&OFFP RC

CNS PMF 3'ioL 87$

I RC

CNS PMf 35___.

FFP J J 1$$1--~----------.------------.-------1 0 200000 AOOOOO eooooo 800000 1000000 Flooding In Streams and Rivers (PMF) 2-76 Snro*nt: & Lt..tndy "

SECURIT¥-RELATED INFORM1'TION - WITHHOLD UNDER 18 CFR 2.998

SECURIT¥*RELATEB INFORMATION - WITI II IOLB UNBER 16 CFR ! .996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT P101ect No.: 11784-017 Figure 2.2*11 : Study Area Overview for the 2*0 Model Flooding in Streams and Rivers (PMF}

2-77 Sargeant: & Lundy

SECURIT't'-RELAl'Ef) INFORMATION - 'ft11TI II IOLB UNBER 16 CFR ! .996

SECURIT¥-RELATES INFORMATION - 't'IITHttOLS UNSER 16 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZAA.D R EEVALUATION R EPORT Project No.: 1178-4-017 Figure 2.2-12: Spatial Distribution of Land Use Classes to Determine Manning's Roughness Coeffic ients

- Open Water

- Wetland

- Forest

- Grassland

- RowCrops

- Urban

- Roads Flooding in Streams and Rivers (PMF) 2-78 Sarg11nt & Lundy SECURITY-RELATES INFORMATION - WITHHOLS UNSER 18 CFR 2.998

SECURITY-RELATED INFORMATION - WITI II IOLD UNDER 18 CFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-01 7 Figure 2.2-13: Computational Mesh Overview Floodin g In Streams and Rivers (PMF) 2-79 Snrg*MC & Lundy SECURITY-RELATED INFORMATION - WITI II IOLD UNDER 18 CFR 2.998

SECURIT¥=RELATEB INFORMATION - 'NITltltOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Pro1ect No.: 11784-017 Figure 2.2-14: Computational Mesh Near CNS Flooding In Streams and Rivers (PMF) 2-80 Sorg..nr: & Lundy SECURIT¥-RELATEB INFORMATION - WITHHOLB UNBER 16 CFR 2.996

SECURlfY-RELATEE> INFORMATION - WITI II IOLE> UNE>ER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVAI.UATION REPORT Project No.: 11784-017 Figure 2.2-15: 2-D Model Inflow Hydrographs 500.000 450,000 400,000 350,000 300,000 r 2so.000 -

M 1\>0\III lelt Ovtlb~1k M,s,ourl ~ ,n Ch.llllN'I i

0 -l1Ule N~m.il1' 200.000 - ~nabotna 150,000 100,000 50,000 0

0 so 100 150 200 250 300 Time (hour)

Flooding In Streams and Rivers (PMF) 2-81 Sorg-&Lundy SECURIT¥-RELATEE> INFORMATION - WITI II IOLD UNDER 16 CFR 2.996

SECURITY-RELATED INFORMATION - 't't~ITHHOLD UNDER 16 C~R 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD H AZARD R EEVALUATION R EPORT Project No.: 11784-017 Figure 2.2-16: Comparison of Disc harge Hydrographs through the Study Reac h 900,000 800,000 700,000 600,000

[ 500,000

..l' - U/S Modtl Boond.l1y (RM 556) 1i - HillllburB,IA(RM So!S) 2i 400,000 - CNS (RM 533)

- O/S ~ I Boundary (RM SI 0) 300,000 200,000 100,000 0

0 50 100 1SO 200 250 300 Time (hours)

Flooding in Streams and Rivers (PMF) 2-82 Sorganl: & Lundy

SECURITY-RELATED INFORMATION - 'NITI II IOLD UNDER 18 CFR 2.998

SECURIT¥*RELATED INFORMATION - WITI II IOLD UNDER 18 CFR 2.398 Neb raska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD R .EEVALUATION REPORT Project No.: 1178'1-017 Figure 2.2-17 : Contours of Maximum Water Surface Elevation for PMF Event - Large Scale Flooding in Streams and Rivers (PMF) 2-83 G*rgeno:: & Lun dy SECURIT¥ -RELATED INFORMATION - WITI II IOLD UNDER 18 CFR 2.998

SECURIT¥*RELATED INFORMATION - WITHHOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-01 2450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-1...()17 Figure 2.2-18: Contours of Maximum Water Surface Elevation for PMF Event - Small Sc ale Flooding in Streams and Rivers (PMF) 2-84 Sorgon t & Lundy SECURIT¥-RELATEO INFORMATION - WITI II IOLB UN BER 16 CFR 2.996

SECURIT¥-RELATED INFORMATION - WITHHOLE> UNE>ER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178'1-017 Figure 2.2-19: Contours of Maximum Depth for PMF Event* Overview Flooding in Streams and Rivers (PMF}

2-85 S.nrgor& & Lundy SECURITY-RELATEE> INFORM1'TION - \'VITI II IOLD UNDER 16 CFR 2.996

SECURIT¥-RELATEB INFORMATION - WITHHOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1 178-017 Figure 2.2-20: Contours of Maximum Depth for PMF Event - Small Scale Flooding in Streams and Rivers (PMF) 2-86 B orgnnt) & Lundy SECURITV-RELAl'EB INFORMATION - WITI II IOLB UN BER 18 CFR 2.998

SECURIT¥*RELATED INFORMi!tTION - WITHHOtt, UNDER 16 CFR 2.396 Nebraska Pu blic Power District SL-01 2450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017 Figure 2.2-21 : Contours of Maximum Velocity for PMF Event - Small Scale Velocity (ft/s) 0 85 8

75 7

65 Flooding In Streams and Rivers {PMF) 2-87 Sorganc, Q Lundy SECURIT¥-RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.396

SECURITY-RELATEE> INFORMATION - WITHHOLE> UNE>ER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.2-22: Fetches from Embankment Points of Interest Legend Fetches 0 Points or Interest

- 1 Ft Depth Contour

- Federal Levees Water Depth High : 63.3 ft NAVD88 Low : 0 ft NAVD88 Flooding in Streams and River s (PMF) 2-88 SECURIT't'-RELATEE> INFORM1'TION - WITI II IOLE> UNE>ER 16 CFR 2.996

SECURITY-RELATEB INFORMATION - WITI II IOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-0 17 Figure 2.2-23: Labeled Points of Interest

= Perimeter Erroankmeot 0 Pocnts Of Interest Flooding in Streams and Rivers (PMF) 2-89 SECURITY-RELATED INFORMATION * 't'IITI II IOLD UNDER 16 CFR 2.996

SECURIT¥-RELATED INFORMATION - WITtttlOLB UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017 (b)(3) 16USC §824o-1(d)

Figure 2.2-24: (b)(4) (b)(7)<F) 0w 00375

- 0075 0225 Flooding in Streams and Rivers (PMF) 2-90 Sur-gone & Luridy S,ECURIT¥-RELATEB INFORMATION - \\llTI II IOLD UNDER 16 CFR 2.996

SECURITY-RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-01 2450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 117~ -017 Figure 2.2-25: Expected Maximum Extent of Wave Runup at Representative Locations (b)(3) 16 USC § u24o 1(d) (b1(4) b1(7 (f)

Flooding In Streams and Rivers (PMF}

2-91 S.rgant: Q Lundy 9ECURIT¥=RELATED INFORMATION - WITt It IOLD UNDER 18 CFR 2.998

9ECUfUfY-ftELATED INPOffMATION - WITHHOLD UNBEft 18 eFft 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT 2.3 DAM BREACHES AND FAILURES The flooding reevaluation for Cooper Nuclear Station (CNS) adopted the approach and methodology for estimating the flood wave generated by upstream dam failure scenarios using the most current data available and the numerical modeling software Hydrologic Engineering Center-River Analysis System (HEC-RAS), Reference 2.3-1; Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS), Reference 2.3-2, from the U.S. Army Corps of Engineers (USAGE); and TUFLOW FV Flexible Mesh Modeling, Reference 2.3-3, from BMT WBM. In particular, the CNS analysis fo!llows the guidance of ANSI/ANS 2.8-1992 (Reference 2.3-4) for the assessment of the potential dam failure modes and the specification of the antecedent and combined event conditions, consistent with the recommendations of NUREG/CR-7046 (Reference 2.3-5). The U.S. Nuclear Regulatory Commission (NRC) guidance on acceptable dam failure analysis methodologies is published as the Dam Failure lnteriim Staff Guidance (ISG) titled "Guidance for Assessment of Flooding Hazards Due to Dam Failure" (Reference 2.3-6), and was followed iri this assessment. The methodology prescribed in the Dam Failure ISG document was the basis of the reevaluation for flooding effects at CNS due to upstream dam failures.

The complexity of the Missouri River hydrologic condition along with System and Non-System dams is discussed in Section 2.2 of this report. The locations of all System dams and all Non-System dams in

~~~1~-~-~)~f~)-- - -tFh,~ ~!~~~~~i River watershed downstream of (4) (b)(?)(F) 2 1gure .3- .

I I

Dam and upstream of CNS are shown in As discussed in Section 2.8.5 of this report, the Bank Stabilization and Navigation Program (BSNP) was authorized under various Congressional acts since 1912. Fort Peck Dam was authorized under the Rivers and Harbors Act of 1935. The lower five dams (Garrison, Oahe, Big Bend, Fort Randall, and Gavins Point) were authorized under the Flood Control Act of 1944. Additional bank stabilization projects were authorized by various Flood Control Acts. Further stream bank erosion controls were authorized under the various Water Resourc.es Development Acts. The navigational channel project was declared officially finished in 1981 , with the terminus of the project at RM 734.8 at Sioux City, Iowa.

the USACE actively maintains the channel. It is unknown whether the USACE plans to* revise channel maintenance procedures or the System dams.

Following the guidance of ANSI/ANS-2.8-1992 (Reference 2.3-4), the combined effects of wind setup anq wave runup for a two-year design wind speed occurring coincidently with the maximum still water level as a result of the postulated upstream dam breach scenario were analyzed specifically for CNS Main Building facilities and Intake Structure.

As specified in the Dam Failure ISG , a large number of the dams in the watershed may have no impact on flooding at a site due to a combination of small dam size or large distance from the site. The Dam Failure ISG defines "inconsequential dams" as those dams that can be removed from consideration without analysis because they meet the criteria of having minimal or no adverse failure consequences beyond the dam owner's property. The Dam Failure ISG further suggests a second screening analysis for all dams that remain after removing the inconsequential dams, using several simplified modeling approaches for identifying dams whose failure would likely have negligible impacts on flooding at a nuclear power plant. Such dams are termed "noncritical dams." After the second screening, all Dam Breaches and Failures 2-92 ((

Sorgcr'C & Lundy* 1 c

)../

SEeURITY-ftELATEB INFORMATION - WITHHOLB UN BER 18 eFft 2.998

9ECURIT¥*RELATEB INp;QRMATION - WITI IHOLB UN BER 16 ep;R 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 remaining dams are considered "potentially critical dams," and detailed analyses are required to assess these potentially critical dams to show which are truly critical to the flood hazard estimates at the CNS site. The potentially critical dams that are not shown to be critical through detailed analyses are assigned to the "noncritical dams* category. The Dam Failure ISG specifies that the cumulative effect of all noncritical dams should be carried forward and added to refined estimates for the critical dams. A screening-level analysis was performed to identify dams whose failure will have no impact to the CNS site.

The six System dams that are upstream of the CNS site on the mainstem of the Missouri River are critical dams. The salient features of these dams are presented in Table 2.3-1 from the Master Manual of Missouri River Mainstem Reservoirs (Reference 2.3-7). In addition to the information shown, more critical data related to each dam and its operations are required to erform the detailed u stream dam failures anal sis for these S stem dams l> (J) 16 USC § 8240 l(dl (b)(4) (l>)(7XF) ese resu ts were used to determine an overall dam failure flood hazard water surface elevation (WSEL) at the CNS site. The main steps followed for the upstream dam failures (combined System and Non-System dams) related to the CNS site are as follows:

(0)(J)1oUSL; §8>4o1(<l) (l>)\4 1D)(/),,f)

Dam Breaches and Failures 2-93 SECURIT¥-RELATEB INf-ORMATION - WITHHOLB UN BER 16 Cf-R 2.996

SECURIT¥-RELATED INFORM311cTION - WITI II IOLD UNDER 18 OFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZA.RD R.ll'!VALUATION REPORT Project No.: 11784-017 (b)(3) 16 USC § 8240 l(d) !b)(4) (b) 7)\FJ Data used for the evaluation in this section include all dams located within the Missouri River Basin, downstream of Gavins Point Dam and upstream of the CNS site, as maintained in either federal or state inventories. The USACE National Inventory of Dams (NID) database (Reference 2.3-8) was queried for those states encompassed within the Missouri River Basin downstream of Gavins Point Dam and upstream of the CNS site. The states within the study area are Colorado, Iowa, Minnesota, Nebraska, North Dakota, South Dakota, and \Nyoming. The NID database does not publish dam hazard classification; dam inventories maintained by each state's respective dam safety agency or state*

engineer's office contain these hazard classifications. Therefore, additional dam inventory data were obtained directly from relevant state agencies.

The 3,327 remaining dams after screening the inconsequential dams from the total Non-System dam list within the Missouri River Basin downstream of Gavins Point Dam and upstream of the CNS site are shown in Figure 2.3-2. In accordance with NUREG/CR-7046 (Reference 2.3-5) and Dam Failure ISG (Reference 2.3-6), the effort for evaluating the flood levels occurring due to dam failure was reduced by grouping dams together and representing them as hypothetical dams. Altogether, 49 hypothetical dams on different tributaries entering the Missouri River or the Platte River were considered. Dam break parameters of each hypothetical dam are presented jn Table 2.3-2.

2.3.1 Flood Protection Level at the CNS Site Maintenance Procedure 7 .0.11 of CNS Operations Manual (Reference 2.3-9) reports that flood barriers are designed for a river flood water elevation of 906.00 ft CNS Plant Datum (906.37 ft NAVD88).The conversion from CNS plant datum to NAVD88 datum is provided in Reference 2.3-10.

2.3.2 Hydrologic Evaluation 2.3.2.1 HEC-HMS Model Dam Breaches and Failures

,..(

2-94 B arga~ & , Lundy *~ *

)./

9ECURIT¥-RELATEf> INFORMATION - WITHI IOLD UNDER 16 CFR 2.996

SECURIT¥-RELATED INFORMATION - WITI II IOLB UNBER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT (bJ(3}.16 USC § B24o-1(d}, (b)(4) (b}(7}(F}

2.3.2.2 Flow Hydrographs for Non-System Dams (b)(3) 16 USC § 824o-1(d). (b}(4) (b)(7}(F}

Dam Breaches and Failures 2-95 SECURIT¥=RELATEB INFORMATION - WITHHOLB UNBER 18 CFR 2.998

SECURIT¥-RELATED INFORMATION - WITHHOLB UNBER. 16 CFR. 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 (b)(3) 16 U SC § 8240-1 (d) (b)(4) (b)(7)(F) 2.3.2.3 Base Flow Data (b)(3) 16 USC§ 8240 1(d), (b)(4) (b)(/)(r-)

Dam Breaches and Failures ,,,.

2-96 (\

Sargent: & Luncty' '*

"j,)

SECUR.IT'l'-RELATEB INFOR.MATION ='IIITtit IOLD UNDER 18 CFR 2.996

8ECURIT't'-RELA'fEB INFORMATION

V-tlTHHOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION Rl!PORT (b)(3) 16 U SC § tl24o 1(d) (b)(4) (b)(7)(F) 2.3.2.4 USACE Dam Failure Hydrographs The NRC transmitted the USAGE analyses results for all six System dams for hydrologic and sunny-day dam failure. The USAGE did not provide hydrographs resulting from seismic failure of the System dams because it concluded that the dams are seismically robust and not subject to failure during a seismic event. The USACE did not provide a descr,iption of its approach or assumptions used: however, the NRC confirmed that the detailed analyses performed by the USACE were in compliance with the Dam Failure ISG requirements. The USACE analysis of System dams included failure of Non-System dams upstream of Gavins Point Dam. The USACE provided hydrographs resulting from failures of the six System dams at a location immediately downstream of Gavins Point Dam. The USACE discharge hydrographs directly downstream of Gavins Point Dam were used for the combined System and Non-System dam failure analyses. Seven dam failure scenarios were selected for the combined System and Non-System dam failure analysis. These selections were based on bounding values of peak flow and timing to eak flow at the CNS plant site. The seven selected scenarios are listed below.

(b)(3) 16 USC

1.* ,,. . drolo ic Fail r : (bl( ) 1 U 5 § 8 o I ( ) ( ( ), ( )(7 ( )

§ 8240 1(d) (tlJ (4) (b)(7)(F) ( ( 1 s L 8240 1( (b) ( )( (r This scenario was se ec e ecause o I s 1g magn u e o pea ow.

~b~~l~~<~)~(~r*. . .2, .. [:J Sunny-Day Failure: This scenario was selected because of its high magnitude of peak flow. --- (b)(3) 16 USC § 8240 1 (4) (b)({)(r)

(~)(~) IO \Jr.le I b14o 1ltt}i (IJf : :... ***-~;- +*

l l::lydrologic. pa.ffl:1red * .. *

Us th d b 4 b 7 F The hydrologic failure

14) (b)(r)W) scenar ~ cted because of Its high magmtu e of pea flow. UE : j results indicated

' that th (b)(3 1 sunny-day dam failure does not result in failure of *

Dam downstream (b)( 3l 16 u 5 c

- ' §8*24o*l(d) (b) so the sunny-day dam failure scenario is bounded by other events and was not (4) (b)(7)(FJ selected for detailed analysis.

. ***4;** f * ** * ** !Hydrotogic F.lauuce* I hi'L')cenario was selected because I .. JDamisthe (b)(3J 16 us c

................ closest upstream dam to * **** * * * * ****** JDam and would result in the snortest time to peak ai (~~~~~*))W\ (bl

( (lI c Dam of the upstream hydrologic failure scenarios.

§824o 1(d},(b) ,---- 3 16 S 5* ..........................

_ .,...unny-Day Failure** This scenario was selected because '-*- - - ~ -loam is the I .. . . . . . . .... . *

(bl( ) u c

§8240°1(d) (b)

. . . . . . . .. ..~

*. .. . . . e.a m damtol-** .. ***** IDam and _would resul~ in the shortest time to peak at (4) (b)(7)(r)

. . . . ..... . . **** ***

Dam of the upstream sunny-d .

6; :* *. . Hydro/ogicFailure+ I 4 is the rb)\J) 16 u 8 c § 824o- 1(dJ. (bl( l* (b)(T) The hydrologic failure scenario w~ d because of its high magnitude of peak flow. US~ suits

. . . . ....indicatedthatthe l=:__Jsunny-day dam failure does not result in failure of L=JJam . . . . . . . . t~~l;!~,S(~)

(4) (b)(?)(F)

Dam Breaches and Failures 2-97 S a rgorl~ &: Luncty'~ "

SECURIT'f -R:ELATEB INFORMATION - WITHHOLD UNDER: 18 Cfi" 2.396

SECURITY-RELATED INFORMATION - WITHHOLB UNDER 16 CPR ! .396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 1

I downstream, so thet %=~1 ~ a sunny-day dam failure scenario is bounded by other events and was not selected for detailed analysis.

(b){3) 16 USC

§ 824o-1(dr(b)

7, 10X3) 16 us c § a2.io.11d !bx4I ,~ F H drolo ic Failure: While (b)(3) 16 USC § 824o-1(d). (b)(4). (b)(7)(F}

this scenano was see e o s ow a comparison e een (4), (b}(7)(F) pea ow an 1me o pea WI o her scenarios at the CNS site.

(b)(3l 16 u 5 c NoneoUbenam failure-hydrographs fo~ - - !Dam were consider,ed. The failure results for this

§ 824o-1(d},(b}

(4) (b)(7)(F) dam are not bounding in terms of flow magnitude or time to peak at the CNS site.

The seven dam failure scenarjos li~ ed above were selected for detailed hydraulic analysis. The dam (b)(3l 16 u 5 c Jailuiehydrog.raphs-at-1------* !Dam due to both hydrologic and sunny-day failures of the System

§ 824o-1{d} {b)

(4) (b)(7)(F) dams are presented in Figure 2.3-5 and Fi ure 2.3-6, respectively. The seven selected System dam failure hydrographs downstream of t h ) Dam used for the combined System dam and Non-System dam failure analysis are presen e m 1gure 2.3-7 .

.2.3.3 Hydraulic Evaluation A one-dimen~ D) HEC-RAS model of the Missouri River between I

l oam * - .. .. ~b~~l~!(~ls(~l

~b~~l~~.(~)~(;} (approximateL=......J and Rulo, Nebraska (approximate RM 498) was developed for the PMF for the (4) (b)(7)(F)

(4). (b)(7)(F) CNS site, and it was modified and used to route the dam breach hydrographs and compute the peak WSEL at the CNS site due to upstream dam failures. The results from the 1-D basin-scale routing model were then used as upstream and downstream boundary conditions for a reach-scale two-dimensional (2-D) hydraulic model. In addition, the results of 1-D basin-scale hydraulic model were used to determine the travel time and Hooding duration. This reach-scale model, approximately 46 miles long, was further used to predict the complicated interaction between the river channel and overbank areas that provides an estimate of flow distributions near CNS. The results from this 2-D reach-scale model were used to predict water surface elevations (WSELs), depths, and velocities at CNS for the dam failure scenarios.

2.3.3.1 Route Dam Failure Hydrographs for Non-System Dams t,o CNS Site Using One-Dimensional HEC-RAS Model The HEC-RAS model with the full floodplain geometry was used for upstream dam failure evaluation.

Similar assumptions made for the model geometry for PMF were used. A summary of unsteady HEC-RAS model computational parameters is presented in Table 2.2-3 and Table 2.2-5. Initially, the Non-System dam failure analysis (peak flow estimated as 1.3 million cfs) was performed with no changes in the HEC-RAS model geometry. However consideriJ significant increases in the peak flow and volume (b)(3} 16Y SC _of the Syst.emd.amJallure._hydrographs (i ffs} compared to PMF runs, minor modifications 0

§ 8240- 1(dl {b) to the floodplain geometry were made to otam mod stability without compromising model

"' ,cu-,,,r, conservatism for the Non-System dam failure analysis.

Hydraulic Table Parameter (HTab) increments were increased by 10% and the number of points set to 100 at all cross sections to prevent the maximum discharge from exceeding the range of cross section HTabs. These HTab vertical increments ranged from 1.0 ft to 1.25 ft in the PMF HEC-RAS model, and ranged from 1.1 ft to 1.375 ft for dam break flood evaluation. All bridge features and cross sections Dam Breaches and Failures ,,,,./.-

/' \

2-98 , '

Sargll?li.f ~.Lundy\~-:

SECURIT'i'*REL>\TED INFORMATION - WITHHOLB UNf>Eft f6 CFft 2.396

SECURITY-RELATEE> INFORMATION =WITI II IOLD UNDER 16 CPR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 upstream and downstream of the bridges were removed, which prevented water from being stored behind embankments, thus resulting In Jess attenuation and faster translation of hydrographs.

Evaluating the upper end of peak dam failure flows showed that removing bridges and cross sections

{when compared to simulations with bridges and sections included) did not have an effect on the peak WSEL or time to peak; however, this did improve model stability at bridge structure locations.

Sensitivity analyses were performed for the Non-System dam failure HEC-RAS model with both sets of geometries (with and without the changes described in paragraphs above) and found that the resulting WSELs differed only by a few tenths of a foot. For consistency, the same geometry with the above-described changes was used for Non-System dam failure analysis and combined System dam and Non-System dam failure analysis.

Figure 2.3-8 shows that the land use types are classified into nine broad categories over the model domain. Research provided by Chow (Reference 2.3-14) and Fread (Reference 2.3-15) indicates that when the channel banks are exceeded and shallow flow exists in the floodplain, the total resistance has a tendency to remain the same or increase, since the overbank roughness is generally higher than the channel roughness. However, as flow stages increase in the overbank, as occur especially in larger systems in the United States, the resistance effect can remain the same or slightly decrease. Based on graphical data provided by Chow and Fread showing Manning's roughness coefficient (also known as Manning's n) versus discharge on the Mississippi River, the Manning's roughness coefficient can remain the same or decrease up to 20% for stages above bankfull. On the Nishnabotna River, Chow provides tabular data that indicate Manning's roughness coefficient for a corn field would not decrease for depths greater than 4 feet (ft), while for a pasture, Manning's roughness coefficient could decrease approximately 20%. These data suggest that the reduction of Manning's roughness coefficient up to 20% may be appropriate for some land use coverage to account for depth of flow.

Because the expected depth of flow on the floodplain near the facility could exceed 30 ft, for purposes of dam failure modeling, the Manning's roughness coefficients were reduced 20% for the grassland, wetlands, and row crops land use areas within the modeled domain. Despite Chow's data, for conservatism, it was assumed that corn and other row crops would be flattened and/or uprooted at the depths expected during a dam failure flood event. Therefore, the roughness value for row crops was also decreased by 20%. Row crops occupy over 75% of the floodplain land use within the modeled domain (Figure 2.3-8). Roughness coefficients were not decreased for the open-water land use areas (channel and other water bodies) because the roughness would not change due to depth. It is also assumed that the forest or urban land obstructions would remain in place during a dam failure event, which would occupy the majority of the water column. Therefore, Manning's roughness coefficients for forested and urban areas were not decreased. However, Manning's roughness coefficients on the site were reduced since the buildings were explicitly represented. Based on values provided in Reference 2.3-14, and accounting for the presence of various concrete barriers and appurtenances, a value of 0.025 was selected for paved. In addition, the switchyard areas were assigned a value of 0.08 since there are numerous concrete foundations and metal structures consistent with treed areas.

Table 2.3-7 lists the Manning's roughness coefficient associated with each land use type used in the PMF, Non-system dam failure analysis and Combined System and Non-system Dam failure analysis.

Dam Breaches and Failures 2-99 SECURl'f'f-"l=LATEO INFORMA'flON - 't"ill'I fl fOLD UN BER 16 CFR 2.996

9ECURIT¥*RELATED INFORMATION - 'i'IITttHOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD Rl!l!VALUATION REPORT Project No.: 11784-017 According to guidance from the Dam Failure ISG (Reference 2 .3-6), levees that provide flood protection for the plant site should be considered to fail when overtopped. Although there is no levee that protects the CNS site, there are levees on the left and right banks of the Missouri River in the vicinity of the site.

Consistent with this guidance for levees that protect the site, levees adjacent to the site would be considered to fail once overtopped. A full floodplain flow for the Non-System dam failure condition was considered as the WSEL would be near top of levee at the start of the simulation, which is the 500-year discharge in the Missouri River. Additional flows from the Non-System dam failure would provide enough discharge to overtop the levees early in the simulation. This consideration would have impact only on the rising limb of the dam breach hydrograph until the time that the levees overtop, and therefore, this condition was not expected to impact peak stage or discharge.

The 500-year flow from the USACE UMRSFFS report (Reference 2.3-12) was considered as the dam release from Gavins Point Dam for the Non-System dam failure analysis. The locations and peak inflows of the combined Non-System dam failure and 500-year flow hydrographs used in the model are summarized in Table 2.3-6. The peak computed WSEL at the CNS site was checked against the plant flood protection level to identify ~ny potentially,eritical dams that require evaluation with detailed , 1 methods.

Based on the Dam Failure ISG, as discussed in Section 2.3 of this report, the peak WSEL was calculated. In accordance with the Dam Failure ISG, the cumulative effects of the noncritical dams were carried forward and added to refined estimates for the critical dams. The stage and discharge hydrographs at the CNS site and the comparison between the peak of the stage hydrograph and the design flood protection level at the CNS site are presented in Figure 2 .3-9. The comparison of peak stage from hydrograph with CNS design flood protection level is presented in Table 2.3-8. The combined hypothetical dam failure hydrographs produce a peak stage of 903.09 ft NAVD88 at the CNS site, which is less than the existing plant flood protection level of 906.37 ft NAVD88; therefore, all Non-System dams below Gavins Point Dam and above the CNS site were classified as noncritical.

All HEC-RAS model simulations were executed and finished with stable and converged results.

2.3.3.2 Route Combined System and Non-System Dam Failure Hydrographs to the CNS Site Using One-Dimensional HEC-RAS Model (b)(3) 16 U.s C § tl24o-1(d) (b)(4) (b)(7)(F)

Dam Breaches and Failures .*,

/

2-100 /

Sarge nt:&

\

. Lunctyt,c

/

))

9ECURIT¥=RELATED INFORMATION

WITI II IOLD UNDER 16 CFR 2.996

SECURIT'f-RELATEB INFORMATION - WITHHOLO UNOE" 16 CI-R 2.S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 fLDOD HAZARD REEVALUATION REPORT Project No.: 11784-017 .

2.3.3.3 Water Level Magnitude and Timing Using One-Dimensional HEC-RAS Model (b)(3)16USL f I

§ 8240 1(dJ(b) Asdlscussecnn- s-ectRm- 2:3*:3-:-n ,r this report, alll..._ __,__,.,:,-,~ ams were found to be noncritical and

'~' " " "c, 1 7 the cumulative effect of these noncritical dams were carried forward and added to refined estimates for the critical dams.

The stage and discharge h~drographs at the CNS site from the seven! !dam failure scenarios ~b~~l-~~(~ls(~l (bX3l 16 u 8 c . .~ combined with I ] dam failure hydrographs are presented in Figure 2.3-1 O and Figure 2.3-11 , (4) (bJ(7)(F)

~::;(~t* 4 (b)t ! respectively, with the results tabulated in Table 2.3-9. As discussed in Section 2.3.1 of this report, CNS flood barriers provide protection for floo~ n elevation of 906.37 ft NAVD88. As shown Jn Table

~;~:.~:(~. 2.~..- .. . hydrologic failure scenario of D would result in the highest estimated peak stage r&~8 4¥a~"0 .*:ofl....._Jft NAVD88 at the CNS site. The Dam hydrologic failure scenario would result in (4), (b}(7)(Fi f l the ~J~~ aq;\~ ~f69f&Y'N1alt 1tfiBoTNS site, with an estimated peak stage of (7tt NAVD88 arriving .. __ (b)(3)_16 USC afte~ ~~ (

1 Jrom the start of the dam breach. The! -** IDam failure ~~l~it~

s~enario est~mat~d peak s~age was less th~n the ~lant Hood_protection level. The dam failure s~narjo ielci~¥~lCT !;(~

. S site having an estimated peak flood stage that.

I ~8740 .1(d) (b)

( ( l 11:1 t § ,, 0 l(dl (bX l \b) drolo ic failure scenario, for which the estimated peak stage (4) (b)(7)(F)

~b~1l~~i~t(;l is fl NAVD88, arriving abou ( -'> 1b ~c 11c (t>) 1 *b l fter the dam breach. By default, (4) (b)(7)(F) HE - AS computes the flow distribution across t e cross section, divided Into left overbank, main channel, and right overbank (Reference 2.3-16).

2.3.3.4 Two-Dlmenslonal Hydraulic Model A detailed 2-D hydraulic model of the Missouri River near CNS was developed using TU FLOW FV software to evaluate the PMF at CNS. That model is described In detail in Sections 2.2.3.3.1 and 2.2.3.3.2. The modeled (i.e., 2-D) reach of the Missouri River extended from north of Hamburg, Iowa (approximate RM 556), to north of Craig, Missouri (approximate RM 510)- see Figure 2.3-12. The existing 2-D model was further revised to better address hydraulics of the study area during the dam failure event and used to determine spatially and temporally varying information about WSELs, depths, and velocities at CNS for the dam failure scenarios. Modifications to the original 2-0 PMF model are described in Sections 2.3.3.4.1 through 2.3.3.4.5 below. AU other parameters were kept unchanged.

The modified PMF TUFLOW model is referred to as the Dam Failure TUFLOW Model.

2.3.3.4.1 Study Area At the upstream boundary of the model (RM 556.16), the PMF model extended to levee R573 on the right overbank rather than the bluff. This approach simplified model setup and the upstream boundary condition sensitivity analysis, performed using the PMF model, and showed that flow distribution at the upstream boundary of the model did not affect the model results in the area of interest near CNS. For the dam failure model, the model was extended west at the upstream boundary to the Missouri River Dam Breaches and Failures 2-101 SECURIT'f-R!Ll<'fEfJ INflORMATION - WITHHOLB UNBER 16 Cf" 2.998

SECUFtlT'f ~FtELATEB INFOFtMATION

WITtitlOLE> UNE>ER 16 CFFt 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 bluff line because the increased discharges associated with the dam failure event reduced the significance of the levees.
2.3.3.4.2 Land Use Roughness Modifications Adjusted Manning's roughness coefficients, as described in Section 2.3.3.1, were used in the 2-D dam failure study.
2.3.3.4.3 Computational Mesh Modifications The study area is represented by a computational mesh containing 294,322 unstructured elements. As illustrated in Figure 2.3-13 and Figure 2.3-14, the mesh is coarser in areas that are farther away from CNS and finer in areas where moire detail is required. Node spacing at CNS was increased from approximately 5 ft in the PMF TUFLOW Model to approximately 20 ft in the Dam Failure TUFLOW Model. Node spacing near the bluffs surrounding the river valley was reduced from approximately 800 ft tp to appro)(imately 400 ft because the WSELs for the dam f~ilure extend a higher elevation than the PMF. T"e modifications to the PMF TUFLOW Model to develop the Dam Failure TU FLOW Model described in Section 2.2 included decreasing the mesh resolution in the vicinity of CNS to allow for reasonable runtimes and incorporating building rooftop elevations (Figure 2.3-15), rather than representing the buildings as blocked ineffective areas of infinite height, to allow the buildings to be overtopped.
2.3.3.4.4 Scenarios for Two-Dimensional Mod11J The following two scenarios are considered for 2-D analysis:
r~~6~JJ
~) ~(~-)~i&~ . . . . . ., .,.,.,.,.,
IThe
(~)(f)(F)
IHydro/ogle Failure~*! hs one of the three largest of the System dams.
hydrologic failure scenario was selected because of its high magnitude of peak flow due to cascading failure of the downstream System dams. HEC-RAS model results indicate that this event would be bounding for WSEL, velocity, and inundation duration at CNS.
~bi11~ ~ (~)~(~)* * . . ** . . ***E ]sunny-Day Failure: This scenario was selected because of its high magnitude of (b)(3) 16 USC (4) (b}(7)(Fl peak flow with shorter lead time compared to thel ******** JHydrologic Dam Failure.
§82 o l*(d) (b}
Lead time is considered as the time from initiation of dam failure to peak WSEL arrival (4) (b}(?)(r) at CNS.
2.3.3.4.5 Boundary Conditions The location and type of boundary conditions are shown in Figure 2.3-16. Three inflow discharge HEC-RAS Unsteady Model (see Section 2.3.3.3) results for both the F
boundaries were used: one for each overbank and one for the channel. The flow distribution between the overbanks and main channel for the Missouri River was determii :d u~inri Updated Dam Failure
. . .. ..ydr.ologic.and r = J ___ (b}~~~ ~ 5 ~
Sunny-Day dam failures. As part of the HEC-RAS water surface pro I e ca cu a ion procedure, L....::::=f ~ (b)(7)v) ( )
conveyance calculations were performed to determine discharge conveyed in both the overbanks and main channel. A stage hydrograph from the Updated Dam Failure HEC-RAS Unsteady Model was used Dam Breaches and Failures 2-102 ((
Sorgc::,nt::& l...&.Jndy'
11
)J SECUFtlT¥ -RELATEB INFORMATION - WITI II IOLD UNDER 18 CFFt 2.998
SECURIT¥-RELATEE> INFORMATION - WITHHOLE> UNE>ER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nucle*ar Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-01 7 as the downstream boundary condition for the Dam Failure TUFLOW Model. The inflow and stage hydrographs, for both the dam failure scenarios are shown in Figure 2.3-17 andFigure 2.3-18.
Only flows from the System and Non-System dams were considered for inflow boundary conditions; no tributary inflows were added to the model domain below the upstream boundary. Table 2.3-10 provides a summary of the maximum discharge at the upstream boundary and maximum WSEL at the downstream boundary for both scenarios.
2.3.3.4.6 Sensitivity Analysis Sensitivity analyses were performed for Fort Peck Hydrologic failure to estimate the influence of WSEL and velocity at CNS for upstream boundary conditions and for the Smagorinsky coefficient. For the upstream boundary, discharges were reduced 20% in the left overbank and increased in the right overbank and the main channel such that the original discharge distribution was maintained between the main channel and right overbank. The Smagorinsky coefficient was also changed within its acceptable range. Results of the boundary sensitivity analysis are shown in Table 2.3-11 . Results showed that their influence on the hydraulic characteristics at the site was negligible.
2.3.3.4.7 Two-Dimensional Hydraulic Model Results As discussed in Sections 2.3.3.4.4 and 2.3.3.4.5, the I :::--h tydrologic*andr-==:kun-ny-Qay.dam....
failure hydrographs combined with Non-System dam failure hydrograph describecfin'Se~tion 2.3.2 .2 of (4) (ll)(7)(1")
,f.~;~~\s(~i this document were used as the upstream boundary conditions for the*ir respective reach-scale 2-D model. Based on the HEC-RAS Unsteady model, the! :=Jhydrologic-damJailur.:e.simv.11'!tion .... (bl(3l 16 us c 4
Produced the highest peak discharge and thus highest peak discharge through the site. §-S:2(b}(7)(Fl (4) o-1(d}, (bl Water surface elevation, velocity magnitude, and depth were monitored at 10 points throughout the CNS site model at key facilities within the protected area and around the site (see Figure 2.3-19). A summary of rade elevation, maximum W~ aximum velocity, and maximum depth at monitoring
~0!ii~-~~~~ lsJo.r ----* .. l:lydr.ologic.failure and - Sunny-day failures are provided in Table 2.3-12 and (4), n,)~M ( Table 2.3- respectively. The highest-m e velocities on the site are at the comers of buildings, where flow accelerates around the corners and in areas between buildings that are aligned with the rima direction of flow. As shown in Table 2.3-12, the highest velocities on site e e_ roxim_ately (b)(3 l-16 us c § 824 0-l(dl !bH4 J (bl(7 ><Fl at the Intake Structure for the ------. Hydrol.ogic (bl(3 l 16 us c
§ *S24eA(dl (bl am a1 ure. (4) (bl(7J(Fl Point 11 (see Figure 2.3-19) is located upstream of the plant area, with the velocity vectors perpendicular to the plant buildings. Basically, Point 11 has the highest applicable velocity within the power block area. Other high velocities exist, but are either parallel to or away from the power block area. Therefore, the maximum velocity of Monitoring Point 11 was used for evaluating the accociated effects. <?verview,_ mid-lev~I view and_site-level v!ew of spatial distribution _o f v~locity for r . . . .). . . ,. . . ,bl(3) 16 usc hydrolog1c dam failure at time of maximum velocity at point 11 are shown m Figure 2.3-to, Fig Ure § 82 0 4
bi (~ (bl 2.3-21 , and Figure 2.3-22. Overview, mid-level view and site-level view of water surface elevations for ( l ( )( )( l
~~~1~-~(~):(;il ..
(4l (b)(7l(Fl ...__ __.
lhydrologic dam failure at time of maximum WSEL at CNS site are shown in Figure 2.3-23, Dam Breaches and Failures J 2-103 ( \
Snrgo nt: &. Lundy * ' "
j7 SECURIT¥-RELAfEE> INFORMATION - WITHHOLE> UNE>ER 16 CFR 2.996
SEOURIT¥*RELATED INFORMi8cTION - WITHHOte UNl:>ER 16 eFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.3-24, and Figure 2.3-25. The WSEL time series was reported at Monitoring Point 9 on the north side of the turbine generator building.
(b)(3) 16 U S .C As shown in Table ~ maximum WS~ from **
orthAmericanVerticalDatum ~8240-l(d) (bl
~b1~l~~1/4;,;~ ~e.!lJfl.NAVD88)tct=___JNAVD88forthe t = _ JHydro 091c am failure. (4 ) (b)(?)(F)
(4), (b}(7)(F}
2.3.4 Combined Effects Impact at the CNS site resulting from wind wave action during an upstream dam failure in the Missouri River was evaluated. The contribution of waves to flood levels resulting from associated wind wave for the Main Building Complex and the Intake Structure was evaluated. The ! JHydrologicE.ai!Yr~.,..... (~~~~;~ ~s ~
determined to be the bounding scenario at the CNS site based on estimated peak flow and stage, was [4 ) (b){7)\J) ( )
used for this evaluation.
The elevation of the top of foundation mat at the Intake Structure is 852.5 ft Plant Datum (852.9 ft NAVD88) and was used for computation of wave runup and total water levels for the Intake Structure.
The nominal site grade of 903.00 ft Plant Datum (903.37 ft NAVD88) was used for the computation of wave runup and total water levels at the plant buildings. The 2-year mean recurrence inteival annual extreme-mile wind speed from ANSI/ANS-2.8-1992 (Reference 2.3-4) was used for the estimation of wind wave heights. The fetch geometry was determined by extending lines at directional (radial angle) increments of 22.5 degrees from a representative point at the CNS site to the extent of the river cross sections in all directions as shown in Figure 2.3-26. Wind-driven waves were calculated using the Wind Speed Adjustment and Wave Growth module of the Automated Coastal Engineering System (ACES) in the Coastal Engineering Design & Analysis System (CEDAS) Version 4.03 (Reference 2.3-17). The ACES analysis was completed for each fetch. A controlling fetch was determined for each cardinal direction relative to the Plant North direction based on the largest wave height to approach from each direction. The fetches used to determine each cardinal direction are Identified in Figure 2.3-27 and Figure 2.3-28. Wind setup was calculated using Equation 4 of U.S. Bureau of Reclamation (USBR)
ACER Technical Memorandum No. 2 (Reference 2.3-18). The calculated wind setup was added to this base WSEL for subsequent wave run up computations. In accordance with EM 1110-2-1614, Equation 2-2 (Reference 2.3-19) and ANSI/ANS-2.8-1992 (Reference 2.3-4), the minimum of the H1% (the average wave height of the highest 1% of waves) and breaker *
he Significant Wave height [Hs]) was used as the controlling wave height. The (b}( ) 16 u 5 § 8240*1(d) is composed of multiple buildings with various roof elevations, as shown in Fi . - . when the wave crest is at the wall was calculated on the Intake Structure and (b)(3l 16 u 5 c § 8240* 1(d}, n accordance with the Goda pressure formula as described in CEM Table Vl-5-53 (Reference 2.3-20). Individual calculations were performed on Plant North, Plant East, Plant South, and Plant West directions using the highest building elevation exposed to each direction to determine the maximum wind wave runup experienced.
(b)(3) 16 USC§ 824o-1(d) (b)(4) (b)(7)(F)
Dam Breaches and Failures
./( "
2-104 ', '
s~rg113n\&_>L1....lindyll1.
,) **~'° SECURITY-RELATEB INFORMi8cTION - WITIIIIOLB UNBER 18 eFR 2.398
SECURIT¥-RELATEl:l INFORMATION * 'N ITI II IOLB UNl:lER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.3.5 Associated Flooding Impacts 2.3.5.1 Erosion and Sedimentation (b){3)16USC ~
§ 824o-1(d}{b)* The ** hydrologic dam failure resulted in the highest peak discharge at the CNS site and, (4) (b)(7)(F) the ore, was considered for the evaluation of flooding effects. Velocity and deptr were evaluated. The velocity contours from the time of approximate maximum velocity at CNS for the_ ****-!Hydrologic ~i~l 1
~~)s{~)
Dam Failure are shown in Figure 2.3-21 and Figure 2.3-22. Figure 2 .3-24 and Figure 2.3-25 show the {4l*(bJ(?)(Fk WSEL from the time of approximate maximum WSEL at CNS for the I --*- !Hydrologic Dam .Eai!µr~,(? ~;"5i ~ ~
Generally, maximum velocity magnitudes at CNS range from 2 to 5 fps. There are some locations, ? 8 4 ) (b)(7)Vi ( )
where struc~ures or embankments overtop or where flow is conveyed between buildings, with local maximum velocities up to 10 fps. Maximum velocity at the Intake Structure is 7.1 fps.
Common groundcover at CNS was based on aerial photography shown in Figure 2.3-30. The common groundcover at CNS Includes turf {permissible velocity 7 fps), concrete (permissible velocity >18 fps),
and 1-inch gravel {permissible velocity 5 fps) as listed in Reference 2.3-21 . The overbank velocity at CNS is generally 2 to 5 fps, which is near the lower threshold for turf, below the threshold for concrete, and near the upper threshold for 1-inch gravel. This may lead to local erosion In areas that contain 1-inch gravel. Areas at the corners of buildings and structures, in paved areas between buildings, or where embankments overtop have velocities up to 10 fps, which exceeds the permissible range for both turf and 1-inch gravel. In these locations, erosion of turf and 1-inch gravel may occur. After periods of long inundation {exceeding 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months ), research has shown that the permissible velocity of average turf cover is reduced to approximately 2 fps {Reference 2.3-21 ). This may lead to local erosion in areas outside of the protected area and switchyard due to the duration of the event The maximum velocity at the Intake Structure (7.1 fps) is less than the permissible velocity of concrete {>18 fps) {Reference 2.3-21 ). Riprap is placed on the banks of the river and around the Intake Structure. The maximum velocity around the Intake Structure {7.1 fps) is below the permissible velocity of riprap {10 to 13 fps).
The USACE did not provide specific information with respect to the flow and stage hydrograph at each System dam, nor did it provide the dam breach parameters or estimated quantity of available source sediment from the breach, including material deposited behind the dam. Therefore, the sediment transport evaluation for the Missouri River during a System dam failure was qualitatively characterized based on available literature from the 2011 flood. It was assumed that the dam breach flows from a sediment transport perspective would be analogous to the 2011 dam releases, though at a much larger scale. The dam breach flows, much like the 201 1 releases, would not i nclude significant runoff and sediment from tributary inflows, but would include mobilized reservoir sediments.
The 2011 flood originated upstream of the mainstem dams in eastern Montana and western North Dakota and South Dakota {Reference 2.3-22). The flood flows were conveyed through the mainstem dam system, resulting in record discharge releases. As flows were conveyed from upstream of Fort Peck Dam through Gavins Point Dam, some of the sediment was deposited within the mainstem dam Dam Breaches and Failures 2-105 (
/(.
S.ar"gOnt: & L.undy'\ C
\ )
)'
SECURIT't'-RELATEl:l INFORMATION - 't1VITI II IOLD UNBER 16 CFR 2.598
SECUftlT'{ -ftELATEB INFORMATION - WITHHOLB UNDEft 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784--017 system. The prolonged flooding on the lower Missouri River that lasted over three months was primarily from the Gavins Point Dam releases, which were essentially sediment-free (Reference 2.3-23).
(b)(J) Hi U SL § 8240 1(d) (b)(4) (b)t ll\~ I 2.3.5.2 Inundation Section 9.4 of the Dam Failure ISG (Reference 2.3-6) recommends developing inundation maps to provide assistance in identifying Systems, Structures, and Components (SSCs) important to safety that may require protective and/or mitigation measures from flooding due to dam breach. Inundation maps were generated using GIS, based on the TUFLOW FV model results. f hel lhydrologic da.m (b)(3)16USC
§ 824eA(d) (b) failure case was selected for inundation estimation because it resulted in the highest water surface (4) (b)(7)(F) elevation at the CNS site.
Using the ArcGIS 10.2 software (Reference 2.3-24), the maximum flooding depth grid was converted into a raster format. Figure 2.3-31 shows the inundation mapping at a large scale with aerial imagery in the background, and provides an overview of the extent of inundation for the Missouri River adjacent to and upstream of the CNS site. The medium-scale map showing flood velocity information is presented in. Figure 2.3-32. The medium-scale map also shows that the de th grids surrounding the plant site are
~b)(3) 16 u~a:: inJherange."o4-----
~~9£?Ji!.\
~ of depth..ofwate~in tl'te l- - 1
_ The small-scale map with names of
~ SSCs, elevations, and local water depths is presented in Figure 2.3-33. A depth of water above the roof at these SSC buildings and other structures is presented in Table 2.3-16. As shown in the Table 2.3-16 enerator Building, Heating and Fan Building, and~ Building-2, flood levels are~ (b)(3) 16 us c
~b~11~~<~;\~, ele~ati_ons. The ~o?d levels at other buildings areL___J elevation even though the~ ~~l}:~
(4) (b)(7)(F) ng 1ns1de the buddings. (4) (b)(7)(F)
I""'" 6 u SC ! 824<>-l(d) ,,,,, ,,,,' "
Dam Breaches and Failures 2-106 8EOUR'IT11'-RELATEfl INFORMATION - WITHHOLB UNBER 16 CFR 2.996
SECURIT¥-RELATEB INF8RMATION
WITHH8LD UNDEt;: 16 CFt;: 2.390 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Pro/ect No.: 11784-017 (b)(J) 16USC §824o-1(d) \b)<4) tb)(7)(FJ 2.3.5.3 Hydrostatic and Hydrodynamic Forces Hydrodynamic impacts at the CNS site resulting from wind and wave action, and from currents during an upstream dam failure in the Missouri River were evaluated. The contribution of waves to nood levels, associated wave loads (as applicable), and c urrent loads (as applicable) for the Main Building C0mplex and the Intake Structure was evaluated.
The elevation of the top of the foundation mat at the Intake Structure is 852.5 ft Plant Datum (852.9 ft NAVD88) and was used for computation of hydrodynamic and hydrostatic forces for the Intake Structure. The nominal site grade of 903.0 ft Plant Datum (903.37 ft NAVD88) was used for the comput~tion of hydrostatic and hydrodynamic forces on plant buildings. Wind wave setup, wind wave heights; and total water levels evaluated, as discussed In Section 2.3.4; were used for estimation of hydrostatic and hydrodynamic forces on the plant structures.
Wave-induced hydro mi o when the wave crest is at the wall were calculated on the Intake Structure and ( ( 'It u *n accordance with the Goda pressure formula as described in CEM Ta e - - e erence 2.3-20). The wave runup extent on the structures was also estimated. Wave-induced hydrodynamic pressures when the wave trough is at the wall were calculated on the Intake Structure and Main Building Complex in accordance with the Sainnou pressure formula as described in Coastal Engineering Manual (CEM) Table vt-5-52 (Reference 2 .3-20). In addition, hydrostatic pressures were calculate= ~ : ~*~:~
during the upstream dam failure. The '1 '> r. ~
p~r:~er and the depth of submerged structure l is composed of multiple bulldlngs with various roof elevations, as shown in ~ 2 ua
~n ivi calculations were performed on Plant North, Plant East, Plant South, and Plant West directions using the highest building elevation exposed to each direction to determine the maximum pressure experienced.
(b)('3) 16 U C § 8240 1(0) (b)(4) ib)(l FJ 2.3.5.4 Debris Impact Loads A review of possible flood debris items was undertaken to develop a spectra of nood debris sources.
The following items are considered to represent a range of debris sources available upstream of the Dam Breaches and Failures ,**
\
2-107 t \
Sorgont:.&L.a..tndy'1<
\ ..-'
)/
9ECURIT¥=RELATEB INFORM,\TleN - 't'VITI ti IOLB UNDER 1:e CPR 2.998
SECURIT,'~RELATEB INFORMATION - Wl"FHHOLO UNOER 16 Cf-R 2.S96 Nebraska Public Power District SL-01245O Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-01 7 CNS plant. Two debris sources and masses are based on ASCE 7-10 (Reference 2.3-26) recommendations and the barge mass is based on typical barge sizes on the Missouri River. Additional vehicle and marine vessel masses are based on manufacturer data available on the Internet.
ASCE 7-10 miscellaneous debris - 1 kip
Large natural debris (ice, trees) - 4 kips
Large vehicles and boats (tug boat, bus, mobile home) - 40 kips
Tank-type debris (train cars, chemical tanks, semi-trailers) - 100 kips
Barge - 5, 100 kips Flood debris impact loads were calculated for the first two debris objects using the methodology presented in Chapter CS of ASCE 7-10 (Reference 2.3-26), with the following considerations:
Duration of impact load of 0.03 seconds was recommended based on Reference 2.3-26, Section C5.4.4, with the pulse shape taken as a half sine wave.
Velocity of the debris was considered ta be equal to the water velocity, which may dlffer for each debris type, depending on the expected debris path.
Importance factor value of 1.3 for Risk Category IV was used (Reference 2.3-6, Section 4.2.8).
Depth coefficient was selected from Table CS-2 of Reference 2.3-26.
Orientation coefficient value of 0.80 was used, as recommended in Equation C-5 of Reference 2.3-26.
Blockage coefficient from Table C5-3 of Reference 2.3-26, considering sheltering within 100 ft upstream was used.
Dynamic load factor depends on the fundamental vibration period of the impacted structure, and the maximum value from Table C5-4 of Reference 2.3-26 was conservatively used.
Flood debris impact loads were calculated following the methodology presented in Section 3.14.8 of AASHTO (Reference 2.3-27). As Equation 3.14.8-1 of Reference 2.3-27 is calibrated for impacts of large vessels, its results for the Large Vehicles and Boats, Tank-Type Debris, and Barge sources are considered more applicable than the ASCE 7- 1O(Reference 2.3-26) method.
Estimated debris impact loads due to dam failure flood for different debris were determined using the input values identified above and based on overbank velocities and are presented above in Table 2.3-20. As shown in the table, a barge with the overbank velocity of 10 fps will result in a maximum impact load of 3,919 kips.
It is conservatively assumed that the debris objects do not decelerate as they redirect from the channel toward the plant area. Figure 2.3-22 shows that the maximum channel velocity is approximately 10 fps.
Dam Breaches and Faifures _;(
l .. \
2-108 Snl""'QD .;!= & ,Lundy l *r.
. ./'
_) .,..
SECURIT\"-RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.998
SEOURITY*RELATED INFORMATION - WITI IIIOLB UNDER 18 CFR ! .S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Projed No.: 11784-017 2.3.6 References 2.3-1. U.S. Army Corps of Engineers (USAGE). January 2010. River Analysis System HEC-RAS Version 4.1. USAGE, Hydrologic Engineering Center, Davis, California.
2.3-2. U.S. Army Corps of Engineers (USAGE). August 2010. Hydrologic Modeling System HEC-HMS Version 3.5. U.S. Army Corps of Engineers, Hydrologic Engineering Center: Davis, California.
2.3-3. BMT WBM, 2013, TUFLOW FV User Manual. Flexible Mesh Modeling, Version 2013.02.056_dev.
2.3-4. American Nuclear Society. 1992. ANSI/ANS-2.8-1992. Determining Design Basis Flooding at Power Reactor Sites.
2.3-5. United States Nuclear Regulatory Commission (NRC). 2011 . Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America. NUREG/CR-7046 PNNL-20091. U.S. Department of Energy, Office of Nuclear Regulatory Research :
Richland, Washington.
2.3-6. United States Nuclear Regulatory Commission (NRC). July 29, 2013. Guidance far Assessment of Flooding Hazards Due to Dam Failure, Japan Lessons-Learned Project Directorate JLD-ISG-2013-01 .
2.3-7. Missouri River, Mainstem Reservoir System, Reservoir Regulation Manual, Master Manual, U.S. Army Corps of Engineers, Omaha, Nebraska, 1979.
2.3-8. U.S. Army Corps of Engineers (USACE). National Inventory of Dams Database.
2.3-9. Nebraska Public Power District CNS Operations Manual, Maintenance Procedure 7.0.1 1, Rev. 29, "Flood Control Barriers."
2.3-10. Nebraska Public Power District Engineering Evaluation (EE) Number 12-035, Revision 0, "Review of 2012 Topographic Survey of CNS," March 2013.
2.3-11 . United States Department of the Interior Bureau of Reclamation, ACER Technical Memorandum No. 11, December 1988: Downstream Hazard Classification Guidelines, 2.3-12. U.S. Army Corps of Engineers (USAGE), November 2003, Upper Mississippi River System Flow Frequency Study, Hydraulics and Hydrology Appendix F, Missouri River, USACE Omaha District, Omaha, NE.
2.3-13. United States Geological Survey {USGS). 2013. USGS National Water Information System (NWIS) . Washington, D.C. , http://walerdata.usgs.gov/nwis/.
2.3-14. Chow, 1959. Open Channel Hydraulics. McGraw Hill.
2.3-15. Fread, Danny L. 1989. "Flood Routing Models and the Manning's n." Proceedings of the International Conference on Channel Flow and Catchment Runoff, University of Virginia, Charlottesville, Virginia, May 22-26, 1989, pp 421-435.
Dam Breaches and Failures
,*-(
2-109 i '
S F l t - g C ~ &.~ndy 1 ' "
'~*/
SECURITY~"ELATEO INflORMATION - WITI IIIOLD UNDER 16 CFR 2.996
seeURIT'f-RELATEB INFORMATION - Wl'fHHOLE> UNE>fR 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION Rl!PORT Project No.: 1178-4-017 2.3-16. U.S. Army Corps of Engineers (USAGE). January 2010. HEC-RAS River Analysis System, Hydraulic Reference Manual. USACE Hydrologic Engineering Center, Davis, CA.
2.3-17. CEDAS-ACES Version 4.03 (2014). Veri-Tech, Vicksburg, MS.
2.3-18. United States Bureau of Reclamation. 1981 . Freeboard Criteria and Guidelines for Computing Freeboard Allowances for Storage Dams. ACER Technical Memorandum No. 2.
2.3-19. U.S. Army Corps of Engineers (USAGE). 1995. Engineer Manual 1110-2-1614. Design of Coastal Revetments, Seawalls, and Bulkheads.
2.3-20. U.S. Army Corps of Engineers (USAGE). 2008. Coastal Engineering Manual. EM 1110-2-1100, Washington, D.C. (in 6 volumes).
2.3-21. Fischenich, C. May 2001. Stability Thresholds for Stream Restoration Materials. Ecosystem Management and Restoration Research Program, U.S. Army Engineer Research and Development Center, Vicksburg, MS.
2.3-22. United States Department of Commerce. May 2012. The Missouri/Souris River Floods of May -
August 2011. Prepared by the National Oceanic and Atmospheric Administration, National Weather Service, Kansas City, MO, and Salt Lake City, UT.
2.3-23. United States Geological Survey 2013a. "Characteristics of Sediment Transport at Selected Sites along the Missouri River during the High-Flow Conditions of 201 1 ." U.S. Geological Survey Paper 1798-F, 27p. http://pubs.usgs.gov/sir/2013/5006/sir13-5006.pdf.
2.3-24. ArcMap Version 10.2 (.2013). ESRI, Redlands, CA.
2.3-25. Dean, R. and Dalrymple, R. 1991. Water Wave Mechanics for Engineers and Scientists. World Scientific. Hackensack, NJ.
2.3-26. ASCE 7-10, "Minimum Design Loads for Buildings and Other Structures."
2.3-27. AASHTO, "LRFD Bridge Design Specifications, "7th Edition.
Dam Breaches and Failures 2-110 9ECURIT¥-RELATfD INFORM,tcTION - 'lt1ITI l~IOLE> UNE>ER 16 SFR 2.998
SECURITY-RELATED INFORMATION - VilTI ti IOLB UN BER 16 CF ft 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.3.7 Tables Tables associated with Section 2.3 are presented on the following pages.
Dam Breaches and Faifures 2-111 Snrgnnt & t_ur,dy'
c SECUfUf¥-REL.AfEE) INFORMATION - 't'tlTI II IOLB UNl:>ER 16 CFfi( ! .396
SECURIT¥*RELATED INFORMATION * 't'Vll'HHOLD UNDER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.3-1 : Salient Features of Missouri River Malnstem Dams Parameter Gavins Point I Fort Randall I Big Bend (b)(J) 1ti U SC ::i tll4o-1 (0), (b)(4) (b)(l)(F)
I Oahe l Garrison I
Fort Peck River Mile Top of dam elevation (ft MSL)
Spillway crest elevation (ft MSL)
Maximum operating pool elevation (ft MSL)
Maximum normal operating pool elevation (ft MSL)
Base flood control elevation (ft MSL)
Minimum' operating pool elevation (ft MSL)
Gross storage elevation range (ft MSL)
Gross storage (ac-ft)
Dam Breaches and Failures ,,,,-
2-112 ( \
Sorge ~ 6:J Lvndy' , c
/
SECUR11'¥-RELA1'ED INI-ORMAl'ION -WITHHOLD UNDER 18 01-R 2.998
SECU"l'f¥-"ELA1'EB INI-O"MAl'ION - WITltHOLE> UNBER 16 eFR 2.996 Nebraska Public Power District SL-012450 Cooper Nudear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.3-2: Dam Break Parameters for Hypothetical Dams Breach Breach Dam Breach Peak Max. Dam Crest Dam Bottom Fonnation Breach Bottom River/Creek Storage Elevation Height Width (ft) Time (hrs)
Elevation Outflow (ac*ft) (ft NAVD88) (ft) USSR USSR (ft NAVD88) (cfs)
Equation Equation James u/s 605,585 1,355.7 1,295.7 60.0 180.0 0.60 256,459 Dam James dis 163,540 1,185.7 1,151.7 34.0 102.0 0.34 62,108 Dam Beaver Creek 1,167 1,202.7 1,179.7 23.0 69.0 0.23 21,789 Dam Antelope Creek 3,142 1,218.1 1,179.2 38.9 117.0 0.39 73,644 Dam Bow Creek 375 1,150.6 1,140.7 9.9 29.7 0.10 2,816 Dam Vermillion Creek 3,160 1,148.7 1,126.7 22.0 66.0 0.22 20,709 Dam Aowa Creek 15,774 1,147.4 1,100.6 46.8 140.0 0.47 131,832 Dam Elk Creek 53 1,263.5 1,236.5 27.0 81 .0 0.27 4,581 Dam Big Sioux 12,030 1,135.3 1,096.7 38.6 116.0 0.39 81 ,841 Dam Perry Creek 1,211 1,114.3 1,099.7 14.6 44.0 0.15 7,444 Dam Floyd River 16,560 4,952 1,107 1,086.9 20.1 60.0 0.20 Dam Bacon Creek 2,934 1,161.1 1,118.6 42.5 128.0 0.43
82,505 Dam Pigeon Creek 7,654 1,186.4 1,136.2 50.2 151.0 0.50 142,379 Ditch Dam Omaha Creek 238 1,102.5 1,085.5 17.0 51 .0 0.17 9,582 Dam Dam Breaches and Failures 2-113 9ECURl1'¥-RELA1'EB INFORMATION _rt't,ITliltOLD UNBER 16 eFR 2.996
SECURITY-RELATEB INFORMATION - WITHHOLB UNBER 10 CfiR 2.390 Nebraska Pub lic Power District SL-01 2450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REl!VALUATION REPORT Project No.: 11784-017 Table 2 .3-2: Dam Break Parameters for Hypothetical Dams, continued Breach Breac h Dam Breach Peak Max. Dam Crest Dam Bottom Formatio n Bottom Breach River/Creek S torage Elevation Height Width (ft) Time (hrs)
Elevation Outflow (ac-ft) (ft NAVD88) (ft) USBR USSR (ft NAVD88) (cfs)
Equation Equation Blackbird Creek 125 1,066.0 1,052.1 13.9 42.0 0.14 5,718 Dam Elm Creek 204 1,108.6 1,063.6 45.0 135.0 0.45 110,983 Dam Big Whisky 1,917 1,107.5 1,086.7 20.8 62.0 0.21 17,504 Creek Dam WF Little 8,665 1,188.8 1,136.2 52.6 158.0 0.53 156,182 Sioux Dam Wolf Creek 9,971 1,145.7 1,080.7 65.0 195.0 0.65 229,603 Dam Cottonwood Weber 1,607 1,129.6 1,097.6 32.0 96.0 0.32 44,397 Creek Dam Little Sioux 57,984 1,066.8 1,039.5 27.3 82.0 0.27 35,938 River Dam Maple Creek 18,622 1,058.3 1,035.6 22.7 68.0 0.23 22,556 Dam Tekamah 13,144 1,112.4 1,043.2 69.2 208.0 0.69 286,481 Creek Dam Silver Creek 2,591 1,088.5 1,041 .4 47.1 141.0 0.47 108,240 Dam Soldier River 5,542 1,042.3 1,030.6 11.7 35.0 0.12 4,305 Dam Cameron Ditch 981 1,071.8 1,045.5 26.3 79.0 0.26 29,244 Dam Long Creek 943 1,038.7 1,000.0 38.7 116.0 0.39 51,803 Dam De Soto Bend 45,400 1,005.5 980.5 25.0 75.0 0.25 28,722 Dam Moores Creek 411 1,039.7 1,005.4 34.3 103.0 0.34 24,614 Dam Boyer River 37,174 1,015.9 981.5 34.4 103.0 0.34 63,610 Dam Deer Creek 1,095 1,049.8 1,019.9 29.9 90.0 0.30 38,270 Dam Dam Breaches and Failures ..
I '
2-114 Sor gmn ~ & J Lundy 11 r
OEOURIT't -RELATEB INFORM2'TION - Vl"ITHHOLB UNDER 16 CFR 2.396
SECURITY-RELATEE> INFORMATION
Vt,ITI II-IOLE> UNDER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD Rl!l!VALUATION REPORT Project No.: 11784-017 Table 2.3-2: Dam Break Parameters for Hypothetical Dams, continued Breach Breach Max.
Dam Breach Peak Dam Crest Dam Bottom Fonnatlon Elevatlon Bottom Breach River/Creek Storage Height Width (ft) Time (hrs)
Elevation Outflow (ac-ft) (ftNAVD88) (ft) USBR USBR (ftNAVD88) (cfs)
Equation Equation Pigeon Creek 5,113 1,007.1 981.3 25.8 77.0 0.26 30,620 Dam Mosquito 5,661 1,009.9 970.7 39.2 118.0 0.39 81,804 Creek Dam Papillion Creek 103,252 10,16.9 950.4 66.5 200.0 0.67 321,533 Dam Seminoe Dam 1,519,519 6,426.9 6,150.9 276.0 828.0 2.76 10,048,395 Pathfinder 1,128,432 5,919.8 5,625.2 294.6 884.0 2.95 10,476,655 Dam Glendo Dam 1,348,025 4,724.9 4,503.9 221 663.0 2.21 6,080,174 North Platte at 2,887,978 2,862.4 2,747.9 114.5 344.0 1.15 1,288,984 ConfDam South Platte at 3,468,545 2,870.4 2,747.9 122.5 368.0 1.23 1,5~3,906 Conf Dam Platte D/S 1,105,332 1,051.3 940.30 111 333.0 1.11 1,173,884 Dam Plattsmouth 365 996.4 968.5 27.9 84.0 0.28 24,120 Dam Pony Keg 9,608 996.8 956.1 40.7 122.0 0.41 93,408 Creek Dam Rock Creek 1,3454 1,030.4 938.0 92.4 277.0 0.92 303,052 Dam Waubonsie 16,318 1,024.9 932.4 92.5 278.0 0.93 429,799 Creek Dam Rakes Creek 671 969.1 939.4 29.7 89.0 0.30 30,909 Dam Weeping Water Creek 16138 965.3 924.6 40.7 122.0 0.41 94,837 Dam Nebraska City 74 955.5 918.5 37.0 111.0 0.37 50,699 Dam Horse Creek 210 967.3 942.6 24.7 74.0 0.25 17,231 Dam Camp Creek 285 952.5 908.5 44.0 132.0 0.44 66,847 Dam Dam Breaches and Failures
. , /\
2-115 I \
Sargent ~Lundy*' *
)/
SECURITY-RELATEE> INFORMATION - WITI II IOLD UNDER 18 OFR 2.998
SECURIT¥*RELATED INFOftMATION
WITHHOLB UNDER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017 Table 2.3-3: HEC-HMS Model Input Parameters and Definitions Parameter Definition Muskingum-Cunge Channel Routing Channel length -2000* - -580,000' Channel slope Average sl0pe for the whole channel (0.0001-0.004)
Channel Manning's roughness Average Manning's roughness coefficient for the whole length of the main coefficient channel, exclusive of the overbank areas (0.02-0.065).
Channel shape Shape of channel (eight-point cross section)
Channel width Width of channel (-800' - -8000')
Left bank Marnning's roughness Manning's roughness coefficient for the left overbank of the channel (0.05-0.085) coefficient Right bank Manning's roughness Manning's roughness coefficient for the right overbank of the channel (0.05-coefficient 0.085)
Reservoir Routing method Outflow Structures Storage method Elevation Storage curve using 1Om DEM data Initial storage Pool elevation at dam height (Assumes the reservoir is full)
Tailwater method Provides the tailwater at the reservoir outflow. For this Calculation, no tailwater was assumed. (Assumes reservoir tailwater has no effect on the reservoir outflow.)
Time step control Automatic Adaption (1-minute time step for control specification).
Dam Breaches and Failures 2-116 t(
Snrgm~ & Lundy** *
. )
y SECURIT¥=RELATED INFORMJf<TION - 'IWITHIIOLD UNDER 18 CFR 2.998
3ECURIT¥*RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.996 Nebraska Publlc Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD Rl!EVALUATION Rl!PORT Project No.: 11784-017 Table 2.3-3: HEC-HMS Model Input Parameters and Definitions, continued Parameter Definition Dam Tops Represents top of dam where water goes over the dam top in an uncontrolled manner.
Level dam top Assumes flow over the dam can be represented as a broad-crested weir.
Crest elevation Elevation of the dam top Length of dam Total crest length over which water passes Discharge coefficient Accounts for energy losses as water approaches the dam top and flows over the dam.
Dam Break Overtop dam break Represents failures caused by overtopping of the dam.
Top elevation Top of the dam face Bottom' elevation Elevation of the bottom of the trapezoidal or rectangular opening in the dam face when the breach is fully developed.
Bottom width Width of the bottom of the trapezoidal or rectangular opening in the dam face when the breach is fully developed.
Left and right side slope Units or horizontal distance per one unit of vertical distance (0 for rectangular breach).
Development time Total time for the breach to form from initiation to reaching the maximum breach size (in hours).
Trigger method: Elevation Pool elevation when the failure starts. This is set slightly below the elevation of maximum storage.
Progression method Determines how breach grows from initiation to maximum size during the development time. For linear method, breach grows in equal increments of depth and width.
Dam Breaches and Failures 2-117
({
S n rgo~ ,Lu,,dy***
/
3ECURIT¥ -RELATEB INFORMATION - WITHHOLD UNBER 16 CFR 2.996
3ECURIT¥*RELATED INFORM.ATION - 'NITHHOLB UNE>ER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.3-4: Hypothetical Dam Outflow Summary from HEC-HMS Model Peak Breach River Mile Dam Failure Hypothetical Outflow at (as in HEC-RAS Hydrograph Peak Dam Name Remarks Reservoir model) of Lateral at Lateral Inflow Outlet (cfs) Inflow Location (cfs)
James U/S Dam flow is James uls Dam 256,459 NIA NIA being routed down lo
.Junction JJR1.
Routed flow from James uls Dam and outflow from James d/s Dam 62,108 797.73 120,810 James dis is being reported at Junction JJR1, Beaver Creek Dam 21 ,789 806.23 21,789 Antelope Creek Dam 73,644 803.85 73,644 Bow Creek Dam 2,816 787.75 2,816 Vermillion Creek Dam 20,709 771.9.0 20,709 Aowa Creek Dam 131 ,832 745.1 9 131,832 Elk Creek Dam 4,581 737.4.0 4,581 Big Sioux Dam 81,841 734.00 81 ,841 Perry Creek Dam 7,444 731.76 7,444 Floyd River Dam 16,560 730.95 16,560 Bacon Creek D.im 62,505 730.54 62,505 Pigeon Creek Ditch Dam 142,379 720.03 142,379 Omaha Creek Dam 9,582 719.62 9,582 Blackbird Creek Dam 5,718 697.41 5,718 Elm Creek Dam 110,983 690.95 110,983 Outflow from WF Little Sioux, Wolf Creek, Big Whisky Creek Dam 17,504 669.83 400,997 Cottonwood, Weber Creek, and Big Whisky Creek being reported at Junction TUMI.
Dam Breaches and Failures 2-118 SECURIT¥-RELATEB INFORMATION - WITHHOLB UNBER 16 CFft 2.396
SECURIT'f*RELATED INFORMATION - WITHHOLE> UNDEFt 16 CFR ! .396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD Rl!EVALUATION R l!PORT Project No.: 11784-017 Table 2.3-4: Dam Outflow Summary from HEC-HMS Model, continued Peak Breach River Mile Dam Failure Hypothetical Outflow at (as in HEC-RAS Hydrogr:aph Peak Remarks Dam Name Reservoir model) of Lateral at Lateral Inflow Outlet (cfs) Inflow Location (cfs)
Outflow is being reported at WF Little Sioux Dam 156,182 NIA NIA Junction TUM!.
N/A Outflow is being reported at Woff Creek Dam 229,603 NIA Junction TUMI.
Cottonwood Weber Creek Outflow is being reported at Dam 44,397 NIA NIA Junction TUM!.
Outflow from Maple Creek and Little Sioux River being Little Sioux River Dam 35,938 669.23 58,429 combined at Junction Little Sioux-Maple Junction.
Outflow is being r;ported at Maple Creek Dam 22,556 NIA NIA Junction Little Sioux-Maple.
Outflow from Silver Creek and Tekamah Creek being Tekamah Creek Dam 286,481 664.56 297,824 combined at Junction Tekamah-Silver.
Outflow is being reported at Silver Creek Dam 108,240 N/A N/A Junction Tekamah-Silver.
Soldier River Dam 4,305 664.00 4,305 Cameron Ditch Dam 29,244 658.91 29,244 Long Creek Dam 51,803 645.15 51 ,803 De Soto Bend Dam 28,722 641.91 28,722 Moores Creek Dam 24,614 640.73 24,614 Boyer River Dam 63,610 635.22 63,6 10 Deer Creek Dam 38,270 632.99 38,270 Pigeon Creek Dam 30,620 622.16 30,620 Mosquito Creek Dam 81,804 605.87 81,804 Papillion Creek Dam 321 ,533 596.47 321 ,533 Dam Breaches and Failures /
2-119 ( \
Sorgc~., ,Luncty ** *
,J/
SECURIT'l'*RELATEO INFORMATION - WITIIIIOLD UNDER 18 CFR 2.998
SECURITY-RELATED INFORMATION - Wl'fl II IOLB UNBEft: 16 CFft: 2.S96 Nebraska Public Power District Sl*012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.3*4: Dam Outflow Summary from HEC*HMS Model, continued Peak Breach River Mile Dam Failure Hypothetical Outflow at (as in HEC-RAS Hydrograph Peak Remarks Dam Name Reservoir model) of Lateral at Lateral Inflow Outlet (cfs} Inflow Location (cfs)
Seminoe Dam flow is being Seminoe Dam 10,048,395 N/A N/A routed down to Junction Platte_DS_JN.
Pathfinder Dam flow is being Pathfinder Dam 10,476,655 N/A NIA routed down to Junction Platte_DS_JN.
Glendo Dam flow is being Glendo Dam 6,080,174 N/A N/A routed down ta Junction Platte_ DS_JN.
North Platte at conf Dam North Platte at Conf Dam 1,288,984 N/A N/A flow is being routed down to Junction Platte_DS_JN.
South Platte at conf Dam South Platte al Conf Dam 1,523,906 NIA NIA flow is being routed down to Junction Platte_ DS_JN.
Routed flow from Seminoe, Glendo, Pathfinder, North and South Platte at conf Platte DIS Dam 1,173,884 594.82 1,so1 :s21 Dams and outflow from Platte D/S is being reported at Junction Platte_DS_JN.
Plattsmouth Dam 24,120 594.14 24,120 Pony Keg Creek Dam 93,408 587.06 93,408 Rock Creek Dam 303,052 584.21 303,052 Waubonsie Creek Dam 429,799 580.16 429,799 Rakes Creek Dam 30,909 577.29 30,909 Weeping Waler Creek 94,837 568.67 94,637 Dam Nebraska Crty Dam 50,699 562.74 50,699 Horse Creek Dam 17,231 561 .13 17,231 Camp Creek Dam 66,847 549.02 66,847 Dam Breaches and Failures 2*120 SECUR:ITY-ftELATED INFORMATION - WITI II IOLD UNDEft: 18 CFft: 2.998
SECURIT¥-R:ELATEB INFORMA:l'ION - WITHHOLD UNDER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Rtvision 1 FLOOD HAZARD REEVALUATION REPORT Project No,: 11764-017 Table 2.3-5: 500-Year Flow on Missouri River at Drainage Locations Cumulative 500-Year Event Flow Contributing 500-Year Flow (cfs)
Name (cfs) On MiHouri River on Missouri at Drainage Location Gavins Point Dam 123,500 123,500 James River 141,500 18,000 Vermillion River 145,100 3,600 Elk Creek <1l 145,000 -100 Big Sioux River 185,400 40,300 Perry Creek 185,600 200 Floyd River 192,900 7,300 Omaha Creek 195,000 2,100 Blackbird Creek 197,300 2,300 Decatur, NE 197,700 400 Big Whisky & M&H Ditch 205,400 7,700 LittJe Sioux River 232,200 26,800 Tekamah Div. Ditch 233,300 1,100 Soldier River 236,500 3,200 Old Soldier R. Ditch 237,800 1,300 Fish Creek 238,800 1,000 Boyer River 245,900 7,100 Pigeon Creek 247,700 1,800 Omaha, NE 247,900 200 Mosqurto Creek 248,400 500 Papillion Creek 249,000 600 Platte River 344,400 95,400 Watkins Ditch 344,700 300 Weeping Water Creek 345,300 600 Nebraska City, NE 345,400 ,00 Nishnabotna River 361,000 15,600 Little Nemaha River 365,900 I 4,900 Note:
1. Elk Creek shows a negative 100 els as contributing 500-year flow to Missouri River. In this analysis, as a conservative approach, a O c1& !low was assumed as contributing 500-year now from Elk Creek into Missouri River.
Dam Breaches and Failures 2*121 ' \
!Sorgo~ &.1 L.undy* l'
,,r SECUR

ITV-RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.396
SECURIT¥*RELATED INFORMATION
V.1ITI ti IOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL*012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.3-6: Peak Flow at HEC*RAS Inflow Locations Dam Failure Hydrograph Dam Failure Hydrograph Lateral Peak + 500 Yr Flow (cfs) Peak + Mean Monthly Flow (cfs)
Inflow Name Inflow 1 (Non-System Dam Failure (System and Non-System Dam River Mlle Analysis) Failure Analysis)
Beaver Creek 806.23 (b)(3) 16 USC § 21,789 ~24o 1(d) (b)(4),
Antelope Creek 603.85 73,644 (b)(7)(F)
James River 797.73 138,810 Bow Creek 787.75 2,816 Vermllfion River 771.90 24,309 Aowa Creek 745.19 131,832 Elk Creek 737.40 4,581 Big Sio4x River 734.00 122,241 Perry Creek 731.76 7,644 Floyd River 730.95 23,860 Bacon Creek 730.54 82,505 Pigeon Creek Ditch 720.03 142,379 Omaha Creek 719.62 11,682 Blackbird Creek 697.41 8,016 Decatur Junction (ll 691.35 400 Elm Creek 690.95 110,963 Big Whisky Creek 669.83 408,697 Little Sioux River 669.23 85,229 Tekamah Creek 664.56 298,924 Soldier River 664.00 7,505 Cameron Ditch 658.91 29,244 Old Soldier R. Ditch <11 649.19 1300 Fish Creek <11 647.57 1000 Long Creek 645.1 5 51,803 Dam Breaches and Failures 2-122 SECURIT*RELATED INFORMATION - WITI II IOLD UNDER 16 CFR 2.996
SECURIT¥-RELATED INFORMATION - WITHHOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD RHVALUATION REPORT Project No.: 11784-017 Table 2.3-6: Peak Flow at HEC-RAS Inflow Locations, continued Dam Failure Hydrograph Dam Failure Hydrograph Lateral Peak + 500 Yr Flow (cfs) Peak+ Mean Monthly Flow (cfs)
Inflow Name Inflow 1 (Non-System Dam Failure (System and Non-System Dam River Mlle Analysis) Failure Analysis)
De Soto Bend 641.91 28,722 ,0/\-)/ l\i USC§ Moores Creek 640.73 24,614 8240-1(d) (b)
(4) (b)(7)(F)
Boyer River 635.22 70,710 Deer Creek 632.99 38,270 Pigeon Creek 622. 16 32,420 1
Omaha Junction '> 616.07 200 Mosquito Creek 605.87 82,304 Papillion,Creek 596.47 322,133 Platte River 594.82 1,697,327 Plattsmouth 594.14 24,120 Watkins Ditch 587.44 300 Pony Keg Creek 587.06 93,408 Rock Creek 584.21 303,052 Waubonsie Creek 580. 16 429,799 Rakes Creek 577.29 30,909 Weeping Water Creek 568.67 95,437 Nebraska City 562.74 50,799 Horse Creek 561.13 17,231 Camp Creek 549.02 66,847 Nishnabotna River 542.10 15,600 Little Nemaha River 527.80 4,900 Note:
1. No outflow hydrograph from HEC-HIMS model. USACE UMRSFFS report, Appendix F (Reference 2.3-12), reports 500-year flow at these locations. Thus, these Inflows. are present only in the Non-System dam failure analysis.
Dam Breaches and Failures . *(
2-123 / \
Sargcrlt: & Luncly tlc 1
)-/
SECURITY-RELATED INFORMATION - WITHt'IOLB UNBER 16 CFR 2.998
SECURITY-RELATED INFORMATION - WITHHOLB UNDER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11764-017 Table 2.3-7: Land Use Types and Manning's Roughness Coefficients I Combined System and PMF and Non-System Dam L.and Use Cover Non-System Dam Failure Failure Analysis Analysis Open Water 0.025 0.025 Wetlands 0.040 0.032 Forest 0.100 0.100 Grassland 0.040 0.032 Row Crops 0.040 0.032 Urban 0.120 0.120 Roads 0.015 0.015 Paved and Gravel Areas at Site - 0.025 Switchyards - 0.080 Table 2.3-B; Non-System Dam Failure Peak Stage at CNS and Plant Flood Protection Level Estimated Date -Time of Elapsed Time to Plant Flood Protection Estimated Peak Stage Estimat ed Peak Estimated Peak Level (ft NAVD88) Peak Flow (cfs)
(ft NAVDB8) Stage Stage 1/513000 4 days, 5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months , 906.37 903.09 1,332,697 5:52 52 minutes Dam Breaches and Failures 2-124 S.arga,;~ &, Lundy lo"
\ .'
../ '
9ECURIT¥-RELATED INFORMATION - WITHHOLB UNBER 16 CFR 2.996
SEOURIT¥*RELATED INFORMATION * 'l'ilTI II IOLD UNDER 18 CFR ! .398 Nebraska Public Power District SL-O1245O Cooper Nuclear Station Revision 1 F LOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.3~9: Peak Stage/Flow at CNS for Combined System and Non-System Dam Failure Estimated System Date and Estimated Duration of Estimated Peak Elapsed Time Estimated Dam Time of Elapsed Time to Stage Above Stage to Estimated Peak Failure Estimated Plant Flood Plant Flood (ft NAVD88) Peak Stage Flow(cfs)
Scenario Peak Stage Protection Level Protection Level (b)(3) 16 USC ,, ............ I
§ 8240-1 {d) (15)' (b)(J) 16 USC§ 824o-1(d) (b(41 (b), 7)(f-)
(4) (b}(?)(F) Hydrologic (b)(3) 16 USC
§ 8240-1 (d)**(b}-** ~ Sunny (4) (b)(7)(F) ay (b)(3) 16 USC I
§ 824o-1{d); (b)'
Hydr oiogic (4) (b)(?)(F)
(b)(3) 16 USC ********'" I
§ 824o-1(d)""(6}
(4). (b)(7)(F) Hydrologic (b)(3)16 USC .,,......- ****** I
§ 8240-1 (d) (15)
Hydrologic fgjd~l/el[j:~C ********"'""
I
§ 824o-1(d) (bT (4) (b)(7)(F) Sunny-Day (b)(3) 16 USC *-*-************* I
§ 824o-1(d) "(b} Hydrologic (4) (b)(?)(F)
Dam Breaches and Failures 2-125 Sarge~ & , Lundy
1
SECURITY-RELATEE> INfiORMATION
WITI II IOLD UNDER 18 CFR ! .398
SECURIT¥:.RELATEB INFORMATION - WlfHHOLB UNBER 16 CFR :2.S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No,: 11764-01 7 Table 2.3-10: Model Boundaries for TUFLOW Scenario Boundary Condition Maximum Value (b)(3) 16 USC
§ 824o-1(d} (b) *********"""'""""""'"'-*"*"'
Hw,*M-*
I*-** I Hydrologic Failure Inflow Discharge (b)(3) 16 USC § 8240 1(d) (b)(4) (b)(7}(F)
(4), (b}(7)(F)
(b)(3) 16 USC
§ 8240-Hd};-H, (4) (b)(7)(F) 8 Sunny-Day Failure Downstream WSEL Inflow Discharge Downstream WSEL Table 2.3-11 : Maximum Channel and Right Overbank Discharge and WSEL at CNS for Upstream Boundary
Sensitivity Analysis Scenario Location Discharge (cfs)
I WSEL (ft NVADBB)
Base Left Overbank 1bi(3) 16 U.S G § 8240-l(d) {b}(4) (b)(7)(F)
Channel Right Overbank 20% Decrease in Left Overbank Left Overbank Channel Right Overbank Dam Breaches and Failures ./
r' ..
2-126 So,-.gar\t &. L.ul"\dy i::
', ,.)
,/
SECURIT¥-RELATED INFORMATION - WITHHOLB UNBER 16 CFR 2.S90
SECURITY-RELATED INPORMATION - WITHHOLD UNDER 16 CFR 2.996 .
Nebraska Public Power District SL-012450 Cooper Nuclear Station (b)(3) 16 Revision 1 IJSC § Project No.: 11784-017 FLOOD H AZARD REEVALUATION REJIORT 8240-l(d)
(b)(4) (b)(7)
,F)
Table 2.3-1 2: Monitoring Point Summary fo, Hydrologic Dam Failure Monitoring Point I
Grade Elevation (ft NAVD88) I Maximum WSEL (ft NAV088)
I Maximum Velocity (fps)
I Maximum Depth (ft)
(b)(3) 16 USC § 824o-1(d) (b)(4) (b)(7)(1-)
Notes :
1. W SEL on the river side of the Intake Structure.
2. Velocity paraUel to the Intake Structure on the river side.
(b)(3)*16 USC Table 2.3-13: Monitoring PoiQt Summary fo Sunny: Oay Dam Fa11ure - - -- --,:;. 8240*l(d). (b)
(4 ) (b)(7)(F)
Grade Elevation Maximum WSEL Maximum Maximum Monitoring Point (ft NAV088) (ftNAVD88) Velocity (fps) Depth (ft)
(b){3) 16
1. ISFSI-N
2. ISFSI-S 903.8 903.8 KD)\J/ 1 ti USC§
~ 24o-1(d) 7.4 6.3 USC§ 8240
-1(d) (b)(4) -
3, Fire Pump House-N 903.1
~b)(4) (b) 4.4 (b)(7)(F) -
117)(1=)
4. Multipurpose Facility-NW 903.5 7.4
5. Augmented Radwaste Bldg-NW 902.8 7.3
6. Diesel Generator Bldg-NE 903.1 5.3
7. Diesel Generator Bldg-E 902.7 6.5
8. Technical Support Bldg-NW 902.2 7.4
9. Turbine Bldg-N 902.8 1.3
10. Intake Structure-E - 5.8(2)
11. Point of Interest 903.3 3.8 Notes:
1. WSEL on the river side of the Intake Structure.
2. Velocity paraUel to the Intake Structure on the river side.
Dam Breaches and Failures 2-127 9EOURIT¥-RELATED INFORM:ATION -WITI II IOLD UNDER 18 OFR 2.996
SECURITY-RELATED INFORMJ&<TION - WITHHOLD UNDER 16 eFR %.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2 .3-14: Calcu lation of Wind-Driven Waves and Wind Setup Approaching CNS Controlling Average Effective Design Wind Wind Fetch Depth Fetch Wind S peed Hmo Tp Wavelength H1*,1, Direction Setup Angle Along Length Speed Duration {ft) (s) (ft) (ft)
(ft)
(deg) Fetch (ft) (ft) (mph) (min)
Plant North 0.0 rsr-
~3) 16 75,564.30 44.6 55 6.1 0 4.71 112.37 0.44 10.19
J s (,
Plant I§ 8240 135.0 137,392.09 43.6 85 7.66 5.37 144.97 0.66 12.79 East 1(d)
~b)(4)
Plant Kb)(7) 135.0 137,392.09 43.6 85 7.66 5.37 144.97 0.66 12.79 South KF)
Plant West 157.5

135,273.58 43.6 85 7.04 5.16 133.71 0.71 11.76 Table 2.3-15: Summary of Wind Setup, Wave Runup, and.Total Water Levels at SSCs Maximum Water Still Water Wind Wave Wind Level, including SSC Level Setup Runup Direction Setup and Runup (ft NAVD88) (ft) (ft)

(ft NAVDBB) lnlake Structure Control Building Plant East Plant South
,;O)IJ)lo I SC~
S240-1(d)
(b)(4) (b)(7) 0.66
<i.66 19.19 19.19 (O)(J) lti USC § 8240-1(d) (b)(4), (b)
(7)(F)
Reactor Building Radwaste Building Plant South Plant West (F)
F, 0.66 0.71 19.19 17.64 -
I Diesel Generator, Heating and ,16U::,C §824ol(C1) rb(4J rb1/
l ib)
Fan Building Dam Breaches and Failures 2-128
' &. 1-..J...lndyi l
c Sargc::i~t:.
\
__ ,,.,, ,1 SECURITY-RELATED INFORMATION - Wl"fHHOLD UNDER 10 CF" 2.S90
SECURIT't'-RELATEB INFORMATION - \'ilTHHOLB UNBER 16 CPR 2.S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1
,D)\J) 16 FLOOD HAZARD REEVALUATION REPORT USC.§8240 Proiect No.: 11784-017
-1(d) (b)(4)
(b)(?)(F)
Table 2.3-16: Summary of Water Depth at Important Plant Structures Structure Name Roof Elevation (ftNAVD88)
WSEL (ft NAVD88)
I Water Death (b)(3) 16 USC I * * * * * * * *
KftL §824o4(d), (b)
(b)(3) 16 (b)(3) 16 USC§ 824o-1(d) (b)
Radwaste Building-1 USC § 8240- (4) (b)(7)(F) (4) (b)(7)(F) 1(d), (b)(4), (b)
Radwaste Building -2 (7)(F) -
Radwaste Building-3 Radwaste Building-4 Control Building Reactor Building Office Building Turtiine Generator Building Intake Structure Maintenance Shop Water Treatment Building Diesel Generator, Heating and Fan Building-1 Diesel Generator, Heating and Fan Building-2 Controlled Corridor Multi-Purpose Facility Unnamed Building-1 Unnamed Building-2 Unnamed Building-3 Unnamed Building-4 Unnamed Building-5 Unnamed Buildlng-6 Dam Breaches and Failures 2-129 9EOURIT¥-RELATED INFORMATION - WITHHOLD UNDER 18 OFR 2.998
SECURIT¥-RELATEE> INFORMATION - 'NITHHOLE> UNDER 10 CI-R :Z.S!6 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT ,,b)(3) 1ti USC § 8240 Project No.: 11784-017 1(d) (bX4) (b)(7){F)
Table 2.3-17: Summary of Water Depth at Important Bridges Estimated \At~*-* n- -*i.
Bridge Name Bridge Deck Elevation WSEL (ft NAVD88) l(b}(J) lb I JS C 6 il24o I Duwigo Q.f I Inundation I .,....
(b)(3) 16USC
§824oHd) (b)
(ft NAVD88) (4). (b)(7)(F)
NE State Hwy 67 and Little Nemaha (b)(3) 16 US § 8240 1(d) (b)(4) (b)(7)(F) 959 River (near Brock, NE)
US Hwy 75 and Little Nemaha River 935 US Hwy 136 and Little Nemaha River 927 US Hwy 75 and South Table Creek 1 975 NE State Hwy 67 and Little Nemaha 903 River (near Nemaha, NE)
State HI/VY 67 and Honey Creek 951 92s3 US Hwy 136 & Missouri River Notes:
1. Bridge Is located upstream of model domain. WSEL al this location is based on 1-0 model results.
2. lnunda~on period extends beyond 20 simulation time. Duration or inundation from this location was estimated based on 1-D model results.
3. Estimated bridge deck elevation from Hydraulic Model.
Dam Breaches and Failures 2-130 S a rgant: & _Luncly 11 1t
,; \ ***
SECURIT¥-RELATEE> INFORMATION - WITHHOLD UNBER 16 CFR 2.S98
8ECURIT¥=RELATEE> INf-ORMATION - WITHHOLE> UNDER: 16 CPR: 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD Rl!l!VALUATION REPORT Project No.: 11784-017 Table 2.3-18: Resultant Forces and Elevations on Main Building Complex Structures Hydrostatic Hydrodynamic C!"'st Hydrodynamic Trough Current-Induced Resultant Resultant Resultant Resultant Force Force Force Force Force Force Force Force Direction (lb/ft of (lb/ft of (lb/ft of (lb/ft of Elevation Elevation Elevation Elevation wall) wall) wall) wall)
(ft NAV088) (ftNAVD88) (ft NAVD88) (ft NAVD88)
Plant (b)(3) 16 U SC § 8240-1 (d) (bJ(4) (b)(7)(F)
North Plant East Plant South Plant West Table 2.3-19: Resultant Forces and Elevations on Intake Structure Force Resultant Force Structure Type (lb/linear ft of wall) Elevation (ft NAV088)
Hydrostatic Hydrodynamic crest Hydrodynamic trough Current-induced Dam Breaches and Fa/lures 2-131 8ECURIT¥ -RELATEE> INFOR:MATION - WITHHOLE> UNE>ER: 16 CFR 2.396
SEOURIT,'*RELATED INFORM>\TION - WITHHOLE> UNDER 16 ep;ft 2.996 Nebraska Publlc Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 2.3-20: Debris Impact Loads Maximum Velocity Debrii. Source Impact Load (kip)
(b)(3) 16U::;r.; § 1000 lb miscellaneous debris 8240 1(d) (b)(4)
(b)(7)(F) 4000 lb large natural debris Channel Large vehicles and boats Tank-type debris Barge 1000 lb miscellaneous debris (b)(3) 16 U SC
§ 8240 1(d}: (b) **
1,1, /1.-\J"'1\I,--\
...... * ....... . .o,.,,,n;_ .8. 1 4000 lb large natural debris Large vehicles and boats Tank-type debris Barge Note:
1. Intake Structure Is assumed to be out of service after a dam failure event.
Dam Breaches and Failures 2*132 Sarge~&_. Lundy 11 t SECURIT'f-R.l!L>\TEB INFORM>'.TION - 't'ilTI II IOLD UNBER 18 CPR 2.998
Sl:CURIT¥-RELATEB INFORMATION - WITtlllOLB UNBER 18 CPR 2.398 Nebraska Public Power District SL-01245O Cooper Nuclear Station Revision 1 Project Ne.: 11784-017 FLOOD HAZARD REEVALUATION REPORT 2.3.8 Figures Figures associated with Section 2.3 are presented on the following pages.
Dam Breaches and Failures 2-1 33 Sorg ~~&_ Lundy* .,:
9ECURIT¥-RELATED INFORMATION -WITtltlOLD UNDER 18 erR 2.398
SECURIT¥*RELATEE> INFORMATION - WITtlllOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178'4-017 Figure 2.3* 1: Non-System Dams Downstream of Gavlns Point Dam Forl
' Peel<
A Gamaon
~
t\ "',
,,;* Ill"'~" U l~ *'* t
fl
.*-'*. 1**-. ....
A .*,'***: ..
C Legend
A Stations System Dams All Non- System Dams Below Gavins Point 0 25 50 75 100 Miles
~DvfClt ro,p t*t OIICO UIOI 0tlO1111t "Hdn * "C* l1.1r,ty t ~*111010 I.tin N4\ll£0
-1.,...
fOMlOlft ll"llftrnep J40 NPI NlltCA.H O*ol1H ION M( rt ,,,. c",,.. Ho,.,
efld ' " ' GI$ U1-1 CO"'"'""ll'f' 1ncrtfl'IIAI P'
~******' Nl
'*"91 Dam Breaches and Fa/lures 2-134 S11rg11nc & Lundy
SEOURIT\'*RELATED INFORMATION - WITHHOLD UNDER 16 CFfit 2.396
SECURITY-RELATEE> INFORMATION - WITHHOLB UNE>ER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 1178-4-017 FLOOD HAZARD REEVALUATION REPORT Figure 2.3-2: Remaining Non-System Dams Downstream of Gavlns Point after Screening Inconsequential Dams 0 *-.
Legend
Stations Non-System Dams Below Gavtns Point Note lnconsequentJal Dams Screened Out
.* U,*.:*
~,:,
'l ..
' I) ...
\
0
- 25 50 75 100 Miles 1* 1 t J*
fu
,., ae , c.o t
DtL* 111* "i&V1[0 fl*fo1111
h ia aJ * .. tt* ..
IOS '-'O JrtPS N9'.C A.. G**l
u ti f:'lf J***f'! M ' I t,,
11* GIi U1e t C11W1.*1te h (ft IU Jo!l"f ). OftQ ,
t ~
0 ~ 1'* 111 **'-t ~1 Dam Breaches and Failures 2-135 Sorgonc & L.uncty SECURIT¥=RELATEE> INFORMATION - WITHHOLE> UNE>ER 18 CFR 2.398
9ECURIT¥-RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017 Figure 2.3-3: HEC-HMS Plan for Missouri River below Gavins Point Dam to Omaha, NE (b}(3) 16 USC § !l240-1{d) (b)(4J (b)(7l{f-)
Dam Breaches and Failures 2-136 Baro* nt:&Luncly SECURITY-RELATED INFORMATION - WITI II IOLE> UNDER 16 CFR 2.996
SECUFUTY-RELATEB INFORMATION - 1/tlTI II IOLD UNDER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No .: 1178'1-017 Figure 2.3-4: HEC-HMS Plan for Missouri River from Omaha, NE to CNS (b)(3) 16 USC § 824o-1(d) (b)(4) (b)(7)(F)
Dam Breaches and Failures 2-137 Sorgcint & Lundy ' "
SECURITY-RELATED INFORMATION - 'NITI II IOLD UNDER 16 CFR 2.396
SECURIT¥-RELATEB INFORMATION - WITI II IOLB UNBER 18 CFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 117~17 liOJ!3)1bUSC
!l 824o--1(d) b 114 'b 7 !F Figure 2.3-5: Dam Failure Hydrographs a Dam due to System Hydrologic Dam Failure b)(j, lo U:::; ,:_; $ o.<"0--i(d 10)14 (b 11-Dam Breaches and Failures 2-138 S..rg*nl: &. LL*ndy C SECURIT¥-RELATEB INFOl'ATION - 'N ITI II IOLB UNBER 16 CFR 2.398
SECURITY-RELATED INFORM>9LTION - WITI II IOLD UNDER 18 CFR 2.398 Nebras ka Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD H AZARD R EEVALUATION R EPORT (D)(J).lb LJ:,;i.;
Project No.: 1178~17
§ 824o-1(d), (bl (4),(b)(7)(F)
Figure 2.3-6: Dam Failure Hydrographs a Dam due to System Sunny-Day Dam Failure (b)(3) 16 U.S C § 824o-1(d), (b)(4), (b)(7l(F)
Dam Breaches and Failures 2-139 S..r-ge...., &. Lundy SECURIT¥-RELATED INFORM>9LTION - WITI II IOLD UNDER 18 OFR 2.398
SECURIT¥-RELATED INfORMJ!tTION - WITIHIOLD UNDER 18 CPR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD H AZARD REEVALUATION R.E PORT P!Ojed No..* 1178-4~17 b)i3j 16 USC S B24o-1(a b)
Figure 2.3-7: Selected Dam Failure Hydrographs at .. (b ~)(F Dam due to System Dam Failure (t J) 1- U.::i ~ !l l;lL4v- 'ldJ : H4 IOI' f-Dam Breaches and Failures 2-140 SECURJT¥-RELATED INfORMl9<TION - WITI II IOLD UNDER 18 CFR 2.398
SECUfUfY-ffELATEB INFORM~TION - WITtlllOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Projed No.: 11784-017 Figure 2.3-8: Land Use Classes Used for Manning's Roughness Coefficient
- Op,enWater
- W..iland
- Fores,
- Granland Roads and Impervious Areas CNS Paved and Gravel Areas CNS Sw,tchyards Dam Breaches and Failures 2-141 S..rgo,w. & Lundy 9ECURIT¥-RELATEB INFORMATION - WITMHOLD UNBER 16 CFR 2.996
SEeURIT't'-RELATED INFORMATION - WITHHOLD UNDER 16 eFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1 I 78'4-017 Figure 2.3-9: Estimated Peak Stage at CNS due to Non-System Dam Failure (b)(3) 16 USC § B24o-1(d). (b)(4) (b)(7)(F)
Dam Breaches and Failures 2-142 S..rgant & Lundy sceURIT¥-RELATED INFORMATION - WITHHOLD UNDER 16 eFR 2.396
SECURITY-RELATED INFORMATION - WITIIHOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017 Figure 2.3-10: Estimated Peak Stage at CNS due to System and Non-System Dam Failure (b)(3) 16 USC § 824e-1(d) (b)(4) (b)(7)(1-)
Dam Breaches and Failures 2-143 Sere*nc & Lunc:tv ..
SECURITY-RELATED INFORMATION - WITIIIIOLD UNDER 16 CFR 2.396
SECURITY-RELATED INFORMATION - 1*11TiH HOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178'1-017 Figure 2.3-11 : Estimated Peak Discharge at CNS due to System and Non-System Dam Failure (b)(3) 16 U SC § 8240 1(d) (b)(4) (b)(f)\F)
Dam Breaches and Failures 2-144 SOrgen t & Lundy SECURITY-RELATED INFORMATION - 1*11THHOLB UNBER 16 CFR 2.996
!ECURl'f¥-RELATEB INFORMATION - WITI It IOLB UN BER 18 CFR 2.398 Neb*raska Public Power District SL-012450 Cooper Nuclear Statlon Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 117~ -017 Figure 2.3-12: Study Area Overview Dam Breaches and Failures 2-145 So_rganio: & Lundy SECURITY-RELATEB INFORM:ATION - \'flTtitlOLB UN BER 18 CFR 2.998
9ECURIT¥-RELATEE> INFORMATION - fffll'HHOLE> UNDER 18 CFR ! .S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178'1-017 Figure 2.3-13: Computational Mesh Overview Dam Breaches and Failures 2-146 Sorgen t & Lun ctv SECURIT'f-RELATEE> INFORMATION - WITHHOLE> UNE>ER 16 CFR ! .S96
seeURIT¥-RELATEB INFORM>\TION - WITI IHOLB UNBER 18 CFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784--017 Figure 2.3-14: Computational Mesh Near CNS Dam Breaches and Failures 2-147 s ..rg......, & Lundy SECURIT't' -RELATEB INFORM1'TION - 'lt'ITI II IOLB UNDER 18 0FR 2.398
SECURITY-RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.996 Nebraska Publlc Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017 Figure 2.3-15: Building Roof Elevations Included In Model (ft NAV088)
Dam Breaches and Failures 2-148 9ECURIT¥-RELATEO INFORMATION - WITI II IOLD UNDER 16 CFR 2.996
SECU"ITY-RELATEB INFORMATION - 'h11Ttlt'IOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT Figure 2.3-16: Model Boundary Condition Location and Type Dam Breaches and Failures 2-149 s ..rg ..nl; & Lundy 9ECURIT'f-RELATEB INFORMATION - WIT~tttOLB UNBE" 116 CFR ! .396
SECURln'=RELATED INFORMATION - fh1ITI II IOLD UNDER 18 CFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 1178-4-017 FLOOD HAZARD REEVALUATION REPORT Figure 2.3-17: Discharge Hydrographs for Upstream Boundary and Stage Hydrograph for Downstream (b)(3) 16 U s C _ .Boundar.v 4 - - I Hvdrologic Failure
§824o-1{d}{ll) ' (b)(J)16USC !l<u4D-1(dJ (b)(4) (b)'7)(~J (4) (b)(7)(F)
Dam Breaches and Failures 2-150 Sftrgant> & Lundy SECURln'-RELATED INFORMATION - WITHHOLD UNDER 18 CFR 2.398
9ECURIT¥=RELATED INFORMATION - 't'll'fHHOLD UNDER 16 CPR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178'4-017 Figure 2.3-18: Discharge Hydrographs for U r m Boundary and Stage Hydrograph for Downstream (bJ(3) 16 USC Boundary Sunny-Day Failure
§ 8240* l (d) tu) . (b)( ) 1 U . C § 8 4o-1 (d) (b)(4) (b)( XF)
(4) (b)(7)(F)
Dam Breaches and Failures 2-151 Sorg*rw.& Luncty SECURITY-RELATED INFORMJ\TION - YrlTI II IOLD UNDER 16 CPR ! .396
SECURIT¥-RELATEE> INFORMATION - WITtUIOLE> UNE>ER 16 CPR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.3-19: Site Mo nitoring Points for WSEL Depth and Velocity During Dam Fallure Events Dam .Breaches and Failures 2-152 S..rg* nt: & Lundy '
SECURIT\'*RELATEE> INFORMit<TION - VtlTli~IOLE> UNE>ER 16 CPR 2.996
SECURIT¥-RELATEB INFORMATION - \'IITHHOLe UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 117,µ.011 (b)(3) 16 USC
§ 8240-1 (d}.(b} ***** Flgure2;3~2o:r = 7 Hyd. Failure* Overview of Velocity Magnitude at 1/10/3000 20:30 (4) (b}(7)(F) (time of maxim~ ity with WSEL above plant flood protection elevation at Point 11)
(b}(3) 16 USC § 8240-l(d) (b)(4) (b)17)1F)
Dam Breaches and Failures 2-153 S.r-gar c & Lundy SECURITY-RELATEE> INFORMATION - WITtU10LB UNBER 16 CFR 2.996
SECURITY-RELATED INFORMATION * 't'IITI It IOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-017 (b)(3) 16 USC
§ 824o-1(d){b} * **** Figure2;3~21J IHyd. Failure - Mid-Level View of Velocity Magnitude at 1/10/3000 20:30 (4) (b)(7)(F) (time of maximum velocity with WSEL above plant flood protection elevation at Point 11)
(b)(3)16 USC § 824o-1(d) (b)(4} (b)(7}(F)
Dam Breaches and Failures 2-154 Snrgdnt & Lundy SECURIT¥-RELATED INFORMATION - 1't1ITHIIOLD UNDER 16 CFR 2.996
SEOURIT¥*RELATED INFORMATION - 't'/ITI II IOLD UNDER 16 OFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017
~~~l~~{~):(~) ..... Figure2;3-22J !Hyd. Failure* Site-Level View of Velocity Magnitude at 1/10/3000 20:30 (4) (b)(7)(F) (time of maximum velocity with WSEL above plant flood protection elevation at Point 11)
(b)(3) 16 USC § 8240-1 (d) (b)(4) (b)(7)(F)
Dam Breaches and Failures 2-155 Sorgnnt: & Lundy
SE0URIT¥-RELATEt> INFORMATION - \\1ITI II IOLD UNDER 16 0FR :2.996
SECURITY-RELATED INFORM.ATION - WITHHOLD UNDER 16 CFR ! .396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 1178-4-017 FLOOD HAZARD R EEVALUATION R.EPORT (b)(3) 16 U SC
§ 824o1(d}(o) ..........- -*********
I Figure 2;3a23*: *----
IHyd. Failure* WSEL Overview at 1/11/3000 20 :20 (4). (b)(7)(F) (time of max. WSEL at Site) b)(J) 16 U SC § 8240-1 {d) (bJ(4) (b)(7){F)
Dam Breaches and Failures 2-156 Snrgen t & Lundy SEOURIT'1'-RELATED INFORMATION - WITttttOLD UNDER 16 CFR ! .396
SECURITY-RELATED INFORMATION - 'IIIT~1ttOLB UNDER 18 CFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017 Dam Breaches and Fa/lures 2-157 s ..rg.no: & L..unc:tv SECURIT¥-RELATED INFORMATION - WITHHOLD UNDER 18 CFR 2.998
SECURITY-RELATED INFORMATION - 'frlTI II IOLD UNDER 18 CFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178'4-017 r~~l~~i~:{~)- . . . .... . . .-- *F*igure2;3;25*+ IHyd. Failure* WSEL Site-Level View at 1/11 /3000 20 :20 (4) (b}(7)(F) .___ __, (time of max. WSEL at Site)
(b)(3) rn Us C § ti24o-1(d) (b)(~) (b}({)(~)
Dam Breaches and Falfures 2-158 SECURITY-RELATED INFORMATION - 'NITI II IOLD UNDER 18 CFR 2.398
SECURIT¥*RELATEB INFORMATION - WITI II IOLO UNBER 18 Cf'R ! .998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178'4-017 Figure 2.3-26: WSEL with Fetc h Overlay b)(J) 1ti U !:i c.; § 8l4o-1(d) (bl(4) (b)(l~Fi Dam Breaches and Failures 2-159 Smrgnnt:. & Lundy SECU"IT¥ -ftELATEB INf'OftMATION - WITHHOLD UNBEft 18 Cf'ft ! .998
SECU"ITY-RELATEI:> INFORMATION - \\11TI fl IOLB UNDER 18 CFR 2.398 Nebraska PUJbllc Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178'4-017 Figure 2.3-27: Fetch Directions for Waves Approaching Plant East and Plant West Dam Breaches and Failures 2-160 Sargnnt & Lundy
SECURITV-RELATEI:> INFORMATION - WITt~I-IOLO UNDER 18 CFR 2.998
SECURITY-RELATED INFORMATION - WITHHOU) UNDER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017 Figure 2.3-28: Fetch Directions for Waves Approaching Plant North and Plant South Dam Breaches and Failures 2-161 SECURITY-RELATED INFORMATION - 't'IITI II IOLD UNDER 18 CFR 2.998
SECURITY -RELATED INFORMATION
WITI II IOLD UNDER 18 eFR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD R .EEVALUATION REPORT Project No.: 1178-4-017 l(b)(3) 16 U SC § 8240-1 (d) (b)(4)
Fiaure 2.3-29: Plan View of Pressure Calculation Surfaces torl(b)(l)(F)
(b)(3)16 USC§ 824o-1{d) {b)(4) (b)(7)(F)
Dam Breaches and Failures 2-162 S ....-g* nt; & '-'-'" dv
SECURITY-RELATED INFORMATION - WITI II IOLD UNDER 18 eFR 2.998
SE6URIT)'*RELATEB INFORMATION - WITtUIOLB UNBER 18 6FR 2.998 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No .: 1178-4-017 Figure 2.3-30: Groundcover in Vicinity of CNS Dam Breaches and Failures 2-163 S.rgen,, & L..undy SE6URIT¥-RELATEB INFORMATION - 't't11THHOte UNBER 16 6PR 2.396
SECURIT¥-RELATEE> INFORMATION - \'YITHHOLE> UNE>ER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017 (b)(3)16usc r
§ 8240-l(d)(b) .. Ffgure2:j:n:l iiundation Map forC 1Hydrologlc Dam Failure Scenario (Large-Scale Map)
(4), (b)(7 )(F) (b)(3) 16 USC § 824o-1(d) (b)(4) ib'(7J(F)
Dam Breaches and Failures 2-164 Sorg*r'II: & Lundy 9EOURIT¥*RELATED INFORMATION - 'it1ITI II IOLB UN BER 16 CFR 2.996
SECURITY*RELATED INFORMi8<TION - WITHHOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.' 1178'1-017 (b)(3) 16 USC
§ 824o-1(d}(b} FigUfe2-:3~32:fffundation Mapfo~ IHydrologic Dam Failure Scenario (Medium-Scale Map)
(4), (b)(?)(F)
(D)(3) 16 U ~ 1., § t!Z4o-l(d) (b)(4J \b){f ~I Dam Breaches* and Failures 2-165 ..rg* - & L u n d y SECURIT¥-RELATEf> INFORMATION - WITIIIIOLB UNDER 16 CFR 2.996
SECURIT¥*RELATED INFORMATION - WITl lttOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017 (b)(3) I 6USC
§ 8240- l(d) (b) ******** ***** ** Frgure *2:3-33: Inundation Map fo~ ****** Hydrologlc Dam Failure Scenario (Small-Scale Map)
(4 ) (b)(?)(F) (D)(j) 16 U:; t; 9 tlL40-1(a). (b (4) (b)(f)(I-Dam Breaches and Failures 2-166 a ...,,,....., & Lundy SECURIT¥ -RELATED INFORMATION - VtlTI II IOLD UNDER 16 CFR 2.996
SECURITY=RELATEO INFORMATION - WITHHOLO UNOER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178'4-017 Figure 2.3-34: Bridge Location Map Dam Breaches and Failures 2-167 Sargon t & Lun dy SECURIT¥ -RELATEO INFORMATION - WITI II IOLO UNDER 16 CFR 2.996
SECUR:IT'f-R:ELATEB INI-OftMATION - WITHHOLB UNDl!fit 10 Cflft 2.390 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1*
FLOOD HAZARD Rl!l!VALUATION Rl!PORT Project No.: 11784-017 2.4 STORM SURGE Storm surge is a rise in offshore water elevations caused principally by the shear force of winds acting on the water surfaces, typically associated with tropical storms (Reference 2.4-1, Section 3.5). The Cooper Nuclear Station (CNS) is not near any large bodies of water for which storm surge flooding would apply; therefore, the risk to the plant from a storm surge event that could cause flooding at CNS is not expected to be a potential flooding hazard. According to ANSI/ANS-2.8-1992 guidance (Reference 2.4~2 2), the region of occurrence of a hurricane shall be considered for United States coastline areas and areas within 100 to 200 miles bordering the Gulf of Mexico. Because CNS is located far from any coastline and at a site grade of 903.37 ft NAVD88, hurricanes do not present potential flooding hazards.
Therefore, storm surge was screened out as a credible flooding mechanism for CNS.
2.4.1 References I
2.4-1. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, NUREG/CR-7046, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, November 2011 .
2.4-2. American Nuclear Society. 1992. ANSI/ANS-2.8-1992: Determining Design Basis Flooding at Power Reactor Sites. American Nuclear Society Publishing, La Grange Park, IL.
Storm Surge 2-168 SECURIT'f-R:l!L>'cTl!t, INP'OR:MATION - WITI II IOLD UNDER: 10 CI-R 2.390
SECURIT't'-RELATEB INFORMATION - WITHHOLB UNDER 16 CI-R 2.S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.5 SEICHE A seiche is an oscillation of the water surface in an enclosed or semi-enclosed body of water initiated by an external cause. Once started, the oscillation may continue for several cycles; however, over time it gradually decays because of friction (Reference 2.5-1, Section 3.6).
The potential flooding hazard from a seiche at the Cooper Nuclear Station (CNS) is judged to be negligible because of the site's riverine setting. The Missouri River channel in the CNS area is narrow (less than 0.5 mile), shallow (35 fl or less), and meandering, which constrains and limits the geometry needed to develop a seiche and it s oscillation propagation. The river geometry also limits the height of any seiche oscillations and causes rapid attenuation of any seiche oscillations.
Therefore, seiche was screened out as a credible flooding mechanism for CNS.
2.5.1 References 2.5-1. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, NUREG/CR-7046, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, November 2011 .
Se/che 2-169 ' '\
SorgaMt & Lundy 1 1
1 SEOURIT¥-RELATEB INFORMATION - WIT~tt10LB UNBER 16 CFR 2.S96
SECURIT¥-RELATEB INFORMATION
VilTI IHOLB UNDER: 16 CI-R 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.6 TSUNAMI A tsunami is a series of water waves generated by a rapid, large-scale disturbance of a water body due to seismic, landslide, or volcanic tsunamigenic sources (Reference 2.6-1, Section 1.1). As an inland site, the Cooper Nuclear Station (CNS) is not susceptible to oceanic tsunamis (Reference 2.6-1, Section 2.1).
Therefore, tsunami was screened out as a credible flooding mechanism for CNS.
2.6.1 References 2.6-1 . Tsunami Hazard Assessment at Nuclear Power Plant Sites in the United States of America, NUREG/CR-6966, Office of New Reactors, U.S. Nuclear Regulatory Commission, Washington, D.C.
Tsunami 2-170 Sorgo;;t;: Sa: Lundy ** *
)*
SECURIT¥-RELATEB INFORMATION - WITI II IOLD UNBER 16 CFR ! .396
SECURIT'f-RELATEB INFORMATION - VilTI II IOLB UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project Na.: 11784-017 2.7 ICE-INDUCED FLOODING As per the U.S. Nuclear Regulatory Commission (NRC) guideline (NUREG/CR-7046, Reference 2. 7-1 ),
ice jams and ice dams can form in rivers and streams adjacent to a site and may lead to flooding by two mechanisms: (1) collapse of an ice jam or an ice dam upstream of the site can result in a dam breach-like flood wave that may propagate to the site and (2) an ice jam or an ice dam downstream of a site may impound water upstream of itself, thus causing a flood via backwater effects.
2.7.1 Methodology The NUREG guidance (Reference 2.7-1) identifies that, while it is possible to assess whether a site may possess hydroclimatic conditions that are precursors to ice jam or ice dam formation, it is not possible to accurately predict the exact location and severity of the ice blockage. Therefore, it is not possible to accurately predict a probable maximum ice jam or ice dam. Alternatively, it is recommended that historical records of ice jams and ice dams be searched to determine the most severe historical event in the vicinity of the site.
The hierarchical hazard assessment (HHA) approach described in Reference 2.7-1 was used far the evaluation of the effects of ice-induced flooding on the water surface elevation (WSEL) at Cooper Nuclear Station (CNS). In regard to ice-induced flooding on the Missouri River, the HHA used the following steps:
1. Identify the largest historic ice-induced flooding event and calculate ice jam height upstream and downstream of the site.
2. Conservatively calculate peak water surface elevation resulting from failure of an upstream ice jam.
3. Conservatively calculate peak water surface elevation from backwater effects resulting from a downstream ice jam.
2.7.2 Most Severe Historical Ice Jam Event The U.S. Army Corps of Engineers (USAGE) National Ice Jam Database (Reference 2.7-2) was searched to determine the most severe historical ice jam event in the Missouri River and its major tributaries downstream of Gavins Point Dam, such as the Missouri, James, Big Sioux, Little Sioux, Elkhorn, Platte, and Nishnabotna rivers (Figure 2.7-1). U.S. Geological Survey (USGS) hydrologic unit code (HUC) boundaries were further utilized to identify the regional search area. The ice jam record represents a USGS gage location (Reference 2.7-3), which provides a gage height for the ice jam event. Using the datum of the gage and ice jam gage height, the peak flood elevation was determined.
A normal WSEL was conservatively estimated for each USGS gage using the minimum value from the field measurement data. The difference between the peak elevation and normal WSEL was used as an initial estimate of the ice jam height. If the initial estimate of the ice jam's height presents a challenge, the normal WSEL is refined more rigorously based on a mean monthly gage height during the cool-season. The largest historic ice-induced upstream flooding event occurred 200 miles upstream of CNS on April 23, 1881 at Sioux City, Iowa. The estimated ice dam height was 21 .75 ft at RM 732.2, which is Ice-Induced Flooding 2-171 SECURIT'f-ffELATEB INFORMATION - WITH HOLE> UN BER 16 CFR ! .396
SE6URITY*RELATED INFORMATION - Wl'ft It ICLB UNDER 16 CFR 2.S96 Nebraska Public Power District SL-O12450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 equivalent to a stage of 1079.48 ft National Geodetic Vertical Datum of 1929 (ft NGVD29).The largest historic ice-induced downstream flooding event occurred 34.5 miles downstream of CNS on December 29, 1972 at Rulo, Nebraska. The estimated i ce jam height was 14.45 ft at RM 498, which is equivalent to a stage of 857.97 ft NGVD29.
2.7.3 Upstream Breach of an Ice Dam For an ice jam collapse, the National Weather Service (NWS) simplified dam failure equation (Reference 2.7-4) was used to determine a peak outflow. The outflow was transposed to CNS without attenuation. Although NUREG/CR-7046 (Reference 2.7-1) does not specify any coincident flows during an ice jam brea_ch, the cold season (December through March) mean monthly flow was added to this flow to calculate a conservative discharge. A corresponding WSEL was then determined based on the stage-flow frequency data for the Missouri River at different River Miles (RMs) from the Upper Mississippi River System Flow Frequency Study ([UMRSFFS] Reference 2.7-5). The peak outflow was then calculated, after evaluating all seven rivers, for an ice dam forming and breaching at the US
. Highway 77 and Missouri River Bridge (called Sioux City Highway Bridge) located at RM 732.38.The
' resultant calculated peak flow (breach plus mean monthly) at the Sioux City Highway Bridge, as a result of the historic 21.75-foot high ice jam, was estimated as159,075 cfs. The peak WSEL at CNS due to an ice jam forming and breaching at the Sioux City Highway Bridge is 896.54 ft NGVD29 (896.8 ft NAVD88).
2.7.4 Downstream Ice Jam and Resulting Backwater For ice jam backwater, the stage-flow frequency (Reference 2.7-5) data were first used to determine the associated flood flow at the gage downstream of the site based on the ice jam height. Then the cold season (December through March) mean monthly flow at CNS was added to establish a conservative flood flow. The associated stage for such flow is found in Reference 2.7-5 at the gage. In order to postulate the established flood stage at CNS, first the maximum water surface slope was calculated between the two locations (based on Reference 2.7-5), one located at the ice jam and the other at the site. That maximum slope was then used to t ranslate the downstream flood stage to the WSEL at CNS.
The maximum WSEL at CNS due to backwater from the most severe ice jam forming in the Missouri River near Rulo, Nebraska was 896.6 ft NGVD29 (896.86 ft NAVD88).
2.7.5 Effect of Ice-Induced Flooding The peak WSEL at CNS resulting from the upstream ice jam I ice dam breach was conservatively calculated to be 896.54 ft NGVD29 (896.8 ft NAVD88). The peak WSEL at CNS as a result of backwater caused by the ice jam at Rulo, Nebraska was conservatively calculated to be 896.6 ft NGVD29 (896.86 ft NAVD88). According to Reference 2.7-6, the finished floor elevations for Principal Class 1 Structures are equal to 903.5 ft Plant Datum, which is equal to 903.66 ft NGVD29 (903.92 ft NAVD88). Therefore, the maximum ice-induced flood water level will still be 7.06 ft below the minimum floor elevation for all of the safety related facilities.
Ice-Induced Flooding 2-172 Sargor'I~ *JL.undy'1 ;
9EOURIT¥-Rl!LAT!E> INF8RMATION ~ 'tVITI-I I-IOLE> UNE>!" 16 Cf'" 2.396
SECURITY-RELATED INFORMATION
WITHHOLfl UNDER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.7.6 References 2.7-1. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, NUREG/CR-7046, PNNL-20091, United States Nuclear Regulatory Commission (USNRC), November 2011 .
2.7-2. Cold Region Research Engineering Laboratory (CRREL), U.S. Army Corps of Engineers (USACE), National Ice Jam Database, Bulletin and Survey, Website http://lcejams.crrel.usace.army.mil/ accessed June 2014.
2.7-3. United States Geological Survey (USGS), National Water Information System (NWIS), Web Interface, USGS Water Data for the Nation, Website http://waterdata.usgs.gov/nwis, accessed June 2014.
2.7-4. The NWS Simplified Dam-Break Flood Forecasting Model, Abstract, by Jonathan N. Wetmore and Danny L. Fread, Office of Hydrology, National Weather Services, NOAA, Maryland.
http://www.nws.noaa.gov/oh/hrl/hsmb/docs/hydraullcs/papers_ before_2009/hl_154.pdf 2.7-5. Upper Mississippi River System Flow Frequency Study, Hydrology and Hydraulics Appendix F, Missouri River, U.S. Army Corps of Engineers, Omaha District, November 2003.
2.7-6. Cooper Nuclear Station, Updated Safety Analysis Report (USAR), Section 11-4, p 11-4-5 (01/16/01); and Section Xll-2, p Xll-2-1 (02/18/05) and p Xll-2-6 (02/18/05).
Ice-Induced Flooding
/'. '.
2-173 S o rge ~ ~ & , Lun d y
1 c
\
SEOURIT¥-RELATEfl INFORMATION - 'l'tlTlit IOLfl UNflER 16 OFR 2.396
SECURITY-RELATED INFORMJ!cTION - 1Yl'fHHOLE> UNEIER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Proj ect No.: 11 784-017 2.7.7 Figure The figure associated w ith Section 2. 7 is presented on the followi ng page.
Jee-Induced Flooding 2-174 SECURITY-RELATED INFORM>\.TION - WITHHOLEI UNE>ER 16 CFR 2.396
!Cet:1111"' 11EUtfE0 n*re"MllCTIOI* - Wlfl 111eto tlP~BER 18 eFl1 ! .!198 Nebraska Public Power District SL.012450 Cooper Nuclear Station R0\11110111 PLOOD H.AZ.A.RD lll.trVALUATION 11..I PORT PnljeU No 117M-017 Figure 2.7-1: Hydrologlc Unit Code (HUC) for Ditterent Wata,sheds Upstream and Down111ream of the Sile B19 Sioux M1ssoun James Platte
--no 2-175
SECURITY-RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD Rl!EVALUATION Rl!PORT Project No.: 11784-017 2.8 CHANNEL MIGRATION OR DIVERSION Natural channels may migrate or divert either away from or toward the site, and the relevant event for flooding is diversion of water towards the site. There are no well-established predictive models for channel diversions. Therefore, it is not possible to postulate a probable maximum channel diversion event. Instead, as suggested in NUREG/CR-7046 (Reference 2.8-1) historical records and hydrogeomorphological data are used to determine whether an adjacent channel, stream, or river has exhibited the tendency to meander towards the site.
2.8.1 Historical Channel Migration or Diversion Prior to regulation, the Missouri River, a meandering alluvial river, carried large amounts of sediment.
Streambank erosion tended to be most severe as flood waters were rising, with substantial deposition of sediment occurring as flood waters receded. The Missouri River existed in a dynamic equilibrium within its floodplain, frequently redistributing sediment between its channel and floodplain (Reference 2.8-2).
As Missouri River flows increased in the spring and summer, the river would erode sediment from its bed and its banks. The river bed would undergo rapid physical changes during this period; degrading due to erosion, the channel would migrate laterally, backwaters and the main river channel would be -
connected by overbank flows, and banks would erode and wash downstream. As flows receded (the hydrograph's receding limb) and water volume and velocity decreased, the degraded channel would refill with sediment, the braided channels and meanders would become isolated from the main channel, and fresh substrates would be deposited (Reference 2.8-2).
A typical cross section of the Missouri River prior to construction of the System dams contained a deep channel, multiple side channels, oxbow lakes, islands, sandbars and dunes, and backwater habitats interspersed by areas of higher land (Reference 2.8-3). Figure 2.8-1 shows the Missouri River in 1879 in the area where Cooper Nuclear Station (CNS) was constructed (Reference 2 .8-3). The river meandered eastward just east of the future CNS site and then flowed in a southwesterly direction for several miles downstream.
The variability that characterized hydrology of the Missouri River prior to construction of the System .
dams had diminished (as it is shown in Figure 2.8-1 to Figure 2.8-8) along most of the river following the Flood Control Act of 1935 and the Rivers and Harbors Act of 1945. U.S. Army Corps of Engineers (USAGE) had channelized most of the Missouri River through a combination of engineering structures, natural and engineered hard points, revetments, and dikes. Construction of the lower five Missouri River mainstem dams began in the 1950s, and the reservoirs were filled to operating levels by 1967 (Reference 2.8-4). Figure 2.8-3 shows an aerial image dating from 1965 (Reference 2 .8-5), showing the Missouri River navigational channel being established, and bank stabilization structures visible on both banks of the river. Most of the old meanders and side channels on the west side of the river were no longer visible. Additionally, levees had been ,constructed on both the eastern and western banks of the river.
Chan*n el Migration or Diversion 2-176 6,7 S a rgent& Lundy ' ' c
),
SECURIT¥-RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.998
SECURIT,1 -RELAT!B INflORM)l!l[TION - WITI II IOLD UNDER 16 CPR 2.996 Nebraska Public Power District SL--012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REl!VALUATION REPORT Project No.: 11784-017 By the 1980s and 1990s, the navigational channel had been established for decades, and the banks no longer migrated and were highly vegetated. On July 23, 1993, the U.S. Geological Survey (USGS) measured a flow of 196,000 cubic feet per second (cfs) at the gage at Nebraska City, Nebraska (Reference 2.8-6). This is the second highest flow measurement since the construction of the System dams. Neither the 1993 image (Figure 2.8-4) nor the 1999 image (Figure 2.8-5) show any evidence of floodplain inundation or channel diversion from this event. Aerial photography of the CNS site and the Missouri River upstream and downstream for the years 1993, 1999, 2003, and 2005 are shown in Figure 2.8-4 through Figure 2.8-7, respectively. These images show a stable, unmoving channel. The banks, having not migrated for over four decades, were highly vegetated. Bank stabilization was firmly in place and being maintained. There were no visible changes to the banks or old meanders to the north or south of the CNS site during this time.
An aerial image dating from 2010 (Figure 2.8-8, Reference 2.8-7) shows inundation of the floodplain in the old channel meanders to the north and to the south of the CNS site. The image also shows inundation of the floodplain on the east side of the river. The peak flow measured at the USGS gage at Nebraska City, Nebraska, in 2010 was 168,000 cfs (Reference 2.8-6) and is one of the top ten largest recorded flows since the construction of the System dams. There is no evidence in this image of the main navigation channel migrating in any way. The water that was inundating the floodplain showed no evidence of forming new channels or meanders. On the west bank, there was no visible river inundation west of the levee. On the east bank, there was ponding water east of the levee. This was likely due to interior drainage ponding.
2.8.2 Regional Topographic Evidence The following information was used in conjunction with the historical channel diversion information documented in Section 2 .8.1 to evaluate whether a future diversion may or may not occur. The results were used to assess the possibility of channel diversion near the site that may affect CNS.
2.8.2.1 Literature Review NUREG-0800 (Reference 2.8-8) references two documents that suggest methodologies for assessing channel diversion potential. The first document is titled "Engineering and Design Channel Stability Assessment for Flood Control Projects" and is published by USACE (Reference 2.8-9). The second document is titled "Methodology for Predicting Channel Migration" and is published by National Cooperative Highway Research Program (NCHRP) (Reference 2.8-10). These documents were reviewed, and pertinent information was used for the qualitative geomorphic analysis. The techniques discussed in these two documents are most useful for natural channels. USAGE constructed river training structures and bank stabilization, and continues to maintain a self-sustaining navigational channel. Therefore, Mure meandering is not anticipated outside of what might occur during flood events (Reference 2.8-9).
USACE's Missouri River Stage Trends Technical Report (Reference 2.8-11) was also reviewed to establish the current or near-future state of the river near CNS as aggradational, degradational, or stable. The stage trend , or specific gage analysis, is performed to evaluate trends in bed elevation based on a recorded stage for a given discharge over time. The measurements (Reference 2.8-6)
Channel Migration or Diversion , (*
2-177 Sarga£,-~ Lundy' "
\ I
~--*"
S!CURIT¥-RELATED INFORMATION - WITllltOLD UNDER 16 CPR 2.996
SEOURIT¥*RELATED INFORM,trTION - WITHHOLD UNDER 16 CPR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVA1.UATION REPORT Project No.: 11784-017 between O and 100,000 cfs show a stable channel, and the measurements above 100,000 cfs recorded in 2012 and later also conform to the same general trend of the measured data of the previous rating curve and, therefore, indicate channel stability. The 2011 measurements with discharges above 150,000 cfs seem to show channel degradation.
2.8.2.2 Soil Survey Data Figure 2.8-9 through Figure 2.8-11 (References 2.8-12 and 2.8-13) show hydric soil data, geomorphic classification of the soil data, and soils texture in the vicinity of the CNS, respectively.
Hydric soils are highlighted and clearly show locations where the old Missouri River meandered and the old channels had been. Traces of the old meanders on the west side of the Missouri River, both to the north and south, can be seen in the hydric soil data. On the east bank, hydric soils are contained within the boundary of the levee, although the Missouri River had been east of the levee.
The current channel is classified as water, and the old meanders and the entire area between the levees an~ classified as floodplains. On the Nebraska side, west of the levee, the area is classified as uplands, while on the Missouri side, east of the levee, the area is classified as river valley and terraces.
The textures include combinations of sand, clay, silt, and loam. These soil textures were used to compare allowable velocities.
The USDA NRCS gSSURGO database (References 2.8-12 and 2.8-13) contains a field for soil erosivity; however, the values for the soils in the vicinity of CNS are listed as either null or none.
Therefore, soil erosivity in the vicinity of CNS was not evaluated.
2.8.2.3 Missouri River Bank Stabilization and Navigation Maps The Missouri River navigational charts (Reference 2.8-14) show that bank stabilization structures and levees have been placed all along the Missouri River channel. In the immediate vicinity of CNS, stabilization of the bank along the concave alignment of the design curve was accomplished with pile and stone fill revetments. Dikes were constructed along the convex bank, approximately perpendicular to the flow. These dikes were designed to prevent bank erosion and to promote accretion, forcing the channel to develop and maintain itself along the design alignment.
2.8.2.4 2011 Flood Documentation The 2011 flood is the flood of record since the System dams were constructed. USACE developed the After Action Report, which chronicled emergency actions taken during the 2011 flood (Reference 2.8-15).This document describes several incidents regarding the overtopping and breaching of levees upstream of CNS.
In addition, flooding at CNS as a result of potential diversion was assessed by USACE, as recommended by NUREG-0800 (Reference 2.8-8). A USGS document titled "Geomorphic Changes Caused by the 2011 Flood at Selected Sites Along the Lower Missouri River and Comparison to Historical Floods" (Reference 2.8-16) was reviewed as well.
Channel Migration or Diversion
, /.
\
2-178 ( '
Sargon~ &:1Luncty 11 111
)/
SECURIT¥-RELATEB INFORMATION - WITHHOLB UNBER 16 CPR 2.996
SECURll"t'-RELATEf> INFOKMA:TION ~ WITHHOLf> UNDEft 16 CFR ~.S96 Nebraska Public Power District SL-0124S0 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Satellite images (Figure 2.8-12, Reference 2.8-17) show that flood waters had inundated the floodplain in many of the areas where the Missouri River had once meandered within the boundaries of the levees.
During the 2011 flood, significant overbank flooding resulted in some erosion of the eastern overbank, but the channel was contained within the levees. This is consistent with the analysis reported in Reference 2 .8-16. Pronounced changes in channel bed were noted as a result of the 2011 flood at the three stream gages evaluated: Sioux City, Iowa; Omaha, Nebraska; and Kansas City, Missouri.
However, channel width change was not evident at the gage locations, likely the result of the Missouri River bank stabilization and navigation projects (BSNP). In summary, emergency technical assistance was provided by USAGE to CNS personnel during the 201 1 flood event, and measures were implemented to allow the plant to remain fully operational.
2.8.3 Ice Causes Cold Regions Research and Engineering Laboratory (CR REL) maintains a database of ice jam and ice buildup incidents. The database was queried for the Missouri River in the vicinity of CNS to document the most severe ice-induced conditions with respect to diversion, flooding, and low flow conditions.
According to the CRREL database (Reference 2.8-18, several ice events have occurred along the Missouri River. The CRREL information is listed at each USGS gage; however, the location of the ice condition (upstream or downstream of the gage) is not provided. Flooding from ice effects (further described in Section 2.7) near CNS, and close enough to CNS to cause increased WSELs and/or channel diversion, will not be exacerbated by releases from Gavins Point Dam (Reference 2.8-4).
Therefore, flooding should be a concern only when an ice jam is combined with a rain-induced flood event in the uncontrolled tributaries downstream of Gavins Point Dam. Given this information, a channel diversion due to an ice jam is possible.
2.8.4 Flooding of Site Due to Channel Migration or Diversion The Hydrologic Engineering Center River Analysis System (HEC-RAS) steady-state model along with the reach-scale TU FLOW 2D model used in Sections 2.2 and 2.3 provide information on flow distribution and hydraulic characteristics for bankfull flow, peak flow during the PMF, and flooding due to upstream dam failures. The field measurements (collected by USGS [Reference 2.8-61) and the HEC-RAS model results show that bankfull flow is most likely between approximately 80,000 and 100,000 cfs. The channel and overbank velocities were obtained by executing the HEC-RAS steady-state model for a discharge of 100,000 cfs.
To evaluate channel erosion potential, USACE suggests using an allowable velocity approach (Reference 2.8-9). Figure 2.8-11 shows the soil types in the vicinity of CNS. The area soils are reported as a mix of silty clays, loams, and sands, which have allowable velocities ranging from 2 to 6 fps (Reference 2 .8-9). The velocities in the left and light overbanks are almost zero because at bankfull condition (100,000 cfs), there is no flow in the overbanks at this cross section. The velocities in the channel for the bankfull condition range from just under 0.4 fps to 7.7 fps. For the PMF condition (approximately 797,600 cfs), the velocities in the left and right overbank are less than 3.0 fps. For the PMF condition, the velocities in the channel range between 7.0 fps and 9.0 fps. For flooding due to Channel Migration or Diversion 2-179 ~nrgnrlc Ei.,LL.nr::ty* l c SECURITY-RELATEB INFORMATION - ftYITI II IOLD UNBER 18 CFR 2.998
SECURl1*RELATED INFORMJlcTION - WITH HOLE> UNE>ER 16 CPR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017
~b~~~ 1~(~)~(~: upstreamdamfailures(approximatef~ lets), the velocities in the left overbank range between
,., ,L~;_,"r: 5.0 fps and 10.0 fps, while the velocities m the nght overbank range between 3.0 fps and 10.00 fps. The velocities in the channel range between 2.0 fps and 10.0 fps. The velocities predicted by the hydraulic models for the bankfull, PMF, and flooding due to upstream dam failure conditions are generally greater than the allowable velocities for the various soil textures, indicating erosion and diversion potential.
2.8.5 Human-Induced Changes of Channel Diversion The BSNPs were authorized under various Congressional acts since 1912. Fort Peck Dam was authorized under the Rivers and Harbors Act of 1935. The lower five dams-Garrison, Oahe, Big Bend, Fort Randall, and Gavins Point-were authorized under the Flood Control Act of 1944. Additional BSNPs were authorized by the Flood Control Acts of 1941 , 1946, 1948, 1963, 1968, 1974, and 1978.
Further streambank erosion controls were authorized under the Water Resources Development Acts of 1974, 1986, and 1988. The navigational channel project was officially declared finished in 1981, with the terminus of the project at RM 734.8 at Sioux City, Iowa (References 2.8-4 and 2.8-19). USACE actively maintains the channel. It is unknown whether USAGE plans to revise channel maintenance procedures or the System dams. The potential of channel diversion from human-induced causes is not applicable because any channel diversion for the CNS plant site would likely include coordination with U.S. Nuclear Regulatory Commission (NRC) and CNS staff prior to construction.
2.8.6 Conclusions Prior to the construction of the Missouri River System dams and the Missouri River BSNP, regular floods occurred along the Missouri River, and the channel continually meandered as banks were eroded on one side and sediment was deposited on the other. Historical images show signs of meanders to the north and south, and the channel progressing westward in the vicinity of CNS.
Analysis of field measurements shows that the navigational channel has been through aggradational and degradational trends, and is currently generally either stable or slightly aggrading. During the 2011 flood, the channel degraded, but between 2012 (Figure 2.8-13) and 2014, has shown signs of recovery.
The soils in the channel are erodible at the velocities experienced during bankfull flow. In addition, the soils in the channel and possibly in the overbank are erodible at the velocities that may be experienced during a PMF and/or flooding due to upstream dam failures. During the 2011 flood, significant overbank flooding resulted in some erosion of the eastern overbank, but the channel was contained within the levees. Levee breaches (for location see Figure 2.8-14) that occurred upstream of CNS caused flooding behind the levees on the eastern side of the river.
This information, in conjunction with the historical meander patterns, indicates that the potential exists for the Missouri River to temporarily rechannelize into an old meander or divert away from the current navigational channel during the PMF and/or the flooding due to upstream dam failures. However, during bankfull flow, there is no significant possibility for channel migration due to the presence of the Missouri River BSNP.
Channel Migration or Diversion 2-180 SECURIT'f-RELATEB INFORMATION - WITHHOLE> UNE>ER 16 CFR 2.996
SECURITY-RELATED INFORMATION - Yt'ITHttOLB UNDER 16 Ct-R 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017 Given that erosion occurred along the eastern overbank of the Missouri River and that several levee breaches were documented for peak flows of approximately 229,000 cfs, it appears possible that the channel could migrate either east or west of its current position during the PMF with maximum flow of 797,600 cfs. This would likely result in the loss of the uhimate heat sink because the CNS Intake Structure would no longer be able to access water from the Missouri River. In addition, it is possible that the PMF flows could cause the channel to migrate either east and away from its current position, or west of its current position and onto the CNS site. This could damage the functionality of other SSCs due to erosion on the CNS site that could damage underground utilities required for the SSCs to function as designed.
Because the flooding due to upstream dam failures has a potential flow of approximately 8,627,000 cfs, it is possible that the Missouri River channel would migrate away from the CNS site, through the CNS site, or both during different stages of the flood. Therefore, t he potential for channel diversion during a flood event due to upstream dam failures could affect safety-related SSCs.
With the construction of the System dams and the Missouri River BSNP, the Missouri River channel has been stabilized and has maintained its designed alignment for over 50 years. Under various Congressional authorities and the Missouri River BSNP, USAGE performs annual maintenance, as well as emergency repairs, on bank stabilization and navigation structures along the channel of the Missouri River. If, during a flooding event, the channel migrates toward or away from the designed alignment, it is possible that USAGE would move the channel back to its orig inal alignment, especially in the vicinity of major infrastructure like CNS. However, depending on the severity of the flood damage, it may be some time before those repairs/channel realignments could be performed.
2.8.7 References 2.8-1. United States Nuclear Regulatory Commission (NRC). 2011. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America. NUREG/CR-7046, PNNL-20091. U.S. Department of Energy, Office of Nuclear Regulatory Research:
Richland, Washington.
2.8-2. National Research Council. 2002. The Missouri River Ecosystem: Exploring the Prospects for Recovery Committee on Missouri River Ecosystem Science. National Academy Press, Washington, D.C.
2.8-3. U.S. Army Corps of Engineers (USAGE). Missouri River Recovery Program. Accessed March 15, 2014. http://moriverrecovery.usace.armv.mil/mrrpgis/.
2.8-4. U.S. Army Corps of Engineers (USACE). March 2006. Missou:ri River Mainstem Reservoir System, Master Water Control Manual, Missouri River Basin. USACE Northwest Division, Missouri River Basin, Omaha, NE.
2.8-5. Nebraska Maps and More 2014. School of Natural Resources Map and Publication Store.
Lincoln, NE. http://nebraskamaps.unl.edu/productcart/pg'home.asp.
2,8-6. United States Geological Survey (USGS). 2013. USGS National Water Information System (NWIS). Washington, D.C. Accessed March 5, 2014. http://waterdata.usgs.gov/nwis/.
Channel Migration or Diversion 2-181 9ECURIT¥-RELATEf> INt-ORMATION - WITHHOLD UNDEft 16 Ct-R 2.396
SECURl1-RELATEB INFORMATION - WITHHOLB UNBER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.8-7. Nebraska Department of Natural Resources. NAIP aerial photography. Accessed March 15, 2014. http://dnr.nebraska.gov/data.
2.8-8. United States Nuclear Regulatory Commissi~n (NRC). March 2007. Standard Review Plan.
NUREG-0800, Section 2.4.9, Channel Diversions. U.S. Department of Energy, Office of Nuclear Regulatory Research: Richland, Washington.
2.8-9. U.S. Army Corps of Engineers (USACE). October 31 , 1994. EM 1110-2-1418, Engineering and Design Channel Stability Assessment for Flood Control Projects. USACE, CECW-EH-D, Washington, DC 20314-1000.
http://www.publications.usace.anny.mil/Portals/76/Publications/EngineerManuals/EM 1110 1418.pdf.
2.8-10. Lagasse, P.F., L.W. Zevenbergen, W.J. Spitz, and C.R. Thome. August 2004. Methodology for Predicting Channel Migration. National Cooperative Highway Research Program (NCHRP)
Web-Only Document 67 (Project 24-16). Prepared for National Cooperative Highway Research Program, Transportation Research Board.
http://onlinepubs.trb.org/on linepubs/nchrp/nch rp w67 .pdf.
2.8-11. U.S. Army Corps of Engineers (USACE). August 2012. Missouri River Stage Trends Technical Report. USACE Northwest Division, Missouri River Basin Water Management Division, Omaha, NE.
http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/MRStageTrends2012.pdf.
2.8-12. United States Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS). December 1996. National Engineering Field Handbook, Part 650, Chapter 16.
Streambank and Shoreline Protection Code 580, Companion Document 580-10.
2.8-13. United States Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS). 2013. Gridded Soil Survey Geographic (gSSURGO) Database for Nebraska.
Accessed March 15, 2014. http://soils.usda.gov/survey/geography.
2.8-14. U.S. Army Corps of Engineers (USACE). July 2011. Missouri River Navigation Charts - Sioux City, Iowa to Rulo, Nebraska. U.S. Army Engineer District, Omaha Edward Zorinsky Federal Building 1616 Capitol Ave. Omaha, Nebraska 68102.
2.8-15. U.S. Army Corps of Engineers (USACE). No date. After Action Report: Missouri River and Tributaries Flood of 2011 . Received from John Remus, USACE, via email on October 1, 2013.
See Attachment 5.
2.8-16. United States Geological Survey (USGS). 2014. Geomorphic Changes Caused by the 2011 Flood at Selected Sites Along the Lower Missouri River and Gomparison to Historical Floods.
U.S. Geological Survey Professional Paper 1798-H.
http://dx.doi.org/10.3133/pp1798H.
2.8-17. United States Geological Survey (USGS). 2011 . Earth Resources Observation & Science Center (EROS), accessed April 15, 2014. http://earthexplorer.usgs.gov/
Channel Migration or Diversion _.,.,
,* I 2-182 S orge ~' S, . Lundy' ' '
)/
SECURIT'f *RELATED INFORl'\bfcTION - WITHHOLB UNBER 18 CFR 2.598
SECURITY-RELATED INFORMATION
WITHHOLE> UNE>ER 16 CFR ! .396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.8-18. U.S. Army Corps of Engineers (USACE). CRREL Database. Accessed April 1, 2014.
http://icejams.crrel. usace .army. mil/.
2.8-19. U.S. Army Corps of Engineers (USACE). March 2003. Final Supplemental Environmental Impact Statement for the Missouri River Fish and Wildlife Mitigation Project. USACE, Kansas City and Omaha Districts.
Channel Migration or Diversion 2-183 Sorgar'I!: & 1Lundy ' ' ,r SECURIT¥ -RELATEE> INFORMATION - Vt11TI:11 IOLE> UNE>ER 18 CFR ! .396
SECURIT¥-RELATEB INFORMATION - WITHHOLB UNBER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.8.8 Figures The figures associated with Section 2.8 are presented on the following pages.
Channel Migration or Diversion
\
2- 184 \
Sorg o n ~ ~ Lundy* 1 i::
/*
SECUR.IT¥ -RELATEB INFORMATION - WITHHOLD UNBER 16 CFR 2.396
SECURITY-RELATEB INFORM>9<TION - WITHHOLB UNDER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.8-1 : 1879 Land Cover
~L C
C
~ "'.'1ss o u r i t 0
0
~
2u7 ~
2 S u
0 2.000 4,000 Land Conr USACE MRRP Feel hnp:/hnonvorrecO¥ery.uu.ct.army.millmrrpg,sl Reference 2.8-3 Note:
1. Current river path is overlaid and Is in faded blue.
Channel Migration or Diversion 2-185 Sargon.I:. & Lundy "
SECURIT¥-RELATED INFORMATION - 'frlTI lltOLB UNBER 18 CFR 2.998
SECURl'fY-RELATEB INFORM)f!('flON - WITHHOLB UNBER 16 CFR ! .996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.8-2: 1940 Aerial Photography Frei Reference 2.8-5 Channel Migration or Diversion 2*186 Sor--gan t & t..undy SECURIT'l'=RELATEE> INFORMATION - WITI II IOLB UNBER 16 CFR ! .996
SECURIT¥-"ELATEB INFORMATION - WITHHOLE> UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Projed No.: 11784-017 Figure 2.8-3: 1965 Aerial Photography 0 2.000 <4.000 Feel Reference 2.8-5 Channel Migration or Diversion 2-1 87 Sorg* nl: & Lundy SECURIT¥-RELATEB INFORMATION - WITI II IOLD UNBER 18 CFR 2.998
SECURIT'f -RELATEB INFORMATION - 't\11TttHOLB UNBER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.8-4: 1993 Aerial Photography Feet Reference 2.S-7 Channel Migration or Diversion 2-188 Sarg*nt & Lundy SECURIT¥-RELATEB INFORMATION
WITHHOLB UNDER 18 CFR 2.998
SECURITY-RELATEE> INFORMATION - WITHHOLE> UNE>ER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD R .E EVALUATION REPORT Project No.: 11784-017 Figure 2.8-5: 1999 Aerial Photography Feet Reference 2.8-7 Channel Migration or Diversion 2-189 Bargant: Q Lundy SECURIT¥ -RELATEE> INFORMATION - WITI II IOLE> UNDER 16 CFR 2.996
SECURIT¥*RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZ.ARD REEVALUATION REPORT Profect No.: 117~-017 Figure 2 .8-6: 2003 Aerial Photography Reference 2.8-7 Channel Migration or Diversion 2-190 S..rgant & L.uncfV
SECURITY-RELATED INFORMATION - WITI II IOLD UNDER 18 CFR 2.396
SECURIT¥*RELATEB INF6RMA'flON - WITI II t6LB UN BER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1 HS.-017 Figure 2.8-7: 2005 Aerial Photography Reference 2.8-7 Channel Migration or Diversion 2-191 s ..ro......, & Lundy SECURl'f¥-RELA'fED INF6RM>\'fl6N - Vt1ITI ti 16LB UNDER 16 CPR 2.996
SECURIT¥-RELATED INFORMATION - WITI It IOLD UNDER 16 CFR 2.996 Nebraska Publlc Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 1178-4-017 Figure 2.8-8: 2010 Aerlal Photography Feet Reference 2.8-7 Channel Migration or Diversion 2-192 SECURIT¥*RELATED INFORMATION - WITHHOLD UNDER 16 CFR 2.996
SECURIT¥=RELATEB INFORMATION - WITI IMOLB UNBER 18 CFR 2.996 Nebraska Public Power District Sl-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.8-9: Hydric Soils 0 Al!ttal Photogr.,phy 2012 NAIP hllp.//ctnr nobta&~* govldnta S011, Grldc:wd Soil Survry GoogrnpMc(gSSURGO) USDA NRCS hltp //.0,1, u>d* surwy/gooqt,oph References 2.8-12 and 2.8- 13 Channel Migration or Diversion 2-193 S org*"" & u.;ndy SECURIT¥-RELATEB INFORMATION - WITI II IOLB UN BER 16 CFR 2.998
SECURIT't'-RELATEB INFORMATION - WITHHOLB UNBER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 117!W-017 Figure 2.8-10: Geomorphlc Soil Description Geomorphic Descri pt ion depressions divides on uplands flood plains flood plains on valleys h1ilslopes on uplands sewage lagoons stream terraces on valleys Feet References 2.8-12 and 2.8-13 Channel Migration or Diversion 2-194 Snro..nt:.& Lundy SECURIT¥*RELATED INFORMATION - 't'YITtftfOLB UNBER 16 CFR 2.396
SECURIT¥-RELATEB INFORMATION - WITHHOLB UNBER 16 CFR 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 1178+017 F LOOD H AZARD REEVALUATION R .E PORT Figure 2.8-11 : Soil Textures Legend clay loam loamy fine sand Slh loam s1hy clay s,hy clay loam Feet References 2.8-12 and 2.8-13 Channel Migration or Diversion 2-195 Sor-g*nt: & Lundy 9ECURIT¥-RELATEB INFORMATION - WITI II IOLD UNDER 18 CFR 2.398
SECUftlT¥-RELATED INFORMATION
WITHHOLB UNDER 16 CFR ! .S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11764-017 Figure 2.8-12: 2011 Landsat Thematic Mapper Surface Reflectance On-demand Reference 2.8-17 Channel Migration or Diversion 2-196 SE0URIT¥*RELATED INFORMATION - WITI II IOLD UNDER 16 CFR ! .S96
SECURIT¥-RELATEB INFORMATION - WITf If IOLB UN BER 16 CFR 2.996 Nebr aska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Projed No.: 1178-4-017 Figure 2.8-13: 2012 Aerial Photography Reference 2.8-7 Channel Migration or Diversion 2-197 SO,-g*nc&Lundy 9EOURIT¥-RELATEB INFORMATION - 'fl'ITI II IOLD UNDER 1'8 OFR 2.398
SECURIT¥-RELATEB INFORMATION - WITI II IOLB UNBER 16 CFR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Figure 2.8-14: 201 1 Flood Breach Locations Channel Migration or Diversion 2-198 S..ro*nt. & Lundy SECURITY-RELATEE> INFORMATION - WITI II IOLB UN BER 16 CFR 2.996
SECUR:IT¥-R:ELATEB INFORMATION - WITHHOLB UNDER 16 CFR ! .396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.9 COMBINED EFFECTS The combined effect of different flood-causing mechanisms is discussed in Sections 2.1 through 2.8, where applicable. The combined effect flooding criteria for this reevaluation are based on the guidelines presented in ANSI/ANS-2.8-1992 (Reference 2.9-1) and NUREG/CR-7046 (Reference 2.9-2).
2.9.1 References 2.9-1 . American Nuclear Society. 1992. ANSI/ANS-2.8-1992: Determining Design Basis Flooding at Power Reactor Sites. American Nuclear Society Publishing, La Grange Park, IL.
2.9-2. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, NUREG/CR-7046, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, November 2011.
Combined Effects ,,, ***
2-199 ( \
S o rgont:.& Lundy '
', 7
.,),,
SECUR:IT¥-RELATEB INFORMATION - WITI ti IOLB UN BER 16 CFR ! .996
SECUfitl'fY-RELA'fEB INFORMATION - Vil'fllllOLB UNDER 16 CFR 2.398 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017
3. COMPARISON OF CURRENT AND REEVALUATED FLOOD-CAUSING MECHANISMS Table 3.14-1 summarizes the comparison of current and reevaluated maximum flood levels for all possible flood-causing mechanisms. The table indicates which of the reevaluated flood-causing mechanisms are bounded by the current licensing basis (CLB) flood hazard. The comparison shows that the reevaluated flood elevation due to dam failure event exceeds the current design basis flood elevation at the site. Additionally, the reevaluated hazard includes the associated flood effects of debris loading and flood duration, which were not considered in the CLB. The interim actions are identified in Section 4 of this report.
3.1 LOCAL INTENSE PRECIPITATION The Cooper Nuclear Station (CNS) Updated Safety Analysis Report (USAR [Reference 3-11) indicates that the site drainage is designed such that any excess rainfall not immediately absorbed into the ground will flow away from the buildings to be discharged into drywells or low-lying areas adjacent to the plant site. The plant area has a general site grade elevation of approximately 903 feet (ft) mean sea level (MSL [903.37 ft NAVD88]) and a finished Hoer elevation of 903.5 ft MSL (903.87 ft North American Vertical Datum of 1988 [NAVD88]).
The reevaluated flooding impacts due to the local intense precipitation (LIP) are presented in Section 2.1. The reevaluation used a combination of Hydrometeorological Reports 51 and 52 (HMR 51 and HMR 52) to obtain the point rainfall intensities and distributions. The rational method with conservative runoff coefficients (i.e.,1.0) was used for computation of peak probable maximum precipitation (PMP) runoff from different drainage areas of the plant site. The Hydrologic Engineering Center River Analysis System (HEC--RAS) Version 4.1 computer model was used to determine the maximum water surface elevation (WSEL) and flow velocity. The analysis was performed assuming underground storm drains and culverts, as well as roof drains, are clogged and not functioning during the LIP event.
The simulated peak WSELs at the site varied between 903.56 ft NAVD88 and 903.87 ft NAVD88. The simulated peak flow velocities varied between 2.87 feet per second (fps) and 5.02 fps, which are not expected to produce any erosion hazards, as described in Section 2.1. However, velocities on the steep slope at the periphery of the main plant area may cause local erosion of the sloped surface, but there would be no effect on safety-related facilities. Since the USAR does not specifically consider flooding from an LIP event, and the reevaluated LIP event shows WSELs below the finished floor level, significant inundation above the finished floor elevations is not expected. However, the potential for minor flooding at the entrances of these structures may exist during the peak of the event.
3.2 FLOODING IN STREAMS AND RIVERS The CNS USAR (Reference 3-1) refers to flooding in streams and rivers, also called probable maximum flood (PMF), analysis performed by the U.S. Army Corp of Engineers (USACE) and the U.S. Atomic Comparison of Current and Reevaluated Flood-Causing Mechanisms 3-1 SECURIT\' ~ftELATEB INFORWcTION - WITHHOLD UNl:>Eft 16 Cfift ! .996
SEOURIPl'*RELATED INFORM>9cTION - WITI-IHOLD UNDER 16 CFR 2.598 Nebraska Public Power District SL-01245O Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT Energy Commission (AEC) with a maximum still water level of 903.37 fl NAVD88. This WSEL, concurrent with wind effects, would result in a maximum water level of 909.57 ft NAVD88 outside of the Intake Structure and 905.37 ft NAVDBB on other exposed systems, structures, and components (SSCs). These water levels (excluding Intake Structure combined WSEL of 909.57) are below the site flood protection level of 906.37 ft NAVDBB (Reference 3-1 ). A higher water level outside of the Intake Structure will not affect safety-related structures and components (Reference 3-1 ). The peak PMF discharge is reported as 600,000 cubic feet per second (cfs) in the USAR.
The reevaluation of flooding in streams and rivers is presented in Section 2.2. The reevaluation used a combination of HMR 51 and HMR 52 to establish the PMP storm depth, spatial distribution, centering, and orientation. Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS) software was used to apply the PMP storm on the Basin upstream of CNS and downstream of Gavins Point Dam to generate runoff hydrographs. To estimate the PMF water levels, a multi-leveled modeling approach was adopted in this flood hazard reevaluation study. A 310-mile basin-scale one-dimensional (1-D)
HEC-RAS unsteady model was used to predict the PMP hydrograph. The results from the 1-D basin-scale routing model were then used to perform a reach-scale two-dimensional (2-D) hydraulic model.
The results from this 2-D reach-scale model were used to predict WSELs and velocities at CNS for the PMF.
The reevaluated analysis resulted in a peak WSEL (PMF plus wind setup plus wave runup) of 904.1 ft NAVD88 and 908.4 ft NAVD88 at the embankments surrounding the CNS Main Building Complex and on the vertical wall of the Intake Structure, respectively. Both water levels are lower than the associated flood level reported in the USAR. The reevaluated peak PMF discharge is 769,135 cfs, which is greater than values reported in the USAR. Since flood protection levels of 906.37 ft NAVD88 for the MSC and 919.57 ft NAVD88 for the Intake Structure are higher than the reevaluated PMF water levels, CNS would not adversely impacted from hazards associated with flooding in streams and rivers.
3.3 DAM BREACHES AND FAILURES (b){3) 16 U SC § 8240-1 {d) (b){4) {b)(7){F)
Comparison of Current and Reevaluated Flood-Causing Mechanisms 3-2 SECURIT'f -RELATEt> INFORMATION - WITHHOLt> UNt>ER 16 CFft :2.996
SECUfUf'f-fU!LATEB INFORMATION - Wlfllli6LD UNDER 16 CPR ! .S96 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 (b)(3) 16 USC § 824o-1(d) (b)(4) (b)(?)(F) 3.4 STORM SURGE The CNS USAR (Reference 3-1) does not evaluate flooding due to storm surge. Reevaluation of flooding due to storm surge, as discussed in Section 2.4, concludes that there is no plausible mechanism whereby a storm surge could cause flooding at the CNS site. Therefore, CNS is not impacted from hazards associated with flooding due to storm surge and this event is thus bounded by the CLB.
3.5 SEICHE
' I
' *I The CNS USAR (Reference 3-1) does not evaluate flooding due to a seiche. Reevaluation of flooding due to a seiche, as discussed in Section 2.5, concludes that there is no plausible mechanism whereby a seiche could cause flooding at the CNS site. Therefore, CNS would not be adversely impacted from hazards associated with flooding due to a seiche and this event is thus bounded by the CLB.
3.6 TSUNAMI The CNS USAR (Reference 3-1) does not evaluate flooding due to a tsunami. Reevaluation of flooding due to a tsunami, as discussed in Section 2.6, concludes that there is no plausible mechanism whereby a tsunami could cause flooding at the CNS site. Therefore, CNS would not be adversely impacted from hazards associated with flooding due to a tsunami and this event is thus bounded by the CLB.
3.7 ICE-INDUCED FLOODING Flooding due to an ice jam is qualitatively discussed from a low water level standpoint in the CNS USAR (Reference 3-1 ). The USAR further states that flooding caused by ice blockage is possible only at river levels significantly lower than the PMF.
Reevaluation of flooding due to an upstream ice jam failure, as discussed in Section 2.7, indicates that the peak WSEL resulting from an upstream ice jam breach is approximately 896.80 ft NAVD88. The peak WSEL at CNS as a result of backwater caused by an ice jam downstream of the plant is estimated to be 896.86 ft NAVD88. These calculated flood levels, which are highly conseNative, indicate that CNS would not be adversely impacted from hazards associated with flooding due to an upstream ice jam break or downstream ice jam blocking the river. Since the WSEL associated with this flooding phenomenon does not exceed site grade, this event is considered bounded by the CLB.
Comparison of Current and Reevaluated Flood-Causing Mechanisms 3-3 Snrgo~&,Lundy**"-
SECURITY-RELATED INFORMATION - WITI II IOLD UNBER 16 CFR 2.996
SECUfitlT't' -fitELATEB INFOfitM)!(TION - WITHHOLB LINDE" 16 CFfit 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 3.8 CHANNEL MIGRATION OR DIVERSION The CNS USAR (Reference 3-1) does not evaluate flooding due to channel migration or diversion, indicating a major channel diversion is unlikely after channel stabilization performed by USACE.
However, the USAR discusses this mechanism only with respect to channel.migration away from the site and the potential loss of the heat sink.
Reevaluation of flooding due to channel migration or diversion, as discussed in Section 2.8, indicates that the potential exists for the Missouri River to temporarily rechannelize into an old meander or divert away from the current navigational channel during the PMF and/or the flooding due to upstream dam failures. However, if, during a flooding event, the channel migrates toward or away from the designed alignment, it is possible that USACE would move the channel back to its original alignment, especially in the vicinity of a major infrastructure like CNS. In such a scenario, depending on the severity of the flood damage, it may be an extended length of time before those repairs/channel realignments could be performed. Therefore, CNS can be impacted from hazards associated with flooding due to channel migration or div,ersion and thi;;, event is not bounded by the CLB.
3.9 COMBINED EFFECTS Combined effects of different flood-causing mechanisms are discussed in Sections 3.1 through 3.8, where applicable. The combined effects of wind setup and wave run up were considered in the reevaluation of the PMF and dam break hazards. The total WSEL at critical locations around the plant structures, as discussed in Section 3.3, are not bounded by the CLB. Therefore, CNS would adversely be impacted from combined effects of the dam break reevaluated hazard.
3.10 ASSOCIATED EFFECTS An assessment of associated effects is required as discussed in Reference 3-3. The phrase "associated effects" is defined in Reference 3-4 as the hydrostatic and hydrodynamic loading, erosion and sedimentation, and debris impact effects caused by a plausible flood event. Reevaluation of these associated effects for both PMF and dam break events is discussed in Sections 2.2 and 2.3, respectively, where applicable.
3.10.1 Hydrostatic and Hydrodynamic Loads The CNS USAR (Reference 3-1) states that principal structures are designed for a hydrostatic load of WSEL up to the flood protection level of 906.37 ft NAVD88. The USAR does not address hydrodynamic loads.
The reevaluated flood analysis considered the hydrostatic forces on the vertical face of the Intake Structure up to PMF WSEL of 903.0 ft NAVD88 and up to dam break WSEL ofr-=ltt NAVD88onthe (~~~l~~ ~s ~
vertical faces of the Main Building Complex. The reevaluated flood analysis co~ d the ~4 ), (b)(?)~;) ( l hydrodynamic forces on the vertical face of the Intake Structure up to PMF Combined WSEL of 908.4 ft (b)(3) 1aus c NAVD88 and upJ9dam_breakcombinedWSEL ofr:=7ft NAVD88 on the vertical faces of the Main r~.~!J(ilio/)
4
{ti) Building Complex. In addition to hydrostatic and hy'aroay'namic forces, current-induced forces were Comparison of Current and Reevaluated Flood-Causing Mechanisms ..,f' 3-4 I '
Sorgor\~ & , Lundy
1 11
)**'*
9ECURIT¥-RELATEB IINFOfitM)!(TfON - WITHHOLB UNBER 18 CFR 2.998
Sl!CUfitl'fY-fitELATEB INI-OfitMATION - Vt'ITHHOLB UNBEfit 16 CI-R 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION Rl!PORT Project No.: 11784-017 estimated as part of the reevaluation study. Table 2.2-13 and Table 2.3-19 provide additional detail regarding loads calculated during the flood hazard reevaluation for PMF and dam break flood events, respectively. The comparison between CLB and reevaluated values shows that hydrostatic forces are bounded by CLB only during a PMF event. Hydrodynamic forces were not compared since they are not provided as part of the CLB.
3.10.2 Debris Loads The CNS USAR does not specifically address the debris loads; however, it does discuss runaway barge details.
Debris forces were calculated using both maximum channel and overland velocities for PMF and dam break flood events as part of the flood hazard reevaluation study. The range of debris forces is presented in Table 3.14-2. The maximum PMF and dam break debris loads are 3,332 kips and 3,919 kips, respectively. Table 2.2-14 and Table 2.3-20 provide details of debris loads calculated during the flood hazard reevaluatlor for PMF an9 dam break flood events, respectively. Debris loac;ls were not compared since they are not provided,as part of the CLB.
3.10.3 Erosion and Sedimentation The CLB for CNS (Reference 3-1 ) does not include evaluation of the effects of erosion and sedimentation on critical safety-related structures. As discussed in Sections 2.1.5, 2.2.5.2 , and 2.3.5 .1, the reevaluated hazard from erosion and sedimentation during the LIP, PMF, and dam break events is considered minimal and localized. Therefore, CNS would not be adversely impacted by erosion and sedimentation related to any reevaluated flooding hazard and the reevaluated hazard is considered bounded by the CLB.
3.11 OTHER PERTINENT FACTORS 3.11.1 Flood Duration As discussed in Section 2.3, flood duration is another pertinent factor in the assessment of the reevaluated flood hazard. Reference 3-4 defines flood duration as the total time comprising the preparations for a flood event, the period of inundation, and the recession of flood waters from the site.
Specific details are provided in Table 2.3-8 through Table 2.3-10.
3.11.2 Overtopplng As discussed in Section 2.2.5.1, overtopplng discharges are calculated using USACE coastal engineering manual equations for overtopped embankments during the PMF event. An overtopping discharge of 45 gallons per minute per linear foot was estimated.
Comparison of Current and Reevaluated Flood-Causing Mechanisms 3-5 SEOURIT¥-RELATEB INI-ORMATION - WITHHOLB UN BER 16 01-R 2.398
SECURIT'f=RELATED INFORMATION
WITHHOLB UNDER 16 CPR 2.996 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT 3.11.3 Inundation Section 9.4 of the Dam Failure Interim Staff Guidance (ISG) (Reference 3-2) recommends developing inundation maps to provide assistance in identifying SSCs important to safety that may requlre protective and/or mitigation measures from flooding due to a dam breach. As discussed in Section 2.3.5.2, a combination of ArcGIS 10 T FLOW software was used to map inundation
~b~~/4 6~(~)5.(;, Jimit~Jorthe most critical darn failure event dam h drolo ic . The Inundation limits shown in (4) (b)(7 l(Fl Figure 2.3-31 indicate that the plant site as well as (bl(3 1~ u 40*1 would be flooded.
1 3.12 CONCLUSIONS The comparisons between the CLB WSELs and the reevaluated flood hazard WSELs concluded that the safety-related structures at CNS are protected from flood-causing mechanisms once the~ ood rotection features are in lace. However, as discussed above, the dam break event WSEL _ *** .. J. . .~?.~~~-~-~~)s(~)
( (3 I . o 1( . (l.l (l.l ( J( (4). (b)(7)(r) 3.13 REFERENCES 3-1. Updated Safety Analysis Report (USAR), Cooper Nuclear Station.
3-2. U.S. Nuclear Regulatory Commission, "Interim Staff Guidance for Estimating Flooding Hazards due to Dam Failure," JLD-ISG-2013-01, July 29, 2013.
3-3. U.S. Nuclear Regulatory Commission, "Trigger Conditions for Performing an Integrated Assessment and Due Date for Response," ML12326A912, December 3, 2012.
3-4. U.S. Nuclear Regulatory Commission, "Interim Staff Guidance for Performing the Integrated Assessment for External Flooding," JLD-ISG-2012-05, November 30, 2012.
Comparison of Current and Reevaluated Flood-Causing Mechanisms _,.,,,-
3-6 ' \
S o r-g"'nt:. ~Lundy'"
,..'1,,1 SECURITY~"ELATEB INflORMATION
WITHHOLB UNBER 16 CFR 2.996
SECUfUfY-REL:Al'EB INFORMATION - Wll'IIIIOLB UNDER 16 CFR ! .SS6 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11 78'1-017 3.14 TABLES Tables associated with Section 3 are presented on the following pages.
Comparison of Current and Reevaluated Flood-Causing Mechanisms 3.7 ' S.._Lunny1 1ic S.t..1rg1.,1,.::.~
9EOURIT¥-RELATED INFORMATION =WIT! II tOLD UNDER 16 OFR 2.996
SECURITY'-RELATEB INPORM]8[TION - Wf'ITHHOLB UNBER 16 CPR ! .396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Table 3.14-1 : Current Licensing Flood Elevations and Reevaluated Flood-Causing Mechanisms Flooding Current Maximum Reevaluated Maximum Comparison 141 Mechanism Flood Level (ft NAVD88) Flood Level (ft NAVD88)
Local Intense Not specifically addressed in the USAR 903.87 Not described in the USAR Precipitation Flooding in Streams OtherSSCs 905.37 111 904.1 (2)
Bounded and Rivers 111 908.40 (2)
Intake Structure 909.57 r l 3 160 sc §6240-
a,. rb3, '6 1(3)1 7~* \UJ(.)) b ' .SC§ Dam Breaches and Failures Storm Surge (bl 4 , (b 7)(F Not plausible I - d u5 e, § b24o b 4 b - F Not plausible NofBouridea -~ ~,?~ aJ Tb)(4 ), (b l Not plausible Seiche Not plausible Not plausible Not plausible Tsunami Not plausible Not plausible Not plausible Ice-Induced Flooding Not specifically addressed in the USAR 896.86 (3) Not described in the USAR The USAR is silent on potential site flooding due to channel migration or diversion. However, the USAR The potential for channel diversion during a flood event Channel Migration or discusses this mechanism only with respect to channel due to PMF or upstream dam failures could affect Not Bounded Diversion migration away from the site and the potential loss of safety-related SSCs.
heat sink.
Combined Effects Not specifically addressed in the USAR See Section 3.9 Not described in the USAR Associated Effects Not specifically addressed in the USAR See Section 3.10 Not described in the USAR Notes:
1. The flood levels are a combination of still water levels and wave runup.
2. The flood levels are a combination of still water levels, wind setup, and wave runup.
3. The flood levels are still water levels only.
4. Flood event is considered bounded if the reevaluated effect is lower than the current licensing basis.
Comparison of Cun-ent and Reevaluated Flood-Causing Mechanisms /.
3-8 C \
Sarge~&. Luncty~l c-
).* /
SECURITY'*RELATEB INFORMlfcTION - WITttl IOLB UNBER 16 CFR ! .998
SECUfitlTY-RELATEB INFORMATION - \~ITHHOLB UNBER 16 CI-R 2.396 Nebraska Public Power Distrlct SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT P roject No.: 11784-017 Table 3.14-2: Debris Impact Loads Summary Flood Event Location Maximum Minimum Channel 3,332 15.54 PMF (kip)
Overland 784 3.66 1.,bJ13) 16 USC § 1240-t(d) (t5)(4) (5)
Channel (7)(F)
Dam Break (kip)
Overland Comparison of Current and Reevaluated Flood-Causing Mechanisms
3-9 SECURIT¥-RELATEB INI-ORMATION - WITI II IOLB UNBER 16 CFR 2.996
Nebraska Public Power District SL-012450 Cooper Nudear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017
4. INTERIM EVALUATION AND ACTIONS TAKEN OR PLANNED 4.1 REGULATORY BACKGROUND The U.S. Nuclear Regulatory Commission (NRC) 50.54(f) letter of March 12, 2012 provides that flood hazard reevaluations be performed using present-day regulatory guidance and methodologies applicable to new nuclear plant applications. For the sites where the reevaluated flood hazard exceeds the design basis, licensees are requested to submit an interim action plan that documents actions planned or taken to address the reevaluated hazard through the hazard evaluation.
Because the existing plants were not designed using the methods and assumptions given, any issues identified from the reevaluated hazards should not be treated as Current Licensing Basis (CLB) deficiencies or require operability review. If the reevaluated flood hazard at a site is not bounded by the current design basis, licensees are requested to perform an Integrated Assessment per NRC direction.
4.2 EVALUATION OF THE IMPACT OF THE REEVALUATED FLOOD LEVELS ON STRUCTURES, SYSTEMS, AND COMPONENTS (SSCs)
Section 2 of this report presents the reevaluation of flood hazards at Cooper Nuclear Station (CNS) using present-day regulatory guidance and methodologies. Section 3 of this report summarizes the comparison of the CLB flood elevation to the reevaluated flood elevation for each of the following flood-causing mechanisms:
Local Intense Precipitation (LIP)
Ffooding in Streams and Rivers
Dam Breaches and Failures
Storm Surge - Not a credible hazard
Seiche - Not a credible hazard
Tsunami - Not a credible hazard
Ice-Induced Flooding
Channel Migration or Diversion As stated in Section 3, the site would be affected by two flood-causing mechanisms, Dam Breaches and Failures and Channel Migration or Diversion. Interim actions associated with each of these flood-causing mechanisms are described in following sections.
Interim Evaluation and Actions Taken or Planned 4-1 9EOURIT¥*RELATED INFORMATION - WITHHOLD UNDER 18 OFR 2.998
Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 F LOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 4.3 INTERIM EVALUATION AND ACTIONS TAKEN OR PLANNED FOR CNS 4.3.1 Dam Failure The interim mitigation and monitoring plan was based on the fact ,hat the U.S. Army Corps of Engineers (USAGE) Upper Missouri Reservoir System has a very large storage capacity and that it is both unlikely*and predictable in advance that the reservoirs will reach the hydrologic or sunny-day reservoir levels over the course of a water year. In cooperation with the USAGE, the licensee will analyze the projected reservoir conditions based on snowpack and predicted runoff to determine the projected worst-case scenario for the current water year. The hydraulic model of the Missouri River developed for this flood hazard reevaluation will be used to estimate the maximum water surface elevation (WSEL) at CNS for the projected reservoir conditions. This yearly hazard evaluation would then be what the plant flood protection and/or mitigation must be capable of meeting for the following year until the reservoir forecasts are revised. To be certain that the current conditions do not exceed the analyzed conditions, a monitoring plan was established {Reference 4-1).
Several yearly forecast conditions are published by USAGE for their mainstem dams. These include the Lower Basic - a lower than average condition, Basic - an average condition, and Upper Basic - an above average condition. These forecasts are updated on a monthly basis, but offer a band of WSEL in which the dams will operate. For CNS, a yearly hazard evaluar e Upper Basic forecast was perf~rmed by using ~odified USACE results for_the Sunn -Da - dam ~~ ribed in **--*-****** ~~;~ls(~
(b)(3) 16 us c ~:~~~~e~-~~-~;~~~s;~~~~~~~:~~%a~:~~a,lu~s at ~~~~~~a~~:ii~~t~d n*~o';l'(~~(b).
[4~~~)(~)%\{b} cJownsfream"toCNS by the river model developed ......,...,,.
fo_r_u_se in_th.,..,...
is reevaluation to produce the maximum 141 tW'f\lF\
expected dam break flood for the year.
4 .3.1.1 Dam Monitoring Plan A procedure implementing the Monitoring Plan as well as trigger points for plant protection was established as a part of commitments NLS2014052-01 and NLS2014052-02 from Reference 4-1. In the Monitoring Plan, the volume of the reservoir system in the lower four dams is reviewed on an established frequency to determine if triggers have been met and to evaluate the continued adequacy of the yearly hazard evaluation.
4.3.1.2 Trigger Points The trigger points were established to maintain flood protection and mitigation capabilities as necessary for dam failure. Because of the spontaneous nature of a sunny-day dam failure, if at any time the reservoir system volume is large enough to surpass the design flood conditions in the event of a dam failure, a Beyond Design Basis flood could occur. This means that the time available to deploy the mitigation equipment is limited to the time elapsed from the dam failure until the WSEL exceeds the design basis at the site. It is also possible that a System dam could fail coincident with a flood on the Missouri River downstream of the System. As such, some of the trigger actions have an alternate flood trigger value in addition to a reservoir trigger values to ensure that the equipment is in place before the site is rendered inaccessible.
Interim Evaluation and Actions Taken or Planned 4-2 SECURIT*RELATED INFORMATION ~WITHHOLD UNDER 18 CFR 2.998
SECURl'fY-RELAl'ED INFORMATION - VIITHHOLD UNDER 16 CI-R 2.396 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 As for the other USACE dams, CN S is built 1 foot higher than the levees in the surrounding floodplain and is therefore less subject to flooding. Because of this, the lower three System dams do not cause site flooding on their own.
4.3.1.3 Mitigation Equipment A Beyond Design Basis flooding plan was established to maintain the core and spent fuel pool temperature below 200 degrees Fahrenheit for an extended period of time. This plan uses cooling towers and fan coil units in conjunction with several heat exchangers positioned on Main Building Complex rooftops. Much of the necessary equipment is currently off site but the companies will provide the necessary equipment immediately upon request. This plan will be refined as a part of the Integrated Assessment.
4.3.2 Channel Migration or Diversion The .CNS site buildings will be assessed for adequacy of the foundation while subject to the dam failure floods presented in the previous sections.
4.4 REFERENCE 4-1 . Letter from Nebraska Public Power District to U.S. Nuclear Regulatory Commission, NLS2014052, "Nebraska Public Power District's Flood Hazard Reevaluation Interim Actions for Cooper Nuclear Station; Cooper Nuclear Station, Docket No 50-298, DPR-46," June 2014.
Interim Evaluation and Ac tions Taken or Planned 4-3 Sargon~&, Lundy
IC SECURITY-RELATED INFORMATION - WITI II IOLD UNDER 18 OFR 2.998
SECURIT¥-RELATED INFORMATION - WITHHOLD UNBl!R 10 Cf-R 2.390 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 1 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017
5. ADDITIONAL ACTIONS No additional actions are required.
Additional Actions 5-1 S a rgo n ~ & . Lun cfy* *c SEOURIT¥*RELATED INFORMATION - WITI II IOLD UNDER 18 CFR 2.396 j

ML20366A011: Difference between revisions

Latest revision as of 19:13, 7 March 2021

Text

Navigation menu

NRC-2017-000688 (Formerly FOIA/PA-2017-0690) - Resp 5 - Final, Agency Records Subject to the Request Are Enclosed, Part 3 of 15
Person / Time
ML20366A011
Issue date:	12/29/2020
From:	NRC/OCIO
To:
Shared Package
ML20366A007	List: ML20366A008 ML20366A009 ML20366A010 ML20366A011 ML20366A012 ML20366A013 ML20366A014 ML20366A015 ML20366A016 ML20366A017 ML20366A018 ML20366A019 ML20366A020 ML20366A021 ML20366A022 ML20366A023
References
FOIA, FOIA/PA-2017-0690, NRC-2017-000688
Download: ML20366A011 (262)
v • d • e

ML20366A011: Difference between revisions

Latest revision as of 19:13, 7 March 2021

Text

Navigation menu

Search