ULNRC-05967, 124939/13, Rev. 0, Callaway Energy Center Unit 1 Flooding Hazard Reevaluation Report. Part 1 of 2

124939/13, Rev. 0, Callaway Energy Center Unit 1 Flooding Hazard Reevaluation Report. Part 1 of 2

ML13071A316
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Site:	Callaway
Issue date:	02/06/2013
From:	Ellsworth C J Paul C. Rizzo Associates
To:	Office of Nuclear Reactor Regulation
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ML130710492	List: ML13071A315 ML13071A316 ULNRC-05967, 124939/13, Rev. 0, Callaway Energy Center Unit 1 Flooding Hazard Reevaluation Report. Part 1 of 2 ULNRC-05967, 124939/13, Rev. 0, Callaway Energy Center Unit 1 Flooding Hazard Reevaluation Report. Part 2 of 2 ULNRC-05967, Transmittal of Ameren Missouri Flooding Hazard Reevaluation Report in Response to NRC Request for Information Regarding Recommendation 2.1, Flooding, of the Near-Term Task Force Review of Insights from the Fukushima Dai-Ichi Accident
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ULNRC-05967 124939/13, Rev 0
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Flood Hazard Reevaluation Report 124939/13 Rev. 0 (February 6, 2013)

CALLAWAY ENERGY CENTER UNIT 1 FLOODING HAZARD REEVALUATION REPORT P ROJECT N O.12-4939 R EVISION 0 F EBRUARY6,2013 P AUL C.RIZZO ASSOCIATES ,I NC.500 P ENN CENTER BOULEVARD B UILDING 5,S UITE 100 PITTSBURGH ,PENNSYLVANIA 15235 TELEPHONE:(412)856-9700 TELEFAX:(412)856-9749 WWW.RIZZOASSOC

.COM

Flood Hazard Reevaluation Report 124939/13 Rev. 0 (February 6, 2013)

CHANGE MANAGEMENT RECORDProject No.:

12-4939Report Name: Callaway Energy Center Unit 1 Flooding Hazard Reevaluation Report REVISION N O.D ATE DESCRIPTIONS OF CHANGES/AFFECTED PAGES PERSON AUTHORIZING CHANGE A PPROVAL 10 February 6, 2013 Rev 0 N/A N/A Notes: 1Person authorizing change shall sign here for the latest revision.

Flood Hazard Reevaluation Report124939/13 Rev. 0 (February 6, 2013) TABLEOFCONTENTS PAGELIST OF TABLES ............................................................................................................. ii iLIST OF FIGURES ........................................................................................................... iv

1.0INTRODUCTION

...................................................................................................11.1PURPOSE AND S COPE ....................................................................................11.2D ESCRIPTION OF S TUDY AREA ......................................................................11.3S ITE BACKGROUND AND H ISTORY ................................................................12.0FLOOD HAZARDS AT THE SITE ........................................................................22.1H ISTORIC FLOODS .........................................................................................22.2D ETAILED SITE INFORMATION ......................................................................32.2.1Designed Site Information .............................................................32.2.2As-Built Site Information ..............................................................42.3C URRENT D ESIGN B ASIS ...............................................................................52.4F LOOD-RELATED C HANGES TO THE L ICENSING B ASIS ..................................62.4.1Description of Hydrological Changes and Flood Elevations ......................................................................................62.4.2Description of Flood Protection Changes (Including Mitigation) .....................................................................................62.5C HANGES TO THE WATERSHED AND L OCAL AREA .......................................72.5.1Description of Watershed and Local Area at the Time of License Issuance ............................................................................72.5.2Description of any Changes to the Watershed and Local Area since License Issuance ..........................................................72.6C URRENT L ICENSING B ASIS F LOOD P ROTECTION .........................................82.7ADDITIONAL S ITE DETAILS ...........................................................................82.7.1Recommendation 2.3 Walkdown Results ......................................82.7.2Site-Specific Visit Results .............................................................93.0FLOODING HAZARD REEVALUATION ANALYSIS .....................................103.1

SUMMARY

OF RECOMMENDATION 2.1 ........................................................103.2F LOOD C AUSING MECHANISMS ..................................................................103.2.1Local Intense Precipitation ..........................................................11 TABLE OF CONTENTS (CONTINUED)

PAGEFlood Hazard Reevaluation Report ii124939/13 Rev. 0 (February 6, 2013) 3.2.2River Flooding .............................................................................153.2.3Dam Failure Flooding ..................................................................193.2.4Storm Surge Flooding ..................................................................203.2.5Seiche Flooding ...........................................................................213.2.6Tsunami Flooding ........................................................................213.2.7Ice Flooding .................................................................................213.2.8Channel Diversion Flooding ........................................................233.2.9Combined Events .........................................................................264.0COMPARISON OF CURRENT AND REEVALUATED PREDICTED FLOOD LEVELS ..................................................................................................294.1C OMPARISON OF CURRENT AND R EEVALUATED F LOOD CAUSING MECHANISMS ..............................................................................................294.2A SSESSMENT OF THE CURRENT D ESIGN B ASIS F LOOD E LEVATIONS TO THE R EEVALUATED F LOOD E LEVATIONS ...............................................294.3S UPPORTING DOCUMENTATION ..................................................................304.3.1Technical Justification of the Flood Hazard Analysis .................304.3.2Technical Justification by the Walkdown Results .......................304.4C ONCLUSIONS .............................................................................................315.0INTERIM EVALUATION AND ACTIONS ........................................................325.1E VALUATION OF THE IMPACT OF THE R EEVALUATED F LOOD L EVELS ON SSC S .....................................................................................................325.2A CTIONS T AKEN TO A DDRESS HIGHER F LOODING H AZARDS .....................326.0ADDITIONAL ACTIONS ....................................................................................3

37.0REFERENCES

......................................................................................................34TABLES FIGURES Flood Hazard Reevaluation Report iii124939/13 Rev. 0 (February 6, 2013)LIST OF TABLES TABLE NO. TITLE TABLE 2-1 HISTORIC FLOODS NEAR THE SITE TABLE 2-2 LIST OF SAFETY-RELATED STRUCTURES, SYSTEMS, AND COMPONENTS AND THEIR ELEVATIONS TABLE 2-3 DESIGN PARAMETERS IN THE LICENSE DOCUMENT TABLE 2-4 LICENSED WATER LEVELS DUE TO ALL FLOODING MECHANISMSTABLE 3-1 SITE DRAINAGE AREA DETAILS TABLE 3-2 REEVALUATED FLOOD LEVELS TABLE 3-3 COMPARISON OF CURRENT DESIGN BASIS AND FLOODING REEVALUATION ASSUMPTIONS TABLE 3-4 COMPARISON OF CURRENT DESIGN BASIS AND FLOODING REEVALUATION ANALTICAL INPUTS TABLE 3-5 COMPARISON OF CURRENT AND REEVALUATED FLOOD LEVELS Flood Hazard Reevaluation Report iv124939/13 Rev. 0 (February 6, 2013)

LIST OF FIGURES FIGURE NO. TITLE FIGURE 1-1 LOCATION MAP OF THE SITE FIGURE 2-1 DESIGN SITE LAYOUT AND TOPOGRAPHY FIGURE 2-2 LOCATIONS OF SAFETY-RELATED STRUCTURES, SYSTEMS AND COMPONENTS FIGURE 2-3 AS-BUILT SITE LAYOUT AND TOPOGRAPHY FIGURE 3-1 THE HHA DIAGRAM FOR LOCAL INTENSE PRECIPITATION FLOODING ANALYSIS FIGURE 3-2 LOCAL INTENSE PRECIPITATION HYETOGRAPHS FIGURE 3-3 HEC-HMS MODEL FOR THE SITE DRAINAGE ANALYSIS FIGURE 3-4 INUNDATION MAP OF THE REEVALUATED DESIGN FLOOD LEVELFIGURE 3-5 THE HHA DIAGRAM FOR RIVER FLOODING ANALYSIS FIGURE 3-6 WATERSHED MAP FIGURE 3-7 WATERSHED HYETOGRAPH FIGURE 3-8 HEC-HMS MODEL FOR THE WATERSHED DRAINAGE ANALYSIS FIGURE 3-9 HEC-RAS MODEL FOR RIVER FLOODING FIGURE 3-10 THE HHA DIAGRAM FOR DAM BREAK ANALYSIS FIGURE 3-11 LOCATIONS OF DAMS NEAR THE SITE FIGURE 3-12 CENTRAL STABLE REGION FIGURE 3-13 THE HHA DIAGRAM FOR COMBINED EVENTS FLOODING ANALYSIS Flood Hazard Reevaluation Report 1124939/13 Rev. 0 (February 6, 2013)

CALLAWAY ENERGY CENTER UNIT 1 FLOODING HAZARD REEVALUATION REPORT

1.0INTRODUCTION

1.1PURPOSE AND S COPEThe U.S. Nuclear Regulatory Commission (NRC) issued a letter on March 12, 2012 pursuant to Title 10 of the Code of Federal Regulations (CFR), Section 50.54(f) related to the implementation of Recommendations 2.1, 2.3, and 9.3 from the Near-Term Task Force (NTTF),

a portion of which calls for performing flood hazard reevaluations at all Nuclear Power Plants (NPPs) in the United States (NRC, 2012a). As part of Westinghouse Electric Company (WEC) requirements of service to address NRC Recommendation 2.1, Paul C. Rizzo Associates, Inc.

(RIZZO) has prepared this Flooding Hazard Reevaluation Report for Callaway Energy Center, for submittal to WEC with due consideration to the most recent guidance and regulations. This Flooding Hazard Reevaluation Report will ultimately become part of the Callaway response submittal to NRC Recommendation 2.1.

1.2DESCRIPTION

OF S TUDY A REAThe Callaway Energy Center Site is located in Callaway County, Missouri, approximately 25 miles northeast of Jefferson City. A general site location map is seen on Figure 1-1. The site is positioned on a plateau which ranges from 830 to 850 feet (ft) in elevation, approximately 325 ft above the Missouri River floodplain, and approximately five miles north of the Missouri River (Mile 115). Surface drainage is intercepted by the Auxvasse Creek and one of its tributaries Cow Creek to the north and west of the site; whereas surface drainage to the east is intercepted by Logan Creek, and to the southwest by Mud Creek. The Missouri River is used as the principal source of makeup water for the cooling tower system (Ameren Missouri, 2012a). 1.3SITE BACKGROUND AND HISTORYThe Callaway Energy Center is owned by Ameren Corporation and operated by Ameren Missouri. Callaway Energy Center, which is Missouri's only commercial nuclear unit, began commercial operation in December, 1984. In 2008, Ameren Missouri submitted an application for a potential second unit at the site, located northwest of Unit 1.

Flood Hazard Reevaluation Report 2124939/13 Rev. 0 (February 6, 2013)2.0FLOOD HAZARDS AT THE SITE Section 2.0 has been prepared in response to Requested Information Item 1.a. of NRC Recommendation 2.1 (NRC, 2012a).2.1HISTORIC F LOODSHistorical flooding at the Callaway Energy Center Site is of interest mainly with respect to the Missouri River, although other smaller tributaries exist near the site. The Callaway Energy Center Site is a topographic high in the area, with surface runoff draining radially into small intermittent streams (Ameren Missouri, 2012a). These streams are branches of Logan, Mud, Cow, and Auxvasse Creeks. The preceding river and streams were identified based on an initial qualitative screening of rivers, streams, and creeks in the vicinity of the Callaway Energy Center Site. This was carried out based on the distance from and location relative to the Site, as well as

historical flow rates and low-flow considerations.All elevations in this Report are given with respect to mean sea level (MSL), unless otherwise specified on a case-by-case basis. Historical floods of record near the site have most commonly been attributed to heavy rainfall and snowmelt, leading to the flooding of the Missouri River floodplain (Ameren Missouri, 2012a). Ice formation on the Missouri River has occurred, however, no record of ice jams or ice-induced flooding exists at the Site. Records of landslides or tsunami source induced flooding events at the Site are also non-existent (Ameren Missouri, 2009). A list of the most significant historical floods with respect to the maximum water levels near the Callaway Energy Center Site

is provided in Table 2-1.The flood of record near the Callaway Energy Center Site on the Missouri River occurred in 1993, and is regarded as one of the most significant and damaging natural disasters in the region.

The United States Geological Survey (USGS) gauge stations nearest the Site are Boonville (06909000) and Hermann (06934500), upstream and downstream, respectively of Missouri River mile 115. The maximum recorded flow for both stations was in late July, 1993. At the Boonville gauge station, a flow of approximately 755,000 cubic feet per second (cfs) and a flood level at 602.5 ft was recorded. The Boonville gauge station lies over 50 miles west-northwest of Flood Hazard Reevaluation Report 3124939/13 Rev. 0 (February 6, 2013) the Callaway Energy Site (see Figure 1-1). At the Hermann gauge station, the recorded flow and flood level were 750,000 cfs and 518.53 ft, respectively (Ameren Missouri, 2009). Also of note is the flood of 1844, the first year of continuous streamflow recording, with estimated peak streamflows of 700,000 cfs at the Hermann gauging station and 710,000 cfs at the Boonville gauging station. These flows are equivalent to a flood level of 539 ft near the Callaway Energy Center Site under present channel conditions (Ameren Missouri, 2009).

The Site is at an elevation of 840 ft on an upland plateau located north of the Missouri River.The highest flood recorded for the Missouri River near the Site was approximately 300 ft below

the Site's elevation (Ameren Missouri, 2012a).2.2DETAILED SITE I NFORMATION Section 2.2 has been prepared in response to Requested Information Item 1.a.i. of NRC Recommendation 2.1 (NRC, 2012a). The following sections present detailed information

regarding the Callaway Energy Center Site, including information regarding on-site topography, a description of relevant safety-related Structures, Systems, and Components (SSCs), and a description of the Ultimate Heat Sink (UHS). 2.2.1Designed Site Information Designed site information describes characteristics considered for the original licensing basis of the Callaway Energy Center Site.

Figure 2-1 shows the Callaway design site layout and topography. A list of the Callaway Energy Center safety-related structures, systems, and components can be found in Table 2-2. A list of design parameters found in the license document (Ameren Missouri, 2012a) is included in Table 2-3.2.2.1.1Site Topography The Callaway Energy Center Site is part of the Ozark Plateaus Province, located atop a plateau within the Auxvasse Creek watershed, and Missouri River basin (Ameren Missouri, 2009). The plateau, approximately five miles north of the Missouri River (Mile 115), ranges from 830 to 850 ft in elevation compared to the Missouri River basin elevation of 525 ft (Ameren Missouri, 2009). The Callaway Energy Center Site itself sits at approximately 840 ft elevation, with all Flood Hazard Reevaluation Report 4124939/13 Rev. 0 (February 6, 2013)Safety-Related Structures at 840.5 ft, except the UHS retention pond at 840 ft (Ameren Missouri, 2012a).2.2.1.2Description of Safety-Related Structures, Systems, and Components The Callaway Energy Center Site contains several safety-related SSCs. Safety-related SSCs at the Site include the Reactor Building, Fuel Building, Control Building, Diesel Generator Building, Auxiliary Building, Essential Service Water System (ESWS) Pipelines, Refueling

Water Storage Tank, UHS Cooling Tower, UHS retention pond, and ESWS Pumphouse (Ameren Missouri, 2012a). A list of all designed Callaway Energy Center safety-related SSCs

and their elevations can be found in Table 2-2 , and their locations can be seen on Figure 2-2

.2.2.1.3Description of the Ultimate Heat Sink The source of safety-related cooling water for the Callaway Energy Center Site is the UHS retention pond, which can supply 56.03 acre-ft of water to the UHS Cooling Tower in the case of an emergency safety shutdown (Ameren Missouri, 2012a). The UHS retention pond has a

surface area of about 4.1 acres and is located 400 ft southeast of Callaway Energy Center Unit 1.

The normal water surface elevation and normal water depth of the pond is 836 ft and 18 ft, respectively (Ameren Missouri, 2012a). The UHS retention pond is underlain by accretion-gley and glacial till, which have extremely low permeability. Seepage losses through these materials do not significantly affect pond storage (Ameren Missouri, 2012a). Grading around the UHS retention pond is designed to prevent surface runoff from flowing into the pond. The plant yard is also graded away from the pond to prevent Site runoff from entering the pond. In addition, an overflow spillway keeps the pond water level below an elevation of 836.5 ft (Ameren Missouri, 2012a). The graded elevation around the UHS retention pond provides a 4 ft minimum free board at normal pond water level (Ameren Missouri, 2012a). 2.2.2As-Built Site Information As-built site information describes changes to the Callaway Energy Center Site which occurred since the current licensing basis, which may have the potential to influence the reevaluation of hydrological and flooding hazards.

Figure 2-3 shows the as-built site layout and topography.

Flood Hazard Reevaluation Report 5124939/13 Rev. 0 (February 6, 2013)2.2.2.1Site Topography All flooding analyses described in this Report, and described in Section 3.0, have been undertaken with consideration and implementation of current techniques, software, and methods used in present-day standard engineering practice to develop the flood hazard. Changes to regional and site topography since the time of license issuance have been considered within these analyses. 2.2.2.2Description of Safety-Related Structures, Systems, and Components As stated in the Post Fukushima Flooding Walkdown Report for Callaway Energy Center (Ameren Missouri, 2012b), "-the walkdown visual inspection has verified that the Callaway site permanent safety-related SSCs are acceptable, not degraded, and capable of performing the design function as credited in the current licensing basis." Furthermore, "(t)here is reasonable assurance that the flood protection features are available, functional, and capable of performing their specified functions as set forth in the current licensing basis" (Ameren Missouri, 2012b).

Flood related changes to the licensing basis are discussed in Section 2.4. The results of the flooding hazard reevaluation, with respect to safety-related SSCs, are presented in Section 3.0

.2.2.2.3Description of the Ultimate Heat Sink The UHS Retention Pond was completed on April 10, 1980, and from May 5 to September 26, 1980, a test was performed to determine the rate of seepage from the pond (Ameren Missouri, 2012a). The average seepage rate was found to be less than 0.5 acre-ft for a 30-day period and likely on the order of 0.3 acre-ft. A seepage loss of 0.5 acre-ft would result in an approximately 1.5 in. drop in the retention pond water surface at the normal operating level (Ameren Missouri, 2012a). If the maximum weekly seepage rate calculated from the seepage test data was projected to 30 days, the seepage loss would be slightly less than 1.0 acre-ft (Ameren Missouri, 2012a). 2.3CURRENT DESIGN BASIS Section 2.3 has been prepared in response to Requested Information Item 1.a.ii of NRC Recommendation 2.1 (NRC, 2012a). The current design basis, as presented in the Final Safety Analysis Report (FSAR) for the Callaway Energy Center Site, indicates that all safety-related structures, systems, and components, except the UHS Retention Pond, are not subject to flooding, wave action, or wave run-up and do not require flood or wave protection (Ameren Flood Hazard Reevaluation Report 6124939/13 Rev. 0 (February 6, 2013)

Missouri, 2012a). The UHS retention pond is the only safety-related structure that is subject to wind wave activity and wave run-up. The UHS retention pond has relatively short dimensions with riprap-covered side slopes. Therefore, the wind wave activity does not represent a major concern. The wave run-up is also not a major concern due to the maximum wave run-up reaching

an elevation of 838.3 ft, which is below the Site grade elevation. The Site is at an elevation of 840 ft, and all safety-related structures, systems, and components are located at an elevation of

840.5 ft or above, on an upland plateau located north of the Missouri River. The highest flood recorded for the Missouri River near the Site was approximately 300 ft below the Site's elevation (Ameren Missouri, 2012a). Since snow and ice can be prevalent in the Site area, the design of the roofs for the safety-related buildings have included consideration for accumulation of snow and ice. In addition, adequate drainage for the Site is available and will prevent the safety-related structures from being flooded, and will direct flood water and storm runoff away from the Site towards the surrounding stream systems via drainage ditches and contour grading (Ameren

Missouri, 2012a).2.4F LOOD-RELATED CHANGES TO THE LICENSING B ASIS Section 2.4 has been prepared in response to Requested Information Item 1.a.iii. of NRC Recommendation 2.1 (NRC, 2012a).2.4.1Description of Hydrological Changes and Flood Elevations The design basis flood elevations for the Callaway Energy Center are summarized in Table 2-4.A description of flood protection changes is provided in Section 2.4.2. Reevaluated flood elevations are presented in Section 3.0, and are summarized in Table 3-2.2.4.2Description of Flood Protection Changes (Including Mitigation) The Post Fukushima Flooding Walkdown Report for Callaway Energy Center states that, "(t)he reviews determined Callaway site flood protection features would be capable of performing their

intended flood protection function if subjected to a design basis flooding hazard," and that "(n)o flooding walkdown observations were deemed to be a deficiency per Section 3.8 of NEI 12-07" (Ameren Missouri, 2012b).

Flood Hazard Reevaluation Report 7124939/13 Rev. 0 (February 6, 2013)2.5CHANGES TO THE WATERSHED AND L OCAL A REA Section 2.5 has been prepared in response to Requested Information Item 1.a.iv. of NRC Recommendation 2.1 (NRC, 2012a). Any changes to the contributing watershed within which the Callaway Energy Center Site is situated since the time of license issuance have the potential to influence potential flooding hazards. A description of the watershed at the time of license issuance and pertinent changes to the watershed since license issuance are presented in the

following sections.2.5.1Description of Watershed and Local Area at the Time of License Issuance The Callaway Energy Center Site is situated on a plateau approximately five miles north of the Missouri River at a site grade elevation of 840 ft within the Missouri River watershed. The Missouri River flows in an east-west valley at an elevation of approximately 328 ft below the Callaway Energy Center Site (Ameren Missouri, 2012a). The Probable Maximum Flood (PMF) on the Missouri River, near the Site, is estimated to be 548 ft, based on an estimated PMF peak

discharge of 1,300,000 cfs. The PMF was estimated based on data provided by flood studies of the Missouri River by the United States Army Corps of Engineers (USACE). With the estimated PMF of 548 ft for the Missouri River, the Callaway Energy Center Site will not be affected due to the large difference in elevation between the Missouri River and the Site grade of 840 ft (Ameren Missouri, 2012a). Natural surface runoff around the Site flows easterly into the Logan Creek drainage basin, and southwesterly into the watershed area of Mud Creek. Logan Creek drains approximately 16.7 square miles, and is located within two miles of the Site, flowing into the Missouri River. Mud Creek is located about one and a half miles south of the Site; eventually flowing to its confluence with Logan Creek. Cow Creek is located to the north of the Site and flows west to its confluence with Auxvasse Creek. Auxvasse Creek then flows into the Missouri River (Ameren Missouri, 2012a).2.5.2Description of any Changes to the Watershed and Local Area since License Issuance Changes to the watershed since the time of license issuance, mostly in the form of changes in land use and land development, have occurred. All flooding analyses described in Section 3.0have been undertaken with consideration and implementation of current techniques, software, and methods used in present-day standard engineering practice to develop the flood hazard. For Flood Hazard Reevaluation Report 8124939/13 Rev. 0 (February 6, 2013)each delineated watershed, detailed information was considered regarding the current land use and soil types within each subbasin. As such, any such changes to the watershed and local area, as represented by the existing conditions, have been considered within these analyses. 2.6CURRENT LICENSING B ASIS F LOOD PROTECTION Section 2.6 has been prepared in response to Requested Information Item 1.a.v. of NRC Recommendation 2.1 (NRC, 2012a). The safety-related structures, systems, and components at the Callaway Energy Center Site are all located approximately 290 ft above the highest expected flood level of the Missouri River. Therefore, flood protection for the safety-related structures, systems, and components for floods from the Missouri River is not necessary (Ameren Missouri, 2012a). The current licensing basis PMF water level near the Site is estimated at 548 ft, which is

well below the Site grade elevation of 840 ft. The UHS retention pond is surrounded by a sloped grading to keep storm surface water from entering the pond. To prevent the water surface in the pond from exceeding the outlet crest elevation of 836.5 ft, an outlet structure and spillway are provided to drain excess storage (Ameren Missouri, 2012a). The Site is located on the crest of a plateau which has a natural drainage system and the Site drainage facilities of the Site direct runoff into the natural drainage system. Ice accumulation on the roofs of the safety-related structures has been taken into consideration for the Site drainage system (Ameren Missouri, 2012a).2.7ADDITIONAL SITE DETAILS Section 2.7 has been prepared in response to Requested Information Item 1.a.vi. of NRC Recommendation 2.1 (NRC, 2012a).2.7.1Recommendation 2.3 Walkdown Results The Post Fukushima Flooding Walkdown Report for Callaway Energy Center (Ameren Missouri, 2012b) gives results of the walkdown, including key findings and identified degraded, non-conforming, or unanalyzed conditions, and includes detailed descriptions of the actions taken or planned to address these conditions. The Post Fukushima Flooding Walkdown Report for Callaway Energy Center states that, "(t)here are no other planned or newly installed flood protection systems or flood mitigation measures to further enhance the external flood protection at Callaway site" (Ameren Missouri, 2012b).

Flood Hazard Reevaluation Report 9124939/13 Rev. 0 (February 6, 2013)2.7.2Site-Specific Visit Results The RIZZO representatives conducted a site visit from 24-26 September 2012. RIZZO personnel met with WEC and Callaway Energy Center representatives to discuss the overall scope of work for the Flood Hazard Reevaluation. RIZZO personnel also inspected the cooling water intake structure on the Missouri River. Additionally, photographs were taken of the site

and site area which were later used to aid in developing the appropriate inputs to the hydrologic

models such as Manning's n roughness coefficients.

Flood Hazard Reevaluation Report 10124939/13 Rev. 0 (February 6, 2013)3.0FLOODING HAZARD REEVALUATION ANALYSIS Section 3.0 has been prepared in response to Requested Information Item 1.b. of NRC Recommendation 2.1 (NRC, 2012a).3.1

SUMMARY

OF RECOMMENDATION 2.1 To respond to Phase 1 of NRC Recommendation 2.1 (NRC, 2012a) and the 2012 Appropriations Act, the NRC requested that each licensee provide a reevaluation of all appropriate external flooding sources, including the effects from local intense precipitation on the Site, PMF on streams and rivers, storm surges, seiches, tsunamis, and dam failures. Natural events may reduce or limit the available safety-related cooling water supply, and the reevaluation should verify that an adequate water supply exists to shut down the Plant under conditions requiring safety-related cooling. A hazard evaluation should be performed for each reactor licensed under 10 CFR Part 50, including the spent fuel pool and the various modes of reactor operation. The reevaluation should apply present-day regulatory guidance and methodologies being used for Early Site Permit (ESP) and Combined Operating License (COL) reviews. The reevaluation should employ

current techniques, software, and methods used in present-day standard engineering practice to develop the flood hazard. The work presented in this Flood Hazard Reevaluation Report will ultimately become part of the overall response submittal to NRC Recommendation 2.1. 3.2F LOOD CAUSING MECHANISMSThe NRC NUREG/CR-7046 (NRC, 2011) recommends using a Hierarchical Hazard Assessment (HHA) method for evaluating the safety of SSCs. The HHA method is a progressively refined, stepwise estimation of site-specific hazards that evaluates the safety of the Site with the most conservative plausible assumptions consistent with available data. The HHA process proceeds as follows (NRC, 2012a): a)Select one flood causing mechanism to be reanalyzed. b)Develop a conservative estimate of the site-related parameters using simplifying assumptions for a flood causing mechanism and perform the reevaluation. c)Determine if the reevaluated flood hazard elevation (from Step b) is higher than the original design flood elevation for the selected flood causing mechanism. If not, use this flood elevation for this causal mechanism for comparison of reevaluation against the current design basis.

Flood Hazard Reevaluation Report 11124939/13 Rev. 0 (February 6, 2013)d)Determine if the site-related parameters can be further refined. If yes, perform reevaluation (repeat Step c). If no, use this flood elevation for this causal mechanism for comparison of reevaluation against the current design basis. e)Determine if all flood causing mechanisms have been addressed. If yes, continue to the following. If no, select another flood causing mechanism (Step a). For each flood causing mechanism, compare the final flood elevations from the hazard reevaluation against the current design basis flood elevations.Using this comparison, determine whether the design basis flood bounds each reevaluated hazard. If it is determined that the current design basis flood bounds all of the reevaluated hazards, the reevaluation report is submitted. If not, additional analysis may be necessary. Any potential additional analysis will be conducted in the Integrated Assessment (NRC, 2012a). Each potential flood causing mechanism has been evaluated based on present-day methodologies and regulatory guidance. Details regarding the considerations and outcome of the analyses regarding each flood causing mechanism are presented herein. 3.2.1Local Intense Precipitation Section 3.2.1 addresses the effects of Probable Maximum Precipitation (PMP) on the local area of the Callaway Energy Center Site. The HHA diagram for local intense precipitation flooding

can be seen on Figure 3-1

.3.2.1.1Site-Specific Probable Maximum Precipitation The local intense PMP was evaluated to determine the Probable Maximum Storm (PMS) event capable of generating the maximum amount of direct runoff (or peak discharge) at the Callaway Energy Center Site. The local intense PMP for the site drainage basin was calculated using the Hydrometeorological Report No. 52 (HMR 52) (National Weather Service [NWS], 1982). The Callaway Energy Center Site drainage basin boundary utilized for the calculation of the local intense PMP encloses an area of 41.9 acres or 0.07 mi

2. The peak one-hour storm event acting on an area of 1 mi 2 (1-hour, 1-mi

2) was determined for utilization as input to the reevaluation of the Callaway Energy Center local site drainage HEC-HMS model. The PMP depth generated by the 1-hour 1-mi 2 storm event acting on the Callaway Energy Center Site was determined using the isohyet chart presented on Figure 24 of the HMR 52 report (NWS, 1982).

Flood Hazard Reevaluation Report 12124939/13 Rev. 0 (February 6, 2013)The FSAR for the Callaway Energy Center Unit 1 states that an all-season six-hour rainfall with an accumulation of 25.4 inches (in.) is the governing PMP event affecting the surface runoff aspects of the SSCs, and gives a 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> PMP of 35 in. (Ameren Missouri, 2012a). A comparison of relevant assumptions and analytical inputs used in the reevaluation to those of the

current design basis are provided in Tables 3-3and 3-4 , respectively.

The calculated results of the flooding reevaluation pertaining to Callaway Energy Center utilizing HMR 52 Figure 24 give a 1-hour 1-mi 2 PMP depth of 18.3 in. Local intense precipitation hyetographs are provided on Figure 3-2

.3.2.1.2Effects of Local Intense Precipitation The local PMF at the Callaway Energy Center Site was calculated per the HHA method (NRC, 2011) by first using the Rational Runoff Transformation Method (see description below) and second using more site-specific data in the HEC-HMS software. The site drainage basin model used to calculate the local PMF divides the total power plant site area into 51 subbasins (see

Figure 3-3). The area of each of the 51 subbasins is listed in Table 3-1.As per the HHA method for local intense precipitation analysis (Figure 3-1

), six scenarios were simulated with decreasing levels of conservatism. The six scenarios are as follows: Scenario 1: Calculation of runoff using Rational Runoff Transformation Method. Scenario 2: Calculation of runoff using the HEC-HMS model with no runoff transformation. Scenario 3: Calculation of runoff using the HEC-HMS model and the Snyder Runoff Transformation Method with a peak runoff coefficient of 0.7. Scenario 4: Calculation of runoff using the HEC-HMS model and the Snyder Runoff Transformation Method with a peak runoff coefficient of 0.5. Scenario 5: Calculation of runoff using the HEC-HMS model and the Snyder Runoff Transformation Method with a peak runoff coefficient of 0.4. Scenario 6: Calculation of runoff using the HEC-HMS model and the Snyder Runoff Transformation Method with a peak runoff coefficient of 0.4 and a catchment shape coefficient of 1.8.

Flood Hazard Reevaluation Report 13124939/13 Rev. 0 (February 6, 2013)The Rational Runoff Transformation Method is appropriate for small basins, especially in areas that are mostly paved. The Rational Runoff Transformation Method assumes that the maximum rate of runoff from a drainage basin occurs when all parts of the watershed contribute and that the rainfall is uniformly distributed over the catchment area. No runoff losses were assumed and the runoff coefficient was assumed to be 1.0. The 1-hour 1-mi 2 reevaluated PMP described in Section 3.2.1.1 was converted to rainfall intensity with consideration of the rainfall depth and duration. The peak runoff for each subbasin was calculated based on the rainfall intensity and

subbasin area, as well as the runoff coefficient. The calculated rainfall intensity and peak runoff for each subbasin is listed in Table 3-1.In accordance with the approach of the HHA method (Figure 3-1), a more refined and more detailed evaluation of runoff at the Callaway Energy Center Site was performed using HEC-

HMS 3.5 (USACE, 2010).

Figure 3-3 shows the HEC-HMS model watershed routing layout for the 51 subbasins.The plant footprint area was assumed to be impervious, which implies that the Callaway Energy Center Site is assumed to have no losses (according to the HHA method). This assumption is per NUREG/CR-7046 guidance (NRC, 2011). Time of concentration (T c), which is the time for runoff to travel from the hydraulically most distant point of the watershed to a point of interest within the watershed, was used to calculate the lag time (Natural Resources Conservation Service [NRCS], 2010). The HEC-HMS model utilizes the reevaluated PMP discussed above. A summary of site area drainage details, including peak runoff, calculated for both the Rational Runoff Transformation Method and using the HEC-HMS model are shown in Table 3-1.Utilization of the HEC-HMS model, which incorporates more site-specific data, yields less conservative results than the Rational Runoff Transformation Method. The determination of water levels due to local intense precipitation at the Callaway Energy Center Site is discussed in

Section 3.2.1.3

.3.2.1.3Water Level due to Local Intense Precipitation Following the standards of the HHA method, six scenarios were considered with each less conservative than the next. In Scenario 1, peak runoff rates estimated in HEC-HMS were used, assuming no rainfall losses and no runoff transformation. It was assumed that conveyance structures and opening along the Vehicle Barrier System (VBS) were blocked. The VBS was

modeled as 42 in. high and to have 36 in. openings at specified locations along its length.

Flood Hazard Reevaluation Report 14124939/13 Rev. 0 (February 6, 2013)Scenario 2 is like Scenario 1, except that the VBS openings in areas of potential inundation were represented as open. Scenario 3 is like Scenario 2 except that the Snyder Runoff Transformation Method was used to reduce peak runoff rates, and the coefficient of peak runoff was set to a value of 0.7. Scenario 4 is like Scenario 3, except that peak runoff rates, estimated by HEC-HMS, were calculated using a value of 0.5 for the coefficient of peak runoff. Scenario 5 is like Scenario 4, except that peak runoff rates, estimated by HEC-HMS, were calculated using a value of 0.4 for the coefficient of peak runoff. Scenario 6 is like Scenario 5, except that the shape coefficient used to calculate lag time was increased from 0.4 to 1.8.

Figure 3-3 shows the HEC-HMS model corresponding to Scenario 5, and shows the model subbasins which were used to

represent the conditions of Scenario 5.

Table 3-1 lists the peak discharge rates for each subbasin calculated with Scenario 1 using the Rational Runoff Transformation Method and in the HEC-HMS simulations associated with Scenario 5. For the first four scenarios, water levels at the Callaway Energy Center Site exceeded 840.5 ft, which is the critical flood elevation for the Site. For Scenario 5, simulated peak water levels do not exceed 840.5 ft. The sixth and least conservative assumption was included for additional information beyond Scenario 5. A peak water level of 840.17 ft North American Vertical Datum of 1988 (NAVD88) was simulated at the Callaway Energy Center Site for Scenario 5.

Figure 3-4 illustrates the simulated peak water levels and inundation area for each subbasin modeled using Scenario 5. A comparison of relevant assumptions and analytical inputs used in

the reevaluation to those of the current design basis are provided in Tables 3-3and 3-4

,respectively. 3.2.1.4Wind Waves and Run-up Coincident with Local Intense Precipitation The maximum water level due to wind-wave activity in the UHS retention pond coincident with local intense precipitation was evaluated. The wave setup and run-up generated by a two-year

return period wind speed were added to the PMF still water elevation to determine the maximum water level at the UHS retention pond. The use of a two-year return period wind speed is consistent with the approaches presented in NUREG/CR-7046 (NRC, 2011). Methodologies used to determine the wind wave activity are based on the USACE Coastal Engineering Manual (CEM) (USACE, 2008). As recommended in the CEM (USACE, 2008), the longest possible straight line fetch over the UHS retention pond of approximately 690 ft was used. The UHS pond is represented as Flood Hazard Reevaluation Report 15124939/13 Rev. 0 (February 6, 2013) subbasin 58 (see Table 3-1). Wave run-up was determined for the scenarios (Scenarios 1 through 6) utilized and described for the determination of the still water level due to local intense precipitation (Section 3.2.1.3). The maximum water surface elevations including run-up for Scenarios 1 through 6 are 839.31, 839.36, 838.74, 838.41, 838.04, and 837.84 ft, respectively. The only area at the Callaway Energy Center Site where wind-wave activity has the potential to affect the SSCs is at the UHS retention pond. The water levels in the UHS retention pond after wave run-up do not reach the Site grade of 840 ft for Scenarios 1 through 6. Thus, water is

contained in the UHS retention pond, and the Callaway Energy Center SSCs including those in the power block area will not be flooded by wind-wave activity coincident with local intense

precipitation on the UHS retention pond. Ponded areas in the vicinity of the power block are

shown on Figure 3-4. Fetch lengths over ponded areas near the power block are small and so run-up on SSCs besides the UHS retention pond does not apply. This approach is consistent with the FSAR for Callaway Energy Center Unit 1 (Ameren Missouri, 2012a), which reports the maximum water level including wave run-up in the UHS

retention pond as 838.3 ft. 3.2.2River Flooding River flooding at the Callaway Energy Center Site is of interest with respect to the Auxvasse Creek watershed and is discussed in this section. The HHA diagram for river flooding analysis

is provided on Figure 3-5. Dam failure flooding is discussed in detail in Section 3.2.3

.3.2.2.1Probable Maximum Precipitation for River Flooding The PMP was calculated for the Auxvasse Creek basin in accordance with the criteria specified in HMR 52 (NWS, 1982). Basin-average precipitation for the PMS was determined in accordance with the temporal and spatial storm patterns associated with the PMP estimates provided in Hydrometeorological Report No. 51 (HMR 51) (NWS, 1978). The current design basis determined the PMF for Auxvasse Creek by imposing the PMP as obtained from Hydrometeorological Report No. 33 (HMR 33) upon the catchment (Ameren Missouri, 2012a). The boundaries of the Auxvasse Creek watershed were defined within the HMR 52 computer program based on the reevaluated watershed delineation. The Auxvasse Creek watershed can be Flood Hazard Reevaluation Report 16124939/13 Rev. 0 (February 6, 2013) seen on Figure 3-6. For the delineated watershed, detailed information was considered regarding the current land use and soil types within each subbasin. The location of the Auxvasse Creek watershed was utilized, along with the HMR 51 PMP isohyet charts to determine generalized estimates of the all-season PMP for storm areas from 10 to 20,000 mi 2 with durations of 6, 12, 24, 48, and 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. The storm center coordinates were conservatively placed at the basin centroid resulting in higher runoff. A time interval of five minutes was selected in estimating the rainfall distribution. The critical storm area for Auxvasse Creek was found by HMR 52 software to be 300 mi 2 with a critical storm orientation of 150 degrees and a critical 72-hour storm PMP rainfall of 28.63 in.

An estimation of the 72-hour PMP total is not presented in the FSAR for Callaway Energy Center Unit 1 (Ameren Missouri, 2012a).

The FSAR for Callaway Energy Center Unit 1 gives a PMP of 25.4 in. in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> on an area of 75 acres in the Callaway Energy Center vicinity (Ameren Missouri, 2012a). A comparison of relevant assumptions and analytical inputs used in the reevaluation to those of the current design

basis are provided in Tables 3-3and 3-4 , respectively. The PMS rainfall hyetograph developed for Auxvasse Creek was used as input when developing the Auxvasse Creek watershed HEC-HMS models to determine the maximum runoff. The

watershed hyetograph is provided on Figure 3-7

.3.2.2.2Probable Maximum Flood for Auxvasse Creek Watershed The Soil Conservation Service (SCS) Curve Number, Clark Unit Hydrograph, and Muskingum-Cunge methods were used to calculate the basin loss, transformation, and routing for Auxvasse Creek. The Clark Unit Hydrograph method was chosen for transform calculations. The Manning's n roughness coefficient for the main channels was conservatively taken as 0.033 (for a channel that is straight, full, no rifts or deep pools, but more stones and weeds). Transmission losses through the reaches were assumed to be zero for all scenarios, which is conservative because all runoff that reaches the channel will be routed through the channel instead of being absorbed. The developed land use within the Auxvasse Creek watershed was used as a basis for the percentage of impervious area. Because the Auxvasse Creek watershed is controlled, representative flow rates could not be used for calibration purposes. It is noted that the FSAR for Callaway Energy Center Unit 1 (Ameren Missouri, 2012a) did not perform model calibration.

Flood Hazard Reevaluation Report 17124939/13 Rev. 0 (February 6, 2013)As per the HHA method for river flooding (Figure 3-5), several scenarios were simulated in HEC-HMS with decreasing levels of conservatism. Reaches and junctions for the Auxvasse

Creek watershed can be seen on Figure 3-8. The different scenarios considered in the HEC-HMS model for Auxvasse Creek are as follows: Scenario 1: No SCS Curve Number loss, no rainfall-to-runoff transformation, no routing through the channels. Scenario 2: No SCS Curve Number loss, Clark Unit Hydrograph transformation, no routing through the channels. Scenario 3: No SCS Curve Number loss, Clark Unit Hydrograph transformation, includes routing through the channels. Scenario 4: SCS Curve Number loss method, Clark Unit Hydrograph transformation, include routing through the channels - Existing conditions. Scenario 5: SCS Curve Number loss method, Clark Unit Hydrograph transformation, include routing through the channels, but with assumed 5 percent increase in percent impervious area for each subbasin - Projected

conditions.The reevaluated calculated flow values from Junction 20 and from Subbasin 57 near the Site (from Scenario 4 - Existing conditions) are approximately 262,124 cfs and 23,213 cfs, respectively. Combined effects are discussed separately in Section 3.2.9

.The FSAR for Callaway Energy Center Unit 1 (Ameren Missouri, 2012a) did not include a comparable PMF analysis. A comparison of relevant assumptions and analytical inputs used in

the reevaluation to those of the current design basis are provided in Tables 3-3and 3-4

,respectively. The outflows from the different scenarios are utilized for the determination of the water level due to the PMF as described in Section 3.2.2.3

.

Flood Hazard Reevaluation Report 18124939/13 Rev. 0 (February 6, 2013)3.2.2.3Water Level Due to Probable Maximum Flood The potential for river flooding at the Callaway Energy Center Site due to the PMF was evaluated using a HEC-RAS model to determine water surface flood elevations during the PMF on the Auxvasse Creek watershed. The HEC-RAS model for the Auxvasse Creek watershed is

shown on Figure 3-9

.With regards to the construction of the HEC-RAS models, contraction coefficients of 0.1 and expansion coefficients of 0.3 were used for normal flowing cross sections. When an obstruction

was encountered, such as a bridge, a contraction coefficient of 0.3 was used with an expansion coefficient of 0.5 for cross sections immediately upstream and downstream of the bridge. A

Manning's n roughness coefficient of 0.035 was used for stream channel (used for natural stream, clean, straight, full stage, no rifts or deep pools, with stones and weeds). A Manning's n roughness coefficient of 0.1 was used for the overbanks (used for floodplains; brush; medium to dense brush). The FSAR for Callaway Energy Center Unit 1 did not model the Auxvasse Creek watershed (Ameren Missouri, 2012a). A comparison of relevant assumptions and analytical

inputs used in the reevaluation to those of the current design basis are provided in Tables 3-3 and 3-4 , respectively. Flow was assumed to be steady and one-dimensional for this analysis and, hence, a steady state analysis was conducted, which is a conservative assumption. Since both supercritical and subcritical flows were anticipated, a mixed flow regime was assumed. The upstream boundary condition was set at normal depth, whereas the downstream boundary condition was set at critical depth for the Auxvasse Creek model and at known water surface elevation for the Logan Creek/Mud Creek model. The runoff rates resulting from the PMP events described in Section 3.2.2.1 were used as input into the models. There is only one USGS gauge located along the portion of Auxvasse Creek that is modeled in HEC-RAS. However, no USGS gauges are located along the portion of Logan Creek or Mud Creek modeled in HEC-RAS. Since there is no record of measured discharge along all of the streams modeled in HEC-RAS, the model is not calibrated. The five different scenarios considered in the HEC-RAS model are as follows: Scenario 1: No SCS Curve Number loss, no rainfall-to-runoff transformation, no routing through the channels.

Flood Hazard Reevaluation Report 19124939/13 Rev. 0 (February 6, 2013) Scenario 2: No SCS Curve Number loss, Clark Unit hydrograph transformation, no routing through the channels. Scenario 3: No SCS Curve Number loss, Clark Unit hydrograph transformation, includes routing through the channels. Scenario 4: SCS loss, Clark Unit hydrograph transformation, include routing through the channels - Existing conditions. Scenario 5: SCS loss, Clark Unit hydrograph transformation, include routing through the channels, but with assumed 5 percent increase in percent impervious area for each subbasin - Projected conditions. Maximum predicted water surface elevations near the Site on Auxvasse Creek for Scenarios 1 through 5 are 772.71, 717.47, 709.77, 709.05, and 709.09 ft, respectively. Thus, it can be concluded that the maximum predicted water surface elevations for all scenarios will not exceed the site grade of 840 ft. The reevaluated PMF flood elevations are presented along with the

current design basis flooding elevations in Table 3-5. HEC-RAS predicted water surface profiles for Auxvasse Creek, Logan Creek, and Mud Creek in Scenario 4 are shown on Figure 3-9. Flow from Cow Creek into Auxvasse Creek near the Site is accounted for in the HEC-HMS models.3.2.2.4Wind Waves and Run-up coincident with Probable Maximum Flood The reevaluated flood levels due to the PMF as presented in Section 3.2.2.3 indicate an elevation difference between water levels in streams in the Site vicinity and the Site grade elevation of

greater than 100 ft. As such, wind waves and run-up coincident with the PMF will not affect the Site and no further analysis is necessary. 3.2.3Dam Failure Flooding The potential flooding of the Callaway Energy Center Site due to simultaneous failure of all dams on the Auxvasse Creek watershed was evaluated. The HHA diagram for dam failure

flooding can be seen on Figure 3-10. The locations of dams near the Site can be seen on Figure 3-11

.The total combined maximum storage of the reservoirs is 16,148 acre-ft. Auxvasse Creek is located approximately three miles west of the Site and the discharge from all upstream dams

would pass through this creek. The plant grade elevation is at 840 ft, and the flood elevation for SSCs is 840.5 ft. The potential flooding of the Site was considered in two parts. The first part Flood Hazard Reevaluation Report 20124939/13 Rev. 0 (February 6, 2013) was used to address the potential for flood waters to reach the plant grade and second to ascertain the potential for flood elevations starting at the plant grade elevation of 840 ft to exceed 840.5 ft and flood the SSCs with the simultaneous failure of all upstream dams. The most conservative assumption regarding dam failure is that all upstream inflows from the PMP event and all reservoirs upstream of the Site in Auxvasse Creek fail simultaneously. Flood waters resulting from a watershed-wide PMP event of 28.63 in. combined with the concurrent failure of all upstream dams would not reach an elevation 810 ft adjacent to the Site. Alternatively, only that storage between the elevations of plant grade (840 ft) and the SSCs (840.5) should be considered for storage of all upstream reservoirs. Furthermore, the upstream watershed storage between the elevation of 840 and 840.5 ft is 3.6 times greater than the combined storage of all upstream reservoirs. This indicates that flood waters would not reach plant grade and even if flood waters reached plant grade, the combined storage of all upstream dams (many of which would already be under water) would not flood the Callaway Energy

Center Site. 3.2.3.1Wind Waves and Run-up Coincident with Dam Failure Flooding The analysis regarding dam failure flooding as presented in Section 3.2.3 determines that water levels in streams in the Site vicinity do not approach the Site grade elevation. As such wind

waves and run-up coincident with dam failure will not affect the Site and no further analysis is

necessary. 3.2.4Storm Surge Flooding The Callaway Energy Center Site 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 the Site is not expected to be a potential flooding hazard. According to ANSI/ANS-

2.8-1992 guidance (ANSI/ANS, 1992), 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 the Callaway Energy Center is located greater than 620 miles inland from the Gulf of Mexico, and at a site grade of 840 ft, hurricanes do not present potential flooding hazards.

Flood Hazard Reevaluation Report 21124939/13 Rev. 0 (February 6, 2013)3.2.5Seiche Flooding The Callaway Energy Center Site is not near to any bodies of water for which seiche flooding would apply. Therefore, seiche flooding is not a risk to the Site.3.2.6Tsunami Flooding The Callaway Energy Center Site is not near any large bodies of water for which tsunami flooding would apply. The Callaway Energy Center Site is over 620 miles from the Gulf of Mexico and the plant grade is approximately 840 ft above sea level. Therefore, tsunami flooding is not a risk to the Site. Furthermore, NRC (2008) indicates that if regional screening identifies that the site region is not subject to tsunamis, no further analysis for tsunami hazard is required. 3.2.7Ice Flooding The potential for flooding hazards due to ice jams, and ice formation and accumulation at the Callaway Energy Center Site was evaluated. A review of the USACE Cold Regions Research & Engineering Laboratory Ice Jams Database (USACE, 2012) demonstrates that no new ice jam events have occurred since those events discussed in the FSAR for Callaway Energy Center Unit 2 (Ameren Missouri, 2009). According to the Callaway Energy Center Unit 2 FSAR, the closest ice jams to the Site were recorded at Boonville, Missouri on December 19, 1945. To date such events have not affected the operation

of the Callaway Energy Center (Ameren Missouri, 2009). The Callaway Energy Center is located on a plateau at an approximate elevation of 840 ft, which is the topographic high in the area, and surface runoff from the site vicinity drains into small intermittent streams located at lower elevations than the Callaway Energy Center Site. Streams close to the Site have small drainage areas and would not pose the potential of ice flooding at the Site (Ameren Missouri, 2009). The historical air temperatures in the region of the Callaway Energy Center were also considered. Consistent with the FSAR for Unit 2 (Ameren Missouri, 2009), historical air temperatures recorded at the NWS observation station at the Columbia Regional Airport were examined (National Climatic Data Center [NCDC], 2012). There are no major terrain feature Flood Hazard Reevaluation Report 22124939/13 Rev. 0 (February 6, 2013)differences between Columbia Regional Airport and the Callaway Energy Center Site (Ameren Missouri, 2009). The maximum potential ice thickness that could form on the Missouri River and the UHS retention pond was estimated using historic daily air temperatures from the closest NWS meteorological station to the Site. Historical air temperatures from Columbia, Missouri for the recorded periods between 1970 through 2012 were downloaded from the NCDC (2012).

According to USACE, 2004 methods, theoretical ice thickness can be estimated by analysis of Freezing Degree-Days (FDD), defined as the summation of the difference between 32 degrees Fahrenheit and average daily air temperature. For this analysis, the historic average daily air temperature data was used for the estimation of ice thickness. The maximum calculated theoretical ice thickness for the Missouri River was estimated to be approximately 4.43 in. As discussed in the Callaway Energy Center Unit 1 FSAR (Ameren

Missouri, 2012a), the water supply intake and water discharge structures on the Missouri River

are not safety-related structures and are not required for safe shutdown of the plant. Ice or ice flooding will not be a problem at the discharge structure, as the warm discharge water will keep

the outfall open. The maximum calculated theoretical ice thickness on the UHS retention pond was estimated to be approximately 20.67 in. The invert elevation of the Essential Service Water System (ESWS) pumphouse and the invert of the discharge pipes are approximately 26 ft and 17.5 ft below the water surface of the UHS retention pond, respectively (Ameren Missouri, 2012a), which are approximately 24.28 ft and 15.78 ft below the maximum estimated ice sheet, respectively. An evaluation of the potential for frazil ice blockage of the ESWS pumphouse was performed in 1996 (Daly, 1996). The analyses concluded that the probability of frazil ice accumulation blocking the Essential Service Water (ESW) pump intakes is quite low. This is due to the small size of the UHS retention pond, its location sheltered from the wind, formation of ice cover over the surface of the pond, and warm water inflow from the ESW return line to the UHS pond (Daly, 1996).For the reasons discussed above, ice effects are not a potential threat to safety-related SSCs at the Callaway Energy Center.

Flood Hazard Reevaluation Report 23124939/13 Rev. 0 (February 6, 2013)3.2.8Channel Diversion Flooding Flooding hazards due to potential diversion or rerouting of the Missouri River and its associated tributaries located near the Callaway Energy Center Site were evaluated. Per NRC Regulatory Guide (RG) 1.206, the Site was evaluated with respect to seismic, topographical, and geologic

evidence in the region (NRC, 2007). Also evaluated was the potential diversion or rerouting of the source of makeup water for the Callaway Energy Center due to channel diversions. A qualitative assessment of the streams and rivers in the vicinity of the Callaway Energy Center Site was undertaken in conjunction with a review of information presented in the FSARs for Callaway Energy Center Unit 1 and Unit 2 (Ameren Missouri, 2012a; Ameren Missouri, 2009).

The evaluation of the potential for channel diversions consisted of the following considerations: River and stream morphology and hydrological characteristics. Human induced development on the Missouri River. Topographical, seismological, and geological evidence for channel diversion. Potential for diversion or rerouting of the source of makeup water for the Site.

Each consideration is discussed separately in Sections 3.2.8.1 through 3.2.8.4.3.2.8.1River and Stream Morphology and Hydrological Characteristics The Missouri River, which is the principal source of makeup water for Callaway Energy Center Unit 1, flows over 2,300 miles in a generally east-southeast direction. From the confluence of the Gallatin, Madison, and Jefferson Rivers in Montana, the Missouri River flows through seven

states before joining the Mississippi River near St. Louis, Missouri (Spooner, 2000). Today the Missouri River is divided into three subsections: the free-flowing upper section, impounded middle section, and channelized lower section (Spooner, 2000). The Callaway Energy Center Site is located approximately five miles north of the Missouri River near River Mile 115, which is located within the channelized lower section of the Missouri River (Ameren Missouri, 2009).

Because the Callaway Energy Center is located on a plateau, a topographic high in the area, surface runoff drains into several intermittent streams near the Site (Ameren Missouri, 2009).

The streams located nearest the Site are Logan, Mud, Cow, and Auxvasse creeks. Mud Creek is

a tributary of Logan, while Cow Creek is a tributary of Auxvasse. Logan and Auxvasse Creeks are in turn tributaries of the Missouri River.

Flood Hazard Reevaluation Report 24124939/13 Rev. 0 (February 6, 2013)3.2.8.2Human Induced Development on the Missouri River Prior to the 1800's, the pre-regulated Missouri River was characterized by the migration of its channel meanders and channel avulsion, with both processes resulting in the reworking of its floodplain deposits (Spooner, 2000). Channel meanders tend to migrate due to lateral erosion and the associated deposition of sediments. Particularly on the lower Missouri River this process has led to the formation of features such as levees, terraces, abandoned channels, and oxbow lakes (Spooner, 2000). Prior to the development of large scale river control activity, this dynamic equilibrium of continuous bank erosion and deposition constantly reshaped the channel

and floodplain of the Missouri River (USGS, 1998).As settlement of the Missouri River basin increased in the early 1800s, significant efforts were made to control the Missouri River's unpredictable nature and adapt it for transportation, farming, and urban development purposes (USGS, 1998). The results of the various programs implemented since then have progressively altered the natural features of the Missouri River, transforming it into a navigation system that is regulated by reservoirs and by bank stabilization and flood control structures (Spooner, 2000).Specifically in the 1940s and 1950s, programs implemented by the USACE and the Bureau of Reclamation transformed the Missouri River into a system of main stem reservoirs and altered reaches influenced by regulated flows, self-

channelization, and bank stabilization (USGS, 1998).As a result of the extensive man-made alterations to the physical features of the Missouri River, 35 percent of the river is impounded, 32 percent is channelized, and the remaining 33 percent is unchannelized (Ameren Missouri, 2009). In the upper Missouri River, deep water reservoirs have replaced free-flowing currents. In the lower river, channelization has eliminated sandbars, extensive depth variations, and connections with side channels and backwaters (Ameren Missouri, 2009). Wing dikes and revetments have concentrated flow, and levees keep the channel in place and disconnect it from the floodplain, morphing the river into a deep single-thread channel (Ameren Missouri, 2009). As a result of man-made alteration, channel avulsion and migration have become a rare occurrence along the lower Missouri River (Spooner, 2000). 3.2.8.3Topographical, Seismological, and Geological Evidence for Channel Diversion The Callaway Energy Center Site lies within the Central Stable Region (Figure 3-12) of the United States near the border between the Dissected Till Plains and Ozark Plateaus physiographic provinces (Ameren Missouri, 2009). This region is tectonically and seismically Flood Hazard Reevaluation Report 25124939/13 Rev. 0 (February 6, 2013)stable, experiencing only infrequent and minor earthquake activity, with the closest epicenter located 38 miles from the Callaway Energy Center Site (Ameren Missouri, 2009). Based on the lack of evidence of deformation zones, and capable fa ults, and with consideration of the location of the Site on an isolated plateau with deeply incised drainage patterns extending around the plateau and to the Missouri River valley, channel diversion due to seismic activity is not expected during the lifetime of the plant (Ameren Missouri, 2009). The Missouri River valley between Glasgow, Missouri and its confluence with the Mississippi River near St. Louis has been characterized as a bedrock trench of Ordovician and Mississippian limestone and dolomite filled with up to 120 ft of silt and sand with intermixed gravel and boulders (Spooner, 2000). Downstream from Glasgow, including the Site Area, bedrock lithology along the river valley is dominated by more resistant limestone and dolomite (Spooner, 2000). This more erosion resistant bedrock lead to the development of a narrow river valley with steep sides, as opposed to the river valley upstream of Glasgow characterized by broad meanders

and softer channel bedrock (Spooner, 2000). The narrow river valley with steep sides is less prone to a meandering channel behavior leading channel diversion or migration. During the early to mid-Pleistocene or Pre-Illinoian stage, approximately 2.5 to 0.3 million years ago (National Atlas, 2012), glacial advance throughout North America had a profound effect upon the flow path of the Missouri River, for the most part establishing the river's present course. Evidence of channel diversion of the Missouri River during this time period has been found near Kansas City, Missouri. The Blue and Little Blue Rivers each became temporary diversion channels during glacial advance, and were abandoned during glacial retreat, allowing the Missouri River to reoccupy its pre-glacial channel (Spooner, 2000). Since glacial retreat, no evidence of channel diversion of this magnitude has been found. The Missouri River channel has since stabilized, and continues to follow its pre-glacial route. 3.2.8.4Potential for Diversion or Rerouting of the Source of Makeup Water for the Site The source of makeup water for the Callaway Energy Center is the makeup water intake structure located on the Missouri River approximately at Missouri River Mile 115. The intake structure is not a safety-related structure and is not required for safe shutdown of the Callaway Energy Center. No geologic or seismic hazards near the site have been identified, but the possibility of mass wasting in the Missouri River valley does exist. An event such as this would result in collapsed material deposited at the shoreline location of the event (Ameren Missouri, 2009). The result of this event would disperse sand, soil, and other materials over a large area.

Flood Hazard Reevaluation Report 26124939/13 Rev. 0 (February 6, 2013)This, coupled with dredging activities conducted by the USACE and the design of the makeup water intake structure, limits the possibility of a loss of makeup water supply. As discussed previously, the flow of the Missouri River is heavily regulated and controlled by the USACE, and has been progressively altered in the past. Due to this control, it is highly unlikely any made-made events or actions would result in the channel flooding or diversion of the Missouri River during the lifetime of the plant. Based on the assessment presented in Sections 3.2.8.1 through 3.2.8.4 , it is concluded that flooding hazards due to potential channel diversions, and potential impacts on the source of

cooling water due to channel diversions do not present a flooding threat to the Callaway Energy Center Site. This conclusion is consistent with the Callaway Energy Center Unit 1 and Unit 2 FSARs (Ameren Missouri, 2012a; Ameren Missouri, 2009). 3.2.9Combined Events The water level due to combined event precipitation flooding was determined, as recommended by Section 9.2.1.1 of ANSI/ANS-2.8-1992 (ANSI/ANS, 1992) and NUREG/CR-7046 guidance (NRC, 2011). The combined events analysis was based on precipitation flooding due to the inland location of the Callaway Energy Center Site. The aforementioned guidance recommends three different alternatives consisting of a combination of events. The Callaway Energy Center Site is located on a plateau at an elevation of 840 ft, which is approximately 325 ft above the flood plain of the Missouri River (Ameren Missouri, 2012a). Because the maximum or 100-year snowpack coincident with the PMF will still not flood the Site, the following combined events were evaluated step by step: Mean monthly (base) flow Median Soil Moisture Antecedent (or subsequent) rain: the lesser of 1) rainfall equal to 40 percent of the PMP, and 2) a 500-year rainfall PMP Waves induced by two-year wind speed applied along the critical direction The FSAR for Callaway Energy Center Unit 1 (Ameren Missouri, 2012a) did not perform a combined events analysis. The mean monthly base flow for Auxvasse Creek was obtained from USGS gauge 06927240. The highest of the average monthly flows were used as the base flow Flood Hazard Reevaluation Report 27124939/13 Rev. 0 (February 6, 2013)for conservatism. The base flow measurements from the USGS gauge were adjusted to each subbasin of Auxvasse Creek based on the gauge area and subbasin area. The adjusted base flows

were then utilized in the HEC-HMS model for Auxvasse Creek, which is discussed in Section 3.2.2.2.The 72-hour, 5-minute interval PMP hyetograph for Auxvasse Creek calculated using HMR 52 and discussed in Section 3.2.2.1 was utilized. Antecedent rain equal to 40 percent of the PMP event for 72-hours followed by a PMP event for 72-hours (6-day, 5-minute incremental PMP) was used as input into the HEC-HMS models for Auxvasse Creek, along with the adjusted base flows. The HEC-HMS models were run for the following scenarios as per the HHA method for combined events flooding (Figure 3-13). Scenario 1: No SCS Curve Number loss, no rainfall-to-runoff transformation, no routing through the channels - Most conservative case. Coincides with Scenario 1 presented in Section 3.2.2.2

. Scenario 2: No SCS Curve Number loss, includes Clark Unit Hydrograph transformation, no routing through the channels. Coincides with Scenario 2

presented in Section 3.2.2.2

. Scenario 3: No SCS Curve Number loss, includes Clark Unit Hydrograph transformation, include routing through the channels. Coincides with Scenario 3 presented in Section 3.2.2.2

. Scenario 4: Includes loss, Clark Unit Hydrograph transformation and routing through the channels - Existing conditions. Coincides with Scenario 4 presented in Section 3.2.2.2

. Scenario 5: Includes loss, Clark Unit Hydrograph transformation and routing through the channels - Projected conditions with an assumed 5 percent increase in percent impervious area for each subbasin. Coincides with Scenario 5 presented in Section 3.2.2.2

.The PMF values determined using the approach described above were input into the HEC-RAS models for Auxvasse Creek, with the other inputs and parameters (discussed in Section 3.2.2.3

)remaining the same. These scenarios also included the combined events as described earlier in this section. The maximum predicted water surface elevations due to combined events flooding for Scenarios 1 through 5 in Auxvasse Creek, are 772.76, 717.56, 710.02, 709.86, and 709.92 ft, respectively.

The FSAR for Callaway Energy Center Unit 1 (Ameren Missouri, 2012a) did not evaluate Flood Hazard Reevaluation Report 28124939/13 Rev. 0 (February 6, 2013)flooding due to combined events. Thus, a comparison of the reevaluated results to the results of the FSAR for Callaway Energy Center Unit 1 is not possible. 3.2.9.1Wind Waves and Run-up Coincident with Combined Events Flooding The reevaluated flood levels due to combined events flooding as presented in Section 3.2.9

,results in an elevation difference between predicted water levels in streams in the Site vicinity and the Site grade elevation of greater than 100 ft. As such wind waves and run-up coincident with combined events will not affect the Site and no further analysis is necessary.

Flood Hazard Reevaluation Report 29124939/13 Rev. 0 (February 6, 2013)4.0COMPARISON OF CURRENT AND REEVALUATED PREDICTED FLOOD LEVELS Section 4.0 has been prepared in response to Requested Information Item 1.c. of NRC Recommendation 2.1 (NRC, 2012a).4.1COMPARISON OF CURRENT AND R EEVALUATED F LOOD CAUSING MECHANISMSThe flood causing mechanisms evaluated under the current design basis are local intense precipitation, river flooding, including wave run-up at the Site and dam failure flooding, storm surge and seiche flooding, tsunami flooding, ice flooding, and channel diversion flooding (Ameren Missouri, 2012a). Flood causing mechanisms considered under the flooding reevaluation include local intense precipitation, river flooding, dam failure flooding, storm surge and seiche flooding, tsunami flooding, ice flooding, channel diversion flooding, and combined

events flooding. The primary difference between the current and reevaluated flood causing mechanisms are that water levels were not determined for combined events under the current licensing basis.

Additionally, dam failure flooding under the current licensing basis reports the maximum water level only on the Missouri River and not on Auxvasse Creek near the Site (Ameren Missouri, 2012a). The potential for storm surge and seiche flooding, tsunami flooding, ice flooding, and channel diversion flooding is qualitatively dismissed under both the current design basis (Ameren Missouri, 2012a) and reevaluated analyses. 4.2ASSESSMENT OF THE CURRENT D ESIGN BASIS F LOOD ELEVATIONS TO THE REEVALUATED FLOOD ELEVATIONS The current design basis, as presented in the FSAR for Callaway Energy Center Unit 1 indicates that all safety-related structures, except the UHS Retention Pond, are not subject to flooding, wave action, or wave run-up and do not require flood or wave protection (Ameren Missouri, 2012a). The UHS retention pond is the only safety-related structure that is subject to wind wave activity and wave run-up. The UHS retention pond has relatively short dimensions with riprap-covered side slopes, therefore, the wind wave activity does not represent a major concern. The wave run-up is also not a major concern due to the maximum wave run-up reaching an elevation

of 838.3 ft, which is below the Site grade elevation. The Callaway Energy Center grade is at elevation 840 ft, while the peak water level is at 548 ft for the PMF on the Missouri River Flood Hazard Reevaluation Report 30124939/13 Rev. 0 (February 6, 2013)(Ameren Missouri, 2012a). As such, design basis flooding on the Missouri River does not pose a risk to the Callaway Energy Center Site. A list of Callaway Energy Center licensed water levels and corresponding flooding mechanisms can be found in Table 2-4.All reevaluated flood levels for each individual flood causing mechanism are discussed in Section 3.0. A comparison of all of the current design basis flooding elevations and each of the reevaluated flood elevations for each flood causing mechanism presented in Attachment 1 to

NRC Recommendation 2.1 (NRC, 2012a) is provided in Table 3-5.Although the reevaluated flood levels for river flooding do not exceed the plant grade or that of the SSCs, they do, however, differ from the current design basis (Table 3-5). However, the reevaluated water level for river flooding is determined for Auxvasse Creek and is not directly comparable to the current design basis water level, which is reported on the Missouri River. 4.3S UPPORTING DOCUMENTATION RIZZO has prepared 18 separate calculation briefs in support of the flooding hazard reevaluation at Callaway Energy Center on which the reevaluated flood levels are based. Additionally, the Post Fukushima Flooding Walkdown Report for Callaway Energy Center (Ameren Missouri, 2012b) provides further information regarding the design basis flood hazard levels, as well as flooding protection and mitigation features. 4.3.1Technical Justification of the Flood Hazard Analysis All flooding analyses described in this Report have been undertaken with consideration to and implementation of current techniques, software, and methods used in present-day standard engineering practice to develop the flood hazard. The technical basis for, and key assumptions utilized in the determination of the reevaluated flooding levels for each flood causing mechanism, are discussed individually in Section 3.0

.4.3.2Technical Justification by the Walkdown Results With respect to the implementation and conclusions of the flooding hazard reevaluation, there are a few primary results from the Post Fukushima Flooding Walkdown Report for Callaway Energy Center (Ameren Missouri, 2012b) that have been taken into consideration.

Flood Hazard Reevaluation Report 31124939/13 Rev. 0 (February 6, 2013)"-(T)he walkdown visual inspection has verified that the Callaway Site permanent safety-related SSCs are acceptable, not degraded, and capable of performing their design function as credited in the current licensing basis" and "(t)he reviews determined that Callaway Site flood protection features would be capable of performing their intended flood protection function if subjected to a design basis flooding hazard" (Ameren Missouri, 2012b). The Post Fukushima Flooding Walkdown Report for Callaway Energy Center (Ameren Missouri, 2012b), also states that "(t)here is reasonable assurance that the flood protection features are available, functional, and capable of performing their specified functions as set forth

in the current licensing basis." Also, "(t)he Callaway external flood protection features are effective and able to perform their intended flood protection function when subject to a design basis external flooding hazard" (Ameren Missouri, 2012b). The reevaluated determination of runoff due to local intense PMP at the Callaway Energy Center Site, as described in Section 3.2.1, assumed that all hydraulic structures were blocked, including (initially) the VBS openings. Thus, no allowance is given for water drained by these facilities which conservatively maximizes the estimation of runoff or peak discharges at the Site.

However, when determining the water level due to local intense precipitation, the calculated

peak discharges are routed through natural drainage paths at the Site.

4.4CONCLUSION

SThe reevaluated water levels associated with the most refined analysis for each flood causing mechanism do not exceed the elevations of SSCs at the Callaway Energy Center Site. A comparison of all of the current design basis flooding elevations and each of the reevaluated flood elevations for each flood causing mechanism is provided in Table 3-5. It has been determined that the current design basis flood levels do not bound the reevaluated hazards for river flooding. However, the reevaluated water level which is reported on Auxvasse Creek is not directly comparable to the current design basis which is reported on the Missouri River. It should be noted that some of the mechanisms considered in the reevaluation were not part of the original design basis and so direct comparisons may not be practicable in some cases (Table 3-5).

Flood Hazard Reevaluation Report 32124939/13 Rev. 0 (February 6, 2013)5.0INTERIM EVALUATION AND ACTIONS Section 5.0 has been prepared in response to Requested Information Item 1.d. of NRC Recommendation 2.1 (NRC, 2012a).5.1EVALUATION OF THE IMPACT OF THE REEVALUATED FLOOD LEVELS ON SSC SThe reevaluated flooding levels due to all potential flood causing mechanisms, as presented in Section 3.0, do not exceed the elevations of SSCs at the Callaway Energy Center Site.5.2A CTIONS TAKEN TO A DDRESS HIGHER FLOODING HAZARDSRequested Information Item 1.d. of NRC Recommendation 2.1 (NRC, 2012a) specifies that the flooding reevaluation contain an interim evaluation and actions taken or planned to address any higher flooding hazards relative to the design basis, prior to completion of the integrated assessment, if necessary. The Post Fukushima Flooding Walkdown Report for Callaway Energy Center (Ameren Missouri, 2012b) states that "-the walkdown visual inspection has verified that the Callaway Site permanent safety-related SSCs are acceptable, not degraded, and capable of performing their design function as credited in the current licensing basis." Furthermore, "(t)he reviews determined Callaway Site flood protection features would be capable of performing their intended flood protection function if subjected to a design basis flooding hazard" (Ameren

Missouri, 2012b). Lastly, "(t)here are no other planned or newly installed flood protection systems or flood mitigation measures to further enhance the external flood protection at the

Callaway Site."

Flood Hazard Reevaluation Report 33124939/13 Rev. 0 (February 6, 2013)6.0ADDITIONAL ACTIONS Section 6.0 has been prepared in response to Requested Information Item 1.e. of NRC Recommendation 2.1 (NRC, 2012a).At this time, there are no additional actions beyond Requested Information Item 1.d. of NRC Recommendation 2.1 (NRC, 2012a) (Section 5.0)which have been taken or are planned to address flooding hazards at the Callaway Energy Center.Per the guidance for performing the integrated assessment for external flooding (NRC, 2012b), addressees are requested to perform an integrated assessment if the current design basis flood hazard does not bound the reevaluated flood hazard for all mechanisms. Furthermore, "The integrated assessment will evaluate the total plant response to the flood hazard, considering multiple and diverse capabilities such as physical barriers, temporary protective measures, and

operations procedures (NRC, 2012b)."

Flood Hazard Reevaluation Report 34124939/13 Rev. 0 (February 6, 2013)

7.0REFERENCES

Ameren Missouri, 2009, "Final Safety Analysis Report (FSAR), Callaway Energy Center Unit 2," Revision 2, 2009. Ameren Missouri, 2012a,"Final Safety Analysis Report (FSAR), Callaway Energy Center Unit 1," Revision OL-19a, July 2012. Ameren Missouri, 2012b, "Post Fukushima Flooding Walkdown Report for Callaway Energy Center," PEUS-WR-12-4, Revision 1, November 2012. American National Standards Institute/American Nuclear Society (ANSI/ANS), 1992, "Determining Design Basis Flooding at Power Reactor Sites," ANSI/ANS-2.8-1992, La Grange

Park, IL, 1992. Daly, S.F., 1996, "Evaluation of Potential Frazil Ice Blockage of the Essential Service Water Pump House at the Callaway Nuclear Plant," United States Army Cold Regions Research and

Engineering Laboratory, Hanover, NH, August 1996. National Atlas, 2012, "Glacial Limits," NationalAtlas.gov, Website: http://www.nationalatlas.gov/articles/geology/a_glacial.html , date accessed: 29 November 2012. National Climatic Data Center (NCDC), "Columbia Regional Airport Temperature Data,"

Website"http://www.1.ncdc.noaa.gov/pub/orders/102092.csv , data accessed: 30 October 2012.

Natural Resources Conservation Services (NRCS), 2010, "National Engineering Handbook,"

Chapter 15, May 2010. National Weather Service (NWS), 1978, "Hydrometeorological Report No. 51 (HMR No. 51):Probable Maximum Precipitation Estimates, United States East of the 105th Meridian," June

1978.National Weather Service (NWS), 1982, "Hydrometeorological Report No. 52 (HMR No. 52):Application of Probable Maximum Precipitation Estimates - United States East of the 105 th Meridian," August 1982.

Flood Hazard Reevaluation Report 35124939/13 Rev. 0 (February 6, 2013)Nuclear Regulatory Commission (NRC), 2007, "Combined License Applications for Nuclear Power Plants," Regulatory Guide 1.206, Washington D.C., June 2007. Nuclear Regulatory Commission (NRC), 2008, "Tsunami Hazard Assessment at Nuclear Power Plant Sites in the United States of America," NUREG/CR-6966, PNNL-17397, NRC Job Code J3301, Washington, DC, August 2008. 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, NRC Job Code N6575, Washington DC, November 2011. Nuclear Regulatory Commission (NRC), 2012a, "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," Washington

DC, March 12, 2012. Nuclear Regulatory Commission (NRC), 2012b, "Guidance for Performing the Integrated Assessment for External Flooding," Interim Staff Guidance, Revision 0, JLD-ISG-2012-05, November 20, 2012. Spooner, J., 2000, "The evolution of the Lower Missouri River: A Discussion of the Geology and a Proposal for Research at Lisbon Bottom," Open-File Report 01-176, 2000. United States Army Corps of Engineers (USACE), 2004, "Ice Engineering, Method to Estimate

River Thickness Based on Meteorological Data," June 2004. United States Army Corps of Engineers (USACE), 2008, "Coastal Engineering Manual," EM 1110-2-1100.United States Army Corps of Engineers (USACE), 2010, Hydrologic Engineering Center (HEC), HEC-HMS 3.5 Computer Program Build 1417, release date: August 2010. United States Army Corps of Engineers (USACE), 2012, "Ice Jams Database, Total Number of Events by River for the State of MO," Website: http://rsgisias.crrel.usace.army.mil/icejam/, date accessed, 18 November 2012.

Flood Hazard Reevaluation Report 36124939/13 Rev. 0 (February 6, 2013)United States Geological Survey (USGS), 1998, "Lower Missouri River Ecosystem Initiative," Final Report 1994 - 1998, Columbia, Missouri, December 1998. United States Geological Survey (USGS), 2012a, "Streamflow Measurements Data for USGS 06926500 Osage River Near St. Thomas, MO," United States Geological Survey (USGS),

Website:http://waterdata.usgs.gov/nwis/measurements/?site_no=06926500&agency_cd=USGS

, date accessed, 10 November, 2012. United States Geological Survey (USGS), 2012b, "Streamflow Measurements Data for USGS 06933500 Gasconade River at Jerome, MO," United States Geological Survey (USGS), Website:

http://waterdata.usgs.gov/nwis/measurements/?site_no=06933500&agency_cd=USGS , date accessed, 10 November, 2012.

Flood Hazard Reevaluation Report 124939/13 Rev. 0 (February 6, 2013)

TABLES Flood Hazard Reevaluation Report 38124939/13 Rev. 0 (February 6, 2013) TABLE 2-1 HISTORIC FLOODS NEAR THE SITE RIVER/STREAM D ATE G AUGING STATION MAX W ATER LEVEL (ft)DISCHARGE (cfs)Missouri River July 29, 1993 06909000 602.5 755,000 Osage River May 20, 1943 06926500 **571.73 216,000 *Gasconade River January 6, 1897*N/A *N/A 120,000 Gasconade River April 15, 1945 06933500 **685.34 101,000 LT-1 Notes:

• The 1897 flood occurred outside of the period of record, discharge was estimated near Jerome, Missouri. ** Water Levels taken from USGS Streamflow Measurements Data

References:

Ameren Missouri, 2012, "Final Safety Analysis Report (FSAR), Callaway Energy Center Unit 1,"

Revision OL-19a, 2012. Ameren Missouri, 2009, "Final Safety Analysis Report (FSAR), Callaway Energy Center Unit 2," Revision 2, 2009. USGS, 2012a, "Streamflow Measurements Data for USGS 06926500 Osage River Near St. Thomas, MO," United States Geological Survey (USGS), Website:

http://waterdata.usgs.gov/nwis/measurements/?site_no=06926500&agency_cd=USGS

, date accessed, 10 November, 2012. USGS, 2012b, "Streamflow Measurements Data for USGS 06933500 Gasconade River at Jerome, MO," United States Geological Survey (USGS), Website:

http://waterdata.usgs.gov/nwis/measurements/?site_no=06933500&agency_cd=USGS

, date accessed, 10 November, 2012.

Flood Hazard Reevaluation Report 39124939/13 Rev. 0 (February 6, 2013) TABLE 2-2 LIST OF SAFETY-RELATED STRUCTURES, SYSTEMS, AND COMPONENTS AND THEIR ELEVATIONS SSC E LEVATION (ft)Reactor Building 840.5Control Building 840.5Auxilliary Building 840.5Diesel Generator Building 840.5Fuel Building 840.5Essential Service Water Pump House 840.5Ultimate Heat Sink Retention Pond 840.0Ultimate Heat Sink Cooling Tower 840.5Refueling Water Storage Tank *835.5Essential Service Water System Pipes **Variable LT-2 Notes:

• Elevation of bottom slab is 835.5 ft. ** When not protected by concrete, all Essential Service Water System pipes are buried a minimum depth of 4.5 ft. All Essential Service Water System electrical duct banks are reinforced concrete structures which are buried a minimum depth of 3.5 ft.

Reference:

Ameren Missouri, 2012, "Final Safety Analysis Report (FSAR) Callaway Energy Center Unit 1," Revision OL-19a, 2012.

Flood Hazard Reevaluation Report 40124939/13 Rev. 0 (February 6, 2013) TABLE 2-3 DESIGN PARAMETERS IN THE LICENSE DOCUMENT DESIGN PARAMETER V ALUE Grade Level (SSCs except UHS, Refueling Water Storage Tank, and ESWS Pipes) 840.5 ft Probable Maximum Precipitation 35 in. (48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> PMP) Maximum Water Level at the Site Including Wave Run-up 551 ft Cooling Water Flow Rate 38,000 gpm Elevation of Intake Structure 525 ft Annual Mean Temperature 55.6 °F LT-3

Reference:

Ameren Missouri, 2012

,"Final Safety Analysis Report (FSAR) Callaway Energy Center Unit 1," Revision OL-19a, 2012.

Flood Hazard Reevaluation Report 41124939/13 Rev. 0 (February 6, 2013) TABLE 2-4 LICENSED WATER LEVELS DUE TO ALL FLOODING MECHANISMS FLOODING MECHANISM W ATER L EVEL (ft)Local Intense Precipitation The PMP Calculations Document that Ponding Elevations will be less than 840.5 838.3 Including Wave Run-up in the UHS retention pondRiver Flooding 537 / 548

• Dam Failure Flooding 551Storm Surge and Seiche Flooding N/A Tsunami Flooding N/AIce Flooding N/AChannel Diversion Flooding N/ACombined Events N/A LT-4 Note:

• The FSAR for Callaway Energy Center Unit 1 reports 537 ft as the Standard Project Flood (SPF) and 548 ft as the Probable Maximum Flood (PMF).

Reference:

Ameren Missouri, 2012

,"Final Safety Analysis Report (FSAR) Callaway Energy Center Unit 1," Revision OL-19a, 2012.

Flood Hazard Reevaluation Report 42124939/13 Rev. 0 (February 6, 2013)TABLE 3-1 SITE DRAINAGE AREA DETAILS DRAINAGE S UB BASIN A REA (mi 2)R AINFALL I NTENSITYI(inch/hr)

P EAK R UNOFF Q(cfs)(RATIONAL METHOD)P EAK R UNOFF Q(cfs)(HEC-HMSMODEL , SCENARIO 5*)10 0.076 45.01 2196 1019 12 0.043 30.78 854 444 13 0.007 47.16 220 97 17 0.015 46.83 440 196 18 0.002 47.16 48 21 19 0.005 47.16 140 62 20 0.025 40.36 651 332 21 0.006 47.16 172 76 22 0.024 47.16 721 320 24 0.001 47.16 44 20 25 0.030 45.21 880 407 26 0.004 47.16 119 53 30 0.006 47.16 168 75 31 0.005 47.16 154 68 33 0.005 41.87 131 65 34 0.001 47.16 44 20 35 0.006 47.16 177 78 37 0.003 47.16 102 45 41 0.012 37.39 279 149 42 0.010 40.43 266 135 43 0.046 35.84 1059 544 47 0.004 47.16 126 56 48 0.013 44.98 368 171 49 0.004 47.16 134 59 50 0.002 47.16 52 23 51 0.002 47.16 48 21 52 0.001 47.16 16 7 53 0.003 47.16 84 37 54 0.002 47.16 48 21 55 0.001 47.16 42 19 56 0.007 45.25 216 100 58 0.009 47.16 266 118 1091 0.002 47.16 72 32 1092 0.003 47.16 89 40 1093 0.003 47.16 91 40 1094 0.029 36.65 679 355 1095 0.006 47.16 184 82 TABLE 3-1 SITE DRAINAGE AREA DETAILS (CONTINUED)Flood Hazard Reevaluation Report 43124939/13 Rev. 0 (February 6, 2013)

DRAINAGE S UB BASIN A REA (mi 2)R AINFALL I NTENSITYI(inch/hr)

P EAK R UNOFF Q(cfs)(RATIONAL METHOD)P EAK R UNOFF Q(cfs)(HEC-HMSMODEL , SCENARIO 5*)1098 0.008 46.47 239 107 1099 0.010 47.16 291 129 1101 0.001 47.16 43 19 1102 0.005 47.12 152 67 1112 0.022 41.39 580 288 1113 0.019 44.18 551 260 1114 0.041 40.06 1060 545 1130 0.004 47.16 109 48 1131 0.005 45.30 148 68 1132 0.001 47.16 39 17 1133 0.006 35.03 142 72 1134 0.002 47.16 68 30 1135 0.002 47.16 46 20 1136 0.003 45.53 99 46 LT-5 Note:

• Peak runoff estimated using Snyder Runoff Transformation Method and the peak runoff coefficient set to 0.4 and a shape factor of 0.4.

.

Flood Hazard Reevaluation Report 44124939/13 Rev. 0 (February 6, 2013) TABLE 3-2 REEVALUATED FLOOD LEVELS FLOODING MECHANISM W ATER L EVEL (ft)Local Intense Precipitation 840.17 NAVD88 (Scenario 5) 838.04 (Scenario 5 + Wave Run-up in the UHS retention pond)

River Flooding 709.05 (Scenario 4, Existing Conditions) Dam Failure Flooding N/A*Storm Surge and Seiche Flooding N/ATsunami Flooding N/AIce Flooding N/A Channel Diversion Flooding N/ACombined Events Flooding 709.86 (Scenario 4, Existing Conditions)

LT-7 Note:

• The dam failure analysis determined that flood levels for the PMP and concurrent failure of all upstream dams would be more than 30 ft below plant grade. Also, it was determined that even if flood waters due to dam failure reached plant grade, the combined storage of all upstream dams would not flood the SSCs at the Site.

Flood Hazard Reevaluation Report 45124939/13 Rev. 0 (February 6, 2013) TABLE 3-3 COMPARISON OF CURRENT DESIGN BASIS AND FLOODING REEVALUATION ASSUMPTIONS ASSUMPTIONS REEVALUATED HAZARDS CURRENT DESIGN BASISProbable Maximum Precipitation (PMP) Calculation HMR 52 HMR 33 Station used for Wind Speed AnalysisColumbia, Missouri Columbia, Missouri PMF Estimation Clark Unit Hydrograph Method No PMF analysis SCS LossesCalculated in reevaluation Not Modeled Base FlowNone Not Modeled PMP3 day PMP 2 day PMP RoutingMuskingum Cunge 8-point Method Not Modeled Transform MethodClark Unit Hydrograph Not Modeled Transformation LossesNone Not Modeled LT-10

Reference:

Ameren Missouri, 2012

,"Final Safety Analysis Report (FSAR) Callaway Energy Center Unit 1,"

Revision OL-19a, 2012.

Flood Hazard Reevaluation Report 46124939/13 Rev. 0 (February 6, 2013) TABLE 3-4 COMPARISON OF CURRENT DESIGN BASIS AND FLOODING REEVALUATION ANALYTICAL INPUTS ASSUMPTIONS REEVALUATED HAZARDS CURRENT DESIGN BASIS6-hour PMP 27.64 inches 25.4 inches Maximum Sustained Wind (MSW) Return Period 2 10 50 100 MSW 40.41 52.43 61.01 64.23 MSW 42.92 54.47 59.77 69.51Subbasin Delineation63 subbasins 4 subbasins Auxvasse Creek Watershed Area347.2 square miles 371.7 square miles 72-hour PMP28.63 inches Not Presented Mannings roughness coefficient for channel and overbanks in the Auxvasse Creek Watershed.(n channel) 0.035, (n bank) 0.1 Not Calculated for Auxvasse CreekPeak outflow from PMF analysis in Auxvasse Creek Watershed 262,124.3 cfs Not Calculated for Auxvasse Creek Highest Average Monthly Base Flow 718.72 cfs Not Calculated for Auxvasse CreekWater surface elevations due to PMF709.09 ft Auxvasse Creek N/A, Modeled only on the Missouri River 675.02 ft Logan Creek 577.51 ft Mud Creek LT-11

Reference:

Ameren Missouri, 2012

,"Final Safety Analysis Report (FSAR) Callaway Energy Center Unit 1,"

Revision OL-19a, 2012.

Flood Hazard Reevaluation Report 47124939/13 Rev. 0 (February 6, 2013) TABLE 3-5 COMPARISON OF CURRENT AND REEVALUATED FLOOD LEVELS FLOODING MECHANISM REEVALUATED WATER LEVEL (ft)CURRENT LICENSING B ASIS W ATER L EVEL (ft)Local Intense Precipitation 840.17 NAVD88 (Scenario 5) The PMP Calculations Document that Ponding Elevations will be less than 840.5838.04 (Scenario 5 + Wave Run-up in the UHS retention pond)838.3 Including Wave Run-up in the UHS retention pond River Flooding 709.05 (Scenario 4, Existing Conditions) 537 / 548

• Dam Failure Flooding N/A**551Storm Surge and Seiche Flooding N/A N/A Tsunami Flooding N/A N/A Ice Flooding N/A N/A Channel Diversion Flooding N/A N/A Combined Events Flooding 709.86 (Scenario 4, Existing Conditions)

N/A LT-8 Notes:

• The FSAR for Callaway Energy Center Unit 1 reports 537 ft as the Standard Project Flood (SPF) and 548 ft as the Probable Maximum Flood (PMF). The FSAR reports water levels on the Missouri River whereas the reevaluated water level is on Auxvasse Creek. ** The dam failure analysis determined that flood levels for the PMP and concurrent failure of all upstream dams would be more than 30 ft below plant grade. Also, it was determined that even if flood waters due to dam failure reached plant grade, the combined storage of all upstream dams would not flood the SSCs at the Site. The FSAR for Callaway Energy Center Unit 1 reports 551 ft as the water level on the Missouri River and does not present a value for Auxvasse Creek near the Site.

Reference:

Ameren Missouri, 2012

,"Final Safety Analysis Report (FSAR) Callaway Energy Center Unit 1,"

Revision OL-19a, 2012.

Flood Hazard Reevaluation Report 48124939/13 Rev. 0 (February 6, 2013)

FIGURES