ML17164A308

Staff Assessment of Response to 10 CFR 50.54(F) Information Request - Flood-Causing Mechanism Reevaluation (CAC Nos. MF6096 and MF6097)

ML17164A308
Person / Time
Site:	Cook
Issue date:	06/15/2017
From:	Tekia Govan Japan Lessons-Learned Division
To:	Gebbie J Nuclear Generation Group
Govan T, NRR/JLD, 415-6197
References
CAC MF6096, CAC MF6097
Download: ML17164A308 (32)

Text

J. Gebbie If you have any questions, please contact me at (301) 415-6197 or e-mail at Tekia.Govan@nrc.gov.

Tekia Govan , Project Manager Hazards Management Branch Japan Lessons-Learned Division Office of Nuclear Reactor Regulation Docket Nos. 50-315 and 50-316

Enclosure:

Staff Assessment Related to the Flood Hazard Reevaluation Report for D.C. Cook cc w/encl: Distribution via Listserv

STAFF ASSESSMENT BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO FLOODING HAZARD REEVALUATION REPORT NEAR-TERM TASK FORCE RECOMMENDATION 2.1 DONALD C. COOK NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS. 50-315 AND 50-316

1.0 INTRODUCTION

By letter dated March 12, 2012 (NRC, 2012a), the U.S. Nuclear Regulatory Commission (NRC) issued a request for information to all power reactor licensees and holders of construction permits in active or deferred status, pursuant to Title 1O of the Code of Federal Regulations (10 CFR), Section 50.54(f) (hereafter referred to as the "50.54(f) letter). The request was issued in connection with implementing lessons-learned from the 2011 accident at the Fukushima Dai-ichi nuclear power plant, as documented in the NRC's Near-Term Task Force (NTTF) report (NRC, 2011 b). Recommendation 2.1 in that document recommended that the NRC staff issue orders to all licensees to reevaluate seismic and flooding hazards for their sites against current NRC requirements and guidance. Subsequent staff requirements memoranda associated with SECY-11-0124 (NRC, 2011c) and SECY-11-0137 (NRC, 2011d) directed the NRC staff to issue a request for information to licensees pursuant to 10 CFR 50.54(f) to address this recommendation . to the 50.54(f) letter (NRC, 2012a) requested that licensees reevaluate flood hazards for their respective sites using present-day methods and regulatory guidance used by the NRC staff when reviewing applications for early site permits (ESPs) and combined licenses (COLs). The required response section of Enclosure 2 specified that NRC staff would provide a prioritization plan indicating Flooding Hazard Reevaluation Report (FHRR) deadlines for individual plants. On May 11 , 2012, the staff issued its prioritization of the FHRRs (NRC, 2012c).

By letter dated March 6, 2015 (Indiana Michigan Power Company, 2015b) , Indiana Michigan Power Company (the licensee) , provided the FHRR for Donald C. Cook, Units 1 and 2 (D.C.

Cook) . The NRC staff conducted a site audit with the licensee on July 15, 2015. The NRC staff issued an audit report summarizing additional information obtained during this audit (NRC, 2015c). The licensee provided a supplement to the D.C. Cook FHRR dated November 10, 2016 (IMP, 2016b).

By letter dated December 4, 2015, the NRC staff issued an interim staff response (ISR) letter to the licensee (NRC, 2015b). The purpose of the ISR letter is to provide the flood hazard information suitable for the assessment of mitigating strategies developed in response to Order EA-12-049 (NRC, 2012b) and the additional assessments associated with Enclosure 2 of the 50.54 (f) letter. The ISR letter also made reference to this staff assessment, which documents NRC staff's basis and conclusions. The flood hazard mechanism values presented in the ISR letter's enclosures match the values in this staff assessment without change or alteration .

Enclosure

As mentioned in the ISR letter, the reevaluated flood hazard results for the local intense precipitation (LIP) is not bounded by the plant's current design basis (COB) hazard. Consistent with the 50.54(f) letter and amended by the process outlined in COMSECY-15-0019 and Japan Lessons-Learned Division (JLD) Interim Staff Guidance (ISG) JLD-ISG-2016-01 , Revision O (NRG, 2015a and NRG, 2016b) , the NRG staff anticipates that the licensee will perform a focused evaluation for LIP and associated site drainage that assesses the impact of the LIP hazard on the site and evaluates and implements any necessary programmatic, procedural , or plant modifications to address this hazard exceedance.

Additionally, for any reevaluated flood hazards that are not bounded by the plant's COB hazard, the licensee is expected to develop flood event duration (FED) parameters and associated effects (AE) parameters. These parameters will be used to conduct the mitigating strategies assessment (MSA) and focused evaluations or revised integrated assessments.

2.0 REGULATORY BACKGROUND 2.1 Applicable Regulatory Requirements As stated above, Enclosure 2 to the 50.54(f) letter (NRG, 2012a) requested that licensees reevaluate flood hazards for their sites using present-day methods and regulatory guidance used by the NRG staff when reviewing applications for ESPs and COLs. This section of the staff assessment describes present-day regulatory requirements that are applicable to the FHRR .

Sections 50.34(a)(1), (a)(3) , (a)(4) , (b)(1) , (b)(2) , and (b)(4) of 10 CFR describe the required content of the preliminary and final safety analysis reports, including a discussion of the facility site with a particular emphasis on the site evaluation factors identified in 10 CFR Part 100. The licensee should provide any pertinent information identified or developed since the submittal of the preliminary safety analysis report in the final safety analysis report.

General Design Criterion 2 in Appendix A of 10 CFR Part 50 states that structures, systems, and components (SSCs) important to safety at nuclear power plants must be designed to withstand the effects of natural phenomena, such as earthquakes, tornados , hurricanes, floods, tsunamis, and seiches without the loss of capability to perform their intended safety functions.

The design bases for these SSCs are to reflect appropriate consideration of the most severe of the natural phenomena that have been historically reported for the site and surrounding area.

The design bases are also to have sufficient margin to account for the limited accuracy, quantity, and period of time in which the historical data have been accumulated.

Section 50.2 of 10 CFR defines the design-basis as the information that identifies the specific functions that an SSC of a facility must perform, and the specific values or ranges of values chosen for controlling parameters as reference bounds for design which each licensee is required to develop and maintain. These values may be (a) restraints derived from generally accepted "state of the art" practices for achieving functional goals, or (b) requirements derived from analysis (based on calculation , experiments, or both) of the effects of a postulated accident for which an SSC must meet its functional goals.

Section 54.3 of 1 O CFR defines the current licensing basis (CLB) as "the set of NRC requirements applicable to a specific plant and a licensee's written commitments for ensuring

compliance with and operation within applicable NRC requirements and the plant-specific design-basis (including all modifications and additions to such commitments over the life of the license) that are docketed and in effect." This includes 10 CFR Parts 2, 19, 20, 21 , 26, 30, 40, 50, 51 , 52, 54, 55, 70, 72, 73, 100 and appendices thereto; orders; license conditions ;

exemptions; and technical specifications, as well as the plant-specific design-basis information as documented in the most recent updated final safety analysis report (UFSAR). The licensee's commitments made in docketed licensing correspondence , which remain in effect, are also considered part of the CLB.

Present-day regulations for reactor site criteria (Subpart B to 10 CFR Part 100 for site applications on or after January 1O, 1997) state, in part, that the physical characteristics of the site must be evaluated and site parameters established such that potential threats from such physical characteristics will pose no undue risk to the type of facility proposed to be located at the site. Factors to be considered when evaluating sites include the nature and proximity of dams and other man-related hazards (1 O CFR 100.20(b)) and the physical characteristics of the site , including the hydrology (1 O CFR 100.21 (d)).

2.2 Enclosure 2 to the 50.54(f) Letter Section 50.54(f) of 10 CFR states that a licensee shall at any time before expiration of its license, upon request of the Commission, submit written statements, signed under oath or affirmation , to enable the Commission to determine whether or not the license should be modified, suspended, or revoked . The 50.54(f) letter (NRC, 2012a) requested , in part, that licensees reevaluate the flood-causing mechanisms tor their respective sites using present-day methodologies and regulatory guidance used by the NRC tor the ESP and COL reviews.

2.2.1 Flood-Causing Mechanisms to Enclosure 2 of the 50.54(f) letter discusses flood-causing mechanisms tor the licensee to address in its FHRR (NRC, 2012a). Table 2.2-1 lists the flood-causing mechanisms the licensee should consider and lists the corresponding Standard Review Plan (SRP) (NRC, 2007) section(s) and applicable ISG documents containing acceptance criteria and review procedures.

2.2.2 Associated Effects In reevaluating the flood-causing mechanisms, the "flood height and associated effects" should be considered. Guidance document JLD-ISG-2012-05 (NRC, 2012d) defines "flood height and associated effects" as the maximum stillwater surface elevation plus:

• Wind waves and runup effects;

• Hydrodynamic loading, including debris;

• Effects caused by sediment deposition and erosion;

• Concurrent site conditions, including adverse weather conditions ;

• Groundwater ingress; and

• Other pertinent factors .

2.2.3 Combined Effects Flood The worst flooding at a site that may result from a reasonable combination of individual flooding mechanisms is sometimes referred to as a "combined effects flood ." It should also be noted that for the purposes of this staff assessment, the terms "combined effects" and "combined events" are synonyms. Even if some or all of these individual flood-causing mechanisms are less severe than their worst-case occurrence, their combination may still exceed the most severe flooding effects from the worst-case occurrence of any single mechanism described in the 50.54(f) letter (see SAP Section 2.4.2, "Areas of Review" (NRC, 2007)). Attachment 1 of the 50.54(f) letter describes the "combined effect flood" as defined in American National Standards Institute/American Nuclear Society (ANSI/ANS) 2.8-1992 (ANSI/ANS, 1992), as follows:

For flood hazard associated with combined events, American Nuclear Society (ANS) 2.8-1992 provides guidance for combination of flood causing mechanisms for flood hazard at nuclear power reactor site's . In addition to those listed in the ANS guidance, additional plausible combined events should be considered on a site specific basis and should be based on the impacts of other flood causing mechanisms and the location of the site.

If two less severe mechanisms are plausibly combined per ANSl/ANS-2.8-1992 (ANSI/ANS, 1992), then the NRC staff will document and report the result as part of one of the hazard sections. An example of a situation where this may occur is flooding at a riverine site located where the river enters the ocean. For this site, storm surge and river flooding are plausible combined events and should be considered.

2.2.4 Flood Event Duration Flood event duration was defined in JLD-ISG-2012-05 (NRC, 2012d) as the length of time during which the flood event affects the site. It begins when conditions are met for entry into a flood procedure, or with notification of an impending flood (e.g. , a flood forecast or notification of dam failure) , and includes preparation for the flood . It continues during the period of inundation ,

and ends when water recedes from the site and the plant reaches a safe and stable state that can be maintained indefinitely. Figure 2.2-1 illustrates flood event duration.

2.3 Actions Following the FHRR For the sites where the reevaluated flood hazard is not bounded by the CDB flood hazard elevation for any flood-causing mechanisms, the 50.54(f) letter (NRC, 2012a) requests licensees and construction permit holders to:

• Submit an interim action plan with the FHRR documenting actions planned or already taken to address the reevaluated hazard; and

• Perform an integrated assessment to: (a) evaluate the effectiveness of the CDB (i.e.,

flood protection and mitigation systems); (b) identify plant-specific vulnerabilities ; and (c) assess the effectiveness of existing or planned systems and procedures for protecting against and mitigating consequences of flooding for the flood event duration .

If the reevaluated flood hazard is bounded by the CbB flood hazard for all flood-causing mechanisms at the site, licensees were not required to perform an integrated assessment.

COMSECY-15-0019 (NRC, 2015a) outlines a revised process for addressing cases in which the reevaluated flood hazard is not bounded by the plant's COB. The revised process describes an approach in which licensees with LIP hazards exceeding their COB flood will not be required to complete an integrated assessment, but instead will perform a focused evaluation. As part of the focused evaluation , licensees will assess the impact of the LIP hazard on their sites and then evaluate and implement any necessary programmatic, procedural, or plant modifications to address the hazard exceedance. For other flood hazard mechanisms that exceed the COB, licensees can assess the impact of these reevaluated hazards on their site by performing either a focused evaluation or a revised integrated assessment (NRC, 2015a and NRC, 2016b).

3.0 TECHNICAL EVALUATION

The NRC staff reviewed the information provided for the flood hazard reevaluation of D.C. Cook (IMP, 2015b). The licensee conducted the hazard reevaluation using present-day methodologies and regulatory guidance used by the NRC staff in connection with ESP and COL reviews .

To provide additional information in support of the summaries and conclusions in the D.C. Cook FHRR, the licensee made calculation packages available to the NRC staff via an electronic reading room . The NRC staff did not rely directly on these calculation packages in its review; they were found only to expand upon and clarify the information provided in the D.C. Cook FHRR , and so those calculation packages were not docketed or cited.

3.1 Site Information The 50.54(f) letter includes the SSCs important to safety in the scope of the hazard reevaluation. The licensee included pertinent data concerning these SSCs in the D.C. Cook FHRR. The NRC staff reviewed and summarized this information as follows in the sections below.

3.1 .1 Detailed Site Information The D.C. Cook FHRR (IMP, 2015b) described the site specific information related to the flood hazard evaluation. The D.C. Cook site is located on the southeastern bank of Lake Michigan in Berrien County, Ml, about 2 miles north of the town of Bridgman, Ml. The site consists of 650 acres with approximately 4,350 feet (ft) of lake-frontage.

The site grade and design-basis of features related to plant safety is elevation 594.6 ft National Geodetic Vertical Datum of 1929 (NGVD29). All elevations in this staff assessment are given with respect to the NGVD29. Table 3.1-1 provides the summary of controlling reevaluated flood-causing mechanisms, including associated effects, the licensee computed tp be higher than the powerblock elevation. The D.C. Cook FHRR states that the site is on a flat area above the Lake Michigan shoreline and at an elevation of 609 ft for most of the protected area. The site grade falls to 594 ft for the area west of the screen house and turbine building. The plant is flood protected from the maximum (monthly mean) high lake water level, but a design-basis

seiche event when the lake is at its maximum recorded level will cause flooding in the turbine building screen house.

3.1.2 Design-Basis Flood Hazards The COB flood levels are summarized by flood-causing mechanism in Table 3.1-1 of this staff assessment. The licensee presented CLB flood elevation information in the D.C. Cook FHRR, Table 4-1. The licensee stated that the only mechanism that has a COB is seiche. The licensee reported that all other mechanisms were not evaluated in terms of CLB flood elevations. The NRC staff reviewed the information provided and determined that sufficient information was provided to be responsive to Enclosure 2 of the 50.54(f) letter.

3.1.3 Flood-Related Changes to the Licensing Basis The licensee reported in the D.C. Cook FHRR that there are no flood related changes to the CLB. The NRC staff reviewed the information provided and determined that sufficient information was provided to be responsive to Enclosure 2 of the 50.54(f) letter.

3.1.4 Changes to the Watershed and Local Area The licensee reported in the D.C. Cook FHRR that there have been a number of new structures, security barriers, and area paving that have been added since the initial plant license. The D.C.

Cook FHRR, Table 2-1 , includes all of the specific areas and plant structures that may impact the site flooding analysis. The NRC staff reviewed the information provided and determined that sufficient information was provided to be responsive to Enclosure 2 of the 50.54(f) letter.

3.1.5 Current Licensing Basis Flood Protection and Pertinent Flood Mitigation Features The licensee reported that there are no changes in the CLB and COB. The licensee stated in the DC Cook FHRR that the site COB flood was based on a weather-driven seiche occurring on Lake Michigan with a maximum water height of 11 ft above record high lake level. This flood would result in water reaching an elevation of 594.6 ft NGVD29. In the D.C. Cook FHRR, Section 2.3, the licensee described the flood mitigation features for the safety-related buildings at the site. The NRC staff reviewed the information provided and determined that sufficient information was provided to be responsive to Enclosure 2 of the 50.54(f) letter.

3.1.6 Additional Site Details to Assess the Flood Hazard The licensee made available for review electronic copies of the input/output files used for a numerical model related to the analysis of LIP. The NRC staff reviewed that material and determined that sufficient information had been provided in response to Enclosure 2 of the 50.54(f) letter.

3.1.7 Results of Plant Walkdown Activities The 50.54(f) letter (NRC, 2012a) requested that licensees plan and perform plant walkdown activities to verify that current flood protection systems are available, functional , and implementable. Other requests described in the 50.54(f) letter asked the licensee to report any relevant information from the results of the plant walkdown activities (NRC, 2012a) .

By letter dated November 26, 2012 (IMP, 2012) , the licensee provided the requisite flood walkdown report for D.C. Cook. The NRC staff issued a staff assessment on June 18, 2014 (NRC, 2014), which documented its review of the flooding walkdown report and concluded that the licensee's implementation of flooding walkdown methodology met the intent of the 50.54(f) letter.

3.2 Local Intense Precipitation and Associated Site Drainage The licensee reported in the D.C. Cook FHRR that the reevaluated flood hazard for LIP and associated site drainage is based on a stillwater-surface elevation of 594.8 ft NGVD29. This flood-causing mechanism is not discussed in the licensee's COB for flooding related to LIP.

To reevaluate the hazards for the LIP event, the licensee used the two-dimensional (20) hydrodynamic computer model FL0-20 Pro, Build 14.11.09 (referred to hereafter as FL0-20).

The NRC staff confirmed this version of the model was applied during a D.C. Cook site audit (NRC, 2015c) . The computational boundary of the model was delineated based on the D.C.

Cook topographic data (IMP, 2015b). The licensee used the 6-hour (h) 1-square-mile (1-mi 2) site-specific LIP hyetograph as input to the FL0-20 model (IMP, 2015b).

The reevaluation of flood hazard for LIP is based on the 6-h, 1-mi2 site-specific probable maximum precipitation (ssPMP) of 20.2 in (IMP, 2015a; 2016a). The licensee created the front-end , 6-h distribution for the synthetic PMP hydrograph and used equal increments of rainfall for the remaining 5 hrs of the storm to obtain the 20.2 in of precipitation estimated using the site-specific PMP approach. The total rainfall for the 1-h rainfall is approximately 12.8 in.

NUREG/CR-7046 (NRC, 2011e) recommends the use of the 1-h, 1-mi2 PMP. However, as the 6-h , 1-mi2 ssPMP encompasses the 1-h, 1-mi2 PMP, the licensee used the 6-h storm as a conservative approach.

The licensee modeled the D.C. Cook site and its surrounding area using a 10-ft by 10-ft square FL0-20 grid over the 0.2 mi 2 contributing watershed with elevations from a combination of 2013 regional Light Detection and Ranging (LiDAR) maps. The boundary of the site includes all on-site buildings and was delineated based on the topography. The licensee assumed an overall conservative nature for the model such that all rainfall is converted directly to runoff and that all drainage routes (e.g. , culverts) are completely blocked. These assumptions are consistent with NUREG/CR-7046 (NRC, 2011e) . Rainwater infiltration into natural sands in the area (dune sand) was derived from U.S. Soil Conservation Service (SCS) information and no evaporation losses were considered (IMP, 2016b) .

Consistent with NUREG/CR-7046, the onsite storm drain system (yard drainage) is considered to be operational at 25-percent capacity. Buildings within the watershed are considered to be solid and impervious. Security barriers, consisting of both concrete jersey barriers and heavy steel fencing are considered pervious where they might block water from access to the site (upstream) and impervious where they might allow off site (downstream) to make the estimation of flood levels conservative. Rooftop drains are considered to be blocked with debris or otherwise overwhelmed and ineffective. Runoff from the building roofs is generally directed to adjacent ground surface cells with the FL0-20 model.

By visual assessment of the imagery, the licensee assigned a Manning's n coefficient of flow resistance for each land cover. The higher, more conservative values from the suggested

ranges provided in the FL0-2D reference manual (FL0-2D, n.d.) were used in the licensee's model. The licensee also noted that the lower n value is more reflective of the maintenance of the grass at the D.C. Cook site and that the overall conservativeness of the model would account for slight variation in roughness coefficients.

The licensee identified, based on general site and plant configuration and plant walkdown , 1O critical area locations where LIP runoff could impact SSCs important to safety of the plant as shown on Figure 3.2-1 . These 1O locations are identified to be locations of potential SSC vulnerability where predicted flood elevations exceed surveyed threshold elevations and have the potential to produce adverse conditions. Additional realistic or conservative assumptions used in the LIP modeling are:

• Watershed surfaces are assigned a realistic site-specific SCS Curve Number (CN) based on soil type, vegetation, and land use;

• Runoff from the rooftop of parapet style building roofs is allowed to flow to an internal storm drain within the building, then offsite not to adjacent ground surface cells;

• Security barriers on the upstream edges of the model are not considered to block incoming storm water and are omitted from the model;

• Jersey barriers on the downstream edges of the site are considered impervious;

• Delay barriers on the downstream edges of the protected area are assumed to be 50 percent porous;

• The D.C. Cook protected storm drain is considered to be operational at 25 percent capacity - consistent with NUREG/CR-7046, Appendix B.2, Case 2: "Fully Functional Site Grading and Partially Blocked Drainage Channels (NRC, 2011e)." The combined outfall section is adequate to convey inflow from all trench drains; and

• No evaporation losses were considered. Buildings within the watershed are considered to be solid and impervious.

In order to determine the significance of the use of a ssPMP on the estimated LIP flood hazard at the D.C. Cook site, the NRC staff independently evaluated the sensitivity of the licensee's FL0-2D model to that parameter using the value obtained alternatively from HMR 51 (NOAA, 1982). The HMR-based 1-hr PMP value was 17.5 in or about 27 percent larger than the licensee's ssPMP value of 12.8 in. Aside from changing the PMP value, no other changes were made to the licensee-provided model. A comparison of maximum water surface elevations at the same 1O monitoring locations to those reported by the licensee in the D.C. Cook FHRR revealed that the maximum differences in estimated water depths owing to the use of an HMR-derived PMP value was about 0.2 ft. In light of these small differences, the NRC staff concluded that the licensee's application of a ssPMP does not impact the maximum water-level estimates compared to those for the HMR-based flood levels, and that staff's review of the ssPMP values or methodology was not necessary for the purposes of the 50.54(f) letter.

The NRC staff reviewed details of the licensee's FL0-20 model implementation and determined that the approaches and assumptions were conservative and appropriate. The model output files reviewed by NRC staff did not report any errors related to model stability or mass balance.

Based on a confirmatory run of the licensee-provided FL0-20 model, the NRC staff determined that the licensee's conclusions, based on results produced by the model, are reasonable.

The NRC staff confirmed that the licensee's reevaluation of the hazard for LIP and associated site drainage used present-day methodologies and regulatory guidance. The NRC staff also confirmed the licensee's conclusion that the reevaluated flood hazard for LIP and associated drainage is not bounded by the COB flood hazard. Therefore, the NRC staff expects that the licensee will submit a focused evaluation for the LIP and associated site drainage flood-causing mechanism for the D.C. Cook site.

3.3 Streams and Rivers The licensee reported in the D.C. Cook FHRR that the reevaluated flood hazard for streams and rivers is screened out because no surface water channels, rivers, or streams are present within or adjacent to drainage paths, which contribute surface water runoff to the D.C. Cook protected area or other important-to-safety locations. This flood-causing mechanism is not discussed in the licensee's COB.

The licensee focused on the streams and rivers flooding assessment on the northeast side of the property (IMP, 201 Sa; 2016b). The licensee stated that there are no hydrologic features identified by the United States Geological Survey's (USGS) National Hydrography Dataset (USGS, 2013), such as perennial or intermittent streams in the vicinity of the area. The Thornton Valley is the only nearby channel , and a preliminary screening dismisses the need for a PMF of this drainage feature since it is not adjoining, adjacent to, or in the same drainage basin or watershed as the SSCs important to safety. The licensee identified that local topography defines a watershed basin division between the Thornton Valley drain and the onsite watersheds (see Figure 3.3-1 of this staff assessment). There is no indication that a PMF event on the Thornton Valley drain watershed would present a flooding hazard to the D.C. Cook site.

The NRC staff confirmed the licensee's conclusion that the streams and rivers flood-causing mechanism could not inundate the D.C. Cook site. Therefore, the NRC staff determined that streams and rivers flooding does not need to be analyzed in a focused evaluation or an additional assessment.

3.4 Failure of Dams and Onsite Water Control/Storage Structures The licensee reported in the D.C. Cook FHRR that the reevaluated hazard for failure of dams and onsite water control or storage structures is based on a water-surface elevation of 588.6 ft NGVD29, which considers wind waves and runup effects as this value is based on a historical maxima. This flood-causing mechanism is not discussed in the licensee's COB.

The licensee reported the use of the hierarchical hazard assessment approach to reevaluate dam failure flood hazards. The licensee stated that there are no onsite water control/storage structures that could inundate SSCs important to safety. Alternatively, the licensee considered a postulated failure of the locks between Lake Superior and Lakes Huron and Michigan, which

could potentially be contributing to a rise in the water level of Lake Michigan at the plant site.

Water is continually flowing from the headwaters of Lake Superior via the St. Mary's River to Lakes Huron and Michigan, which are connected by the deep Straits of Mackinac and are considered to be one lake hydraulically, having a common water level. Assumptions for this flooding analysis were conservatively based on existing physical conditions. The water level in Lakes Michigan and Huron depends, in part, on discharge from Lake Superior through a lock system. The analysis conservatively assumed that the entire lock system between Lake Superior and Lakes Michigan and Huron fails along with man-made water diversion structures, simultaneously. Historical evidence suggests that water levels on Lake Michigan and Lake Huron were 5 ft higher within the last 1,000 years, than they have been since the recording of lake levels in 1865 according to the U.S Army Corps of Engineers (USAGE) (USAGE, 1999).

The D.C. Cook COB uses a maximum lake elevation of 583.6 ft as a component of a maximum flood height at Lake Michigan. Therefore , the licensee determined that a conservatively assumed 5 ft increase due to dam failure on Lake Michigan would result in a maximum water elevation of 588.6 ft NGVD29 for this flood-causing mechanism.

The NRC staff confirmed the licensee's conclusion that the reevaluated flood hazard for failure of dams and onsite water control or storage structures remains below the plant grade and determined this mechanism is bounded by the COB for flooding from Lake Michigan (elevation 594.6 ft). Therefore , the NRC staff determined that flooding from failure of dams or on-site water storage facilities would not inundate the plant site and, therefore , does not need to be analyzed in a focused evaluation or an additional assessment.

3.5 Storm Surge The licensee reported in the D.C. Cook FHRR that the reevaluated elevation for the flooding due to storm surge is a stillwater elevation of 590.3 ft NGVD29, and a total maximum (combined effects) water elevation of 593.3 ft NGVD29. A separate flood elevation for this particular flood-causing mechanism is not included in the licensee's COB, although the COB for flooding (seiche) from Lake Michigan is elevation 594.6 ft NGVD29.

The licensee evaluated the potential for storm surge flooding by selecting a peak (base) water elevation for Lake Michigan , and then superimposing a stochastically-determined storm surge, including wave runup. The licensee estimated the peak (base) Lake Michigan water surface elevation using historical data (NOAA, 2012, and USAGE, 2012a; 2012b) , which was an elevation of 583.2 ft NGVD29. For the stochastic portion of the analysis, the licensee applied the Empirical Simulation Technique (EST; Scheffner et al. , 1999a and 1999b) after first identifying 150 historic severe storm events as input data. Hydrodynamic storm su rge modeling was performed using the Advanced CIRculation (ADCIRC) model (Luettich et al. , 1992 and 2004). Wave runup were derived from data developed by the USAGE in their comprehensive ADCIRC study of water levels in Lake Michigan (Jensen , 2012; Melby, 2012; Nadal-Caraballo, 2012; Scheffner et al. , 2013) . The licensee's final results are summarized in the D.C. Cook FHRR, Table 3-3, and results in a stillwater elevation of 590.3 ft NGVD29 (D.C. Cook FHRR ,

Figure 3-14) plus 3.0 ft of wave runup for a maximum (total) reevaluated storm surge elevation of 593.3 ft NGVD29.

Due to the complexity associated with stochastic/probabilistic storm surge analyses and their limited application in NRC licensing applications, the NRC staff first performed a simpler deterministic storm surge analysis to determine if the licensee's values were reasonable. The

NRC staff selected the previously-developed Great Lakes Storm Surge Planning Program model developed by NOAA (Schwab and Lynn, 1987). The NRC staff selected a sustained wind speed of 100 miles per hour and varied the wind direction by 10-degree increments between 10- and 360-degrees to determine the wind direction which produced the highest storm surge elevation at the site. The results of the NRC staff analysis was a maximum storm surge elevation of 593.0 ft NGV029, which is higher than the licensee reevaluated value but less than the COB for flooding from Lake Michigan.

As part of the O.C. Cook audit, NRC staff requested information regarding use of wave information from Holland, Ml , as being representative of the site's wave characterization. The licensee provided a response by letter dated October 27, 2016 (IMP, 2016a). The response included a figure that showed bathymetry profiles near both Holland, Ml, and the O.C. Cook site, and the licensee sufficiently demonstrated their bathymetric similarities. The NRC staff used this information to compute a bottom slope of 0.0071 for the O.C. Cook site.

The NRC staff performed wave runup calculations based on guidance in Chapter Vl-5 of the USAGE Coastal Engineering Manual (CEM) (USAGE, 2002). The NRC staff applied fetch length and storm duration limits to estimate the maximum offshore wave height of approximately 35 ft based on waves approaching the site perpendicular to the shoreline. The NRC staff found that the maximum wave height observed in offshore Lake Michigan was 22.9 ft on September 30, 2011 (NOAA/NWS, n.d.).

• Nearshore, the gentle beach slope at the O.C. Cook site (UFSAR, 2015; Figures 2.6-1, 2.6-9 and 2.6-10) would dampen the offshore waves and result in spilling breakers at the site. Thus, the NRC staff calculated a maximum wave runup of approximately 0.9 ft (using maximum historical offshore parameters) and 1.4 ft (using maximized fetch for 100-mph winds approaching directly onshore) at the O.C. Cook site. Using the maximum of these two values results in a total water surface elevation of 594.4 ft NGV029, which is less than the COB for flooding from Lake Michigan of 594.6 ft NGV029. Therefore, since the licensee's reevaluated results are approximately equal to staff's deterministic results, and both are below the COB for flooding from Lake Michigan, the NRC staff determined review of the licensee's stochastic methodology was not necessary for the purposes of the 50.54(f) letter.

The NRC staff confirmed the licensee's conclusion that the reevaluated storm surge flood-causing mechanism is bounded by the COB for flooding from Lake Michigan (elevation 594.6 ft).

The NRC staff also confirmed the licensee's conclusion that flooding from storm surge alone could not inundate the O.C. Cook site. Therefore, the NRC staff determined that flooding from storm surge does not need to be analyzed in a focused evaluation or an additional assessment.

3.6 Seiche The licensee reported in the O.C. Cook FHRR that the reevaluated hazard for site flooding from seiche would not inundate the site. This flood-causing mechanism is described in the licensee's COB, and the maximum computed flood elevation from Lake Michigan is 594.6 ft NGV029.

The licensee describes its evaluation of site flooding from seiche hazards against the relevant regulatory criteria based on present-day methodologies and regulatory guidance.

The NRC staff reviewed the licensee's results and confirmed the licensee's statements regarding wind effects on seiche resonance. The NRC staff agrees with the licensee's conclusion that the primary storm surge will occur along the eastern and/or southern shorelines

of the lake with potential seiches propagating to the west and/or north after the squall line has passed completely over the lake (Bechle and Wu , 2014). For Lake Michigan , the mean seiche period for primary mode oscillation along the long axis is approximately 9-h while the cross-lake primary mode period is approximately 2-h with typical seiche events lasting for 1- to 3-days with amplitudes of 1 to 5 ft (USACE, 2012a; 2012b).

The NRC staff confirmed the licensee's conclusion that the seiche flood-causing mechanism could not inundate the O.C. Cook site. The NRC staff confirmed that the reevaluated hazard for flooding from seiche is bounded by the COB flood hazard. Therefore, the NRC staff determined that flooding from seiche does not need to be analyzed in a focused evaluation or an additional assessment.

3.7 Tsunami The licensee reported in the O.C Cook FHRR that the reevaluated hazard for site flooding from tsunami would not inundate the site. This flood-causing mechanism is not described in the licensee's COB.

The licensee described its evaluation of the O.C Cook site flooding from tsunami hazards against the relevant regulatory criteria based on present-day methodologies and regulatory guidance below.

The licensee based their tsunami evaluation on historical records, databases and relevant scientific literature (NRC , 2009) which resulted in the following conclusions:

• As an inland site, the O.C. Cook site is not subject to oceanic tsunamis ; however, tsunami-like waves (seiches) have occurred in the Great Lakes region . Most of the reported waves were caused by meteorological conditions , but two were related to earthquakes and one to a landslide (NOAA, 2014a; 2014b) ;

• The potential for earthquake-generated tsunamis are limited because the required level of seismic activity for development of a tsunami , i.e., an earthquake with a magnitude greater than 6.5, is essentially absent within a 100-mile radius of the O.C. Cook site ;

• Subaqueous landslides are unlikely to generate an observable tsunami-like wave due to the limited bathymetric relief of ridges and their respective vertical slopes and orientation (NOAA, 2013a; 2013b ); and

• Subaerial landslides around the west, north, and east perimeter of the Lake Michigan is unlikely to affect O.C. Cook because topographic trends would direct any resultant tsunami-like wave away from the site. The exception is the southwest lake perimeter, where the topography is oriented such that a landslide and resultant tsunami-like wave , if it occurred, would be directed toward O.C. Cook. However, given a landslide, it would cause little, if any, effect to the O.C. Cook site because of the limited topographic relief and slope angles.

The NRC staff reviewed the methodologies and references used by the licensee to determine the severity of the tsunami phenomena reflected in this analysis and noted that they are consistent with present-day methodologies and guidance.

The NRC staff confirmed the licensee's conclusion that the reevaluated hazard for flooding from tsunami is bounded by the COB flood hazard. Therefore, the NRC staff determined that flooding from tsunami does not need to be analyzed in a focused evaluation or an additional assessment.

3.8 Ice-Induced Flooding The licensee reported in the D.C. Cook FHRR that the reevaluated hazard for ice-induced flooding does not inundate the plant site and would be bounded by flooding due to storm surge.

This flood-causing mechanism is not discussed in the licensee's CDB.

The licensee concluded in its FHRR that ice-induced flooding is not a credible event at the D.C. Cook site for the following reasons:

• Lake Michigan surface ice is common during winter and can cover over 90 percent of the lake's surface, with the surface ice cover forming from the shore outwards toward the center of the lake. However, there is negligible risk that surface ice will result in any flooding impact on the plant site because the lake surface is well below the lowest elevation of the plant grade (i.e., about 6 ft of margin). The D.C. Cook site has no historical records of flooding issues due to lake ice affecting the plant;

• There are no perennial streams close to the site that would accumulate and contribute to the potential for ice-induced flooding at the plant site. Surface runoff is minor and is restricted to a small intermittent stream that traverses the eastern portion of the site and discharges into Lake Michigan; and

• Any potential for ice flooding at the plant site related to Lake Michigan is bounded by the storm-surge flood-causing mechanism discussed in Section 3.5 of this staff assessment.

The NRC staff confirmed that the licensee's reevaluation of the hazard from ice-induced flooding used present-day methodologies and regulatory guidance. The NRC staff confirmed the licensee's conclusion that the reevaluated hazard for ice-induced flooding of the site is bounded by the COB flood hazard. Therefore , the NRC staff determined that ice-induced flooding does not need to be analyzed in a focused evaluation or an additional assessment.

3.9 Channel Migrations or Diversions The licensee reported in the D.C. Cook FHRR that the reevaluated hazard for channel migrations or diversions does not inundate the plant site. This flood-causing mechanism is not discussed in the licensee's COB.

The licensee stated in the D.C. Cook FHRR that cooling water canals and channels are not part of the plant design. Therefore, the licensee screened out channel migration or diversion as a plausible flood-causing mechanism for the D.C . Cook site. The NRC staff evaluated the potential for flooding resulting from channel migrations and diversions using the licensee

provided site layout and Google maps. The NRC staff agreed with the licensee's conclusion for this flood-causing mechanism.

The NRC staff confirmed the licensee's conclusion that the channel migrations or diversions flood-causing mechanism could not inundate the D.C. Cook site. Therefore, channel migration or diversion flooding does not need to be analyzed in a focused evaluation or an additional assessment.

4.0 REEVALUATED FLOOD ELEVATION, EVENT DURATION AND ASSOCIATED EFFECTS FOR HAZARDS NOT BOUNDED BY THE COB 4.1 Reevaluated Flood Elevation for Hazards Not Bounded by the COB Section 3 of this staff assessment documents the NRC staff review of the licensee's flood hazard water elevations results. Table 4.1-1 of this staff report contains the maximum flood height results, including waves and run-up, for flood mechanisms not bounded by the COB, which are presented in Table 3.1-1 of this staff assessment. The NRC staff agrees with the licensee's conclusion that LIP flood-causing mechanisms are not bounded by the COB.

Consistent with the process and guidance discussed in COMSECY-15-0019 (NRC, 2015a), the NRC staff anticipates the licensee will submit a focused evaluation for LIP and associated site drainage.

4.2 Flood Event Duration for Hazards Not Bounded by the COB The NRC staff reviewed information provided in licensee's 50.54(f) response (IMP, 2015b, 2015c, and 2016b) regarding the FED parameters needed to perform the additional assessment of plant response for flood hazards not bounded by the COB. The FED parameters for the flood-causing mechanisms not bounded by the COB are summarized in Table 4.2-1 of this staff assessment.

For the LIP flood-causing mechanism, the licensee stated in the D.C. Cook MSA (IMP, 2016c) that the plant response to a LIP flood event does not credit warning time because entrance into the FLEX support guideline (FSG) is based on loss of all alternating current power and other equipment/system conditions and not based on potential weather conditions. The NRC staff notes that the licensee may adopt (as needed) the warning time procedures followed by the alternative trigger method allowed by NEI 15-05 (NEI , 2015a) .

The D.C. Cook MSA provides the periods of inundation rang ing from 2 to 7 hrs depending on the locations within the power block area, and the period of recession of up to 3 days. The licensee used the 2-D numerical model described in the D.C Cook FHRR to determine these inundation and recession periods. The NRC staff reviewed the licensee's model and concluded that the licensee's modeling and the estimation of the FED parameters are acceptable for use in the D.C. Cook MSA, as they used present-day methodologies and regulatory guidance.

The NRC staff determined that the licensee-provided FED parameters for the LIP flood-causing mechanism are acceptable as the approach to estimate these parameters is consistent with the guideline provided by Appendix G of NEI 12-06, Revision 2 (NEI , 2015b).

4.3 Associated Effects for Hazards Not Bounded by the CDS The NRG staff reviewed the information provided in licensee's 50.54(f) letter response (IMP, 2015b, 2015c, 2016b) regarding the AE parameters for flood hazards not bounded by the CDS.

The AE parameters related to water surface elevation (i.e. , stillwater elevation with wind waves and runup effects) were previously reviewed by the NRG staff, and were transmitted to the licensee via an ISR dated December 4, 2015 (NRG, 2015b). The AE parameters not directly associated with water surface elevation are discussed below and are summarized in Table 4.3-1 of this staff assessment.

For the LIP flood-causing mechanism , the licensee concluded in the D.C. Cook that the AE parameters related to water-borne loads, including hydrostatic, hydrodynamic, debris, and sediment loads, would induce minimal impacts to plant operations due to the shallow water depths and slow water velocities . The licensee concluded that other associated effects, including sediment deposition and erosion , concurrent site conditions, and effects on groundwater intrusion are insignificant at the plant site. The licensee estimated the water depths and velocities using a two-dimensional numerical modeling method as described in the D.C. Cook FHRR. The NRG staff reviewed the LIP modeling and concluded that the modeling approach used present-day methodologies and regulatory guidance. The NRG staff determined that the licensee's assessment of the AE parameters for the LIP flood-causing mechanism are acceptable for use in the D.C. Cook MSA.

The NRG staff determined that the licensee-provided AE parameters for the LIP flood-causing mechanism are acceptable as the approach to estimate these parameters is consistent with the guideline provided by Appendix G of NEI 12-06, Revision 2 (NEI , 2015b).

4.4 Conclusion Based upon the preceding analysis, NRG staff confirmed that the reevaluated flood hazard information defined in Section 4 of this staff assessment is an appropriate input to the additional assessments of plant response as described in the 50.54(f) letter (NRG, 2012a) , COMSECY 0019, and associated guidance.

5.0 CONCLUSION

The NRG staff has reviewed the information provided for the reevaluated flood-causing mechanisms for the D.C. Cook site. Based on its review of available information provided the licensee's 50.54(f) response (IMP, 2015b; 2016b), the NRG staff concludes that the licensee conducted the hazard reevaluation using present-day methodologies and regulatory guidance used by the NRG staff in connection with ESP and COL reviews.

Based upon the preceding analysis, the NRG staff confirmed that the licensee responded appropriately to Enclosure 2, Required Response 2, of the 50.54(f) letter, dated March 12, 2012.

In reaching this determination, the NRG staff confirmed the licensee's conclusions that the reevaluated flood hazard results for the LIP flood-causing mechanisms is not bounded by the CDS flood hazard; additional assessments of plant response will be performed for the LIP flood-causing mechanisms; and the reevaluated flood-causing mechanism information is appropriate input to the additional assessments of plant response as described in the 50.54(f) letter and COMSECY-15-0019.

The NRG staff has no additional information needs with respect to licensee's 50.54(f) response related to flooding .

6.0 REFERENCES

Notes: ADAMS Accession Nos. refers to documents available through NRC's Agencywide Documents Access and Management System (ADAMS). Publicly-available ADAMS documents may be accessed through http://www.nrc.gov/reading-rm/adams.html.

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NRC, 2009, NUREG/CR-6966, "Tsunami Hazard Assessment at Nuclear Power Plant Sites in the United States of America," March 2009, ADAMS Accession No. ML091590193.

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NRC, 2011 d, "Prioritization of Recommended Actions to be Taken in Response to Fukushima Lessons Learned ," Commission Paper SECY-11-0137, October 3, 2011 , ADAMS Accession No. ML11272A111 .

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2.3, and 9.3, of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident," March 12, 2012, ADAMS Accession No. ML12056A046.

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NRG, 2012c, letter from Eric J. Leeds, Director, Office of Nuclear Reactor Regulation , to All Power Reactor Licensees and Holders of Construction Permits in Active or Deferred Status, "Prioritization of Response Due Dates for Request for Information Pursuant to Title 1O of the Code of Federal Regulations 50.54(f) Regarding Flooding Hazard Reevaluations for Recommendation 2.1 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, May 11 , 2012, ADAMS Accession No. ML12097A510.

NRG, 2012d, "Guidance for Performing the Integrated Assessment for External Flooding,

Japan Lessons-Learned Project Directorate, Interim Staff Guidance JLD-ISG-2012-05, Revision 0, November 30, 2012, ADAMS Accession No. ML12311A214.

NRG, 2013a, "Guidance for Performing a Tsunami, Surge, or Seiche Hazard Assessment,

Japan Lessons-Learned Project Directorate, Interim Staff Guidance JLD-ISG-2012-06, Revision 0, January 4, 2013, ADAMS Accession No. ML12314A412.

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NRG, 2014, "Donald C. Cook Nuclear Plant, Units 1 and 2 - Staff Assessment of the Flooding Walkdown Report Supporting Implementation of Near-Term Task Force Recommendation 2.3 Related to the Fukushima Dai-ichi Nuclear Power Plant Accident (TAC Nos. MF0218 and MF0219) , June 18, 2014, ADAMS Accession No. ML14147A329.

NRG, 2015a, "Mitigating Strategies and Flood Hazard Reevaluation Action Plan, Commission Paper COMSECY-15-0019, June 30, 2015, ADAMS Accession No. ML15153A104.

NRG, 2015b, "Donald C. Cook Nuclear Plant, Units 1 and 2 - Interim Staff Response to Reevaluated Flood Hazards Submitted in Response to 10 CFR 50.54(f) Information Request-Flood-causing Mechanism Reevaluation {TAC Nos. MF6096 and MF6097) , dated December 4, 2015, ADAMS Accession No. ML15334A424.

NRG, 2015c, "Nuclear Regulatory Commission Report for the Audit of Indiana Michigan Power Company's Flood-causing Mechanism Reevaluation Report Submittals Relating to the Near-Term Task Force Recommendation 2.1-Flooding for Donald C. Cook Nuclear Plant, Units 1 and 2 {TAC Nos. MF6096 and MF6097) , dated November 3, 2015, ADAMS Accession No. ML15300A236.

NRG, 2016a, "Compliance with Order EA-12-049 Order to Modify Licenses with Regard to Requirements for Mitigation Strategies for Beyond-Design-Basis External Events," Interim Staff Guidance JLD-ISG-2012-01 , Revision 1 and Comment Resolution , January 22 , 2016, ADAMS Accession No. ML15357A142.

NRG, 2016b, "Guidance for Activities Related to Near-Term Task Force Recommendation 2.1 ,

Flooding Hazard Reevaluation ; Focused Evaluation and Integrated Assessment," Interim Staff Guidance JLD-ISG-2016-01 , Revision 0, July 11 , 2016, ADAMS Accession No. ML16162A301.

NRC, 2016c, "Nuclear Regulatory Commission Audit Report for the Audit of Indiana and Michigan Power, lnc.'s Flood Hazard Reevaluation Report Submittals Relating to the Near-Term Task Force Recommendation 2.1-Flooding for Donald C. Cook Nuclear Power Plant,"

April 12, 2016, ADAMS Accession No. ML16072A035.

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Table 2.2 Flood-Causing Mechanisms and Corresponding Guidance SRP Section(s) and Flood-Causing Mechanism JLD-ISG Local Intense Precipitation and SRP 2.4.2 Associated Drainage SRP 2.4.3 SRP 2.4.2 Streams and Rivers SRP 2.4.3 Failure of Dams and Onsite Water SRP 2.4.4 Control/Storage Structures JLD-ISG-2013-01 SRP 2.4.5 Storm Surge JLD-ISG-2012-06 SRP 2.4.5 Seiche JLD-ISG-2012-06 SRP 2.4.6 Tsunami JLD-ISG-2012-06 Ice-Induced SRP 2.4.7 Channel Miorations or Diversions SRP 2.4.9 Notes:

• SRP is the Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition (NRG, 2007).

• JLD-ISG-2012-06 is the "Guidance for Performing a Tsunami , Surge, or Seiche Hazard Assessment" (NRG, 2013a) .

• JLD-ISG-2013-01 is the "Guidance for Assessment of Flooding Hazards Due to Dam Failure" (NRG, 2013b).

Table 3.1 Summary of Controlling Flood-Causing Mechanisms Reevaluated Flood-Causing Mechanisms and Associated Effects that May Exceed the ELEVATION, ft NGVD29 Powerblock Elevation, (594.6 ft NGVD29) 1 Local Intense PreciQitation and Associated Drainage CL 1: 1-DR-TUR201 (Turbine 594.8 Building Unit 1 West Rollup Door)

CL2: 2-DR-TUR220 (Turbine 596.0 Building Unit 2 West Rollup Door)

CL3: 2-DR-TUR260 (Turbine 609.2 Building Unit 2 East Rollup Door)

CL4: Valve-Shed RWST 1-TK-33 609.9 CL5: Valve-Shed PWST/CST 1 609.9 CL6: Valve-Shed RWST 2-TK-33 609.5 CL?: Valve-Shed PWST/CST 2 609.6 CL8: Supplemental DGs 609 .6 CL9: 1-DR-TUR253 (Turbine 609.8 Building Unit 1 East Rollup Door)

CL 1O: 12-DR-AUX381 (Auxiliary Building North 609.9 Rollup Door) 1 Flood height and associated effects as defined in JLD-ISG-2012-05, Guidance for Performing the Integrated Assessment for External Flooding" (NRC, 2012d).

Table 3.1 Current Design Basis Flood Hazards Current Design Basis Stillwater Associated Flood (COB) Elevation, Flooding Mechanism Elevation, Reference Effects ft ft NGVD29 ft NGVD29 Local Intense Not included in Not included in FHRR Precipitation and Not included in COB COB COB Table 4-1 Associated Drainage Not included in Not included in FHRR Streams and Rivers Not included in COB COB COB Table 4-1 Failure of Dams and Onsite Water Not included in Not included in FHRR Not included in COB Control/Storage COB COB Table 4-1 Structures Not included in Not included in FHRR Storm Surge Not included in COB COB CDB Table 4-1 Storm Surge at Not included in Not included in FHRR Not included in COB Screenwell COB COB Table 4-1 Not included in FHRR Seiche 594.6 594.6 COB Table 4-Not included in Not included in FHRR Tsunami Not included in COB COB COB Table 4-1 Not included in Not included in FHRR Ice-Induced Not included in COB COB COB Table 4-1 Channel Migrations or Not included in Not included in FHRR Not included in COB Diversions COB COB Table 4-1 Source: IMP (2015a; 2016a), NRC (2015c)

Table 4.1 Reevaluated Hazard Elevations for Flood-Causing Mechanisms Not Bounded by the COB Flood-Causing Stillwater Waves/Run- Reevaluated Reference Mechanism Elevation (ft up Hazard NGVD29) Elevation (ft NGVD29)

Local Intense Precipitation and Associated Drainage CL 1: 1-DR-TUR201 (Turbine Building Unit 1 594.8 Minimal 594.8 FHRR Table 3-2 West Rollup Door)

CL2: 2-DR-TUR220 (Turbine Building Unit 2 596.0 Minimal 596.0 FHRR Table 3-2 West Rollup Door)

CL3: 2-DR-TUR260 (Turbine Building Unit 2 609.2 Minimal 609.2 FHRR Table 3-2 East Rollup Door)

CL4: Valve-Shed RWST 1-609.9 Minimal 609.9 FHRR Table 3-2 TK-33 CL5: Valve-Shed 609.9 Minimal 609.9 FHRR Table 3-2 PWST/CST 1 CL6: Valve-Shed RWST 2-609.5 Minimal 609.5 FHRR Table 3-2 TK-33 CL?: Valve-Shed 609.6 Minimal 609.6 FHRR Table 3-2 PWST/CST 2 CL8: Supplemental DGs 609.6 Minimal 609.6 FHRR Table 3-2 CL9: 1-DR-TUR253 (Turbine Building Unit 1 609.8 Minimal 609.8 FHRR Table 3-2 East Rollup Door)

CL1 O: 12-DR-AUX381 (Auxiliary Building North 609.9 Minimal FHRR Table 3-2 609.9 Rollup Door)

Source: AEP (2015) NRC (2015c)

Note: Reported values are rounded to the nearest one-tenth of a foot.

Table 4.1 Reevaluated Hazard Elevations for Flood-Causing Mechanisms Not Bounded by the COB: LIP Flood Elevations at Eight Additional Locations Identified in the MSA report (IMP, 2016c)

Flood-Causing Stillwater Waves/Run- Reevaluated Reference Mechanism Elevation up Hazard (ft Elevation (ft NGVD29) NGVD29)

Local Intense Precipitation and Associated Drainage ML 11: Service Building 606.4 Minimal 606.4 MSA Table 7-1 Extension Northwest ML 12: Service Building 609.0 Minimal 609.0 MSA Table 7-1 Annex Northeast ML 13: Service Building 609.7 Minimal 609.7 MSA Table 7-1 Annex Southeast ML 14: Top of Ramp for 595.9 Minimal 595.9 MSA Table 7-1 CL2, 2-DR-TUR220 ML 15: Bottom of Ramp for 596.0 Minimal 596.0 MSA Table 7-1 CL2, 2-DR TUR220 ML 16: Low Point in Primary Plant Access Road used for 601.8 Minimal 601.8 MSA Table 7-1 FLEX Deployment ML 17: Service Building 608.0 Minimal 608.0 MSA Table 7-1 Extension Northeast Corner ML 18: Auxiliary Bu ilding 609.8 Minimal 609.8 MSA Table 7-1 Track Bay East Wall Source: from D.C. Cook MSA, Table 7-1 (IMP , 2016c)

Table 4.2 Flood Event Duration for Flood-Causing Mechanisms Not Bounded by the COB Time Available Flood-Causing Duration of Time for Water to for Preparation Mechanism Inundation of Site Recede from Site for Flood Event Local Intense Use NEI 15-05 Precipitation and Guide (NEI , 2 to 7 hours0.292 days <br />0.0417 weeks <br />0.00959 months <br /> Up to 3 days Associated 2015a)

Drainaqe (1 )

Notes: from D.C. Cook MSA (IMP, 2016c)

1. The licensee has the option to use NEI guideline 15-05 (NEI, 2015a) to estimate the warning time necessary for flood preparation .

Table 4.3 Associated Effects Parameters Not Directly Associated with Total Water Height for Flood-Causing Mechanisms Not Bounded by the COB Associated Effects Factor Local Intense Precipitation 1 Hydrodynamic loading at plant grade Minimal Debris loading at plant grade Minimal Sediment loading at plant grade Minimal Sediment deposition and erosion Minimal Concurrent Conditions, including adverse Minimal weather Groundwater ingress Minimal Other pertinent factors (e.g., waterborne Minimal projectiles) 1 1nformation provided in MSA Table 7-3 (IMP, 2016c}

flood event du ration

• site preparation j period of

• recession of

• for flood event inundation water from site Conditions are met Arrival of flood Water begins to Water completely for entry into flood waters on site recede from site receded from site procedures or and plant in safe notification of and stable state impending flood that can be maintained indefinitely Figure 2.2 Flood Event Duration (NRC JLD-ISG-2012-05, Figure 6)

Figure 3.2 D.C. Cook site critical monitoring locations selected for LIP flood analysis (from D.C. Cook FHRR , Figure 3-4 (IMP, 2015b))

Crltieal Locations of Q)

C1> SS Cs 0

Figure 3.3 Watershed draining to CNP critical locations taken from the D.C. Cook FHRR Figure 3-5 (IMP, 2016b))

Figure 3.5 Wind wave transects 1-5 and SWAN output locations (T1-T5) (adapted from FHRR unnumbered figure and FHRR Figure 3-44; locations are approximate); licensee determined that maximum combined flood hazard elevation location TS. (Source of base figure is Google Earth (Google Earth, 2016)).

ML17164A308 *via email OFFICE NRR/JLD/JHMB/PM NRR/JLD/LA NRO/DSEA/RHM1 NRO/DSEA/RHM1 /BC NAME TGovan Slent HAhn* CCook*

DATE 6/14/201 7 6/14/2017 05/17/201 7 05/17/2017 OFFICE NRR/JLD/JHMB/BC NRR/JLD/JHMB/PM NAME NSanfilippo TGovan DATE 6/15/201 7 6/15/201 7