ML14153A006

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Revision 4 to Local Intense Precipitation Evaluation Report
ML14153A006
Person / Time
Site: Dresden  Constellation icon.png
Issue date: 04/29/2014
From: Mann J
AMEC Environment & Infrastructure
To:
Exelon Generation Co, Document Control Desk, Office of Nuclear Reactor Regulation
Shared Package
ML14153A003 List:
References
RCN: LIP-099, RS-14-22
Download: ML14153A006 (19)
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Enclosure 4 Dresden Nuclear Power Station, Units 2 and 3 Local Intense Precipitation Evaluation Report Revision 4 (18 Pages)

LOCAL INTENSE PRECIPITATION EVALUATION REPORT, Rev 4 For the DRESDEN NUCLEAR POWER STATION 6500 North Dresden Road, Morris, IL 60450 Exeton Exelon Generation Company, LLC (Exelon)

P.O. Box 805387 Chicago, Illinois 60680-5387 Prepared by:.

AMEC-Envimnmenttinfrastructure;,In..

751 Arbor Way, Suite 180, Blue Bell, PA 19422 Revision 4 submittal date: April 29, 2014 Printed Name Affiliation r Date Originaton 4 l4/4,' k e, AMEC 03-5; Y /A Verifier~ TE1.1 _FKNL AMEC q/3 V)

Approver: f a. V Ih AMEC v :ij Lead Responsible Englneer Branch Manager Ju1 .kLfd7zj V/

Senior Manager Design Engineering: ~ + (L d-e- '(I Corporate eptancs: Joe Bellini Exelon 5/8/14 RCN: UP-099 Page I of 18

Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4 Contents

1. List of Acronym s ......................................................................................................................................... 3
2. PURPOSE .................................................................................................................................................... 3
a. Background ............................................................................................................................................ 3
b. Site Description ...................................................................................................................................... 4
c. Vertical Datum ....................................................................................................................................... 4
d. Sum m ary of Current Licensing Basis Flood Hazards ........................................................................ 5
3. M ETHODOLOGY ......................................................................................................................................... 6
a. M odeling Approach ................................................................................................................................ 6
b. Topography ............................................................................................................................................ 9
c. Land Cover ............................................................................................................................................. 9
d. Probable M axim um Precipitation .................................................................................................... 10
4. RESULTS .................................................................................................................................................... 11
5. COMPARISON OF CURRENT AND REEVALUATED LIP FLOOD HAZARD .............................................. 17
6. REFERENCES ............................................................................................................................................. 18 Table of Figures Figure 1: Site Location ........................................................................................................................................ 4 Figure 2: FLO-2D M odel Boundary (Elevations in NAVD 88) ........................................................................ 8 Figure 3: 1-hr/1-sq-m i site-specific PM P Distribution .................................................................................. 11 Figure 4: Locations of Doors and Bays ......................................................................................................... 16 Table of Tables Table 1: Assigned M anning's Roughness Coefficients (n-values) ............................................................... 10 Table 2: 1-hr/1-sq-m i site specific PM P Distribution ................................................................................. 11 Table 3: LIP Predicted Flooding Results ....................................................................................................... 13 Table 4: LIP Predicted Flooding Results at the Main Doors and Bays of the Site Buildings ........................ 14 Table 5: LIP Predicted Flood Results at the Critical Doors and Bays of the Sites Buildings ......................... 15 RCN: LIP-099 Page 2 of 18

Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4

1. List of Acronyms ASME American Society of Mechanical Engineers CLB Current Licensing Basis DEM Digital Elevation Model ft foot / linear foot fps feet per second GIS Graphical Information System lb Pound Force LiDAR Light Detection and Ranging LIP Local Intense Precipitation MSL Mean Sea Level Datum NAVD 88 North American Vertical Datum of 1988 NGVD 29 National Geodetic Vertical Datum of 1929 NRC Nuclear Regulatory Commission PMP Probable Maximum Precipitation SEP Systematic Evaluation Program Sq mi Square Miles WRF Width Reduction Factor WSE Water Surface Elevation
2. PURPOSE
a. Background AMEC Environment & Infrastructure, Inc. (AMEC) on behalf of Exelon Corporation (Exelon) performed an evaluation of site runoff generated from a Local Intense Precipitation (LIP) event to supplement the on-going flooding studies at Dresden Nuclear Power Station (Dresden Station). AMEC performed this work under a Quality Assurance (QA) Program that conforms to the requirements of ASME NQA-1 and 10.CFR.50 Appendix B. The LIP evaluation was performed in accordance with the Nuclear Regulatory Commission's (NRC's) "Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America," dated November 2011 (NUREG/CR-7046) (Reference 12).

NUREG/CR-7046 (Reference 12) identifies the LIP under causative mechanisms for design based floods and states that these mechanisms or causes be investigated to estimate the design-basis flood for nuclear power plant sites. Local flooding is associated with inundation caused by localized, short-duration, intense rainfall events. The focus of this study was to evaluate the adequacy of the site's grading, drainage, and runoff-carrying capacity. It was assumed for this analysis that all active and passive drainage system components (e.g., pumps, gravity storm drain systems, small culverts, inlets, etc.) are non-functional during the local intense rainfall event, per Case 3 in NUREG/CR-7046 (Reference 12). As such, only overland flow and open channel systems were modeled and considered in the local flooding analysis.

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Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4 Per NUREG/CR-7046 (Reference 12), the LIP event is defined as a 1-hour/i-square mile Probable Maximum Precipitation (PMP). The PMP is the greatest depth of precipitation, for a given duration, that is theoretically possible for a particular area and geographic location (Reference 12). For Dresden, the 1-hour/i-square-mile PMP depth and temporal distribution was based on a site-specific PMP study (Reference 9).

b. Site Description The Kankakee and Des Plaines watershed is approximately 7,300 square miles. Dresden Station is situated on the south bank just below the junction where the Kankakee and the Des Plaines Rivers join to form the Illinois River (Reference 11).

Figure 1: Site Location

c. Vertical Datum Elevations provided in this report were presented in the North American Vertical Datum of 1988 (NAVD 88) and the Mean Sea Level (MSL) Datum to relate calculated results to the Current Licensing Basis (CLB) documents. Elevations provided in the CLB documents were in the MSL datum. The topographic, Light RCN: LIP-099 Page 4 of 18

Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4 Detection and Ranging (LiDAR), and survey data used for the calculations were in the NAVD 88 datum.

According to the United States Army Corps of Engineers engineering manual EM1110-1-1005 (Reference 8) the National Geodetic Vertical Datum of 1929 (NGVD 29) was previously identified as the "Mean Sea Level Datum of 1929". In 1973, the "Mean Sea Level Datum of 1929" identifier for the datum was changed to NGVD 29 to eliminate the "Mean Sea Level" reference. Dresden Station went online in 1960 and, therefore, the MSL references would be in reference to the NGVD 29 datum.

A conversion was required to compare elevations reported in the NGVD 29 and NAVD 88 datums.

According to the NOAA VERTCON website (Reference 10) the datum shift from NGVD 29, or MSL, to NAVD 88 for the Dresden Station's latitude and longitude (41.3895, -88.2703) would require adjustment per Equation 1:

Equation 1 Elevation in ft NAVD 88 = Elevation in ft MSL - 0.29 ft

d. Summary of Current Licensing Basis Flood Hazards Per the CLB documents, the design plant grade is elevation 516.71 ft NAVD 88 (517.0 ft MSL) and non-watertight openings in walls begin at elevation 517.21 ft NAVD 88 (517.5 ft MSL) (Reference 11). The lowest elevation hydraulically connected to safety-related equipment is 508.71 ft NAVD 88 (509.00 feet MSL) in the Crib House (Reference 11).

There are no flood protection barriers (e.g., levees, dikes, gates) in place that will prevent external flooding of the facility. The site relies almost exclusively on flood emergency procedures to mitigate the effects of the Probable Maximum Flood (PM F) and prevent the loss of safe plant control during the PMF. Based on the Updated Final Safety Analysis Report (UFSAR), the PMF is estimated to reach a peak Stillwater Elevation of 524.71 ft NAVD 88 (525.0 ft MSL). Wave run-up (wind generated waves) increases the maximum water surface elevation to 527.71 ft NAVD 88 (528.00 ft MSL) (Reference 6). Both predicted maximum water surface elevations are significantly above both the plant grade and the lowest opening hydraulically connected to safety-related equipment.

Topographic relief at the site is characterized by grades averaging approximately 2%. The site grading generally slopes away from the center of the site toward the cooling canals to the north and west, the Kankakee River to the east, and a concrete drainage channel along the western boundary of the site. No off-site areas drain onto the site; however, some off-site drainage does drain to the channel along the southern boundary of the site (Reference 11).

The design basis evaluation includes a site drainage analysis during the local PMP, as discussed in the SER, topics 11-3.A and 11-3.B (Reference 11). The rate of runoff for the 29-acre study area was computed using the Rational Method and flood depths were calculated using the Manning's formula. This site drainage analysis was performed using the 24-hour maximum probable point discharge of 31.2 inches and a maximum 13-minute intensity of 58.3 inches per hour (Reference 11). Two site drainage analyses were performed to determine the depth of flooding adjacent to the plant buildings (Reference 11). The first site drainage analysis was performed to evaluate the capacity of the drainage channel located on the south and west sides of the plant (Reference 11). This evaluation showed that for a water surface at plant grade, the channel can carry twice the flood generated by the PMP (Reference 11).

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Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4 The second analysis evaluated the runoff between the buildings and the flood channel for the site's subbasin with the largest surface area, shallowest slopes, largest peak discharge, and the longest travel distance to the flood channel to reflect the most conservative conditions (Reference 11). The one-dimensional approach estimated the flooding depth by using the Manning's formula and a cross section along the subbasin (Reference 11).

Both analyses assumed an average ground slope between the buildings and the flood channel of 0.0022 ft/ft (Reference 11). An average Manning's n-value of 0.022 was assigned to the channel reach to reflect a combination of values for concrete, earth, asphalt, and grass (Reference 11).

The results of the second analysis predicted that the water surface elevations created by the local PMP would not exceed the finished floor elevation of the plant (Reference 11). This scenario calculated a flow depth of 0.45 foot, which is 0.05 feet below the plant's elevation for non-water tight openings (Reference 11). The design basis analysis concluded that the slope of the land surface and channels were sufficient to carry away runoff generated from the LIP event without the flood level exceeding the plant design finished floor elevation of 517.21 ft NAVD 88 (517.50 ft MSL) (Reference 11).

3. METHODOLOGY
a. Modeling Approach This evaluation uses a two-dimensional (2D) hydrodynamic model, FLO-2D, to evaluate the flow characteristics of the runoff caused by an LIP event. The FLO-2D model boundaries were set along the cooling canals to the north and west of the site and at the slope breaks with drainage away from the site to the south and east. Figure 2 shows the exterior boundary of the FLO-2D model and landmarks referenced in this document.

To estimate the effect that grid size has on the predicted water surface elevation, a sensitivity analysis was conducted to compare results between a 5-ft by 5-ft grid spacing and a 20-ft by 20-ft grid spacing. The maximum difference in water surface elevation was estimated to be +/- 0.5 ft between the two models. The greatest differences were observed in the grids directly adjacent to the edges of the buildings and boundaries, where the smaller grids allow for more detail. The 5-ft by 5-ft grid provides a greater level of resolution; however the model consisted of 224,616 grid elements, which required significant computational resources.

Based on the sensitivity analysis, a FLO-2D model consisting of 10-ft by 10-ft grids (68,449grids) was determined to be appropriate for the LIP analysis. The 10-ft by 10-ft grid size provided an adequate level of detail in the study results while maintaining reasonable computational time. The difference in calculated water surface elevations between the 10-ft by 10-ft grid and the 5-ft by 5-ft grid models were within

+/- 0.1 ft.

The FLO-2D model required the following inputs to evaluate LIP (Reference 5):

  • Topography to characterize grading, slopes, drainage divides, and low areas of the site;
  • Manning's Roughness Coefficients (n-values) to characterize the land cover of the site and its effects on flow depths and velocities; and RCN: LIP-099 Page 6 of 18

Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4

  • 1-hour PMP Event to characterize the local intense precipitation event (volume, distribution, and duration).

The model was run with the above inputs to evaluate the adequacy of the site grading and runoff carrying capacity during the LIP event. The model provides information on the following parameters:

" Flood elevations;

  • Flood depths;

" Flooding conditions;

  • Velocities (magnitude and direction);
  • Resultant static loads; and

" Resultant impact loads.

It is assumed that all active and passive drainage system components (e.g., pumps, gravity storm drain systems, small culverts, inlets, etc.) are non-functional or completely blocked during the LIP event, per Case 3 in NUREG/CR-7046 (Reference 12). NUREG/CR-7046 discusses that it is extremely rare that the passive site drainage network would remain completely unblocked during the LIP event. Assuming blocked conditions was considered reasonable during a LIP event because the expectation is that: 1) a significant volume of debris/sediment would be transported, delivered, and accumulated at drainage structures and 2) conveyance capacity of the drainage system is very limited, even if completely open, relative to the peak flow rates during a LIP event. Furthermore, the NRC would require the utility to provide substantial justification for crediting partial or full conveyance from drainage structures (Reference 12).

The LIP evaluation was conducted independently of external high-water events. That is, the LIP event was assumed to have occurred non-coincidental to a river flood. Therefore, backwater or tailwater was not considered. Per recommendations provided by NUREG/CR-7046, runoff losses were ignored during the LIP event to maximize the runoff from the event. The site is predominantly impervious and, therefore, accounting for losses would have very minimal impact on the results. The soil types in pervious surfaces are classified by the USDA-NRCS as being within Hydrologic Soil Group (HSG) C (Reference 7), which is characterized as having saturated infiltration rates between approximately 0.20 to 0.60 inches per hour (Reference 7), which can be considered negligible compared to the rainfall intensity for an LIP event. The NRC will require the utility to provide justification for crediting losses (Reference 12). Only overland flow and open channel systems were modeled and considered in the LIP flooding analysis.

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Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4 Figure 2: FLO-2D Model Boundary (Elevations in NAVD 88)

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Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4

b. Topography The FLO-2D model was developed using a Digital Elevation Model (DEM) produced from available LiDAR data and supplemental field survey to characterize grading, slopes, drainage divides, and low areas of the site.

Publically available LiDAR data was collected in 2008 (Reference 1). According to the December 12, 2008 Aero-Metric Vertical Accuracy Assessment Report for Grundy County, Illinois, the data has a vertical accuracy of +/- 6 inches and was accompanied with digital orthoimagery (Reference 1). AMEC validated the LiDAR data through a commercial grade dedication process under AMEC's 10CFR50 Appendix B Quality Assurance Program.

AMEC considered the available LiDAR data sufficient as a baseline for the LIP evaluation. However, supplemental field survey of the site allowed for the incorporation of site features that were not identified by the LiDAR survey. The features included depressions/low points, isolated concrete barriers/blocks, concrete pads, and adjacent building elevations, which did not appear to be considered in the design basis evaluation. The field survey was performed in July, 2012 by a Professional Land Surveyor licensed in the State of Illinois.

The supplemental field survey data was incorporated into the LiDAR data using AutoCAD Civil3D software to produce the DEM. The DEM was clipped to match the FLO-2D model limits shown in Figure 2 above.

c. Land Cover The FLO-2D model uses Manning's Roughness Coefficients (n-values) to characterize the site's surface roughness and calculate affects on flow depths and velocities. Land cover for the site was evaluated using interpretation of orthoimagery that was verified in the field by AMEC during visits to the site. N-values were assigned to each land cover type and were based on ranges described on page 22 of the FLO-2D Reference Manual (Reference 5). The assigned n-values are provided in Table 1 below.

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Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4 Table 1: Assigned Manning's Roughness Coefficients (n-values)

Land Cover Surfaces' Recommended Range of n-values2 Assigned n-value  % Coverage Bermuda and dense grass, dense vegetation 0.17 - 0.48 0.32 38 Shrubs and forest litter, pasture 0.30 - 0.40 0.40 9 Asphalt, concrete, and Buildings3 0.02 - 0.05 0.035 32 Gravel4 0.05 15 Water surface- 0.02 6 1Land cover surface per orthoimagery and field verification.

2 Recommended ranges of Manning's n-values per Reference 5.

3 Building obstructions are accounted for in the model through the use of Area and Width Reduction Factors 4(Reference 3)

Gravel surfaces were assigned n-values from the upper range for Asphalt/Concrete to reflect the roughness of the material.

5Water surfaces assigned n-values from the lower range for Asphalt/Concrete to reflect its smoothness.

As noted in Table 1, the n-values assigned for gravel and water land cover surfaces are assigned values from the recommended range for asphalt/concrete to reflect their surface roughness. Gravel is assigned the higher end of the range to account for typical irregularities in the gravel surface. The Manning's n value for water is assigned the low end of this range to account for internal friction. Shrubs and forest litter were assigned a Manning's n value at the upper end of the recommended range to account for the observed dense brush surface. The rest of the land cover surface categories were assigned the middle of their respective recommended ranges.

A sensitivity analysis was performed on the n-values to evaluate the effect this parameter has on the maximum water surface elevation. As part of the analysis, the upper and lower ranges of the Manning's n values presented in Table 1 were run through the FLO-2D model. The results indicate that the difference in water surface elevations between the upper and lower range of the Manning's n values presented in Table 1 are within +/- 0.03 ft. . This also suggests that the LIP peak flood levels for much of the site are controlled by floodwaters ponding or backing-up at constrictions (e.g. catch basins and small culverts), reducing the affect of surface friction on flow depths and reinforcing the reasons discussed previously for the increases above the current design basis

d. Probable Maximum Precipitation Per NUREG/CR-7046, the LIP event is defined as a 1-hour/i-square-mile PMP event. For Dresden Station, the 1-hour/i-square-mile PMP depth and temporal distribution were based on a site-specific PMP study (Reference 9). The 1-hr PMP distribution is provided in Table 2 and Figure 3 below. The 1-hour PMP event was used as an input in the FLO-2D model to evaluate the potential site flooding.

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Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4 Table 2: 1-hr/1-sq-mi site specific PMP Distribution Time Cumulative Depth Percent Total PMP (minutes) (inches) (%)

0 0.0 0.0%

5 4.7 33.7%

15 7.4 53.1%

30 10.6 76.2%

60 13.9 100%

20 18 S16

. 14 0.S12 a 10 i-S8 S4 2

0 0 10 20 30 40 50 60 Time (minutes)

Figure 3: 1-hr/1-sq-mi site-specific PMP Distribution

4. RESULTS The LIP flooding evaluation, as per the Case 3 assumptions of NUREG/CR-7046, Section 3.2 (Reference 12) produced results that include flooding depths, water surface elevation, velocities, resultant static loads, and resultant impact loads for the full duration of a LIP event at the site. The maximum resultant impact load and maximum resultant static load are expressed as pounds per unit width. Multiplying these loads by the horizontal width of the structure within the grid element will provide the magnitude of the resultant force.

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Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4 Detailed calculations, results, and figures are presented in the Dresden LIP Evaluation Calculation Package LIP-DRE-001 (Reference 2). The calculated maximum values for these parameters are presented in Table 3.

Overall, the FLO-2D model shows peak LIP flood elevations around the plant (reactor and turbine buildings) ranging between 517.19 and 517.76 feet NAVD 88 (517.48 and 518.05 feet MSL), 0.04 to 0.61 feet higher than the design basis peak LIP flood elevation of 517.15 feet NAVD 88 (517.45 feet MSL). In comparing I

available information from the design basis evaluation (Reference 11), the increase appears to be attributable to assumptions and methods used in developing the design basis flood levels. The design basis evaluation appears to have discounted the affects of structures and other features constricting flow and affecting flood levels. According to the FLO-2D model, features such as small culverts in the drainage channel, grated catch basins, and other constrictions/obstructions, control much of the flooding during an LIP event. The design basis evaluation appears to have assumed that overland and channel conveyance was uninhibited.

Results provided in this report are direct outputs from the FLO-2D model. The FLO-2D model reports results to the hundredth of a foot. However, based on the sensitivity analysis of grid size and Manning's n values, an accuracy of +/- 0.1 foot should be taken into consideration when evaluating the reported results.

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Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4 Table 3: LIP Predicted Flooding Results Max. Max. Max.

Building Max. Water Surface Flooding Depth 4 Max. Resultant Impact Resultant Static Load Building Name No.' Velocity Load ft (NAVD88) ft (MSL) ft ft/sec. lb/ft lb/ft New Administration &Training 1 517.41 - 517.56 517.70 - 517.85 0.27- 2.05 0.16- 0.67 0.01- 0.60 2.23 - 130.58 Administration 1 517.38 - 517.58 517.67 - 517.87 0.53- 1.44 0.29-1.29 0.07-2.84 8.65-64.44 HPCl & Diesel Generator 18 517.45 - 517.61 517.74 - 517.90 0.29-1.58 0.06-0.73 0.01-0.65 2.69-78.30 Recycle Floor Drain Surge Pipe 26 517.59 - 517.61 517.88 - 517.90 0.33-1.34 0.14-0.69 0.01-1.11 3.46-56.23 Fuel Handling 28 517.28 - 517.57 517.57 - 517.86 0.10-0.87 0.17-0.59 0.01-0.20 0.31-23.50 Heating Boiler 34 517.38 - 518.99 517.67 - 519.28 0.10-1.20 0.20- 1.19 0.02-0.76 0.32-44.62 Reactor Building, Unit 1 50 517.19 - 517.38 517.48 - 517.67 0.10-1.43 0.13-1.16 0.01-1.93 0.32-64.24 Reactor Building, Unit 2 51 517.57 - 517.61 517.86 - 517.90 0.34-1.24 0.08-0.61 0.01-0.39 3.65-48.27 Reactor Building, Unit 3 52 517.57 - 517.76 517.86 - 518.05 0.10-1.42 0.08-0.86 0.01-1.05 0.32-63.11 Off Gas Recombiner Room 53 517.24 - 517.26 517.53 - 517.55 0.62-1.08 0.18-0.80 0.01-0.84 11.9-36.54 Shop & Warehouse 63 517.33 - 517.37 517.62 - 517.66 0.40-1.09 0.19-0.51 0.01-0.37 4.95-36.97 Turbine Building, Unit 1 66 517.38 - 517.50 517.67 - 517.79 0.44-1.53 0.19-0.86 0.01-1.31 6.09-73.33 Turbine Building, Unit 2 67 517.45 - 517.61 517.74 - 517.90 0.29-1.58 0.06-0.73 0.01-0.65 2.69-78.30 Turbine Building, Unit 3 68 517.26 - 517.61 517.55 - 517.90 0.53-1.39 0.16-1.35 0.02-2.96 8.76-60.34 Visitors Center 71 517.40 - 517.56 517.69 - 517.85 0.36-1.17 0.13-1.11 0.01-1.87 3.99-42.50 Radiation Sampling 78 517.60 - 517.85 517.89 - 518.14 0.10-1.35 0.19-0.86 0.01-1.05 0.31-56.71 I Exelon Drawing No. M-1, Property Plat, Revision D, DCP 00036290B 2 Exelon Drawing No. M-1D, Plant Development Plan, Revision C, DCP 00036290B 3 Dresden Calculation Package No. LIP-DRE-001, Appendix A, Figures A-5a to A-Se 4 Dresden Calculation Package No. LIP-DRE-001, Appendix A, Figures A-7a to A-7e 5 Dresden Calculation Package No. LIP-DRE-001, Appendix A, Figures A-l0a to A-lOe 6 Dresden Calculation Package No. LIP-DRE-001, Appendix A, Figures A-12a to A-12e 7 Dresden Calculation Package No. LIP-DRE-001, Appendix A, Figures A-14a to A-14e RCN: LIP-099 Page 13 of 18

Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4 The maximum predicted LIP flooding results at the critical entrances to the site buildings are provided in Table 4.

Table 4: LIP Predicted Flooding Results at the Main Doors and Bays of the Site Buildings Max. Max. Max.

Reference Grid Max. Water Surface 1 Flooding Max. Resultant Resultant Door/Bay No.' Element No. Depth 2 Ve Impact Load 4 Static Load s ft (NAVD88) ft (MSL) ft ft/sec. lb/ft lb/ft Bay 124 32060 517.60 517.89 0.74 0.54 0.15 17.28 Door 125 27979 517.58 517.87 0.54 0.23 0.01 8.96 Door 126 25725 517.57 517.86 0.68 0.29 0.02 14.52 Bay 127 24591 517.57 517.86 0.80 0.27 0.09 20.05 Door 128 23848 517.58 517.87 0.90 0.42 0.13 25.29 Bay 129 20577 517.60 517.89 1.42 0.25 0.20 63.11 Door 130 19161 517.61 517.90 1.05 0.71 0.83 34.59 Door 131 16735 517.61 517.90 0.91 0.37 0.04 25.61 Bay 132 13733 517.60 517.89 0.82 0.48 0.12 20.81 Door 133 13400 517.59 517.88 0.72 0.62 0.62 16.18 Door 134 12103 517.56 517.85 1.34 0.67 1.41 55.79 Door 135 11156 517.48 517.77 0.79 0.93 1.59 19.50 Door 136 12120 517.34 517.63 0.81 0.33 0.16 20.58 Door 137 18152 517.24 517.53 0.61 0.28 0.04 11.60 Door 138 18848 517.24 517.53 0.69 0.30 0.02 14.98 Door 139 16096 517.22 517.51 0.78 0.76 1.09 18.96 Bay 140 29139 517.43 517.72 0.60 0.60 0.51 11.15 Door 141 42933 517.36 517.65 0.95 0.27 0.04 28.36

'Dresden Calculation Package No. LIP-DRE-001, Appendix A,Figures A-5a to A-5e 2 Dresden Calculation Package No. LIP-DRE-001, Appendix A, Figures A-7a to A-7e 3 Dresden Calculation Package No. LIP-DRE-O01, Appendix A,Figures A-10a to A-10e 4 Dresden Calculation Package No. LIP-DRE-001, Appendix A,Figures A-12a to A-12e 5 Dresden Calculation Package No. LIP-DRE-001, Appendix A, Figures A-14a to A-14e RCN: LIP-099 Page 14 of 18

Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4 The predicted LIP flooding depths and duration above the lowest non-watertight opening elevations at the critical entrances to the site buildings are provided in Table 5.

Table 5: LIP Predicted Flood Results at the Critical Doors and Bays of the Sites Buildings Max. Flooding Depth Above the Lowest Non- Flooding Duration Door/Bay No. Reference Grid Water Tight Opening Above 517.5 (ft MSL)

Element No. (517.5 ft MSL) 1 ft hrs Bay 124 32060 0.39 1.48 Door 125 27979 0.37 1.31 Door 126 25725 0.36 1.29 Bay 127 24591 0.36 1.25 Door 128 23848 0.37 1.25 Bay 129 20577 0.39 1.25 Door 130 19161 0.40 1.25 Door 131 16735 0.40 1.23 Bay 132 13733 0.39 1.21 Door 133 13400 0.38 1.20 Door 134 12103 0.35 1.15 Door 135 11156 0.27 1.06 Door 136 12120 0.13 0.74 Door 137 18152 0.03 0.20 Door 138 18848 0.03 0.23 Door 139 16096 0.01 0.05 Bay 140 29139 0.22 1.07 Door 141 42933 0.15 0.95 Non-watertight opening elevation of 517.5 ft MSL per UFSAR Section 2.4 (Reference 6).

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Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4 Figure 4: Locations of Doors and Bays RCN: LIP-099 Page 16 of 18

Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4

5. COMPARISON OF CURRENT AND REEVALUATED LIP FLOOD HAZARD The plant grade elevation of Dresden Station is 516.71 ft NAVD 88 (517.00 ft MSL) and non-watertight openings in walls are at elevation 517.21 ft NAVD 88 (517.50 ft MSL). According to the UFSAR (Section 2.0),

(Reference 6) the previous LIP investigation concluded that the LIP water surface elevations would not exceed the finished floor elevation of the plant.

The design basis LIP analysis calculated a flow depth of 0.45 ft, which is 0.05 ft below the plant's elevation of 517.21 ft NAVD 88 (517.50 ft MSL) for non-water tight openings (Reference 11). The results of the reevaluated LIP flood hazard show the predicted maximum LIP flooding water surface elevations at the main doors and bays of the site buildings range from 517.22 ft to 517.61 ft NAVD 88 (517.51 ft to 517.90 ft MSL), which is 0.01 ft to 0.40 ft higher than the lowest non-watertight opening elevation. The results in Table 5 show that the approximate water surface elevations could be above the non-watertight door opening elevation for approximately 0.05 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> (3 minutes) to 1.48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> (89 minutes).

RCN: LIP-099 Page 17 of 18

Local Intense Precipitation Evaluation Report Dresden Nuclear Power Station Exelon Corporation April 29, 2014 Rev 4

6. REFERENCES
1. Aero-Metric Photogrammetry and Geospatial Data Solutions (2008). Vertical Accuracy Assessment Report for U.S. Army Corps of Engineers, St. Louis Direct, Grundy County, IL. Available at http://www.isgs.uiuc.edu/nsdihome/webdocs/ilhmp/county/grundy.html accessed June 6, 2012.
2. AMEC Calculation Package LIP-DRE-001 (2012). Dresden Local Intense Precipitation.
3. Exelon Corporation (2012). Dresden Generating Station Profile.

http://www.exeloncorp.com/powerplants/dresden/Pages/profile.aspx. Accessed: October 10, 2012.

4. FLO 2D (2009). Data Input Manual. Version 2009.06
5. FLO 2D (2009). Reference Manual. Version 2009.
6. Dresden (2009). UFSAR Section 2.0 Site Characteristics,Revision 8, June 2009.
7. Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture (2012). Web Soil Survey. Available online at http://websoilsurvey.nrcs.usda.gov/. Accessed

[10/12/2012].

8. United States Army Corps of Engineers (2007), Engineering publication EM 1110-1-1005, Appendix C- Development and Implementation of NAVD 88.
9. ENERCON (2014). Calculation number DRE14-0017. I
10. United State Department of Commerce, National Oceanic and Atmospheric Administration (NOAA),

VERTCON- Vertical Datum Conversion Map. Available at: http://www.ngs.noaa.gov/cgi-bin/VERTCON/vert-con.prl. Accessed August 27, 2012

11. United States Nuclear Regulatory Commission (1982) Systematic Evaluation Report (SER) topics II-3.A and 11-3.B.
12. United States Nuclear Regulatory Commission (2011). NUREG/CR-7046, Design-Basis Flood Estimationfor Site Characterizationat NuclearPower Plants in the United States of America.

RCN: LIP-099 Page 18 of 18

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