ML16355A172

Storm Surge Technical Evaluation Report Surry Power Station Hazard Reevaluation Review

ML16355A172
Person / Time
Site:	Surry
Issue date:	12/20/2016
From:	Taylor Engineering
To:	Office of New Reactors
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Download: ML16355A172 (47)

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Storm Surge Technical Evaluation Report Surry Power Station Hazard Reevaluation Review Prepared for By December 2016

TECHNICAL EVALUATION REPORT STORM SURGE 1.0 Historical Storm Surge Data.

Information Submitted by the Licensee As documented in the Flood Hazard Reevaluation Report (FHRR), the licensee performed a detailed site and region-specific hurricane climatology study to develop the hurricane meteorological parameters for storm surge analyses at the Surry Power Station (SPS). For the meteorological analysis, the study relied on HURDAT2 hurricane data, best track hurricane data, and synthetic hurricane data (representing 10,013 synthetic tropical cyclone tracks) generated and filtered within a 200-kilometer (km) radius of the Chesapeake Bay opening (Figure 1). The licensee validated the synthetic data through comparison with historic data and considered the synthetic storm parameters as more conservative (i.e., predicting greater effects) than historical storm data (FHRR, Sec. 2.4.1.1).

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Figure 1. Historical Hurricane Tracks near the Study Area (200 km radius from Chesapeake Bay) (Source: FHRR, Figure 2.4-3)

The licensee also: (1) reviewed recorded water level data from the NOAA CO-OPS stations at Sewells Point, Virginia (Station 8638610), Chesapeake Bay Bridge Tunnel (Station 8638863),

and Kiptopeke, Virginia (Station 8632200), to identify the events that caused historical extreme Page 3 of 36

water levels; (2) compared with the recorded water level data the NOAA Sea, Lakes, and Overland Surges (SLOSH) model predicted extreme water levels for Category 1 through Category 4 hurricane storm surge at the three NOAA CO-OPS stations; and (3) reviewed 1851-2010 historical hurricanes with tracks in the vicinity of SPS. Figure 2 shows the historical storm tracks that the licensee considered as intersecting the area of interest, including those storms responsible for many of the recorded high water levels at the stations identified above (FHRR, Sec. 2.4.2.1.1).

Figure 2. Tracks of Selected Historical Hurricanes that affected the SPS Vicinity (Source: FHRR, Figure 2.4-4)

Staff Technical Evaluation The staff concluded that the licensee reviewed a sufficiently large amount of storm surge data.

The staff verified that the licensee identified, adequately described, and appropriately evaluated all relevant storms and surges through an independent storm surge analysis.

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2.0 Probable Maximum Hurricane.

Information Submitted by the Licensee Following NUREG/CR-7046, the licensee applied a Hierarchical Hazard Assessment to deterministically evaluate the PMH. HURDAT2 hurricane data, best track hurricane data, and synthetic hurricane data provided data for the deterministic evaluation. During this process, the licensee generated 10,013 synthetic tropical cyclone tracks and validated the synthetic data through comparison with historic data. The licensee states the synthetic storm parameters are considered as being more conservative than historical storm data.

The licensee generated an initial storm set from a combination of 11 potential storm bearings (-

120º to -20º in 10º intervals) and five potential landfall locations for a shoreline segment appropriate for the SPS site (between NWS 23 Mile Posts 2200 and 2300, Figure 3). This procedure produced an initial storm set of 1,620 hypothetical events; assigned maximum wind speeds for each storm track based on the bearing-specific values derived from the SPS PMH evaluation; and expanded each potential storm track into a set of storms using the bearing-specific ranges of forward speed and radius of maximum wind(Table 1). The licensee divided each range into finite units and created a unique synthetic storm for each combination (FHRR, Sec. 2.4.1.2).

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Figure 3. Simulated Storm Tracks in the SPS Vicinity Bearings Ranging from -120 º to -20º (Source: FHRR, Figure 2.4-36)

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Table 1. Recommended PMH-level Parameters and Parameter Ranges (Source: FHRR, Table 2.4-4)

The licensee used the SLOSH model as the screening-level assessment modeling tool to identify:

(a) the sensitivity of storm surge at SPS to different storm parameters (i.e., storm track, radius of maximum winds, etc.) (see Figures 4 and 5); and (b) the specific combinations of storm parameters and storm tracks that result in the largest predicted storm surges at SPS. The licensee performed the SLOSH simulations with steady-state conditions. The licensee ranked storms from the initial storm set based on the SLOSH simulated maximum stillwater elevations (that exceeded 23 ft-NAVD88) at the SPS intake and discharge locations to generate a refinement storm set (FHRR, Sec. 2.4.1.2).

The licensee compared the Maximum of MEOW (MOM, where MEOW represents Maximum Envelope of Water) (Table 2) to the recorded water levels (Table 3). The licensee opines that historic extra tropical storms have caused storm surges roughly equivalent to those predicted for a simulated Category 1 hurricane. The licensee also concludes that Table 2 confirms that recorded water levels resulting from historic hurricanes have caused storm surges roughly equivalent to those predicted for simulated Category 1 and 2 hurricanes (FHRR, Sec. 2.4.2.1.1).

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Figure 4. Screening Results SLOSH-simulated Stillwater Elevation as a Function of Storm Bearing and Forward Speed (Source: FHRR, Figure 2.4-34)

Figure 5. Screening Results SLOSH-simulated Stillwater Elevation as a Function of Storm Bearing and Radius to Maximum Winds (Source: FHRR, Figure 2.4-35)

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Table 2. NOAA SLOSH MOM Water Levels at Selected Gage Locations (Source: FHRR, Table 2.4-2)

Table 3. Top 10 Extreme Water Levels (Source: FHRR, Table 2.4-1)

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Table 3. Top 10 Extreme Water Levels (Continued) (Source: FHRR, Table 2.4-1)

Based on a review of the NOAA CO-OPS stations historical extreme water level data; an examination of the SLOSH model predicted extreme water level events from hurricane storm surge at three NOAA CO-OPS stations located near SPS; and a review of available historical storm information, the licensee concluded that the probable maximum storm surge (PMSS) at SPS will be from a major hurricane (the PMH) (FHRR, Sec. 2.4.2.1.1).

The licensee used SLOSH model results to complete a screening-level assessment to determine specific storm parameter combinations that provide the highest stillwater surge elevations at SPS.

The licensee used the ADCIRC model to further evaluate storm parameter combinations. Table 4 summarizes the parameter combinations associated with the refinement storm set events. The 15 storms making up the refinement storm set represent five different potential storm bearings, three potential landfall locations, three potential forward speeds, and three potential radii of maximum winds. By varying the timing of the storm landfall, the licensee determined that a storm landfall occurring one hour prior to high tide at Sewells Point results in the highest surge elevations at SPS (FHRR, Sec. 2.4.2.2.4).

Based on the 15 refinement storm set events simulations, the licensee found a deterministic PMH with the following parameters: Track Direction () = -60°; Landfall Mile Post = 2225 (Latitude 35.913°, Longitude -75.596°); Radius of Maximum Winds (Rmax) = 35 nm; Forward Speed (Vf)

= 15 kt; Maximum 1-min, 10-m Overwater Wind Speed (Vm) = 119.9 kt; and Central Pressure Deficit (CPD) = 98 mb (FHRR, Sec. 2.4.2.2.5).

Staff Technical Evaluation The licensee provided details of the FHRR analyses that deterministically developed PMH. The staff concluded that the licensee has identified and described an acceptable PMH.

To develop an independent storm surge modeling effort, NRC staff completed an independent PMH development as detailed below.

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Table 4. Refinement Storm Set Parameters (Source: FHRR, Table 2.4-5)

Notes: Vm is maximum sustained wind speed; CPD is central pressure deficit; and Rmax is radius of maximum wind.

General Philosophy The independent meteorological analysis aimed to determine a track, intensity, translation speed, and wind structure which generates the maximum surge in a deterministic storm surge simulation for the most extreme yet plausible wind stress. Three general components are used for this realization: 1) tropical cyclone climatology; 2) Maximum Potential Intensity (MPI) theory; and 3) a series of synthetic track runs based on parameters established by climatology and MPI, refined in each simulation series to determine the optimum parameters and track for the peak surge.

In all cases, staff examined Schwerdt et al. (1979), also sometimes referred to as NWS 23 for its technical report designation, for initial parameter guidance. This large report, funded by NRC and the U.S. Army Corps of Engineers (USACE), provides parameters for a Standard Project Hurricane and a PMH as well as a wealth of other information. Specifically, for a Gulf of Mexico or Atlantic landfall location (NWS 23s Figures 1.1 and 1.2), one can determine a value (or range) for central pressure ( ) in kPa, pressure deficit ( = ) in kPa, radius of maximum winds

( ) in nm, translation speed (T) in kts, and track direction ( ) in degrees (deg) (NWS 23s Figs 2.1-2.9). In this project, software input requires pressure units to be in mb, and and track bearing to be used instead. In context, a storm moving from south to north is 0 deg, a storm moving from east to west is -90 deg, and a storm moving from west to east is +90 deg. The surge determination continued in the NWS 23 philosophy for using physically plausible parameters of

, , , T, and .

However, additional parameters were required to complete the metrological review and storm development. NWS 23s Chapter 16 provides some graphics and analysis for , decrease after landfall as well as an equation for peak wind decrease, but no formal equation is provided for .

NWS 23 instead refers the reader to Ho et al. (1975) for post-landfall equations. Many newer versions have since been formulated, and with larger datasets. NWS 23 also does not address wind profile, which also influences peak surge values. Since for a given intensity, larger hurricanes (as defined by faster outer-core winds for the same peak winds) impose higher surge, relative conservatism was introduced through a wind profile parameter (details below).

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Finally, some deviation was also required from NWS 23, which is 36 years old as of this writing.

The hurricane database sample size has increased, reanalyses have resulted in database changes, new databases have been developed, and new MPI formulations have been introduced.

However, even when accessing the latest climatology, the solid foundation behind NWS 23 still provided well-posed solutions for storm speed and direction. The MPI formulations still were also generally close to NWS 23s . However, often required larger values than NWS 23 provided for east coast storms, and often did not match the latest climatology.

Track, Angle, Translation Speed, and The storm center distance is tested at increments of 0.5 , 0.75 , 1.0 , or 2.0 west of the site, thus constraining the right-front quadrant near the site. Irish et. al (2008) have shown the peak surge will be within 0.5-1.0 , whereas 2.0 is used to examine surge sensitivity outside the eyewall. As most sites are inland, a script using Generic Mapping Tool (GMT) commands increments at the reverse track angle to determine the landfall point (http://gmt.soest.hawaii.edu). The Global Self-consistent, Hierarchical, High-resolution Shoreline Database (GSHHSD) is accessed to determine the coast (Wessel and Smith 1996). Because water may actually be a bay system too far inland to properly represent landfall, nearby buddy checks were added to the code and then examined with http://itouchmap.com to insure an open-ocean coastline was used for the landfall location.

Climatology provides the constraints for determining the track suites. Specifically, climatology provides bounds where track angles are not physically possible for an intense landfalling hurricane. For example, as background assessment, the recently revised hurricane database HURDAT2 (http://www.aoml.noaa.gov/hrd/hurdat/Data_Storm.html) was used (Landsea and Franklin 2013). This database now includes landfall data and updated track information based on a systematic committee process that checks for errors and previously unknown measurements.

For example, with regards to plants located in New England, the 1938 hurricane which caused the highest storm surge for this location, had its pressure and wind revised. Since HURDAT2 only begins in 1850, earlier storms were also consulted, such as the 1821 Long Island Hurricane.

Track angles were computed for intense hurricanes from HURDAT2 and plotted as histograms and box plots. Graphically, another useful tool was http://coast.noaa.gov/hurricanes, in which multiple tracks could be overlain based on search radius and intensity.

However, as these data samples are limited, it is assumed any track is possible for an intense hurricane as long as it comes from a direction with supporting water temperatures. In most cases in the northeast, tracks were just removed from long land fetches or those far removed from the Gulf Stream. In general, these angle parameters were consistent with NWS 23.

Each track angle has a genesis point in the deep tropics, then generally curves and parallels the Gulf Stream to its landfall location, then slowly recurves in the poleward region. Steps to develop each track included determining the landfall location, setting the waypoints, and coding into a spline routine. Once each track angle was established, the refinements with a new required limited effort. The landfall angle is set as a straight line before and after landfall to maintain consistency with surge results.

Storm speed is computed from HURDAT2. To account for curvature and accelerations, an Akima spline (Akima 1970) and finite differencing was applied to allow development of accurate translation speeds for the last HURDAT2 point. Plausible speed ranges are then determined near the landfall point from statistical metrics, histograms, and box plots. However, since wind stress is important, especially for the extratropical transitioning phase of fast-moving storms, an upper Page 12 of 36

range was chosen physically consistent with such storms. Generally, these were close to NWS 23.

The parameter has only recently been quantified in a database known as the extended best track (EBT) (http://rammb.cira.colostate.edu/research/tropical_cyclones/tc_extended_

best_track_dataset). Basic statistical metrics, histograms, and box plots were examined within 5 deg of a site, and cross-examined against the most intense historical hurricanes. In most cases, EBT showed ranges of larger than NWS 23. Values of within 1-1.5 quartiles were used for testing. The independent analysis did not apply the largest EBT values, as extreme intensity is generally limited for large eyewalls by gradient wind balance.

Data is output hourly along the spline, consistent with storm speed specifications. Landfall in all runs are shifted so they occur on the same day and hour for easier comparison among the multiple surge simulations.

Pressure Storm intensity is the most important parameter, but fortunately well-constrained by water temperature and empirical relationships for fast-moving storms. The post-landfall weakening rate is also well-established by empiricism. There are three phases of pressure trends.

In the deep tropics, a tropical depression is ramped up to an intense steady-state hurricane. To avoid transient effects on the surge simulation and to not shock the storm surge model, this deepening should occur reasonably far from the landfall site.

At the landfall locations, storms making landfall in the lower latitudes have a peak intensity established by the MPI theories of Holland (1997) and Emanuel (1988). If landfall is a higher latitude, values of Kubat (1995) and DeMaria and Kaplan (1994) are used in which a hurricane is weakening over cooler water, but moving fast enough to retain high winds. To include a measure of uncertainty for extreme rare events, the MPI is then lowered an additional 10 mb. The MPI values are determined from a monthly water temperature climatology database from the National Climate Data Center, then three standard deviations are added to the water temperature to include the extreme high sea surface temperature (SST) events. In general, these values are close to NWS 23.

After landfall, pressure follows the formulation = , where =

and t is the hours after landfall. The constant a follows Vickery (2005) which varies regionally and includes an error term, since pressure increase after landfall varies for each storm.

Vickery uses = + + , in which and vary regionally for New England, mid-Atlantic, Florida, and the Gulf Coast. To impose conservatism so the storm weakens slower after landfall, we increase a at three standard deviations of .

The EBT database includes a measure of known as the outer closed isobar. is then determined by adding 2 mb to this parameter. Statistics showed this value to generally be 1013 mb, which sometimes contrasted with higher values in NWS 23. 1013 mb is an established operational parameter, and used in these runs.

Section 8 contains details of the final storm developed by the independent meteorological review and storm development effort.

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Wind Profile Wind profile is not addressed by NWS 23 other than with . Holland (1980) showed a variety of wind profiles were possible radially outwards from , characterized by a scaling parameter B that generally varies from 0.75 to 2.5 in conjunction with a parametric gradient wind formulation.

Wind profiles with B>1.5 generally have a peaked wind and a radial wind profile that decreases sharply. Wind profiles with 1.5>B>0.75 have a flatter radial wind profile in which tropical storm-force winds extend far from the eyewall. Fitzpatrick (2013) and Brouillette et al.

(2013) have shown that tropical cyclones with flatter wind profiles cause higher storm surge compared to a smaller storm with the same peak wind, speed, and . However, gradient wind constraints show it is difficult for intense storms to have a small and small B. To mimic a conservatively large tropical cyclone, a value of 1.1 was used for B. More research is needed to assess wind structure in extreme tropical cyclones, and to determine the lower limits of B.

3.0 Probable Maximum Wind Storm Information Submitted by the Licensee The licensee did not consider the PMWS because the licensee estimated the highest storm surge elevation from the PMH.

Staff Technical Evaluation Staff agrees that the PMH will develop the highest storm surge.

4.0 Antecedent Water Levels Information Submitted by the Licensee The licensee calculated the 10% exceedance high tide of 3.524 ft-NAVD88 using observed monthly maximum tide data obtained over a continuous 21-year period (January 1, 1993 through December 31, 2013) at the Sewells Point, Virginia NOAA tidal gaging station. The licensee estimated Cumulative Sea Level Rise (SLR) using the annual rate at the Sewells Point station and projected SLR over 50 years. The licensee added the estimated SLR to the 10% exceedance high tide to obtain an Antecedent Water Level (AWL) of 4.3 ft-NAVD88 (FHRR, Sec. 2.4.2.2.1).

Staff Technical Evaluation Table 5 provides the staff-estimated tidal datums from NOAA tidal gage station data.

Table 5. NOAA Tidal Datums near SPS NOAA 8638610 - Sewells Station Name Point, VA Latitude 36° 56.8' N Longitude 76° 19.8' W Tide Datum Elevation (ft-NAVD88)

Mean Higher High Water (MHHW) 1.15 Page 14 of 36

Mean High Water (MHW) 0.94 Mean Sea Level (MSL) -0.26 Mean Tide Level (MTL) -0.27 Mean Low Water (MLW) -1.49 Mean Lower Low Water (MLLW) -1.61 NGVD29 -0.85 Plant Datum MSL Plant Datum Elevation -0.26 The licensee followed the appropriate method to estimate the AWL. However, the FHRR does not provide details on the SLR rate used in the projection of SLR over the next 50 years.

Staff performed an independent evaluation of AWL. Using available water level data and SLR annual rate at the Sewells Point, Virginia NOAA tidal gaging station, staff estimated a 10%

exceedance high tide of 3.03 ft-NAVD88 and a SLR projected to 50 years of 0.79 ft to provide an estimated AWL of 3.83 ft-NAVD88. A comparison of staff-estimated AWL and licensee-estimated AWL shows that the licensee applied a more conservative (larger) AWL in the surge simulations.

Thus, the licensee used an acceptable antecedent water level for the PMSS analyses.

5.0 Storm Surge Models 5.1 Surge Propagation Models Information Submitted by the Licensee The licensee applied SLOSH versions 1.65b and 3.97 simulations with steady-state conditions to rank storms from the initial storm set based on the SLOSH-simulated maximum stillwater elevations at the SPS intake and discharge locations. From the ranking, the licensee generated a refinement storm set consisting of 15 storms (FHRR, Sec. 2.4.2.2.4).

The licensee applied the steady-state ADCIRC model to evaluate the maximum stillwater elevations for the 15 storms in the refinement storm set and to identify and develop the final PMSS stillwater elevations (FHRR, Sec. 2.4.2.2.5).

Staff Technical Evaluation Based on the FHRR documentation, staff concludes the FHRR analysis applied appropriate storm parameters and conditions for the SLOSH modeling. The staffs independent analysis allowed the staff to conclude that the licensees ADCIRC model had sufficient resolution to differentiate various surge elevations at different parts of SPS.

5.2 Wave Models Information Submitted by the Licensee For evaluations of combined effect, the licensee used deterministic PMSS results from three storms (STORMIDs 948, 1097and 1098) as input to the ADCIRC+SWAN model. The licensee states that due to the direction of waves throughout the PMSS, most waves will move away from the site (i.e. predominantly in the south west and north east directions). The licensee applied a Page 15 of 36

combined ADCIRC and SWAN model to include the simulation of waves with the worst storm (Hurricane Isabel) surge in the evaluation of the deterministic combined effects and probabilistic combined effect flood (FHRR, Sec. 2.9.1.1).

Staff Technical Evaluation The FHRR does not provide information on storm surge wave modeling, specifically the model version, model input and result files, conditions or scenarios for the modeling, and the model parameter values applied in the model. However, the staffs independent analysis allowed the staff to evaluate the accuracy of the wave propagation modeling results.

5.3 Topography and Bathymetry Information Submitted by the Licensee The FHRR does not provide detailed information on data source, resolution, processing, and application into SLOSH, ADCIRC, and SWAN model grids of the topography and bathymetry data used in the storm surge and wave modeling.

Staff Technical Evaluation The FHRR does not provide discussion of the bathymetry and topography data. However, the staffs independent analysis allowed the staff to evaluate the appropriateness and accuracy of the bathymetric and topographic data and grid resolutions and conclude that it was reasonable and acceptable.

6.0 Numerical Model Validation Information Submitted by the Licensee The FHRR does not provide: (1) detailed discussion/description of the storm surge model and wave models validation (verification); (2) information on the model parameters, model input data, and conditions applied for the model validation; (3) criteria to measure model performance; and (3) information on SLOSH, ADCIRC, and SWAN model performances for the simulations.

Staff Technical Evaluation The staffs independent analysis allowed the staff to evaluate the model validation and determine that it was reasonable and acceptable.

7.0 Numerical Model Error and Uncertainty Information Submitted by the Licensee The licensee performed hundreds of SLOSH model surge simulations using a range of PMH parameters to identify: (a) the storm parameters associated with significant changes in storm surge at SPS; and (b) the storm parameters and storm tracks combinations that can provide the highest predicted storm surges at SPS (see Figure 4 and Figure 5). For conservative results (i.e.,

for higher estimation of higher storm surge stillwater elevations), the licensee selected for the refinement level assessment, 15 storms which have storm parameters and storm tracks combinations that provide the highest predicted storm surges at SPS (FHRR, Sec. 2.4.1.2).

The licensee performed five ADCIRC model simulations to determine the sensitivity of the simulated maximum storm surge at SPS with the timing of the storm arrival time. The licensee found that the storm surge at SPS is highest when the storm made landfall one hour before the peak tide at Sewells Point station. Therefore, for conservative results in the PMSS calculations, Page 16 of 36

the licensee applied a storm that made landfall one hour before the peak tide at Sewells Point station (FHRR, Sec. 2.4.1.2).

The licensee included an uncertainty effects of 0.8 feet in the evaluation of deterministic combined effects flooding high water level.

The licensee included epistemic uncertainty and aleatory variability in the estimation of the probabilistic maximum storm surge. The licensee included the following sources of significant uncertainty in the probabilistic analysis: (1) uncertainty in representing tide occurring coincidentally with surge; (2) bias or uncertainty in numerical surge and wind field models; and (3) uncertainty due to sampling.

Staff Technical Evaluation The FHRR does not provide detailed description of the methodology and estimation of deterministic SLOSH, ADCIRC, and ADCIRC+SWAN model error and uncertainty so staff could not evaluate the uncertainty included in the estimation of deterministic PMSS.

The FHRR does not provide detailed description of the methodology and estimation of epistemic uncertainty and aleatory variability, However, the staffs independent and deterministic analysis precluded the necessity to evaluate the uncertainty included in the licensees estimation of probabilistic maximum storm surge.

8.0 Storm Surge Water Levels Information Submitted by the Licensee The licensee applied the steady-state (storm parameters did not vary from the initial specifications) ADCIRC model to: (1) further evaluate the 15 storms in the refinement storm set; and (2) develop the final PMSS stillwater elevations. Notably, Storm 1097 in Table 4 provides the parameters for the PMSS. Timing the storm landfall to occur one hour before high tide at Sewells Point in the ADCIRC modeling of the 15 refinement storms, the licensee found a PMSS of 21.3 ft-NAVD88 or 22.74 ft-MSL (discharge location) and 20.9 ft-NAVD88 or 22.34 ft-MSL (intake location) for the PMSS (FHRR, Sec 2.4.3).

The licensee provided a deterministic combined effects flooding high water level of 24.2 ft-MSL.

This elevation is the combination of the maximum modeled stillwater (inclusive of wave setup and the 25-year river flood flow) elevation of 21.0 ft-MSL, uncertainty effects of 0.8 feet, and the difference between the peak simulated tide elevation at Sewells Point, Virginia, and the antecedent water level of 2.374 ft, which includes applicable sea level rise (FHRR, Sec. 2.9.3).

The FHRR focuses on the probabilistic peak total water level, which is below the deterministic value, as the FHRR states the probabilistic results provide the more refined analysis conducted as part of the reevaluation.

Staff Technical Evaluation The licensee developed separate deterministic and probabilistic stillwater and total water levels near SPS. The FHRR focuses on the probabilistic water levels, which the FHRR states are based on the more refined analysis conducted as part of the reevaluation. The storm parameters developed and applied for the FHRR PMH (Table 1; FHRR Table 2.4-4) indicate a general weakening of storms (reduction in wind speed) as storms head in a more westerly direction. The discussion below shows the results of the independent storm surge simulations conducted to provide additional estimates of the deterministic PMH storm surge water levels near SPS.

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Independent Simulations NRC staff developed and executed independent storm surge simulations to develop an independent estimate of the deterministic PMSS at SPS. The independent simulations for SPS applied the SWAN+ADCIRC model. The SWAN+ADCIRC model applied SWAN+ADCIRC mesh from the FEMA Region III Coastal Storm Surge Study. Staff applied the FEMA Region III mesh in a test simulation on Taylor Engineerings high performance computer, Merlin, that demonstrated the ability to replicate model results from the FEMA study output files provided to NRC. Figure 6 shows a comparison of the Merlin and FEMA Region III study water level results near SPS for the Merlin validation test run (Hurricane Isabel).

Figure 6. Water Level Time Series Comparison at Cape Henry, VA, Near SPS (during Hurricane Isabel)

The independent simulations applied time-varying, two-dimensional wind and pressure fields for tropical storms with varying parameters. Staff developed the tropical storm parameter combinations to produce the MPI storm conditions at SPS. Table 6 presents the range of parameters tested in the initial sensitivity simulations. Figures 7 and 8 show the storm tracks for basin and regional views. The site location, well up the James River Estuary, created a complex storm surge response at the site, which required examination of many storm track angles and landfall locations.

Table 6. Tropical Storm Parameters in ADCIRC Sensitivity Simulations Central Pressure (mb) 895, 905 Radius to Maximum Winds (Rmax) (NM) 20, 40, 60 Page 18 of 36

Forward Velocity (kt) 15, 25, 35 Track Angle at Landfall (degrees counter-60, 45, 30, 0 clockwise from north)

Landfall Location (Rmax from site; to west) 0.5, 0.75, 1 Figure 7. Storm Tracks for Independent Simulations; Basin View The initial test simulations applied only the ADCIRC (hydrodynamic) model to expedite run times which allow examination of storm surge sensitivity to the tropical storm parameters. Staff completed 25 ADCIRC simulations based on Table 6. Based on these results, the final simulations applied the SWAN+ADCIRC model, which couples the hydrodynamic model to a spectral wave model (SWAN) to allow calculation of wave-induced water level effects near the site. Review of the refined simulation results showed angles at landfall of 60 degrees counter-clockwise from north produced the highest water levels at the site. Due to the site location, several landfall location and storm track angle combinations created similar storm surge levels at the site. The final nine SWAN+ADCIRC simulations applied the parameter values and ranges listed in Table 7.

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Figure 8. Storm Tracks for Independent Simulations; Regional View Table 7. Tropical Storm Parameters in SWAN+ADCIRC Final Simulations Central Pressure (mb) 895, 905 Radius to Maximum Winds (Rmax) (NM) 40 Forward Velocity (kt) 15 Track Angle at Landfall (degrees counter-60, 45 clockwise from north)

Landfall Location (Rmax from site; to west) 0.5, 0.75, 1 Review of FHRR Storm Surge Simulations The FHRR documents the storm surge analyses as part of the SPS reevaluation. The reevaluation applied the SWAN+ADCIRC model with the highly resolved mesh developed during the FEMA Region III Coastal Storm Surge Study. The FHRR presents results from both probabilistic and deterministic storm surge analyses. For the deterministic analysis, the FHRR applied SLOSH simulations to perform a screening analysis of storm surge at SPS. The deterministic analysis applied the ADCIRC to evaluate further storm conditions shown to produce high water levels at SPS in the SLOSH simulations. These ADCIRC simulations allowed development of the PMSS at SPS for the deterministic analysis. In addition, the FHRR documents a probabilistic modeling approach designed to develop the 1E-6 Annual Exceedance Probability (AEP) stillwater elevation at SPS (probabilistic approach to PMSS). The probabilistic analysis applied SLOSH to develop screening-level simulations and ADCIRC to develop refined model results for specific storms.

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Comparison of FHRR and Independent Simulation Water Levels The results from the independent simulations with the MPI forcing allow comparison of the FHRR PMSS (deterministic and probabilistic) water levels. Table 8 presents details of the final three independent simulations with comparisons to the FHRR PMSS water levels for the SPS East location shown in Figure 9. The FHRR values are for the combined events analysis that includes the effects of waves and river flow. To understand the effects of the tropical storm forcing at the site, the independent simulations apply zero river flow in the SWAN+ADCIRC simulations as listed in Table 8. Table 8 presents the final water level values in Mean Sea Level (MSL) with the conversion between MSL and NAVD88 listed. Notably, the FHRR contains a MSL to NAVD88 conversion that differs from the conversion determined from local NOAA tide stations. The table includes separate data for the still water level, 10% exceedance high tide, and sea level rise estimate. Independent Run 1 provides the most suitable MPI storm given historical data and meteorological forcing in the SPS region. Independent Runs 2 and 3 present additional results for storms with different landfall location and central pressure to show sensitivity of the final model results to these parameters. Notably, as shown in Table 8, the independent simulations apply similar storm size, forward velocity, and landfall angle as compared to the FHRR PMH storm, but the independent simulations apply lower central pressure values.

The stillwater levels for the NRC staff independent simulations compare well with the FHRR deterministic stillwater level with the NRC staff independent results above the FHRR value.

Notably, the FHRR value includes an uncertainty term and the NRC staff independent results do not. Both the FHRR and NRC deterministic stillwater values exceed the Current Design Basis (CDB) and current flood protection level at some buildings as listed in FHRR Table 3.0-1. The FHRR probabilistic stillwater level is below the CDB and the current flood protection level.

Review of wave conditions in Table 8 shows the NRC staff independent simulation results produce slightly lower wave heights than the FHRR deterministic model results on the east side of the site. Analysis of the wave and water level results allows for estimation of wave runup with application of the runup equations as listed in USACE Coastal Engineering Manual (CEM)

Chapter VI-5. Table 8 and the wave runup analysis apply different runup equations for the low level intake embankment (sloped, grass covered structure) and the low level intake structure (vertical wall). Importantly, the embankment structure has a crest elevation of 36 ft-MSL and the runup will cause overtopping. Combining the stillwater level with the wave runup estimates allows calculation of the total water level. Total wave levels at the east side of SPS near the intake structure for the FHRR deterministic analysis are very similar to the NRC staff independent simulation results with the FHRR values within 1.5 ft of the independent results. These values exceed the CDB total water levels as listed in FHRR Table 3.0-1. The FHRR probabilistic total water levels are below the deterministic total water levels, but above the CDB total water level for the intake structure.

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Table 8. SWAN+ADCIRC Final Simulation Parameters and Water Level Comparisons: SPS East Surry FHRR PMH Staff SWAN+ADCIRC Staff SWAN+ADCIRC Staff SWAN+ADCIRC Parameter (StormID 948) Independent Run#1 Independent Run#2 Independent Run#3 Peripheral Pressure (mb) 1020 1013 1013 1013 Central Pressure (mb) 930 (DeltaP = 90 mb) 895 895 905 Radius of Maximum Winds (NM) 35 40 40 40 Forward Speed (kt) 15 15 15 15 Angle at Landfall (deg CCW from N) -70 -60 -60 -60 Landfall Location 36.3N, -75.8W -0.75 Rmax -1.0 Rmax -1.0 Rmax 10% Astronomical High T ide (ft-NAVD88) 1 3.5 3.03 3.03 3.03 Sea Level Rise (ft) 2 0.8 0.79 0.79 0.79 Location SPS East SPS East SPS East SPS East FHRR Revaluated Deterministic Stillwater (ft-MSL; T able 2.9-7) 24.2 25.9 25.7 24.4 FHRR Revaluated Probabilistic Stillwater (ft-MSL; T able 2.9-7/3.0-1) 20.8/18.9 N/A N/A N/A FHRR T able 3.0-1 CDB Stillwater (ft-MSL) 22.7 22.7 22.7 22.7 FHRR T able 3.0-1 Current Flood Varies (24 to 27.5; Varies (24 to 27.5; Varies (24 to 27.5; Varies (24 to 27.5; Protection Elevation (ft-MSL) most 26.5) most 26.5) most 26.5) most 26.5)

Low Level Low Level Low Level Low Level Low Level Low Level Low Level Low Level Location Intake Intake Intake Intake Intake Intake Intake Intake Structure Embankement Embankement 3 Structure4 Embankement 3 Structure4 Embankement 3 Structure4 9.8/5.6 9.5/5.3 9.0/5.2 Reevaluated Deterministic PMH SWAN 11.2/6.4 (headed 10 deg Hs/T p [FHRR T able 2.9-3] (ft/sec)

(headed 19 deg South of (headed 6 deg South of (headed 5 deg South of North of West)

West) West) West)

Reevaluated Probabilistic PMH SWAN 9.9/6.4 (headed 12 deg North Hs/T p [FHRR T able 2.9-5] (ft/sec)

N/A N/A N/A of West)

FHRR T able 2.9-4 Reevaluated Deterministic T otal Water Level 39.9 38.8 43.6 40.3 41.4 38.2 41.1 37.9 (ft-MSL)

FHRR T able 2.9-6 Reevaluated Probabilistic T otal Water Level 36.3 31.4 N/A N/A N/A (ft-MSL)

FHRR T able 3.0-1 CDB T otal Water Level (ft-MSL)

N/A 28.6 28.6 28.6 28.6 1)

Conversion between MSL and NAVD88 Datum: MSL = NAVD88+1.44 ft (FHRR value) [NRC Staff value MSL = NAVD88+0.26 ft; NOAA Station]

2)

Apply projection for 50 years (remaining operating life of plant) 3)

Apply USACE CEM method for sloped embankements with grass slopes and wave height equal to Hs (Embankment crest at 36.0 ft-MSL) 4)

Apply USACE CEM method for vertical walls with wave height equal to Hs and runup equal to 1.5*Hs Page 22 of 36

Figure 9. Station Locations for Independent Analysis Water Levels Table 9 presents details of the final three independent simulations with comparisons to the FHRR PMSS water levels for locations on the west side of SPS as shown in Figure 9. The FHRR stillwater levels match those from SPS East in Table 8 and the NRC independent simulation results are 0.1 ft lower than for SPS East. As the output locations for SPS East and West are not separated by a great distance, similar stillwater levels are expected. Both the FHRR and NRC deterministic stillwater values exceed the CDB, but are below the current flood protection level at the west side of SPS as listed in FHRR Table 3.0-1. The FHRR probabilistic stillwater level is below the CDB and the current flood protection level.

Review of wave conditions in Table 9 shows the NRC staff independent simulation results produce lower wave heights than the FHRR deterministic model results. While the wave heights and periods are different, both the FHRR results and the NRC staff independent results show the waves heading to the west or southwest. Importantly, these waves will not cause wave runup to occur on structures at the west side of SPS. Therefore, the wave runup will be negligible and the total water level should equal the stillwater level.

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Table 9. SWAN+ADCIRC Final Simulations Parameters and Water Level Comparisons:

SPS West S urry FHRR PMH Staff SWAN+ADCIRC Staff SWAN+ADCIRC Staff SWAN+ADCIRC Parameter (S tormID 948) Independent Run#1 Independent Run#2 Independent Run#3 Peripheral Pressure (mb) 1020 1013 1013 1013 Central Pressure (mb) 930 (DeltaP = 90 mb) 895 895 905 Radius of Maximum Winds (NM) 35 40 40 40 Forward Speed (kt) 15 15 15 15 Angle at Landfall (deg CCW from N) -70 -60 -60 -60 Landfall Location 36.3N, -75.8W -0.75 Rmax -1.0 Rmax -1.0 Rmax 10% Astronomical High T ide (ft-NAVD88) 1 3.5 3.03 3.03 3.03 Sea Level Rise (ft) 2 0.8 0.79 0.79 0.79 Location SPS West SPS West SPS West SPS West FHRR Revaluated Deterministic Stillwater (ft-MSL; T able 2.9-7) 24.2 25.8 25.6 24.3 FHRR Revaluated Probabilistic Stillwater (ft-MSL; T able 2.9-7/3.0-1) 20.8/18.9 N/A N/A N/A FHRR T able 3.0-1 CDB Stillwater (ft-MSL) 22.7 22.7 22.7 22.7 FHRR T able 3.0-1 Current Flood Protection Elevation (ft-MSL) 26.5 26.5 26.5 26.5 Location SPS West SPS West SPS West SPS West 11.2/6.4 (headed 10 deg 5.9/4.8 5.8/4.8 5.4/4.7 Reevaluated Deterministic PMH SWAN North of West; no effect on (headed 51 deg South of West; (headed 43 deg South of West; (headed 42 deg South of West; Hs/T p [FHRR T able 2.9-3] (ft/sec)

Western structures) no runup) no runup) no runup) 9.9/6.4 (headed 12 deg North Reevaluated Probabilistic PMH SWAN Hs/T p [FHRR T able 2.9-5] (ft/sec) of West; ; no effect on N/A N/A N/A Western structures) 1)

Conversion between MSL and NAVD88 Datum: MSL = NAVD88+1.44 ft (FHRR value) [NRC Staff value MSL = NAVD88+0.26 ft; NOAA Station]

2)

Apply projection for 50 years (remaining operating life of plant)

To evaluate the effect of flow on the James River, NRC staff developed a version of Independent Run #1 that included the FHRR listed 25-yr James River flow value (267,300 cfs). Table 10 shows the stillwater level and total water level results for the FHRR analysis, NRC staff Independent Run

1. 1 with no river flow (also in Table 8), and NRC staff Independent Run #1 with the FHRR 25-yr James River flow. The results indicate that adding in the river flow increases the NRC independent stillwater level by 0.7 ft at SPS East. The inclusion of river flow and the small increase in stillwater level does not alter wave conditions at SPS East. The total water levels in Table 10 show increases of 0.8 ft at the low level intake embankment and the low level intake structure. Notably, staff developed an independent estimate of the 25-yr James River flow and the value was 192,915 cfs, which is well below the FHRR-stated value. Application of the staff 25-yr flow value would decrease the influence of the river flow on the water levels.

The total water level results in Table 10 produce the same conclusions as determined for the results in Table 8. The NRC staff independent simulation results produce slightly lower wave heights than the FHRR deterministic model results on the east side of the site. Total wave levels at the east side of SPS near the intake structure for the FHRR deterministic analysis are very similar to the NRC staff independent simulation results with the FHRR values within 2.5 ft of the independent results (when river flow is considered in the Independent Run #1 simulation). These values exceed the CDB total water levels as listed in FHRR Table 3.0-1. The FHRR probabilistic total water levels are below the deterministic total water levels, but above the CDB total water level for the intake structure.

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Table 10. SWAN+ADCIRC Final Simulations Parameters and Water Level Comparisons: SPS East Including River Flow in Independent Simulations Staff SWAN+ADCIRC Confirmatory Surry FHRR PMH Staff SWAN+ADCIRC Independent Parameter Run#1; FHRR 25-year James River (StormID 948) Run#1; no river flow Flow Peripheral Pressure (mb) 1020 1013 1013 Central Pressure (mb) 930 (DeltaP = 90 mb) 895 895 Radius of Maximum Winds (NM) 35 40 40 Forward Speed (kt) 15 15 15 Angle at Landfall (deg CCW from N) -70 -60 -60 Landfall Location 36.3N, -75.8W -0.75 Rmax -0.75 Rmax 10% Astronomical High T ide (ft-NAVD88) 1 3.5 3.03 3.03 Sea Level Rise (ft) 2 0.8 0.79 0.79 Location SPS East SPS East SPS East FHRR Revaluated Deterministic Stillwater (ft-MSL; T able 2.9-7) 24.2 25.9 26.6 FHRR Revaluated Probabilistic Stillwater (ft-MSL; T able 2.9-7/3.0-1) 20.8/18.9 N/A N/A FHRR T able 3.0-1 CDB Stillwater (ft-MSL) 22.7 22.7 22.7 FHRR T able 3.0-1 Current Flood Varies (24 to 27.5; Varies (24 to 27.5; Varies (24 to 27.5; Protection Elevation (ft-MSL) most 26.5) most 26.5) most 26.5)

Low Level Low Level Low Level Intake Low Level Intake Low Level Intake Low Level Intake Location Intake Embankement 3 Structure4 Embankement 3 Structure4 Intake Structure Embankement Reevaluated Deterministic PMH SWAN 11.2/6.4 9.8/5.6 9.8/5.6 Hs/T p [FHRR T able 2.9-3] (ft/sec) (headed 10 deg North of West) (headed 19 deg South of West) (headed 6 deg South of West)

Reevaluated Probabilistic PMH SWAN 9.9/6.4 Hs/T p [FHRR T able 2.9-5] (ft/sec)

N/A N/A (headed 12 deg North of West)

FHRR T able 2.9-4 Reevaluated Deterministic T otal Water Level 39.9 38.8 43.6 40.3 44.4 41.1 (ft-MSL)

FHRR T able 2.9-6 Reevaluated Probabilistic T otal Water Level 36.3 31.4 N/A N/A (ft-MSL)

FHRR T able 3.0-1 CDB T otal Water Level (ft-MSL)

N/A 28.6 28.6 28.6 1)

Conversion between MSL and NAVD88 Datum: MSL = NAVD88+1.44 ft (FHRR value) [NRC Staff value MSL = NAVD88+0.26 ft; NOAA Station]

2)

Apply projection for 50 years (remaining operating life of plant) 3)

Apply USACE CEM method for sloped embankements with grass slopes and wave height equal to Hs (Embankment crest at 36.0 ft-MSL) 4)

Apply USACE CEM method for vertical walls with wave height equal to Hs and runup equal to 1.5*Hs 9.0 Wave Runup, Inundation, and Drawdown.

Information Submitted by the Licensee The licensee estimated wave characteristics for three alternative flood scenarios along the shoreline adjacent to SPS (FHRR, Sec. 2.9.2.1.2).

1) Alternative 1 The maximum flow rate for the one-half PMF in the James River at SPS was calculated at 430,500 cfs. The tide corresponding to the static antecedent 10% high tide Page 25 of 36

and the wind field for extra-tropical storm Isabel (worst regional hurricane) were simulated together in ADCIRC. The licensee calculated a resulting maximum water surface elevation of 11.9 ft-NAVD88 (13.3 ft-MSL) and 12.4 ft-NAVD88 (13.8 ft-MSL) at the SPS intake and discharge canals.

2) Alternative 2 The PMF peak flow rate at SPS was calculated as 867,300 cfs. The 25-year surge height was calculated to be 5.2 feet. The 10% exceedance high tide used for this alternative was 3.5 ft-NAVD88 (4.9 ft-MSL) at SPS. The licensee calculated a resulting maximum water surface elevation of 14.1 ft-NAVD88 (15.5 ft-MSL) at SPS.

3) Alternative 3 The 25-year flood flow was calculated as 267,300 cfs. The deterministic PMSS is the maximum result from the following events: a) STORMID 1097 - a slow-moving (i.e., 15 knots), intense (i.e., maximum wind speed of 119.9 knots) hurricane bearing in a west-of-north direction (i.e., -600 bearing) and making landfall along the Outer Banks of North Carolina; b) STORMID 948 - a slow-moving (i.e., 15 knots) intense (i.e., maximum wind speed of 115.1 knots) hurricane bearing in a west-of-north direction (i.e., -700 bearing) and making landfall near the Virginia/North Carolina border; and c) STORMID 1098 - a slow-moving (i.e.,

15 knots) intense (i.e., maximum wind speed of 119.9 knots) hurricane bearing in a west-of-north direction (i.e., i.e., -600 bearing) and making landfall near the Virginia/North Carolina border. The licensee applied ADCIRC+SWAN to estimate maximum SWELs from STORMID 948 of 24.2 ft-MSL and 24.1 ft-MSL (22.8 and 22.7 ft-NAVD88) at the SPS intake and discharge canals.

The licensee applied the Technical Advisory Committee for Water Retaining Structures method to estimate wave runup at the intake embankments as a result of the deterministic PMSS and used ASCE 7-10 guidance to estimate standing wave crest heights due to depth limited waves.

Table 11 presents wave runup and wave crest elevations caused by the deterministic PMSS. The licensee estimated a significant wave height of 11.2 ft, wave peak period of 6.4 s, and wave direction of 170 degrees for the deterministic PMSS (FHRR, Sec. 2.9.2.1.2).

Table 11. Wave Runup and Wave Crest Elevations Caused by the Deterministic PMSS (Source: FHRR, Table 2.9-4)

The licensee also calculated wave runup at the SPS intake for the probabilistic PMSS. Table 12 presents wave runup and wave crest elevations caused by the probabilistic PMSS. The licensee Page 26 of 36

estimated a significant wave height of 9.9 ft, wave peak period of 6.4 s, and wave direction of 168 degrees for the probabilistic PMSS (FHRR, Sec. 2.9.2.1.2).

Table 12. Wave Runup and Wave Crest Elevation Caused by the Probabilistic Storm Surge (Source: FHRR, Table 2.9-6)

For combined effects flooding, the licensee opines that the PMSS conditions will result in a small portion of inundation encroaching upon the site. However, due to heavy vegetation and the groins present at the discharge canal, it is extremely unlikely for waves to form within this area.

Therefore, the licensee further opines that wave runup effects are negligible on the western portion of the site and are not included in licensees calculations (FHRR, Sec. 2.9.1.1).

The licensee provided the area of inundation during the deterministic PMSS (Figure 10) and probabilistic PMSS (Figure 11). The licensee shows the deterministic and probabilistic PMSS stillwater elevations relative to the intake canal embankment profile (Figure 12) and low level intake structure profile (Figure 13).

Page 27 of 36

Figure 10. Deterministic PMSS Stillwater Elevation Inundation Map (Source: FHRR, Figure 2.9-4)

Page 28 of 36

Figure 11. Probabilistic PMSS Stillwater Elevation Inundation Map (Source: FHRR, Figure 2.9-7)

Figure 12. Intake Canal Earthen Embankment Profile (Source: FHRR, Figure 2.9-12)

Page 29 of 36

Figure 13. Low Level Intake Structure Profile (Source: FHRR, Figure 2.9-11)

The licensees estimates of combined event maximum water elevations show the deterministic PMSS provides the highest water level when wave crest is included (Table 13). However, the licensee opines that as the probabilistic PMSS estimation is more refined than the deterministic PMSS estimation. Therefore, the probabilistic PMSS provides the appropriate estimated maximum water elevation.

Table 13. Summary of Combined Event Maximum Water Elevations (Source: FHRR, Table 2.9-7)

Staff Technical Evaluation The licensee provided wave height and period information and runup estimation methodology information and results for each scenario.

Based on Figure 12 and using the USACECEM method, staff estimated an average slope of 3.1:1 at the intake embankment for all scenarios. Staff then calculated the reduction factor values required to achieve the report runup for each scenario. This calculation indicated a possible Page 30 of 36

inconsistency in the application of the runup methodology (i.e., staff obtained inconsistent reduction factors); however, without more detailed information, staff could not evaluate the accuracy of the PMSS induced wave runup.

The licensee calculated the most severe tsunami drawdown at -3.6 ft-MSL (as a result of a near-field submarine mass failure) which is less severe than existing site low water thresholds (-4.8 ft-MSL). Due to the lack of detailed information, staff could not evaluate the accuracy of the PMSS drawdown results.

Figures 10 to 13 show that the deterministic and probabilistic PMSS do not inundate the main SPS plant buildings (the power block), but the PMSS includes wave run-up on the intake embankment and the intake structure, which are above the CDB. The run-up is calculated to exceed the height of the intake canal. Based on these three figures, staff concludes the PMSS does not inundate the main portion of SPS, but the PMSS does exceed the CDB for the intake embankment and intake structure. The results of the independent NRC storm surge modeling and wave runup analysis confirm these results.

10.0 Flood Event Duration Information Submitted by the Licensee The FHRR includes Figure 14 (FHRR Figure 2.9-13) that shows the storm surge hydrographs at the SPS Discharge and SPS Intake for the deterministic analysis of the Alternative 3 scenario. However, the FHRR does not directly discuss the duration of the storm surge at SPS.

Figure 14. Stage Hydrographs (surge+wave setup) for Alternative 3 deterministic (FHRR Figure 2.9-13)

Staff Technical Evaluation FHRR Figure 2.9-13 (Figure 14) provides the storm surge hydrograph for the deterministic analysis of Alternative 3. The FHRR does not directly discuss the duration of water levels above Page 31 of 36

certain datums or design levels. The licensee did not estimate flood duration because the estimated PMSS (probabilistic analysis shown in FHRR Figure 2.9-15) does not inundate SPS at the main plant buildings (the power block).

11.0 Hydrostatic and Hydrodynamic Forces.

Information Submitted by the Licensee The licensee calculated hydrostatic, hydrodynamic, and wave forces at the SPS intake under three scenarios: a) the controlling deterministic combined flood effects due to precipitation; b) the controlling deterministic combined flood effects along the SPS shoreline (Alternative 3); and c) the probabilistic combined flood effects due to storm surges (FHRR, Sec. 2.9.2.3).

The licensee conservatively estimated velocities by assuming floodwaters can approach from the most critical direction relative to the site and applied the upper bound flood velocity to calculate hydrodynamic and impact loads. Tables 14 to 17 provide the results of the calculations of hydrostatic forces, upper bound flow velocity, and hydrodynamic forces at the emergency service water pump and oil storage room for each of the considered scenarios and non-breaking wave forces on vertical walls at the SPS intake (FHRR, Sec. 2.9.2.3).

Table 14. Estimated Hydrostatic Forces for the Emergency Service Water Pump and Oil Storage Room (Source: FHRR, Section 2.9.2.3)

Table 15. Upper Bound Flow Velocity for Hydrodynamic Load Calculations (Source: FHRR, Section 2.9.2.3)

Table 16. Estimated Hydrodynamic Forces for the Emergency Service Water Pump and Oil Storage Room (Source: FHRR, Section 2.9.2.3)

Table 17. Estimated Breaking Wave Forces Calculated for Vertical Walls at the SPS Intake Page 32 of 36

(Source: FHRR, Section 2.9.2.3)

Staff Technical Evaluation The licensee evaluated the hydrostatic, hydrodynamic, and wave forces for the above three scenarios.

Licensee appears to have performed force calculations using freshwater specific weight. Licensee did not discuss or specify this choice. Because the SPS lies on the James River, 30 miles from Chesapeake Bay, it may be reasonable to use freshwater. However, because storm surge constitutes the major source of elevated water level, some discussion is warranted. Using seawater water weight would increase force calculations by 2.5%.

Staff independently verified the hydrostatic force and elevation calculations using the licensees water surface and ground elevations. Staff could not verify licensees water surface and ground elevations.

The licensee calculated the upper bound flow velocities at the emergency service water pump and oil storage room using FEMA P-55, section 8.5.6 method based on the shallow water wave celerity. Staff independently verified the calculations using the licensees water surface and ground elevations. Staff could not verify licensees licensee water surface and ground elevations.

Staff independently calculated the hydrodynamic force using the licensees water surface and ground elevations and previously verified velocities. The FHRR does not specify the required drag coefficient, nor the emergency service water pump and oil storage room dimensions required for independent verification of the drag coefficient.

Staff determined the licensee used the minimum drag coefficient of 1.25 (suitable for a building with width-to-height ratio of 12 or less) and verified licensee calculations of hydrodynamic force and force application elevation. Staff could not verify licensees licensee water surface and ground elevations, or the licensees drag coefficient.

The licensee applied ASCE 7-10, 5.4.4.2 and FEMA P-55, 8.5.8.2 formulas to estimate the breaking wave loads in the three scenarios. Staff verified the licensee applied the highest Risk Category IV dynamic pressure coefficient and verified the breaking wave loads estimated by the licensee. Staff could not verify licensees values for depth used in the calculation.

The Licensee stated, Loads due to non-breaking waves were calculated as the hydrostatic and hydrodynamic loads described above. However, the staff noted that this method and the referenced calculations do not account for increased pressures due to wave crest elevations.

12.0 Debris and Water-Borne Projectiles.

Information Submitted by the Licensee The licensee calculated debris impact loads near the SPS intake under three scenarios: a) the controlling deterministic combined flood effects due to precipitation; b) the controlling deterministic Page 33 of 36

combined flood effects along the SPS shoreline (Alternative 3); and c) the probabilistic combined flood effects due to storm surges. Table 18 provides the results of the calculations of debris impact loads at the emergency service water pump and oil storage room for each of the considered scenarios. The licensee opined that due to the relatively shallow flooding at the low level intake structure and the location of the structure on the fringe of the floodplain, most large debris would remain in the main channel of the James River (FHRR, Sec. 2.9.2.3).

Table 18. Estimated Debris Impact Loads for the Emergency Service Water Pump and Oil Storage Room (FHRR Section 2.9.2.3)

Staff Technical Evaluation The licensee evaluated the debris impact loads for the above three scenarios. Staff evaluated the licensee application of ASCE 7-10, 5.4.5 and FEMA P-259, 4.1.2.9 formulas to estimate the debris impact load.

• Staff considers the debris weight of 2,000 lbs reasonable and conservative.

• Licensee did not provide formula coefficient values for evaluation.

• Staff independently calculated the debris impact load using the licensees debris weight, depths, and flow velocities and conservative coefficient values. Staff estimates were within 8% of the licensees estimates.

Staff confirmed the licensee provided a reasonably conservative debris load estimate. Staff could not verify licensees values for depth, flow velocity, and formula coefficient values.

13.0 Effects of Sediment Erosion and Deposition.

Information Submitted by the Licensee The licensee estimated flow depth over the top of the intake canal embankment at 0.9 ft. The licensee used the FEMA methodology from Atlantic Coast Guidelines to calculate an overtopping rate of 1,400 cfs at the intake canal embankment during PMSS. The licensee opined that erosion of the grassed intake canal embankment due to the overtopping and associated wave action is likely.

Staff Technical Evaluation Other than that mentioned above, the FHRR does not provide any information on potential erosion or deposition at SPS.

14.0 Consideration of Other Site-Related Evaluation Criteria.

Information Submitted by the Licensee The FHRR does not provide discussion of how seismic and non-seismic information was used in the postulation of worst-case storm surge scenarios.

Staff Technical Evaluation Page 34 of 36

The FHRR does not discuss how seismic and non-seismic information was used in the postulation of worst-case storm surge scenarios.

15.0 Conclusion The information on flooding from storm surge that is specific to the data needs of the Integrated Assessment is described in Section 4 of the FHRR.

Staff confirmed the licensees conclusion that the reevaluated hazard for flooding from combined effects with storm surge is not bounded by the current design basis flood hazard; therefore, the licensee should include flooding from combined effects with storm surge within the scope of an additional assessment.

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Brouillette, R., D. Minton, N. Dill, J. Suhayda, P. Fitzpatrick, and R. Jacobsen, 2013: GNO flood protection notice of construction completion design assessment by non-federal sponsor, Coastal Protection and Restoration Authority technical report.

DeMaria, M., and J. Kaplan, 1994: Sea surface temperature and the maximum intensity of Atlantic tropical cyclones. J. Climate, 7, 1324-1334.

Emanuel, K., 1988: The maximum intensity of hurricanes. J. Atmos. Sci., 45, 1143-1155.

Fitzpatrick, P. J., 2013: Tropical cyclones. Encyclopedia of Natural Resources. Y. Q. Wang, Ed.

CRC Press, Taylor & Francis group, 1060-1068.

Ho, F. P., R. W. Schwerdt, and H. V. Goodyear, 1975: Some climatological characteristics of hurricanes and tropical storms, Gulf and East Coasts of the United States. NOAA Technical Report NWS 15, 87 pp.

Holland, G. J., 1980: An analytical model of the wind and pressure profiles in hurricanes. Mon.

Wea. Rev., 108, 1212-1218.

Holland, G. J., 1997: The maximum potential intensity of tropical cyclones. J. Atmos. Sci., 54, 2519-2541.

Irish, J. L., D. T. Resio, and J. J. Ratcliff, 2008: The influence of storm size in hurricane surge. J.

Phys. Oceanogr., 38, 2003-2013.

Kubat, G. B., 1995: Tropical cyclone intensity relationships. Masters Thesis, Colorado State University, 86 pp. Available at: http://www.dtic.mil/dtic/tr/fulltext/u2/a300097.pdf .

Landsea, C. W., and J. L. Franklin, 2013: Atlantic hurricane database uncertainty and presentation of a new database format. Mon. Wea. Rev., 141, 3576-3592 Schwerdt, R. W., F. P. Ho, and R. R. Watkins, 1979: Meteorological criteria for Standard Project Page 35 of 36

Hurricane and Probable Maximum Hurricane wind fields, Gulf and East Coast of the United States. NOAA Technical Report NWS 23, 317 pp.

Vickery, P. J., 2005: Simple empirical models for estimating the increase in the central pressure of tropical cyclones after landfall along the coastline of the United States. J. Appl.

Meteor., 44, 1807-1826.

Wessel, P., and W. H. F. Smith, 1996: A Global Self-consistent, Hierarchical, High-resolution Shoreline Database, J. Geophys. Res., 101, 8741-8743.

Zachry Nuclear Engineering, Inc. (ZNE) 2015.Dominion Flooding Hazard Reevaluation Report for Surry Power Station Units 1 and 2. Stonington, Connecticut.

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