RS-16-002, Supplemental Response to NRC Audit Review Request for Additional Information Regarding Fukushima Lessons Learned - Flood Hazard Reevaluation Report

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Supplemental Response to NRC Audit Review Request for Additional Information Regarding Fukushima Lessons Learned - Flood Hazard Reevaluation Report
ML16020A497
Person / Time
Site: Limerick  Constellation icon.png
Issue date: 01/13/2016
From: Jim Barstow
Exelon Generation Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-16-002
Download: ML16020A497 (15)
v • d • e


Text

E~xelt Generation 10 CFR 50.54(f)

RS-1 6-002 January 13, 2016 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DO 20555-0001 Limerick Generating Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-39 and NPF-85 NRC Docket Nos. 50-352 and 50-353

Subject:

Supplemental Response to NRC Audit Review Request for Additional Information Regarding Fukushima Lessons Learned - Flood Hazard Reevaluation Report

References:

1. Exelon Generation Company, LLC Letter to USNRC, Flood Hazard Reevaluation Report Pursuant to 10 CFR 50.54(f) Regarding the Fukushima Near-Term Task Force Recommendation 2.1: Flooding, dated March 12, 2015 (RS-15-064)
2. NRC Letter, Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated March 12, 2012
3. Exelon Generation Company, LLC Letter to USNRC, Response to NRC Audit Review Request for Additional Information Regarding Fukushima Lessons Learned - Flood Hazard Reevaluation Report, dated October 28, 2015 (RS-1 5-268)
4. NRC Email from T. Govan to D. Distel, Request for Additional Limerick Information Needs Responses and Input/Output Files on the Docket, dated December 1, 2015 In Reference 1, Exelon Generation Company, LLC (EGC) provided the Flooding Hazard Reevaluation Report (FHRR) for the Limerick Generating Station, Units 1 and 2 in response to the March 12, 2012 Request for Information Enclosure 2, Recommendation 2.1, Flooding, Required Response 2, (Reference 2). The NRC conducted an auditiwebinar review of the Limerick Generating Station, Units 1 and 2 FHRR on September 24, 2015. In support of the FHRR audit, the NRC provided audit information needs items. The information provided by EGC to address the audit information needs items was subsequently reviewed by the NRC during the audit. Reference 3 provided the responses to the NRC requested additional information items identified during the Limerick Generating Station, Units 1 and 2 FH-RR audit review on September 24, 2015.

U.S. Nuclear Regulatory Commission Supplemental Response to NRC Audit Review Request for Additional Information (Flooding Hazard Reevaluation Report)

January 13, 2016 Page 2 The purpose of this letter is to provide the responses to the additional NRC requested additional information items identified in Reference 4. Enclosure 1 to this letter provides the individual responses to each of the items identified in Reference 4. Enclosure 2 to this letter provides the Limerick FHRR model input/output files also requested in Reference 4.

This letter contains no new regulatory commitments.

If you have any questions regarding this report, please contact Ron Gaston at (630) 657-3359.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 13 th day of January 2016.

Respectfully submitted, James*arsto*w

  • Director - Licensing & Regulatory Affairs Exelon Generation Company, LLC

Enclosures:

1. Limerick Generating Station, Units 1 and 2 Supplemental Response to NRC Audit Review Request for Additional Information Regarding Fukushima Lessons Learned - Flood Hazard Reevaluation Report
2. DVD labeled: LGS FHRR Electronic Files for NRC Docket, Limerick Generating Station, December 2015 Document Components:

HMS LGS Information Need 1 Electronic Files LM-0699 Local Intense Precipitation LM-070 1 Proba~ble Maximum Flood-Hydraulics LM-0702 Dam Failure LM-0704 Error Uncertainty cc: NRC Regional Administrator - Region I NRC Project Manager, NRR - Limerick Generating Station NRC Senior Resident Inspector - Limerick Generating Station Ms. Tekia Govan, NRR/JLD/PPSD/HMB, NRC Director, Bureau of Radiation Protection - Pennsylvania Department of Environmental Resources (w/o Enclosure 2)

R. R. Janati, Chief, Division of Nuclear Safety, Pennsylvania Department of Environmental Protection, Bureau of Radiation Protection (w/o Enclosure 2)

Enclosure 1 Limerick Generating Station, Units 1 and 2 Supplemental Response to NRC Audit Review Request for Additional Information Regarding Fukushima Lessons Learned - Flood Hazard Reevaluation Report (11 pages)

Supplemental Response to Request for Additional Information (FHRR)

Page 1 of 11 Information Need 5: Streams and Rivers - PMP Spatial Distribution for Possum Hollow Run and Sanatoga Creek Drainages Backg~round: It is not clear if the point PMP is used for the Possum Hollow Run and Sanatoga Creek drainages. The staff was unable to find isohyets for these drainages. Using an isohyetal pattern over the two drainages can significantly affect the water-surface elevation near the LGS site.

Request: The FHRR states that all-season PMP estimates for the Possum Hollow Run and Sanatoga Creek drainages were developed using BOSS HMR52 software. From the FHRR and the calculations, it is not clear which spatial distributionsfor the PMP are used for these two drainages. Because the drainage areasfor these two drainagesare less than lOmi2, typically the point PMP is used. The staff requests details of the spatial distribution, including isohyetal plots, of the PMP over Possum Hollow Run and Sanatoga Creek drainages.

Response

The Possum Hollow Run watershed has a 1.4 mi2 drainage area. The smallest isohyet area (ellipse) from the HMR-52 standard elliptical pattern, shown on Figure 5.1, is 10 mi2 for "Isohyet Area A." This means all the drainage area of Possum Hollow Run is contained within isohyet area A as shown on Figure 5.2. For this reason, BOSS HMR52 does not produce an isohyetal plot showing spatial distribution of the PMP for the Possum Hollow Run watershed.

incremental 72-hr PMP for the Possum Hollow Run watershed is provided in Table 5.1. As per HMR-52 reference manual, "the 10-mi2 isohyet is taken to be the same as point rainfall." The reasons BOSS HMR52 SOftware is used is to develop the default PMP temporal distributions and to evaluate the effect of storm centering.

The Sanatoga Creek watershed has a 7.1 mi2 drainage area. The smallest isohyet area (ellipse) from the HMR-52 standard elliptical pattern, shown on Figure 5.1, is 10 mi2 for "Isohyet Area A." However, as shown on Figures 5.3 and 5.4, the Sanatoga Creek watershed intersects ellipse A at three locations. This means the PMP for the Sanatoga Creek watershed includes PMP from isohyet areas A and B. However, the majority of the Sanatoga Creek watershed is within isohyet area A. Therefore, the majority of the PMP is from the 10 mi 2 area which is considered to be the same as point rainfall. Incremental 72-hr PMP for the Sanatoga Creek watershed is provided in Table 5.2. The main reason the BOSS HMR52 software is used is to develop PMP temporal distributions and to evaluate the effects of storm centering. Because of the irregular shape of the Sanatoga Creek watershed, PMP that occurs outside the area of isohyet Area A is captured when using BOSS HMR52.

These rainfall configurations are the bases for the Possum Hollow Run and Sanatoga Creek portions of Limerick PMP Calculation (LM-0698). However, a sensitivity analysis was performed to evaluate the effects of using a 1-Square Mile, 1-Hour PMP on Possum Hollow Run and Sanatoga Creek watersheds. The 1-Square Mile, 1-Hour PMP was obtained from HMR-52 as explained in Calculation LM-0698. The 1-Square Mile, 1-Hour PMP also incorporated the 10-mi,6-hr duration PMP from the second hour to the sixth hour based on recommendations in NUREG/CR-7046. Also, the 1-Square Mile, 1-Hour PMP was conservatively assumed to be uniformly distributed over the 1.4 and 7.1-Square Mile watersheds for Possum Hollow Run and Sanatoga Creek, respectively. PMP values used in the sensitivity analysis are provided in Table

Supplemental Response to Request for Additional Information (FHRR)

Page 2of 11 5.3. The HEC-HMS model for Possum Hollow Run and Sanatoga Creek watersheds developed in Calculation LM-0700 were re-run using the PMP values from Table 5.3 (1-Square Mile, 1-Hour PMP; 10- Square Mile, 6-Hour duration). The Schuylkill River HEC-RAS model that contains the Possum Hollow Run reach and the Sanatoga Creek HEC-RAS model, both developed in Calculation LM-0701, were updated based on the revised flows from the HEC-HMVS models for the Possum Hollow Run and Sanatoga Creek watersheds. The downstream boundary condition for Sanatoga Creek is also revised based on the new results from the Schuylkill River and Possum Hollow Run HEC-RAS model. A water level of 169.27 ft NGVD29 from the confluence of Sanatoga Creek with the Schuylkill River HEC-RAS model at cross-section 48.41 was used as the downstream boundary condition for the Sanatoga Creek HEC-RAS model.

The results from the HEC-HMS and the HEC-RAS models are summarized in Table 5.4. As shown in Table 5.4, the HEC-RAS model results when using 1-Square Mile, 1-Hour PMP produce higher water surface elevations compared to the previous analysis that uses 10-Square Mile PMP only obtained from the HMR-52 program. As shown in Table 5.4, the increase in water level at LGS on the Schuylkill River is due to the increase flow resulting from the 1-Square Mile PMP added from Possum Hollow (conservatively assuming coincidental peaks).

Based on the HEC-RAS model results, the revised peak PMF water surface elevation in the Schuylkill River, Possum Hollow Run, and Sanatoga Creek at LGS are still below the "lowest grade level entrance to any safety related structure" of 217 feet NGVD29 referenced in the LGS UFSAR.

Figure 5.1: Standard Elliptical Isohyetal Pattern from LIMR-52

Supplemental Response to Request for Additional Information (FHRR)

Page 3 of 11 Figure 5.2: GIS Figure Showing Isohyetal Pattern and Orientation of PMP Storm for Possum Hollow Run Watershed

Supplemental Response to Request for Additional Information (FHRR)

Enclosure 1 Page 4 of 11 Table 5.1: Incremental 72-hr PMP for Possum Hollow Run Watershed (Obtained from Calculation LM-0698 page 431 of 1327)

ISOHYET DEPTH VS. DURATION INCREMENTAL PRECIPITATION STORM RAINFALL DEPTHS (inches) FOR TIME INCREMENTS ISOHYET SMIN lOMIN 1SMIN 30NIN 1-HR 2-HR 3-HR 6-HR 12-HR 18-HR 24-HR 30-HR 36-HR 42-HR 48-HR 54-HR 60-HR 66-HR 72-HR m-A-- 1.63 3.26 4.87 9.39 14.96 18.66 21.60 26.88 31.01 33.21 34.71 35.86 36.79 37.56 38.23 38.82 39.35 39.82 40.25i C .23 .47 .70 1.40 2.81 5.57 8.11 12.90 14.89 15.94 16.66 17.21 17.66 18.03 18.35 18.63 18.89 19.11 19.32 D .18 .37 .55 1.11 2.22 4.40 6.41 10.21 11.83 12.68 13.27 13.72 14.08 14.38 14.64 14.87 15.08 15.26 15.43 E .15 .29 .44 .88 1.76 3.48 5.07 8.06 9.30 9.96 10.41 10.76 11.04 11.27 11.47 11.65 11.80 11.95 12.07 F .12 .23 .35 .70 1.41 2.78 4.06 6.45 7.44 7.97 8.33 8.61 8.83 9.02 9.18 9.32 9.44 9.56 9.66 G .09 .18 .28 .55 1.11 2.20 3.20 5.11 5.93 6.37 6.67 6.90 7.09 7.24 7.38 7.50 7.60 7.69 7.78 H .07 .14 .20 .41 .82 1.62 2.37 3.76 4.34 4.65 4.86 5.02 5.15 5.26 5.35 5.43 5.51 5.57 5.63 I .05 .10 .15 .29 .59 1.16 1.69 2.69 3.10 3.32 3.47 3.59 3.68 3.76 3.82 3.88 3.93 3.98 4.02 J .03 .06 .09 .17 .35 .69 1.01 1.61 1.90 2.04 2.14 2.22 2.28 2.33 2.37 2.41 2.44 2.47 2.50 K .01 .02 .03 .06 .11 .23 .33 .54 .66 .73 .77 .81 .83 .86 .88 .90 .91 .93 .94 1 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 N .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 N .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 P .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 o .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 R .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 S .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 r---------------------------------------------------------------------------------------------m---------m m m m m m m m m m m m m m m m m m I AVERAGE 1.63 3.26 4.87 9.39 14.96 18.66 21.60 26.88 31.01 33.21 34.71 35.86 36.79 37.56 38.23 38.82 39.35 39.82 40.25' L----------------------------------------------------------------------------------------

Figure 5.3: Isohyetal Pattern/Spatial Distribution and Orientation of PMP Storm for Sanatoga Creek Watershed (Obtained from Calculation LM-0698 page 441 of 1327)

BASIN P?45 ISONYET PLOT:

  • =f Basin Boundary * *

= Storm Area Boundary *

  • SOHYETA S*1--ttt *tt.+tt*\*

Supplemental Response to Request for Additional Information (FHRR)

Page 5of 11 Figure 5.4: GIS Figure Showing Isohyetal Pattern/Spatial Distribution and Orientation of PMP Storm for Sanatoga Creek Watershed

Supplemental Response to Request for Additional Information (FHRR)

Enclosure 1 Page 6 of 11 Table 5.2: Incremental 72-hr PMP for Sanatoga Creek Watershed (Obtained from Calculation LM-0698 page 442 of 1327)

ISOHYFT DEPTH VS. DURATION DINCREMENTALPRECIPITATION 5TORM RAINFALL. DEPThS (inches) FOR TIME INCREMENTS ISOHYET 5MIN 1OM4IN1SMIN 3OMIN 1-HR 2-HR 3-HR 6-HR 12-HR 18-HR 24-HR 30-HR 36-HR 42-HR 48-HR 54-HR 60-HR 66-HR 72-HR

  • A 1.332 .79.39 14.96 18.66 21.60 26.88 31.01 33.21 34.71 35.86 36.79 37.56 38.23 38.82 39.35 39.82 40.25 0 .18 .37 .55 1.11 2.22 4.40 6.41 10.21 11.83 12.68 13.27 13.72 14.08 14.38 14.64 14.87 15.08 15.26 15.43 E .15 .29 .44 .88 1.76 3.48 5.07 8.06 9.30 9.96 10.41 10.76 11.04 11.27 11.47 11.65 11.80 11.95 12.07 F .12 .23 .35 .70 1.41 2.78 4.06 6.45 7.44 7.97 8.33 8.61 8.83 9.02 9.18 9.32 9.44 9.56 9.66 G .09 .18 .28 .5S 1.11 2.20 3.20 5.11 5.93 6.37 6.67 6.90 7.09 7.24 7.38 7.50 7.60 7.69 7.78 H .07 .14 .20 .41 .82 1.62 2.37 3.76 4.34 4.65 4.86 5.02 5.15 5.26 5.35 5.43 5.51 5.57 5.63 I .05 .10 .15 .29 .59 1.16 1.69 2.69 3.10 3.32 3.47 3.59 3.68 3.76 3.82 3.88 3.93 3.98 4.02 1 .03 .06 .09 .17 .35 .69 1.01 1.61 1.90 2.04 2.14 2.22 2.28 2.33 2.37 2.41 2.44 2.47 2.50 K .01 .02 .03 .06 .11 .23 .33 .54 .66 .73 .77 .81 .83 .86 .88 .90 .91 .93 .94 L .00 .00 .00 .00D .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 N4 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 N .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 P .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 Q .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 R .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 S .00 .00 .00 .OO .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .OO .00 AVERAGE 1.55 3.10 4.63 8.94 14.28 17.98 20.95 26.29 30.34 32.49 33.97 35.09 36.00 36.76 37.41 37.99 38.50 38.96 39.38

Supplemental Response to Request for Additional Information (FHRR)

Page 7 of 11 Table 5.3: 1-Hour 1-Square Mile and 6-Hour 10-Square Mile PMP for Sensitivity Analysis Area/

Duration J(minutes)

Time Time (hours)

[Incremental Rainfall (in)

ICumulative jRainfall (in) IAreal Duration Time (minutes) J(hours)]Rainfall ITime 1Incremental [Cumulative (in) Rainfall (in) 0 0.00 0.00 0.00 185 3.08 0.15 21.65 5 0.08 6.00 6.00 190 3.17 0.15 21.80 10 0.17 1.73 7.72 195 3.25 0.15 21.95 15 0.25 1.73 9.45 200 3.33 0.15 22.10 20 0.33 1.36 10.81 205 3.42 0.15 . 22.25 25 0.42 1.36 12.17 210 3.50 0.15 22.40 1-Square 30 0.50 1.36 13.53 215 3.58 0.15 22.55 Mile, 1-Hour PMP 35 0.58 0.73 14.26 220 3.67 0.15 22.70 40 0.67 0.73 14.99 225 3.75 0.15 22.85 45 0.75 0.73 15.72 230 3.83 0.15 23.00 50 0.83 0.73 16.44 235 3.92 0.15 23.15 55 0.92 0.73 17.17 240 4.00 0.15 23.30 60 1.00 0.73 17.90 245 4.08 0.15 23.45 65 1.08 0.15 18.05 250 4.17 0.15 23.60 70 1.17 0.15 - 18.20 255 4.25 0.15 23.75 260 4.33 0.15 23.90 75 80 T1.331.25 0.15 0.15 18.35 18.50 265 4.42 0.15 24.05 1 ,-I Q vJ 10-Square 270 4.50 0.15 24.20 Mile, 6-90 1.50 0.15 18.80 Hour 275 4.58 0.15 24.35 95 1.58 0.15 18.95 PMP 280 4.67 0.15 24.50 100 1.67 0.15 19.10 285 4.75 0.15 24.65 105 1.75 0.15 19.25 290 4.83 0.15 24.80 110 1.83 0.15 19.40 295 4.92 0.15 24.95 115 1.92 0.15 19.55 300 5.00 0.15 25.10 10-Square 120 2.00 0.15 19.70 305 5.08 0.15 25.25 Mile, 6-Hour PMP 125 2.08 0.15 19.85 310 5.17 0.15 25.40 130 2.17 0.15 20.00 315 5.25 0.15 25.55 135 2.25 0.15 20.15 320 5.33 0.15 25.70 140 2.33 0.15 20.30 325 5.42 0.15 25.85 145 2.42 0. 15 20.45 330 5.50 0.15 26.00 150 2.50 0.15 20.60 335 5.58 0.15 26.15 155 2.58 0.15 20.75 340 5.67 0.15 26.30 160 2.67 0.15 20.90 345 5.75 0.15 26.45 165 2.75 0.15 21.05 350 5.83 0.15 26.60 170 2.83 0.15 21.20 355 5.92 0.15 26.75 175 2.92 0.15 21.35 360 6.00 0.15 26.90 180 3.00 0.15 21.50 L L . a a ___________ L J U

Supplemental Response to Request for Additional Information (FHRR)

Page 8 of 11 River/HEC-RAS Station Table 5.4: Summary of Sensitivity Using 10 -Square Mile PMP on Analysis Using 1 -Hour, 1-Square Mile and Lowest Level Freeboard Possum Hollow Run and 6-Hour, 10-Square Mile PMP on Entrance (ft)

Sanatoga Creek Watershed Possum Hollow Run and Sanatoga Elevation (B-A)

(As reported in CalculationLM- Creek Watershed from LGS 0701, Section 8.0) (New Sensitivity Analysis) UFSAR (ft PMF Peak Water Level PMF Peak Water. Level NGVD29)

Discharge (ft NGVD29) Discharge (ft NGVD29)

(cfs) (cfs) "A" "..B" Schuylkill River at LGS 397,200 163.9 397,200 167.96 217 49.04 (River Mile 47.41)

Possum Hollow Run at 17,300 167.8 47,375 176 217 41.0 LGS (River Mile 0.458)

Sanatoga Creek at LGS 83,500 153.7 241,045 170.83 217 46.17 (River Mile 0.63) ________________ _____ _________________________

Supplemental Response to Request for Additional Information (FHRR)

Page 9 of 11 Information Need 9: Streams and Rivers - HEC-RAS Model Setup Backg~round: The FHRR does not state why the channel cross-sections estimatedfor Schuyllkill River, Possum Hollow Run, and Sanatoga Creek are conservative. The staff did not find this information in the calculations included in the ERR. The shape of channel cross-section can significantly influence the water-surface elevationfor a given discharge.

Request: The FHRR states that the licensee assumed the Schuylkill River cross-sections to be triangular in shape. The FHRR also states that the bathymetry information on the Possum Hollow Run and Sanatoga Creek were conservatively ignored. The staff request detailed description of how channel bathymetry for Schuylkill River, Possum Hollow Run, and Sanatoga Creek were determinedandwhy the assumptions stated in the FHRR are conservative.

Response

The channel bathymetry for the Schuylkill River is approximated as a triangle reflecting no width to the thalweg of the stream bed. The top surface of the natural river course, from left stream bank to right stream bank, at each cross section is developed from the river width for the water level at the time LiDAR was flown using the digital elevation model of Pennsylvania, obtained from the PAMAP LiDAR Program. The edge of water elevation was determined directly from the PAMAP LiDAR data. The corresponding channel invert elevations of the Schuylkill River are based on the stream bed profiles included in the Federal Emergency Management Agency (FEMA) Flood Insurance StUdy (FIS) for Berks, Montgomery and Philadelphia counties. The channel inverts are applied to the cross sections as a single point, midway between the stream bank stations, creating the approximated triangular shape.

Calibration of the hydraulic model incorporating the triangular bathymetry for the Schuylkill River was approached conservatively. Calibration of the channel was not attempted to achieve a tight fit with the observed data. All modelled peak water surface elevations for calibration events were greater than observed values, by up to as much as 2.7 feet. This was to ensure selected roughness coefficients were not too low and compensate for uncertainties surrounding stream bed geometry, although the effects of an approximated stream bed geometry is expected to be insignificant during high PMF flows. Even with the conservatisms incorporated into the hydrologic and hydraulic modeling for the Schuylkill River, the site grade is still at least 53.1 feet above the computed flood level for the PMF and at least 24.5 feet above the computed level for the PMF with dam failures included.

Bathymetry for Possum Hollow Run and Sanatoga Creek is completely ignored. Therefore, additional cross-sectional area below the water level at the time LiDAR was flown that would be available for flood conveyance is conservatively ignored. The edge of water elevation was determined directly from the PAMAP LiDAR data. Due to the lack of observed data, Manning "n" roughness coefficients were conservatively selected based on published values. For both Possum Hollow Run and Sanatoga Creek, the selected Manning's "n" roughness coefficients for the channel and overbank areas are 0.06 and 0.12, respectively. This is compared to a published range from 0.025 to 0.060 for natural channels that are clean and straight to winding with some pools, weeds, and stones, and a published range from 0.025 to 0.110 for flood plains of pasture to

'dense brush.

Supplemental Response to Request for Additional Information (FHRR)

Page 10 of 11 Furthermore, the roadway crossing Possum Hollow Run downstream of the site is conservatively modeled with the culvert completely blocked. Even with the conservatisms incorporated into the hydrologic and hydraulic modeling for Possum Hollow Run and Sanatoga Creek, the site grade is still at least 49.2 feet above the computed flood level for the Possum Hollow Run PMF and at least 63.3 feet above the computed level for the Sanatoga Creek PMF.

Supplemental Response to Request for Additional Information (FHRR)

Page 11 of 11 Information Need 14: Combined Events - Wind-wave Calculations

Background:

The FHRR does not provide a justifi cationfor using a wind speed slower than that suggested in ANSI/ANS-2.8-1992, Figure 1 for the LGS site. Wind speeds can affect the wave setup and runup and therefore, the combined effects water-surface elevation at the LGS site.

Request: The FHRR and the combined events calculationreport that the 2-year.return period, 2-minute wind speed is estimated to be 39.7 mi/h. Figure 1 of ANSI/ANS-2.8-1992 shows that annual extreme-mile, 30-ft above ground, 2-year mean recurrence interval wind speed to be slightly less than 50 mi/h. The staff requests a justificationfor using the slower wind speed for wind-wave estimates.

Response

Guidance in Appendix H of NUPEG/CR-7046 states that combined effects for floods caused by precipitation events should include, "Waves induced by 2-year wind speed applied along the critical direction." The combined effects calculation for Limerick (LM-0707), computed a site-specific, 2-year return period, 2-minute wind speed by statistical analysis of climate station data using the Gumbel Distribution, a Generalized Extreme Value (GEV) Distribution. This approach is consistent with the guidance in ANSI 2.8 which indicates .in Section 9.1.4 that a site specific wind analysis is "highly desirable" and, if performed, should be used in the combined events analyses (in lieu of ANSI/ANS-2.8-1992 Figure 1).

The best available data with the longest duration that is available from the National Climatic Data Center (NCDC) is the 2-minute duration wind speed. The fastest 10-meter altitude, 2-minute duration wind speed from the nearby Reading Spaatz Field, PA gage (GHCND USW000 147 12) was selected because it had the best available data within the vicinity of LGS.

Station GHCND USW00014712 is located at Reading Spaatz Field, PA, approximately 30 miles Northwest of LGS. Station GHCND USW000 14712 is located on flat ground with no obstruction from trees and buildings. Due to its proximity to LGS and similar terrain features, the Reading Spaatz Field gage is representative of the 2-minute duration wind speed at LGS.

The period of record for the gage is a 16 year range from 1999 to 2014. The maximum yearly wind speeds for the period of record range from 16.1 to 21.9 m/s with a mean of 18.0 m/s (36.0 to 49.0 mph with a mean of 40.2 mph). Applying the Gumbel Distribution, the resulting site-specific, 2-year return period, 2-minute wind speed is 39.7 mph.

Enclosure 2 Limerick Generating Station, Units 1 and 2 DVD labeled: LGS FHRR Electronic Files for NRC Docket, Limerick Generating Station, December 2015

E~xelt Generation 10 CFR 50.54(f)

RS-1 6-002 January 13, 2016 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DO 20555-0001 Limerick Generating Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-39 and NPF-85 NRC Docket Nos. 50-352 and 50-353

Subject:

Supplemental Response to NRC Audit Review Request for Additional Information Regarding Fukushima Lessons Learned - Flood Hazard Reevaluation Report

References:

1. Exelon Generation Company, LLC Letter to USNRC, Flood Hazard Reevaluation Report Pursuant to 10 CFR 50.54(f) Regarding the Fukushima Near-Term Task Force Recommendation 2.1: Flooding, dated March 12, 2015 (RS-15-064)
2. NRC Letter, Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated March 12, 2012
3. Exelon Generation Company, LLC Letter to USNRC, Response to NRC Audit Review Request for Additional Information Regarding Fukushima Lessons Learned - Flood Hazard Reevaluation Report, dated October 28, 2015 (RS-1 5-268)
4. NRC Email from T. Govan to D. Distel, Request for Additional Limerick Information Needs Responses and Input/Output Files on the Docket, dated December 1, 2015 In Reference 1, Exelon Generation Company, LLC (EGC) provided the Flooding Hazard Reevaluation Report (FHRR) for the Limerick Generating Station, Units 1 and 2 in response to the March 12, 2012 Request for Information Enclosure 2, Recommendation 2.1, Flooding, Required Response 2, (Reference 2). The NRC conducted an auditiwebinar review of the Limerick Generating Station, Units 1 and 2 FHRR on September 24, 2015. In support of the FHRR audit, the NRC provided audit information needs items. The information provided by EGC to address the audit information needs items was subsequently reviewed by the NRC during the audit. Reference 3 provided the responses to the NRC requested additional information items identified during the Limerick Generating Station, Units 1 and 2 FH-RR audit review on September 24, 2015.

U.S. Nuclear Regulatory Commission Supplemental Response to NRC Audit Review Request for Additional Information (Flooding Hazard Reevaluation Report)

January 13, 2016 Page 2 The purpose of this letter is to provide the responses to the additional NRC requested additional information items identified in Reference 4. Enclosure 1 to this letter provides the individual responses to each of the items identified in Reference 4. Enclosure 2 to this letter provides the Limerick FHRR model input/output files also requested in Reference 4.

This letter contains no new regulatory commitments.

If you have any questions regarding this report, please contact Ron Gaston at (630) 657-3359.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 13 th day of January 2016.

Respectfully submitted, James*arsto*w

  • Director - Licensing & Regulatory Affairs Exelon Generation Company, LLC

Enclosures:

1. Limerick Generating Station, Units 1 and 2 Supplemental Response to NRC Audit Review Request for Additional Information Regarding Fukushima Lessons Learned - Flood Hazard Reevaluation Report
2. DVD labeled: LGS FHRR Electronic Files for NRC Docket, Limerick Generating Station, December 2015 Document Components:

HMS LGS Information Need 1 Electronic Files LM-0699 Local Intense Precipitation LM-070 1 Proba~ble Maximum Flood-Hydraulics LM-0702 Dam Failure LM-0704 Error Uncertainty cc: NRC Regional Administrator - Region I NRC Project Manager, NRR - Limerick Generating Station NRC Senior Resident Inspector - Limerick Generating Station Ms. Tekia Govan, NRR/JLD/PPSD/HMB, NRC Director, Bureau of Radiation Protection - Pennsylvania Department of Environmental Resources (w/o Enclosure 2)

R. R. Janati, Chief, Division of Nuclear Safety, Pennsylvania Department of Environmental Protection, Bureau of Radiation Protection (w/o Enclosure 2)

Enclosure 1 Limerick Generating Station, Units 1 and 2 Supplemental Response to NRC Audit Review Request for Additional Information Regarding Fukushima Lessons Learned - Flood Hazard Reevaluation Report (11 pages)

Supplemental Response to Request for Additional Information (FHRR)

Page 1 of 11 Information Need 5: Streams and Rivers - PMP Spatial Distribution for Possum Hollow Run and Sanatoga Creek Drainages Backg~round: It is not clear if the point PMP is used for the Possum Hollow Run and Sanatoga Creek drainages. The staff was unable to find isohyets for these drainages. Using an isohyetal pattern over the two drainages can significantly affect the water-surface elevation near the LGS site.

Request: The FHRR states that all-season PMP estimates for the Possum Hollow Run and Sanatoga Creek drainages were developed using BOSS HMR52 software. From the FHRR and the calculations, it is not clear which spatial distributionsfor the PMP are used for these two drainages. Because the drainage areasfor these two drainagesare less than lOmi2, typically the point PMP is used. The staff requests details of the spatial distribution, including isohyetal plots, of the PMP over Possum Hollow Run and Sanatoga Creek drainages.

Response

The Possum Hollow Run watershed has a 1.4 mi2 drainage area. The smallest isohyet area (ellipse) from the HMR-52 standard elliptical pattern, shown on Figure 5.1, is 10 mi2 for "Isohyet Area A." This means all the drainage area of Possum Hollow Run is contained within isohyet area A as shown on Figure 5.2. For this reason, BOSS HMR52 does not produce an isohyetal plot showing spatial distribution of the PMP for the Possum Hollow Run watershed.

incremental 72-hr PMP for the Possum Hollow Run watershed is provided in Table 5.1. As per HMR-52 reference manual, "the 10-mi2 isohyet is taken to be the same as point rainfall." The reasons BOSS HMR52 SOftware is used is to develop the default PMP temporal distributions and to evaluate the effect of storm centering.

The Sanatoga Creek watershed has a 7.1 mi2 drainage area. The smallest isohyet area (ellipse) from the HMR-52 standard elliptical pattern, shown on Figure 5.1, is 10 mi2 for "Isohyet Area A." However, as shown on Figures 5.3 and 5.4, the Sanatoga Creek watershed intersects ellipse A at three locations. This means the PMP for the Sanatoga Creek watershed includes PMP from isohyet areas A and B. However, the majority of the Sanatoga Creek watershed is within isohyet area A. Therefore, the majority of the PMP is from the 10 mi 2 area which is considered to be the same as point rainfall. Incremental 72-hr PMP for the Sanatoga Creek watershed is provided in Table 5.2. The main reason the BOSS HMR52 software is used is to develop PMP temporal distributions and to evaluate the effects of storm centering. Because of the irregular shape of the Sanatoga Creek watershed, PMP that occurs outside the area of isohyet Area A is captured when using BOSS HMR52.

These rainfall configurations are the bases for the Possum Hollow Run and Sanatoga Creek portions of Limerick PMP Calculation (LM-0698). However, a sensitivity analysis was performed to evaluate the effects of using a 1-Square Mile, 1-Hour PMP on Possum Hollow Run and Sanatoga Creek watersheds. The 1-Square Mile, 1-Hour PMP was obtained from HMR-52 as explained in Calculation LM-0698. The 1-Square Mile, 1-Hour PMP also incorporated the 10-mi,6-hr duration PMP from the second hour to the sixth hour based on recommendations in NUREG/CR-7046. Also, the 1-Square Mile, 1-Hour PMP was conservatively assumed to be uniformly distributed over the 1.4 and 7.1-Square Mile watersheds for Possum Hollow Run and Sanatoga Creek, respectively. PMP values used in the sensitivity analysis are provided in Table

Supplemental Response to Request for Additional Information (FHRR)

Page 2of 11 5.3. The HEC-HMS model for Possum Hollow Run and Sanatoga Creek watersheds developed in Calculation LM-0700 were re-run using the PMP values from Table 5.3 (1-Square Mile, 1-Hour PMP; 10- Square Mile, 6-Hour duration). The Schuylkill River HEC-RAS model that contains the Possum Hollow Run reach and the Sanatoga Creek HEC-RAS model, both developed in Calculation LM-0701, were updated based on the revised flows from the HEC-HMVS models for the Possum Hollow Run and Sanatoga Creek watersheds. The downstream boundary condition for Sanatoga Creek is also revised based on the new results from the Schuylkill River and Possum Hollow Run HEC-RAS model. A water level of 169.27 ft NGVD29 from the confluence of Sanatoga Creek with the Schuylkill River HEC-RAS model at cross-section 48.41 was used as the downstream boundary condition for the Sanatoga Creek HEC-RAS model.

The results from the HEC-HMS and the HEC-RAS models are summarized in Table 5.4. As shown in Table 5.4, the HEC-RAS model results when using 1-Square Mile, 1-Hour PMP produce higher water surface elevations compared to the previous analysis that uses 10-Square Mile PMP only obtained from the HMR-52 program. As shown in Table 5.4, the increase in water level at LGS on the Schuylkill River is due to the increase flow resulting from the 1-Square Mile PMP added from Possum Hollow (conservatively assuming coincidental peaks).

Based on the HEC-RAS model results, the revised peak PMF water surface elevation in the Schuylkill River, Possum Hollow Run, and Sanatoga Creek at LGS are still below the "lowest grade level entrance to any safety related structure" of 217 feet NGVD29 referenced in the LGS UFSAR.

Figure 5.1: Standard Elliptical Isohyetal Pattern from LIMR-52

Supplemental Response to Request for Additional Information (FHRR)

Page 3 of 11 Figure 5.2: GIS Figure Showing Isohyetal Pattern and Orientation of PMP Storm for Possum Hollow Run Watershed

Supplemental Response to Request for Additional Information (FHRR)

Enclosure 1 Page 4 of 11 Table 5.1: Incremental 72-hr PMP for Possum Hollow Run Watershed (Obtained from Calculation LM-0698 page 431 of 1327)

ISOHYET DEPTH VS. DURATION INCREMENTAL PRECIPITATION STORM RAINFALL DEPTHS (inches) FOR TIME INCREMENTS ISOHYET SMIN lOMIN 1SMIN 30NIN 1-HR 2-HR 3-HR 6-HR 12-HR 18-HR 24-HR 30-HR 36-HR 42-HR 48-HR 54-HR 60-HR 66-HR 72-HR m-A-- 1.63 3.26 4.87 9.39 14.96 18.66 21.60 26.88 31.01 33.21 34.71 35.86 36.79 37.56 38.23 38.82 39.35 39.82 40.25i C .23 .47 .70 1.40 2.81 5.57 8.11 12.90 14.89 15.94 16.66 17.21 17.66 18.03 18.35 18.63 18.89 19.11 19.32 D .18 .37 .55 1.11 2.22 4.40 6.41 10.21 11.83 12.68 13.27 13.72 14.08 14.38 14.64 14.87 15.08 15.26 15.43 E .15 .29 .44 .88 1.76 3.48 5.07 8.06 9.30 9.96 10.41 10.76 11.04 11.27 11.47 11.65 11.80 11.95 12.07 F .12 .23 .35 .70 1.41 2.78 4.06 6.45 7.44 7.97 8.33 8.61 8.83 9.02 9.18 9.32 9.44 9.56 9.66 G .09 .18 .28 .55 1.11 2.20 3.20 5.11 5.93 6.37 6.67 6.90 7.09 7.24 7.38 7.50 7.60 7.69 7.78 H .07 .14 .20 .41 .82 1.62 2.37 3.76 4.34 4.65 4.86 5.02 5.15 5.26 5.35 5.43 5.51 5.57 5.63 I .05 .10 .15 .29 .59 1.16 1.69 2.69 3.10 3.32 3.47 3.59 3.68 3.76 3.82 3.88 3.93 3.98 4.02 J .03 .06 .09 .17 .35 .69 1.01 1.61 1.90 2.04 2.14 2.22 2.28 2.33 2.37 2.41 2.44 2.47 2.50 K .01 .02 .03 .06 .11 .23 .33 .54 .66 .73 .77 .81 .83 .86 .88 .90 .91 .93 .94 1 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 N .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 N .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 P .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 o .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 R .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 S .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 r---------------------------------------------------------------------------------------------m---------m m m m m m m m m m m m m m m m m m I AVERAGE 1.63 3.26 4.87 9.39 14.96 18.66 21.60 26.88 31.01 33.21 34.71 35.86 36.79 37.56 38.23 38.82 39.35 39.82 40.25' L----------------------------------------------------------------------------------------

Figure 5.3: Isohyetal Pattern/Spatial Distribution and Orientation of PMP Storm for Sanatoga Creek Watershed (Obtained from Calculation LM-0698 page 441 of 1327)

BASIN P?45 ISONYET PLOT:

  • =f Basin Boundary * *

= Storm Area Boundary *

  • SOHYETA S*1--ttt *tt.+tt*\*

Supplemental Response to Request for Additional Information (FHRR)

Page 5of 11 Figure 5.4: GIS Figure Showing Isohyetal Pattern/Spatial Distribution and Orientation of PMP Storm for Sanatoga Creek Watershed

Supplemental Response to Request for Additional Information (FHRR)

Enclosure 1 Page 6 of 11 Table 5.2: Incremental 72-hr PMP for Sanatoga Creek Watershed (Obtained from Calculation LM-0698 page 442 of 1327)

ISOHYFT DEPTH VS. DURATION DINCREMENTALPRECIPITATION 5TORM RAINFALL. DEPThS (inches) FOR TIME INCREMENTS ISOHYET 5MIN 1OM4IN1SMIN 3OMIN 1-HR 2-HR 3-HR 6-HR 12-HR 18-HR 24-HR 30-HR 36-HR 42-HR 48-HR 54-HR 60-HR 66-HR 72-HR

  • A 1.332 .79.39 14.96 18.66 21.60 26.88 31.01 33.21 34.71 35.86 36.79 37.56 38.23 38.82 39.35 39.82 40.25 0 .18 .37 .55 1.11 2.22 4.40 6.41 10.21 11.83 12.68 13.27 13.72 14.08 14.38 14.64 14.87 15.08 15.26 15.43 E .15 .29 .44 .88 1.76 3.48 5.07 8.06 9.30 9.96 10.41 10.76 11.04 11.27 11.47 11.65 11.80 11.95 12.07 F .12 .23 .35 .70 1.41 2.78 4.06 6.45 7.44 7.97 8.33 8.61 8.83 9.02 9.18 9.32 9.44 9.56 9.66 G .09 .18 .28 .5S 1.11 2.20 3.20 5.11 5.93 6.37 6.67 6.90 7.09 7.24 7.38 7.50 7.60 7.69 7.78 H .07 .14 .20 .41 .82 1.62 2.37 3.76 4.34 4.65 4.86 5.02 5.15 5.26 5.35 5.43 5.51 5.57 5.63 I .05 .10 .15 .29 .59 1.16 1.69 2.69 3.10 3.32 3.47 3.59 3.68 3.76 3.82 3.88 3.93 3.98 4.02 1 .03 .06 .09 .17 .35 .69 1.01 1.61 1.90 2.04 2.14 2.22 2.28 2.33 2.37 2.41 2.44 2.47 2.50 K .01 .02 .03 .06 .11 .23 .33 .54 .66 .73 .77 .81 .83 .86 .88 .90 .91 .93 .94 L .00 .00 .00 .00D .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 N4 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 N .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 P .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 Q .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 R .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 S .00 .00 .00 .OO .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .OO .00 AVERAGE 1.55 3.10 4.63 8.94 14.28 17.98 20.95 26.29 30.34 32.49 33.97 35.09 36.00 36.76 37.41 37.99 38.50 38.96 39.38

Supplemental Response to Request for Additional Information (FHRR)

Page 7 of 11 Table 5.3: 1-Hour 1-Square Mile and 6-Hour 10-Square Mile PMP for Sensitivity Analysis Area/

Duration J(minutes)

Time Time (hours)

[Incremental Rainfall (in)

ICumulative jRainfall (in) IAreal Duration Time (minutes) J(hours)]Rainfall ITime 1Incremental [Cumulative (in) Rainfall (in) 0 0.00 0.00 0.00 185 3.08 0.15 21.65 5 0.08 6.00 6.00 190 3.17 0.15 21.80 10 0.17 1.73 7.72 195 3.25 0.15 21.95 15 0.25 1.73 9.45 200 3.33 0.15 22.10 20 0.33 1.36 10.81 205 3.42 0.15 . 22.25 25 0.42 1.36 12.17 210 3.50 0.15 22.40 1-Square 30 0.50 1.36 13.53 215 3.58 0.15 22.55 Mile, 1-Hour PMP 35 0.58 0.73 14.26 220 3.67 0.15 22.70 40 0.67 0.73 14.99 225 3.75 0.15 22.85 45 0.75 0.73 15.72 230 3.83 0.15 23.00 50 0.83 0.73 16.44 235 3.92 0.15 23.15 55 0.92 0.73 17.17 240 4.00 0.15 23.30 60 1.00 0.73 17.90 245 4.08 0.15 23.45 65 1.08 0.15 18.05 250 4.17 0.15 23.60 70 1.17 0.15 - 18.20 255 4.25 0.15 23.75 260 4.33 0.15 23.90 75 80 T1.331.25 0.15 0.15 18.35 18.50 265 4.42 0.15 24.05 1 ,-I Q vJ 10-Square 270 4.50 0.15 24.20 Mile, 6-90 1.50 0.15 18.80 Hour 275 4.58 0.15 24.35 95 1.58 0.15 18.95 PMP 280 4.67 0.15 24.50 100 1.67 0.15 19.10 285 4.75 0.15 24.65 105 1.75 0.15 19.25 290 4.83 0.15 24.80 110 1.83 0.15 19.40 295 4.92 0.15 24.95 115 1.92 0.15 19.55 300 5.00 0.15 25.10 10-Square 120 2.00 0.15 19.70 305 5.08 0.15 25.25 Mile, 6-Hour PMP 125 2.08 0.15 19.85 310 5.17 0.15 25.40 130 2.17 0.15 20.00 315 5.25 0.15 25.55 135 2.25 0.15 20.15 320 5.33 0.15 25.70 140 2.33 0.15 20.30 325 5.42 0.15 25.85 145 2.42 0. 15 20.45 330 5.50 0.15 26.00 150 2.50 0.15 20.60 335 5.58 0.15 26.15 155 2.58 0.15 20.75 340 5.67 0.15 26.30 160 2.67 0.15 20.90 345 5.75 0.15 26.45 165 2.75 0.15 21.05 350 5.83 0.15 26.60 170 2.83 0.15 21.20 355 5.92 0.15 26.75 175 2.92 0.15 21.35 360 6.00 0.15 26.90 180 3.00 0.15 21.50 L L . a a ___________ L J U

Supplemental Response to Request for Additional Information (FHRR)

Page 8 of 11 River/HEC-RAS Station Table 5.4: Summary of Sensitivity Using 10 -Square Mile PMP on Analysis Using 1 -Hour, 1-Square Mile and Lowest Level Freeboard Possum Hollow Run and 6-Hour, 10-Square Mile PMP on Entrance (ft)

Sanatoga Creek Watershed Possum Hollow Run and Sanatoga Elevation (B-A)

(As reported in CalculationLM- Creek Watershed from LGS 0701, Section 8.0) (New Sensitivity Analysis) UFSAR (ft PMF Peak Water Level PMF Peak Water. Level NGVD29)

Discharge (ft NGVD29) Discharge (ft NGVD29)

(cfs) (cfs) "A" "..B" Schuylkill River at LGS 397,200 163.9 397,200 167.96 217 49.04 (River Mile 47.41)

Possum Hollow Run at 17,300 167.8 47,375 176 217 41.0 LGS (River Mile 0.458)

Sanatoga Creek at LGS 83,500 153.7 241,045 170.83 217 46.17 (River Mile 0.63) ________________ _____ _________________________

Supplemental Response to Request for Additional Information (FHRR)

Page 9 of 11 Information Need 9: Streams and Rivers - HEC-RAS Model Setup Backg~round: The FHRR does not state why the channel cross-sections estimatedfor Schuyllkill River, Possum Hollow Run, and Sanatoga Creek are conservative. The staff did not find this information in the calculations included in the ERR. The shape of channel cross-section can significantly influence the water-surface elevationfor a given discharge.

Request: The FHRR states that the licensee assumed the Schuylkill River cross-sections to be triangular in shape. The FHRR also states that the bathymetry information on the Possum Hollow Run and Sanatoga Creek were conservatively ignored. The staff request detailed description of how channel bathymetry for Schuylkill River, Possum Hollow Run, and Sanatoga Creek were determinedandwhy the assumptions stated in the FHRR are conservative.

Response

The channel bathymetry for the Schuylkill River is approximated as a triangle reflecting no width to the thalweg of the stream bed. The top surface of the natural river course, from left stream bank to right stream bank, at each cross section is developed from the river width for the water level at the time LiDAR was flown using the digital elevation model of Pennsylvania, obtained from the PAMAP LiDAR Program. The edge of water elevation was determined directly from the PAMAP LiDAR data. The corresponding channel invert elevations of the Schuylkill River are based on the stream bed profiles included in the Federal Emergency Management Agency (FEMA) Flood Insurance StUdy (FIS) for Berks, Montgomery and Philadelphia counties. The channel inverts are applied to the cross sections as a single point, midway between the stream bank stations, creating the approximated triangular shape.

Calibration of the hydraulic model incorporating the triangular bathymetry for the Schuylkill River was approached conservatively. Calibration of the channel was not attempted to achieve a tight fit with the observed data. All modelled peak water surface elevations for calibration events were greater than observed values, by up to as much as 2.7 feet. This was to ensure selected roughness coefficients were not too low and compensate for uncertainties surrounding stream bed geometry, although the effects of an approximated stream bed geometry is expected to be insignificant during high PMF flows. Even with the conservatisms incorporated into the hydrologic and hydraulic modeling for the Schuylkill River, the site grade is still at least 53.1 feet above the computed flood level for the PMF and at least 24.5 feet above the computed level for the PMF with dam failures included.

Bathymetry for Possum Hollow Run and Sanatoga Creek is completely ignored. Therefore, additional cross-sectional area below the water level at the time LiDAR was flown that would be available for flood conveyance is conservatively ignored. The edge of water elevation was determined directly from the PAMAP LiDAR data. Due to the lack of observed data, Manning "n" roughness coefficients were conservatively selected based on published values. For both Possum Hollow Run and Sanatoga Creek, the selected Manning's "n" roughness coefficients for the channel and overbank areas are 0.06 and 0.12, respectively. This is compared to a published range from 0.025 to 0.060 for natural channels that are clean and straight to winding with some pools, weeds, and stones, and a published range from 0.025 to 0.110 for flood plains of pasture to

'dense brush.

Supplemental Response to Request for Additional Information (FHRR)

Page 10 of 11 Furthermore, the roadway crossing Possum Hollow Run downstream of the site is conservatively modeled with the culvert completely blocked. Even with the conservatisms incorporated into the hydrologic and hydraulic modeling for Possum Hollow Run and Sanatoga Creek, the site grade is still at least 49.2 feet above the computed flood level for the Possum Hollow Run PMF and at least 63.3 feet above the computed level for the Sanatoga Creek PMF.

Supplemental Response to Request for Additional Information (FHRR)

Page 11 of 11 Information Need 14: Combined Events - Wind-wave Calculations

Background:

The FHRR does not provide a justifi cationfor using a wind speed slower than that suggested in ANSI/ANS-2.8-1992, Figure 1 for the LGS site. Wind speeds can affect the wave setup and runup and therefore, the combined effects water-surface elevation at the LGS site.

Request: The FHRR and the combined events calculationreport that the 2-year.return period, 2-minute wind speed is estimated to be 39.7 mi/h. Figure 1 of ANSI/ANS-2.8-1992 shows that annual extreme-mile, 30-ft above ground, 2-year mean recurrence interval wind speed to be slightly less than 50 mi/h. The staff requests a justificationfor using the slower wind speed for wind-wave estimates.

Response

Guidance in Appendix H of NUPEG/CR-7046 states that combined effects for floods caused by precipitation events should include, "Waves induced by 2-year wind speed applied along the critical direction." The combined effects calculation for Limerick (LM-0707), computed a site-specific, 2-year return period, 2-minute wind speed by statistical analysis of climate station data using the Gumbel Distribution, a Generalized Extreme Value (GEV) Distribution. This approach is consistent with the guidance in ANSI 2.8 which indicates .in Section 9.1.4 that a site specific wind analysis is "highly desirable" and, if performed, should be used in the combined events analyses (in lieu of ANSI/ANS-2.8-1992 Figure 1).

The best available data with the longest duration that is available from the National Climatic Data Center (NCDC) is the 2-minute duration wind speed. The fastest 10-meter altitude, 2-minute duration wind speed from the nearby Reading Spaatz Field, PA gage (GHCND USW000 147 12) was selected because it had the best available data within the vicinity of LGS.

Station GHCND USW00014712 is located at Reading Spaatz Field, PA, approximately 30 miles Northwest of LGS. Station GHCND USW000 14712 is located on flat ground with no obstruction from trees and buildings. Due to its proximity to LGS and similar terrain features, the Reading Spaatz Field gage is representative of the 2-minute duration wind speed at LGS.

The period of record for the gage is a 16 year range from 1999 to 2014. The maximum yearly wind speeds for the period of record range from 16.1 to 21.9 m/s with a mean of 18.0 m/s (36.0 to 49.0 mph with a mean of 40.2 mph). Applying the Gumbel Distribution, the resulting site-specific, 2-year return period, 2-minute wind speed is 39.7 mph.

Enclosure 2 Limerick Generating Station, Units 1 and 2 DVD labeled: LGS FHRR Electronic Files for NRC Docket, Limerick Generating Station, December 2015

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