ML15093A284

Enclosure 2: Flood Hazard Reevaluation Report for Oyster Creek Nuclear Generating Station, Rev. 1

ML15093A284
Person / Time
Site:	Oyster Creek
Issue date:	02/23/2015
From:	Balan S Enercon Services
To:	Office of Nuclear Reactor Regulation
Shared Package
ML15093A289	List: ML15093A283 ML15093A284 ML15093A285 RA-15-015, Response to March 12, 2012, Request for Information Enclosure 2, Recommendation 2.1, Flooding, Required Response 2, Flood Hazard Reevaluation Report and Request for Relief from Flooding Integrated Assessment
References
RA-15-015, RS-15-063 FHRR-OYS-001, Rev 1
Download: ML15093A284 (52)

Text

Enclosure 2 Oyster Creek Nuclear Generating Station Flood Hazard Reevaluation Report Revision 1 (51 pages)

FLOOD HAZARD REEVALUATION REPORT IN RESPONSE TO THE 50.54(f) INFORMATION REQUEST REGARDING NEAR-TERM TASK FORCE RECOMMENDATION 2.1: FLOODING for the OYSTER CREEK NUCLEAR GENERATING STATION Route 9 South Forked River, NJ 60450-9765

" Exelon.

Exelon Generation Company, LLC Route 9 South Forked River, NJ 08731 Prepared by:

O ENERCON

&Ce)frnCe-4ve YPMOjeCL Ey doya Enercon Services Inc.

1601 NW Expressway, Suite 1000 Oklahoma City, OK 73118 FHRR-OYS-001 Revision 1 Submitted Date: February 19, 2015

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 Contents

1. Purpose I 1.1 Ba c kg ro un d ...................................................................................................... 1 1.2 Requested Actions ...................................................................................... 1 1.3 Requested Information ............................................................................... 2

2. SITE INFORMATION 3 2.1 Detailed Site Information ............................................................................. 3 2.2 Current Design Basis .................................................................................. 3 2.2.1 Local Intense Precipitation .................................................................... 3 2.2.2 Flooding in Streams and Rivers ........................................................... 3 2.2.3 Dam Breaches and Failures ................................................................ 4 2.2.4 Storm Surge ........................................................................................ 4 2.2.5 Seiche ................................................................................................. 4 2.2.6 Tsunam i............................................................................................... 4 2.2.7 Ice-Induced Flooding .......................................................................... 4 2.2.8 Channel Migration or Diversion ............................................................ 4 2.2.9 Combined Effect Flood (including Wind-Generated Waves) ................. 4 2.3 Flood-Related Changes to the License Basis .............................................. 5 2.4 Changes to the Watershed and Local Area since License Issuance ....... 5 2.5 Current Licensing Basis Flood Protection and Pertinent Flood Mitigation Features ...................................................................................................................... 5

3.

SUMMARY

OF FLOOD HAZARD REEVALUATION 5 3.1 Flooding in Streams and Rivers .................................................................. 7 3.1.1 Basis of Inputs ...................................................................................... 7 3.1.2 Computer Software Programs .............................................................. 8 3.1.3 Methodology .......................................................................................... 8 3.1.4 Results .............................................................................................. 10 3.2 Dam Breaches and Failures ...................................................................... 10 3.2.1 Basis of Inputs ..................................................................................... 10 3.2.2 Computer Software Program s ............................................................ 10 3.2.3 Methodology ....................................................................................... 11 3.2.4 Results ................................................................................................ 12 3.2.5 Downstream Dam Failure .................................................................... 13 3.3 Storm Surge .............................................................................................. 13 3.3.1 Probable Maxim um Hurricane (PM H) ............................................... 13 OYSTER CREEK NUCLEAR GENERATING STATION #

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 3.3.2 Basis of Inputs .................................................................................... 13 3.3.3 Computer Software Programs ............................................................ 13 3.3.4 Methodology ....................................................................................... 14 3.3.5 Results and Conclusions ..................................................................... 16 3.4 Probable Maxim um Storm Surge (PMSS) ................................................ 16 3.4.1 Basis of Inputs .................................................................................... 16 3.4.2 Computer Software Programs ............................. 17 3.4.3 Methodology ...................................................................................... 17 3.4.4 Results and Conclusions ..................................................................... 20 3 .5 Se iche ............................................................................................................. 20 3.5.1 Basis of Inputs .................................................................................... 20 3.5.2 Computer Software Programs ............................................................ 21 3.5.3 Methodology ....................................................................................... 21 3.5.4 Results and Conclusions .................................................................... 22 3.6 Tsunami ...................................................................................................... 23 3.6.1 Basis of Inputs .................................................................................... 23 3.6.2 Computer Software Programs ............................................................ 23 3.6.3 Methodology ...................................................................................... 23 3.6.4 Results and Conclusions .................................................................... 28 3.7 Ice-Induced Flooding .................................................................................. 29 3.8 Channel Migration or Diversion .................................................................. 29 3.9 Combined Effect Flood (including Wind-Generated Waves) ..................... 29 3.9.1 Basis of Inputs .................................................................................... 29 3.9.2 Computer Software Programs ............................................................ 30 3.9.3 Methodology ....................................................................................... 30 3.9.4 Results and Conclusions .................................................................... 32 3.10 Error Uncertainty ........................................................................................ 33 3.10.1 Basis of Inputs .................................................................................... 34 3.10.2 Computer Software Programs ............................................................ 34 3.10.3 Methodology ...................................................................................... 34 3.10.4 Results and Conclusions .................................................................... 35 3.11 Associated Effects .................................................................................... 36 3.11.1 Basis of Inputs .................................................................................... 36 3.11.2 Computer Software Programs ............................................................ 36 3.11.3 Methodology ...................................................................................... 36 OYSTER CREEK NUCLEAR GENERATING STATION ii

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 3.11.4 Results and Conclusions ..................................................................... 38

4. COMPARISON WITH CURRENT DESIGN BASIS 42

5. REFERENCES 45 OYSTER CREEK NUCLEAR GENERATING STATION iv

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015

1. PURPOSE 1.1 Background In response to the nuclear fuel damage at the Fukushima-Dai-ichi power plant due to the March 11, 2011, earthquake and subsequent tsunami, the United States Nuclear Regulatory Commission (NRC) established the Near Term Task Force (NTTF) to conduct a systematic review of NRC processes and regulations, and to make recommendations to the NRC for its policy direction. The NTTF reported a set of recommendations that were intended to clarify and strengthen the regulatory framework for protection against natural phenomena.

On March 12, 2012, the NRC issued an information request pursuant to Title 10 of the Code of Federal Regulations, Section 50.54 (f) (10 CFR 50.54(f) or 50.54(f) letter) (NRC March 2012) which included six (6) enclosures:

1. [NTTF] Recommendation 2.1: Seismic

2. [NTTF] Recommendation 2.1: Flooding

3. [NTTF] Recommendation 2.3: Seismic

4. [NTTF] Recommendation 2.3: Flooding

5. [NTTF] Recommendation 9.3: EP

6. Licensees and Holders of Construction Permits In Enclosure 2 of the NRC-issued information request (NRC March 2012), the NRC requested that licensees "reevaluate the flooding hazards at their sites against present-day regulatory guidance and methodologies being used for early site permits (ESP) and combined operating license reviews."

On behalf of Exelon Generation Company, LLC (Exelon) for the Oyster Creek Nuclear Generating Station (OCNGS), this Flood Hazard Reevaluation Report (Report) provides the information requested in the March 12th 50.54(f) letter; specifically, the information listed under the "Requested Information" section of Enclosure 2, paragraph 1 ('a" through "e"). The "Requested Information" section of Enclosure 2, paragraph 2 ("a" through "d"), Integrated Assessment Report, will be addressed separately if the current design basis floods do not bound the reevaluated hazard for all flood-causing mechanisms.

1.2 Requested Actions In Enclosure 2 of the NRC-issued information request (NRC March 2012), the NRC requested that licensees "reevaluate the flooding hazards at their sites against present-day regulatory guidance and methodologies being used for early site permits (ESP) and combined operating license reviews."

On behalf of Exelon Generation Company, LLC (Exelon) for the Oyster Creek Nuclear Generating Station (OCNGS), this Flood Hazard Reevaluation Report (Report) provides the information requested in the March 12, 50.54(f) letter; specifically, the information listed under the "Requested Information" section of Enclosure 2, paragraph 1 ("a" through "e"). The 'Requested Information' section of Enclosure 2, paragraph 2 ("a" through "d"), Integrated Assessment Report, will be addressed separately if the current design basis floods do not bound the reevaluated hazard for all flood-causing mechanisms.

OYSTER CREEK NUCLEAR GENERATING STATION Page 1 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 Subsequently, addressees should perform an integrated assessment of the plant to identify vulnerabilities and actions to address them. The scope of the integrated assessment report will include full power operations and other plant configurations that could be susceptible due to the status of the flood protection features. The scope also includes those features of the ultimate heat sinks (UHS) that could be adversely affected by the flood conditions and lead to degradation of the flood protection (the loss of UHS from non-flood associated causes are not included). It is also requested that the integrated assessment address the entire duration of the flood conditions.

A definition of vulnerability in the context of [Enclosure 2] is as follows: Plant-specific vulnerabilities are those features important to safety that when subject to an increased demand due to the newly calculatedhazard evaluation have not been shown to be capable of performing theirintended functions.

1.3 Reguested Information Per Enclosure 2 of NRC-issued information request 50.54(f) letter, the Report should provide documented results, as well as pertinent OCNGS information and detailed analysis, and include the following:

a. Site information related to the flood hazard. Relevant structures, systems, and components (SSCs) important to safety and the UHS are included in the scope of this reevaluation, and pertinent data concerning these SSCs should be included. Other relevant site data includes the following:

i. Detailed site information (both designed and as-built), including present-day site layout, elevation of pertinent SSCs important to safety, and site topography, as well as pertinent spatial and temporal data sets.

ii. Current design basis flood elevations for all flood-causing mechanisms.

iii. Flood-related changes to the licensing basis and any flood protection changes (including mitigation) since license issuance.

iv. Changes to the watershed and local area since license issuance.

v. Current licensing basis flood protection and pertinent flood mitigation features at the site.

vi. Additional site details, as necessary, to assess the flood hazard (i.e., bathymetry, walkdown results, etc.).

b. Evaluation of the flood hazard for each flood-causing mechanism, based on present-day methodologies and regulatory guidance. Provide an analysis of each flood-causing mechanism that may impact the site including LIP and site drainage, flooding in streams and rivers, dam breaches and failures, storm surge and seiche, tsunami, channel migration or diversion, and combined effects. Mechanisms that are not applicable at the site may be screened out; however, a justification should be provided. Provide a basis for inputs and assumptions, methodologies and models used, including input and output files and other pertinent data.

c. Comparison of current and reevaluated flood-causing mechanisms at the site. Provide an assessment of the current design basis flood elevation to the reevaluated flood elevation for each flood causing mechanism. Include how the findings from Enclosure 2 of the 50.54(f) letter (i.e., Recommendation 2.1 flood hazard reevaluations) support this determination. If the current design basis flood bounds the reevaluated hazard for all flood causing mechanisms, include how this finding was determined.

OYSTER CREEK NUCLEAR GENERATING STATION Page 2 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015

d. Interim evaluation and actions taken or planned to address any higher flooding hazards relative to the design basis, prior to completion of the integrated assessment described below, if necessary.

e. Additional actions beyond requested information item 1.d taken or planned to address flooding hazards, if any.

2. SITE INFORMATION 2.1 Detailed Site Information The OCNGS site is located on the eastern coastline of New Jersey, about two miles inland from the shore of Barnegat Bay and about seven miles west northwest of Barnegat Light. It is approximately nine miles south of Toms River, New Jersey, 50 miles east of Philadelphia, Pennsylvania, and 60 miles south of Newark, New Jersey (OCNGS UFSAR).

Site grade elevation is 23 feet (ft) mean sea level (MSL). The deck elevation of the intake structure is set at elevation 6.0 ft MSL. Hurricane storm surge analysis performed after the completion of the OCNGS concluded a probable maximum hurricane (PMH) still water level of +22 ft MSL could occur at the site. During such an event, the safety related buildings and structures at the plant island remain above flood levels. However, the intake structure deck, which is at an elevation of 6 ft, will become flooded. The circulating water, service water and emergency service water pumps installed on this deck will have to be shut down, leading to the shutdown of the reactor (OCNGS UFSAR).

2.2 Current Design Basis The current design basis is defined in the OCNGS UFSAR and by reference to an NRC Systematic Evaluation Program (SEP). The following is a list of flood-causing mechanisms and their associated water surface elevations that were considered for the OCNGS current design basis.

2.2.1 Local Intense Precipitation The UFSAR indicates that the topography of the plant site is such that the surface drainage flows from the high point in the center of the island towards the intake canal to the north and west, the discharge canal to the south and west, and Route 9 to the east. The UFSAR by reference to the SEP indicates that due to the time lag between the runoff and rainfall, some local site ponding occurs but it does not result in flooding of the site. The flood elevation for the probable maximum precipitation (PMP) was established at 23.5 ft. MSL (OCNGS UFSAR).

2.2.2 Flooding in Streams and Rivers The UFSAR by reference to the SEP identifies that no flooding due to PMF on streams and rivers that would affect safety related structures has been postulated for the site. Water levels in Barnegat Bay and at the plant site are influenced solely by storm and tidal action. There is no significant stream flow in either the Oyster Creek or the Forked River. Floods or droughts in these streams will not have a measurable effect on the water levels at the plant (OCNGS UFSAR).

STATION Page 3 of 47 OYSTER NUCLEAR GENERATING CREEK NUCLEAR OYSTER CREEK GENERATING STATION Page 3 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 2.2.3 Dam Breaches and Failures Two small dams are located on the Oyster Creek. Incremental flood flows were calculated based on their breaching by any unspecified cause as part of the SEP. It was determined that no flooding which would affect safety-related structures is postulated for the site (OCNGS UFSAR).

2.2.4 Storm Surge Due to the proximity of the site to Barnegat Bay and the Atlantic Coast, and the relatively small size of the onsite freshwater streams, it was noted in the design stage that storm and tidal flooding should be used as the design basis in establishing the elevations of various plant components.

Several detailed studies of flooding potential due to probable maximum surges and wind wave action have been performed. The two more important were conducted by Eaton and Haeussner, Consulting Engineers, and Dames and Moore, Inc. The maximum flood still water level is based on storm surge from the probable maximum hurricane (PMH). The maximum flood still water level at the plant site is identified as Elevation 22 feet MSL, with an additional height of less than 1 foot that represents the maximum wave run-up at the plant site (OCNGS UFSAR).

2.2.5 Seiche Seiche was not considered in the OCNGS UFSAR.

2.2.6 Tsunami The UFSAR indicates flooding due to tsunamis was not considered for OCNGS. Tsunamis were not considered typical of the eastern coast of the United States and were not included in the design basis (OCNGS UFSAR).

2.2.7 Ice-Induced Flooding The UFSAR indicates that during normal plant operation, icing has been limited to the canal area outside of the steel trash grates. The area in close proximity to the intake, where the suction of the pumps is taken, is kept from freezing by the thermal dilution gates, which recirculate discharge water through the intake bay, and by the turbulence induced by the circulating water pumps. The discharge canal remains free of ice during normal operation due to the plant heated effluent (OCNGS UFSAR).

The UFSAR also indicates that it is unlikely that ice blockage would cause problems to any safety-related systems as the emergency service water flow utilizes approximately only 3 percent of the design capacity of the 6 screens on the intake structure (OCNGS UFSAR).

2.2.8 Channel Migration or Diversion Channel migration and diversion was not considered in the OCNGS UFSAR.

2.2.9 Combined Effect Flood (including Wind-Generated Waves)

The UFSAR indicates that the PMH stillwater level at the plant site was calculated to be 22.0 feet MSL. The UFSAR also indicates that an additional height of less than 1.0 feet represents the maximum wave runup at the plant site (OCNGS UFSAR).

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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 2.3 Flood-Related Changes to the License Basis OCNGS is in the process of implementing strategies to better cope with PMF flooding under the current licensing basis. No other physical modifications have been installed specifically in support of the external flooding response, with the exception of the dike at the diesel generator building.

Plant procedures in response to external flooding have been revised to reflect abnormal conditions such as high intake levels throughout the life of the plant.

2.4 Changes to the Watershed and Local Area since License Issuance The watershed contributory to the Oyster Creek is 11.4 square miles and the watershed contributory to the South Branch of the Forked River is 2.5 square miles (Exelon 2013a). Based on aerial images of the watershed, the changes to the watershed include commercial and residential development within the watershed area. The changes to the local area sub watershed for the OCNGS include building and security barrier upgrades that have been added to the site since license issuance.

2.5 Current Licensing Basis Flood Protection and Pertinent Flood Mitigation Features The current license basis maximum flood level due to PMH is elevation 22 ft MSL. The plant grade, elevation 23 ft MSL, is one foot above the PMH flood level. Therefore, the flood will not find its way into the plant buildings, the floor levels of which are generally six inches above grade at elevation 23'-6". The intake structure with its deck at elevation 6 ft will be under water. This deck supports, apart from the other equipment, the circulating water pumps, service water pumps and the emergency service water pumps. During a PMH flood, the circulating water, service water pumps and the emergency service water pumps will become inoperable and thus emergency plant procedures have been instituted which require the plant to be shutdown when flood waters reach a predetermined level as to ensure the capability for safe shutdown under either normal or abnormal conditions.

The two entrances to the emergency diesel generator building are at elevation 23 ft. MSL, which is 6 inches below the flooding level which would be caused by local probable maximum precipitation (23.5 ft. MSL). A 6-inch high asphalt dike is provided at these entrances to provide protection against internal flooding of the emergency diesel generator building (OCNGS UFSAR).

3.

SUMMARY

OF FLOOD HAZARD REEVALUATION NUREG/CR-7046 Design-Basis Flood Estimation for Site Characterizationat Nuclear Power Plantsin the United States of America (NUREG/CR-7046), by reference to the American Nuclear Society (ANS), states that a single flood-causing event is inadequate as a design basis for power reactors and recommends that combinations should be evaluated to determine the highest flood water elevation at the site. For the OCNGS site, the combination that produces the highest flood water elevation at the site is the probable maximum storm surge due to a probable maximum hurricane combined with the probable maximum flood due to all-season PMP on the Oyster Creek and South Branch of Forked River watershed and the effects of coincident wind wave activity.

The UFSAR Section 2.4 provides elevations in MSL datum. The hazard reevaluation calculations provide elevation results based on the North American Vertical Datum (NAVD 88). Based on the datum information available from the nearest National Oceanic and Atmospheric Administration GENERATING STATION Page 5 of 47 OYSTER OYSTER CREEK NUCLEAR GENERATING CREEK NUCLEAR STATION Page 5 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 (NOAA) gage at Barnegat Inlet (NOAA 2013), the difference in datum between MSL and NAVD88 is 0.02 ft. NOAA 2013 suggests that MSL (ft) = NAVD88 (ft) - 0.02 The elevations reported in this report are obtained from hazard revaluations which are then converted to MSL datum based on the above conversion.

Calculation C-1 302-120-E31 0-010 (Exelon 2013g) defines the probable maximum stillwater level for the OCNGS site. The probable maximum stillwater elevations at OCNGS is calculated to be 23.18 ft MSL (23.2 ft NAVD88) at the intake structure, 22.78 ft MSL (22.8 ft NAVD88) at the reactor building, 22.68 ft MSL (22.7 ft NAVD88) at the material warehouse, 22.68 ft MSL (22.7 ft NAVD88) at the independent spent fuel storage installation (ISFSI), 22.88 ft MSL (22.9 ft NAVD88) at the site emergency building, 22.78 ft MSL (22.8 ft NAVD88) at the administration building, 23.18 ft MSL (23.2 ft NAVD88) at the turbine building, and 23.08 ft MSL (23.1 ft NAVD88) at the emergency diesel generator building. Flooding from the bounding combined events scenario does not extend to the new radiation waste building and the low level radiation waste building.

Calculation C-1302-120-E310-010 (Exelon 2013g) presents the maximum coincident wind setup and wave runup for the OCNGS site. The probable maximum wave runup at OCNGS varies by location and ranges from 0.7 to 3.7 ft. The probable maximum water level elevations at OCNGS are calculated to be 23.18 ft MSL (23.2 ft NAVD88) at the intake structure, 23.48 ft MSL (23.5 ft NAVD88) at the reactor building, 24.78 ft MSL (24.8 ft NAVD88) at the material warehouse, 25.38 ft MSL (25.4 ft NAVD88) at the ISFSI, 26.58 ft MSL (26.6 ft NAVD88) at the site emergency building, 25.38 ft MSL (25.4 ft NAVD88) at the administration building, 25.88 ft MSL (25.9 ft NAVD88) at the turbine building, and 23.08 ft MSL (23.1 ft NAVD88) at the emergency diesel generator building. The maximum elevation with added runup is 3.58 ft above the existing design basis flood elevation of 23 ft MSL.

LIP is addressed under a separate report titled, "Local Intense PrecipitationEvaluationReport for the Oyster Creek Nuclear GeneratingStation" (Exelon 2013i).

The methodology used in the flooding reevaluation for OCNGS is consistent with the following standards and guidance documents:

• NRC Standard Review Plan, NUREG-0800, revised March 2007 (NUREG-0800)

• NRC Office of Standards Development, Regulatory Guides, RG 1.102 - Flood Protection for Nuclear Power Plants, Revision 1, dated September 1976 (NRC RG 1.102)

• RG 1.59 - Design Basis Floods for Nuclear Power Plants, Revision 2, dated August 1977 (NRC RG 1.59)

• NUREG/CR-7046 "Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America," dated November 2011 (NUREG/CR-7046)

• NUREG/CR-6966 "Tsunami Hazard Assessment at Nuclear Power Plant Sites in the United States of America" dated March 2009 (NUREG/CR-6966)

• American National Standard for Determining Design Basis Flooding at Power Reactor Sites (ANSI/ANS-2.8-1992), dated July 28, 1992 OYSTER CREEK NUCLEAR GENERATING STATION Page 6 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 NEI Report 12-08. Overview of External Flooding Reevaluations (NEI August 2012)

The following provides the flood-causing mechanisms and their associated water surface elevations that are considered in the OCNGS flood hazard reevaluation.

3.1 Floodingq in Streams and Rivers The PMF in rivers and streams adjoining the site are determined by applying the PMP to the drainage basin in which the site is located. The PMF is based on a translation of PMP rainfall on a watershed to flood flow. The PMP is a deterministic estimate of the theoretical maximum depth of precipitation that can occur at a time of year for a specified area. A rainfall-to-runoff transformation function, as well as runoff characteristics, based on the topographic and drainage system network characteristics and watershed properties are needed to appropriately develop the PMF hydrograph. The PMF hydrograph is a time history of the discharge and serves as the input parameter for other hydraulic models which develop the flow characteristics including flood flow and elevation.

3.1.1 Basis of Inputs The inputs used in PMP, snowmelt and PMF analysis are based on the following:

3.1.1.1 PMP & Snowmelt Analysis

" Oyster Creek and the South Branch of the Forked River watershed locations, areas, boundaries and configurations:

o Oyster Creek Watershed Area: 11.4 square miles o South Branch of the Forked River Watershed Area: 2.5 square miles

• Historic rainfall and other meteorological data collected by the National Weather Service (NWS) at numerous recording and cooperative climate stations and available from the National Climatic Data Center (NCDC).

• NWS Hydrometeorological Report No. 52 (HMR-52), standard isohyetal patterns, storm orientation, percentage of 6-hour increment of PMP, and standard isohyetal geometry information.

" NWS HMR-53 for seasonal PMP values.

• Median and Extreme Daily Snow Cover by Month; Toms River, New Jersey, data is downloaded from the NCDC.

" Snow melt-rate (energy budget) equations and constants are based on U.S. Army Corps of Engineers (USACE) Engineering Manual EM-1 110-2-1406.

3.1.1.2 PMF Analysis Digital Elevation Model (DEM). The DEM used for the PMF calculation is New Jersey Department of Environmental Protection (NJDEP) 10-meter Digital Elevation Grid of the Barnegat Bay Watershed Management Area (WMA 13), NJDEP, Office of Information Resources Management (OIRM) and Bureau of Geographic Information and Analysis (BGIA).

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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015

• Elevation Datum Conversions. Elevations in National Geodetic Vertical Datum 1929 (NGVD 29) are converted to North American Vertical Datum 1988 (NAVD 88), using VERTCON: North American Vertical Datum Conversion, by National Geodetic Survey.

• Probable maximum precipitation (PMP) 72-hour and 6-hour PMPs for the subject watershed area (Exelon 2013a).

• Dam Information: Dam data including height, storage capacity and spillway hydraulic characteristics from National Inventory of Dams (NID).

• Rainfall-Runoff Gage Data:

o Data for United States Geologic Survey (USGS) Stream Gage 01409095 on Oyster Creek, Brookville, New Jersey o Daily precipitation gage data at Tom's River Station (GHCND: USC00288816) and Lakehurst (Naval Air Station) (GHCND: USW00014780) o Hourly precipitation gage data at Lakehurst (Naval Air Engineering Station)

(AWS: 724090) and Atlantic City International Airport Station (Coop ID:

280311)

" Baseflow: USGS surface-water monthly statistics and continuous gage data at the USGS stream gage 01409095.

" Soil Type: The soil types within the project watershed are developed using National Resources Conservation System (NRCS) soil information.

• Land Use: The land use information for the watershed is obtained from NJDEP.

" Manning's roughness coefficients.

• 2-year 24-hour rainfall from NOAA Atlas 14 Point Precipitation Frequency Estimates.

3.1.2 Computer Software Programs 3.1.2.1 PMP & Snowmelt Analysis

" ArcGIS Desktop 10

• BOSS HMR52v1.10 3.1.2.2 PMF Analysis

• ArcMap 10

" HEC-HMS 3.5 3.1.3 Methodology The PMF analysis included the following steps:

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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015

" Delineate watersheds and determine watershed areas. For purposes of the hydrologic modeling effort, Oyster Creek is subdivided into three sub-watersheds based on the presence of two dams and one USGS stream gage. The North Branch of the Forked River is subdivided into three sub-watersheds based on the presence of three dams. The South and Middle Branches of the Forked River are not subdivided. The portion of the drainage areas of the Middle and North Branches located within the tidal area is delineated as a separate watershed. The calculated areas are checked by comparing to values provided in basin characteristic reports developed using the USGS New Jersey StreamStats internet-based computer program.

" Calculate HEC-HMS rainfall-runoff model input parameters. The Soil Conservation Service (SCS, now known as Natural Resources Conservation Service or NRCS) method is used to develop the curve number (CN) and lag time (L) for each sub-watershed. The CN values are estimated based on hydrologic soil groups and land use data within each delineated sub-watershed area.

" Incorporate dam structures into HEC-HMS rainfall-runoff model. Two dam structures on the Oyster Creek (Wells Mill Reservoir Dam and Freshwater Impounding Pond Dam) and three dam structures on the North Branch of the Forked River (Deer Head Lake Dam, Barnegat Lake Dam and Parker Street Dam) are incorporated into the HEC-HMS model.

• Compare rainfall-runoff model to observed stream flow data. The procedure involves the following steps:

o Evaluate stream flow data to identify candidate storms for the basis of comparison.

Candidate storms are, ideally, isolated events which occur during the same time frame as the PMP (i.e., June-November). However, due to small sample size of available stream flow data, this criteria is not utilized in the PMF calculation.

Instead, the largest storms within the stream gage's continuous period of record are used and peak flow observations (without continuous data) for the largest PMP-seasonal storms are used.

o Obtain available stream flow data and corresponding precipitation data for each candidate storm.

o Perform HEC-HMS simulation for each candidate storm.

o Compare HEC-HMS simulation results to observed stream gage data.

• Perform PMF simulation using PMP design rainfall input. The PMF is the flood resulting from the PMP (Exelon 2013a). This PMP is also applied to the Middle and North Branches of the Forked River. The temporal distribution of the PMP is calculated in accordance with recommendations in HMR-52 wherein individual 6-hr increments decrease progressively to either side of the greatest 6-hr increment. The runoff from the PMP is transformed to a discharge hydrograph using HEC-HMS 3.5 computer program. For each sub-watershed, simulations are performed for:

o The total 72-hour PMP: 39.8 inches.

o The 6-hour PMP: 25.4 inches.

The 72-hour PMP hyetograph is constructed using 40 percent of the PMP depths during the first 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, followed by a dry 72-hour period, and finally followed by the full 72-hour PMP storm.

OYSTER CREEK NUCLEAR GENERATING STATION Page 9 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 Calculation of CN and lag time are performed in accordance with procedures outlined in NUREG/CR-7046 Appendix C, including use of ARCIII for CN calculation. Two PMF simulations are performed for each PMP scenario (72-hour or 6-hour):

• ARC II (normal) CN

" ARC III (wet) CN The PMF simulations above are re-run to account for potential non-linear basin response in accordance with NUREG/CR-7046.The peak of each unit hydrograph is increased by one-fifth and the time-to-peak is reduced by one-third. The remaining hydrograph ordinates are adjusted to preserve the runoff volume to a unit depth over the drainage area. Snowmelt is not the controlling mechanism for PMF flooding as demonstrated (Exelon 2013a). Baseflow is calculated for each sub-watershed based on USGS Surface-Water Monthly Statistics data. The maximum monthly flow of 34 cfs is selected, which is linearly scaled by watershed areas to calculate the baseflows for all sub-watershed areas.

3.1.4 Results

" The PMF at OCNGS results from the 72-hour PMP (total rainfall depth of 39.8 inches).

• The PMF peak discharges based on ARCIII conditions are considered to apply to OCNGS.

" With non-linearity adjustments under ARCIII conditions as per NUREG/CR-7046, the PMF peak discharge from Oyster Creek is 52,000 cubic feet per second (cfs).

" With non-linearity adjustments under ARCIII conditions as per NUREG/CR-7046, the PMF peak discharge from the South Branch of the Forked River is 11,500 cfs.

• With non-linearity adjustments under ARCIII conditions as per NUREG/CR-7046, the combined PMF peak discharge from the Middle and North Branches of the Forked River is 62,700 cfs.

3.2 Dam Breaches and Failures 3.2.1 Basis of Inputs Inputs used for dam breach and failure evaluation include:

" HEC-HMS model developed in the PMF analysis.

" Dam Information - The National Inventory of Dams (NID) is used to identify the watershed dams.

3.2.2 Computer Software Programs

" ArcGIS Desktop 10

" HEC-HMS 3.5 OYSTER CREEK NUCLEAR GENERATING STATION Page 10 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 3.2.3 Methodology The criteria for evaluation of flooding from dam breaches and failures are provided in NUREG/CR-7046. Two scenarios of dam failures are recommended and discussed in NUREG/CR-7046.

" Failure of individual dams (i.e., groups of dams not domino-like failures) upstream of the site.

• Cascading or domino-like failures of dams upstream of the site.

Two failure mechanisms were considered for dam failure analysis are:

" Hydrologic

• Sunny Day Seismically-induced dam failures are a function of the combined events defined in NUREG/CR-7046 for floods caused by seismic dam failures. NUREG/CR-7046 identifies the following alternative combinations for seismic dam failures.

Alternative 1 - Combination of:

• A 25-year flood

• A flood caused by dam failure resulting from a safe shutdown earthquake (SSE), and coincident with the peak of the 25-year flood

" Waves induced by 2-year wind speed applied along the critical direction Alternative 2 - Combination of:

" The lesser of one-half of the PMF or the 500-year flood

" A flood caused by dam failure resulting from an operating basis earthquake (OBE),

and coincident with the peak of the flood

" Waves induced by 2-year wind speed applied along the critical direction Two dam structures on the Oyster Creek (Wells Mill Reservoir Dam and Freshwater Impounding Pond Dam) and three dam structures on the North Branch of the Forked River (Deer Head Lake Dam, Barnegat Lake Dam and Parker Street Dam) are incorporated into the HEC-HMS model. Dam failures of all five dams during PMF (via over topping including domino failure of dams located in series) was analyzed in the combined event calculation (Exelon 2013g), Seismic dam failure is bounded by considering dam failures of all five dams during PMF. Design inputs are obtained from published dam reports and/or data sheets with the exception of the following:

• Spillway weir coefficients are assigned based on the Handbook of Hydraulics.

GENERATING STATION Page ii of47 OYSTER OYSTER CREEK NUCLEAR GENERATING CREEK NUCLEAR STATION Page 11 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015

• Reservoir elevation-area functions are developed using the available information for the dams and existing site topography (based on the DEM data) to derive elevation-storage relationships.

" Dam breaches are evaluated in the combined event calculation (Exelon 2013g).

The more conservative ARCIII curve numbers are used. Structural heights of Wells Mill Reservoir Dam, Freshwater Impounding Pond Dam, Deer Head Lake Dam, Barnegat Lake Dam, and Parker Street Dam are 9, 8, 9.4, 18 and 10.3 feet, respectively. The average breach I width used is 5 times the structural height for each dam (Exelon 2013g).

3.2.4 Results The results of the dam breach simulation indicated the following peak flows as listed in Table 1:

Table 1 - Dam Failure Results (Exelon 2013g)

Dam Name Peak Flow with No Peak Dam Breach Total Peak Outflow Dam Breach (cfs) I Flow (cfs) with Dam Breach (cfs)

Probable Maximum Flood Dam Failure Wells Mill Reservoir Dam 15,000 4,400 19,400 Freshwater Impounding Pond 700 44,100 Dam 43,400 Oyster Creek Discharge with Non-Linearity 52,000 900 52,900 Adjustments Deer Head Lake Dam 37,300 1,100 38,400 Barnegat Lake Dam 37,600 3,500 41,100 Parker Street Dam 37,700 3,700 41,400 North Branch Forked River With Non-Linearity 45,200 4,500 49,700 Adjustments Sunny Day Dam Failure Wells Mill Reservoir Dam 20 2,560 2,580 Freshwater Impounding Pond 50 2,750 2,800 Dam Deer Head Lake Dam 60 1,570 1,630 OYSTER CREEK NUCLEAR GENERATING STATION Page 12 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 Dam Name Peak Flow with No Peak Dam Breach Total Peak Outflow Dam Breach (cfs) Flow (cfs) with Dam Breach (cfs)

Barnegat Lake Dam 70 14,600 14,670 Parker Street Dam 70 11,050 11,120 3.2.5 Downstream Dam Failure There is no plausible risk that safety-related facilities and functions of the plant will be adversely affected by downstream dam failure at OCNGS. The UFSAR provides assessment of low water conditions by examining failure modes that could contribute to the blockage of the canal. Plant operating procedures have been instituted which require the plant to be shut down when intake water levels decline to a predetermined level as to ensure the capability for safe shutdown under either normal or abnormal conditions (OCNGS UFSAR).

3.3 Storm Surge 3.3.1 Probable Maximum Hurricane (PMH) 3.3.2 Basis of Inputs The inputs used in PMH analysis are based on the following:

• Historical storm database from NOAA.

" Water level data from NOAA gage stations.

" NOAA Technical Report NWS 38.

" NOAA SLOSH model results

• Site and region-specific meteorology and climatology study for the OCNGS (Exelon 2013c).

3.3.3 Computer Software Programs

• FORTRAN

" Mathematica Computer software models are not used to evaluate PMH. However, computer programs are used in preparation of the site and region-specific meteorological and climatological study for OCNGS.

The analysis utilized data available from NOAA's National Hurricane Center (NHC) North Atlantic Hurricane Database or HURDAT. Initially, univariate distributions of maximum sustained wind speed, storm forward speed and bearing, central pressure deficit, and 6-hourly tendencies of bearing and central pressure are developed for the study region and OYSTER CREEK NUCLEAR GENERATING STATION Page 13 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 their statistical significance relative to the distributions of all coastal storms and to storms in coastal regions further south has been examined.

The HURDAT data set is read by a FORTRAN program, which reformats the data into a form more easily read by the Mathematica notebook, where data analysis is conducted.

3.3.4 Methodology The calculation methodology includes the following steps:

" Determination of controlling storm event. The probable maximum storm surge (PMSS) is defined as the surge that results from a combination of meteorological parameters of a PMH, a probable maximum windstorm (PMWS) or a moving squall line and has virtually no probability of being exceeded in the region involved. The PMH and PMWS are of primary concern in oceanic coastal areas while squall lines are dominant in large lakes (e.g. the Great Lakes). The first step is to confirm which type of storm event controls the PMSS. This evaluation is performed by: 1) reviewing recorded water level data from the NOAA Co-Op Stations at Atlantic City, NJ, and Sandy Hook, NJ to identify the events that resulted in historical extreme water levels; and 2) examining the extreme water level events associated with predicted hurricane storm surge elevations developed by NOAA at the two NOAA co-op stations located near the OCNGS.

" Review of the historical hurricane data. A preliminary review of the details of the historical hurricanes that occur in the vicinity of OCNGS is performed using historical storm data from the years 1851-2010 (Exelon 2013c).

" Development of the PMH meteorological parameters using NWS 23. The specific calculation steps include:

o Using the NWS 23 locator map, calculate the distance of the site (in nautical miles) from the U.S.-Mexico border.

o Determine the peripheral pressure (Pw). The Pw is the sea-level pressure at the outer limits of the hurricane circulation and represents the average pressure around the hurricane where the isobars change from cyclonic to anticyclonic curvature. Per NWS 23, the Pw (at the site location) is kept constant at a value of 30.12 in (102.0 kPa).

o Calculate the central pressure (Po) using NWS 23. The Po is the lowest sea-level pressure at the hurricane center. In general, the Po increases with latitude.

o Calculate the permissible range (based on upper limit and lower limit) of the radius of maximum winds (Rw) using NWS 23. The Rw is the radial distance from the hurricane center to the band of strongest winds within the hurricane wall cloud, just outside the hurricane eye. In general, the Rw increases with latitude.

o Calculate the permissible range (based on upper limit and lower limit) of forward speed (T) using NWS 23. The T refers to the rate of translation of the OYSTER CREEK NUCLEAR GENERATING STATION Page 14 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision I February 19, 2015 hurricane center from one geographical point to another. It is one component of the wind field of a moving storm and results in higher wind speeds on the right side of the storm and lower wind speeds on the left.

o Calculate the permissible range (based on upper limit and lower limit) of the track direction (e) using NWS 23. The e is the path of forward movement along which the hurricane is coming (measured clockwise from north). Per NWS 23, the permissible track direction is limited based on "possible" directions over the open ocean, sea-surface temperatures and other meteorological features. The permissible range is also a function of T. As the angle between the coastal orientation and e decreases, the slower hurricane weakens more than the faster-moving hurricane. NWS 23 is used to select the speed category.

Evaluation of the applicability of NWS 23 for development of the hurricane meteorological oarameter inout to the PMSS calculation. The parameters developed in NWS 23 are compared with the comprehensive set of hurricane climatology statistics for the Atlantic and Gulf Coasts of the United States for hurricanes during the period of 1900 through 1984. Based on that review, it is concluded that certain PMH parameter ranges presented in NWS 23 appear inconsistent with the current state of knowledge. Therefore, a site and region-specific meteorological and climatological study, involving detailed statistical analysis of hurricane and atmospheric data through 2012 (including Hurricane Sandy), is performed to evaluate the applicability of the parameters presented in NWS 23 and (where justified) recommend revised ranges of permissible parameters.

NUREG/CR-7046 acknowledges that, since NWS 23 was published in 1979, advances in the understanding of hurricane wind fields and development of more detailed data and models have occurred. Consistent with the hierarchal hazard assessment (HHA) approach presented in NUREG/CR-7046:

• Performs a site and region-specific evaluation of the hurricane trends and parameters that are consistent with current science and available meteorological data.

" Revises the ranges of PMH parameters (where justified) that are recommended for use in a deterministic analysis of the coastal flood storm surge, evaluation of the combined flood events and determination of the flood elevation at the site.

" Develops probability distributions for each of the key hurricane parameters.

The statistical analyses performed for this study are generally consistent with the methodologies used by Federal Emergency Management Agency (FEMA) and others.

Specifically, updated HURDAT data have been used in conjunction with data from Technical Report NWS 38 and the National Centers for Environmental Prediction (NCEP) to analyze distributions of the relevant hurricane parameters required for storm surge simulations. In view of the limited sample size of historical storms in the vicinity of the OCNGS, a Capture Zone approach is used to study characteristics of tropical cyclones in a 5' x 5" coastal section north of 37"N. Distributions of all relevant parameters are formed by a non-parametric kernel method rather than an assumed parametric distribution. In the case of hurricane intensity, an extreme value distribution is used. In addition, the covariance of hurricane parameters is OYSTER CREEK NUCLEAR GENERATING STATION Page 15 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 investigated empirically and using synthetically-generated parameter vectors that capture the empirical co-variability.

3.3.5 Results and Conclusions The following summarizes the PMH calculation (Exelon 2013c) results and conclusions:

The site and region-specific meteorological and climatological study recommended revision of certain hurricane parameters presented in NWS 23. The following ranges of PMH parameters are recommended for use in deterministic storm surge evaluations at OCNGS.

About 90 percent of the historical storms in this region tracked to the northeast. By inspection, however, these storms are not expected to cause the most significant storm surges in the vicinity of OCNGS.

Generally consistent with NWS 23, the parameters recommended are for track ranges from 75 to 185 degrees. For the remaining range of 161 to 180 degrees track direction, it is recommended that the upper bound on forward speed be increased to 50 knots. This reflects the distinct difference between storms heading north and those heading in a westward direction. All other values remain unchanged.

" Based on the examination of historical water level data and NOAA-predicted storm surges using SLOSH, the PMH is determined to be to be the most critical event in determining storm surge levels at OCNGS.

• The range of permissible PMH meteorological parameters is developed based on a site and region specific study (Exelon 2013c).

" The PMH surge simulations should track to the left of OCNGS (facing the direction of forward storm movement) by a distance of Rw sin (1150), where Rw is the radius of maximum winds.

3.4 Probable Maximum Storm Surge (PMSS)

In accordance with NUREG/CR-7046, the PMSS is required to be evaluated coincidentally with an antecedent water level equal to the 10 percent exceedance high tide. The 10 percent exceedance high tide is the high tide level that is equaled or exceeded by 10 percent of the maximum monthly tides over a continuous 21 year period (ANSI/ANS-2.8-1992).

3.4.1 Basis of Inputs The inputs used in PMH analysis are based on the following:

" Tides and Currents Tide, Historic Tide Data, Sandy Hook, NJ, Station 8531680.

• Tides & Currents, Seaside Heights Tide Offset, Seaside Heights, NJ, Station 8533071.

• Tides & Currents, Sea Levels Online, Mean Sea Level Trend, 8534720 Atlantic City, New Jersey.

OYSTER CREEK NUCLEAR GENERATING STATION Page 16 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015

• Tides & Currents, Sea Levels Online, Mean Sea Level Trend, 8531680 Sandy Hook, New Jersey.

" NOAA's Defaware Bay SLOSH Basin (model grid) with integrated topography, bathymetry, geographic features, and obstructions.

• Range of PMH parameters developed in PMH Analysis (Exelon 2013c).

3.4.2 Computer Software Programs

" ArcMap 10.0

• SLOSH 3.97 3.4.3 Methodology The calculation methodology includes the following steps:

" Development of the antecedent water level.

" Performance of multiple SLOSH model simulations representing the range of meteorological hurricane parameters and storm track directions.

• Identification of the model simulations that result in the "worst case" combination of meteorological hurricane parameters and storm track directions. The "worst case" combination of meteorological hurricane parameters and storm track directions are those that "cause the probable maximum surge as it approaches the site along a critical path at an optimum rate of movement."

• Development of the surge hydrographs for the "worst case" simulations for the model cells along the plant coastal frontage, including the cooling water canals, for input into the two-dimensional hydrodynamic flow model.

• Development of maps showing the envelope of high water (EOHW) elevations for each of the "worst case" simulations.

" Development of maps showing the wind field for each of the "worst case" simulations.

• Development of maps showing the maximum water surface elevation over the entire grid for all the model simulations. This map is analogous to the maximum of maximum envelope of water (MEOW) (MOM) maps developed by NOAA for each hurricane category in each basin.

The following describes the methodologies used in the PMSS calculation.

Development of the Antecedent Water Level In accordance with ANSI/ANS-2.8-1992, the 10 percent exceedance high tide can be determined from recorded tide data or from predicted astronomical tide tables. If predicted tides are used, sea level anomaly shall be added. The sea level anomaly (also known as initial rise) is an anomalous departure of the tide level from the predicted astronomical tide and is estimated by comparing long term recorded and predicted tides. The PMSS analysis OYSTER CREEK NUCLEAR GENERATING STATION Page 17 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 calculates the 10 percent exceedance high tide using recorded tide data from the NOAA Sandy Hook, NJ (Station 8531680) co-op station, which is approximately 46 miles from OCNGS. The 10 percent exceedance high tide is statistically calculated using the Weibull plotting position equation.

NOAA maintains a secondary tidal prediction station in the vicinity of OCNGS at Seaside Heights, NJ (Station 8533071). This station is only 12 miles from OCNGS. Seaside Heights has a documented offset coefficient from Sandy Hook. This offset is used to convert the 10 percent exceedance high tide elevation calculated for Sandy Hook to the Seaside Heights station. The 10 percent exceedance high tide at Seaside Heights is representative of the 10 percent exceedance high tide at the open coast nearest OCNGS.

In accordance with NUREG/CR-7046, consideration should be given to the long-term effect of sea level rise (for the lifetime of the plant). This effect should be included in calculation of the PMSS antecedent water level to establish whether the site can adequately accommodate potential changes in the design-basis flood due to climate change. The recorded, long-term rate of sea level rise is available from both the NOAA Sandy Hook, NJ (Station 8531680) and Atlantic City, NJ (Station 8534720) stations. Using the annual rates provided by both gages, expected sea level rise over a 10-year period (the expected remaining operational life of the plant) is calculated. This 10-year sea level rise rate, which is the same for both Sandy Hook and Atlantic City is added to the 10-percent exceedance high tide to calculate the total antecedent water level used as input to SLOSH for evaluation of the PMSS.

SLOSH 3.97 Model The "Sea, Lake and Overland Surge from Hurricanes" (SLOSH 3.97) model was developed by the NOAA NWS Meteorological Development Laboratory (MDL). The SLOSH 3.97 model uses storm track, pressures, radius of maximum winds, and forward speed to calculate storm surge heights. The model accounts for both the hurricane wind field and the pressure differential when calculating storm surge. SLOSH 3.97 is used for the U.S. East Coast, Gulf of Mexico, Hawaii, Guam, Puerto Rico, and the U.S. Virgin Islands to predict hurricane storm surges, both operationally and for planning purposes.

The SLOSH 3.97 model requires two primary inputs: 1) a parameterization of a hurricane wind field; and 2) a grid representing the region of interest. The inputs to the SLOSH 3.97 model include:

• The basin bathymetry and topography (DEM).

• Meteorological storm parameters, including:

o Delta-P (difference between central and peripheral barometric pressures);

o The radius of maximum wind (Rw); and o The hurricane forward speed.

• The storm track direction (measured clockwise from north).

" The landfall location.

Page 18 of 47 OYSTER CREEK OYSTER GENERATING STATION NUCLEAR GENERATING CREEK NUCLEAR STATION Page 18 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 SLOSH Model Basin, DEM and Grid The basin bathymetry and topography and model grid are developed and provided by NOAA.

All operational and retired SLOSH basins are included within SLOSH 3.97 model. Three operational basins provide sufficient coverage and resolution near the OCNGS site: Atlantic City (acy); Delaware Bay (de3); and New York (ny3). The Atlantic City basin is older and has not yet been updated from the NGVD29 vertical datum.

The Atlantic City basin also has the coarsest resolution in the region of OCNGS at approximately 1.5 miles. Both the Delaware Bay and New York basins have been updated to the NAVD88 vertical datum. Of these basins, Delaware Bay has a slight advantage for use in this calculation in that it provides higher resolution in the vicinity of OCNGS (approximately 0.7 miles). The New York basin resolution near OCNGS is on the order of 1.2 miles. Basin vertical datum updates from NGVD29 to NAVD88 began in 2007, so the current version of the Delaware Bay basin is less than six years old.

SLOSH Model 3.97 Simulations

• Multiple SLOSH 3.97 model simulations are performed representing the range of meteorological hurricane parameters and storm track directions. The range of PMH parameters include:

o Central and peripheral pressures o T- forward speed o e - storm track o Rw- radius of maximum winds In addition, for each simulation the hurricane landfall strike distance is calculated to the left of the site (as recommended in ANSI/ANS-2.8-1992). For critical combinations of PMH parameters the impact of landfall distance on surge elevation is also investigated by varying the ratio of landfall distance to radius of maximum winds.

The simulations are initially run with a wide range of meteorological parameters, track directions and landfall strike distances. The results are compared to identify the parameters that are the most sensitive (i.e., cause the greatest effect) to surge elevation. A second round of simulations is then performed to refine the range of parameters, focusing on the most sensitive parameters.

For each storm simulation, the model simulations are evaluated to identify the combination of meteorological parameters and storm track direction that result in the "worst case" storm surge elevation. The "worst case" combination of meteorological hurricane parameters and storm track directions are those that "cause the probable maximum surge as it approaches the site along a critical path at an optimum rate of movement."

For each storm simulation, the surge hydrographs for the "worst case" simulations are developed for the model cells along the plant coastal frontage, including the cooling water canals, for input into the two dimensional hydrodynamic flow model used in combined events flood assessment (Exelon 2013g).

OYSTER CREEK NUCLEAR GENERATING STATION Page 19 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision I February 19, 2015 Development of Envelopes of High Water (EOHW) and Map of Maximum Water Surface Elevation Maps showing the EOHW are developed for each of the simulations. Maps showing the maximum water surface elevation over the entire grid for all model simulations are also developed using ArcMap 10.0TM.

3.4.4 Results and Conclusions The maximum coastal storm surge is 24.58 ft MSL (24.6 ft NAVD88) at the intake structure and 24.78 ft MSL (24.8 ft NAVD88) at the discharge canal (Exelon 2013g). This elevation is reached for a storm with forward speed of 30 knots, a radius of maximum winds of 24 nautical miles, a track direction of 900, and landfall distances of about 0.8Rw to 0.9Rw nautical miles.

Several additional simulations produced storm surge elevations quite close to the maximum, generally with similar track directions between 80 0 and 1000.

3.5 Seiche Seiches are long period standing waves occurring in closed or partially closed bodies of water.

Seiches are initiated by external forcing, typically due to atmospheric, tsunami, or seismic (earthquake) events. Due to reflections from the ends of the water body wave, oscillations continue after cessation of the external force resulting in a standing wave that dissipates over time due to friction. Atmospheric forcing includes barometric fluctuations, rapid variation in wind speeds and directions and storm surges. Tsunami-induced forcing includes interaction of tsunami wave trains with local geometry. Seismic forcing includes sloshing due to seismically-induced bottom displacements. In closed water bodies, seiches are generally caused by direct external forcing on the water surface (i.e. variations in barometric pressure and wind). While seiches can be caused by seismically induced bottom displacements, this type of forcing is considered rare in comparison to meteorological forcing.

Seiche periods are independent of the external forcing mechanism and depend only on geometry and depth of the basin. Periods generally range from tens of seconds to several hours. In contrast to the periods, initial amplitudes are strongly dependent on the external forcing but generally decay rapidly due to friction in the absence of additional forcing. However, ifthe natural period of oscillation of the water body matches the frequency of the external forcing, the resulting resonance can result in seiches with larger amplitudes.

3.5.1 Basis of Inputs Inputs include the following:

" Aerial dimensions and bathymetry of Barnegat Bay

• Department of Commerce (DOC), National Oceanic and Atmospheric Administration (NOAA, National Ocean Service (NOS), Special Projects (SP)

• NOS Estuarine Bathymetry: Bamegat Bay, NJ. June 06, 1998

" NOAA National Geophysical Data Center (NGDC), U.S. Coastal Relief Model

• USGS 1/3 Arc-Second National Elevation Dataset OYSTER CREEK NUCLEAR GENERATING STATION Page 20 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 3.5.2 Computer Software Programs a ArcMap 10.0.

3.5.3 Methodology The calculation methodology includes the following steps:

• Perform a review of historical seiche activity at Barnegat Bay.

" Calculate the fundamental period of Barnegat Bay.

The oscillations of a seiche are known as the natural modes. The mode with the lowest frequency (longest period) is the fundamental mode. Since a seiche is a standing wave, the currents and elevation phase are shifted by 90 degrees. For the fundamental mode, when the water surface is elevated at one end of the basin, it is depressed at the other. The nodes of the standing wave are located at interior points along the axis of the basin and represent locations of no vertical motion. The fundamental mode has a single node at the center of the basin. Antinodes, which are the points of maximum elevation, are located at the ends of the basin for the fundamental mode. Water moves only in the horizontal direction at the nodes and only in the vertical direction at the antinodes.

Seiches can occur from end-to-end (longitudinal) or from side-to-side (transverse) configurations within the bay. The fundamental period is calculated as follows:

" Confirm the basin type (i.e., closed, semi-closed).

" Evaluate the OCNGS location and environmental setting and the geometry of Bamegat Bay relative to the characteristics of the one-dimensional model used to calculate the fundamental period (e.g., rectangular, triangular, parabolic, etc.).

• Calculate the longitudinal axis dimension (i.e., north to south) and the transverse axis dimension (i.e., east to west) of Barnegat Bay.

, Calculate the average depth of Barnegat Bay.

" Calculate the fundamental Bamegat Bay periods (transverse and longitudinal) based on the bay geometry and depths using a one-dimensional model. The natural period of oscillation of a seiche can be characterized using shallow water theory, assuming that the length of the water body is large compared to the depth. In closed basins, the fundamental natural period of oscillation can be estimated from Merian's formula.

" Evaluate the potential for seiche wave resonance. Resonance occurs when the fundamental period of oscillation in the Bay is equal to the resonance caused by an external forcing. Typical values for natural periods associated with external forcing events are used to compare to the calculated fundamental periods of the Bay to determine whether resonance is likely.

" Calculate the barrier spit elevations from the USGS National Elevation Dataset (NED) 1/3 arc-second resolution DEM.

STATION Page 21 of 47 OYSTER NUCLEAR GENERATING CREEK NUCLEAR OYSTER CREEK GENERATING STATION Page 21 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015

• Assuming that seiches can occur at Barnegat Bay, evaluate the limitations of a seiche to flooding at OCNGS based on the site conditions (i.e., by comparing OCNGS plant elevation to the barrier spit elevation).

3.5.4 Results and Conclusions The following summarizes the results and conclusions:

• No documentation of historical seiches in Barnegat Bay is identified (with the exception of the following). A Google search identified a local forum that documents anecdotal evidence of a seiche in Barnegat Bay during October, 2008. Posts include discussions of a wind-generated seiche in the northern end of Barnegat Bay.

Comments state that the 2008 event caused the tide to "rise and fall" between 6 and 7 times that day, and took several days for the sloshing to subside.

• No information is found on water elevations for this specific event. Comments also indicate that seiches can occur in the longitudinal bay direction (northeast-southwest),

when strong, consistent southerly or northerly winds occur.

" The characteristics of Barnegat Bay as a long, narrow rectangular closed water body are consistent with determination of the fundamental period using a one-dimensional model.

" The natural period of the bay is dependent only on the basin geometry (length and depth), with longer/shorter lengths or shallower/deeper depths causing longer/shorter periods. As expected, both shorter lengths and deeper depths reduce the fundamental natural period of oscillation.

• The fundamental periods of Barnegat Bay are calculated in the longitudinal and transverse directions using Merian's formula, for several different tidal stages and flood elevations. The fundamental periods ranged from 0.1 to 0.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> (transverse) to 3.1 to 6.3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> (longitudinal).

• Based on the calculated fundamental natural periods of oscillation and typical periods of external forcing events, it is inferred that resonance can occur within Bamegat Bay as a result of:

o Wind shifts o Atmospheric pressure fluctuations o Seismic events; and o Storm surges (dependent upon surge period)

• Tides, most storm surges and wind-generated waves are not likely to cause seiche standing wave amplitude resonance within Barnegat Bay. Seismic ground displacements are very unlikely to occur within Barnegat Bay.

• Seiche standing waves with crest elevations greater than the adjacent barrier spit elevation will inundate the barrier spit, limiting the maximum seiche amplitude that can be achieved (i.e., the bay is no longer in a closed condition at that location). Therefore, by OYSTER CREEK NUCLEAR GENERATING STATION Page 22 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 inference, although seiches can occur in Barnegat Bay, they will not result in flooding of OCNGS.

3.6 Tsunami As defined in NUREG/CR-6966, "PMT is that tsunami for which the impact at the site is derived from the use of the best available scientific information to arrive at the set of scenarios reasonably expected to affect the nuclear power plant site, taking into account:

" Appropriate consideration of the most severe of the natural phenomena that have been historicallyreported for the site and surroundingarea, with sufficient margin for the limited accuracy,quantity andperiod of time in which the historicaldata have been accumulated;

" appropriatecombinations of the effects of normal and accident conditions with the effects of the naturalphenomena; and

" the importanceof safety functions to be performed."

3.6.1 Basis of Inputs The tsunami calculation inputs include the following:

• The high water antecedent water level from PMSS analysis (Exelon 2013d)

" Historic tidal water level data (tide gauge at Sandy Hook, New Jersey)

" Bathymetric data used for development of the DEMs

• Model parameters for the tsunamigenic sources

• Tidal water level data

• ETOPO1, 1 Arc-Minute global relief model

" NOAA U.S. coastal relief model

• Tsunamigenic source parameters 3.6.2 Computer Software Programs

• ArcMap 10.0

" Matlab R201 1b

• FUNWAVE -TVD, Version 1.0,

• NHWAVE, Version 1.1

• VDATUM Software, Version 2.3.3 3.6.3 Methodology In accordance with the guidelines presented in NUREGICD-6966, a HHA approach is used to evaluate the tsunami hazard. This approach uses a series of stepwise, progressively more refined analyses to evaluate the hazard. If the safety of the plant can be demonstrated by a OYSTER CREEK NUCLEAR GENERATING STATION Page 23 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 simple and bounding analysis, more refined (and costly) analyses do not need to be performed. Relative to tsunami hazards, the HHA approach includes the following steps:

" A regional screening test involving an evaluation of the regional hazard based on a review of the historical record and the best available scientific data.

• A site screening test to compare the location and elevation of the plant site with the areas affected by tsunamis in the region. This screening test considers, in a very crude way, the local site characteristics of ground elevation (the plant grade relative to the water surface elevation) and the distance of the plant from the shoreline.

• A detailed tsunami hazard assessment is performed since the screening tests do not conservatively establish the safety of the plant. The detailed, site-specific tsunami hazard assessment typically involves identification and modeling of applicable (near-field and far- field) tsunamigenic sources, numerical modeling of wave propagation from the tsunamigenic source to the near shore, and numerical inundation modeling of the plant site and vicinity.

The regional and site screening tests methodology included the following:

" Review of the National Geophysical Data Center (NGDC) tsunami event database and other sources relative to documented historical tsunamis at or near the site (Exelon 2013f).

" A literature search to identify the near field and far field tsunamigenic sources that are considered a risk relative to generation of tsunamis that may impact the site (Exelon 2013f).

" Review of first order screening analyses performed by the NOAA, as part of the National Tsunami Hazard Mitigation Program (NTHMP), for the east coast of the United States (Exelon 2013f).

According to NOAA's NOS Estuarine Bathymetry, depths in the bay reach up to 13.36 m (43.83 feet) at mean low water (MLW). The barrier spit (of an approximate 4 m [13.1 feet]

elevation) separates Barnegat Bay from the Atlantic Ocean. The barrier island complex is breached only at the Barnegat Inlet, located 10.5 km (6.5 miles) southeast of OCNGS. The site elevation of OCNGS is 7 meters (23 feet) above MSL. The maximum recorded high tide on the Barnegat Bay beach front is 2.13 m (7 feet) above MSL, which occurred more than 8 km (5 miles) away in 1962, while the maximum recorded flood at the site is 1.4 m (4.5 ft) above MSL (OCNGS UFSAR).

The detailed tsunami analysis performed a detailed, site-specific tsunami hazard assessment of OCNGS using the numerical software models FUNWAVE-TVD Version 1.0 (Fully-Nonlinear Bousinesq Wave Model) and NHWAVE Version 1.1 (Non-Hydrostatic Wave Model). The calculation components include:

" Calculation of the high and low antecedent water levels;

• Development of the model bathymetry (DEM);

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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-O01 Exelon Generation Company, LLC Revision 1 February 19, 2015

• Selection of source parameters for the tsunamigenic sources to be analyzed; and model analysis including (for each of the three tsunamigenic sources):

" Simulation of the tsunami generation at the tsunamigenic source; o Propagation of the tsunami waves from the far field; and o Near-shore transformation to calculate wave elevations, horizontal water velocities, and envelopes of high water at the OCNGS site.

Submarine landslides located along the Atlantic continental margin, roughly 150 km (about 93 miles) east of OCNGS, have the potential to generate local destructive tsunamis. The available scientific data show potential amplitudes of 7 m (23 feet) (Newfoundland, 1929 earthquake) to 8 m (26 feet) (Currituck Banks, Currituck Landslide) resulting from submarine mass failures (SMFs). While a SMF will cause a tsunami with larger amplitude than potential far-field sources and is the primary candidate for the OCNGS PMT generation, the tsunami waves will also have a shorter wavelength, meaning that they will be more intensely dissipated over the wide shelf than smaller but longer waves generated by distant sources.

For this reason, far-field sources with smaller but significant amplitudes and longer periods must also be considered when evaluating the PMT. Far-field candidates in the OCNGS region include co-seismic tsunamis generated in the Puerto Rico Trench (PRT) and a sub-aerial landslide triggered by Cumbre Vieja flank failure. Both of these will have lower amplitudes and longer periods than local SMF tsunamis, which could ultimately lead to larger run-up based on local geometry and bathymetry in the vicinity of OCNGS.

Development of the Antecedent Water Level In accordance with NUREG/CR-6966, the runup from a tsunami is evaluated coincidentally with a high water antecedent water level. The 10 percent exceedance high tide is the high water level that is equaled or exceeded by 10 percent of the maximum monthly tides over a continuous 21 year period (ANSI/ANS 1992). Similarly, the drawdown from a tsunami is evaluated coincidentally with an antecedent water level equal to the 90 percent low tide. The high water antecedent water level is calculated in calculation C-1 302-120-E310-007 (Exelon 2013d). The procedure to estimate the 10 percent exceedance high tide provided in ANSI/ANS-2.8-1992 is used to calculate the 90 percent low tide. The 90 percent low tide is defined as the low tide level that is equal to or less than 90 percent of the minimum monthly tides over a continuous 21 year period. The 90 percent low tide is calculated by:

• Statistical analysis of recorded tide data from the NOAA Sandy Hook, NJ (Station 8531680) co-op station, which is located approximately 46 miles from OCNGS using the Weibull plotting position equation.

" Conversion of the Sandy Hook 90 percent low tide to the Oyster Creek 90 percent low tide. NOAA maintains a secondary tidal prediction station in the vicinity of OCNGS at Oyster Creek, NJ (Station 8533465), which is located along Oyster Creek just south of OCNGS. The Oyster Creek station has a documented offset coefficient from Sandy Hook. This offset is used to convert the 90 percent low tide elevation calculated for Sandy Hook to the Oyster Creek station. The 90 percent low tide at Oyster Creek is representative of the 90 percent low tide inside Barnegat Bay near OCNGS.

OYSTER CREEK NUCLEAR GENERATING STATION Page 25 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 Model Grids and Bathymetry (DEMs)

In general, as waves approach the shore, their wavelength decreases due to the decreasing depth. In the nearshore region near OCNGS, the wide continental shelf also causes a decrease in wavelength due to dispersion (i.e., undular bores). These shorter wavelength waves, which are "transported" by longer wave components, require finer grids for accurate modeling. The tsunami software model analyzes tsunami wave propagation and inundation on a series of nested model grids. Fine grids are also required to capture small scale features of the local bathymetry and topography which have the potential to affect the tsunami wave impacts near and at OCNGS. A series of nested grids, varying from 2 arc-minute to 30-meter resolution, are used to model the propagation of each tsunami from the source region to OCNGS. The highest resolution (30 meter) grid is used to resolve the coastal impact at the plant.

A key input to the tsunami models is the establishment of the bathymetry (water depth) at the grid nodes. The nested grids start with large-scale grids to model the Atlantic Ocean (the three tsunamigenic sources analyzed in the detailed tsunami calculation are located far apart; therefore, three different Atlantic grids are used), and use progressively finer grids (utilizing a high resolution, site-specific grid at Barnegat Bay). The large-scale grids use a grid spacing of 2 arc-minute and the highest resolution (site-specific) grid uses a grid spacing of approximately 30 meters. The nested grid approach used by the software models generally increases the resolution from one grid to the next by a factor 4. Two intermediate grids are used to transition from the initial coarse grids in the Atlantic to the finer site-specific 30 meter grid.

Datasets with NAVD88 depths in feet are converted to meters in ArcMap using a conversion factor of 0.3048 meters/foot. Once all datasets are processed into meters and NAVD88 datum, the datasets are aggregated into site specific DEM using ArcGIS 10.0 software:

" The bathymetry datasets for the north and south sections of Barnegat Bay, the land topography and the offshore bathymetry are aggregated using the ArcGIS 10.0 Mosaic tool.

" The LiDAR data are then aggregated into this broader raster dataset using the ArcGIS 10.0 Mosaic tool.

" To fill gaps in the output dataset, the raster dataset is converted to points, merged with CMAP soundings, and used as input to the ArcGIS 10.0 Spline tool (spatial analyst extension).

" The ArcGIS 10.0 spatial analyst mosaic process is used to combine the OCNGS channel extracted from the survey data into the DEM.

Revision of Barnegat Inlet A review of the final grid using aerial imagery indicated that revision of the values around Barnegat Inlet is warranted when the existing bathymetry datasets are outdated and do not accurately represent current conditions in the channel that connects the bay to the ocean.

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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 Removal of the BarrierSpit The degree of erosion and sediment transport that a tsunami would have on the existing barrier spit system is undefined, and detailed erosion and sediment analyses are not performed as part of the tsunami analysis for OCNGS. Consistent with the HHA approach presented in NUREG/CR-7046, the OCNGS tsunami analysis conservatively models the bathymetry assuming maximum erosion (i.e., the barrier spit elevations greater than mean lower low water (MLLW) are assumed eroded). This version of the site-specific DEM is created as follows:

• The site-specific DEM is converted to a polygon feature class separated into zones above and below -0.359663 meters. This value is the difference between NAVD88 and MLLW (Exelon 2013h). The polygons representing the barrier system, intertidal zones around the barriers, and islands in the bay (i.e. with values above MLLW) are selected and used to set those areas of the site-specific DEM to null values.

" Matlab's "natural neighbor triangulated interpolation algorithm" is used to fill the eliminated land and intertidal zones with bathymetric values. The ArcGIS 10.0 spatial analyst focal statistics tool is then used to smooth the results using a circle neighborhood of 4 cells with a mean operator.

Tsunamigenic Source Parameters/initialWave Characterization As described in the PMSS analysis (Exelon 2013d), three Atlantic Ocean Basin (AOB) tsunamigenic sources are identified as sources identified by the industry for tsunamis that could impact OCNGS. These sources are selected based on an extensive literature review as well as results of simulations performed at the University of Rhode Island (URI) for tsunami hazard along the U.S. East Coast, as part of NOAA's National Tsunami Hazard Mitigation Program (NTHMP) (Exelon 2013h). The AOB sources are:

" An extreme co-seismic (earthquake magnitude 9) source in the Puerto Rico Trench (PRT) (Exelon 2013h);

" A subaerial landslide source due to a major collapse of the Cumbre Vieja Volcano (CW) in the Canary Islands (450 km 3 volume) (Exelon 2013h); and

• A submarine mass failure (SMF) source similar to the largest historical SMF known in the area, the Currituck slide (Exelon 2013h) (conservatively located on the continental shelf directly offshore of OCNGS in the analysis).

The parameters characterizing each of these tsunamigenic sources are developed in the references identified above and are used as input to the models, specifically to calculate the initial tsunami wave elevation (i.e. the wave elevation at the source location).

FUNWA VE-TVD 1.0 and NHWA VE 1.1 Model Simulations Propagation of the PRT and CW sources in the AOB, as well as near-shore propagation and coastal impact for all sources are simulated using FUNWAVE-TVD 1.0. The software model is approved for the modeling of tsunamis by the NTHMP. The model is based on nonlinear and dispersive Boussinesq equations and includes bottom friction, energy dissipation and subgrid turbulence. FUNWAVETVD 1.0 can evaluate both near and far field sources with large differences in periods between the far field and near field sources, which is a fully OYSTER CREEK NUCLEAR GENERATING STATION Page 27 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 nonlinear and dispersive Boussinesq long wave model. FUNWAVETVD 1.0 has spherical (latitude/longitude) and Cartesian (x,y) coordinate implementations.

NHWAVE 1.1, is a three-dimensional non-hydrostatic model used to generate the SMF source for a short initial time of propagation, based on a specified space and time varying seafloor boundary condition. NHWAVE 1.1 is developed for modeling fully dispersive surface wave processes. It solves the non-hydrostatic Navier-Stokes equations in a domain over a surface and terrain in the sigma coordinate system. This model solves tsunami waves generated by a prescribed submarine landslide.

For the CW source, FUNWAVE-TVD 1.0 is initialized based on earlier simulations of the extreme sub-aerial landslide source performed by Abadie et al. (Exelon 2013h). The PRT co-seismic source is directly specified as an initial condition in FUNWAVE-'VD 1.0, as is customary for co-seismic tsunami sources (Exelon 2013h). For the SMF source, FUNWAVE-TVD 1.0 is initialized based on NHWAVE 1.1 results. Simulation results are presented in terms of inundation quantified by the maximum tsunami elevation occurring at four select locations, including the Barnegat Bay inlet and outlet and at the plant intake and discharge canal.

3.6.4 Results and Conclusions Three potential tsunami sources are identified as potential risks to OCNGS. These include an extreme flank collapse of the CW, an M9 earthquake that ruptures the PRT, and a local SMF on the continental slope east of the site. For the high antecedent water cases, a direct comparison of both the surface elevation near OCNGS and the horizontal flow velocities for all three cases shows that the CW case would be the most hazardous of the three selected tsunami sources, with a maximum water surface elevation at the site of about 6.98 ft MSL (7 ft NAVD88). The low water antecedent water level scenario is elevation -0.28 ft MSL (-0.3 feet NAVD88). The low water tsunami simulations did not result in water levels significantly below the low water antecedent water level.

The maximum modeled surface elevation is not expected to be high enough to flood the power plant; however, it may result in flood-related impacts, specifically debris in the intake and outflow canals. The model result indicates that each of the three extreme tsunamis modeled could inundate the developed areas located east of the OCNGS, and potentially fill the intake/discharge channels with debris. An analysis of the impact of debris on plant structures is not performed as part of the tsunami analysis. While presently there is no operational network of sensors in the Atlantic to provide a tsunami warning (such as the DART buoys elsewhere), it is expected that there will be warning time of multiple hours before tsunami waves impact the vicinity of OCNGS. The model results indicate that a CW tsunami would not arrive until nearly 9.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after the triggering event in the Canary Islands. Effects of such an event would be reported throughout the Atlantic Basin long before the tsunami reached the U.S. East Coast. Similarly, model results indicate that a PRT earthquake would arrive almost 5.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after the rupture. The model results indicate that the SMF event will provide the least warning because the source is close to the OCNGS. The tsunami resulting from such an event is predicted to arrive only 2.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after it is triggered. However, a large local earthquake would be required to trigger such a massive SMF.

Page 28 of 47 OYSTER CREEK OYSTER GENERATING STATION NUCLEAR GENERATING CREEK NUCLEAR STATION Page 28 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 3.7 Ice-Induced Flooding As identified by NUREG/CR-7046, ice jams and ice dams can form in rivers and streams adjacent to a site and may lead to flooding by two mechanisms:

" Collapse of an ice jam or a dam upstream of the site can result in a dam breach-like flood wave that may propagate to the site.

" An ice jam or a dam downstream of a site may impound water upstream of itself, thus causing a flood via backwater effects.

The UFSAR indicates that during normal plant operation, icing has been limited to the canal area outside of the steel trash grates. The area in close proximity to the intake, where the suction of the pumps is taken, is kept from freezing by the thermal dilution gates, which recirculate discharge water through the intake bay, and by the turbulence induced by the circulating water pumps. The discharge canal remains free of ice during normal operation due to the plant heated effluent (OCNGS UFSAR).

The UFSAR also indicates that it is unlikely that ice blockage would cause problems to any safety related systems as the emergency service water flow utilizes approximately only 3 percent of the design capacity of the 6 screens on the intake structure (OCNGS UFSAR).

3.8 Channel Migration or Diversion There is no plausible risk that safety-related facilities and functions of the plant will be adversely affected by channel diversions or shore line migrations. Any shore line changes that would occur near OCNGS as a result of long-term tidal and wave actions would be relatively gradual with sufficient warning for mitigating actions to be implemented before the safety-related facilities will be adversely impacted. In case the circulating water and service water pumps will become inoperable, emergency plant procedures have been instituted which require the plant to be shut down to ensure the capability for safe shutdown under either normal or abnormal conditions.

3.9 Combined Effect Flood (includina Wind-Generated Waves)

The combined events incorporate the flood causal mechanisms previously discussed for precipitation events and hydrologic or seismic dam failures. Each combined event also incorporates waves induced by 2-year wind speed applied along the critical direction.

3.9.1 Basis of Inputs Dam Failures

• PMF flows and stillwater elevation (Exelon 2013b)

" Dam data including height, storage capacity, and spillway hydraulic characteristics (Exelon 2013b)

Probable Maximum Stillwater Elevation

" DEM of the Barnegat Bay Watershed Management Area, WMA 13

" Intake and discharge canal bathymetric information OYSTER CREEK NUCLEAR GENERATING STATION Page 29 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015

" Manning's Roughness Coefficients for land cover types.

" Land use/land cover information

" PMF flows and stillwater elevation (Exelon 2013b)

" PMSS (Exelon 2013d)

Wind-Wave Effects

• The spatially varying probable maximum stillwater elevation as determined in the PMSS elevation (Exelon 2013d)

• DEM of the Barnegat Bay Watershed Management Area, WMA 13

" Barnegat Bay bathymetry from NOAA's NOS estuarine bathymetry Barnegat Bay, NJ (M070), relative to MLLW vertical datum

" Aerial imagery from ESRIs world imagery web service

• The temporally and spatially varying wind field as determined in PMH analysis (Exelon 2013c) 3.9.2 Computer Software Programs

• FLO-2D, Version 2009.06

" ArcMap 10.0

" HEC-HMS, Version 3.5

• USACE Coastal Engineering Design Analysis System (CEDAS), Version 4.03 3.9.3 Methodology The criteria for combined events are provided in NUREG/CR-7046, Appendix H.3.2. The criteria for a site along the shores of an open or semi-enclosed waterbody (stream-side location) are utilized. The criteria include the following alternatives:

Alternative 1 - A combination of the lesser of one-half the PMF or the 500-year flood, surge and seiche from the worst regional hurricane or windstorm with wind-wave activity, and antecedent 10 percent exceedance high tide.

Alternative 2 - A combination of PMF in the stream, a 25-year surge and seiche with wind-wave activity, and antecedent 10-percent exceedance high tide.

Alternative 3 - A combination of a 25-year flood in the stream, probable maximum surge and seiche with wind-wave activity, and antecedent 10 percent exceedance high tide.

Alternative 4 - For drainage areas of less than 300 square miles in hurricane-prone areas, a combination of PMF in the stream, PMH in the open or semi-enclosed waterbody, and antecedent 10 percent exceedance high tide.

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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 Alternatives 1, 2, and 3 are bounded by Alternative 4, which is the governing scenario for OCNGS. The OCNGS combined events flood considered the combination of PMF with upstream dam failures in the stream, probable maximum storm surge with wind-wave activity in the open or semi-enclosed waterbody, and antecedent 10-percent exceedance high tide.

NUREG/CR-7046 presents updated methodologies relative to Regulatory Guide 1.59 which are incorporated in this calculation. These include:

" Use of computerized hydrologic and hydrodynamic simulation models (i.e., HEC-HMS, SLOSH and FLO-2D) to develop the PMF and PMSS flood elevations.

" Use of HHA approach in the assessment of dam failures (i.e., cascading dam failure without downstream routing).

The combined event evaluation utilized the following steps:

" Calculate the contribution of flooding in streams and rivers to flooding at OCNGS.

o PMF in streams and rivers contributory to OCNGS is determined in the PMF analysis (Exelon 2013b).

o Calculate the contribution of dam failures during the PMF.

o Calculate the contribution of flooding in streams and rivers to flooding at OCNGS due to the combination of upstream dam failures and the PMF.

• Calculate the contribution of storm surge and seiche to flooding at OCNGS.

o Probable maximum storm surge is determined in the PMSS analysis (Exelon 2013d).

o Probable maximum seiche does not affect OCNGS as determined in the PMS analysis (Exelon 2013e).

• Calculate probable maximum stillwater elevation using a two-dimensional hydrodynamic model.

o Combine PMF with dam failure on rivers and streams with the PMSS from Barnegat Bay/Atlantic Ocean; and conduct sensitivity analysis to determine the effects of synchronized riverine and coastal flooding at OCNGS.

" Calculate wind-wave effects: wave height and runup.

• Combine probable maximum stillwater elevation with wind-wave effects to calculate final probable maximum water elevation at OCNGS.

Due to anticipated two-dimensional overland flow characteristics from coincidental storm surge and riverine flooding, a two-dimensional hydrodynamic model, FLO-2D, is used (Exelon 2013g). FLO-2D is a physical process model that routes flood hydrographs and rainfall-runoff over unconfined flow surfaces or in channels using the dynamic wave GENERATING STATION NUCLEAR GENERATING Page 31 of47 OYSTER CREEK NUCLEAR OYSTER CREEK STATION Page 31 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 approximation to the momentum equation. FLO-2D moves flood volume on a series of tiles (grids) for overland flow or through stream segments for channel routing. Overland flow is modeled two-dimensionally. Flood routing in two dimensions is accomplished through a numerical integration of the equations of motion and the conservation of fluid volume for a flood. Channel flow is modeled one-dimensionally with rectangular, trapezoidal, or surveyed cross sections, and is routed using the dynamic wave approximation to the momentum equation. Average flow hydraulics of velocity and depth define the discharge between channel grid elements. Channel overbank flow is computed when the channel capacity is exceeded. Channel to floodplain flow exchange, including return flow to channels, is calculated by an interface routine (Exelon 2013g).

The method of analysis is summarized below:

" Delineate FLO-2D computational boundary.

" Calculate FLO-2D model grid elements.

" Calculate Manning's roughness coefficients.

" Calculate channel cross-section geometries.

• Assign riverine inflow and coastal surge hydrographs.

• Perform flood simulations to establish stillwater elevations and inundation extents.

Wind-Wave Effects Coincident wind wave characteristics are determined using the methodology outlined in the USACE Coastal EngineeringManual:

• Determine the critical wave fetch direction and length.

" Calculate the wind generated waves within Bamegat Bay due to PMH using the shallow water wave generation module of the USACE CEDAS computer program waves.

• Calculate of the depth-limited wave heights based on the breaking wave index.

• Select the design base wave conditions.

" Determine the wave runup elevation using the methodology outlined in the USACE CoastalEngineering Manual.

• Develop maximum and significant wave heights (and associated maximum water level) and wave period at OCNGS.

3.9.4 Results and Conclusions The following summarizes the results and conclusions:

The probable maximum water surface elevation at OCNGS results from a combination of PMF with dam failure in Oyster Creek, and in the South, Middle and North Branches of the Forked River, PMSS with wind-wave activity, and antecedent 10 percent exceedance high tide.

GENERATING STATION Page 32 of 47 OYSTER NUCLEAR GENERATING CREEK NUCLEAR OYSTER CREEK STATION Page 32 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015

• Dam failures of Wells Mill Reservoir Dam and the Freshwater Impounding Pond Dam during the PMF results in a peak PMF discharge of 52,900 cfs (an increase of 900 cfs in the PMF peak discharge from Oyster Creek). Dam failures of the Deer Head Lake I

Dam, Barnegat Lake Dam and Parker Street Dam during the PMF result in a peak PMF discharge of 49,700 cfs (an increase of 4,500 cfs in the PMF peak discharge from the North Branch of the Forked River).

[

" The probable maximum stillwater elevations are summarized in Table 2. Flooding from the bounding combined events scenario does not extend to the new radiation waste building and the low level radiation waste building.

• The probable maximum wave runup at OCNGS varies by location and ranges from 0.7 to 3.7 ft. The probable maximum water level elevations, including wave runup at OCNGS, are summarized in Table 2.

Table 2 - Dam Failure Results (Exelon 2013g)

Peak Peak Probable Probable Stillwater Stillwater Wave Maximum Maximum Time to Safety Structure Elevation Elevation Runup Water Surface Water Surface Peak**

(ft, NAVD88) (ft, MSL) (ft) Elevation Elevation (Minutes)

(ft., NAVD88) (ft, MSL)

Intake Structure 23.2 23.18 0 23.2 23.18 18 Reactor Building 22.8 22.78 0.7 23.5 23.48 19 Material Wareos 22.7 22.68 2.1 24.8 24.78 18 Warehouse Independent Spent Fuel Storage 22.7 22.68 2.7 25.4 25.38 18 Installation New Radiation*

Waste - - - -

Building Site Emergency 22.9 22.88 3.7 26.6 26.58 16 Building Administration 22.8 22.78 2.6 25.4 25.38 16 Building Low Level*

Radiation - - - -

Building Turbine Building 23.2 23.18 2.7 25.9 25.88 18 Emergency Diesel 23.1 23.08 0 23.1 23.08 18 Generator Building ___

• Not affected by the flooding scenario

-* Time to peak is measured from the time the peak surge elevation occurs at the coastline to the time peak elevation occurs at the structure. The peak surge elevation at the coastline occurs at 22 hours2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br />.

3.10 Error Uncertainty The Error Uncertainty for the OCNGS flood hazard reevaluation was analyzed in Calculation C-1302-120-E310-012, Error/Uncertainty Calculation at OCNGS, (Exelon 2013j). The following listed items were evaluated in the Error Uncertainty Calculation:

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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015

1) Verification of the SLOSH 3.97 storm surge model to assess model accuracy;

2) Sensitivity analysis of the FLO-2D hydrodynamic model for different model input parameters; and

3) Parametric analysis of river flows. As noted above, the most significant component of the controlling flood hazard is the storm surge resulting from the PMH.

A site-specific meteorological study determined the storm parameters associated with the PMH for OCNGS. The site-specific meteorological study included a detailed statistical analysis of storm parameters and defined the range of parameters representative of the PMH and estimates the annual exceedance probability of the PMH. The Error/Uncertainty Calculation utilized the results of the site-specific meteorological study to evaluate the probability of the assumed antecedent water level and also calculated the combined joint probability of the antecedent water level and the PMH, to assign a probability to the PMSS (Exelon 2013j).

3.10.1 Basis of Inputs

• 1-year through 1,000-year, 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> rainfall: NOAA Atlas 14 Point Precipitation Frequency Estimates

" Hurricane and tropical storm parameters from NOAA's Hurricane Database (HURDAT)

• Historical storm track information from NOAA's Coastal Services Center 3.10.2 Computer Software Programs

1. HEC-HMS v. 3.5

2. FLO-2D v.2009.06

3. SLOSH v.3.97

4. CEDAS-EST v. 4.03 3.10.3 Methodology The error uncertainty and conservatism of the flood calculations evaluated in the Error/Uncertainty Calculation at OCNGS (Exelon 2013j) is as follows:

1. Riverine Flooding. Error and uncertainty was estimated by performing sensitivity analyses.

of select input parameters.

2. Verification of SLOSH 3.97 storm surge model. The model was verified through review of previous verification studies by others as well as performance of hindcast simulations for two, well-documented historical hurricanes that resulted in storm surge in the vicinity of OCNGS.

OYSTER CREEK NUCLEAR GENERATING STATION Page 34 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015

3. Sensitivity analyses - Storm Surge - Storm surge sensitivity analyses were performed using SLOSH 3.97 in Calculation C-1302-120-E310-007 (Exelon 2013d), by performing hundreds of surge simulations representing a range of PMH parameters and identifying:

" The parameters that are the most sensitive in impacting surge elevation at OCNGS; and

" Identifying the combination of parameters resulting in the highest surge at OCNGS.

4. Sensitivity Analysis - Flood Stage. The hydrodynamic model FLO-2D was used, with a higher resolution grid than SLOSH 3.97, to evaluate the inundation onto land resulting from the combined river flooding and coastal storm surge. The sensitivity of the FLO-2D site model was evaluated by performing multiple simulations, varying roughness (Manning's coefficient) and model grid resolution.

5. PMSS Probability. The probability of the PMSS was estimated based on the probability of the antecedent water level and the combined joint probability of the antecedent water level and the PMH.

3.10.4 Results and Conclusions The following summarizes the results and conclusions (Exelon 2013j and Exelon 2013m):

1. The controlling flood at OCNGS is due to the combined events of the PMSS, wind-generated waves and the PMF. The principal flood component is the storm surge stillwater elevation.

2. The storm surge stillwater elevation was modeled using:

• The SLOSH 3.97 storm surge model to predict the coastal surge elevations; and

" The high resolution, FLO-2D hydrodynamic model to combine the coastal surge and PMF flow to evaluate flood inundation levels within the canals and on land at OCNGS.

3. The accuracy of the SLOSH 3.97 surge model was evaluated by verification analysis and indicated an acceptable degree of accuracy with a minor bias toward over-prediction of the storm surge.

4. The FLO-2D model was determined to be most sensitive to grid size when evaluating the combined events.

5. The river flow analysis (which was determined to be a minor contributor to the combined events flood stage) was determined to be sensitive to lag time, and the most conservative lag time required by regulatory guidance was used in determining the PMF.

6. The probability of the SLOSH computed OCNGS surge elevations for storms with calculated Annual Exceedance Probability is estimated to be 1.7 x1086 . The probability of the OCNGS combined events of the PMH and the antecedent water level is estimated to be extremely low (approximately 2.2 x1 0-12), significantly lower than the I x 10-6 probability typically considered acceptable for a combined event (Exelon 2013m).

7. Due to the relatively shallow water depths in the vicinity of OCNGS associated with storm surge, wave heights will be depth limited with little associated uncertainty.

STATION Page 35 of 47 OYSTER NUCLEAR GENERATING CREEK NUCLEAR OYSTER CREEK GENERATING STATION Page 35 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 3.11 Associated Effects The associated effects for flooding were determined in OCNGS calculation C-1302-120-E310-014 (Exelon 2015 K). The flood parameters of the combined events flooding that include storm surge (probable maximum storm surge with wind-wave activity) and riverine flooding (probable maximum flood and dam failures) were obtained from Calculation No. C-1302-120-E310-010 (Exelon, 2013a). The flood parameters of the LIP flood event were obtained from Calculation No. LIP-OYS-001 (AMEC, 2013).

3.11.1 Basis of Inputs

1. Results of the LIP flood event calculation, i.e. the maximum water surface elevation and maximum velocity, were obtained from LIP Calculation (Exelon, 2013i).

2. Parameters for the combined events flooding, i.e. the maximum water surface elevations, maximum velocity, wave height, wave period, wave length, including other relevant information, are obtained from Calculation No. C-1302-120-E310-010 (Exelon, 2013g).

3. Input values for debris and sediment are obtained from various sources such as textbooks, and research papers. The weight of debris applicable to OCNGS was established based on the ASCE guidance, Minimum Design Loads for Buildings and Other Structures. The information for heavy loads, such as floating boats, was obtained from internet sources (Exelon, 2015k).

3.11.2 Computer Software Programs None 3.11.3 Methodology A HHA approach described in NUREG/CR-7046 was used for the Associated Effects Calculation. Guidance for Performing the Integrated Assessment for External Flooding Guidance (NRC November 2012) defines the "flood height and associated effects" as the maximum stillwater surface elevation plus the following factors:

• Wind waves and run-up effects;

" Hydrodynamic loading, including debris;

• Effects caused by sediment deposition and erosion;

" Concurrent site conditions, including adverse weather conditions;

" Groundwater ingress; and

" Other "pertinent factors" including flood event duration and warning time.

A screening approach was followed to identify the associated effects at OCNGS. Calculation C1302-120-E310-010 (Exelon, 2013g) was reviewed to determine PMSS and combined events flooding mechanisms can potentially have associated effects on the safety-related structures of OCNGS.

In addition, the associated effects due to the LIP flooding event were reviewed based on the results determined in LIP calculation (Exelon, 2013i). The maximum water depth is below the building floor elevation for all except one door. The depth of flow is minimal (less than 1 ft) at OYSTER CREEK NUCLEAR GENERATING STATION Page 36 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 the door where the maximum water depth exceeds the building floor elevation and the velocity of flow is low (less than 1 ft/s), resulting in insignificant hydrostatic and hydrodynamic load. Therefore, the hydrostatic and hydrodynamic loads due to LIP flooding event is not evaluated for OCNGS Site.

The evaluation of other associated effects due to the LIP flooding event, such as debris impact loading, sediment deposition and erosion, was limited to a review of the maximum flow depths and velocities to verify ifthese hazards are applicable for OCNGS given the site specifics and flooding scenario. Itwas determined that the shallow flow depth and low velocity due to the LIP are not expected to cause debris impact loading, sediment deposition, or erosion hazards at the OCNGS site. Because the majority of the ground surface at the power block is paved, erosion and correspondingly sediment are not applicable hazards due to the low flow depth and velocity (Exelon 2015k).

The Associated Effects Calculation (Exelon 2015k) examined the forces exerted by flood water and coincident wind-forced waves during the combined events flooding at OCNGS.

The total pressure distribution on a vertical wall consists of two time-varying components: the hydrostatic pressure component due to the instantaneous water depth at the wall, and the dynamic pressure component due to the acceleration of the water particles.

Hydrostatic Loading The hydrostatic component was determined at the maximum still water elevation plus the incident wave height (Exelon 2015k).

Standing and slow-moving water induces horizontal hydrostatic forces against a structure, especially when flood water levels on opposite sides of a structure are not equal. The hydrostatic pressure increases in proportion to depth measured from the water surface because of the increasing weight of fluid exerted downward from the force above (Exelon 2015k).

Hydrodynamic Loading Water flowing around a building (or structure) imposes loads on the building. Hydrodynamic loads, which are a function of flow velocity and structure geometry, include frontal impact on the upstream face, drag along the sides and suction at the downstream side. A basic hydrodynamic equation was used to calculate the total hydrodynamic pressure due to water flowing around the buildings (Exelon 2015k). The velocity and maximum flow water depth for the combined flood event was obtained from Calculation No. C-1302-120-E310-010 (Exelon, 2013g).

The hydrodynamic load due to wave action was determined by using the Sainflou formula for nonbreaking/partially breaking waves. The Sainflou formula for conditions under wave crest and wave trough were derived theoretically for the case of regular waves and a vertical wall.

This formula cannot be applied in cases where wave breaking and/or overtopping takes place. Due to the site-specific conditions, application of this methodology is justifiable because as stated in the Coastal Engineering Manual wave breaking at vertical structures will not occur if the seabed in front of the structure has a mild slope (< 1:50) over a distance of several wavelengths from the structure. This condition is true for OCNGS because the site is flat around buildings and walls (Exelon, 2015k).

OYSTER CREEK NUCLEAR GENERATING STATION Page 37 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 Debris Impact Loading Combined Events Calculation (Exelon, 2013g), indicates that the critical path for wave propagation from Barnegat Bay to the OCNGS plant is almost directly east-west, and the combined events flood is considered to follow a general east-west direction. Debris is also expected to travel in an east-west direction along the flow direction of the combined events flood. The safety-related structures located in the eastern part of OCNGS would be subjected to the maximum debris impact loads, while those west of the power building would be subjected to minimal or no debris impact loads except buildings very close to the canal system.

As stated in the ASCE guidance (Exelon 2015k), impact loads are divided into three categories: (1) normal impact loads, which result from the isolated impacts of normally encountered objects; (2) special impact loads, which result from large objects, such as broken up ice floats and accumulations of debris, either striking or resting against a building, structure, or parts thereof; and (3) extreme impact loads, which result from very large objects, such as boats, barges, or collapsed buildings, striking the building, structure, or component under consideration. The equation from the ASCE guidance is revised to accommodate local conditions. Nuclear power plant buildings are rigid concrete structures, and as a result all conservative value of coefficients were utilized to calculate debris load impacts (Exelon, 2015k).

Soil/Sediment Loading It is conservatively assumed that soil/sediment pressure will act over the same area as the hydrostatic pressure. High velocity flood flows may result in scouring or erosion. Locations where there is an abrupt change in velocity vectors have the potential for sediment deposition. Maximum velocities at the OCNGS area were taken from the Combined Events Calculation (Exelon, 2013g) and compared with typical permissible velocities for selected ground-cover materials.

The description of the OCNGS site condition, including the soils, was obtained from the "Seismic Hazard and Screening Report' (Exelon, 20141). The report states that OCNGS is located in the New Jersey Coastal Plain and is underlain by a thick wedge of unconsolidated sediment ranging from Cretaceous to recent in age. According to the report, the soils in the site area are relatively homogeneous deposits of sands and silty sands with some gravel.

The velocity beyond which erosion is caused for sandy and sandy loam soils vary between 1.5 fps (sand) and 2.0 fps (sandy loam). Average velocity of 1.75 fps was considered to evaluate erodibility of the soil around the safety related structures. Hence, all unpaved areas along the way of the flood water which are exposed to higher velocity vectors are subjected to erosion. All areas including paved areas with lower flow velocities are generally exposed to sedimentation. Due to paved surfaces around the structures, erosion around the structures is not expected to occur.

3.11.4 Results and Conclusions Hydrostatic Loading Hydrostatic loads are those caused by water above or below the ground surface, free or confined. These loads are equal to the product of the water pressure multiplied by the surface area on which the pressure acts. Hydrostatic pressure is equal in all directions and always OYSTER CREEK NUCLEAR GENERATING STATION Page 38 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision I February 19, 2015 acts perpendicular to the surface on which it is applied. The hydrostatic pressure resulting from a PMSS at the representative locations (Table 3) of the structures vary between 720 Ibs/ft 2 at the intake structure, and 77 Ibs/ft2 at the emergency diesel generator building.

Table 3 - Hydrostatic Loading during PMSS at OCNGS Safety-Related Structures Max water Wave Total Hydrostatic Location depth, hs Height Depth Pressure (ft) (ft) (hs+Hw) (IbIft2 )

Intake Structure 11.2 0 11.2 720 Reactor Building 0.9 0.7 1.6 103 Material Warehouse 2.6 1.8 4.4 284 Independent Spent Fuel Building 3.3 2.6 5.9 380 Site Emergency Building 4.3 3.4 7.7 495 Administration Building 3.2 2.5 5.7 367 Turbine Building 1.3 0.0 1.3 84 Emergency Diesel Generator Building 1.2 0.0 1.2 77 Hydrodynamic Loading The velocity calculated at representative locations of the safety-related structures are shown in Table 4. Due to low flow velocity, the hydrodynamic load for OCNGS during a PMSS is low compared to the hydrostatic load acting on the safety-related structures.

Table 4 - Hydrodynamic Loading during PMSS at OCNGS Safety-Related Structures Max Flow Hydrodynamic Location Velocity Pressure, Fd (fps) (IbWft 2 )

Intake Structure 2.3 10.5 Reactor Building 0.9 1.6 Material Warehouse 1.5 4.5 Independent Spent Fuel Building 2.3 10.5 Site Emergency Building 1.9 7.2 Administration Building 1.1 2.4 Turbine Building 0.6 0.7 Emergency Diesel Generator 3.5 24.4 Building OYSTER CREEK NUCLEAR GENERATING STATION Page 39 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision I February 19, 2015 Wave loads are those loads that result from water waves propagating over the water surface and striking a building (or other structure). As shown in Table 5, all the safety-related structures except the intake structure, turbine building and emergency diesel generator building face varying degrees of loads due to wave action. The hydrodynamic load due to wave action was determined using the Sainflou formula for nonbreaking/partially breaking waves. The loads due to wave action are presented in Table 5.

Table 5 - Hydrodynamic Loading due to wave action at Safety-Related Structures Max Still WaeWave Wave 0, p2, 131, P2 with p1 with Location Depth, Length, Height, ft Ibft2 Ibft2 FS=32 FS=3,2 hs, ft L, ft Hw, ft Iblft iblft Intake Structure 11.2 0.0 0.0 - -

Reactor Building 0.9 29.4 0.7 0.28 44.2 53.1 132.6 159.3 Material Warehouse 2.6 50.2 1.8 0.64 109.8 134.2 329.5 402.7 Independent Spent 3.3 106.5 2.6 1.03 164.0 197.2 492.1 591.7 Fuel Building Site Emergency 4.3 64.4 3.4 1.42 208.4 256.3 625.1 756.8 Building Administration Building 3.2 120.2 2.5 0.99 158.5 189.9 475.6 569.8 Turbine Building 1.3 - - - - - -

Emergency Diesel 1.2 Generator Building Debris Impact Loading For woody debris, a 2000 lbs weight was used, as this is the largest in a range of typical weights for woody debris. For ice debris, a 4000 lb weight was used as the most conservative debris weight for ice. For potential water-borne boats in areas vulnerable to floating boat impact, a weight of 8,125 lbs was estimated and used (Exelon, 2015k). The debris velocity used was the summation of the maximum flow velocity and wave velocity. The resultant debris loads are shown in Table 6. The debris loads are applied between the still water elevation and the elevation of the maximum wave height corresponding to each safety-related structure. If there is no wave action, the debris load is applied at the still water elevation.

Page 40 of 47 OYSTER CREEK GENERATING STATION NUCLEAR GENERAliNG CREEK NUCLEAR STATION Page 40 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 Table 6 - Debris Impact Loads at Safety-Related Structures Max Wave Combined Impact Force, F (Ibs)

Location Flow Velocity debris Velocity (fps) velocity* F8125 F4000 F2000 F1000 F500 F200 (fps) (fps)

Intake Structure 2.3 0.00 2.30 - 1871 748 Reactor Building 0.9 2.09 2.99 - 2435 974 Material Wareos 31 1.5 316 4.66 46206 22748 11374 7583 3791 1517 Warehouse Independent 4.05 Spent Fuel 2.3 6.35 62994 31012 15506 10337 5169 2067 Building I Site Emergency 1.9 4.65 6.55 64950 31975 15988 10658 5329 2132 Building Administration 1.1 5.07 50211 24719 12360 8240 4120 1648 Building Turbine Building 0.6 0.00 8.81 - - - 488 195 Emergency Diesel 0.00 3.50 - 2847 1139 Generator Building I I I Note 1: F8125 is impact load from boat debris; F2000, F1000, F500, and F200 indicate load from trees, logs, etc.

Note 2: Large object debris velocity greater than 1000 lb is reduced by 25% (see Section 6.3.3 for justification)

• Combined velocity is the sum of the flow velocity and wave velocity SoilslSediment Loading High velocity flood flows may result in scouring or erosion. Locations where there is an abrupt change in velocity vectors have the potential for sediment deposition. The velocity of flow at some locations are less than the permissible velocity for erosion initiation. However, it may be an area for sedimentation for soils carried by the moving water. The soil buoyant unit weight was used to determine the lateral force acting on each safety-related structure and subsequent equations used to estimate the vertical and the horizontal pressures. The Sediment Loads are listed in Table 7.

Table 7 - Sediment Loads at Safety-Related Structures Water Depth Sediment vertical Sediment Lateral Location (ft) Pressure (Iblft2 ) Pressure (lb/ft2)

Intake Structure 11.2 682.6 327.6 Reactor Building 0.9 54.9 26.4 Material Warehouse 2.6 159.2 76.4 Independent Spent Fuel Building 3.3 201.9 96.9 Site Emergency Building 4.3 262.3 125.9 Administration Building 3.2 195.2 93.7 Turbine Building 1.3 79.3 38.1 Emergency Diesel Generator 1.2 73.2 35.1 Building 1.2 73.2 _35.1 OYSTER CREEK NUCLEAR GENERATING STATION Page 41 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 The total load at the OCNGS safety-related structures due to LIP flooding event is not applicable load to OCNGS site. The flood height and its associated effects analysis indicates that the hydrostatic force, hydrodynamic loads, groundwater ingress, and sediment transport are not anticipated to adversely affect safety-related equipment at the screen house and the power block area.

Flood Duration and Warning Time The flood elevation time plots stage hydrograph for the Intake Structure, Reactor Building, Material Warehouse, Independent Spent Fuel Storage Installation, Site Emergency Building, Site Emergency Building, Administration Building, Turbine Building and Emergency Diesel Generator Building are presented in the Combined Event Calculation.

The flood elevation time plots for the stillwater elevations, along with the wave runup height were used to determine the flood duration. The PMSS stillwater elevations at OCNGS range from 22.68 ft MSL to 23.18 ft MSL. The PMSS elevations with added wind wave at OCNGS range from 23.18 ft MSL to 26.58 ft MSL. The Peak Surge at Coastline occurs at 22 hrs and the Peak Elevation at OCNGS Turbine Building occurs at 22.3 hrs.

Therefore the warning time is 22.3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> starting from the onset of the PMH. The duration of inundation above 23 ft MSL for the Turbine Building due to the PMSS Peak Elevation is 0.3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> (Exelon, 2013g).

A local intense precipitation event has no appreciable warning time except those provided by a weather (precipitation) forecast.

4. COMPARISON WITH CURRENT DESIGN BASIS The reevaluation maximum stillwater elevation exceeds the current design basis, but does not invalidate the current flood mitigation strategy. The comparison of existing and reevaluated flood hazard is provided in Table 8.

Table 8 - Comparison of Existing and Reevaluated Flood Hazard at OCNGS Flood-Causing Design Basis Comparison Flood Hazard Reevaluation Mechanism Results Flooding in Riverine flooding was not Riverine PMF in Oyster Creek - 52,000 cfs Streams and considered significant in flooding was Rivers the development of the evaluated PMF in South Branch of the Forked design basis. The and will not River - 11,500 cfs potential for flooding due result in to stream flow was flooding at PMF in Middle Branch of the Forked evaluated for the OCNGS. River - 22,000 cfs OCNGS as part of the SEP and it was PMF in North Branch of the Forked determined that "no River - 45,200 cfs flooding that would affect related structures has OYSTER CREEK NUCLEAR GENERATING STATION Page 42 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision I February 19, 2015 Flood- Flood Hazard Reevaluation Causing Design Basis Comparison Resulti Mechanism been postulated for the site" (UFSAR Section 2.4.3.).

Dam Incremental flood flows Dam Dam failures of Wells Mill Reservoir Breaches and were calculated based breaches Dam and the Freshwater Failures on the breaching by any and failures Impounding Pond Dam during the unspecified cause for were PMF results in a peak PMF two small dams (Wells evaluated discharge of 52,900 cfs (an increase Mill Reservoir and the and will not of 900 cfs in the PMF peak Freshwater Impounding result in discharge from Oyster Creek).

Pond Dam on Oyster flooding at Creek) as part of the OCNGS. Dam failures of the Deer Head Lake SEP and it was Dam, Barnegat Lake Dam, and determined that no Parker Street Dam during the PMF flooding that would affect result in a peak PMF discharge of related structures has 49,700 cfs (an increase of 4,500 cfs been postulated for the in the PMF peak discharge from the site. North Branch of the Forked River).

Storm Surge The current design basis The The probable maximum stillwater maximum flood level due maximum elevations at OCNGS range from to PMH is elevation 22 ft still water 22.68 ft MSL to 23.18 ft MSL.

MSL. level elevations The maximum coastal storm surge from the re - elevation at the coastline is 24.58 ft evaluation MSL.

exceed the current The probable maximum stillwater design basis elevation at the OCNGS intake maximum structure is 23.18 ft MSL.

flood level due to PMH. Antecedent 10 percent exceedance high tide 4.28 ft MSL.

Seiche This flood-causing Seiche was Although seiches can occur in mechanism is not evaluated Barnegat Bay, they will not result in considered in the and will not flooding of OCNGS.

UFSAR. result in I flooding at OCNGS.

Tsunami This flood-causing The probable The Cumbre Vieja Volcano case mechanism is not maximum resulted as the most hazardous considered in the tsunami was tsunami sources for OCNGS, with UFSAR. evaluated maximum water surface elevation at and will not the site - 6.8 ft MSL.

result in II OYSTER CREEK NUCLEAR GENERATING STATION Page 43 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision I February 19, 2015 Flood- Flood Hazard Reevaluation Causing Design Basis Comparison Results Mechanism flooding at Low water antecedent water level -

OCNGS. (-)0.28 ft MSL. The low water tsunami did not result in water levels significantly below the low water antecedent water level.

Ice-Induced During normal plant Safety- There is no plausible risk that Flooding operation, icing has related safety-related facilities and functions been limited to the canal facilities and of the plant will be adversely area outside of the steel functions of affected by ice-induced flooding.

trash grates. The area in the plant will close proximity to the not be intake, where the suction adversely of the pumps is taken, is affected by kept from freezing by the ice-induced thermal dilution gates, flooding.

which recirculate discharge water through the intake bay, and by the turbulence induced by the circulating water pumps. The discharge canal remains free of ice during normal operation due to the plant heated effluent.

Channel This flood-causing Shore line Any shore line changes that would Migration or mechanism is not changes occur near OCNGS as a result of long Diversion described in the UFSAR. would be term tidal and wave actions would be relatively relatively gradual with sufficient warning for mitigating actions to be implemented before the safety related facilities will be sufficient adversely impacted.

for warning mitigating actions.

Combined PMH stillwater level at The The probable maximum wave runup Effect Flood the site - 22.0 feet MSL. maximum at OCNGS varies by location and (including The UFSAR also water level ranges from 0.7 ft to 3.7 ft.

wind- indicates that an elevations generated additional height of less from the re- The probable maximum stillwater waves and than 1.0 feet represents evaluation level elevations ranges from 22.68 ft upstream dam the maximum wave exceed the MSL to 23.18 ft MSL.

failure) runup at the plant site. current design basis for wind-OYSTER CREEK NUCLEAR GENERATING STATION Page 44 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision 1 February 19, 2015 Flood- Flood Hazard Reevaluation Causing Design Basis Comparison Results Mechanism generated The probable maximum level waves, elevations with added wind wave for safety structures are:

Intake Structure - 23.18 ft MSL Reactor Building - 23.48 ft MSL Material Warehouse - 24.78 ft MSL Independent Spent Fuel Storage Installation - 25.38 ft MSL Site Emergency Building - 26.58 ft MSL Administration Building - 25.38 ft MSL Turbine Building - 25.88 ft MSL Emergency Diesel Generator Building - 23.08 ft MSL

5. REFERENCES (ANSI/ANS-2.8-1992) American Nuclear Society (ANS), American National Standard for Determining Design Basis Flooding at PowerReactor Sites, prepared by the American Nuclear Society Standards Committee Working Group ANS-2.8, La Grange Park, Illinois, 1992.

(OCNGS UFSAR) Exelon OCNGS Updated Final Safety Analysis Report, Revision 14, October 2009.

(Exelon 2013a) Exelon Calculation C-1302-120-E310-004, ProbableMaximum Precipitation (PMP) for Oyster Creek and South Branch of the Forked River at OCNGS.

(Exelon 2013b) Exelon Calculation, C-1 302-120-E310-005, ProbableMaximum Flood of Oyster Creek and South, Middle and North Branches of the Forked River at OCNGS.

(Exelon 2013c) Exelon Calculation, C-1302-120-E310-006, ProbableMaximum Hurricane (PMH)for Oyster Creek Nuclear Generating Station.

(Exelon 2013d) Exelon Calculation, C-1302-120-E310-007, ProbableMaximum Storm Surge (PMSS) for Oyster Creek Nuclear Generating Station.

(Exelon 2013e) Exelon Calculation, C-1302-120-E310-008, Probable Maximum Seiche (PMS) for Oyster Creek Nuclear Generating Station.

(Exelon 2013f) Exelon Calculation, C-1302-120-E310-009, Probable Maximum Tsunami Screening Tests at OCNGS.

OYSTER CREEK NUCLEAR GENERATING STATION Page 45 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision I February 19, 2015 (Exelon 2013g) Exelon Calculation, C-1302-120-E310-010, Hydrodynamic Model/Combined Events Flood Assessment at OCNGS.

(Exelon 2013h) Exelon Calculation, C-1302-120-E310-0013, Detailed Tsunami Evaluation for Oyster Creek Nuclear Generating Station.

(Exelon 2013i) Exelon Calculation, Local Intense Precipitation Evaluation Report for the Oyster Creek Nuclear Generating Station.

(Exelon 2013j) Exelon Calculation, C-1302-120-E310-0012, Error/Uncertainty Calculation at OCNGS.

(Exelon. 2015k) Exelon Calculation, C-1302-120-E310-0014, Analysis and Determination of Associated Effects at OCNGS.

(Exelon, 20141). Exelon Generation Company, LLC, Seismic Hazard and Screening Report, Response to NRC Request for Information Pursuant to 10 CFR 50.54(f) Regarding Recommendation 2.1 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident.

(Exelon 2013m) Exelon. Calculation, C-1 302-120-E31 0-0011, Flood Frequency Calculation for OCNGS.

(NEI August 2012) Nuclear Energy Institute (NEI), Report 12-08, Overview of External Flooding Reevaluations, August 2012.

(NEI November 2012) Nuclear Energy Institute (NEI), [Draft Rev E]. Supplemental Guidance for the Evaluation of Dam Failures, November 2012.

(NOAA 2013) National Oceanic and Atmospheric Administration (NOAA), Tides and Currents, Bench Mark Sheets for Barnegat Inlet (Inside), NJ (Station 8533615) http://tidesandcurrents.noaa.gov/datamenu. shtml?stn=8533615 Barnegat Inlet (Inside),

NJ&type=Bench Mark Sheets, date accessed April 25, 2013.

(NRC March 2012) U.S. Nuclear Regulatory Commission, Letter to Licensees, 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, March 12, 2012.

(NRC November 2012) U.S. Nuclear Regulatory Commission (NRC), JLD-ISG-2012-05, November 30, 2012. Guidance for Performing the Integrated Assessment for External Flooding, Interim Staff Guidance, Revision 0.

(NRC RG 1.59) U.S. Nuclear Regulatory Commission (NRC), Design Basis Flood for Nuclear Power Plants, Regulatory Guide 1.59, Rev. 2, Washington, D.C., 1977.

(NRC RG 1.102) U.S. Nuclear Regulatory Commission (NRC), Flood Protection for Nuclear Power Plants, Regulatory Guide 1.102, Rev. 1, Washington, D.C., 1976.

GENERATING STATION NUCLEAR GENERATING Page 46 of 47 OYSTER CREEK NUCLEAR OYSTER CREEK STATION Page 46 of 47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FHRR-OYS-001 Exelon Generation Company, LLC Revision I February 19, 2015 (NUREG-0800) U.S. Nuclear Regulatory Commission (NRC), NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition - Site Characteristics and Site Parameters (Chapter 2), ML070400364, March 2007.

(NUREG/CR-7046) U.S. Nuclear Regulatory Commission (NRC), 2011, NUREG/CR-7046, PNNL-20091, Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, MLI1321A195, November 2011.

(NUREG/CR-6966) U.S. Nuclear Regulatory Commission (U.S. NRC), "NUREG/CR-6966:

Tsunami Hazard Assessment at Nuclear Power Plant Sites in the United States of America Springfield, VA: National Technical Information Service, March 2009.

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