RS-15-064, Response to March 12, 2012, Request for Information Enclosure 2, Recommendation 2.1, Flooding, Required Response 2, Flood Hazard Reevaluation Report

Response to March 12, 2012, Request for Information Enclosure 2, Recommendation 2.1, Flooding, Required Response 2, Flood Hazard Reevaluation Report

ML15084A586
Person / Time
Site:	Limerick
Issue date:	03/12/2015
From:	Jim Barstow Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
Shared Package
ML15093A216	List: RS-15-064, Response to March 12, 2012, Request for Information Enclosure 2, Recommendation 2.1, Flooding, Required Response 2, Flood Hazard Reevaluation Report
References
RS-15-064
Download: ML15084A586 (7)

Text

AoExeton Generation 10 CFR 50.54(f)

RS-1 5-064 March 12, 2015 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Limerick Generating Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-39 and NPF-85 NRC Docket Nos. 50-352 and 50-353

Subject:

Exelon Generation Company, LLC Response to March 12, 2012, Request for Information Enclosure 2, Recommendation 2.1, Flooding, Required Response 2, Flood Hazard Reevaluation Report

References:

1. NRC Letter, Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3, of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated March 12, 2012.

2. NRC Letter, Prioritization of Response Due Dates for Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Flooding Hazard Reevaluations for Recommendations 2.1 of the Near-Term Task Force Review of Insights From the Fukushima Dai-ichi Accident, dated May 11, 2012.

3. U.S. Nuclear Regulatory Commission, NUREG/CR-7046, Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, dated November 2011.

4. Letter from David L. Skeen, U.S. Nuclear Regulatory Commission, to Joseph E. Pollock, Nuclear Energy Institute - Trigger Conditions for Performing an Integrated Assessment and Due Date for Response, dated December 3, 2012.

5. U.S. Nuclear Regulatory Commission, JLD-ISG-2012-05, Guidance for Performing the Integrated Assessment for External Flooding, dated November 30, 2012.

6. Letter from Exelon Generation Company, LLC to U.S. Nuclear Regulatory Commission, "180-day Response to NRC Request for Information Pursuant to 10 CFR 50.54(f)

Regarding the Flooding Aspects of Recommendation 2.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated November 19, 2012 (RS-1 2-172).

ADo

U.S. Nuclear Regulatory Commission NTTF Recommendation 2.1 - Flood Hazard Reevaluation Submittal for Limerick Generating Station, Units 1 and 2 March 12, 2015 Page 2 On March 12, 2012, the NRC issued Reference 1 to request information associated with Near-Term Task Force (NTTF) Recommendation 2.1 for Flooding. One of the Required Responses in this letter directed licensees to submit a Flood Hazard Reevaluation Report, including the interim action plan requested in Item 1.d of Reference 1, Enclosure 2, if appropriate. On May 11, 2012, the NRC issued the prioritization plan developed by the NRC and resultant Flood Hazard Reevaluation due dates for all sites. Reference 2, Enclosure 1 identified Limerick Station, Units 1 and 2, as a Category 3 Site requiring a Flood Hazard Reevaluation Report submittal due date of March 12, 2015. The information in the enclosed provides Limerick Station, Units 1 and 2, Flood Hazard Reevaluation Report. The Limerick Station, Units 1 and 2, Flood Hazard Reevaluation Report follows the reevaluation process described in Reference 3.

Information Requested in Reference 1, Enclosure 2

a. Site information related to the flood hazard.Relevant 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. Detailedsite information(both designed and as-built), including present-daysite layout, elevation of pertinent SSCs important to safety, site topography, as well as pertinent spatialand temporal data sets;

Response

• Site layout and topography - See Section 2.1 and Figures 2.1.1 and 2.1.2 of Enclosure 1.

• Pertinent Site Data is provided in Enclosure 2.

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

Response

• See Section 2.2 of Enclosure 1, which describes the current design basis flood hazards for all flood causing mechanisms.

iii. Flood-relatedchanges to the licensing basis and any flood protectionchanges (including mitigation)since license issuance;

Response

• See Section 2.3 of Enclosure 1 for a description of flood-related changes to the licensing basis and any flood protection changes (including mitigation) since license issuance.

U.S. Nuclear Regulatory Commission NTTF Recommendation 2.1 - Flood Hazard Reevaluation Submittal for Limerick Generating Station, Units 1 and 2 March 12, 2015 Page 3 iv. Changes to the watershed and local areasince license issuance;

Response

• See Section 2.4 of Enclosure 1 for a description of changes to the watershed and local area since license issuance.

v. Currentlicensing basis flood protection and pertinent flood mitigation features at the site;

Response

• See Section 2.5 of Enclosure 1 for a description of Current Licensing Basis (CLB) 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.)

Response

• See Reference 6 for results of the flooding walkdowns.

" See Section 3 of Enclosure 1 for additional site and watershed information used to assess the flood hazard.

b. Evaluation of the flood hazard for each flood causing mechanism, based on present-day methodologies and regulatoryguidance. Provide an analysisof each flood causing mechanism that may impact the site including local intense precipitationand site drainage,flooding in streams and rivers, dam breachesand failures, storm surge and seiche, tsunami, channel migration or diversion,and combined effects.

Mechanisms that are not applicableat the site may be screened-out;however, a justificationshould be provided.Provide a basis for inputs and assumptions, methodologies and models used including input and output files, and other pertinent data.

Response

A description of the flood hazard reevaluation for each flood causing mechanism and the basis for inputs, assumptions, methodologies, and models are referenced below. Per NRC/NEI public meeting dated January 16, 2013, input-output files are not included with this submittal package but are available upon request.

• Local Intense Precipitation (LIP) and Site Drainage: See Section 3.1 of Enclosure 1.

• Flooding in Streams and Rivers: See Sections 3.2 of Enclosure 1.

U.S. Nuclear Regulatory Commission NTTF Recommendation 2.1 - Flood Hazard Reevaluation Submittal for Limerick Generating Station, Units 1 and 2 March 12, 2015 Page 4

• Dam Breaches and Failures: See Section 3.4 of Enclosure 1.

" Storm Surge: See Section 3.3 of Enclosure 1.

• Seiche: See Section 3.3 of Enclosure 1.

" Tsunami: See Section 3.3 of Enclosure 1.

• Ice-Induced Flooding: See Section 3.6 of Enclosure 1.

• Channel Migration or Diversion: See Section 3.7 of Enclosure 1.

" Combined Effects (including wind-waves and runup effects): See Section 3.5 of Enclosure 1.

" Other Associated Effects (i.e. hydrodynamic loading, including debris; effects caused by sediment deposition and erosion; concurrent site conditions; and groundwater ingress) are addressed in the respective flood-causing mechanism sections and Sections 3.9 and 4 of Enclosure 1.

" Flood Event Duration Parameters (i.e. warning time, period of site preparation, period of inundation, and period of recession) are addressed in the respective flood-causing mechanism sections and Sections 3.9 and 4 of Enclosure 1.

• Error/Uncertainty analysis for the governing flood scenarios is addressed in Section 3.8 of Enclosure 1.

c. Comparisonof current and reevaluatedflood causing mechanisms at the site.

Providean assessment of the current design basis flood elevation to the reevaluated flood elevation for each flood causing mechanism. Include how the findings from Enclosure 4 of the 50.54(f) letter (i.e., Recommendation 2.3 flooding walkdowns) support this determination.If the current design basis flood bounds the reevaluated hazard for all flood causing mechanisms, include how this finding was determined.

Response

The current design basis flood does not bound the reevaluated hazard for all applicable flood-causing mechanisms, combined-effect floods, associated effects, and/or flood event duration parameters. A complete comparison of current design basis and reevaluated flood hazards is provided in Section 4 of Enclosure 1 that describes how this finding was determined for the applicable flood hazards. Surge, Seiche, Tsunami, Ice Induced Flooding, Channel Migration or Diversion, and Combinations in Section H.1 and H.2 of Reference 3 for the Schuylkill River and Sanatoga Creek (which includes the "Flooding in Streams and Rivers" and "Dam Breaches and Failures" mechanisms) were either determined to be implausible or completely bounded by the current design basis or other mechanisms.

Limerick Station is considered potentially exposed to the flood hazards listed below. Some

U.S. Nuclear Regulatory Commission NTTF Recommendation 2.1 - Flood Hazard Reevaluation Submittal for Limerick Generating Station, Units 1 and 2 March 12, 2015 Page 5 individual flood-causing mechanisms (i.e. Flooding in Streams and Rivers, Dam Breaches and Failures, and Surge) are addressed in one or more of the combined-effect floods.

1. Local Intense Precipitation (LIP)

The maximum reevaluated flood elevation (218.4 feet Mean Sea Level (MSL)) is bounded by the design basis flood elevation (218.6 feet MSL). The associated effects are also bounded or not applicable, as described in Section 4 of Enclosure 1.

Flood event duration parameters are not applicable to the LIP flood since manual actions are not credited in the Current Licensing Basis (CLB) with providing protection. However, the south side of the plant, near the emergency diesel generators, was not analyzed with the design basis LIP flood, as it was with the reevaluated LIP flood. Therefore, LIP was considered to be unbounded in this area.

2. Combined-Effect Flood in Section H.1, Reference 3, Floods Caused by Precipitation Events (including hydrologic dam failure) for Possum Hollow Run The three alternative precipitation-event combinations specified in Section H.1 of Reference 3, plus hydrologically-induced upstream dam failure, were evaluated for the Possum Hollow Run watershed. The maximum reevaluated stillwater elevation (167.8 feet MSL) for the prevailing alternative is not bounded by the design basis stillwater elevation for the same stream (159.0 feet MSL). However, the reevaluated flood elevation for Possum Hollow Run is bounded by the design basis flood elevations of the Schuylkill River (207 feet MSL). Note that the nominal plant grade elevation is 217 feet MSL Therefore, no further actions are required for this scenario as the station is bounded by the Schuylkill River Flood.

d. Interim evaluation and actions taken or plannedto address any higher flooding hazards relative to the design basis,prior to completion of the integratedassessment describedbelow, if necessary.

Response

Per Enclosure 2 of Reference 1, an Integrated Assessment is required for plants where the current design basis floods do not bound the reevaluated hazard for all flood causing mechanisms. Reference 4 presents four approaches for performing an Integrated Assessment based on the results of the flood hazard reevaluation.

Scenario 1- Reevaluated Hazard Bounded by Design Basis Scenario 2- Only Local Intense Precipitation Scenario 3- All Permanent and Passive Flood Protection Scenario 4- Integrated Assessment Required An Integrated Assessment is not necessary in Scenario 1. Limited evaluations can be conducted and submitted with the Flood Hazard Reevaluation Report under Scenarios 2 and 3 that only address specific sections of the Integrated Assessment Interim Staff Guidance (Reference 5). Licensees in Scenario 4 and those not including limited

U.S. Nuclear Regulatory Commission NTTF Recommendation 2.1 - Flood Hazard Reevaluation Submittal for Limerick Generating Station, Units 1 and 2 March 12, 2015 Page 6 evaluations in the Flood Hazard Reevaluation Report under Scenarios 2 and 3 are required to perform a full Integrated Assessment.

Per "Part c" above, the current design basis flood bounds the reevaluated hazard for all flood causing mechanisms except LIP. Therefore, Scenario 2 (above) applies. Reference 4 states (regarding Scenario 2):

If local intense precipitationis the only portion of the reevaluatedhazard that is not bounded by the currentdesign basis, the licensee can limit the evaluation to only the site drainage. This evaluationshould be performed using Section A. 1.1.6 of Appendix A to the integratedassessment interim staff guidance (ISG) and the applicationof guidance containedin NUREG-0800, "StandardReview Plan for the Review of Safety Analysis Reports for Nuclear Power Plants:LWR [light-waterreactor] Edition." The results of this evaluation should be submitted with the hazard report.

Limerick Station opted to include a limited Integrated Assessment with this submittal based on a limited evaluation of the effects of the LIP flood in the unanalyzed area on the south side of the plant, near the emergency diesel generators. Section A. 1.1.6 of Reference 5 does not apply in this case since the reevaluated LIP flood elevation is lower than the design basis LIP (Enclosure 1, Table 4.0.2). The focus of this limited Integrated Assessment is to determine the impact of LIP at the emergency diesel generators and if additional compensatory measures are needed to maintain plant safety.

Engineering Technical Evaluation 01550669-36 was prepared to analyze the ingress volume of floodwater entering the doors to the diesels. This evaluation reviewed the amount of water that could enter the rooms through a small door undercut and compared it to the allowable volume in the diesel rooms in the diesel pit area. The results of the evaluation showed that there is no effect on safety related equipment in the diesel generator rooms during the LIP flood and no compensating actions are necessary.

Interim Actions No interim actions are required since the limited evaluation, discussed above, demonstrates that the reevaluated LIP flood does not impact plant safety under current configuration.

e. Additional actions beyond Requested Information item 1.d taken or planned to addressflooding hazards,if any.

Response

• None required.

This letter contains no new regulatory commitments and no revision to existing regulatory commitments.

U.S. Nuclear Regulatory Commission NTTF Recommendation 2.1 - Flood Hazard Reevaluation Submittal for Limerick Generating Station, Units 1 and 2 March 12, 2015 Page 7 If you have any questions regarding this submittal, please contact Ron Gaston at (630) 657-3359.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 12 th day of March 2015.

Respectfully submitted, James Barstow Director - Licensing & Regulatory Affairs Exelon Generation Company, LLC

Enclosures:

1. Limerick Generating Station, Flood Hazard Reevaluation Report, Revision 0

2. CD-R labeled: "Limerick Generating Station, Flood Hazard Reevaluation, Pertinent Site Data" Document Components:

Pertinent Site Data (requires AutoCAD or similar program) cc: Director, Office of Nuclear Reactor Regulation (w/o Enclosure 2)

Regional Administrator - NRC Region I (w/o Enclosure 2)

NRC Senior Resident Inspector - Limerick Generating Station, Units 1 and 2 NRC Project Manager, NRR - Limerick Generating Station, Units 1 and 2 Mr. Robert F. Kuntz, NRR/JLD/JHMB, NRC Mr. Victor E. Hall, NRR/JLD/JHMB, NRC Director, Bureau of Radiation Protection - Pennsylvania Department of Environmental Resources (w/o Enclosure 2)

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