View source for RS-14-053, Byron Station, Units 1 and 2, 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

{{Adams
| number = ML14079A421
| issue date = 03/12/2014
| title = Byron Station, Units 1 and 2, 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
| author name = Gaston R W
| author affiliation = Exelon Generation Co, LLC
| addressee name = 
| addressee affiliation = NRC/Document Control Desk, NRC/NRR
| docket = 05000454, 05000455
| license number = NPF-037, NPF-066
| contact person = 
| case reference number = RS-14-053
| document type = Letter
| page count = 6
}}

=Text=
{{#Wiki_filter:SExeLon Generation 10 CFR 50.54(f)RS- 14-053 March 12, 2014 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. STN 50-454 and 50-455 

==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 27, 2012 (RS-12-162).
I U.S. Nuclear Regulatory Commission NTTF Recommendation 2.1 -Flood Hazard Reevaluation Submittal for Byron Station March 12, 2014 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 Byron Station, Units 1 and 2, as a Category 2 Site requiring a Flood Hazard Reevaluation Report submittal due date of March 12, 2014. The information in the enclosures provides Byron Station, Units 1 and 2 Flooding Hazard Reevaluation Report. The Byron 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. Detailed site information (both designed and as-built), including present-day site layout, elevation of pertinent SSCs important to safety, site topography, as well as pertinent spatial and 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-related changes to the licensing basis and any flood protection changes (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.iv. Changes to the watershed and local area since license issuance;Response:
U.S. Nuclear Regulatory Commission NTTF Recommendation 2.1 -Flood Hazard Reevaluation Submittal for Byron Station March 12, 2014 Page 3* See Section 2.4 of Enclosure 1 for a description of changes to the watershed and local area since license issuance.v. Current licensing basis flood protection and pertinent flood mitigation features at the site;Response:* See Section 2.5 of Enclosure 1 for a description of Current License 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 regulatory guidance.
Provide an analysis of each flood causing mechanism that may impact the site including local intense precipitation 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.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 Section 3.2 of Enclosure 1.* 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.
U.S. Nuclear Regulatory Commission NTTF Recommendation 2.1 -Flood Hazard Reevaluation Submittal for Byron Station March 12, 2014 Page 4" 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):
See 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):
See Sections 3.9 and 4 of Enclosure 1.* Error/Uncertainty analysis for the governing flood scenarios:
See Section 3.8 of Enclosure 1.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 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 bounds the reevaluated hazard for all applicable flood-causing mechanisms, combined-effect floods, associated effects, and flood event duration parameters.
A complete comparison of current design basis and reevaluated flood hazards is provided in Section 4 of Enclosure 
: 1. The summary below describes how this finding was determined for the applicable flood hazards. The storm surge, seiche, tsunami, ice-induced flooding, channel migration or diversion, Rock River seismically-induced dam failure, and on-site impoundment failure flood-causing mechanisms were either determined to be implausible or completely bounded by other mechanisms.
Some individual flood-causing mechanisms (i.e. flooding in streams and rivers and dam breaches and failures) are addressed in one or more of the combined-effect floods.1. Local Intense Precipitation (LIP)The maximum reevaluated flood elevation (870.80 feet USGS 1929 in the vicinity of the power block and 870.70 feet USGS 1929 in the immediate station area) is bounded by the design basis flood elevation (870.90 feet USGS 1929). The associated effects are either bounded or not applicable, as described in Section 4 of Enclosure 
: 1. Flood event duration parameters are not relevant to the LIP flood since U.S. Nuclear Regulatory Commission NTTF Recommendation 2.1 -Flood Hazard Reevaluation Submittal for Byron Station March 12, 2014 Page 5 manual actions are not credited in the Current Licensing Basis (CLB) with providing protection.
: 2. Combined-Effect Flood in Section H.1, Reference 3, Floods Caused by Precipitation Events (including hydrologic dam failure)The three alternative precipitation-event combinations specified in Section H.1 of Reference 3, plus hydrologically-induced upstream dam failure, were evaluated for the Rock River watershed.
The maximum reevaluated stillwater elevation (699.20 feet USGS 1929) for the prevailing alternative (Alternative 
: 2) is bounded by the design basis stillwater elevation (708.3 feet USGS 1929). The maximum reevaluated wind-wave runup elevation (707.40 feet USGS 1929) for the prevailing alternative (Alternative 
: 2) is less than the design basis stillwater elevation (708.3 feet USGS-1929).
The effects of the reevaluated wind-wave runup, including impact loads, on the river screen house was evaluated and found to be addressed by the current design basis. In the unlikely event that the safety-related equipment in the river screen house is rendered inoperable the onsite seismically qualified wells will provide makeup for the essential service cooling towers. The other associated effects are bounded, as described in Section 4 of Enclosure 
: 1. Flood event duration parameters are not relevant to this combined-effect flood since manual actions are not credited in the CLB with providing protection for SSCs important to safety.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.
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 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, combined-effect floods, associated effects, and flood event U.S. Nuclear Regulatory Commission NTTF Recommendation 2.1 -Flood Hazard Reevaluation Submittal for Byron Station March 12, 2014 Page 6 duration parameters.
Therefore, Scenario 1 in Reference 4 applies and interim evaluations/actions and an Integrated Assessment are not required for Byron Station, Units 1 and 2.e. Additional actions beyond Requested Information item 1.d taken or planned to address flooding hazards, if any.Response: 0 None required.This letter contains no new regulatory commitments and no revision to existing regulatory commitments.
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 1 2 th day of March 2014.Respectfully submitted, Ronald W. Gaston Manager -Licensing 
& Regulatory Affairs Exelon Generation Company, LLC 

==Enclosures:==
: 1. Byron Nuclear Generating Station, Flood Hazard Reevaluation Report, Revision 0 2. CD-R labeled: "Byron Nuclear Generating Station, 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 III (w/o Enclosure 2)NRC Senior Resident Inspector 
-Byron Station NRC Project Manager, NRR -Byron Station Mr. G. Edward Miller, NRR/DORL/LPL2-1, NRC Illinois Emergency Management Agency -Division of Nuclear Safety (w/o Enclosure 2)}}