Duke STEVEN DCAPPS ztEnergy, Vice President McGuire Nuclear Station Duke Energy MGOJ VP / 12700 Hagers Ferry Rd. Huntersville, NC 28078 980-875-4805 980-875-4809 fax Steven. [email protected] November 26, 2012 10 CFR 50.54(f) U. S. Nuclear Regulatory Commission ATTN: Document Control Desk 11555 Rockville Pike Rockville, MD 20852 Subject: Duke Energy Carolinas, LLC (Duke Energy) McGuire Nuclear Station (MNS), Units I and 2 Docket Nos. 50-369 and 50-370 Renewed License Nos. NPF-9 and NPF-17 Flooding Walkdown Information Requested by NRC Letter, Request for Information Pursuantto Title 10 of the Code of Federal Regulations 50.54(0 Regarding Recommendations 2.1, 2.3, and 9.3, of the Near-Term Task Force Review of Insights from the Fukushima Dai-lchiAccident; dated March 12, 2012 Reference: 1. NRC Letter, Request for Information Pursuantto Title 10 of the Code of FederalRegulations 50.54(0 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. NEI 12-07, Guidelines for Performing Verification Walkdowns of Plant Flood ProtectionFeatures, Revision 0-A, dated May 2012 3. NRC Letter to NEI, Endorsement of Nuclear Energy Institute (NEI) 12-07, "Guidelinesfor Performing Verification Walkdowns of Plant Flood Protection Features",dated May 31, 2012 On March 12, 2012, the NRC staff issued Reference 1. Enclosure 4 of Reference I contained specific Requested Actions, Requested Information, and Required Responses associated with Recommendation 2.3 for Flooding Walkdowns. In accordance with 10 CFR 50.54, "Conditions of licenses," paragraph (0, addressees were requested to confirm within 90 days their intent to use the NRC-endorsed flooding walkdown procedures, and to submit their final response within 180 days of the NRC's endorsement of the walkdown procedure. The 180 day response.is to include a list of any areas that are unable to be inspected due to inaccessibility and a schedule for when the walkdown will be completed. On June 8, 2012, Duke Energy submitted its 90 day response to Enclosure 4 of Reference 1, confirming that the industry guideline, NEI 12-07 (Reference 2), would be used as the basis for the flooding walkdowns at the McGuire Nuclear Station (MNS). NEI 12-07 was endorsed by NRC letter dated May 31, 2012 (Reference 3). wvdw. duke-energy curn United States Nuclear Regulatory Commission November 26, 2012 Page 2 This submittal comprises the aforementioned 180 day response for MNS. The Enclosure contains the flooding walkdown report addressing the items identified in Appendix D of NEI 12-07. There were no deferred walkdowns. This letter contains no new regulatory commitments. This submittal has been reviewed by licensee management, including the technical staff, regulatory staff, and senior management, in accordance with Duke Energy procedures and processes. Should you have any questions concerning this letter, or require additional information, please contact Michael K. Leisure at (980) 875-5171. I declare under penalty of perjury that the foregoing is true and correct. Executed on November 26, 2012. Respectfully submitted, Steven D. Capps Enclosure United States Nuclear Regulatory Commission November 26, 2012 Page 3 xc: V. M. McCree, Regional Administrator U.S. Nuclear Regulatory Commission - Region II Marquis One Tower 245 Peachtree Center Avenue NE, Suite 1200 Atlanta, Georgia 30303-1257 Eric J. Leeds, Director, Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission One White Flint North, Mailstop 13-H16M 11555 Rockville Pike Rockville, MD 20852-2738 J. H. Thompson, Project Manager U. S. Nuclear Regulatory Commission One White Flint North, Mailstop 8 G9A 11555 Rockville Pike Rockville, MD 20852-2738 J. Zeiler NRC Senior Resident Inspector McGuire Nuclear Station Justin Folkwein American Nuclear Insurers 95 Glastonbury Blvd., Suite 300 Glastonbury, CT 06033-4453 United States Nuclear Regulatory Commission November 26, 2012 Enclosure ENCLOSURE McGuire Nuclear Station Flood Walkdown Report McGuire Nuclear Station Flood Walkdown Report Rev. 0 11/15/12 McGuire Nuclear Station Flood Walkdown Report Response To 10CFR50.54(f) Letter: "Recommendation 2.3: Flooding" Executive Summary This report provides the response of McGuire Nuclear Station to the NRC Letter to Licensees, dated March 12, 2012, "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." The flood walkdowns were performed in accordance with the Nuclear Energy Institute flooding walkdown document NEI 12-07, "Guidelines for Performing Verification Walkdowns of Plant Flood Protection Features." This NEI flooding walkdown document provides guidance for assessing external flood protection and mitigation capabilities in accordance with the NRC recommendation in Item 2.3 of SECY 11-0137 and Enclosure 4 of the March 12, 2012 10CFR50.54(f) Letter. I. Describe the Design Basis Flood Hazard Levels For All Flood-Causing Mechanisms, Including Groundwater Ingress. This is a description of the design basis criteria used for the design of flooding on the power block area at McGuire Nuclear Station from two sources of natural phenomena. These two sources are: 1) flooding as a result of rising water on the power block and 2) flooding as a result of precipitation on the power block. Probable Maximum Flood Flood analyses at McGuire Nuclear Station considered the following postulated events in determining the flood levels for the site: 1. Probable Maximum Flood (PMF) resulting from the probable maximum precipitation in the drainage area. 2. Standard Project Flood (SPF) passing through Lake Norman combined with the seismic failure of one of the upstream dams (due to an Operating Basis Earthquake (OBE). The Standard Project Flood is considered equal to one-half of the Probable Maximum Flood. All safety related structures at McGuire Nuclear Station are protected from the possible flooding of Lake Norman. These structures and their components are protected from flooding by an earthen dam which extends from the Cowans Ford Dam. The top of the embankment that is adjacent to the spillway at Cowans Ford Dam is located at Elevation 775.0 feet mean sea level (msl). At the plant site, the embankment crest rises to Elevation 780.0 feet msl. With the consideration of these features, the Category I structures and their components are not subject to flooding caused by the most severe assumed flood condition combined with the highest wave effort. (2, 8, 9,10) The Probable Maximum Flood (PMF) is determined by calculating the Probable Maximum Precipitation (PMP) over each of the reservoir drainage areas upstream of Lake Norman. Each I McGuire Nuclear Station Flood Walkdown Report Rev. 0 11/15/12 flood was routed through the Catawba River system to determine the most critical position for producing the maximum reservoir elevation at the McGuire site. A search for historically great storms that occurred near the Catawba River basin was made to derive a hypothetical flood that would be the most severe, reasonably possible flood to occur at the McGuire site. The greatest storm over the Catawba River basin area is recorded for the period July 13-17, 1916. To arrive at the Probable Maximum Precipitation (PMP) over the Catawba River basin, the July 13-17, 1916 storm was selected based upon meteorological and physiographic considerations as a guide to the determination of time and area rainfall distribution pattern. The following adjustments were made to this storm to increase its magnitude and intensity to such values which are considered to be equal to the Probable Maximum Precipitation over the Catawba River basin: 1. Rainfall depth-duration values were distributed in accordance with that of the 1916 storm. The adjusted July 1916 storm most closely approximates the theoretical Probable Maximum Precipitation depth-area-duration values for the Lake Norman drainage area. 2. The storm position was transposed over a limited distance within the Catawba River basin to produce a maximum concentration of precipitation over a selected area. 3. Precipitation amounts were increased 40 percent. Several trial positions of the storm center were made to determine the most critical position for producing the maximum flood. To determine the probable maximum flood flow, a series of computer simulations were performed using different storm center positioning and different upstream dam failure sequences. The storm center was positioned over each of the reservoir drainage areas in turn and then routed through the Catawba River system. In addition, the direction of the storm travel was assumed in both the upstream and downstream directions for comparison of the maximum runoff. Eleven storm simulations were investigated for this analysis. These storms were numbered 9 through 14, 14A, and 15 through 18. (3,9, 11) Each of the reservoir drainage areas was divided into sub-areas or tributary divisions. There were a total of twenty-two tributary divisions. Each sub-area varied in size dependent upon the number of larger tributary streams flowing into each reservoir. Unit hydrographs of these areas were developed for synthesis in flood routing. Probable Maximum Precipitation was applied to the unit hydrographs with considerations for precipitation losses. A value of 0.5 inches was deducted for an initial loss, and a rate of 0.10 inches per hour was applied for infiltration losses. Water levels in the power block area are predicted by routing the Probable Maximum Flood (PMF) through the Catawba River system. This analysis results in the hydrographs and reservoir elevation at Lake Norman. The Probable Maximum Flood is routed through the system assuming that the discharges from generation of power continue unless reservoir levels overtop bulkheads and embankments. These bulkheads and embankments are used to protect the hydroelectric powerhouses.