The inspectors reviewed station Calculations CALC-94-E-0079-01, Evaluation of Unit 1 Safety-Related Structures for the Effects of Local Intense Precipitation, Revision 0; CALC-94-E-0079-02, Evaluation of Unit 2 Safety-Related Structures for the Effects of Local Intense Precipitation; and 5.8.2, Effects of Local Intense Precipitation on Safety-Related Roofs, Revision 0. During this review, the inspectors noted that Calculation CALC-94-E-0079-01 concluded the installation of five scuppers on the Unit 1 auxiliary building roof that were 12 inches high and 40 inches long was required to prevent the collapse of the roof structure due to excessive ponding from the local intense precipitation. This calculation determined that the resultant maximum amount of ponding after scupper installation on the Unit 1 auxiliary building roof would be 7.5 inches. Calculation CALC-94-E-0079-02 determined that maximum depth of ponding on the Unit 2 auxiliary building roof would be approximately 11.5 inches. The inspectors noted Units 1 and 2 share a common auxiliary building roof. The inspectors also noted that for the Unit 2 intake structure, Calculation 5.8.2 calculated live load for the roof assuming a ponding value of 14.7 inches, which resulted in the roof exceeding the design limit for live load. Subsequently, the inspectors performed walk downs of these areas and noted discrepancies between the calculations and actual facility. Specifically, on the Unit 1 auxiliary building there were only four scuppers installed that were 16 inches high and only 6 inches long, whereas the calculation had determined that five 40-inch long scuppers were needed to maintain the roof loading limit. The inspectors noted a divider installed to separate the roofs of the Unit 1 and 2 auxiliary buildings appeared to be less than 11 inches tall, which would allow spill over from Unit 2 to Unit 1 not analyzed for in Calculation CALC-94-E-0079-01. The inspectors also noted the Unit 2 intake structure roof has grating installed above each
service water pump. This grating is surrounded by berms to prevent water intrusion. However, the berms were only 6 inches tall, which was considerably less than the 14.7 inch depth assumed in Calculation 5.8.2. The inspectors presented this information to the licensee and, the licensee determined that further review was necessary to determine the acceptability of the identified issues. The inspectors determined that the potential vulnerabilities to both the Unit 1 auxiliary building and Unit 2 intake structure roofs as well and the Unit 2
service water pumps during an external flooding event will be treated as an
URI, pending further inspector review of the licensees analysis. A
URI is an issue requiring further information to determine if it is acceptable, if it is a finding, or if it constitutes a violation of NRC requirements. In this case, additional NRC inspection will be required to assess the ability of the Unit 1 auxiliary building and Unit 2 intake structure roofs as well as the Unit 2
service water pumps to cope with an external flooding event. Additional information was needed to determine whether a violation of regulatory requirements occurred. Pending further review of additional information provided by the licensee, this issue is being treated as an
URI 05000368/2007005-02, External Flooding Susceptibility.
