Modifications completed by Duke Energy (NYSE:DUK) at the three-unit Oconee nuclear plant in South Carolina would adequately protect the plant from a potential failure of the Jocassee Dam, the Nuclear Regulatory Commission (NRC) said in a June 17 news release.
The plant is located near Seneca, S.C., about 30 miles west of Greenville. The flood-proofing work is part of a long-running collaboration between Duke and NRC at the plant.
In 2008, the NRC staff issued a letter to Duke requesting information related to external flooding, including the potential failure of the Jocassee Dam, located about 12 miles upstream from the plant.
There were numerous meetings and conversations between the NRC and Duke, and the detailed flood hazard analysis took two years to complete. In 2010, Duke submitted the flood analysis and the NRC issued a confirmatory action letter (CAL) documenting the company’s commitments.
As Duke and the NRC continued to work through the flooding issues, the company also implemented some interim compensatory measures, which were inspected by the NRC in 2010.
The Fukushima Dai-ichi accident happened in 2011 and the NRC issued another letter in 2012 requesting additional information on flooding as the agency worked to ensure that lessons learned from the situation in Japan were applied to U.S. plants including Oconee.
Duke submitted its flood hazard reevaluation report in 2013 and then a revised flood hazard reevaluation report in 2015. The NRC accepted that 2015 report for the purposes of the meeting the CAL. In addition to that report, NRC inspectors have evaluated the Oconee plant’s modifications as the company completed each of those steps. The modifications included building new or enhanced flood walls and other features as well as moving some power lines and equipment to less flood-prone locations.
In April, Duke informed the NRC that the flooding modifications were complete, and a subsequent inspection led the NRC to determine that the company had satisfied the commitments in the 2010 CAL.
“The completion of the commitments in the confirmatory action letter gives the NRC confidence that the Oconee plant is adequately protected from external floods, including scenarios involving the failure of the dam,” said NRC Region II Administrator Cathy Haney.
Haney said the years it took to resolve the flooding issues at Oconee were necessary to ensure that the best analyses were used, that information from the accident in Japan was incorporated and that the plant modifications met all requirements.
The Duke letter stating that the modifications were complete is available on the NRC website. The NRC report closing the CAL is currently available from the Region II Office of Public Affairs and will be available on the website in the next few days.
The work included items such as relocating the back-up power transmission line towers above the floodplain to supply emergency power and the acquisition of new right-of-way. Various measures were also taken to protect the intake dike and the embedded Condenser Circulating Water piping (cooling water supply) by armoring the Intake Dike in high water velocity locations and providing grass cover support as approved by the Federal Energy Regulatory Commission (FERC).
Each of the three pressurized water reactor (PWR) units has a summer operating capacity of roughly 850 MW.