The Nuclear Regulatory Commission (NRC) said Friday it had completed its review of the flood protection improvements at the Oconee Nuclear Plant 30 miles west of Greenville, S.C., and found that modifications completed by Duke Energy at the facility would adequately protect the plant from any possible failure of the Jocassee Dam, which is located 12 miles upstream on the Keowee River.
The dam was completed in 1973, forming Lake Jocassee. It stands 386 feet tall and measures 1,800 feet across. The lake behind the dam has 75 miles of shoreline.
In 2008, the NRC issued a letter to Duke Energy requesting information related to external flooding, including the potential failure of the dam. The so-called “interim compensatory measures” were then reviewed and inspected in 2010.
That may have put the issue to rest. But in March 2011, the accident at the Fukushima Daiichi power plant in Japan highlighted the need to have adequate flood protection, given the possibility that a flood, like the tsunami that knocked out backup power at Fukushima, could cause a catastrophic event at other plants.
As such, 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 comfirmatory action letter (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 in a statement.
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 Oconee plant consists of three Babcock & Wilcox Lowered Loop pressurized water reactors that began operations in Feb. 1973, Oct. 1973 and July 1974, respectively.