The U.S. Nuclear Regulatory Commission (NRC) said electrical breakers installed in a key safety system would not have functioned during certain scenarios at the Duke Energy (NYSE: DUK) three-unit, 2,538 MW Oconee nuclear power plant. That led to the NRC's finding of “substantial safety significance” that will result in increased NRC inspection and oversight of the facility.
NRC inspection findings are evaluated using a safety significance scale with four levels, ranging from “green” for minor significance, through “white” and “yellow” to “red” for high significance. The NRC said that one of two violations at Oconee related to the electrical breakers is “yellow,” having “substantial safety significance,” while the second violation is “green,” having “very low safety significance.”
Oconee plant employees on June 2, 2011 identified pressurizer heater breakers essential to the operation of the plant’s standby shutdown facility would not have functioned if needed. The standby shutdown facility is designed to be used for reactor cooling during certain accident scenarios, including fires and severe storms where other cooling systems might be unavailable or inoperable.
The NRC said the public was never endangered because no actual event occurred. Since the system is counted on for core cooling during certain accident scenarios and the electrical breakers would not have functioned as needed, the facility was vulnerable to core damage if an accident involving a series of unlikely events occurred.
The NRC staff said it will obtain additional information to determine whether the breaker problem represents a current performance issue.
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