The Oconee Nuclear Station’s top leadership claimed responsibility Thursday for safety violations that allowed a crack in its oldest reactor to go undetected for years, but they stopped short of agreeing with nuclear regulators on the severity of the lapse in oversight.
“There’s no doubt we missed the bar,” Preston Gillespie, senior vice president for Duke Energy’s nuclear operations, told U.S. Nuclear Regulatory Commission regulators in a conference in Atlanta.
The company faces potential penalties for failing to detect a small crack in a reactor cooling vessel that resulted in a radioactive water leak.
The leak — first reported by The Greenville News last November — forced a shutdown of the oldest of the station’s three reactors on Lake Keowee, 30 miles west of Greenville.
In June, the NRC issued a notice to Duke of an “apparent violation” that had a safety significance of “greater than green” and ordered the conference to hear from Duke before making a final determination on the severity of the penalty.
Green — followed in severity by white, yellow and red — is the lowest level in the agency’s graduated, color-coded system to evaluate safety conditions at commercial nuclear plants.
A final determination will come in “relatively short order” and likely before the end of August, NRC regional administrator Victor McCree said.
However, Duke representatives said Thursday that the violation was one of “very low safety significance” and presented information from its engineers and private consultants to make a case for a lesser penalty.
The company’s presentation revealed that it had changed its inspection procedures in 2004 in such a way that it couldn’t detect the flaw in a weld in its “high-pressure injection system,” which is used to help cool the 40-year-old Unit 1 reactor in case of an emergency.
The crack wasn’t revealed until the leak was first detected on Nov. 8, according to the presentation, and the unit was shut down and restarted days later after the problem was repaired and deemed not to be a threat.
A report by an independent consultant determined that the crack was slow-forming and not a risk to fail suddenly. The crack occurred in a weld that struggled to withstand vibration in the injection system, according to the Duke presentation.
The company has repaired the problem and taken “robust corrective action” at the station and across its nuclear fleet, Oconee site vice president Scott Batson said.
The November crack is the second apparent violation the company has faced in the past year, when regulators threatened civil fines for the company's repeated missed deadlines in updating fire-protection standards at Oconee.
The NRC later classified the violation as "white."
The agency declined to impose civil fines but ordered Duke to adhere to a strict deadline to update protection standards by November 2016.
In 2010, the NRC approved Duke's plan to implement new fire-protection measures and gave the company two years to complete them.
In summer 2012, Duke asked for an extension until the end of 2014, then four months later asked for another extension to the end of 2015.
The NRC declined to grant the extension and ordered a November 2016 completion.
The company said it is on target to meet that deadline.