The nation's oldest operating commercial nuclear generating station draws enhanced scrutiny by federal regulators. A defect discovered in December 2016 at the Oyster Creek Nuclear Power Plant in Lacey Township led to a finalized determination of a low-to-moderate safety risk this week.

Oyster Creek Nuclear Generating Station (Exelon)

The Nuclear Regulatory Commission (NRC) in its color-coded system, finalized a "white" classification following a March 9 meeting which officials of parent company Exelon requested to elaborate on the operational discrepancy and corrective measures. On a rising scale, classifications are green, white, yellow, and red.

In a statement on behalf of the company, spokesperson Suzanne D'Ambrosio said:

"Exelon Generation and the NRC share a common goal of safe and excellent operations. The conference was a productive and open dialogue between Exelon Generation and NRC staff. While we appreciated the opportunity to discuss our concerns with this potential white finding, we are disappointed in the results. As always, we will continue to work alongside the NRC to ensure that Oyster Creek is operated with the highest level of safety and precision."

One of five electromagnetic relief valves (EMRV) was found to be defective during refueling outage inspections in December. The valves depressurize the reactor during an accident such as a pipe break. The valves permit coolant to enter the core, keeping the fuel covered and cooled during shutdown procedures.

According to NRC's Neil Sheehan, inspectors found that lock washers were missing from the EMRV's cut-out switch lever. While all five valves are not needed at one time, Oyster Creek's technical specifications require them to be fully functional during normal operations.

A valve defect lasting three days or more requires shutting down the reactor and reducing pressure to 110 pounds per square inch gauge within 24 hours. NRC inspectors determined that the valve defect lasted from October 11, 2014, to September 19, 2016, the span between refueling outages.

Sheehan said that the extended time frame does not reflect inadequate oversight or operational defects. "Plant technicians are only able to get a look at these valves once every 18 months or two years.The only way to test those valves would be during a plant shutdown. There are other valves that can do this, and other means of cooling the reactor."

"Nevertheless," Sheehan continued, "the technical specification on how long they can be out of service apparently still applies here, the thinking being that the problem should have been caught before they were placed back into service."

An earlier discrepancy regarding the design of the same valve system generated a "yellow" - substantial safety risk - finding in 2015. Exelon's operations, again, were found to be satisfactory.

"As a result of that," Sheehan explained, "a great deal of care and attention should have been paid to these valves, when they had technicians work on them during this outage."

The finding means enhanced NRC oversight for as many as four quarters from the date of discovery, or until December of this year. If criteria are not met by that time, it would continue into 2018. The next step is a team review. Exelon must notify regulators when it is prepared for the analysis.

"Once they do, we'll look at what they've done in response, any corrective actions, any root cause analysis," Sheehan said. "If they can pass that test, they would return to a more normal level of oversight."

If Exelon's remedial actions satisfy NRC technicians, the team inspection is a one-time event. If not, the inspections and enhanced oversight continue and the escalated safety-risk categorization remains open.

During the meeting, Sheehan said, Exelon contended that the finding should be revised to "green," citing extenuating circumstances, including the valve system redundancies.

"Ultimately, we did not agree," Sheehan said. "We felt that our risk evaluation would still lead us to a 'white' finding, and we notified the company of that. We've agreed to look at some other information that Exelon has put forward for future enforcement actions of this type, but it did not result in any change in this case."

Sheehan added that risk findings of this caliber are not common, citing anywhere from 12 to 19 in any of the last several years among the 99 nuclear generating stations in the United States.

The generating station, operating since 1969, is just over a year-and-a-half away from starting the decommissioning process toward shutdown. The NRC granted a 20-year license extension in 2009. The New Jersey Department of Environmental Protection (DEP) set a requirement of cooling towers, for a self-contained water circulation system with less daily reliance on Barnegat Bay. Disagreement over that contingency led to Governor Chris Christie's intervention, and a reduction of the renewal term to 10 years.

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