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NRC cites Diablo Canyon over broken switch that left cooling system inoperable

One of the cooling systems for the Unit 2 reactor at Diablo Canyon nuclear power plant was inoperable for a year and a half due to a broken switch.
One of the cooling systems for the Unit 2 reactor at Diablo Canyon nuclear power plant was inoperable for a year and a half due to a broken switch. jjohnston@thetribunenews.com

A broken switch at Diablo Canyon nuclear power plant that left a reactor cooling system temporarily inoperable has prompted the Nuclear Regulatory Commission to cite the plant for a low-risk safety finding.

The NRC issued a “white finding” Thursday, claiming the plant failed to adequately maintain an aspect of its emergency core cooling system, resulting in a low-to-moderate safety risk at the plant. The NRC evaluates regulatory performance at nuclear plants by color-coding inspection findings as green, white, yellow or red, in order of increasing safety significance.

PG&E has since corrected the situation, spokesman Blair Jones said, and it plans to appeal the finding.

“We are absolutely committed to the highest safety standards,” he said. “This relentless focus on safety led us to discover this issue and make immediate repairs. We believe it is not reflective of current plant performance.”

The two units at Diablo Canyon are each equipped with two emergency core cooling systems, which use water to cool the reactors if an accident or malfunction occurs. During a scheduled test in May, workers discovered that one of the cooling systems for Unit 2 was inoperable for up to a year and a half; that particular system had last been checked in October 2014.

The problem was determined to be a limit switch that was installed in a way that had it operating beyond its optimal capacity.

Jones said that because there are two cooling systems per reactor, there would have been little risk to the public in the event an accident had occurred while the switch was not working.

“We also believe that in the unlikely event this system were needed, our professional operators, who continually train and drill to meet any potential emergency, would have successfully responded to ensure the equipment met its function,” he said.

If the utility’s appeal is unsuccessful, it means there will be an additional NRC inspection of the plant in the coming year. (The plant already undergoes an annual inspection, per federal law.)

Kaytlyn Leslie: 805-781-7928, @kaytyleslie

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