The Nuclear Regulatory Commission has identified a “white” inspection finding, meaning a potentially low to moderate safety issue, at the Diablo Canyon Power Plant in California.
In a letter Monday to operator Pacific Gas & Electric, the agency detailed the Sept. 12 finding, which is associated with an apparent failure to develop adequate instructions for the installation of external limit switches on the plant’s motor-operated valves. Located about 12 miles southwest of San Luis Obispo, Diablo Canyon is the last operating nuclear plant in California and is scheduled to close by 2025.
According to NRC, PG&E failed to provide maintenance instructions for ensuring that the limit switches were operated within the vendor established overtravel settings. Consequently, a limit switch for Diablo Canyon Unit 2 operated beyond the overtravel setting, resulting in a sheared internal roll pin, which caused the limit switch to fail. That, in turn, resulted in the failure of a valve that controls residual heat removal suction from the containment recirculation sump. PG&E has since restored the valve and replaced the affected components, including the limit switch, according to the NRC.
The NRC is considering taking regulatory action, which could involve escalated enforcement at the plant, and will make a determination within three months. Escalated enforcement could entail altering the plant’s safety rating and increased regulatory oversight.
“We are absolutely committed to the highest safety standards, and constantly inspect the plant to ensure we meet our primary mission to protect public health and safety first,” PG&E spokeswoman Blair Jones said by email Wednesday. “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.”
