Unit 2 at California's Diablo Canyon nuclear plant powered down Thursday night when inspections revealed two faulty screws in emergency diesel generators.
According to a report filed with the Nuclear Regulatory Commission, plant personnel found a failed capscrew on an engine cylinder in one of the diesels during scheduled maintenance. In response, workers inspected the screws in all generators at both units at the plant, and another degraded capscrew was found on a cylinder in a second diesel at unit 2. Although they performed without problems during testing, two of the generators were declared inoperable concurrently, which required shutting down the reactor under NRC regulations. Operators began powering down unit 2 at 8:31 p.m. According to the report, they planned to return one of the affected diesels to service and power back up by the time the reactor reached mode 5 (cold shutdown). Data provided to the NRC indicated unit 2 was at 0 percent power on Friday morning.
The reactor had recently returned to service following a maintenance outage that began July 19, according to Pacific Gas and Electric. Both pressurized water reactors at the plant near San Luis Obispo, Calif., generate about 1,100 megawatts and entered service in the mid-1980s.