Earthquake could trigger San Onofre shutdown, officials say

LATimes:  Officials at the San Onofre nuclear plant said it's possible that vibration sensors in the plant's backup diesel generators could be tripped by an earthquake, leading to shutdown of the generators.

Plant operator Southern California Edison reported the potential issue to the Nuclear Regulatory Commission and said it has disabled the sensors while it looks into the issue.

The diesel generators provide power to the plant and keep safety systems running in the event of a power outage. The generators have sensors that are set up to shut the generators down if they identify excessive vibration that could be caused by mechanical engine damage.

Edison was preparing to replace one of the sensors, originally installed in 1981, when an engineer questioned whether an earthquake could trip the sensor and cause shutdown of the generators, the company reported. An engineering review determined that design documentation did not address that question.

The sensors have been deactivated and will be tested to determine how they would respond in an earthquake.

Edison spokeswoman Jennifer Manfre said the plant has multiple back-up systems in place in the event of a power outage, including manual and steam-driven cooling pumps, and that the generators can be restarted from the control room.

An Edison spokesman said emergency diesel generators at other nuclear plants have similar vibration monitors without the automatic shutdown function.

An NRC spokesman could not be reached for comment.

The plant has been shut down since Jan. 31 because of unrelated equipment issues with steam generator tubes that were wearing out too quickly.