Switch Problem at Coastal Nuclear Plant

Investigators are looking into improper switch settings at California's Diablo Canyon nuclear power plant that could have interfered with the cooling of one of its two reactors during an emergency.

Two switches that are supposed to allow operators to remotely open cooling water valves were improperly set, said Emily Christensen Archer, a spokeswoman for the Pacific Gas & Electric plant on the Central Coast.

The valves are part of a sump system that would collect water draining from a breach in the reactor so it could be recirculated.

Christensen Archer said the improper settings were discovered last week during a maintenance shutdown of the reactor, and the switches were reset and tested. Switches on Diablo Canyon's other reactor were also checked.

If the switches don't work, operators would have to be dispatched to manually open the valves. How much radiation the operators might be exposed to in that event is part of the probe.

Such a loss of coolant would be a serious situation because the nuclear core continues to produce heat, even after a shutdown, and can melt if it overheats.

The Nuclear Regulatory Commission will determine how much risk was posed by the improper settings.

The level of risk will determine how the NRC will respond to the discovery, said Michael Peck, the agency's senior resident inspector.

Diablo Canyon is located on the coastline midway between Los Angeles and San Francisco.

It has been operating commercially since 1985 and supplies enough electricity to power 3 million homes in Northern and Central California.


(Copyright 2009 by The Associated Press. All Rights Reserved.)