June 15, 2004
By Michelle Roberts Rushlo
The Associated Press
PHOENIX — Federal nuclear regulators arrived Tuesday at the Palo Verde Nuclear Generating Station to begin an inspection following the unexpected shutdown of all three units at the plant.
The inspectors planned to look at the causes of the shutdown and the response.
Nuclear regulators were concerned that not all the diesel generators that are supposed to fire up and power the plant's systems following a failure did so, said Victor Dricks, a spokesman for the U.S. Nuclear Regulatory Commission.
The units are supposed to each have two diesel generators that will operate if power is lost. Only one of the generators at Unit 2 worked properly, Dricks said.
"We believe in redundant power capabilities so that's not a good thing," he said.
The plant shut down as a fail-safe on Monday morning after a disruption in the western power grid. The disruption caused roughly 65,000 Arizona customers to lose power for about an hour. Customers in New Mexico and Northern California were also apparently affected.
Power was restored using alternative supplies, said Jim McDonald, a spokesman for Arizona Public Service Co., the utility that operates the plant 50 miles west of Phoenix.
It was expected to take several more days for Palo Verde to be operational again, McDonald said. "We have to make sure everything is ready to start."
Monday's shutdown was the first time all three units at the plant, one of the nation's largest nuclear facilities, automatically shut down because of a disruption.
By Tuesday, APS officials had concluded that the outage started with the failure of an insulator on a large transmission line in northwest Phoenix. The failure should have tripped breakers that are designed to isolate the problem and protect the rest of the grid. But the breakers also failed, causing Palo Verde and a nearby gas-fired plant to shut down.
"What you see is the system protecting itself," said McDonald.
The disruption caused about 30,000 customers in Phoenix and 35,000 customers in Tucson to briefly lose power.
In Albuquerque, N.M., about 16,000 customers lost power for five to 12 minutes, and in San Jose, Calif., about 5,000 people lost power, according to the East Valley Tribune.
Palo Verde supplies power to about 4 million customers in Arizona, New Mexico, Texas and California.
http://regulus.azstarnet.com/hourlyupdate/story.php?id=16