Sep 2 - McClatchy-Tribune Business News Formerly Knight Ridder/Tribune Business News - By Mariecar Mendoza The Tribune, San Luis Obispo, Calif.

The Diablo Canyon nuclear power plant was back to full power early Friday after a water leak prompted the shutdown of one of its two reactors the day before.

Operators worked all night Thursday after the leak was discovered around 10:15 a.m. in one of the reactors. A monitoring system within the reactor's containment dome notified operators that liquid was being lost from the unit, plant spokesman Jeff Lewis said, and they began to power down the unit at 2:10 p.m.

The plant returned to full power around 5:30 a.m. Friday.

The power plant provides about 10 percent of the state's electrical needs.

"We ran the unit down to 73 percent power overnight to isolate and find the leak and make repairs to the system," Lewis said. "Then it was a matter of bringing the unit up to full power."

Though the total amount of water lost is unknown, Lewis said one to two gallons per minute leaked out over a span of several hours Thursday.

The water could contain radioactive material. But the leak flowed into the containment dome, preventing any radioactivity from escaping to the environment, Lewis said.

The matter never approached emergency classification, Lewis said.

"It was an operational issue," he said. "It wasn't that dramatic."