CAMP PENDLETON, Calif. (AP) — Operators of the San Onofre nuclear power plant in Southern California worked to diagnose a problem with a reactor that was shut down because of a possible leak, but officials stressed there was no imminent danger.

Sensors at the plant detected a possible leak Tuesday in one of Unit 3's steam generator tubes, Southern California Edison spokesman Gil Alexander said. Even if a leak is confirmed, it would pose no danger to the public or plant workers, he said.

No release has been made into the atmosphere, he added.

"It is not a major leak. It has not risen to the level where it would cause the unit to automatically shut down," Alexander told U-T San Diego ( "But as a precaution we're shutting the unit down to go in and inspect."

Unit 2 of the nuclear plant is currently offline for maintenance and upgrade.

The utility said it has ample power to meet customer needs while Unit 3 is offline.

Once the problem is resolved, it will still take several days before the reactor comes back online because of an elaborate start-up procedure for nuclear plants, the U-T reported.

The plant is owned by Southern California Edison, San Diego Gas & Electric and the City of Riverside. Southern California Edison serves nearly 14 million residents with electricity in Central and Southern California.

The San Onofre oceanside plant is about 45 miles north of San Diego.