San Onofre

Drivers winding down Interstate 5 early this morning may have noticed clouds of steam being emitted from Unit One of the San Onofre nuclear power plant.

The steam, released over a period of several hours beginning at 1 a.m., was part of a “load reduction” to repair damaged safety equipment, according to David Barron, spokesman for Southern California Edison that operates the plant.

Repairs were completed in less than four hours.

The partial shutdown was classed as an “unusual event”--the lowest level of emergency classifications--and the sheriff’s departments in Orange and San Diego counties were notified, Barron said.

However, both Barron and an official from the Nuclear Regulatory Commission said that there was no danger posed by the load reduction. No radioactivity was released, and service was unaffected by the procedure, which effected only one of the plant’s three units, Barron said.

The equipment that failed was used to monitor the temperature and pressure of steam between the unit’s heat exchanger and the electrical turbines. To fix the equipment, power capacity was reduced to a quarter of normal, Barron said.

Unit 1 was back up to 90% operating capacity at 11:40 a.m., according to Southern California Edison spokeswoman Debbie Van Ness. But another, unrelated event at 1:30 p.m. caused a second power cutback Wednesday afternoon.

Van Ness said condenser tube leaks in the steam side of the plant, not the radioactive side of the plant, prompted the second load reduction.

“It is not an unusual event, it does not have a classification. It could happen at any of our steam plants, not just at a nuclear facility,” she said.

She said it was not known Wednesday night when the unit would be operating at full load again. It was reduced to a minimum load of about 10%.

Unit 1 had returned to operation Saturday after being down eight months for repairs and refueling.