San Onofre

A 450-megawatt reactor at the San Onofre nuclear power plant has been shut down for an indefinite period because of a faulty water pump, a Southern California Edison spokesman said Friday.

The Unit 1 reactor was shut down about two hours after officials determined at 10 p.m. Thursday that the pump was malfunctioning, said David Barron, a spokesman for the utility company.

Barron said there was no release of radiation because of the malfunction and the plant’s operators were able to shut down the reactor without incident.

After the shutdown, authorities declared that an “unusual event” had taken place, the lowest alert level in the nuclear industry. An unusual-event warning must be issued each time a reactor is shut down due to equipment malfunction, Barron said.

Workers will examine the troublesome pump over the weekend and should know by Monday how long repairs will take, he said. Plant operators indicated it appears the pump was operating incorrectly because of a faulty shaft, Barron said. No water leaked during the pump problem, he said.

The pump is on the unit’s feed-water system, which circulates water vapors into the steam generators that produce electricity. The feed water is heated by a separate system, which circulates coolant through the reactor’s nuclear core. Although the reactor coolant is radioactive, fluid in the feed-water system is not.

Unit 1 is expected to be out of service for several days, but the Unit 2 reactor was still operating at 100% power, Barron said.