SAN ONOFRE (CNS) - One of the two electricity-producing turbines at the San Onofre Nuclear Generating Station will be idled for repairs this month.

Southern California Edison, which operates the coastal power plant near the Orange County line, began powering down the generator in mid-December.

Gil Alexander of SCE said the unit was powered down slowly, kind of like taking your foot off a car accelerator and "coasting."

The reactor "vessel head" also will be replaced. It covers the vessel containing fuel rods. The steam-driven turbine that turns an magnet inside a coil to produce electricity also will be renewed or replaced. It is original equipment, he said, about 30 years old.

Alexander called it a "a major technology upgrade." He declined to say how long the job would take, saying the utility planned to purchase power on the open market during the upgrade, and Edison did not want the purchase price to climb.

Once completed, electricity generation should be more efficient, he said.

While the San Onofre unit is off line, SCE will buy electricity on the open market to replace what would have been generated at the plant.

The other generating unit at San Onofre is scheduled to be refurbished in the fall, he said.

SCE owns the biggest stake in the plant. San Diego Gas & Electric and the city of Riverside own smaller portions of the facility.