State’s Oldest Nuclear Generator to Close Nov. 30

California’s oldest commercial nuclear generator--San Onofre Unit 1, alongside Interstate 5 between Oceanside and San Clemente--will shut down for good Nov. 30, ending 25 years of service to Southern California, the U.S. Nuclear Regulatory Commission announced here Friday.

The end of the workhorse’s career was previously conceded by Southern California Edison, which owns 80% of the plant, and San Diego Gas & Electric Co., which owns 20%.

The unit’s retirement was approved in August by the state Public Utilities Commission, after its ratepayers advocacy division argued that its operation was no longer a good deal for ratepayers because it was slipping as a cost-effective generator of electricity.

Besides, the unit faced $125 million or more in improvements by the end of the year.

“In many respects, it’s sad to see a plant shut down,” said Bobby Faulkenberry, deputy regional administrator for the NRC’s Region 5, which includes the Pacific Rim states and Arizona. “As long as they’re producing power, it’s such a loss.”

But he acknowledged that the unit has been declining in efficiency. Over its lifetime, it produced about 51% of its maximum design power. Today, industry standards are closer to 75%.

The landmark, cylindrical-shaped nuclear power plant is the oldest of three at the San Onofre Nuclear Generating Station.

The adjoining twin, dome-shaped plants that were constructed in 1983 and 1984 are expected to remain in operation into the 2020s. Each produces more than twice the amount of electricity as Unit 1, which was designed to produce electricity until 2004.

The shutdown of Unit 1 will leave 108 commercial nuclear generators operating in the United States--with six under construction.