Southern California Edison Co. said it plans to lay off 730 employees at its San Onofre Nuclear Generating Station just south of San Clemente starting in the fourth quarter.

The cuts will leave 1,500 employees at the nuclear plant, which has been offline since January, after the discovery of substantial wear in steam generator tubes. A date for restarting the plant will depend on when regulators of the Nuclear Regulatory Commission “are satisfied that the units are safe to operate,” according to a statement by Rosemead-based Edison.

The San Onofre layoffs have been planned for “more than two years” as part of a general plan to reduce staffing and costs at the facility. Edison has said costs of running the San Onofre plant are “significantly higher than [at] other similar dual unit, non-fleet nuclear power plants.”

The plant’s steam generator had a leak in January, releasing radioactive steam. Regularly scheduled testing and inspection have been ongoing since the shutdown.

More than 3,000 tubes overall at two units of the plant showed some wear, and roughly 1,300 tubes have been “plugged” as of mid-July, mostly for preventative measures, according to Edison. The company said most of the wear was less than 20%, which compares with a 35% wall-thinning regulatory limit.