The troubled San Onofre nuclear power plant will stay shut down until the cause of is fully diagnosed and fixed, the Nuclear Regulatory Commission ordered Tuesday in a letter to Southern California Edison.
The letter formalizes .
Unit 3 of the plant has been offline since Jan. 31, when operators detected a leak in one of its steam generator tubes. The plant's two steam generators are now undergoing extensive testing and inspections to determine their condition and the cause of the leak.
Unit 2 was taken down for planned maintenance Jan. 9.
Southern California Edison, which operates the plant and is losing upwards of $1 million a day during the shutdown, has said previously it would not resume operation until tests confirm everything is safe.
The January leak happened in tubes containing super-heated, high-pressure radioactive water.
The NRC letter said vibration and friction between the tubes and support structures caused the wear, but technicians have not yet determined why the vibration happened.
An NRC inspection team is overseeing the repair and inspection work. Edison officials said Tuesday they were committed to working with the NRC to meet all requirements for restarting the plant.
"We welcome the NRC's letter, which is a formal step in the process of restarting Units 2 and 3,'' Edison President Ron Litzinger said. "Our No. 1 priority is, and always has been, the health and safety of the public and our employees. The utility will only bring the units on line when we and the NRC are satisfied that it is safe to do so.''
Edison has committed in writing to the NRC that it "will proceed deliberately and conservatively to implement these steps, always bearing in mind that safety is our first priority,'' according to the utility.
Experts have warned the lengthy this summer.
-- City News Service contributed to this story.