The San Onofre Nuclear Generating Station remains offline nearly a week after a small water leak forced the shutdown of Unit 3.
The other reactor, Unit 2, was already offline for scheduled maintenance refueling and technology upgrades.
Southern California Edison spokesman Gil Alexander said there is no estimate when the repairs will begin on Unit 3, which was taken offline January 31 as a precaution.
He said equipment will be used to check nearly 10,000 tubes inside the generator at Unit 3 to find the source of the water leak.
"To make sure we know for sure, absolutely what happened inside these 9,727 tubes of this steam generator that would have caused this leak," said Alexander. "We want to be sure we have a clear picture of what repairs are necessary and then we'll proceed on with those repairs."
At the same time, Alexander said the tube inspection process continues at Unit 2, or the northern dome, to verify preliminary findings made public last week by the Nuclear Regulatory Commission.
Victor Dricks with the NRC said last week there is damage to other tubes at the plant, which he called "unusual."
Alexander said initial testing of those steam generator tubes under the northern dome at Unit 2 found accelerated wear.
He said there are no leaks but testing continues to find out what is causing the problem and if, or whether, it will affect the timeline for restarting the unit.
Alexander said the nuclear plant is Southern California's largest single source of power. He said nuclear generation from the plant provides 19 percent of the power needs for Edison customers.
While the plant is completely offline, Alexander said the company is using reserve power contracts with other energy generators to meet electricity demand.
He said there is ample reserve power available.
"We do not anticipate any immediate impact on customers' bills," said Alexander.