LOS ANGELES (AP) -- Can a nuclear reactor operating at 70 percent power actually be running at full power?
Southern California Edison, operator of the troubled San Onofre nuclear power plant in California, contends the answer is yes.
The twin-domed plant between Los Angeles and San Diego has been shut down for more than a year after a tiny radiation leak led to the discovery of unusual damage to hundreds of tubes that carry radioactive water.
Edison has asked the Nuclear Regulatory Commission for permission to restart one of the reactors, Unit 2, and run it at 70 percent power for five months. Edison engineers predict the lower power level will halt vibration and friction that has damaged tubing in the plant's steam generators.
However, NRC officials said late last year that operating rules require San Onofre to ensure that generator tubes retain structural integrity during "the full range of normal operating conditions," including at full power.
NRC said it wanted the company to demonstrate that Unit 2 could meet that threshold, or explain how generator tubes would interact with each other if the plant is operating at maximum capacity.
An Edison response released Tuesday argued that under its restart plan, full power "is 70 percent for the proposed operating period" and meets the federal requirement.
As Edison pushes for a restart, company filings released Tuesday show how uncertainty about the plant's future is putting pressure on Edison International, SCE's parent company.
"The scope of necessary repairs for the steam generators ... or the length of the units' outages could prove more extensive than is currently estimated," the company wrote.
"The cost of such repairs or the substitute market power that must be purchased during the outage could exceed estimates and insurance coverage, or may not be recoverable through regulatory processes or otherwise," it added.
The problems at San Onofre center on steam generators that were installed during a $670 million overhaul in 2009 and 2010. After the plant was shut down, tests found some generator tubes were so badly eroded that they could fail and possibly release radiation, a stunning finding inside the nearly new equipment.
The ability of San Onofre to run safely at lower power — and whether that limit would require an amendment to its operating license — came up in December at a hearing of the Atomic Safety and Licensing Board, an arm of the NRC.
Administrative Judge Gary Arnold asked Edison attorney Steve Frantz if he was confident that the plant could operate at 99 percent power with its ailing generators.
"I do not say that," Franz responded. He argued that running at 70 percent power would fall within San Onofre's license and operating rules.
The generators, which resemble massive steel fire hydrants, control heat in the reactors and operate something like a car radiator. At San Onofre, each one stands 65 feet high, weighs 1.3 million pounds and has with 9,727 U-shaped tubes inside, each three-quarters of an inch in diameter. Hundreds of the tubes have been taken out of service because of damage or as a preventative step.
Edison is planning further testing. Spokeswoman Jennifer Manfre did not immediately respond to emails and a phone call seeking further comment.