NRC inspectors have kept two reactors at California’s San Onofre complex closed since January 2012 amid an inquiry into whether the manufacturer, Mitsubishi Heavy Industries, and perhaps the utility, Edison International, covered up the danger of cracks in the tubes of the reactors’ steam generators.
The utility has denied any wrongdoing, pointing the finger at Mitsubishi.
Documents released Friday said that Mitsubishi and Southern California Edison, a subsidiary of Edison International, jointly investigated the problem of vibrations that could accelerate wear and tear in the steam generators before they were installed. And the documents, released publicly by the NRC after Mitsubishi redacted them to protect trade secrets, state that the companies did not change the design because it would have triggered a lengthy license amendment procedure with the NRC.
“Each of the considered changes had unacceptable consequences and the AVB Design Team agreed not to implement them,” the document said.
San Onofre’s Unit 2 was taken out of service Jan. 9, 2012, for a planned outage. Unit 3 was taken offline Jan. 31, 2012, after station operators detected a leak in a steam generator tube. The tubes had lasted about a year. The closures are costing Edison International hundreds of millions of dollars. Replacing the steam generating system could also cost hundreds of millions of dollars.
The company has asked the NRC to allow Unit 2 to operate at 70 percent of capacity to reduce vibrations, but the NRC has not granted permission.
“Understanding the root cause . . . is a problem,” NRC Chairman Allison M. Macfarlane said in an interview. “We are not going to let the plant restart unless we are sure it can operate safely.”
The NRC has also been keeping an eye on a pair of new reactors the Southern Co. has been building at its Vogtle complex in Georgia. Financing costs were lowered sharply by a promise of a federal loan guarantee by the Obama administration and by a Georgia state law that allows Southern’s subsidiary, Georgia Power, to pass much of the cost along to ratepayers while the plant is under construction. Most states require a power plant to go online before customers have to pay for it.
Within months, however, Southern said that as much as $900 million could be added to its subsidiary’s share of the $14 billion cost. An industry consultant, who requested anonymity to preserve his business relationships, said that the contractor put too much space between steel rebar in the foundations at the heart of the new reactors. To resolve the problem, Southern said it created a 1,000-cubic-yard “mock-up” of the site where concrete would be poured.