A design change that dodged federal inspection caused the that has sidelined San Onofre's nuclear power plant, an environmental group said Tuesday.
When Southern California Edison installed new, $671-million steam generators at the plant, it didn't tell regulators about a key design switch, allowing the equipment to sidestep NRC inspection, according to a report by nuclear expert Arnie Gundersen.
Gundersen, who works for Fairewinds Associates, a nuclear energy consulting firm, was hired by Friends of the Earth to analyze the plant shutdown. He based his conclusions on design documents and other reports by Southern California Edison on the company's decade-long effort to replace steam generators and upgrade the San Onofre plant, completed in 2010.
Edison spokeswoman Jennifer Manfre denied any deception and said safety was the top priority at the plant.
"At all times during the steam generator replacement process and the ongoing outages in Unit 2 and 3, Southern California Edison has provided open and transparent information to the Nuclear Regulatory Commission," she said via email. "SCE's top priority is the health and safety of the public and our workers. As is standard practice in the nuclear industry, SCE has been conducting tests and inspections as part of an in-depth analysis. SCE has been committed from the beginning to not returning Unit 2 or Unit 3 to service until we are satisfied it is safe to do so."
Edison won't be allowed to restart the plant until the NRC determines the root cause of the leak and makes sure Edison fixes the problem, she said.
Meanwhile, Edison continues to test the tubes, hundreds of which have shown unexpected wear in their walls.
One expert said. And the Independent System Operator, which oversees allocating electricity in California,
The January leak happened in tubes containing super-heated, high-pressure radioactive water that has touched the nuclear fuel. This water is supposed to stay in a closed loop, while fresh water is circulated outside the tubes to make steam that turns a turbine and generates electricity.
At least eight of the 129 tubes identified will have to be welded shut before the plant restarts; they failed pressure tests.
Gundersen's report attributed the wear to several factors, including a change in the metal alloy used in previous generators, which had lasted more than 40 years, plus a change in the apparatus that separates the tubes from one another.
Fairewinds said these untested design changes allowed the tubes to vibrate as the super-heated water rushed through, causing the walls of the tubes to wear down prematurely.
An NRC letter issued Tuesday afternoon confirmed that vibration and friction between the tubes and support structures caused the wear, but technicians have not yet determined why the vibration happened. A copy of the NRC press release and letter is attached to this article.
Among other things, it .
According to Fairewinds, Edison also falsely told the Nuclear Regulatory Commission there were no significant design changes in the new steam generators, which it described as a "like for like" replacement. This allowed Edison to sidestep inspections, the report states.
A PDF copy of the full report is attached to this article, as is a video featuring Gundersen when .