Mitsubishi made mistakes in the manufacturing and design process when it built massive new steam generators for San Onofre, the Nuclear Regulatory Commission said Monday night.
The flaws caused in January, a leak . These components are crucial in carrying radioactive water and transferring its heat to pure water that makes steam to turn a turbine that produces electricity.
Elmo Collins, the regional administrator for NRC Region IV, said the problem was difficult and represented a significant danger to the public if the plant were allowed to restart without addressing it.
"We're not satisfied yet," he told a packed public meeting. "There's still a lot of work to do on this difficult technical issue."
The meeting at the San Juan Capistrano Community Center drew an overflowing crowd of almost 400 people; organizers had to send some into the lobby to listen to audio of the meeting because the crowd numbers were violating fire codes for the building.
NRC Branch Chief Greg Werner, who spoke about the leak inspections, said Mitsubishi Heavy Industries underestimated the pressure of the radioactive steam that runs through the tubes. The design calculations predicted pressures 300 percent to 400 percent lower than how the steam actually moves inside the tubes.
Further, manufacturers changed some of their building processes, which caused loosening of support bars that hold in place the "U" bend portion of the thousands of tubes inside the steam generator, Werner said.
The loose supports, coupled with the unplanned high pressure, created "fluid elastic instability" in the tubes, which caused them to rub together and against supports, leading to the wear and ultimate leak.
Collins said that some other problems appeared in the transport and handling of the steam generators as they came to the plant—humidity wasn't controlled and some jostling happened to the generators during transport.
Also, in Unit 3 where the worst problems in the plant were found, Japanese technicians had to repair a cracked divider plate before shipment out of the country to be installed at San Onofre. The divider plate seperates the intake of the scalding radioactive water from the tube output of cooled water that circulates back into the system. The plate was replaced and re-tested.
Collins said these irregularities weren't likely contributors to the leak and tube wear, however.
Also, though an NRC and Southern California Edison spokespeople previously have denied any wrongdoing by the plant, but NRC officials at the meeting said they were still investigating whether Edison should have filed some papers it didn't. But most of the design changes differing from the design of the old steam generators were reviewed by the NRC, officials said.
Collins said the NRC may still assess fines or enforcement against the plant -- the agency has the authority to go after contractors like Mitsubishi, but they typically hold the utility responsible for any problems, considering Southern California Edison's name is on the license and the company has the ultimate responsibility for safety.
Also at the meeting were about 300 to 400 people, many of whom protested against nuclear power, people largely organized by local groups San Clemente Green and Residents Organized for a Safe environment; and national group Friends of the Earth.
Those groups held a press conference outside the San Juan venue before the meeting, bringing .
See the video attached to this article for further details on the problems at San Onofre and quotes from anti-nuclear advocates.
EDITOR'S NOTE: As this article draft was finished at 8:30 p.m. Monday, the San Juan Capistrano meeting was still ongoing. Check back later and Tuesday for more details, video and photos.
More photos added, approximately 9:30 p.m. Monday.
Video, text update, added approximately 1 a.m. Monday.