Revelations of serious flaws in the design of its steam generators have left the idled San Onofre nuclear plant in a kind of regulatory limbo.
Not only a possible date for restart of its reactors, but whether they will be restarted at all remains in doubt.
And as some activists and nuclear energy opponents call for a permanent shutdown of the plant, regulators, as well as plant operator Southern California Edison, continue to analyze a technological maze of troubles. They say they are not ready to propose possible remedies, nor are regulators yet prepared to say whether fines or penalties might be imposed.
"We've seen we can live without the power plant," said Gary Headrick of the local environmental group, San Clemente Green. "Why invest more in the old power plant? Why not move on to new stuff -- renewable energy?"
The plant's two reactors have been idle since January. Unit 2 had been shutdown for routine maintenance; then a leak in a steam-generator tube that released a small amount of radioactive gas prompted the shutdown of the Unit 3 reactor Jan. 31.
The release was too small to place anyone in danger, Edison said. But further investigation revealed extensive wear among the tens of thousands of metal tubes that circulate water heated by the reactors through the steam generators.
The heat turns what is normally a separate loop of water inside the generators into steam. The steam drives turbines that generate
The signs of wear -- especially heavy in Unit 3 -- raised concerns about the steam generators, massive, expensive and essentially new equipment manufactured by Mitsubishi Heavy Industries in Japan.
Monday evening, a special inspection team from the Nuclear Regulatory Commission delivered its long-awaited verdict on the cause of the steam-generator problems.
During the manufacturing process, they said, Mitsubishi used a computer simulation that "underpredicted" how fast water and steam would flow through the steam generators.
That led to a too-high flow rate, which, in turn, was part of the cause of excessive vibration in the steam generator tubes that led to at least some of the wear discovered later during inspection.
Another contributing factor: support structures that were not coupled tightly enough to the steam generator tubes, a problem especially apparent in Unit 3 that allowed some of the tubes to rub together to produce the most severe type of wear.
Both Edison and Mitsubishi, which has taken part in investigations of problems at the plant, declined to comment on which entity bears the most responsibility for flawed design and construction.
Edison had ordered design changes for the steam generators, but NRC officials said they had reviewed the proposed changes before the generators were built. Edison officials say they are looking further into design-change issues.
"The top priority of Mitsubishi is the safe and reliable operation of all the plants and components we design, engineer and support," Mitsubishi said in a statement issued after the meeting. "The steam generators in Units 2 and 3 at San Onofre were designed in line with our customer's specific needs and with customer input, using the best-available data and established industry standards. The NRC's findings as reported at the meeting were preliminary, and we are committed to continue supporting our customer, SCE, in working with the NRC to complete the investigation and to implement solutions to resolve the issue as quickly as possible." Edison is now preparing a plan for repairing and restarting the reactors, which must be submitted to NRC.
The NRC says it will make further inspections, and that possible ways to repair the problems are being developed.