On Jan. 31, alarms alerted the control room at the San Onofre Nuclear Generating Station that a radiation leak was occurring in one of the nearly 39,000 tubes that carry radioactive water in the steam generators.
That failure led to an unparalleled shutdown of one of California’s two nuclear power plants and triggered more than three months of detective work by Southern California Edison officials and federal nuclear regulators that has yet to determine the problem’s root cause or when San Onofre will reopen.
Since then, the outlook for the plant has gotten worse.
Now, about 1,300 tubes — more than 3% of all the plant’s tubes — have been taken out of service because of unexpected wear. And Edison has said that even when San Onofre reopens, it probably won’t run at full capacity.
Figuring out the exact cause of the wear is crucial.
Edison finished installation of the $671-million steam generators less than two years ago, promising customers they would create major energy savings. Now, officials estimate it will cost as much as $65 million to fix the problems and tens of millions more to replace the lost power.
Officials said the investigation has yielded a better understanding about why the tubes are wearing down. When the plant is running at full power, the rate of steam flow is causing the tubes to vibrate, much like a guitar string being plucked. Some tubes vibrated enough that they rubbed against each other, causing the tube walls to wear down much faster than expected.
This is a potential danger because tube ruptures could release radiation and in extreme cases compromise the reactors’ cooling system.
But officials have not yet pinpointed what missteps led to the problem.