The disclosure came two days after a tube leak at the plant's other unit prompted operators to shut down the reactor as a precaution. A tiny amount of radiation could have escaped, but officials say workers and the public were not endangered.

The problems at Unit 2 were discovered during inspections of a steam generator, after the plant was taken off-line for maintenance and refueling. That equipment was replaced recently in both units of the twin-reactor plant, which is located about 45 miles north of San Diego.

In this March 1, 2010 file photo, the San Onofre nuclear
power plant, seen here in north San Diego County, Calif.
- Lenny Ignelzi,File /AP Photo

Read more here: www.thestate.com/2012/02/01/2136493/small-radiation-amount-could-have.html#storylink=cpyIn two tubes, more than a third of the wall had been worn away, requiring them to be plugged and taken out of service. At least 20 percent of the tube wall was worn away in 69 other tubes, and in more than 800, the thinning was at least 10 percent.

"The amount of wear that we are seeing on these tubes is unusual for a new steam generator," Nuclear Regulatory Commission spokesman Victor Dricks said.

"If you have that kind of thinning anywhere along the length of the tube, you have a problem because it degrades the integrity of the tube, which can contribute to leaks," he added.