"LOS ANGELES -- A $670 million overhaul at California's San Onofre nuclear plant was expressly intended to avoid the types of ailments that have sidelined its twin reactors. An overriding goal for a team of engineers who worked on steam generators installed at the plant in 2009 and 2010 was minimizing wear and tear on the nearly 40,000 tubes that carry radioactive water inside the massive machines. Customized design and manufacturing promised years of reliable service for a plant that can power 1.4 million homes in Southern California. But the opposite happened."
"San Onofre's twin reactors have been idle for more than three months in the midst of a federal probe into what went wrong with hundreds of tubes that snake through the generators. Some were so eroded after a brief run in operation they can no longer function safely.
Less than a month before a tube break in January prompted Southern California Edison to take the plant offline, engineers writing in a trade magazine touted a series of modifications to the generators that they believed would improve the plant's dependability and longevity."
Michael R. Blood reports for the Associated Press May 13, 2012.