New details about problems at San Onofre nuclear power plant

Data released by the U.S. Nuclear Regulatory Commission and a leaked analysis by Southern California Edison provide some new insights into the situation at the San Onofre nuclear plant.

The plant has been shuttered since Jan. 31, when a small leak in one of the plant's thousands of steam generator tubes drew attention to the fact that the tubes in the newly replaced steam generators were deteriorating much more quickly than expected.

In particular, some of the tubes were showing an unusual type of wear caused by tubes rubbing against adjacent tubes. Since then, the NRC, plant operator Edison, and steam generator manufacturer Mitsubishi Heavy Industries have been probing the cause of the wear.

The data released by the NRC showed that a total of 3401 tubes in the Unit 2 and Unit 3 reactors-- 8.7% of the 38,908 total tubes in the plant's four steam generators -- had shown some signs of wear.

The NRC-released data also gives more extensive information than was previously available about the location of the tubes and whether the wear was caused by rubbing against adjacent tubes, support structures, or in the case of two tubes, by a foreign object that Edison identified as a piece of welding material.

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