Nuke Inspectors Focus on 'Unusual' Wear on Tubes The integrity of some equipment installed in 2009 at Southern California's San Onofre Unit 2 nuclear plant is drawing concern after unusual wear was found on hundreds of tubes that carry radioactive water. Thursday's disclosure came two days after a tube leak at the plant's other unit prompted operators to shut down the reactor as a precaution. The problems at Unit 2 were discovered during inspections of a steam generator, after the plant 45 miles north of San Diego was taken off-line for maintenance and refueling. The two huge steam generators at Unit 2, each containing 9,700 tubes, were replaced in fall 2009, and a year later in its twin plant, Unit 3, as part of a $670 million overhaul. According to the Nuclear Regulatory Commission, more than a third of the wall had been worn away in two tubes at Unit 2, which will require them to be plugged and taken out of service. "The amount of wear that we are seeing on these tubes is unusual for a new steam generator," NRC 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. Plant operator Southern California Edison did not dispute the figures released by the NRC, but cautioned that testing on the tubes is preliminary. Spokesman Gil Alexander called the tests "an initial snapshot" and said more sophisticated tests will take place. He did not know if the testing would delay the reactor's planned two-month shutdown. "It's not unprecedented in the industry for there to be accelerated wear in small sections of tubes in early years of usage," he said. Alexander said Mitsubishi officials are assisting with the tube analysis at the plant. Hot, pressurized water flowing through the tubes, each about 0.75 inch in diameter, is used to heat water outside the tubes, which is not radioactive.