Unusual wear has been found on hundreds of tubes that carry radioactive water at Southern California's San Onofre Unit 2 nuclear plant, raising questions about the integrity of equipment the company installed in a multimillion-dollar makeover in 2009. 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 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. 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. Retired NRC engineer and researcher Joram Hopenfeld said the company will have to determine why the tubing is degrading so quickly before they do anything else." "I've never heard of anything like that over so short a period of time," Hopenfeld said. "The safety implications could be very, very severe," Hopenfeld added.