Investigators are taking a closer look at tubes that carry radioactive water in reactor #2. Officials said the tubes were being inspected and the unit was taken offline as part of regular maintenance.
"A planned inspection has found in a couple of small points on tubes, these 9700 tubes inside the steam generators, the wear is accelerated, said So Cal Edison spokesman Gil Alexander.
The maker of the tubes, Mitsubishi Heavy Industries, is at San Onofre to determine what's causing the wear and whether any of the tubes will have to be taken out of service.
Mitsubishi released a statement: "The investigation of the incident is being conducted by our customer (Southern California Edison). However, as the manufacturer of the steam generators, we will do whatever we can to support our customer in resolving the issue."
This comes as workers go in to locate a leaky tube in a third reactor- that led to a shutdown of unit 3 as a precaution on Tuesday. Officials said it could take days to do the testing.
"We'll identify how significant or how insignificant the leak is, what will it take to repair it, and we'll do repairs," said Alexander.
Officials say the leak triggered sensors, but the amount of radiation detected in the dome was extremely small.
"There's no risk to public safety or to worker safety," said Alexander.
"I'd be very concerned because it's actually not even a mile off here so it would affect the whole city," said San Clemente resident Ricardo Neri.
Others who live in nearby San Clemente are confident the nuclear power plant is being carefully monitored.
"I don't' think there's much of a scare as far as I'm concerned," said San Clemente resident Mike Vogelgesang.
Officials say SoCal Edison customers will not be affected while the work is under way.