Inspectors have to wait for the 105 degree temperature inside a nuclear reactor to drop enough to make it safe for workers and equipment to get inside to inspect a tube leak that prompted operators to shut down the San Onofre nuclear plant on the California coast, officials say.
Southern California Edison took the San Onofre Unit 3 nuclear plant off-line Tuesday as a precaution, after detecting a leak in the tube that carries radioactive water in a steam generator. A tiny amount of radiation could have escaped into the atmosphere, but officials say no one was endangered.
The tube in the plant located 45 miles north of San Diego is relatively new, and it's not yet clear whether the leak could be related to unusual, premature wear found on hundreds of similar tubes in Unit 2, its twin plant that was shut down earlier this year for routine maintenance.
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. The inspection is continuing.
Edison spokeswoman Jennifer Manfre said Friday that the temperature inside Unit 3 would not drop to cool enough temperatures until the middle of next week.
With the extent of the problem unknown, it's too soon to estimate the cost of repairs or predict when Unit 3 will resume generating power, she added.
The maintenance and refueling at Unit 2 is projected to take two months.
The water leak Tuesday at the Unit 3 reactor was initially estimated at a rate of 85 gallons a day — an amount about half of what would require the plant to shut down. The company said the rate of the leak was "much less," but has not provided a figure.
It's not clear what caused that tube to fail, or whether the company was facing an isolated break in a single alloy tube or a manufacturing defect that might be at issue elsewhere in the massive plant system.
The two huge steam generators at Unit 2, each containing 9,700 tubes, were replaced in fall 2009, and a year later in Unit 3, as part of a $670 million overhaul.
The plant is owned by Southern California Edison, San Diego Gas & Electric and the City of Riverside. Southern California Edison serves nearly 14 million residents with electricity in Central and Southern California.