March 16 (Reuters) - A total of seven steam generator tubes have now failed pressure tests at the 1,080-megawatt San Onofre Unit 3 nuclear reactor, which has been shut since late January due to a small radioactive gas leak, Southern California Edison said.
On Thursday, the U.S. Nuclear Regulatory Commission (NRC) said it would send an augmented inspection team to Unit 3 after the SCE said pressure tests on three tubes failed.
SCE said the NRC team is expected to begin its work Monday.
There is no timeline for how long its inspection will take, according to an NRC spokeswoman.
Both reactors at the 2,150-megawatt (MW) San Onofre Nuclear Generating Station are shut due to premature wear found on parts of tubes in steam generators manufactured by Mitsubishi Heavy Industries and installed in Unit 2 in 2010 and Unit 3 in 2011.
SCE, a unit of California power company Edison International , has said it will pressure test and plug 129, or nearly 1 percent, of the 19,454 steam generator tubes in Unit 3 that showed higher-than-normal wear during an earlier inspection.
Workers have already plugged about 192 of the steam generator tubes in Unit 2 that showed accelerated wear.
SCE has not indicated when either unit will return to service.
SCE operates San Onofre and owns a 78 percent stake. Sempra Energy’s San Diego Gas & Electric unit has a 20 percent stake and the City of Riverside, California, has less than a 2 percent stake.