By Nichola Groom
LAGUNA HILLS, California (Reuters) - Southern California Edison officials faced tough questions from the Nuclear Regulatory Commission on Friday at a packed public meeting during which the utility laid out its case to restart the damaged San Onofre nuclear power plant.
San Onofre, which sits on the Southern California coast halfway between Los Angeles and San Diego, has been closed since January after workers discovered a small radioactive steam leak at one of its two reactors that indicated accelerated degradation of tubes in the plant's new steam generators.
The cost of the prolonged outage to Edison has topped $317 million in repairs, purchase of replacement power and other expenditures.
After months of inspections, the plant's majority owner last month submitted its plan to restart its Unit 2 reactor at 70 percent power for five months. The leak occurred in the Unit 3 reactor, which is shut down indefinitely.
Separately, the utility said this week it found indications of potential tampering with an emergency diesel generator. It has beefed up security at the plant and is continuing to probe the issue.
Edison's efforts to restart the reactor faced vocal opposition from environmental groups and local residents, who said the plan was an experiment that could endanger 8 million people living nearby.
Several activists gathered at the meeting before it started, chanting "No restart, shut it down". Local Buddhist monks began a seven-day fast in support of a permanent closing of the plant. Some of them also attended Friday's meeting.
The meeting, which took place at a hotel ballroom in Laguna Hills, near the San Onofre plant, was the first opportunity for the utility to discuss its plan to restart Unit 2 with NRC staff.
Most of the three-and-a-half hour meeting was taken up by Southern California Edison's presentation of its investigation into the leak and subsequent repairs. A top San Onofre engineer, Thomas Palmisano, argued that operating the plant at reduced power would prevent the excessive vibration that caused the steam generator tubes to bump up against one another, wearing them down.
The company has also plugged hundreds of tubes that showed signs of wear, and hundreds more out of caution, he said.
Palmisano argued that tube wear was far more extensive at the Unit 3 steam generator, which operated for just 11 months. Unit 2, which the utility proposed to restart, had less damage despite its steam generator being operated for twice as long as that of Unit 3, he said.
Edison has said that a complete replacement of the steam generators, which were manufactured by Japan's Mitsubishi Heavy Industries, would take years.
NRC officials probed Palmisano and other Southern California Edison representatives on various technical matters throughout the presentation. Art Howell, the NRC's team manager on San Onofre, said at the conclusion of the meeting that the agency would review Southern California Edison's analyses and modeling to determine whether the power plant could be safely operated.
Members of the public were also given a chance to speak. Many referenced last year's meltdown at the Fukushima nuclear plant in Japan in calling for San Onofre to be decommissioned.
San Onofre is 78 percent-owned by Southern California Edison, a unit of Edison International. The remainder is held by San Diego Gas & Electric, which is a unit of Sempra Energy, and the city of Riverside.
It is the biggest power plant in Southern California, and its closure forced the state grid operator to take steps to bolster power supplies during the summer when customers use air conditioning to escape the heat.
(Reporting By Nichola Groom; Edited By Ronald Grover and Pravin Char)