San Onofre Nuclear Power Plant

Southern California — this just in
March 8, 2013 | 3:52 pm

A report on the root causes of problems at the San Onofre nuclear plant shows that officials considered making design changes to the plant’s new steam generators before they were installed but rejected some fixes in part because they would require further regulatory approvals.

Some of the generators began malfunctioning a year after they were installed, and the nuclear power plant has been shuttered for 14 months. The closure has already cost San Onofre’s operators, Southern California Edison and San Diego Gas & Electric, $470 million.

Ratepayers across the region are already shouldering some of those costs and could be on the hook for hefty future repair bills.

The report was released Friday by the Nuclear Regulatory Commission. It was written by Mitsubishi Heavy Industries, which built the generators.

The report provides the most detailed picture to date of how the flawed system was designed.

But both companies insisted Friday said that they were not aware of the problem that crippled San Onofre. Mitsubishi argued that the changes officials contemplated before installation would not have made a major difference.

Mitsubishi, however, acknowledged that it had made an incorrect input into a computer code that resulted in underestimating the velocity of steam flow in the plant’s replacement steam generators. Again, the company said that that error did not cause the failure.

The report comes amid a furious debate over who is to blame for defects that led to the shutdown.

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