One month after lawmakers said the Nuclear Regulatory Commission (NRC) was sitting on a document that indicated operators of the San Onofre nuclear plant knew in advance about potential problems at the troubled facility, a redacted version was released to the public last week.

Upon review, critics detected the acrid smell of a smoking gun while plant designer Mitsubishi and operator Southern California Edison seemed satisfied they had complied with all regulatory requirements.

Edison said problems at the plant, closed in January 2012 after radioactive steam leaked from damaged tubes, were unknowable and unpredictable when generators were upgraded in 2010 and 2011.

But Senator Barbara Boxer (D-California) and Representative Ed Markey (D-Massachusetts) announced last month that an unreleased report to the NRC written by Mitsubishi and Edison would show that the companies avoided making design modifications they knew were necessary in order to avoid a license renewal process that  would have been problematic for them.   

The companies had skirted the license review when they installed new steam generators and thousands of tubes by arguing that it was a straightforward upgrade of existing equipment with no known complications.   

The highly technical “Root Cause Analysis Report” detailed already-admitted miscalculations made by Mitsubishi that led to heavier vibrations than expected, which caused the critical tubes to degrade almost immediately. The report also reviewed decisions that were made early on to avoid several design adjustments because “these changes had unacceptable consequences.”  

“It was concluded that the final design was optimal based on the overall RSG [replacement steam generator] design requirements and constraints,” the report said. “These included physical and other constraints on the RSG design in order to assure compliance with the provisions of 10 C.F.R. §50.59.”

The San Onofre closure has already cost $470 million, a growing tab that will be fought over by ratepayers, taxpayers and utility shareholders. Foes of nuclear power want the plant, located between Los Angeles and San Diego, shut down permanently. The NRC said it wants Edison to certify that it can operate safely at full power to test the effectiveness of repairs, but the utility wants to initially run at 70% and see what shakes loose.

A decision by the NRC is not expected for at least a couple of months.

–Ken Broder

To Learn More:

Feds Release Confidential Report on Cal Nuke Plant (by Michael R. Blood, Associated Press)

Officials Rejected Some Changes to Crippled San Onofre Generators (by Abby Sewell, Los Angeles Times)

Lawmakers Say Leaked San Onofre Document Implicates Edison and Mitsubishi (by Ken Broder, AllGov California)

Root Cause Analysis Report (Mitsubishi Industries) (pdf)