Washington (Platts)--11Feb2013/422 pm EST/2122 GMT

The US Nuclear Regulatory Commission's Office of Investigations has been conducting an "expansive investigation of the completeness and accuracy of information that Southern California Edison provided to the NRC regarding the steam generators" at San Onofre, NRC Chairwoman Allison Macfarlane said in a Friday letter to two federal lawmakers.

Macfarlane's comment is the first public indication that NRC has been investigating the issue. The investigation has been under way since September 28 and "includes examination of the [Mitsubishi Heavy Industries' root-cause analysis] report along with other evidence," she told Senator Barbara Boxer of California and Representative Ed Markey of Massachusetts, both Democrats.

No information was available on what prompted the probe. "Given the ongoing investigation, the letter represents everything the agency has to say at this point," NRC spokesman Scott Burnell said Monday in an emailed response to questions.

Boxer and Markey on Wednesday asked Macfarlane to investigate information in MHI's root-cause analysis report on the steam generator tube problems that shut San Onofre-2 and -3 in January 2012. MHI manufactured the replacement steam generators for the twin reactors.

The lawmakers had said the report indicates that both SCE and MHI were aware of "serious problems" with the replacement steam generators before they were installed in units 2 and 3 in 2010 and 2011, but did not do some safety modifications because they believed that might jeopardize their ability to justify the replacement steam generator design.

SCE denied that claim on Thursday, saying it would never install steam generators that it did not believe would operate safely.

Markey and Boxer said Friday that NRC "today confirmed that it is investigating the issues raised by our letter." Boxer called the investigation "a critical factor in determining whether it is safe to restart" the San Onofre reactors. SCE needs NRC approval to restart either San Onofre unit.

San Onofre-1 permanently shut in 1992.

--Elaine Hiruo, elaine_hiruo@platts.com 
--Edited by Jeff Barber, jeff_barber@platts.com

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