Southern California Edison was aware of problems with replacement steam generators at its San Onofre nuclear power plant but chose not to make fixes, U.S. Sen. Barbara Boxer charged Wednesday.

Boxer cited a leaked report from Mitsubishi Heavy Industries, the manufacturer of the steam generators, obtained by her office. It is the first indication from government officials that Edison and Mitsubishi knew the system had problems before it was even installed.


The nuclear plant, a prime supplier of power in Southern California, has been off line for more than a year after a small amount of radioactive steam leaked from the plant’s tubing.

The report indicates that Edison and Mitsubishi “were aware of serious problems with the design of San Onofre nuclear power plant’s replacement steam generators before they were installed” and “rejected enhanced safety modifications and avoided triggering a more rigorous license amendment and safety review process,” Boxer and U.S. Rep. Edward J. Markey (D-Mass.) said in a letter to the Nuclear Regulatory Commission.


According to their letter, the Mitsubishi report indicated that some safety modifications were rejected because they carried “unacceptable consequences,” and that decision contributed to the plant’s problems.

The letter quoted the report speaking about “difficulties associated with the potential changes,” including “the possibility that making them could impede the ability to justify the [replacement steam generator] design” without triggering a lengthy license amendment process.


The plant has suffered from unusual wearing of hundreds of steam generator tubes carrying radioactive water.

Edison and San Diego Gas & Electric — which owns a 20% share in the plant — spent a combined $771 million replacing the steam generators, which ratepayers are now repaying.


Edison has proposed restarting one of the units at partial power, which the company contends would alleviate the conditions that led the tubes to vibrate excessively and rub against one another and support structures. The NRC is expected to make a decision on the proposal in late April or May.

“All design decisions for the ... steam generators were made in accordance with well-established and accepted industry standards and practices, along with our own and third-party operating data and experience,” Mitsubishi said in a statement.


The company said it was cooperating with the NRC investigation into San Onofre’s problems.

Edison said it too was cooperating with the NRC’s review process and that the company “takes very seriously all allegations raised by the letter.”


The utility giant did not respond to the specific allegations raised by the lawmakers.

Neither the NRC nor the lawmakers released the Mitsubishi report. NRC spokesman Victor Dricks said the agency had not made it public because it contained proprietary information.


A public NRC document references an Oct. 12, 2012, report with the same name as the one cited by Boxer and Markey, but does not describe its contents.

Dricks said in a statement: “We have received the letter from Sen. Boxer and Congressman Markey and will respond in the normal course of business. As an independent safety agency, we will review all available information in making a judgment as to whether the plant would meet our safety standards if restart were permitted.”


The environmental group Friends of the Earth has alleged that Southern California Edison sidestepped a full NRC review of design changes in the new steam generators that the organization says led to the tube wear. Edison denies that, and the two parties are debating the issue in an NRC proceeding separate from the agency’s review of the restart plan.

Friends of the Earth energy and climate director Damon Moglen said he had not seen the Mitsubishi report, but based on the Boxer letter “it seems that Edison did know that there were serious problems with the design” and chose not to fix them.


“It seems to really underpin the arguments that we were making all along,” he said.

Edison and Mitsubishi officials, along with consultants who worked on the investigation into San Onofre’s issues, were scheduled to brief the five NRC commissioners Thursday.


The meeting, which was scheduled prior to Boxer’s letter, will be the first time since the plant’s shutdown that the full commission will have the opportunity to question Edison directly.

abby.sewell@latimes.com