San Onofre design issues probed by regulatory commission


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The head of the U.S. Nuclear Regulatory Commission said Friday that the agency’s office of investigations is probing the ‘completeness and accuracy’ of information Southern California Edison has given the agency about equipment at its troubled San Onofre nuclear plant.

NRC Chairwoman Allison Macfarlane wrote to Sen. Barbara Boxer (D-Calif.) that the agency had launched an ‘expansive investigation’ on Sept. 28, 2012, into information Edison gave the agency about the plant’s steam generators. The investigation is ongoing.


Macfarlane was responding to a letter sent Wednesday by Boxer and U.S. Rep. Ed Markey (D-Mass.) after they obtained a leaked version of a non-public Mitsubishi report on the cause of problems with the steam generators.

The lawmakers said the report showed that when designing the replacement steam generators, Edison and Mitsubishi had rejected safety modifications in order to avoid triggering a lengthy NRC license amendment process.

The plant has suffered from unusual degradation of steam generator tubes, which resulted in a small leak of radioactive steam more than a year ago and prompted the plant’s shutdown.

The NRC, the lawmakers and Mitsubishi have declined to release the full Mitsubishi report, saying it contains proprietary information.

Markey said Friday in an email that the report showed a team formed by Edison and Mitsubishi when designing the replacement steam generators had identified some conditions that made the system particularly vulnerable to tube wear, but rejected design changes that could have mitigated the problem. The team, formed early in the design process, was focused on the design of anti-vibration bars.

A source familiar with the document who was not authorized to speak on the record said the team was apparently formed as part of the normal early-design process, to minimize potential problems with tube vibration and wear, not because the companies had a specific concern at the time.


However, in the course of the process, the team recognized that the steam in the new steam generator system could be drier than in previous designs, the source said. Dry steam was one of the factors identified by Edison and Mitsubishi as contributing to the excessive tube vibration, along with high steam velocity and inadequate support from the anti-vibration bars.

Markey said in an email, quoting from the leaked report, ‘After ‘numerous technical and design review meetings,’ that team concluded that the steam generator tube design could lead to the tubes vibrating and subsequent wear damage caused by higher amounts of steam.

The team then ‘considered making changes to the design’ to mitigate the problems, but decided not to implement any of them. The only specific reason cited in this document for the decision not to implement the potential design modifications was the desire to avoid a more lengthy license amendment process at the NRC.’

Markey did not say what the design changes were that Edison and Mitsubishi had considered.

Edison spokeswoman Jennifer Manfre said the company would not respond to ‘portions of sentences taken from a report that needs to be taken in its entirety.’ But she denied that the company knowingly manufactured faulty equipment.

‘We don’t think it would be in our customers’ interest, in our business interest, and it totally violates our No. 1 priority, which is the health and safety of the public and of the workers,’ she said.


Mitsubishi spokesman Pat Boyle said Boxer and Markey are “taking portions of a proprietary report out of context” and that the steam generators were made in accordance with industry standards and Southern California Edison’s design specifications.

Macfarlane said in her response to Boxer that the agency is reviewing the Mitsubishi report as part of its investigation.


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