At a public meeting Monday night in San Clemente, officials from the Nuclear Regulatory Commission blamed faulty computer modeling by Mitsubishi Heavy Industries (MHI) as the most likely cause of the unacceptable amount of vibration and wear from rubbing which had been found in the steam generator units, but none of the parties involved can come up with a fix.

The replacement steam generators were supposed to over six decades, specifically, MHI claimed that “60 years” is just design lifetime and the limitation of integrity is considered to be much longer than that. In just a year, tubes in Unit 3 had worn down so much that a break occurred, which has brought the nuclear power plant to an unexpected halt.

Multiple issues yet to be addressed

There are multiple issues at stake, first Mitsubishi seriously undervalued the operating conditions that the steam generator tubes were expected to be subjected to, by a factor of three or four.

Greg Werner, who headed the NRC inspection team, said a Mitsubishi computer analysis vastly misjudged how water and steam would flow in the reactors, and overall failed to predict the type of conditions which could be expected, and resulted in the tube shaking.

There’s a thin line between tubes which are thin enough to transfer heat, and thicker tubes, which are more likely to maintain structural soundness under heavy pressures.

Secondly, there are issues with the V shaped support structures which are only installed in the Unit 3 replacement steam generators, where the worst tube damage has been found.

“This is a significant, serious safety issue,” said NRC Regional Administrator Elmo Collins. “This is a very difficult technical issue, and to be honest, it’s not one we’ve seen before.”

Liability likely to fall on licensee

The NRC official added that even though Mitsubishi did the computer modeling, the ultimate responsibility lies with Edison, and they could face penalties.

The analysis concludes that two or more of the generators may need to be replaced, but the most costly loss would be the expensive decommissioning of the plant due to the enormous financial strain it would put on the already low-performing investment.

“The ultimate responsibly resides with them … because they are responsible for safety,” said Regional Administrator Elmo Collins, the agency’s top official in the western U.S.

The NRC is not above the situation, there was a series of alterations made to the equipment, and known fabrication issues prior to transporting the replacement steam generators from Japan to the United States. On Monday, the environmental group Friends of the Earth said that federal regulators should have reviewed the new steam generator design.

In retrospect, there should have been a much more thorough and inclusive review of the replacement steam generator design, and serious questions are now pointed at the quality assurance program. This is not due to old equipment breaking, rather new equipment that wasn’t up to par in the first place.

The utility notified the NRC in August 2009 that the replacement generators for Unit 3 had developed cracks in a weld that connects a 5-inch-thick steel plate that supports each generator’s innards.

To install the new replacement steam generators, the utility was forced to cut a hole in the vital concrete containment dome for the reactors, as the equipment was too large to fit through the equipment hatch, and required cutting heavy metal tendons which cannot be restored to pre-installation fortitude.

Like-For-Like

Edison admittedly altered the assembly in the Unit 3 steam generators, however overall the new design for both units was nearly 24 tons heavier than the original steam generators and packed in an addition 400 tubes using a different alloy.

Despite all of the noticeable differences, they were stamped with approval from the utility and the regulator as an “in-kind” or identical replacement, which severely limited the federal agencies inspection responsibilities.

Independent analysis lead by Arnie Gundersen of Fairewinds Associates finds that there are numerous changes to the San Onofre steam generators that are not like-for-like or “in-kind”.

“The design codes used to build these replacement steam generators have now been shown calculate the wrong answer by a factor of 400%. This speaks to larger quality assurance problems within Edison and the NRC, both of which went to Japan to inspect this design,” Mr Gundersen said, “How can a 400% error go undetected? Clearly this was not a like for like modification.”

Furthermore, the facts reviewed by Fairewinds makes it clear that if Edison had informed the NRC that the new steam generators were not like-for-like, the more thorough NRC licensing review process would have likely identified the design problems before the steam generators were manufactured.

Depending on the outcome, Edison may be forced to amend its license for the changes.

Other problems are even less able to be adequately defined, but involve what is often perceived as a international track record between utilities and regulators to assume downplay over details based approach. If all else fails, with probabilistic risk scenarios it is easily possible to justify known deficiencies in multiple areas at nuclear power plants, which allow for a plethora of profit-based decisions.

Neither parties, Edison or the NRC did much to better their public relations or set a new reputation thus far in the investigation, and have only continued to field complaints for relying too heavily on rhetoric and forward-looking statements to attempt to “whitewash” the issue.

This is a problem which has haunted the nuclear industry since inception, and critics have long argued that risks are not appropriately mitigated as much as they are compartmentalized and minimized.

Edison has historically not been candid about problems at SONGS, and the distrust of locals has only increased, a far cry from Edison’s stated objectives for the proposed replacement steam generator project in 2004, to “Extend useful life of steam generators, and to ensure continued supply of low-cost power.”

Now, rate payers and investors alike will need to decide if they want to keep investing in boiling water with fission or move to wind and solar and conservation.

SONGS Meeting Slides

Source: Fairewinds

Source: LA Times

Source: Business Week

Source: U/T San Diego

Source: Platts

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