Regulators Again Point to Mitsubishi Heavy Industries' Faulty Modeling of San Onofre Steam Generators

Faulting software errors by Mitsubishi Heavy Industries, federal regulators have determined the steam generator design flaws that ultimately shuttered the San Onofre nuclear plant likely amounted to violations of its license.

San Onofre steam generator tube wear diagram. Source: NRCSouthern California Edison closed the two-unit plant in June, confronted by mounting outage and repair costs for steam generators exhibiting rapid tube wear. On Friday, the Nuclear Regulatory Commission notified SCE of two preliminary findings related to the potentially unsafe conditions caused by the equipment's engineering. A green finding for unit 2 will be considered a non-cited violation, but a white finding for unit 3 will be considered for escalated enforcement action, according to NRC correspondence.

The agency also issued a notice of nonconformance to MHI related to its thermal hydraulic and vibration analyses. According to that document, equipment at three additional reactors was also designed using faulty modeling assumptions. As explained by the NRC:

"The MHI Three-Dimensional Thermal and Hydraulic Analysis computer code (FIT-III) was initially developed in 1978 for use in modifying Westinghouse designed square pitch tube steam generators. In 1992, the MHI Takasago Research and Development Center (Takasago) modified FIT-III for use on triangular pitch tube steam generators. At the time of the conversion to triangular pitch, the output of FIT-III was the wide gap velocity versus the narrow gap velocity required to be input into the flow induced vibration analysis software (FIVATS) vibration analysis code. The MHI Steam Generator Design Section (SGDS) thought the output of FIT-III was the narrow gap velocity. All MHI designed triangular pitch steam generators up through SONGS (total of five nuclear power plants) used the incorrect gap velocities. However, no other operating steam generator has developed fluid elastic instability as found at SONGS."

The NRC has studied the steam generators intensely since their flaws were identified in early 2012. Further technical details can be found in the agency's root cause analysis released earlier this year.

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  • Anonymous

    So... who are the other four plants?

  • It was mentioned in the NRC Report the replacement steam generators for OPPD’s Fort Calhoun Nuclear Generating Station are the only other steam generators designed by MHI operating in the United States. I am not sure where the others are located in the world.

  • Anonymous

    It's interesting that 30 or 40 years ago, the design of the original steam generators was done effectively and accurately by engineers armed with only a pencil and slide rule, maybe a calculator.  It also interesting that with so much on the line, the model used in these analyses is not verified by that same pencil, slide rule and or calculator.

  • Anonymous

    What is sad is that it appears all they needed to do is re-engineer the pipes and move forward, but instead the Federal Government would not approve any plans in a timely manner forcing the plants to close.  Am I missing something here?  Southern California energy prices are going through the roof hurting the poor, elderly, small businesses, and those on a fixed income.

  • Anonymous

    Anonymous....30 and 40 years ago, not the dark ages, engineers had computer models to plan designs...not just pencils and slide rules....lmao!  With the ever growing call for more electricity, all of the companies are trying to find ways to get more electricity out of all of the different kinds of plants in their systems to meet that demand. Support industries like Mitsubishi take a design which has worked well for over 40 years and tweek it to produce more steam or otherwise produce more power and sell it to the plants.  On paper it looks good. Originally, the basic design was built and tested at government facilities to see if it would work...was safe....would endure stresses and explosions. This tweek wasn't. The result of an alteration in one area wasn't tested to see what the effect would be on other components.  It is the need for more energy at the same price that is driving these alterations.

  • Anonymous

    MHI is being used as a scapegoat.  MHI built

    Why would MHI build, and why would Edison purchase, new and different SG's that would not be legal to use ?

    The most glaring issue of all is, how can a utility like Edison redesign it's SG's,

    (remove tube supports, add tubes, for 10% more capacity),

    and say they are "like kind replacements" to try and avoid a lengthy design review process, and a license amendment ?

    By around mid 2012, the only recourse Edison had was to redo the SGR, AND get a license amendment this time, if possible.

    Lead time for new SG's, perhaps 5 years?  more downtime.

    And at a cost, ( $760M first SGR + $300M so far this shutdown since Jan. 2012 ) and growing.

    Plus,  as more and more facts came out,  the local public's anti-nuke outcry was massive and deafening.

    Making any outcome of a public hearing for the required license amendment a bit dim for Edison.

    Coupled with a call by state Senator Boxer for an U.S. Justice Dept. investigation into the actions of Edison management.  

    Edison management was wrong, by skipping the official design review and license amendment process on the SGR project.

    It is unfathomable that they would have even done that.

    Where was the NRC, and why did they not require Edison to follow their license, (buying the "like kind replacement" story).

    Senator Boxer's call for a Justice Dept. investigation, put the pressure on.

    Recognizing relicensing may be futile in light of public outcry and a potentially damaging investigation,

    Edison mgmt. closed the plant not just to stop the bleeding, but also hopefully cover their asses.

    Misrepresenting the facts, hiding the truth, and deceiving the public and plant staff became commonplace.

    Ultimately, a tremendous waste of (ratepayer's) money due to an unscrupulous and arrogant management culture at San O.

  • Anonymous

    It is very sad that the plant will not be repaired and put back into service. The Songs plant had a great staff and was one of the best plants to work.

  • Anonymous

    Best job and place I ever worked. I miss the commute even but my paycheck more.