San Onofre’s steam generator failures could have been prevented

A summary of the Fairewinds report, San Onofre’s steam generators failures could have been prevented, commissioned by Friends of the Earth and released May 2012.

Background

The San Onofre nuclear power plant, located between Los Angeles and San Diego, has been kept shut for the past three and half months by Southern California Edison, after radioactivity leaked into the atmosphere.

During that time there has been no official statement by Edison company to describe the totality of its investigation of the causes of the leak. On the contrary, Edison has been warning the public of blackouts if the plant is not operating and has revealed that it was considering a restart in June 2012, a statement shot down by the chairman of the Nuclear Regulatory Commission.

Friends of the Earth, by retaining Fairewinds, has supplied the public with two technical reports shedding light on the causes and extent of the problem. This is the third report in that series.

It reveals, in unmistakeable detail, why and how an attempt to cut regulatory corners resulted in a clear and present danger to the people of southern California not to mention an eight hundred million dollar mistake.

The reports essential findings are:

• the Edison company deliberately sought approval from the NRC of its new Steam Generators as a “like-for like replacement” to avoid a more thorough license amendment and review process;
• the new design did in fact make seven significant design changes, any one of which required a thorough analysis of the change, a public hearing and approval of a license amendment by the NRC;
• the vital necessity for safety required by the NRC licensing process for a changed design is demonstrated by San Onofre where “it is likely the more thorough review would have identified the design and fabrication inadequacies” – for example the NRC would have identified the fact that Edison used a Mitsubishi computer model to evaluate the changes, even though that model was not capable of analysing the Combustion Engineering (CE) design at San Onofre, but only the very different Westinghouse design;
• the physical changes from the original to new steam generators are very real and very significant, they include:

1 – the original design had a unique tube support to prevent vibration – these supports were changed in the new design;
2 – the main structural stay cylinder was removed;
3 – 400 additional tubes were packed into an already packaged design;

• as a result of the design changes the top of the new steam generator is now “starved of water therefore making tube vibration inevitable”;
• the tubes are now “at risk of bursting in a main steam accident and spewing radioactivity into the air”;
• vibration is the result not the root cause of the steam generators problems at San Onofre;
• plugging cannot repair design changes that cause the tubes to collide with each other;

Non-solutions

Operating at lower power

1 – reducing power does not provide a remedy for the underlying structural problems that are creating the vibration that has damaged and will continue to damage the tubes deep inside the San Onofre steam generators;
2 – reducing power will not change the pressure inside or outside the tubes – previously damaged tubes will continue to vibrate damaging surrounding tubes and tube supports and worsen the existing damage;
3 – lower power might create a resonate frequency at which vibration might increase without notice;
4 – historical evidence at other reactors have shown that operating at lower power has not been an effective solution.

Solutions

1 – repair in place by cutting off top of the steam generators to allow personnel to access, may be possible and would take as long as 18 months and cost an estimated US$ 400 million;
2 – after additional analysis of flow patterns it may be possible to change the internal structure to get more water into the upper U-bend regions or by replacing the steam water separators;
3 – the only solution that minimizes the safety steam generator risks at San Onofre is to replace the existing steam generators through the license amendment process.

Conclusion

A nuclear plant with tube vibration greatly magnifies the risk if a steam line accident were to occur. Vibration induced damage would cause an “inordinate amount of radiation” to contaminate “one of the most heavily populated area in the United States.”

The only solution that would ensure that the steam generators would perform in the same way as the  original generators at San Onofre is to replace them through the license amendment process.

Resources

Read the full report.