Arnie Gundersen, Chief Engineer of Fairewinds, explains why San Onofre’s four defective replacement steam generators cannot safely be repaired, as he demonstrates what happened inside the generators.

Steam generator tube vibrations caused extensive damage due to design changes between the original and replacement generators. See new Fairewinds detailed report San Onofre’s Steam Generator Failures Could Have Been Prevented. See also original version of the report prepared for Friends of the Earth.

Typical Combustion Engineering Steam Generator. Select image to enlarge.

Impact of design changes:

• The tubes are now “at risk of bursting in a main steam accident and spewing radioactivity into the air”.
• The top of the new steam generator is now “starved of water therefore making tube vibration inevitable”.

Significant design changes include:

• The original design had a unique tube support to prevent vibration – these supports were changed in the new design.
• The main structural stay cylinder was removed.
• 400 additional tubes were packed into an already tightly packed design.

Plugging tubes and operating at lower power (as Southern California Edison suggests) are not viable solutions:

• Vibration is the result not the root cause of the steam generators problems at San Onofre.
• Plugging tubes cannot repair design changes that cause the tubes to collide with each other.
• 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.
• 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.
• Lower power might create a resonate frequency at which vibration might increase without notice.
• Historical evidence at other reactors has shown that operating at lower power has not been an effective solution.

Also, the Nuclear Regulatory Commission just released a copy of Southern California Edison’s June 7, 2006 slide presentation – San Onofre Steam Generator Replacement Project Overview.  It shows some of the design changes to the generators.

One of San Onofre’s Unit 3 steam generators leaked radiation into the air after being installed less than a year. The other three replacement steam generators are showing unprecedented premature wear. San Onofre has been shut down since January 31, 2012.

No blackouts have occurred from the shutdown and California’s electricity grid operator stated it is unlikely there will be blackouts during peak summer months. California’s other nuclear power plant, Diablo Canyon, was also shut down recently.  California experienced no blackouts with both nuclear plants shut down.

San Onofre, located in San Diego county, is only a few miles from San Clemente, California. See Steam Generator Section for more information on the steam generator issues.