Energy Industry Report

NRC: No timetable for restart at San Onofre

It was opening day for baseball around the U.S. last week, but at Southern California Edison’s San Onofre Nuclear Generating Station (SONGS), it was looking a lot more like an instance of the legend of the Mighty Case striking out.
The utility still does not know what’s causing the early and excessive wear on hundreds of steam tubes for the steam generators attached to the twin PWRs.
Worse, the media attention surrounding the visit by the NRC Chairman gave U.S. Senator Diane Feinstein (D-Calif) the chance to scare the wits out out of millions of people within a 50 mile radius of the plant. Meanwhile, Rep. Darrell Issa, who’s district includes SONGS, wondered what it would take to turn the plants back on.
In a press conference held late Friday afternoon (April 6), Jaczko said that after the tour of the plant, where both reactors have been shut down since January, he would not put a time table on when the units would be restarted to supply electricity to a power hungry southern California.
Jaczko said he made the long trip to San Onofre to “get to the bottom” of why SONGS is having troubles with new steam generators. He said the NRC will need technical assurances of the safety of the plant before it will be allowed to restart. The utility will have to show that it knows with certainty what caused the problem with the steam tubes and how to fix them.
SONGS tubes off-key

SONGS managers have said the problems are caused by the tubes vibrating and rubbing against each other and the brackets that hold them in place. They don’t know why or what else is happening to them inside the steam generators.
What the utility’s engineers do know is that the excessive wear is taking place way too early in the life of the 9,700 tubes at each unit which were installed by Mitsubishi as part of a $680 million replacement package in 2009. The Japanese firm builds similar steam generators for customers world wide so why this particular installation is having these problems is a mystery.
Some possible causes, none of which have been confirmed by SONGS, include vibration, various forms of internal and external corrosion, and cracking and thinning of tubes. Possible fixes, generically speaking, identified in a nuclear industry technical paper, include improvements to water chemistry, cleaning the tubes, and plugging the ones that are excessively degraded.
Jaczko added in his remarks Friday that SONGS managers and NRC inspectors have told him that the wear in Unit 2, which was shut down for routine maintenance in January, isn’t as severe as Unit 3, which is where the problem was first detected by plant operators. So far SONGS has plugged 300 tubes in Unit 2. Of 129 tubes tests, eight tubes in Unit 3 failed pressure tests give rise to a new set of concerns about the durability of the rest of them.

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