Broken Reactor Components
Problems with Steam Generator Tubes (Part I)
tends to concentrate
in the following areas:
1) where tubes are welded to the tubesheet at the bottom of the steam generator;
2) where tubes pass through support plates;
3) where interior tubes are bent tightly near the top of the steam generatator;
4) where sludge piles accumulate around the tubes.
|Stress and corrosion cause pits, pinholes, and two
types of tube cracks:
axial cracks run the tube length; circumferential cracks run around the tube.
|New cracks are occurring in ways the nuclear industry doesn't understand and can't predict. For example, cracks are appearing in mid-span regions, in between support plates, where there is no ready explanation for their presence.|
|We now know that steam generators were poorly designed and made out of the wrong metal. Crevices, where corrosion readily occurs, are inherent in vertical steam generator designs. And Inconel, the nickel/chromium alloy used to make the tubes, is more susceptible to crevice-corrosion cracking than stainless steel. To quote the senior NSP nuclear engineer who inspired our title:|