On Tuesday evening, January 31st, we heard that the San Onofre unit-3 had been shut down due to leakage of more than 30 gallons per day (found to be 80-100 gpd) of primary coolant through a ruptured steam generator tube. The news sort of got lost in news from the previous day, when the Byron Station nuclear plant unit-2 suffered an emergency shutdown due to a blown transformer caused blackout which vented an 'expected' amount of tritium contamination outside containment via the Emergency Main Steam Dump Valves. The 'expected amount of contamination came from known leaks in Byron unit-2's steam generators (4 of them per unit, but unit-1 was down for outage at the time).
Today Southern California Edison, operator of San Onofre, reported that defects in the interior tubing of Steam Generators at both units 2 and 3 had been discovered. Shortly thereafter, that report was expanded to say that "unprecedented" damage was found in more than 800 tubes in just unit-2's steam generators - the unit that has been down for weeks, not the one shut down the night before last.
Steam generators for nuclear plants are some of the most expensive and complex machinery. Whether straight-tube or U-tube design, leaks in the steam generators are what cause almost all of the annual releases of radioactive contamination from nuclear plants. In theory (and we all know that "in theory" hardly ever describes reality) the primary reactor coolant water is not supposed to mix with the secondary heat removal system's water. This allows nuclear apologists to claim that it's "impossible" for people living near 'normally' operating nukes to be exposed to excess radiation exposure or suffer any health effects from exposure. But that, alas, has never been true, even though the general public is just now becoming aware of why.
The really amazing thing is that while Southern California Edison awaits NRC extension on its operational lifetime, it went ahead and spent ~$680 million just last year to replace all four steam generators at its plants. SCE bought the new ones from Mitsubishi, which reported that there might be some "unforeseen" problems with its bargain level SGs. I say "bargain level" because standard nuclear grade SGs cost between $200 and $400 million apiece. SCE got a heckuva deal, except for the fact that all of 'em leak like sieves.
A primary-secondary systems leak drains primary coolant to the lower pressure system, thus is classified as a LOCA - Loss of Coolant Accident - when it gets to a certain level. Same as any other kind of pipe breach that drains primary coolant.
Can SCE afford to replace their replacement SGs at this price? Is it even worth nearly $2 billion just to keep going for another 20 years hoping they don't melt down first? Isn't there an alternative source of energy that could put nearly $2 billion to better use?
[See Deep Harm's earlier diary:
Deconstructing the San Onofre Radiation Release
and Lucas Hixson's as well:
Minor Problem might spell dramatic and controversial doom for San Onofre Nuclear Plant]