Given that the new components were supposed to last for decades, industry experts were quick to question why the expensive equipment was already leaking at a rate of between 50 and 100 gallons per day. At the time the leak was detected, San Onofre's other reactor ----- Unit 2 ----- was already shut down for refueling and maintenance.
The water supplied to the steam generators must be very pure, free of particles, and chemicals. In the boiling environment of the steam generator these chemicals can concentrate resulting in undesired corrosion.
SC Edison began replacing the steam generators at San Onofre in 2009 with new units manufactured by Mitsubishi Heavy Industries. Edison has indicated the new generators would last until the plant's license expires in 2022. But on Tuesday a leak developed in one of the tubes in the number 2 steam steam generator at Unit 3. Radiation monitors detected an increase in radioactivity levels, plant operators diagnosed the leak, and the unit was depowered at 4:30 p.m. and shut down fully at 5:31 p.m.
“Two of the tubes have thinning so extensive that they need to be plugged and taken out of service. Sixty nine other tubes have thinning greater than 20 percent of the wall thickness, and a larger number have thinning greater than 10 percent of wall thickness.”It should be noted that the nuclear power industry, now with 30 years of experience with this problem, is well equipped to plug or sleeve degraded tubes and return the steam generator to service. The generator contains thousands of tubes so even if some must be blocked the generator can still be used.
HOW NUCLEAR PLANTS WORK
(North County Times, 2/3/2012, The Orange Country Register, 2/2/2012)