The turbines that spin the generators at Southern California Edison’s San Onofre Nuclear Generating Station need steam. But the reactors at SONGS are pressurized – at roughly a ton per square inch – so the water cannot boil. Instead, hot water from the reactor is pumped through thousands of tubes. Cold water flows around those tubes, absorbs the heat of the reactor water, and boils, generating steam for the turbines. The vessels in which this takes place – the steam generators – are huge, each over twenty feet across, over 600 tons.
SCE replaced the steam generators at SONGS in 2009. The new SGs were supposed to last decades. Instead, the SGs are already wearing out. A small amount of radiation escaped the plant as a result. Both SONGS reactors are presently shut down.
In this podcast, nuclear engineer Arnie Gundersen (Fairewinds Associates) describes the SG switch-out, and how the problems may have stemmed from changes to the original design. He ends with an intriguing hypothesis as to why the design might have been changed.