There is a reason I feel much relieved after reading this. Pretty much everything I've read so far implied that once there is a meltdown, all bets are off. We'll have radioactive material boiling in open air, and all the "good" things that come with it. Which sounded very suspicious to me... I mean, isn't containment designed to prevent exactly that? Once the fuel melts, it just makes a hole on the bottom of the containment and pools on the floor? So for me, the money shot was here:
> For that purpose, a large and thick concrete basin is cast under the pressure vessel (the second containment), which is filled with graphite, all inside the third containment. This is the so-called “core catcher”. If the core melts and the pressure vessel bursts (and eventually melts), it will catch the molten fuel and everything else. It is built in such a way that the nuclear fuel will be spread out, so it can cool down.
edit: Plus reading about INES, there was a British plant that had 5 (five) level 4 incidents in 25 years, and a partial core meltdown at a French plant. And many more.
Except that "Fukushima Dai-ichi No.1 Reactor does not have a concrete containment dome. This reactor was built before the now familiar reinforced concrete dome became mandatory for most reactors. Instead, the reactor has a much smaller steel containment vessel around the reactor vessel."
Someone with more knowledge of nuclear power history could surely cross reference the dates here for us and confirm/deny the existence of the 3rd containment layer:
> For that purpose, a large and thick concrete basin is cast under the pressure vessel (the second containment), which is filled with graphite, all inside the third containment. This is the so-called “core catcher”. If the core melts and the pressure vessel bursts (and eventually melts), it will catch the molten fuel and everything else. It is built in such a way that the nuclear fuel will be spread out, so it can cool down.
edit: Plus reading about INES, there was a British plant that had 5 (five) level 4 incidents in 25 years, and a partial core meltdown at a French plant. And many more.