During the crisis, I wasn't quite sure about these reactors, or the stages of meltdown. I've learned a bit.
First of all, you can't get a handle on how huge and high these things are. They are the worst design ever for seismic, which wants to keep things low.
I learned that zirconium burns as well as melts. Whoda thunk?
The happy state now is that everything is flooded with seawater.
But they have these ridiculous high spent fuel pools. Unit 4 had all it's hot fuel out in the pool for maintenance. I think it was boiling even before the earthquake. How stable was that?
It looks like everything was working before the tsunami. They had a wall for a 6 m tsunami, but not the 10m that happened. A tsunami is a big slosh of water, not a wave. Even if they raised a 10 m wall, I wonder if the water would just jump it with the momentum. They have to work on this.
There also may have been some earthquake damage, but they'll never tell us....
ps. that big concrete bottle can't hold all that radioactive water. It is now seeping through concrete cracks to show up anywhere in the plant. Shades of a video game!