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I'm up in the middle of the night because just as I was going to bed, I saw a news blurb that said that the nuclear power plan in Japan, damaged in the recent earthquake/tsunami, had been evacuated of everyone. This was done for the safety of the people working the plant, obviously, and that's good, but I'm worried about how that will play out in the coming days.
I can't do anything about the current situation (other than donating to organizations that are helping with the recovery effort, which I've done). I've been lying in bed for hte last couple of hours thinking about the design of the plants. That's armchair quarterbacking, of course, but I'm trying to understand a basic premise of the design. This isn't useful in terms of the current crisis, but I'm throwing the question out there for myself to perhaps slightly understand the issues going forward. I would love for someone to e-mail me at craigsteffen@gmail.com and tell me what I'm missing.
My understanding is this: when the earthquake hit, the reactors immediately dropped in the control rods, slowing down the primary nuclear reaction going on inside the reactor cores. That seems to have worked fine in all the reactors that were effected. There are secondary nuclear reactions that continue to generate heat over a significant period of time (days at least, weeks?) such that even after the cores are "shut off", they have to be kept actively cooled until the secondary nuclear reactions die away. The current problems have been precipitated by the inability to do this effectively.
Apparently this cooling is done with water, so water being physically delivered into the reactor core is the critical parameter. If water is being delivered to the reactor core (and to the spent-fuel storage pools), then everything's fine and remains stable. If water flow stops, things heat up, cores get uncovered, stuff starts to melt and potentially you have radioactive metals blown all over the landscape. Water flow is key.
The problem was that the cooling/pumping systems all apparently run on electricity? So when the reactor shuts down, it's not generating its own power. Diesel generators kicked in, but then the wave of the tsunami swamped them and shut them down. So suddenly the plant was trying to pump water with no electrical supply, which started the current problems. And they can't draw power from the grid, possibly because it was damaged in the earthquake too?
(commence armchair quarterbacking; my main point is in the next paragraph.) First of all, this seems to like an insufficient level of redundancy. If the plant goes off-line, then all your contingency plans assume that the power grid or diesel will keep working continuously? That's only a two-fold backup against really really bad stuff happening.
Which brings me to my point. Because of the design of the cooling systems, lack of elecrical power is currently the big problem (multiple backup systems, but they all run on electricity). But the fundamental problem is lack of water delivery. So in case of electrical failure, why not provide a water delivery system that doesn't actively use power? Why not have a WATER TOWER next to each reactor building with enough water to, ideally, keep it cool for its entire cool-down time? Maybe that's too much--how about enough water to keep it cool over-night? You make the tower higher than the containment building; you open valves and the water flows by gravity. You install a couple of different ways of putting water INTO the tower. Maybe from water mains, and also perhaps from a fill point half a mile away so that you don't have to get too close.
What am I missing? Why don't these plants have this? I realize a water tower isn't sexy and doesn't have a fancy interlock system with lights in the control room. But I would think that it would be a huge bonus to the current crisis.