I will try to summarize the main facts. The earthquake that hit Japan was 7 times more powerful than the worst earthquake the nuclear power plant was built for (the Richter scale works logarithmically; the difference between the 8.2 that the plants were built for and the 8.9 that happened is 7 times, not 0.7). So the first hooray for Japanese engineering, everything held up.
When the earthquake hit with 8.9, the nuclear reactors all went into automatic shutdown. Within seconds after the earthquake started, the control rods had been inserted into the core and nuclear chain reaction of the uranium stopped. Now, the cooling system has to carry away the residual heat. The residual heat load is about 3% of the heat load under normal operating conditions.
When designing a nuclear power plant, engineers follow a philosophy called “Defense of Depth”. That means that you first build everything to withstand the worst catastrophe you can imagine, and then design the plant in such a way that it can still handle one system failure (that you thought could never happen) after the other.
Go to the link to read the chain of events.
There's some good lessons learnt from this (like compatability of emergency backup generators, main backup generator locating, and steam venting).
Unfortunatly, this event has a major chance of killing nuclear development (at least in the West). Which has the irony of keeping the older plants around longer than if they were replaced by the newer, more robust, plants.
And similar thoughts and comments from Glen Reynolds.
JAPANESE EARTHQUAKE CAUSING antinuclear folks to get frisky. I’d say that members of Congress should take a time-out — and maybe, you know, pass a budget — before they start trying to pass new laws on nukes. They should also explain where the energy is going to come from if we can’t drill for oil, can’t burn coal, can’t dam streams, can’t put windmills where they might spoil a Kennedy’s view, and can’t build nukes. Vague allusions to “green power” don’t count.
But math is hard!
ANOTHER UPDATE: Reader Andrew Medina says we’re lucky to face nuclear-plant problems, because if the tsunami had hit a solar farm instead, “10,000’s of Lbs of lead and cadmium telluride would have been swept into the Sea of Japan poisoning just about everything.”
And then there's this.
And another explosion but worse?
Well, power has to come from somewhere, and unicorns and feelings don't count.