Tuesday, March 15, 2011

Fukushima Daiichi

When I read the initial news on Saturday that the Daiichi reactor had broken down, my first reaction was something like this: "Three Mile Island, Chernobyl, Fukushima. This is the third major nuclear disaster of the modern era, and we'll remember it as such."

I'd like to urge my readers to wait before turning this into a judgment on nuclear power and its dangers, however. We're a long way from knowing what exactly happened at Fukushima, or what happened to the reactor's defenses. We won't really be able to know until the units have calmed down and are safe to examine, which won't happen anytime soon. Any legislative action can only be premature, although Fukushima will almost certainly result in fewer and smaller subsidies for the next generation of US nuclear plants.

While we're waiting, here's a quick glossary of some terms you might be reading in the news:

*Isn't Showing Off His Residual Term Paper Knowledge At All

-Spent fuel pool: When fuel rods are removed from a nuclear reactor, they're kept in a concrete-lined pool for around five years (in the US) to dissipate thermal and nuclear radiation that the rods are still giving off. These pools are usually on the grounds of the reactor that produced them. The Washington Post, among other outlets, has reported that at least one pool's water level dropped to the point where the rods were exposed.

-Boiling Water Reactor (BWR): All the Fukushima reactors use this design, which uses water both to cool the core and to moderate the nuclear reactions in the core by absorbing neutrons (or a 'moderator'). In a BWR, the water is allowed to boil in the core, creating steam which drives the turbines of the plant. It is one of two most common types of reactor, the other being a Pressurized Water Reactor (PWR).

-Core meltdown: When a nuclear plant loses its coolant and moderator, water, the core can overheat and melt down if the coolant isn't restored. That's what the Japanese authorities are attempting to do by pumping seawater mixed with boron into the reactors.

-Iodine-131: a radioactive isotope that was released at the Chernobyl meltdown, and was responsible for an estimated 4,000 cases of childhood thyroid cancers, all but two or three of which were cured. The most commonly accepted explanation is that the iodine passed through cows into milk, which was then given to schoolchildren. It has a half-life of around eight days. It can be blocked by taking potassium iodide pills; the body's thyroid gland absorbs iodine but has a limited capacity for doing so, and ingesting a harmless iodine isotope prevents the body from taking in the harmful iodine-131. There are reports that it has been detected around the Fukushima plant.

-Cesium-137: Another Chernobyl isotope, Cesium-137 has a half-life of around thirty years. It was also detected around Fukushima.

Another Caveat...

The most likely explanation that I've heard for the disaster is that the tsunami flooded the generator building in the Fukushima complex, cutting off power to the reactors, and that the emergency generator building failed as well for the same reason. U.S. reactors would still have safeguards if this happened to one of our reactors in the same situation.

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