DonAithnen (donaithnen) wrote,

Risk calculations

This whole situation with the nuclear reactors in Japan is really frustrating. Everyone is freaking out about it and a lot of analysts are convinced that it's going to have a serious impact on the political/popular feasibility of the use of nuclear power in the future, especially in terms of building new reactors.

Certainly the situation sucks, but there's a couple huge fallacies in the ZOMG nuclear power = BAD! line of thought. The first, that this is what one can usually expect from reactors. The reactors having the biggest problems are about 30-40 years old. The ones that are faring slightly better but still having some problems are 25-30 years old. They were hit with the largest recorded quake in Japanese history, and the fourth largest recorded quake in the world, after which they were doing fairly well until they were then also hit by the tsunami. Yes one has to account for that kind of disaster happening from time to time, but given their age these reactors have fared that badly and newer, more safety conscious designs, would have performed much better.

Second, everyone is focusing on the danger from the nuclear power plants while completely ignoring the problems posed by other methods of generating power and/or heat. Like many earthquakes the one in Japan was followed by the outbreak of numerous fires, many caused by broken gas mains, and more than one major oil refinery burst into flames as well. It's hard to say exactly how big a factor the fires have been in the over ten thousand dead and missing, to say nothing of the property damage, but everyone accepts that because gas and oil are understood by everyone and fires are "expected" after an earthquake. A fire doesn't have "invisible scary magic" numbers associated with it like how many microsieverts you can be exposed to before you need to start worrying.

That said, i'm certainly concerned about and interested in the processes going on at the Japanese nuclear plants right now. Obviously these plants were not designed to be passively safe like the newer models, but i'm curious about what issues are giving them so much trouble. Nuclear fission generally works by bringing pieces of uranium (or some other similar element) "close together" in a relative sense such that the neutrons released by one atom decaying will trigger the decay of other atoms. You stop the reaction by taking the pieces of uranium "apart" from each other. This may or may not involve physically moving the pieces, it's just as possible (and actually more usual) to modulate the space between the pieces of uranium in order to prevent (some of) the neutrons from passing through to the next piece of uranium.

So what i wonder, in short, is what's stopping them from just trashing the reactor core? Do they think they still have some hope of salvaging them and getting them back online at a later date? Or have they given up hope of that and it's only technical problems that are getting in the way? I would have thought that in any kind of worst-case scenario short of actual meltdown the most surefire way to stop the reaction would be to dump a bunch of molten lead into the reactor. Surely lead has got to be at least as absorbent as the materials normally used as control rods in such reactors? Assuming you do so before the reaction gets hot enough to vaporize lead you ought to be able to just fill it up, wait for it to cool, and separate the uranium elements later.

Alternately (and admittedly more risky) why don't they just drop a hand grenade or two in? Or at least go in there (presumably with a robot) and smash the thing with a hammer? If you can knock enough elements out of the array presumably the feedback reaction would stop?

Are those plans too risky somehow? Or would they just not work? Or would it make it "too costly" to clean up the mess afterwards?

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