Inklings: a tumblelog

A simple explanation of what's currently going on in the Fukushima Dai-Ichi power plant from a non-physicist's point of view

Note (2011-03-16): This post only refers to the situation with the first three reactors and the spent fuel rod pool fires, which is a serious problem. When I wrote it, to the best of my knowledge, the other reactors where cool and stable. Keep that in mind as you read it.

As a software developer, I’m not qualified to dispense information things nuclear physicist know much more about than I do, but I thought I’d summarise my understanding of the current events in Japan here. I’ve also put out a request to any physicists I know do double-check my understanding, but I’m almost completely sure it’s correct.

All three explosions happened outside of containment and do not indicate a loss of containment or a breach of containment of any kind. The reported radiation leaks have been in the form of isotopes of nitrogen and noble gases (argon, krypton, xenon, &c.), most of which have short half-lives[^1] or are naturally occurring, or in such low quantities that their effect is negligible at best, along with small amounts of aerosolised caesium and iodine. The explosions were due to the water being used in cooling the reactor, splitting apart into oxygen and hydrogen, and then reacting violently when the became bound as water again when they needed to do a pressure release[^2] from the reactor.

I’m frankly more worried about the fact that they’re having to use seawater rather than demineralised water as salt is a very good thermal insulator, which means that they’re hedging that the ongoing reaction of the transmuted elements in the fuel rods (which is a completely natural consequence of how reactors work rather than a sign that something has gone wrong) will finish and thus have its heat dissipated before the caking on the fuel rod sheaths becomes a problem. So long as they keep the temperature of rods below about 1000°C, there’s no problem. If it goes above that, then you’ve trouble as the melting point of the fuel rod sheath is about 1200°C, and then there’ll be nothing to stop a meltdown of the contents of the fuel rods.

Of course, as Japanese reactors are competently built and ran[^3], the secondary and tertiary containment will be able to contain the meltdown.

There’s likely nothing to panic about so long as primary containment within the reactor holds, but if that doesn’t, the main worry is that (a) the reactor will be rendered a write-off and (b) while the area outside the reactor will be safe, cleaning the reactor up will cost a fortune.

[^1]: See “Isotopes of nitrogen”, “Isotopes of argon”, “Isotopes of argon”, “Isotopes of xenon” on Wikipedia.

[^2]: A boiling water reactor is a lot like a fancy pressure cooker.

[^3]: Unlike Chernobyl was.