Scientific American has a great article on what could be the worst case scenario at the Fukushima plant, though it seems to have been written before it was known that there were two cores, not one, that might be melting down. Physicist Ken Bergeron explains a bit about how the Fukushima reactors differ from some others:
“This is a boiling water reactor. It’s one of the first designs ever developed for commercial reactors in [the United States], and it’s widely used in Japan as well. Compared to other reactors, if you look at NRC studies, according to calculations, it has a relatively low core damage frequency. (That means the likelihood that portions of the fuel will melt.) And in part that’s because it has a larger variety of ways to get water into the core. So they have a lot of options and they’re using them now. Using these steam-driven turbines, for example. There’s no electricity required to run these steam-driven turbines. But they still need battery electricity to operate the valves and the controls.”
“…One of the disadvantages [of the BWR] is that the containment structure is a lightbulb-shaped steel shell that’s only about 30 or 40 feet across—thick steel, but relatively small compared to large, dry containments like TMI [Three Mile Island]. And it doesn’t provide as much of an extra layer of defense from reactor accidents as containments like TMI. So there is a great deal of concern that, if the core does melt, the containment will not be able to survive. And if the containment doesn’t survive, we have a worst-case situation.”
And just what is that worst-case scenario? “They’re venting in order to keep the containment vessel from failing. But if a core melts, it will slump to the bottom of the reactor vessel, probably melt through the reactor vessel onto the containment floor. It’s likely to spread as a molten pool—like lava—to the edge of the steel shell, and melt through. That would result in a containment failure in a matter of less than a day.”
The SciAm article also links to a great 2007 piece Nuclear Mishap or Meltdown? A Matter of Degree, which is helpful in understanding the scale used to evaluate accidents.
The comments on this piece are highly contentious. A commenter listed as Rod Adams has a snarky comment taking issue with the experts consulted:
Interesting choice of experts – a computer modeler and a lawyer whose primary claim to nuclear knowledge is that he was chosen via a political process to be a member of the Nuclear Regulatory Commission. While a commissioner, he was part of the team that spread a great deal of confusion in the aftermath of Three Mile Island because he did not really understand the technology, the chemistry or the physics of what was unfolding.
Adams then blathers some nuclear-industry apologism of the that we’re going to be hearing a lot over the next few weeks. Turns out he’s the proprietor of what appears to be a nuclear power startup, Adams Atomic Engines. Also, here’s his pro-nuclear podcast, and his Twitter account.
I find Adams’ arrogance and abrasive manner irritating in this context; he seems insensitive to peoples’ fears, like a cranky geezer hurling insults at a grandson for being afraid to jump in the deep end. But I got a lot out of his article on his own blog about “the accident consequences from an operator’s perspective.” Remain aware of the source, but also remember that the only people who really know a damn thing about nuclear power are people who work in the industry. They are, generally, advocates, which is one of the reason anti-nuclear information is so often full of misinformation.
Among the many good points Adams makes is that many people in the United States are obsessing about their own safety and the safety of their loved ones, well out of scale with their risk. A very bad end to this saga will have very bad effects for the environment; it’s not good news and it shouldn’t be swept under the rug by nuclear industry apologists. But there aren’t going to be mass deaths in North America.
People are scared of nuclear reactors because nuclear reactions are scary. They seem to violate what we know about the world, which is why you need science to understand them. But science does understand them, so I hope people will let science guide them, not fear.
Adams also links to one last helpful document: a PDF of a 2002 Science article on nuclear reactors as potential terrorist targets.