Wednesday, March 16, 2011

The nuclear crisis in Japan--How bad?

 Update (5/7/2011): Well, it doesn't seem nearly as bad as I hard feared here in the States, what since no major explosions of the reactor vessel or criticality events seem to have happened. The best website I have found for keeping track of the radiation somewhere in U.S. is run by this group of UC-Berkeley nuclear engineers . I probably will delete this post in a few weeks or months, since it is time sensitive and doesn't fit in with the other posts in my blog.

The nuclear crisis in Japan has the potential to be quite disastrous. With three reactors and apparently large quantities of spent fuel rods from six reactors vulnerable, there is more material that can evaporate, burn up, etc., and get into atmosphere than at Chernobyl. The good news is that there hasn't been any fission there for a week or so, and so the short-lived radioisotopes (those with a short half-life) shouldn't be very problematic as they were at Chernobyl. But for the greater public at large, Cesium-137, with its 30-year half-life, will be just as bad as ever, and that's typically a large part of the problem in these situations, anyway. And actually, if the fuel rods melt down, falling to the bottom of the reactor or pool, becoming a lava-like blob, there is no guarantee there will be no criticality created. It wouldn't be an especially explosive fission bomb type criticality, presumably, from what I have read it can't be (but I am not a nuclear expert), but does have the potential as in Chernobyl to create a sudden release of heat leading to somewhat explosive evaporation of nuclear material and steam. This is why they are adding boric acid, to absorb neutrons and discourage criticality. On the whole, I think the expected damage at this point is slightly worse than at Chernobyl. (I am not saying that there is greater than 50-50 chance it will be worse than Chernobyl, but it could be a lot worse than Chernobyl (while it can't be better than the problem it has already been), and so the expected damage is probably worse than Chernobyl. What will be the damage to those not exposed to acute radiation, and How can we estimate this from detected levels of radiation? As a mathematician who minored in physics, who has been gleaning the internet for relevant studies, etc., over past few days, I will throw in my observations, since such observations seem to be inconveniently lacking and hard to find.

Readings at Tokyo of external radiation levels are apparently (as of yesterday) at 0.8 microsieverts per hour, about 24 times normal. According to an article in the IAEA bulletin summarizing WHO findings, in areas of Europe fairly removed from Chernobyl about one-third of the damage to people from Chernobyl was caused by external radiation, about one-third from inhaled radio-isotopes and one-third from ingested radio-isotopes ("in areas of low deposition, all three pathways may
be of similar importance"). So the total effective dose equivalent can be guesstimated by multiplying the result on the radiation meters by three (and multiplying by the number of hours the radiation is received). What are the effects of 2.4 microsieverts per hour? A Rule of thumb I've seen in a couple articles (apparently from the International Commission on Radiological Protection) apparently is that one millisievert increases one's chances of dying from cancer by about 1 in 20,000. In other words, one microsievert increases one's chances by 1 in 20 million. So 2.4 microsieverts increases one's chances of dying from cancer by 1 in 20/2.4 million, i.e., about 1 in 8.3 million. Tokyo has a population of about 13 million. Thus, as a result of these radiation levels, assuming cancer treatment doesn't improve drastically in the next few decades, about every 40 minutes someone in Tokyo is going to be doomed to eventually die of a cancer which wouldn't have happened else. This hopefully can give an idea of the current seriousness of the present increased radiation levels, and how to estimate the seriousness from measured radiation levels should the situation change, and in particular if it gets worse, as I'm guessing it probably will. The workers at the reactor are a totally different situation, of course; if they are exposing themselves to external radiation of 400 millisieverts per hour, as some places near the reactor were emitting, after about 10 hours or so they can expect to die within a few weeks from having received that exposure. Indeed, LD-50 is between 2.5-5 Gy (or Sv, presumably, a technically better way of saying things, imho). They are indeed heroically risking their lives.

Let's look at America, now. The winds in the northern hemisphere at the latitudes of the U.S. and Japan are mostly from the west, and the jet stream is from the west as well. So America could get a good deal of fallout. If the situation ends up somewhat worse than Chernobyl, we may get, say, about half what Northern Italy got from Chernobyl. Estimates from the IAEA article linked to above are that people in Northern Italy received about one millisievert total effective dose equivalent (a little less for adults, a little more for children). So, a guess is that if the accident is somewhat worse than Chernobyl, we'll get about half a millisievert on average. That means an extra 1 in 40,00o risk of dying from cancer. Multiply by a population of about 300 million, and you get 7,5oo Americans dying from cancers they otherwise would not get. It won't be nearly as bad as in Japan, presumably, but it is certainly of significance even here.

Of course, there are other effects as well. Hereditable effects caused by genes mutating tend to be (according to this course lecture) an order of magnitude less than carcinogenic effects, but they last longer, from generation to generation, so that is something to consider (but being mostly ignorant about the matter there's nothing precise I can say about it), and also fetuses are very susceptible to abnormalities from radiation, the teratogenic effects supposedly being (according to same lecture) an order of magnitude worse, but pregnant females aren't as numerous as people at large. So perhaps the carcinogenic risk is the most of the risk. Also, there could be very long-lived isotopes of stuff like plutonium dispersed, having effects for millenia, but again I don't have a good idea of how to estimate that particular risk.

It's surprisingly lame that there are so few publicly available radiation detectors on the internet. The best network I can find for the U.S. is at Radiation Network , which one could use to compare radiation reading with normal readings. Another one is available at Online Ionizing Radiation Detectors . I haven't noticed any changes in those reading yet here in the States.