There are continuous references to “meltdown”, “Three Mile Island” and “Chernobyl”. Its worth looking at these to see what is really behind the references.
Meltdown occurs if the reactor core gets too hot and the tubes containing the fuel melt. The tubes melt at a significantly lower temperature than the fuel, which is essentially a ceramic material. These reactors, and in fact all reactors which are susceptible to meltdown, which isn’t all reactor designs, are designed to cope with meltdown and safely contain the the fuel and radioactive by-products. The main reasons why meltdown is to be avoided are political (you lost control…) and practical (it takes much longer to clean up and get the reactor back into production). In terms of safety and radiation release, it makes no difference.
Three Mile Island was a nuclear generation plant in the USA. It suffered a coolant problem and a partial meltdown. If coolant is lost, meltdown is pretty much guaranteed to occur. As with the Japanese reactors, the Three Mile Island reactor was shut down successfully. That means no new radioactive products are being created, but the old ones take time to decay, that is why the reactor remains hot, and needs cooling long after the nuclear reaction has been shut down. To stop meltdown coolant needs to be used. Basically water. The problem is, its no longer a closed system, so water (steam) escapes, and carries some of the radioactive byproducts with it. This is the “radiation leak”. The Three Mile Island event releases some very small amount of radiation. No-one died, and despite looking really hard, no-one has been able to definitively produce evidence of any long-term effects on anyone. Three Mile Island was effectively a harmless event blown out of proportion by grandstanding politicians, anti-nuclear activists and the media.
Chernobyl was a different case. The reactor design, as with a lot of soviet Russian technology, was rather poor. It was also poorly managed. The meltdown at Chernoblyl occurred while the reactor was at full power, because no-one noticed the problems and shut it down as in Japan and Three Mile Island. It had a graphite core, and the heat caused the graphite to catch fire. The resulting explosion blew the containment systems to pieces. With containment breached and the reactor at full power, there was a significant amount of radioactive material released. Emergency service were not alerted to the radiation danger (basically radioactive particles in the smoke) and 237 people became sick through radiation exposure. 31 of these people died within the three months following the disaster. Over seven years, a total of 216 people died (no-cancer deaths). Because the area was evacuated, many deaths were prevented. Within Russia and beyond the effects of the radioactive fallout was discernible only statistically, looking for increases in types of damage (principally thyroid cancer) associated with this sort of exposure. It is worth mentioning that the successful treatment rate for thyroid cancer is 96%, so in total it is estimated that 15 people died of thyroid cancer induced by radioactive fallout from Chernobyl. Most of these cases were in Belarus, which did not provide citizens with potassium iodide. Other countries which did so saw many fewer instances of thyroid cancer.
So what about Japan? Is it worth worrying about, and what can you do about it?
First, no matter what comparisons are drawn in the media it is worth remembering that this has virtually zero in common with Chernobyl. The reactors are shut down, they are cooling off (in temperature and radiation) all the time. Comparisons with Three Mile Island are meaningless, because that was, in practical terms, a non-event.
It is worth looking in a little detail some background information.
On radiation: There are basically three forms of ionizing radiation; gamma rays, which are purely electromagnetic. In sufficient concentration and at high enough energy they can be damaging. However, its worth remembering that we are constantly being bombarded with gamma radiation from natural materials in the rocks around us and by cosmic rays from space which are essentially the same thing. Most pass right through us with no effect. Next there is beta radiation, which are actual particles, and can do more physical damage. Beta particles are electrons from decaying atoms. They only penetrate skin (and other organs) for a few mm at most. Lastly, there are alpha particles. These are comparatively huge, being part of the atom nucleus and so tend to penetrate even less. A sheet of paper will stop most of them.
The real damage occurs when particles that emit alpha and beta particles are absorbed by the body and concentrated in one place. The classic example is that iodine accumulates in the thyroid gland, so picking up radioactive iodine the body will tend to concentrate it, and its beta particles will damage the tissue in the thyroid, which can lead to thyroid cancer.
The main (radioactive) byproducts of uranium fission are iodine-131, and cesium-137. Cesium is water soluble, and so easily absorbed by the body. However, it doesn’t concentrate anywhere. It is also eliminated from the body fairly quickly. Except in large and continuous doses it is not something to be too concerned about. For larger exposure, Prussian Blue can be administered which binds tightly with it, and is eliminated by the body even more quickly.
Iodine-131 is a bigger concern because of the body’s tendency to concentrate it. However, it also dissipates much more quickly (about 8 days half-life — meaning it loses half of its radioactivity every 8 days, as opposed to ~30 years for cesium).
If the winds take 8 to 10 days to blow radioactive iodine from Japan to the West coast of the US, it has already decreased by more than half.
Accumulation in the thyroid can be blocked by administering potassium iodide, which “fills” the thyroid with iodine, so the iodine-131 does not concentrate there.
Is it worth taking potassium iodide?
Maybe. If there is a much more significant amount of iodine-131 particles around. However keep the following in mind:
- Iodine-131 induced thyroid cancer is practically non-existent in adults. It affects children and adolescents much more.
- A fairly significant proportion of the population can have adverse reactions to potassium iodide.
- It tastes awful.
- Thyroid cancer is very treatable.