The Automatic Earth: March 15 2011: The Fukushima Fallout Files

The Automatic Earth: March 15 2011: The Fukushima Fallout Files



selected passages from the article:
The health damage from exposure to radioactive isotopes comes from the energy they release as they decay from unstable forms to stable ones. Each isotope has a specific decay path over a specific timeframe, defined by the half-life of the element. The half-life is the time it takes for quantity of material to be halved, halved again and so on. A short half life indicates a shorter term risk, as the material will release its decay energy over a short time. In contrast, materials with a long half life will be persistent in the environment.

The health effects will depend on how the particular isotope is taken up in the body, what form the release of its decay energy takes, and what is the residence time of the isotope within the body. Isotopes can decay by releasing alpha, beta or gamma radiation. Alpha radiation is composed of helium nuclei (2 protons and 2 neutrons). These are large and energetic and therefore potentially very damaging), but do not penetrate far. Beta radiation is composed of fast moving electrons, and gamma radiation is composed of photons (light particles). Beta and gamma radiation penetrate to a much greater extent.

The radioactive material of most concern in the initial stages of a nuclear accident is iodine 131, a major fission product which was responsible for the majority of health effects seen so far in the Chernobyl area. Iodine 131 has a half life of only 8 days, so it is of most concern early on. It is taken up by the thyroid gland where it can be retained (especially in young children), greatly raising the risk of thyroid cancer. Taking potassium iodide tablets can protect the thyroid from taking up the radioactive isotope. People in the affected area should be given this option as a preventative measure.

Other isotopes of concern include Caesium 137, with a half life of 30 years, and strontium 90, with a half life of 29 years. Unlike iodine 131, both of these isotopes are persistent in a contaminated area. Caesium 137 is taken up by the body in place of potassium, while strontium 90 is taken up in place of calcium. Caesium accumulates primarily in muscles and organs, while strontium accumulates in bones. The risk is organ damage, leukaemia and bone cancer, depending on the dose. At Chernobyl, caesium 137 appears to have represented a much larger health risk than strontium 90.

Some units at Fukushima ran on MOX fuel (mixed oxide fuel), which would contain a quantity of plutonium 239. Plutonium 239 is an alpha-emitter with a half-life of some 24,000 years. If inhaled or ingested, alpha particles can affect the lungs or digestive system at close range. Explosions at sites where containment is impaired or destroyed are a major risk factor for inhalation of radioactive particles.

It is important to note that the distribution and level of radioactive contamination from the Fukushima disaster is likely to be very much less than at Chernobyl, as boiling water reactors (BWRs) like those at Fukushima do not have the potential for the same failure mode as occurred at the Chernobyl RBMK plant. Chernobyl suffered a nuclear explosion on an abrupt power surge aggravated by a moderator fire.