Fukushima Burning: Anatomy of a Nuclear Disaster via Japan Focus

The May/June edition of Australian magazine Physician Life features a lengthy report on the Fukushima crisis by Melbourne-based nuclear radiologist Dr. Peter Karamoskos.

In the piece, Karamoskos poses and answers key questions for understanding what has taken place at Fukushima and what the likely public health effects will be.

What happens when a nuclear reactor overheats?

When nuclear cores overheat due to a lack of water coolant, they ultimately melt. Remaining water quickly turns to steam preventing replenishment of the water and endangering the integrity of the pressure vessel. Furthermore, the reactor pressure vessel may also melt leaking the melted fuel which may escape into the environment if the primary and secondary containment structures (concrete) have been damaged. Spent fuel is kept at around 25 degrees in cooling ponds for a few decades. The water must be continually replenished to maintain this temperature. If there is a loss of water or a failure of replenishment, the spent fuel will overheat and catch fire, releasing its radiotoxic contents. Note that the longer fuel is irradiated in the reactor core, the more radioactive it becomes due to the build-up of fission by-products which also contaminate the fuel limiting its usable life. Only about 1-2% of the uranium in fuel rods is actually used up in a reactor. It is these fission by-products that pose the greatest immediate danger if released into the environment.

Radioactive fallout and its health effects

Radioactive fallout from a nuclear reactor can be considered in two groups: isotopes of the noble gases (xenon, krypton-133) are radioactive elements with a very low chemical reactivity, relatively short half-lives, are not retained by the body and they remain and become dispersed in the air without ground deposition. Hence they have limited adverse health potential. The second and more dangerous radioactive fallout group is represented by mainly the radioactive isotopes of iodine, cesium, and tellurium. These elements form fine suspended particles in the air (aerosols), which due to their weight will gradually end up falling on the ground when released into the air, contaminating all vegetation, clothing and any other surfaces including water sources. Those that pose the greatest health threat are Cesium-137 (half-life 30 years) and Iodine-131 (half- life 8 days). Iodine-131 is a beta emitter and is absorbed into the blood stream through inhalation and ingestion and concentrated by the thyroid gland where it is highly carcinogenic, predominantly in young people under 18 years of age. Cesium is a gamma and beta emitter. It is also absorbed by the body through the respiratory and gastrointestinal tracts and subsequently into the bloodstream and deposited throughout the body. Cesium takes between 10 days and 100 days for half of it to be excreted from the body so there is significant hazard once it is absorbed. Unlike I-131 therefore which loses most of its potential for harm in a few months, cesium remains hazardous in the environment for several hundred years.

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