Friday, July 20, 2007

The Japan nuclear plant earthquake leak

Robert Merkel does the calculations on the leaks from the nuclear power plant in Japan and makes the point most media missed: the leak of water into the ocean wasn't anything. The media missed the much larger release into the atmosphere--nearly 300 million becquerels, or about 3000x times the amount of radioactive material. (A becquerel is one atom disintegrating per second). But looking only at the total amount of radioactivity doesn't tell the whole story. A release of the noble gas krypton-85, for instance, does not really accumulate in organisms in any way; while a release of iodine-131 would concentrate and damage your thyroid. Half-lifes and the particular radiation emitted is also important in consideration: the weak beta electrons (~18keV) from tritium decay is considered not as hazardous as a multi-MeV alpha particle from polonium-210.

The reprocessing of nuclear fuel rods in France releases huge amounts of krypton-85 into the air: 1.8 × 10^17 Bq in 1994 alone.

The 90,000 becquerels of whatever went into the ocean (I am guessing it was tritium) is actually not that much: your own body has about 4000Bq of potassium-40 and 3000Bq of carbon-14 in it; in addition, at least here, tritium is allowed to be diluted by large amounts of river water in Illinois.

The end result is the release wasn't a lot; it sounded like a lot from the numbers, but that's due to the definition of a Becquerel more than anything else. The reality is most people don't have much of an education on radioactivity, and this affects how they irrationally perceive a risk.

All of this is really just a minor detail though, when the real issue is any delay or hiding of release information, which according to the press is endemic in the Japanese nuclear industry.

UPDATE: I've found descriptions of the leaks here. The spent fuel pool water sloshed onto the floor and leaked out via cabling. The second leak, to the atmosphere, was iodine and radioactive dust from a main exhaust line.

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