Tuesday, April 24, 2012

How Can This Be Even Close To True?

I will not pretend to have the least knowledge of the mechanics of removal of radionuclides from the environment. However, looking at these government projections of radiation exposure potentials in Fukushima over the next 10 years, I found myself baffled.

For a larger view, click on image.

Are these maps not wildly optimistic? Cesium 134 admittedly has a half-life of two years. Cesium 137, however, has a half-life of 30 years. Strontium-90, which has an affinity for deposition in human bones, has a half-life of 29 years.

The most dramatic illustrations of the radiation levels post-disaster are the government maps we have seen of radioactive dispersal based on aerial surveillance of radiation emissions of deposited cesium 134 and 137. The maps for the deposition of the two isotopes are indeed seperated: See Annex 3 of this government report for Cesium 134 and Annex 4 for Cesium 137 (Link). Both show nearly identical hot areas.

Even given heavy rains as a flushing element, would not the virtually all of the Cesium 137 and Strontium-90 still be in the ground 10 years hence?

Well, yes, but what that means in terms of radiation exposure is another matter.

The significant image is not the radiation fallout map but Figure 2 on page 22 of The Final Report of the International Commision of on the Remediation of Large Contaminated Areas Off-Site the Fukushima Daichi NPP. According to the report, Cesium 134 and 137 were released in equal amounts by the multiple explosions at the Fukushima Dai'ichi nuclear power plants. As Figure 2 shows, due to its shorter half-life, decay of Cesium 134 is currently producing more than 70% of the radiation measured. In 10 years, the level of radiation coming from Cesium 134 decay will be 1/32nd the level of today, meaning that virtually all the measurable radiation will be coming from the decay of Cesium 137. Due to Cesium 137's long half-life, however, the number of decays per hour will be significantly lower than are measured at present. In ten year's time, the number of decays will be 1/5th of the amounts currently measured.

For a larger view, click on image.

So as the maps indicate, large areas that are currently uninhabitable could become habitable, at least in so far as scientists can guess regarding the safety of areas with levels of radionuclides emitting radiation at high doses. To what extent radiation at low doses can be considered acceptable for human habitation, nobody really knows.

Image Courtesy: The Asahi Shimbun Asia & Japan Watch

1 comment:

Andrew S. Mooney said...

It seems a bit optimistic to imagine anyone would want to move back there to test the theory, but some issues upon why radionuclide half lives are not the whole story include the following.

Strontium is chemically like calcium, but accumulation in bones is not just about humans - Wild animals have bones and they acquire it as well. When they die, their bones are in the environment but the strontium is chemically "locked up" and buried away. Rats, fieldmice, badgers, dead birds, bears and fishbones do add up to quite a lot of biological matter.


Cesium is a bit harder, but as this site notes, you can regulate the cesium content of your body by ensuring that your potassium is kept correct.

So, for most people it will probably be a case of eating bananas and not worrying about it. Except that they have elevated levels of Potassium 40....So don't blame me if you get cancer that way...