Radiation Dose Estimates according to the US Department of Defense: ずくなしの冷や水


Radiation Dose Estimates according to the US Department of Defense

June 20th, 2014

The Unites States Department of Defense (USDD) has uploaded a report on radiation dose estimates for American civil servants that were in Japan at the time of the Fukushima Daiichi nuclear plant accident.

Operation Tomodachi Registry

a summarised table of radiation dose estimates for all locations and all age groups

According to the USDD the estimates were calculated based on the assumption that one spent “24 hours outdoors, having a constantly high physical activity level and associated breathing rates, and being exposed to the radiation measured in the air, water and soil over the entire 60- day period” from March 12th to May 11th 2011.

Let’s have a look at the adult estimated radiation dose. The left axis is for the thyroid dose estimates and the right axis for the whole-body estimates. N.B. the scale for the right axis is a tenth of the left.

Estimated Radiation Dose for Adults

The second chart gives the estimated radiation dose for non-adults. Here I typically used the case of Hyakuri Air Base but the trend is followed more or less at all locations of the survey. The unit used here is mSv.

The thyroid radiation dose is highest in the age group of 1-2 yrs and then declines in the order of 0-1 yr, 2-7 yrs, 7-12 yrs, 12-17 yrs. The adults’ estimate is more or less the equivalent of that of the 12-17 year olds. As I mentioned before, this trend can be observed at the other locations of the survey. The whole-body radiation doses follow the same pattern as well.

We know from independent reports that at Yokosuka Naval Base measures were taken to insulate the houses from the outside air. In the Atsugi Base families were evacuated from March 17th onwards. On March 21st the aircraft carrier George Washington left Yokosuka as an emergency reaction. However, in Hyakuri, Oyama and Sendai the adult estimated dose rates for the thyroid are even higher than in the before-mentioned bases around Tokyo (4 mSv) with Sendai being the highest (12 mSv). If you include the children, you get the exceptionally high measure of 27 mSv for the 1-2 year olds of Hyakuri Air Base.

The Hyakuri Air Base is a highly contaminated zone. On March 15th and 21st, a radioactive plume passed the nearby city of Hokota.

The following graph that shows the estimated thyroid radiation dose of all the age groups (in mSv) stresses the exceptionally high dose rate for Hyakuri as well.

Thyroid Radiation Dose, All Age Groups

Personally I have doubts about how accurately a radiation dose expressed in Sv can reflect the damage done to the human body. Sv is used to indicate how an object heats up by receiving energy from a radioactive source. It does not indicate the damage that was caused in human cells, their DNA and tissues. Strontium, cesium or radioactive iodine each act differently in the human body and hence have different effects on the organs. I therefore think that it is difficult to predict the scale of health damage simply using figures in Sv.

However, some experts say that concerning the thyroid its dysfunctions occur in proportion to the received radiation dose. If this is true, considering the high radiation dose of the toddlers in the Hyakuri Air Base, I fear that the health deterioration might become very serious there. The toddlers in Hyakuri received more than twice the radiation dose the toddlers in Tokyo or Yokosuka did, places where the radiation dose was considered too high for American civil servants to stay. This thought breaks my heart.

In Japan there has been little information available on the air dose rate of Sendai and when there is, the dose rates are relatively low. Compared to those figures, the thyroid estimates of the USDD for Sendai seems disproportionately high.

A US sailor has filed a lawsuit against Tepco along with 71 other sailors of the Operation Tomodachi. The health damage that he has been suffering from as a result of his mission measuring the contamination at Sendai airport (Natori city and Iwanuma city) doesn’t seem to match the relatively low air dose rate of the city of Sendai published by the Tohoku University.

There is too little information on Internet about the rural areas and it has therefore been difficult for me to grasp the state of health deterioration there but looking at the adult thyroid estimates one can only predict at least as much, if not much more, health deterioration than in Tokyo for Oyama and Sendai.

I presume that the USDD mainly used the raw readings of radioactive iodine to calculate the thyroid estimates of each location. Cesium would have been taken into account as well, since it could cause thyroid dysfunction, yet I can imagine that they would have done it in a conservative way. On the other hand, the whole-body estimates would have been calculated based on the readings of gamma rays in general, like those of cesium, iodine and other nuclides. This assumption enables us to estimate the amount of radioactive iodine and gamma nuclides that the USDD had at each location.

It looks like the USDD applied the estimates of certain places to the nearby cities. So I did the same and created the following maps using their estimates.

posted by ZUKUNASHI at 19:53| Comment(0) | 福島原発事故
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