The US’s Severe Assessment of Radiation Contamination in Japan: ずくなしの冷や水


The US’s Severe Assessment of Radiation Contamination in Japan

April 24th, 2013

The information that was posted on Kota Kinoshita’s blog on April 24th gave me yet another shock. It came from a wife of an American civil servant.

The article said:
- In 2012, a US army personnel was going to be posted to work in Japan. He was going to move into the compound for embassy staff in Roppongi (Tokyo) with his family. However, his posting had to be cancelled at the last minute as he was told that the radiation dose was too high in the area of Akasaka and Roppongi for someone with children to move there.
- - He was told that the entire duct system and the air filters of the houses in the compound had been renewed yet he couldn’t be guaranteed that there wouldn’t be any health issue with his family.
- - A different civil servant who returned to the US from Japan in 2011 had to get rid of all his removal goods because radiation measured inside the removal container was over the legal limit.
I don’t think that the living environment in the compound for the American embassy staff should be any more vulnerable to radiation than the Japanese houses. Even if the houses are designed so that tenants can keep their American style of living, in terms of radiation there shouldn’t be any difference. What’s striking is that they are taking the risk so seriously.

And these are not the only cases where the US is taking serious measures:
1. In Yokosuka Naval Base on March 15th families of personnel started moving back to their country as the air dose rate rose and buildings in the Yokosuka Base were being sealed off by tapes from outside air, as mentioned in my article of July that year.

2. The troops that were placed in Atsugi Base were moved to Guam. Aircraft were also seen flying off south at the Yokota Base on March 15th by residents of the area. March 15th was when the air dose rate started rising sharply. See the table below for the air dose rates at Yokota Base in the early morning of March 15th (converted into Sv by myself).

測定場所 place of measurement 横田基地 Yokota Base

3. On March 21st 2011, at around 13:10 the nuclear powered aircraft carrier USS George Washington was ordered to leave its homeport Yokosuka Naval Base.

4. On the same day, the headquarters of the US Navy said that they had detected small amounts of radioactive matter in Yokosuka and Atsugi Bases and gave orders to the Navy personnel, their dependents and other staff in the bases not to go outside.

The food and drinks for workers at the US Army and other US institutions are carried in by air from their home country. The risk of internal contamination by radiation should therefore be significantly smaller than using food and drinks from Japan. The situation for the US civil servants was much better than the Japanese and still they did all that.

The case of the US Army service member who had to dispose of all his removal belongings coming back from Japan in 2011 because of high contamination was also shocking. It is not clear how much of which nuclides were found, but considering the relatively short half-life of the iodine and the easiness of detecting the cesium, I assume that the contamination detected once back home involved other radionuclides than the two mentioned before, ones that need specific detectors. That means that they must have been alpha or beta nuclides. I strongly suspect Strontium 89 with its 50 days half-life. It must have emitted strong radiation after the accident.

Oh Dear…considering all these measurements that the US took against radiation risk I am obliged to think that perhaps my estimation of possible health deterioration was too optimistic.

I went back to some data to compare. You can see the amount of Iodine 131 detected at Yokota Base in the following chart. On March 21st 2011 at 2:45:00 PM there was 16.4 Bq/m3 in the air.

I’d been thinking that as far as Tokyo was concerned the plume of March 21st hit the eastern part of Tokyo but it seems like that was a mistake. The plume that was covering Tokyo and Kanagawa prefecture at this point must have been fairly dense in radioactivity.

The readings that the US had are in line with the readings of the CTBT radionuclide observatory station in Takasaki (below) so should be considered reliable. Like in the US survey, peaks were observed at the end of March and in the second half of April, which coincides with the observation of CTBT.

So then I had a look at the amount of gross beta particles in Akasaka, Tokyo, measured at the US embassy and found out that there was as much as about 3600 Bq detected at 1 pm on March 23rd.

東京都港区赤坂一丁目 Akasaka, Minato-ku, Tokyo

However, according to the simulation by the Meteorological Research Institute, the plume that was hitting Tokyo from the day before went back and forth between inland and the sea but doesn’t seem to have covered the area of Akasaka that densely.

So then my question was: Why do we get such a time lag? What I can assume is that from March 15th onwards, the sky of Tokyo was hit by several waves of plumes and as a result the air was generally covered by radioactive gas and particles, with higher densities where there were waves. And it was probably those dense parts that were blown down to the ground by wind or downward currents that were caught by the detectors.

If this is true then those who happened to be there when the current brought down the dense plume were surrounded and strongly irradiated by beta sources. That might explain why there would be some that are more irradiated than others.

This thought might also explain why in some places of Tokyo extremely high amounts of radioactive soil samples are found. According to the article of November 22nd 2011 by the newspaper Asahi Shimbun the soil sample that a group of citizens took from the shrubbery in front of the Ministry of Economy, Trade and Industry contained 48 Bq of strontium and 31.233 Bq of strontium.

All in all, it is undeniable that the contamination in Tokyo is high. The risk assessment of the US is a proof of that.

posted by ZUKUNASHI at 15:52| Comment(0) | 福島原発事故
お名前: [必須入力]

メールアドレス: [必須入力]


コメント: [必須入力]