Sunday 9 June 2013

Decontamination: is it necessary?

Decontamination work has become a common sight in Koriyama. First they did all the schools in the city, then the parks in the central area and the houses in the hotspot of Ikenodai. Now houses and parks in the east and north of the city are being cleaned up. Over 3,000 houses done out of 49,000 planned. 

The aim is to bring airborne radiation levels down to 1 mSv/year. By some convoluted logic - spending 8 hours every day outside and 16 hours inside in a wooden house - this was translated into 0.23 μSv/hour which became the magic figure that airborne radiation had to be reduced to. But recent information released by the government and by UNSCEAR seems to be calling these assumptions into question. 

You've heard me talk about Genyu Sokyu, Zen priest and novelist. He does a 5 minute spot once a week on local radio and last week he was talking about a paper produced by the Cabinet Office entitled 'Regarding Annual Levels of 20 mSv'.  (年間20ミリシーベルトの基準について)
If you can read Japanese it's worth a look. The message seems to be that Fukushima is nothing like as serious as Chernobyl (only one sixth of the emissions over an area one sixth the size), that excessively strict levels of evacuation (5 mSv/year at Chernobyl since 1991) cause too much distress, and that estimates and actual exposure are not the same.

For example, Koriyama citizens were estimated to have been exposed to an average of 5.5 mSv/year but most of the 25,500 children and pregnant women who were issued with 'glass badges' to measure accumulated exposure were found to have an actual exposure of 1.0 to 2.1 or less. Airborne levels don't necessarily match individual results.

This is exactly what the Mayor of Date (pronounced Datty, population 65,000) says. He thinks it's unrealistic to decontaminate. What matters is how much each individual has been exposed to. He's issued all those in his borough with glass badges. They get collected from time to time, the data is analysed, and if anyone has a problem they will get advice.

The Fukushima Prefecture radiation map these days, in an attempt to show that things here are not that bad, has levels for the rest of the country in a banner alongside and there's a map of Japan (blue box bottom left) and world map (yellow box bottom right).

On the last page of the above Cabinet Office paper there's a table of radiation levels according to distribution of population. The levels are for external and internal exposure combined but according to this report (UNSCEAR, 2000), 48% of the population of Japan lived in areas with less than 1.5 mSv/year and 52% in areas from 1.5 mSv to 3.0 mSv/year! Which, if you go by current standards for decontamination, means that you'd have to clean all the areas where over half the Japanese population live! In Hong Kong 85% of the population live in areas 1.5 to 3.0 mSv/year and the rest in areas with higher radiation! Nowhere in Hong Kong is below 1.5 mSv/year!

The highly contaminated areas around Fukushima Daiichi obviously need to be cleaned up but is the huge expense of decontaminating areas like Koriyama justified? Surely there are better things to spend the money on?

By the way, if you can understand Japanese it's worth listening to Genyu san's talks. He has a wonderfully comforting voice. (Podcasts on Radio Fukushima)
Bye for now 

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