When the Japanese national government took over responsibility for decontamination of radiation affected areas in and around Fukushima, the initial plan was to decontaminate areas that had over 5 mSv/yr of radiation exposure a year, as determined by aerial survey. However, demands by local governments, based on residents' fear of radiation, have resulted in an expansion of the decontamination area to include any area of above 1 millisievert a year of radiation. This is a 7-fold increase in size, from 1,800 sq kilometers to 13,000 sq kilometers, and includes substantial areas outside of Fukushima itself. Considering that the cost of the first contamination plan was said to be 2.84 billion dollars, the final cost will be colossal indeed. Are they really going to spend 20 billion dollars on removing topsoil, hosing down buildings, and clearing away rubble?
But wait. Decontamination is good, right? It's necessary to ensure the safety of local residents, isn't it?
Well, let's look at 1 millisievert a year (1 mSv/yr) and compare it to other radiation exposures:
- 1.5 mSv/yr is the average natural background radiation of Australia.
- 1.5 mSv/yr is also the average natural background radiation level of Japan, according to a pamphlet on radiation released to schools last week by the Ministry of Education.
- 5 mSv/yr is an exposure typically received by aircrew.
- 50 mSv/yr is the natural background exposure in several parts of the world, places in India, Brazil, Iran, and Europe. Source
- 100 mSv/yr is so low that the risk to human health cannot be measured. Source
- 260 mSv/yr is the natural background level at Ramsar, in Iran, where radioactive spas are used for their beneficial health effects by locals and tourists, and where no increase in cancer has been measured. Source
