Decontamination work is accelerating in Fukushima City but a huge task remains with over 100,000 homes still to be treated.Workers decontaminate a house in Fukushima City (Image: WNN)
The capital of the prefecture, Fukushima City lies 65 kilometres from the Fukushima Daiichi nuclear power plant that suffered a major accident caused by the earthquake and tsunami of 11 March 2011.
The city is not among the most affected by radioactive contamination, the 11 municipalities within about 30 kilometres of the plant that were evacuated and have seen only partial return. In those areas the national government is responsible for decontamination to reduce additional radiation dose to below 20 milliSievert per year (mSv/y) in the short term with an ultimate goal of 1 mSv/y.
Fukushima City is in a second category of 104 municipalities across eight prefectures from which nobody was evacuated and life continues as normal. City authorities and the prefectural government are in charge of cleaning up the caesium-137 released by the accident that has raised ambient doses by 5-10 mSv/y for the city's 290,000 inhabitants.
The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has said radiation at these levels cannot be scientifically linked to any effect on people's health. Nevertheless Japanese authorities are determined to clean up. Decontaminating children's facilities such as schools was the top priority and all 202 of these were tackled by August last year. By December last year, the city's 68 parks were also cleaned up and, by the end of May this year, all the municipality's 5700 hectares of farmland and orchard had been decontaminated. The total cost of this work was Y6.8 billion ($81 million).
Now the focus is on people's homes, with the goal of reducing additional dose to 1 mSv per year. This is primarily done by pressure-washing and wiping down the outside of people's homes, washing ornamental trees and removing a few centimetres of soil from their gardens.Contaminated soil is being held in an interim storage facility near Fukushima City
So far, about 4000 homes have been cleaned. One area saw dose rates of 7 mSv/y after the accident drop to 2 mSv/y after clean-up. The last remaining stage of work there is to clean the roads and gutters, which may yield a further reduction to 1 mSv/y or less. Methods have been fine-tuned with the use of warm water and certain detergents. Run-off water is treated in drains with zeolite that absorbs the caesium and allows the water to be processed in the normal way.
The clean-up team deals with about ten homes per day, but all 110,000 homes in the city are to be cleaned so the work rate must improve in order to finish on schedule in the next five years. In total this will cost around Y31 billion ($370 million).
There is an equally pressing waste management issue, due to the half-tonne of contaminated soil that arises from each home on average. At the same time, many tonnes of soil have been removed from the sides of roads, where it absorbed caesium washed out by rain. Fukushima City currently has only one temporary storage site for all this, with capacity to hold 500,000 tonnes of soil. Each municipality will have to create something similar to store a grand total of 1 to 1.2 million tonnes of soil. Next in the national government's plan is to create a single interim store for all the soil from every municipality - in just three years' time.
Researched and written
by World Nuclear News