The central government will be responsible for decontaminating about 13,000 square kilometers across eight prefectures, or about 3 percent of Japan's total landmass, under new standards for cleaning up radiation from the Fukushima No. 1 nuclear power plant, according to Asahi Shimbun estimates.
The central government will be responsible for decontaminating about 13,000 square kilometers across eight prefectures, or about 3 percent of Japan's total landmass, under new standards for cleaning up radiation from the Fukushima No. 1 nuclear power plant, according to Asahi Shimbun estimates.
The Environment Ministry on Oct. 10 endorsed a basic policy to make the government responsible for decontaminating all areas with radiation levels exceeding 1 millisievert per year.
Based on an earlier annual threshold of 5 millisieverts, the ministry initially said about 1,800 square km of land in Fukushima Prefecture would be subject to decontamination. But under the new standard, the size of the area will grow sevenfold.
Using airborne radiation measurements by the science ministry, the Environment Ministry drew up maps of regions where additional exposure to radiation due to the nuclear accident lies between 1 and 5 millisieverts annually.
The Asahi Shimbun studied the measurements of the affected areas in Fukushima Prefecture as of Aug. 28 and outside the prefecture as of Sept. 18.
The calculation found that about 6,200 square km in Fukushima Prefecture had radiation levels between 1 and 5 millisieverts per year, in addition to the estimated 1,800 square km above 5 millisieverts annually.
In total, about 8,000 square km, or 60 percent of the landmass of Fukushima Prefecture (13,782 square km), will be eligible for decontamination under the new standard.
There were no areas outside Fukushima Prefecture with radiation levels exceeding 5 millisieverts per year.
But the following had annual exposure levels between 1 and 5 millisieverts: 2,100 square km in Gunma Prefecture; 1,700 square km in Tochigi Prefecture; 440 square km each in Miyagi and Ibaraki prefectures; 180 square km in Chiba Prefecture; and 20 square km each in Tokyo and Saitama Prefecture.
The maps do not reflect "hot spots," or localized spots of high radiation levels.
The science ministry is conducting airborne measurements in 22 prefectures. The results for Iwate, Niigata, Nagano and other prefectures have yet to be released, so the total area with radiation levels above 1 millisievert per year could expand.
The costs for the cleanup could also grow.
In late September, the Environment Ministry said that full decontamination in areas above 5 millisieverts per year and partial decontamination for areas between 1 and 5 millisieverts would involve removing about 29 million cubic meters of surface soil and fallen leaves in forests.
It predicted the decontamination measures would cost the central government about 1.2 trillion yen ($15.6 billion).
Following protests by local governments, however, the ministry decided that the central government would assume responsibility for decontaminating all areas above 1 millisievert per year. That basic policy plan was accepted by an expert panel on radioactive contamination on Oct. 10.
(This article was written by Hiroshi Ishizuka and Harufumi Mori.)