Fukushima contamination is much less extensive than Chernobyl

March 14, 2012

The spread of serious soil contamination from the crippled Fukushima No. 1 nuclear power plant was eight times less than that from the 1986 Chernobyl disaster, according to the science ministry.

Soil analysis at 2,200 locations within a 100-kilometer radius of the Fukushima plant since June found that cesium-137 contamination in excess of 1,480,000 becquerels per square meter was significantly less extensive than at Chernobyl. The farthest point, in Namie, Fukushima Prefecture, was 32.5 km from the nuclear plant.

The Ministry of Education, Culture, Sports, Science and Technology released its findings March 13.

Such high-level contamination was found about 250 km from the Chernobyl plant, about 8 times the maximum reach in the Fukushima case, and was exceeded in large parts of the area lying within a 30-km radius of the Soviet plant. If transposed onto a map of Japan, 250 km would extend to the border between Gunma and Nagano prefectures, ministry officials said.

In the Fukushima case, cesium-137 concentrations exceeding 1,480,000 becquerels per square meter were confirmed at only 34 locations, most of them in a belt-like zone extending northwest from the Fukushima No. 1 plant.

The furthest location with cesium-137 soil contamination in excess of 30,000 becquerels per square meter was the Gunma-Nagano prefectural border, about 250 km from the Fukushima plant. After Chernobyl, concentrations exceeding 40,000 becquerels per square meter were found in Norway, 1,700 km from the stricken plant. That is equivalent to finding such high-level contamination in Okinawa Prefecture.

Following the Chernobyl crisis, people were evacuated forcibly from areas with cesium-137 contamination in excess of 555,000 becquerels per square meter. Cesium-137 has a half-life of 30 years.

Meanwhile, the maximum strontium-90 concentration in Fukushima was 5,700 becquerels per square meter at a distance of 4.9 km from the Fukushima No. 1 plant. The maximum combined plutonium-239 and plutonium-240 concentrations were 15 becquerels per square meter at a distance of 18 km from the nuclear plant.

At Chernobyl, strontium-90 concentrations exceeding 111,000 becquerels per square meter and plutonium-239 and -240 concentrations exceeding 3,700 becquerels per square meter were detected in many areas within a 30-km radius of the plant.

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