Extreme soil contamination detected near Fukushima plant

August 30, 2011

Extreme levels of radiation have been detected in soil within 40 kilometers of the quake-stricken Fukushima No. 1 nuclear power plant, the science ministry said.

The finding emerged in a map published Aug. 29 that for the first time shows contamination levels of areas within a 100-km radius of the plant.

One location in the town of Okuma had the highest value at about 30 million becquerels of cesium of all types per square meter.

About 8 percent of the measured areas recorded more than 555,000 becquerels, the figure that required forcible relocation by residents in the 1986 Chernobyl nuclear incident.

The measurements were taken June 6 to June 14, about three months after the Great East Japan Earthquake, by 780 members of 129 universities and specialized organizations from around the nation. Soil samples were collected from about 2,200 locations to identify the concentration levels of radioactive cesium. The results will serve as a basis for information used in reviewing decontamination projects, evacuation areas and other quake-related efforts.

The map shows that areas with high radiation levels are concentrated in a zone to the northwest of the plant within a 40-km radius of the facility.

Many of the areas with such high levels are within the no-entry zone and the planned evacuation zone, but those levels were also detected outside of the zones in parts of Fukushima, Motomiya and Koriyama cities. The no-entry zone is within a 20-km radius area of the plant, while the planned evacuation zone is an area that could see more than 20 millisieverts of accumulated radiation in a year after the March 11 onset of the plant's crisis.

The radiation map for the Chernobyl accident was completed three years after the incident.

Soil samples were collected for each 2-square-km area within an 80-km radius of the plant. Samples were also collected from each 10-square-km area within an 80- to 100-km radius of the facility. The number of sample locations total five for each radius zone. The sample was drawn from the soil 5 centimeters from the surface. The concentration levels of cesium-134 and cesium-137-the half-life periods of which are two years and 30 years, respectively-were estimated as of June 14 in this project.

The Ministry of Agriculture, Forestry and Fisheries on Aug. 29 also compiled a radiation map for agricultural fields, which was drawn by measuring radiation levels at 579 sites in the prefectures of Fukushima, Miyagi, Ibaraki, Tochigi, Gunma and Chiba. Of the 579 sites, radiation levels above safety standards-which prohibit rice planting-were detected at 40 locations in Fukushima Prefecture. Areas showing levels exceeding safety standards are estimated at 8,300 hectares.

The Fukushima prefectural government on the same day released the results of the first measurements of radiation levels of rice paddies in the no-entry zone. The government found levels above safety standards at 20 locations out of the 89 sites examined in areas near the plant, including the no-entry zone and the planned evacuation zone.

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