Japan predicts radiation spread

Japan’s Ministry of Education, Culture, Sports, Science and Technology (MEXT) has released a map of the projected accumulated radiation dose rate in the air through March 11, 2012.

The map was produced by Japanese government nuclear department MEXT, and is reprinted from the Asahi Shimbun newspaper

It has also released results of the measurements of radionuclide concentrations in the soil within the 20-km evacuation zone, according to a report from the Japanese Atomic Industrial Forum.

To estimate the radiation dose rate in the air for a one-year period, MEXT used the method adopted by the Nuclear Safety Commission (NSC) of Japan: namely, the exposure dose rate measured outdoors, multiplied by 0.6. That figure assumes that indoor exposure (in a wooden house) is 40% less than outdoor exposure, and that 16 hours is spent indoors each day and eight hours outdoors. The current dose rates were assumed to continue for a year. The distribution of radioactivity, wind direction and weather conditions on March 17 greatly affected the map, JAIF said.

Soil was sampled from the surface to 5cm deep on April 2. In the Yamada district of Futaba Town, about 4km WNW of the Fukushima Daiichi Nuclear Power Station (NPS), the readings were 990,000Bq/kg of I-131, 370,000 Bq/kg of Cs-134, and 380,000Bq/kg of Cs-137. In the Fusawa district of Okuma Town, about 2km WSW of the plant, the readings were 1,000,000Bq/kg of I-131; 120,000Bq/kg of Cs-134, and 120,000Bq/kg of Cs-137, JAIF said.

MEXT will shortly release a soil map with additional measuring points.

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