After coming under fire, the Nuclear Safety Commission of Japan for the first time on Wednesday released predicted ranges of radiation exposure and radioactive materials from the Fukushima No. 1 nuclear power plant.
After coming under fire, the Nuclear Safety Commission of Japan for the first time on Wednesday released predicted ranges of radiation exposure and radioactive materials from the Fukushima No. 1 nuclear power plant.
The calculations were made using the System for Prediction of Environmental Emergency Dose Information (SPEEDI).
Emphasizing that its predictions were based on extreme conditions, the commission said the thyroid glands of 1-year-old infants could be exposed to more than 100 millisieverts of radiation over a 12-day period--even outside a 30-kilometer radius from the plant--if iodine is dispersed in a northwesterly and southerly directions.
The government had recommended that residents living within a 20-km radius evacuate and that those living between a 20- to 30-km radius remain indoors as much as possible.
"We made the calculations using very extreme conditions. There will be no need to implement measures immediately," NSC Chairman Haruki Madarame said.
The calculations were based on the scenario of infants being outdoors for the entire 12-day period between 6 a.m. March 12 and midnight Wednesday, after the Great East Japan Earthquake struck on March 11 and damaged the nuclear plant.
The calculations found that if the infant remained indoors exposure to iodine would decrease to one-quarter to one-tenth of the most extreme calculation.
The levels of radioactive iodine dispersed were calculated based on radiation monitoring data recorded at various locations, and the exposure calculation was made for a 1-year child whose thyroid gland would be most affected by iodine.
The NSC had previously not released such predictions, saying the data were only rough figures that could be inaccurate. Critics said the commission should release as much information as possible about the nuclear crisis.
According to Wednesday's calculations, the municipalities where infants could be exposed to more than 100 millisieverts of radiation were Minami-Soma, Iitate and Kawamata to the northwest of the Fukushima plant as well as part of Iwaki that lies south of the plant.
The 100-millisievert figure is one factor in determining if an exposed individual should take non-radioactive iodine as a precaution against thyroid gland cancer.
SPEEDI makes its calculations based on the location of the nuclear power plant, the type, amount and height of the radioactive material dispersed, topographical features as well as weather data.