Radiation dosage down 65% in 80-km zone of Fukushima nuke plant

The central government's Nuclear Regulation Authority (NRA) published on Feb. 2 a map depicting the distribution of radiation dosages as of last September in a region within an 80-kilometer radius of Tokyo Electric Power Co.'s crippled Fukushima Daiichi nuclear plant. The data, collected four years and a half after the 2011 nuclear accident there, represented a 65% decrease in the average midair dosage from comparable measurements taken seven months after the disaster. According to the NRA, the margin of decrease in the radioactivity level when considering the effect of physical attenuation of radioactive substances alone was 53%. The greater decline in actual dosages resulted from decontamination work and weathering, NRA officials said. A contaminated belt stretching northeast from the nuclear plant that once showed 19 microsieverts or more in the dosage of midair radiation per hour (equivalent to a 100-millisievert dosage per year) was found to have sharply shrunk in size during the past four and a half years. Also showing a steep fall in the radiation level was a 0.5- to 1.9-microsievert area stretching from the northern part of the Nakadori region in central Fukushima Prefecture to the south. Iwaki city and some other areas saw zones of 0.2 microsieverts or less expand in the period. The measurements were taken by the Japan Atomic Energy Agency in September last year. The agency flew a helicopter equipped with radiation detectors around the prefecture, collecting data on radiation from the ground and calculating dosages 1 meter above ground level. (Translated by Kyodo News)