The results of a study to assess radiation doses following the disaster at the Fukushima Nuclear Power Station (NPS) in March 2011 are published in Scientific Reports this week. The work suggests that the government evacuation of people living within 30 kilometres of the power station was justified from the point of view of radiation protection.
The 9.0-magnitude earthquake in Japan on 11 March this year triggered a tsunami, which caused the power supply for cooling in Fukushima NPS to fail. Subsequent explosions at the power station caused various artificial radionuclides, such as xenon-133, iodine-131 and caesium-134, to be released into the environment. To assess the effects of these radionuclides on the living environment, Shinji Tokonami and colleagues conducted a car-borne survey for radiation dose rate in the air in March and April 2011 along an expressway passing northwest of Fukushima NPS. They also surveyed a high-contamination area, closer to the power station, to estimate the radiation external dose for individuals who lived in this area but were subsequently evacuated.
Dose rates along the expressway (i.e. relatively far away from the power station) were higher after than before 11 March. The maximum dose rate in the high-contamination area was 36 μGy h-1 and the estimated maximum cumulative external dose for evacuees who came from Namie Town (about 20 km from Fukushima NPS) to evacuation sites, such as Fukushima City, was about 68 mSv. The authors therefore report that the evacuation of the high-contamination area was justified in terms of radiation protection.