Long-term predictions of ambient dose equivalent rates after the Fukushima Daiichi nuclear power plant accident

To analyze radiation protection strategies and rehabilitation programs in Fukushima, prediction models have been developed for ambient dose equivalent rate distributions within the 80 km-radius around the Fukushima Daiichi nuclear power plant. The prediction models characterized by ecological half-lives of radioactive caesium for land-use, enable Fukushima residents to obtain distribution maps of ambient dose equivalent rates after the Fukushima Daiichi nuclear power plant accident. Model parameters such as the ecological half-lives for the short-term component and the fractional distribution of short-term component were evaluated using ambient dose equivalent rates through car/vehicle-borne surveys. It was found that the ecological half-lives among land-use differ only slightly, whereas the fractional distributions of the short-term component are clearly dependent on land-use. In addition, uncertainties concerning predictions of ambient dose equivalent rates arising from variability in model parameters were assessed using Monte Carlo simulations. Long-term changes of ambient dose equivalent rates were predicted for different land-use areas. Distribution maps of ambient dose equivalent rates for the next 30 years after the accident, created by the prediction models are expected to be useful for follow-up of the radiological situation since they provide information on the space variation of the ambient dose equivalent rates in inhabited areas.