Radiation monitoring and evaluation of exposure doses to lift the evacuation orders for the zones designated for reconstruction and recovery

Abstract

The Japanese government is beginning to consider radiation protection in the “ specific reconstruc tion reproduction base area” of the Fukushima nuclear power plant, the evacuation order of which will be lifted by 2023. It is essential to grasp the present situation of radiation contamination and evaluate exposure dose in the area to realize the lifting of this evacuation order zone. Many surveys on the evaluation of the distributions of air dose rate have been carried out, and exposure dose has been esti-mated using the results since the Fukushima Daiichi Nuclear Power Plant accident. Nevertheless, more detailed information on exposure is needed for the area because the radiation level is relatively high. This will also be helpful in preparing a prudent evaluation plan. This study is aimed at evaluat-ing the detailed contamination situation in the area and estimating exposure dose with consideration of areal circumstances. Work was carried out for （ 1 ） an airborne survey of the air dose rate using an unmanned helicopter and ground-based measurement （ walk-survey ） , （ 2 ） the evaluation of airborne radiocesium and （ 3 ） the estimation of external / internal effective doses for the typical life patterns as-sumed. Our study resulted in a detailed map of the air dose rate and clarified the distribution pattern in the area. Moreover, the exposure dose of residents was evaluated by considering some life patterns based on this map.