2017 年 52 巻 4 号 p. 259-264
External exposure of workers engaging demolition works of damaged buildings performed near the Fukushima Daiichi Nuclear Power Plants was investigated. Indoor air dose rates recorded near the ceiling were higher than those recorded near the floor, and smaller than outdoor air dose rates. It was found that demolition works at “residence restricted area”, in some cases, might meet specified high dose rate works, because average air dose rate of a demolition work performed in this area exceeded 2.5 µSv/h. Average daily external exposure of workers at residence restricted area was 6.4 µSv, it was higher than that at “zone in preparation for the lifting of the evacuation order,” 4.4 µSv. It may reflect air dose rates recorded at these areas. On the other hands, average cumulative external exposure at “zone in preparation for the lifting of the evacuation order” was 146 µSv, it was higher than that at “residence restricted area,” 89 µSv. This tendency may reflect a long period of demolition work and less of the workers. In demolition works at “zone in preparation for the lifting of the evacuation order,” “removing roofing tiles” was selected as the work which significantly increased external exposures by multiple regression analysis. “Removing interior materials” was also selected as the work which significantly decreased external exposures in demolition works at “residence restricted area.”
