The Effect and Effectiveness of Decontaminating a Pond in a Residential Area of Fukushima

Special reconstruction and revitalization bases were designated in Fukushima’s difficult-to-return zone by the Japanese government as targets of intensive decontamination to drastically lower air dose rates and enable residents to return. A pond amid residences of one of these bases was targeted for decontamination, and this study aimed at evaluating the effect and effectiveness of the decontamination using decontamination factor, air dose rate reduction factor, and the additional annual effective dose to residents. Air dose rates were measured in situ with the second-generation Kyoto University Radiation Mapping system, while soil core samples were collected and measured for radioactivity in the laboratory by gamma spectrometry. Lower decontamination factors were observed for more deeply distributed radiocesium soil profiles, whereas areas covered with gravel demonstrated the largest reduction in air dose rates. Decontamination effectively lowered the radiocesium inventory and air dose rates by 51–93% and 37–91%, respectively. Moreover, the additional annual effective dose to the public changed from 1.7 ± 0.79 mSv to 1.2 ± 0.57 mSv because of decontamination representing a dose aversion of 29%. These findings demonstrate how decontaminating ponds in residential areas can help to further lower the external exposure.