Setting of the normal variation range for the environmental radiation monitoring around the Tokai Reprocessing Plant after the TEPCO's nuclear accident

The result of the environmental monitoring has been evaluated by the "normal range" which was set using by the past measurement values, by referring to the guidance of the environmental monitoring defined by the former nuclear safety commission. The level of the ambient dose and a part of the radioactive concentration in environmental samples had been increased by the radioactive materials accidentally released from the Fukushima Daiichi Nuclear Power Plant since March 2011, so the "normal range" was not revised after 2011. Thus, we investigated the setting method for the "normal range" after the accidental release, to set "normal range" using the measurement data obtained until 2015, and to apply it to the data in 2016 which had no influence from the Tokai reprocessing plant. As a result, most of the data was included in the "normal range." The "normal range" by this method will be applied to the environmental radiation management report based on the law, and be used to evaluate the measurement value. (author)