Study on restricted use of contaminated rubble on Fukushima Daiichi NPS site (2) Validation of reference radiocesium concentration for recycling materials

Tokyo Electric Power Company has been planning that a part of rubbles arising from the accident of the Fukushima Daiichi NPS (1F) will be recycled and applied in a restricted reuse only within 1F site. For ensuring the safety of the restricted reuse, we have been developing a new methodology for evaluation of reference concentration for the restricted reuse, considering current situation of radiation control at the 1F site. In this study, in order to validate the reference radiocesium concentrations of recycling material used for the road (1.0×105 Bq/kg) and the base of a concrete building (1.6×105 Bq/kg), which have been calculated for the restricted reuse of contaminated rubbles, we evaluated (1) additional occupational dose, (2) annual dose at the site boundary, (3) radiocesium concentration in groundwater at the outlet to the ocean. (1), (2) and (3) are should be below 2 mSv/y, 1 mSv/y and 1 Bq/L, respectively. As a result, additional occupational dose was calculated as 1.3 mSv/y. Annual dose at the boundary was 1 mSv/y with condition of more than the distance of 25 m from the road. Calculated radiocesium of 134Cs and 137Cs concentrations in the groundwater at the outlet to the ocean were the below the 1 Bq/L with condition of distance of more than 5 m from the building. The calculated reference radiocesium concentrations were validated for the restricted reuse within the 1F site.