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Shimada, Taro; Miwa, Kazuji; Takeda, Seiji
Progress in Nuclear Science and Technology (Internet), 6, p.203 - 207, 2019/01
Rubbles less than 5 
Sv/h of surface dose rate, which are stored outdoor in the Fukushima Daiichi NPS (1F) site, will be recycled and applied in a restricted reuse only within 1F site in the future. In this study, we suggested a concept for establishing the reference radioactive concentration of recycling material for the restricted use in the 1F site. Reference radiocesium concentration is calculated so that increased dose rate by restricted reuse does not exceed 1 Sv/h which is the minimum value of dose rate map in the 1F entire site. In order to justify the restricted reuse under the reference concentration calculated, additional occupational dose, dose rate at the site boundary and groundwater concentration at the outlet to the ocean are evaluated and confirmed that the values are below 2 mSv/y, 1 mSv/y and 1 Bq/cm
of 
Cs and 
Cs, respectively. And then calculated the reference radiocesium concentrations of the recycling material used for paved roads and the bases of concrete building.
Shimada, Taro; Miwa, Kazuji; Takeda, Seiji
no journal, ,
Rubbles less than 5Sv/h of surface dose rate, which are stored in the Fukushima Daiichi NPS (1F) site, will be recycled and applied in a restricted use only within 1F site in the future. In this study, we suggested a concept for establishing the reference radioactive concentration of recycling material for the restricted use in the 1F site, and then calculated the reference radiocesium concentrations of the recycling material used for paved roads and the bases of concrete building. In order to prevent the working time from being decreased, it is necessary for the restricted use to suppress the additional dose to a level of value. Therefore, focusing on the current background air dose rate in the 1F site, we suggested the required condition that air dose rate increased by use of contaminated recycling material instead of non-contaminated did not exceed the variation range of the background dose rate. In addition, to validate the restricted use under the reference concentration, following three items should be confirmed; (1) additional dose for worker using the recycling material does not exceed 2mSv/y, 10% of worker dose limit; (2) the impact to air dose rate evaluated at the 1F site boundary does not exceed the 1mSv/y including direct and skyshine radiations from wastes stored in the site; (3) the impact of migrated radionuclides into groundwater does not exceed the operational target value. The reference radiocesium concentrations for recycling aggregate taken from contaminated concrete rubbles were evaluated for paved road and bases of concrete building.
Miwa, Kazuji; Shimada, Taro; Takeda, Seiji
no journal, ,
In this study, in order to validate the restricted use of recycling material at the reference radiocesium concentration (determined in series report (1)), we evaluated worker annual doses, air dose rate at the site boundary and impact of migrated radiocesium into groundwater. Firstly, we evaluated the additional annual dose for workers, on the assumption that typical workers coming in contact with the source after construction (Road: 1.3 mSv/y, Building: 1.3 mSv/y). Secondly, we evaluated the air dose rates by distance from road and building including recycling material, and investigated the distance for not exceeding 1mSv/y (including additional dose rate by recycling and background dose rate of 0.6 mSv/y) at the site boundary (Road: 25 m, Building: 1 m). Thirdly, we evaluated the Cs and Sr migration in groundwater, and investigated the distance required for satisfying the operation target value (Cs-134: 1 Bq/L, Cs-137: 1 Bq/L, Sr-90: 5 Bq/L) at the boundary (coastal line) (Road: 10 m, Building: 10 m).
Shimada, Taro; Miwa, Kazuji; Takeda, Seiji
no journal, ,
Rubbles less than 5 Sv/h of surface dose rate, which are stored outdoor in the Fukushima Daiichi NPS (1F) site, will be recycled and applied in a restricted reuse only within 1F site in the future. However, there is no precedent for establishing the reference values such as dose and/or concentration for reuse or recycling under the existing exposure situation. In this study, we suggested a concept for establishing the reference radioactive concentration of recycling material for the restricted use in the 1F site. In addition, based on the concept, we calculated the reference radiocesium concentrations of the recycling material used for paved roads and the bases of concrete building.
