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Shimada, Taro; Miwa, Kazuji; Takeda, Seiji
Nihon Genshiryoku Gakkai-Shi ATOMO
, 61(7), p.531 - 534, 2019/07
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.
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; Takai, Shizuka; Takeda, Seiji
no journal, ,
In order to recycle contaminated debris of which concentration is relatively lower in Fukushima Daiichi Nuclear Power Station, it is necessary to confirm that the mean radioactive concentration is lower than a reference value with consideration of the distribution by measurement and evaluation. We studied a method combining radiation measurement and inverse analysis to obtain the distribution of radioactivity concentration of recycled material. Plastic scintillation fiber will be applied to radiation measurement to obtain dose rates outside the container containing recycled material at many measurement points. As a result of application of 7 inverse analysis methods to typical two types of distribution, GVSPM and ML-EL methods can evaluate true values in the trials.
Miwa, Kazuji; Shimada, Taro; Takai, Shizuka; Nabekura, Nobuhide; Takeda, Seiji
no journal, ,
A part of the debris with relatively lower radioactive concentrations, which have been stored in the site of Fukushima Daiichi Nuclear Power Station (1F), have been planned to be recycled for restricted purpose in the 1F site. In this study, we evaluated reference values of upper radiocesium concentrations which are practicable to recycle materials for some applications such as road. Radiation doses for all workers in the 1F site are controlled. There is no previous reference values estimated for restricted recycling under the condition of controlled radiation doses for workers in the 1F site. Therefore, we evaluated the reference values not to exceed the additional air radiation dose as 1Sv/h with recycling the debris, which is the estimated minimum dose rate in the 1F site regarded as background. As a result, the highest value of radiocesium concentration of recycling materials was evaluated to be 100,000 Bq/kg in the case of use as the sub-base in the concrete paving road.
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.
