Investigation and research on depth distribution in soil of radionuclides released by accident of Fukushima Daiichi Nuclear Power Station, TEPCO, 4; Depth distributions of radionuclides and estimation of the initial inventories

Sato, Haruo; Amano, Kenji  ; Niizato, Tadafumi  ; Tanaka, Shingo; Nohara, Tsuyoshi   ; Iwatsuki, Teruki  ; Murakami, Hiroaki  ; Sugita, Yutaka ; Nakayama, Masashi ; Abe, Hironobu ; Aoki, Kazuhiro ; Nakatsuka, Noboru

Accident of Fukushima Daiichi Nuclear Power Station, TEPCO occurred by Tsunami caused by Tohoku Pacific Ocean Earthquake on 11 March, 2011. Part of the radionuclides in atomic reactors was released and accumulated on soil surface over the wide range of area in Fukushima Prefecture by rain after being transported by wind. This work was carried out as one of the projects which were published by Council for Science and Technology Policy on 19 May and investigation on the depth distribution of radionuclides in soil was carried out. Also the inventories of radionuclides accumulated on soil surface immediately after the occurrence of accident were estimated. In this presentation, we report the apparent diffusion coefficients Da of radionuclides and the inventories of radionuclides on soil surface immediately after the occurrence of accident among a series of investigation and research. Cs and Cs were detected in all investigation points (11 points), and Te and Ag were detected only in areas where spatial dose rate and the inventories of radionuclides have been evaluated to be high. The depth distributions of radionuclides were less than 5cm from surfaces except for the soil of farmland at many points. Radionuclides tended to be detected in deeper positions in the soil of farmland than in the soil of surface. Da values derived from the depth distributions for all radionuclides were nearly 1E-11 (m/s) for the soil of many points except for the soil of farmland. This is considered to be due to that those Da values were controlled by dispersion. The estimated inventories of radionuclides accumulated on soil surface immediately after the occurrence of accident were consistent with monitoring results so far.