Understanding of diffusion-sorption process by evolutional analysis of depth distribution of radiocaesium in soil contaminated by the Fukushima nuclear accident

Sato, Haruo*; Niizato, Tadafumi  ; Tanaka, Shingo*; Abe, Hironobu ; Aoki, Kazuhiro 

The authors derived an analytical theory for calculating apparent diffusion coefficient (D) based on evolution of depth distribution of radiocaesium (Cs-134 and Cs-137) in soil contaminated by the Fukushima Dai-ichi Nuclear Power Plant (1F-NPP) accident in March 2011, and calculated D and distribution coefficient (K) by analyzing evolution of depth distributions from after 3 months to after 1 year from the 1F-NPP accident. In conventional analysis, the D-values of radiocaesium in the investigations after 3 months and 1 year, 10m/s orders and 10m/s orders, respectively, lowered with increasing time. The K-values, also lower than 20ml/g, largely differed from batch K-values. Similar trend is found in the Chernobyl nuclear accident. This is considered because the effect of transport by dispersion with advection of rainwater after radiocaesium deposited is included in the depth distributions. The D-values and K-values from evolutional analysis of depth distributions excluded such effect, 10m/s orders and 1010ml/g, respectively, were consistent with batch K-values.