Vertical distribution of radiocesium in soil deposits on the contaminated areas after the Fukushima Daiichi Nuclear Power Plant accident

Abstract

An accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) occurred on March 11, 2011 which resulted in an environmental contamination with the radiocesium species 134Cs and 137Cs. Vertical distribution of radiocesium is important as it impacts the area dose rate. The vertical distribution of radiocesium is sensitive to wash-off by surface runoff, wind resuspension, and soil to plant transfer. Soil core samples were extracted to develop soil profiles. The purpose of this research is to study the vertical distribution of radiocesium in different soils contaminated after the accident, and to characterize the mechanisms by which the element moves through the soil. The results were compared to data on radiocesium vertical migration observed in Fukushima contaminated area for the year 2015 (Konoplev et al. 1992; Konoplev et al. 2016). The hypothesis is that reliable predictions of future soil contamination can be made based on the results from our soil samples. Predictions regarding radiocesium movement in soils will assist and improve remediation efforts in the Fukushima District. The vertical distribution of radiocesium was found to have a rate of movement of up to 12 cm/y in fluvisol type soils of Inkyozaka, 1 cm/y in andosol soils (Funasawa) and 3 cm/y in terrestrial regosol soils (Kashiramori). The results compared well with previous studies. Movement of radiocesium in Fukushima soils is most likely due to the high precipitation rate, combined with the weak bonding of cesium to fluvisol type soils.