Preliminary study on decontaminating paddy soil contaminated with radioactive materials by using water agitation and soil removal

Abstract

A decontamination method is urgently needed for agricultural lands contaminated with radio-active cesium during the accident at the Fukushima Daiichi Nuclear Power Plant in March 2011. As an ex-perimental site, we selected a paddy fi eld in Iitate Vil-lage, which is in the planned evacuation zone. Prelimi-nary testing showed that 95 % of the radioactive cesium exists within the top 2.5 cm of uncultivated ag-ricultural soil. The cesium was primarily adsorbed with finer fractions of the soil, such as soil particles or aggregates smaller than 0.02 mm Stokes diameter. On the basis of these results, we proposed an experimen-tal method of paddy decontamination by puddling a thin layer of topsoil under flooded conditions and draining the suspended soil particles. We carried out a test on the method using a plastic container (38.0 cm× 53.0 cm × 26.5 cm) before using the method on the paddy field. The process reduced the concentration of radioactive cesium. An important advantage of the technique is that it generates less waste than the method of removal of top soil.