放射性Csの土壌粒度別分布傾向と分級による減容化への取り組み(<シンポジウム特集>粘土とセシウム)

抄録

After the accident in the Fukushima Daiichi Nuclear Power Station caused by the 2011 Tohoku earthquake and tsunami, the decontamination of radioactive cesium spread from the Nuclear Power Station to all over the Fukushima prefecture has still been continued constantly. Moreover, the huge amount of radioactive waste typified by removed contaminated soil have been increasing on a daily basis. It is expected that the contaminated soil encumbers the acceptable amount of the interim storage facility. Therefore, various kinds of volume reduction methods are tackled. The classification method is one of feasible prospects, and is required to optimize. This study focused on the distribution of radioactive cesium in the contaminated soil for improving the volume reduction method by the soil classification. Clay minerals are reported to specifically adsorb cesium. The wet classification test proved that the fine particles classified from the actual contaminated soil in Fukushima clearly accumulated radioactive cesium, and contained clay mineral. The amount of radioactive cesium exceeding tolerance level still remained in the large particles over the size of 0.5 mm. As a result of the observation of particles the size of 0.5 mm 4.75 hand-picked by the difference in optical characters such as color and shape, particle groups showed differences of radiation quantity and composition of minerals. Especially, organic matters and soil aggregation showed high radiation quantity. Furthermore, the group of tabular particles including clay minerals, such as mica and vermiculite, showed demonstrably highest radiation quantity among particle groups. For the future, it is suggested that the classification method for the volume reduction should be improved with a focus on the clay minerals mineralogically, not mechanically.