Mobility and retention of Co-60 in soils in coastal areas

The purpose of this study was to determine the mobility of radioactive cobalt (60Co), a typical operating waste, in soils in coastal areas (where all Japanese commercial reactors are located). The results of this investigation may assist in evaluating a degree of safety for the future disposal of radioactive wastes underground. Freshwater and seawater were examined under both aerobic and anaerobic conditions by simulating the environmental conditions of the soils in coastal areas. More than 80% of 60Co moves freely within soils covered by seawater under anaerobic conditions. Furthermore, the cobalt in the water phase can pass through a dialysis membrane with a pore size of 24 A. This indicates that the cobalt is either in ionic form or associated with materials of low molecular weight. On the other hand, more than 95% of 60Co was retained by soils covered by freshwater under aerobic conditions. This cobalt, once fixed on soils, was not easily desorbed by seawater under anaerobic conditions. The results suggest that the mobility of cobalt disposed of underground is greatly enced by the initial environmental conditions in the soils in coastal areas. (H.K.)