Migration of radionuclides Sr-85, Cs-134/137 and Co-60 in unsaturated Chinese loess

During the period 1988 to 1993, the migration of radionuclides Sr-85, Cs-134/137 and Co-60 in unsaturated Chinese loess was studied with the purpose of establishing a safety assessment method for shallow land disposal of low level radioactive waste. In-situ tracer tests, laboratory simulation tests and laboratory batch experiments were carried out. Artificial rainfall and natural rainfall conditions were used in the in-situ tracer tests to obtain the concentration distributions of these radionuclides in the medium as a function of precipitation. Destructive and non-destructive determination methods were used to obtain the concentration distributions of these radionuclides in a laboratory simulation column. The distribution coefficients of these radionuclides were pre-determined with laboratory batch experiments. Laboratory simulation tests indicated that most Sr-85 migrated down to a depth of 6.0 to 12.0 cm, while both Cs-134 and Co-60 remain at the origin when the 1-year simulation test is completed. In-situ tests indicated that when the 2-year in-situ tests were completed, under both natural and artificial rainfall conditions, the positions of peak concentrations of both Co-60 and Cs-134 are less than 1 cm from their origin. Under natural rainfall conditions, the position of peak concentration of Sr-85 is also less than 1 cm from the origin, while under artificial rainfall conditions, the peak position of Sr-85 had moved down to a depth of about 6 cm.