Distribution coefficients used for safety assessment for shallow land radioactive waste burial

Distribution coefficients (Kd) used for an estimation of radionuclide migration in soil were reviewed. The relation between Kd and soil, water quality and chemical forms in groundwater were examined. The Kd values for generic safety assessment on shallow land burial are proposed as follows on the basis of knowledge of measured Kd values and expected chemical forms in groundwater. Group 1: tritium (Kd = 0 mℓ/g); Group 2: Tc, I etc. existing in groundwater as an anion (Kd = 0 ∼ 10 mℓ/g); Group 3: alkali earth elements which form insoluble carbonate and sulfate (Kd = 5 ∼ 50 mℓ/g); Group 4: rare earth elements or transition elements which form hydroxide or complex (Kd = 10 ∼ 100 mℓ/g); Group 5: actinide elements which form polymer, or elements existing in water as a stable cation such as Cs etc. (Kd = 100 ∼ 1,000 mℓ/g). (author)