The fate of transport of radionuclides is one of the most important factors to be considered for the safety assessment of repositories of radioactive wastes in porous media. Laboratory batch and column experiments were investigated to assess the transport of 137Cs and 60Co in calcareous loam and clay soils leached with groundwater (GW) using convection-dispersion equation model (CDE). Fractionation of Cs and Co in eight sequential fractions in the soils was also measured. Results showed that the distribution coefficient (Kd) values for 137Cs found to be much more as compared to 60Co. It was ranged from 20 to 395 ml/g, depending on soil and radionuclide characteristics. The CDE model provided a fairly good fit to the experimental breakthrough curves (BTCs) of both solutes. The retardation factor (R) was 821 and 118 for137Cs, while it was 65 and 88 for 60Co, for both soils, respectively. The dispersion coefficient (D) was 2.0 and 2.8 for Cs, and 0.6 and 0.7 cm2/min for Co for loam and clay soils, respectively. The silt+clay was the major soil fraction in retaining Cs followed by sand fraction, for both soils, while the carbonate was the major soil fraction in retaining Co followed by silt+clay, Fe oxides, and sand for loam soil, and silt+clay, sand and Fe oxides for clay soil. No large change was observed in 137Cs retaining with leaching. The leaching consistently reduced the magnitude of 60Co bound to carbonate and increased fraction bound to silt+clay.
Key words: Transport parameters, 137Cs, 60Co, fractionation, dispersion, calcareous soils.