New best estimates for radionuclide solid-liquid distribution coefficients in soils. Part 1: radiostrontium and radiocaesium.

Best estimates for the solid-liquid distribution coefficients (K(d)) of radiostrontium and radiocaesium for various soil types, were derived from geometric means (GM) calculated from grouping soils by texture and organic matter content, and also using soil cofactors governing soil-radionuclide interaction. The K(d) (Sr) GM for Sand, Loam, Clay and Organic groups were similar, although the value for the Sand group was significantly lower. The Sr cofactor approach, based on the ratios of cation exchange capacity (CEC) to Ca and Mg concentrations in the soil solution, leads to K(d) (Sr) GM with a lower variability, from which best estimates could be proposed. The K(d) (Cs) GM for Sand and Organic groups differed, although similar values were obtained for Loam and Clay groups. Grouping the K(d) (Cs) according to the Radiocaesium Interception Potential (RIP) and the RIP divided by the K concentration in the soil solution also allows to suggest K(d) (Cs) best estimates with a lower variability.