Laboratory experiments to characterize radiochloride diffusion in unsaturated soils.

Diffusion transport of (36)Cl was examined in seven soils under unsaturated conditions in tubes packed with two portions of each soil having different (36)Cl activity concentrations. Apparent diffusion coefficients (D(a)) derived from diffusion profiles varied within a narrow range (from 3x10(-10) to 7x10(-10) m(2) s(-1)) confirming the minor effect of soil properties on the diffusion of a non-reactive radionuclide like (36)Cl. Instead, packing conditions had a major effect. Solid-liquid distribution coefficients (K(d)) derived from D(a) (0.02-0.2 L kg(-1)) were systematically lower than those obtained from batch experiments (0.6-1.0 L kg(-1)), but with a similar variation pattern among soils. The low values of K(d) (Cl) confirmed an almost negligible radiochloride-soil interaction.