Comparison of laboratory methodologies for evaluating radiostrontium diffusion in soils: Planar-source versus half-cell methods

A planar-source method, initially designed to obtain diffusion coefficients in compacted clay, is adapted here to determine the apparent diffusion coefficient (D-a) of radiostrontium in soils representative of the Spanish territory Experiments were carried out by varying the moisture content (F-moist), and bulk dry density (rho(bulk)) of the soil samples, in order to study the influence of these soil packing parameters on D-a values The moisture in the soil samples was established as the percentage of occupancy of each soil's field capacity (OK) For a similar OK. D-a values in the examined soils ranged by approximately one order of magnitude (e g from 6 2 x 10(-11) to 6 5 x 10(-12) m(2) s(1), at 100% of OFC, from 3 0 x 10 (11) to 3 8 x 10(-12) m(2) s(-1) at 60% of OFC) For a given soil. D-a values increased when water content was increased F-moist and tortuosity (tau) explained D-a variability, with R-2 values usually over 0 9 However, no good simple or multiple regressions between the soil packing parameters and D-a were obtained with the whole dataset of all soils, which indicated that soil sorption capacity affects the diffusion of reactive radionuclides in soils The inclusion of calculated K-d values in the multiple regressions improved the correlations in all cases Finally, D-a values were compared with those obtained by the application of a half-cell method The values of D-a obtained by the planar-source methods were systematically lower than the half-cell ones, with a good correlation between the D-a derived from both methods (R-2 = 0 98) (C) 2010 Elsevier B V All rights reserved