2 / 2021-09-29 19:51:21

A Statistical Evaluation to Compare and Analyze Estimations of the Diffusion Coefficient of Pertechnetate (99TcO4-) in Compacted Bentonite

Keywords: diffusion; MX80 bentonite; HYDRUS-1D ; asymptote; ANOVA

Abstract: Various numerical methods are being extensively used to estimate the diffusion parameters of pertechnetate (⁹⁹TcO₄⁻) in compacted MX80 bentonite clay using through-diffusion (TD) techniques. In this study, an improved TD column test was applied, and the diffusion fluxes of tritium (HTO), as a non-reactive radionuclide, and ⁹⁹TcO₄⁻ with various dry densities, were compared under the same experimental conditions. Similar results were obtained for the apparent diffusion coefficients of HTO and ⁹⁹TcO₄⁻ using three estimation methods: a graphical method applying the asymptote calculation, an analytical solution using Lsqcurvefit installed in MATLAB, and the Marquardt-Levenberg optimization algorithm in the HYDRUS-1D inverse method. The statistical analysis showed that the densities using a one-way analysis of variance (ANOVA) for the three estimation methods ranged from 1200 to 2000 kg/m³, which indicated that there were no obvious differences between HTO and ⁹⁹TcO₄⁻.In general, the diffusion parameters of ⁹⁹TcO₄⁻ were lower than those for HTO due to anion exclusion effects and lower accessible porosity.