Uranium Diffusion in Soils and Rocks

The study presents a comprehensive analysis of uranium diffusion processes in soils and rocks, particularly focusing on compacted bentonite. It begins by discussing the geochemistry of uranium and defining different diffusion coefficients (D*, De, Da). The literature values of these coefficients are summarized and analyzed. The findings reveal that uranium diffusion in compacted bentonite increases semilog linearly with porosity, yet occurs at a significantly slower rate compared to other soils, attributed to semipermeable membrane behavior and the mechanisms of interparticle and intraparticle diffusion acting as attenuation factors. Notably, the attenuation effect fosters greater variability in the Da values compared to D* or De, with compacted bentonite exhibiting more variability than unfractured biotitic granite due to a homogeneous pore structure and a diminished attenuation capacity in the granite. The research underscores the limitations of exclusively reporting Da values in literature, suggesting that this practice hampers the applicability of the information available on uranium diffusion in soils and rocks.