Uranium diffusion in soils and rocks Moore, Stephanie M.; Shackelford, Charles D.
The results of a study undertaken to review the process of diffusion of uranium in soils and rocks are presented and discussed. After some background on the geochemistry of uranium and the different definitions for the diffusion coefficient in porous media, i.e. D*, De, Da, values of D*, De, and/or Da from the literature are summarized, analyzed and discussed. Diffusion of uranium in compacted bentonite is shown to increase semilog linearly with an increase in porosity (decrease in dry density), and appears to be significantly slower than that in other soils, probably due to the existence of semipermeable membrane behavior and interparticle/intraparticle diffusion as an attenuation mechanism. The effect of attenuation is shown to increase the variability in Da relative to that in either D* or De, and the variability in D*, De, and Da is shown to be greater in compacted bentonite than in unfractured biotitic granite, likely due to a more homogeneous pore structure and a lesser attenuation capacity for the biotitic granite. Overall, the typical preference for reporting only Da values is shown to severely restrict the usefulness of the literature on the subject. [All papers were considered for technical and language appropriateness by the organizing committee.]
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