Effects of Heterogeneity on Actinide Diffusion Rates in Tuffaceous Rock

by Marilyn Buchholtz ten Brink, Lawrence Livermore Natl Lab, Livermore, United States,
Douglas L. Phinney, Lawrence Livermore Natl Lab, Livermore, United States,
David K. Smith, Lawrence Livermore Natl Lab, Livermore, United States,



Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1991

Abstract:

The pore structure and mineralogy of Topopah Spring Tuff are heterogeneous on scales less than one cm. This heterogeneity creates spatial variation in transport rates for aqueous actinide species both on the scale of tenths of microns and the scale of mm. The volumetric distribution of fluid paths having very different tortuosity, and potentially differing surface mineralogy and sorptive properties, must be considered in order to provide realistic predictions of transport rates. In addition, size and speciation of actinides in solution must be characterized since coexisting species can diffuse at different rates through the porous material due to both filtration effects and differences in sorption onto exposed mineral surfaces.

Subject Headings: Diffusion (porous media) | Rocks | Heterogeneity | Diffusion (chemical) | Transport rates | Surface properties | Sorption

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