Sorption and porosity heterogeneity: Effects on radionuclide transport
- Lawrence Livermore National Lab., CA (United States)
Diffusive transport rates for aqueous species in porous media are a function of the molecular diffusion rate in solution for the species of interest, any change in its concentration in solution due to sorption or reaction, and the tortuosity of the material`s pore structure. Diffusion rates can be easily predicted when these factors are constant; however, this is not the case for heterogeneous natural materials and the complex solutions derived from many hazardous wastes. When fluid flow is also present, the transport of hazardous materials in heterogeneous geological materials becomes even more difficult to predict. For actinide elements, the coexistence of multiple oxidation states, colloidal species, and numerous complexes in ground- or waste-water solutions suggests that a range also exists for molecular diffusivity, reactivity, and sorptivity. The physical structure of Topopah Spring tuff, and other rocks, often includes void spaces on scales from grain boundaries and intergranular pore spaces to fractures that are centimeters in width. Movement of aqueous species within the rock then depends on the effective length of the voids and their interconnectedness. Void spaces may be filled with secondary phases and fractures lined with precipitates. Differing sorptive mechanisms can also result in large differences between minerals or aqueous species for reversibility and kinetics of sorption. The author measured diffusive transport of {sup 235}U, {sup 238}U, and {sup 239}Pu tracers in groundwater within saturated tuff rocks on spacial scales from 0.1 {mu}m to cm. She found that regions of greater actinide concentration and faster transport are associated with either greater porosity, identifiable micro-fractures, or concentrations of specific elements such as Li. She also found that addition of sodium bicarbonate to solution increased the apparent diffusivity by one to two orders of magnitude and increased the abundance of colloidal sized particles. 2 refs.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 139659
- Report Number(s):
- LA-12325-C; CONF-9009350-; ON: DE92041241; TRN: 94:007286
- Resource Relation:
- Conference: DOE/Yucca Mountain site characterization project radionuclide adsorption workshop, Los Alamos, NM (United States), 11-12 Sep 1990; Other Information: PBD: Aug 1992; Related Information: Is Part Of Proceedings of the DOE/Yucca Mountain Site Characterization Project Radionuclide Adsorption Workshop at Los Alamos National Laboratory, September 11--12, 1990; Canepa, J.A.; PB: 238 p.
- Country of Publication:
- United States
- Language:
- English
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