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Simulation of Effects of Redox and Precipitation on Diffusion of Uranium Solution Species in Backfill

Published online by Cambridge University Press:  28 February 2011

C. L. Carnahan
C. L. Carnahan*
Affiliation:
Earth Sciences Division, MS 50E, Lawrence Berkeley Laboratory, 1 Cyclotron Road, Berkeley, CA 94720.
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Abstract

This investigation addresses the problem of prediction of the rate of migration of redox-sensitive solution species within packing and backfill materials under conditions of variable oxidation potential. Effects of changes of oxidation potential and precipitation of stable uranium compounds during diffusion of uranium from a region of high oxidation potential into a region of low oxidation potential were simulated numerically. Questions of particular interest addressed in the investigation were the existence of a moving “redox front” and the influence of precipitation-dissolution processes on uranium migration. The simulations showed that no expanding redox fronts existed at any simulated time up to 3.2×105 years (1013 s). In simulations where precipitation of stable solids was not allowed, variations of oxidation potential did not affect total uranium concentrations in solution. Concentration profiles could be predicted simply by diffusion of the (constant) source concentrations. In simulations where precipitation of stable solids was allowed, uraninite and calcium uranate accumulated at the source-transport domain interface, while coffinite penetrated further into the transport domain. Total uranium concentrations in regions of precipitation were determined by solubilities of the precipitated solids, and were six to seven orders of magnitude lower than those in the simulations without precipitation, throughout the domain of transport.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 112: Symposium P – Scientific Basis for Nuclear Waste Management XI , 1987 , 293
Copyright
Copyright © Materials Research Society 1988

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