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Actinide Transport in Topopah Spring Tuff: Pore Size, Particle Size, and Diffusion

Published online by Cambridge University Press:  28 February 2011

Marilyn Buchholtz Ten Brink ,
Douglas L. Phinney  and
David K. Smith
Marilyn Buchholtz Ten Brink
Affiliation:
Earth Sciences Department and Nuclear Chemistry Division
Douglas L. Phinney
Affiliation:
Lawrence Livermore National Laboratory, L202, P.O. Box 808, Livermore, CA 94550.
David K. Smith
Affiliation:
Earth Sciences Department and Nuclear Chemistry Division
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Abstract

Diffusive transport rates for aqueous species in a porous medium are a function of sorption, molecular diffusion, and sample tortuosity. With heterogeneous natural samples, an understanding of the effect of multiple transport paths and sorption mechanisms is particularly important since a small amount of radioisotope traveling via a faster-than-anticipated transport path may invalidate the predictions of transport codes which assume average behavior. Static-diffusion experiments using aqueous 238U tracer in tuff indicated that U transport was faster in regions of greater porosity and that apparent diffusion coefficients depended on the scale (mm or μm) over which concentration gradients were measured in Topopah Spring Tuff. If a significant fraction of actinides in high-level waste are released to the environment in forms that do not sorb to the matrix, they may be similarly transported along fast paths in porous regions of the tuff. To test this, aqueous diffusion rates in tuff were measured for 238U and 239Pu leached from doped glass. Measured transport rates and patterns were consistent in both systems with a dual-porosity transport model In addition, filtration or channelling of actinides associated with colloidal particles may significandy affect the radionuclide transport rate in Topopah Spring tuff.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 212: Symposium P – Scientific Basis for Nuclear Waste Management XIV , 1990 , 641
Copyright
Copyright © Materials Research Society 1991

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References

REFERENCES

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