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Impact of Porosity Heterogeneity in the Diffusion of Some Alkali- and Alkaline Earth-Metals in Crystalline Rock

Published online by Cambridge University Press:  10 February 2011

H. Johansson ,
J. Byegård  and
M. Skålberg
H. Johansson
Affiliation:
Dep. of Nuclear Chemistry, Chalmers University of Technology, S-412 96 Göteborg, Sweden
J. Byegård
Affiliation:
Dep. of Nuclear Chemistry, Chalmers University of Technology, S-412 96 Göteborg, Swedenbyegard@nc.chalmers.se
M. Skålberg
Affiliation:
Dep. of Nuclear Chemistry, Chalmers University of Technology, S-412 96 Göteborg, Sweden
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Abstract

Data from diffusion experiments using Na+, Ca2+, Sr2+, Cs+ and Ba2+ as tracers in a crystalline rock type (Äspö diorite, originating from the Äspö Hard Rock Laboratory) have been evaluated using a heterogeneity model. The model concept consists of diffusion in a variety of different channels with different porosities. The porosity distribution used has been obtained from independently performed measurements of porosity distributions using the 14C-polymethylmethacrylate impregnation method. Breakthrough curves in through-diffusion experiments as well as penetration profiles in the matrix have been evaluated using the porosity distributions. In the calculations only two parameters, the pore diffusivity (Dp) and the sorption distribution coefficient (Kd) have been varied in order to fit the experimental data to the proposed model. For the penetration profile of more strongly sorbing tracers, i.e., Cs+ and Ba2+, a significantly better explanation of the data is obtained using a heterogeneity model compared to using a uniform porosity distribution model. The data from the through-diffusion experiments gives a better explanation of the shape at the beginning of the breakthrough curve. The implication of the proposed diffusion model is discussed, both from an in situ sorption experiment application and a performance assessment application.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 608: Symposium QQ – Scientific Basis for Nuclear Waste Management XXIII , 1999 , 191
Copyright
Copyright © Materials Research Society 2000

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References

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