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Diffusion of Cs, Np, Am and Co in compacted sand-bentonite mixtures: evidence for surface diffusion of Cs cations†

Published online by Cambridge University Press:  09 July 2018

T. Sawaguchi ,
T. Yamaguchi ,
Y. Iida ,
T. Tanaka  and
I. Kitagawa
T. Sawaguchi*
Affiliation:
Waste Safety Research Group, Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
T. Yamaguchi
Affiliation:
Waste Safety Research Group, Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
Y. Iida
Affiliation:
Waste Safety Research Group, Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
T. Tanaka
Affiliation:
Waste Safety Research Group, Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
I. Kitagawa
Affiliation:
Hot Material Examination Section, Department of Fukushima Technology Development, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
*
*E-mail: sawaguchi.takuma@jaea.go.jp
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Abstract

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We studied the diffusive transport of Cs, Np, Am and Co in compacted sandbentonite mixtures by using the through-diffusion method. The experiments for Cs were performed under various aqueous compositions. Effective diffusivity (De) values of 4.7×10–10 to 5.9×10–9 m2 s–1 were obtained with a somewhat large variation. Apparent diffusivity (Da) values, on the other hand, showed less variation, ranging from 2.0×10–12 to 6.2×10–12 m2 s–1. The results indicated that diffusive flux was proportional to the concentration gradient on the basis of the amount of Cs in the unit volume of the compacted sand-bentonite mixtures rather than the Cs concentration gradient in pore water. Because the former concentration gradient in the mixtures was nearly equal to that of adsorbed Cs, the diffusion of Cs in the mixtures was probably dominated by the concentration gradient of the Cs adsorbed on the mixtures. In addition, the effective/apparent diffusivity of 237Np(IV) and apparent diffusivity of 241Am(III) and 60Co(II) in the mixtures were determined in 0.3/0.03 mol l–1 (NH4)2CO3/Na2S2O4 solution.

Keywords

diffusioncaesiumbentoniteeffective diffusivityapparent diffusivitysurface diffusionsandbentonite barrierradioactive waste storage
Type
Research Article
Information
Clay Minerals , Volume 48 , Issue 2 , May 2013 , pp. 411 - 422
Creative Commons
Creative Common License - CCCreative Common License - BY
Copyright © The Mineralogical Society of Great Britain and Ireland 2013 This is an Open Access article, distributed under the terms of the Creative Commons Attribution license. (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2013

Footnotes

†

Part of this study was funded by the Secretariat of Nuclear Regulation Authority, Nuclear Regulation Authority, Japan.

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