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Estimation of Effective Diffusivity in Compacted Ben Tonite

Published online by Cambridge University Press:  15 February 2011

H. Kato,
M. Muroi,
N. Yamada,
H. Ishida and
H. Sato
H. Kato
Affiliation:
Naka Energy Research Center, Mitsubishi Materials Corporation, 1002–14, Mukoyama, Naka-machi, Naka-gun, Ibaraki-ken, 311–01 Japan
M. Muroi
Affiliation:
Naka Energy Research Center, Mitsubishi Materials Corporation, 1002–14, Mukoyama, Naka-machi, Naka-gun, Ibaraki-ken, 311–01 Japan
N. Yamada
Affiliation:
Naka Energy Research Center, Mitsubishi Materials Corporation, 1002–14, Mukoyama, Naka-machi, Naka-gun, Ibaraki-ken, 311–01 Japan
H. Ishida
Affiliation:
Naka Energy Research Center, Mitsubishi Materials Corporation, 1002–14, Mukoyama, Naka-machi, Naka-gun, Ibaraki-ken, 311–01 Japan
H. Sato
Affiliation:
Power Reactor and Nuclear Fuel Development Corporation, 4–33 Muramatsu, Tokai-mura, Ibaraki-ken, 319–11 Japan
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Abstract

Effective diffusivities of radioactive nuclides in compacted bentonite were calculated theoretically by using an electric double layer theory. Comparison between calculated diffusivities and measured ones show good agreements.

The effective diffusivity is dominated by pore structure and pore diffusivity Dp. The pore structure can be characterized by effective porosity ε eff, constrictivity δ, and tortuosity Γ. The δ was assumed to be unity. The ε eff and the Γ were determined experimentally. The Dp was estimated by means of the electric double layer theory. In the estimation, smectite interlayer was assumed the space between parallel plane sheets of smectite crystal lattice.

Diffusion experiments were carried out by using Cs+ for monovalent cation, C1- and Tc04 - for monovalent anion, and tritiated water for neutral molecule. The measured and calculated effective diffusivities in different densities showed the same tendency of cation > neutral > anion. The dry density of bentonite became higher, the discrepancy between the estimated and the measured diffusivities became larger. The calculation was limited by the applicability of the electric double layer theory in the near surface region of smectite.

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References

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