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The Effect of Cracks on Diffusive Mass Transport through a Clay Barrier

Published online by Cambridge University Press:  21 February 2011

Nava C. Garisto  and
Frank Garisto
Nava C. Garisto
Affiliation:
Atomic Energy of Canada Limited, Whiteshell Nuclear Research Establishment Pinawa, Manitoba, CanadaROE 1LO
Frank Garisto
Affiliation:
Atomic Energy of Canada Limited, Whiteshell Nuclear Research Establishment Pinawa, Manitoba, CanadaROE 1LO
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Clay-based buffers are often proposed as engineered barriers for underground disposal vaults of used nuclear fuel. Thus, in the Canadian conceptual vault design, each used-fuel container is emplaced in a vertical borehole in rock and surrounded by a compacted buffer material, made up of a mixture of sodium bentonite and sand. There is some evidence, however, that the buffer may be susceptible to cracking due to, for example, cementation or moisture depletion.

In this paper we estimate numerically the consequences of cracking on the diffusion of uranium through a finite buffer layer. In particular, we study how the effects of cracks depend on the rock conditions at the edge of the vault.

For swept-away boundary conditions at the rock/buffer interface (e.g., representing a major fracture zone in granite), the total flux through the cracked buffer system is greater than through the corresponding uncracked buffer, particularly for buffers with a very small effective diffusion coefficient. On the other hand, for the case in which the rock at the rock/buffer interface is intact and, thus, the mass transport of material from the buffer into the rock is small, the effect of the cracks on the total release flux is negligible.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 176: Symposium U – Scientific Basis for Nuclear Waste Management XIII , 1989 , 733
Copyright
Copyright © Materials Research Society 1990

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References

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