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Fitting Element Profiles for Predicting Glass Dissolution Rates in Synthetic Interstitial Clay Water

Published online by Cambridge University Press:  11 February 2011

Marc Aertsens ,
Karel Lemmens  and
Pierre Van Iseghem
Marc Aertsens
Affiliation:
SCK•CEN, Boeretang 200, B-2400 Mol, Belgium
Karel Lemmens
Affiliation:
SCK•CEN, Boeretang 200, B-2400 Mol, Belgium
Pierre Van Iseghem
Affiliation:
SCK•CEN, Boeretang 200, B-2400 Mol, Belgium
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Abstract

An analytical model is developed to derive diffusion coefficients from the element profiles of the most mobile glass elements. Congruent dissolution is considered as a transient phenomenon and neglected. In the model, altered glass consists of two sublayers: a gel layer at the solution side, and a diffusion layer at the pristine glass side. In both layers, mobile glass elements diffuse towards the solution, while hydrogen/water diffuses towards the pristine glass.

Fitting the element profiles of boron, sodium and lithium leads to diffusion coefficients in the diffusion layer, which at 90°C are typically of the order of 10-22 m2/s to 10-21 m2/s. At 40°C, these diffusion coefficients are typically a factor ten lower. The diffusion coefficients in the gel are by less than a factor two hundred larger than those in the diffusion layer.

The diffusion coefficients derived from the profiles in this way are used to predict the dissolution behavior. These predictions, for which a constant value (representing congruent dissolution) is added to the predicted diffusive release, agree reasonably well with the measured dissolution data. Those results support the idea that diffusion determines the long term release of glass matrix elements in synthetic interstitial clay water. Flux conservation at the interface between the gel and the diffusion layer is not consistent with a constant (as a function of time) width of the diffusion layer. Some experimental evidence supports that this width increases with time.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 757: Symposium II – Scientific Basis for Nuclear Waste Management XXVI , 2002 , II5.8
Copyright
Copyright © Materials Research Society 2003

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References

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