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The Influence of Thermal Gradients on the Long-Term Evolution of the Near-Field Environment of High-Level Nuclear Wastes Disposal

Published online by Cambridge University Press:  10 February 2011

C. Poinssot ,
P. Toulhoat  and
B. Goffé
C. Poinssot
Affiliation:
Commissariat à l'Energie A tomique, DCC/DESD/Service for Nuclear waste storage and disposal studies, CEA de Saclay, F-91191 Gif sur Yvette - France Ecole Normale Supérieure, Laboratory for Geology, 24 rue Lhomond, F-75005 Paris, France
P. Toulhoat
Affiliation:
Commissariat à l'Energie A tomique, DCC/DESD/Service for Nuclear waste storage and disposal studies, CEA de Saclay, F-91191 Gif sur Yvette - France
B. Goffé
Affiliation:
Ecole Normale Supérieure, Laboratory for Geology, 24 rue Lhomond, F-75005 Paris, France
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Abstract

The initial stage of some HLW disposal systems will be characterised by a large thermal pulse in the near-field environment, due to the heat of the radioactivity decay. This will lead to the development of a transient spatial thermal gradient between the hot canister and the cold geological medium, which could significantly affect the composition and the elemental distribution within the near-field environment. A coupled experimental and modelling work is presented in order to determine the influence of a thermal gradient on water-rock interaction processes. First experiments with a simulated nuclear glass evidenced mass transfer processes leading to chemical differentiation in the solid phases between the hot and the cold end of the system. The relevance of these experimental results to the case of a HLW disposal is strongly supported by in-situ experiments at Stripa, in which a realistic EBS under thermal gradient developed exactly the same mass transfers.

In order to understand the driving force of these processes, we tried to model simplified experiments by using a mixing cell geochemical model built upon the geochemical code EQ3/EQ6. The discrepancies between modelling and experiments indicate the existence of coupled processes involving irreversible precipitation.

Finally, thermal gradients were applied in nuclear glass-clay interaction experiments to enhance elemental migrations. The main results are: (i) a re-crystallisation of the initial clay toward a more silicic one through incorporation of elements released by the glass, (ii) a strong influence of clay chemistry on the nuclear glass secondary phases.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 506: Symposium – Scientific Basis for Nuclear Waste Management XXI , 1997 , 431
Copyright
Copyright © Materials Research Society 1998

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References

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