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Dissolution Behaviour of UO2 in Anoxic Conditions. Comparison of Ca-bentonite and Boom Clay

Published online by Cambridge University Press:  19 October 2011

Thierry Mennecart ,
Christelle Cachoir  and
Karel Lemmens
Thierry Mennecart
Affiliation:
Tmenneca@sckcen.be, SCK-CEN, Chemistry, Boretang 200, MOL, 2400, Belgium
Christelle Cachoir
Affiliation:
ccachoir@sckcen.be, SCK-CEN, Boeretang 200, MOL, 2400, Belgium
Karel Lemmens
Affiliation:
klemmens@sckcen.be, SCK-CEN, Boeretang 200, MOL, 2400, Belgium
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Abstract

A general concept for the disposal of spent fuel in clay formations is based on the multibarrier principle. In such concept, the barriers for radionuclides released into the environment are the clay host rock, the backfill, the canister overpack and the fuel itself. The innermost barrier is the dissolution of UO2 matrix, which is the main component of spent fuel. However the dissolution of UO2 upon groundwater contact depends strongly on the (geo)chemical constraints prevailing in the repository. In order to determine in how far the clay properties influence the dissolution of spent fuel, two different kinds of clay were considered: Ca-bentonite which presents an initial oxidizing environment, and Boom Clay which is characterized by its strong reducing capacity. The experiments were carried out with depleted UO2 in presence of either compacted dry Ca-bentonite with Boom Clay groundwater or compacted dry Boom Clay with Boom Clay groundwater. The leach tests were performed at 25°C in anoxic atmosphere (glove box under 0.4%CO2/99.6%Ar) for 2 years. The U concentrations were sampled during these 2 years, once every 6 months and the amount of U was determined in the clay after 2 years in order to determine the dissolution rate. After 2 years, an unexpected uranium concentration was found 50 times higher in the system Boom Clay with Boom Clay water (2.10-7 mol/L) than in the system Ca-bentonite with Boom Clay water (4.10-9 mol/L), maybe resulting from a larger colloidal fraction in the system Boom Clay with Boom Clay water. Final results are expected to allow the comparison of the U retention capacity of Ca- bentonite and Boom Clay in anoxic conditions with the U retention of Boom Clay found in reducing conditions.

Keywords

oxidecorrosionwaste management
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 985: Symposium NN – Scientific Basis for Nuclear Waste Management XXX , 2006 , 0985-NN01-07
Copyright
Copyright © Materials Research Society 2007

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References

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