Development and application of a model for the long-term alteration of UO2 spent nuclear fuel Test of equilibrium and kinetic mass transfer models in the Cigar Lake ore deposit

In recent years, we have been building up the thermodynamic and kinetic basis necessary to quantitatively determine the pathway for the long-term oxidative alteration of the UO2 spent fuel matrix. There is a need to complement our thermodynamic description of these processes with kinetic mass transfer models. The development of these kinetic mass transfer models to the long-term oxidative alteration of UO2 has been recently illustrated. The Cigar Lake ore deposit constitutes a unique opportunity to test the validity of these alteration models, since they provide the appropriate time and space scales. The purpose of this paper will be to show the successful testing of equilibrium and kinetic mass transfer models to describe the long-time-low temperature evolution of the uraninite deposit and the contacting groundwaters. In this paper, we will discuss the basic kinetics and thermodynamics of the model as well as the encouraging results so far obtained. The kinetic model has been applied to the aluminosilicates system. The results show that the interactions with clay minerals control the bulk composition of groundwater. The kinetic approach is able to describe the evolution of the groundwater composition along the hydrogeological pathways studied. The uranium system has been modelled by simulating the dissolution of uraninite along the flowpaths investigated. This modelling is based on equilibrium assumptions. The evolution of the redox state of groundwaters along different flowpaths is well reproduced.