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 kineti c basis necessary to quantitatively determine the pathway for the long -term oxidative alteration of the UO2 spent fuel matrix. There is a ne ed to complement our thermodynamic description of these processes with kinetic mass transfer models. The development of these kinetic mass t ransfer models to the long-term oxidative alteration of UO2 has been r ecently illustrated. The Cigar Lake ore deposit constitutes a unique o pportunity to test the validity of these alteration models, since they provide the appropriate time and space scales. The purpose of this pa per will be to show the successful testing of equilibrium and kinetic mass transfer models to describe the long-time-low temperature evoluti on of the uraninite deposit and the contacting groundwaters. In this p aper, we will discuss the basic kinetics and thermodynamics of the mod el as well as the encouraging results so far obtained. The kinetic mod el has been applied to the aluminosilicates system. The results show t hat the interactions with clay minerals control the bulk composition o f groundwater, The kinetic approach is able to describe the evolution of the groundwater composition along the hydrogeological pathways stud ied. The uranium system has been modelled by simulating the dissolutio n of uraninite along the flowpaths investigated. This modelling is bas ed on equilibrium assumptions. The evolution of the redox state of gro undwaters along different flowpaths is well reproduced. (C) 1997 Elsev ier Science B.V.