The aim of this work is to provide credibility to the radiolytic models developed for performance assessment studies. Nowadays, there is a tendency to consider them useful tools for predicting the behaviour of spent fuel matrix under repository conditions, although they still suffer of limitations due, among others, to the following reasons: limited availability of kinetic data, difficulty to handle heterogeneous systems, lack of model validation.
A kinetics-based model to predict the dissolution of UO2 α-doped pellets under initial anoxic conditions is presented and compared with experimental results previously obtained. The uranium and plutonium concentrations in solution are predicted by considering the presence of an α-radiation field and its influence due to radiolysis of water on the pellet surface oxidation and subsequent dissolution.
The initial parameters required by the model in order to reproduce the pellet alteration process are: system geometry, chemical composition of the leachant, physico-chemical characteristics of the leachate and oxidation conditions of the pellet surface (expressed in terms of U(VI)/U(IV) ratio). The last one is the key parameter in the model for simulating the initial quick dissolution process. The results obtained are compared with experimental data. The agreement between the predictions obtained and the experimental published data is good.
The influence on the matrix oxidation – dissolution process due to the α-radiation field as well as the release of Pu are reproducible by the model. The Pu concentration trends as a function of time are explained in connection with the matrix dissolution process and are controlled by the formation of the secondary phase “Pu(OH)4(s)”.