Integration of the H

Different models describing the dissolution mechanism of spent nuclear fuel under repository conditions have been developed in the last years. One of the most evolved ones is the Matrix Alteration Model (MAM), which is an Alteration/Dissolution source term model based on the oxidative dissolution of spent fuel. Oxidant and reducing species can be naturally or radiolytically-generated. The experimentally-observed inhibition of matrix dissolution by H2 , was integrated into MAM by considering that H2 is able to consume the oxidant species responsible for UO2 oxidation, e.g. H2 O2 . As a consequence, MAM predicts lower H2 O2 concentrations for systems containing larger amounts of dissolved H2 . Radiolysis experiments carried out by Pastina and coworkers have shown that under specific conditions such as high linear energy transfer (LET) radiation and absence of solid phase, dissolved H2 has a negligible effect on the H2 O2 concentration, thus suggesting that the H2 inhibition effect catalyzed by the matrix surface has not been properly implemented in MAM. Modelling exercises performed in this work confirm such point and reveal the necessity of considering H2 -activation when modelling this kind of systems. In addition, it has been demonstrated that, for high LET radiation, a clear dependence exists between the extent of the H2 activation and the integral LET of the radiation. The integration of the function describing such dependence allows improving the implementation of the H2 inhibition effect in MAM.Copyright © 2009 by ASME