Modeling the Radiolytic Corrosion of Fractured Nuclear Fuel under Permanent Disposal Conditions

A two-dimensional model has been developed to simulate the corrosion of nuclear fuel pellets under permanent waste disposal conditions in a steel vessel with a corrosion-resistant copper shell. The primary emphasis was on the corrosion behavior within cracks with various dimensions. It was shown that a simplified α-radiolysis model which only accounts for the radiolytic production of H2O2 and H2 provides a reasonably accurate simulation and is a time-efficient alternative to the use of a model including a full α-radiolysis reaction set. Both radiolytic H2O2 and H2 can accumulate inside the cracks. However, the [H2O2] is regulated by its reaction with UO2 to cause corrosion and especially its decomposition to O2 and H2O. This leads to [H2] much greater than [H2O2] within the cracks. The critical [H2], [H2]crit, required to completely suppress corrosion has been calculated for various crack widths and depths. The maximum [H2]crit is only ∼ 12 times that required on a planar surface irrespective of the dimensions of the crack. The build up of H2 within cracks is effectively a shift to more reducing conditions. As a consequence, the redox conditions within cracks begin to decouple from the external redox conditions. This makes the fuel corrosion process at these locations less sensitive than might be expected to the influences of the H2 and Fe2+ produced by corrosion of the steel vessel. © 2014 The Electrochemical Society. [DOI: 10.1149/2.032408jes] All rights reserved.