Modelling Uranium Corrosion by Hydrogen and Formation of Uranium Hydride

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Long-term storage of nuclear fuel requires specialist storage conditions, for both human and environmental safety. Some waste-streams containing uranium metal, e.g. Magnox fuel held at Sellafield, undergo long-term storage before spent fuel reprocessing. During the storage of the metal, the formation of uranium hydride is a recognized hazard, with many potential issues, including the formation of the pyrophoric material and the mechanical stress introduced by the metal-hydride interfaces. The hydride can form whether or not the outer layer of the uranium metal has been oxidized to uranium oxide, as hydrogen percolates through the oxide layer. Understanding the long-term ageing of the nuclear fuel is of vital importance and although the control over the corrosion of the metal by hydrogen and the structure and properties of the resulting hydride are fundamental to addressing the safety concerns of long-term storage, experimental investigation of such systems is hindered by the radioactivity of the samples, making modelling techniques invaluable tools for studying the metal-hydride interface. We will investigate the structure and properties of the interface between uranium metal and hydride using a holistic modelling approach that combines calculations over differing length scales. In order to enhance the safety of the spent fuel during storage by defining the structural details of the metal-hydride interface and its relationship with the mechanical stress and reactivity at the interface. We aim to provide (1) an atomistic model of the early stages of formation of the hydride on the metal, (2) the percolation of hydrogen through the oxide layer formed due to metal corrosion by oxygen, and (3) the defect chemistry at the metal-hydride and metal-oxide interface.