First-principles study of the tritium reaction and diffusion on the γ-LiAlO2 (1 0 0) surface with carbon impurity

Abstract

Carbon (C) deposits have been experimentally found in numerous locations throughout the tritium-producing burnable absorber rods (TPBARs) on virtually every component. It is important to consider the typical C impurity in γ-LiAlO2 pellets investigation. Using the first-principles calculations, we explore the possible C impurities on γ-LiAlO2 (1 0 0) surface and their effect on tritium (T, 3H) reaction and diffusion. Our results show that the C prefers to adsorb on the outmost O-Li bridge site or substitute the outmost Al site. The adsorption C could not stay on the surface for a long time, due to the strong attraction with 3H. With increasing the number of 3H from bulk to the surface, the 3H and C atoms can form tritiated methane (CT4) and desorb from the surface. Therefore, CT4 is an extra product by C impurity from γ-LiAlO2 pellets in TPBARs. For the T/OT diffusion on γ-LiAlO2 (1 0 0) surface with C substitution, the T diffusion is always avoided by the O bonding with the substitutional C, because of the strong C-O covalence. Similarly, the OT diffusion is apart from the substitutional C, due to the repulsion of anion dangling-bond on C. Thus, T/OT diffusion is hampered by C-substituted Al site.