First-principles study of the tritium formation in γ-LiAlO₂ pellets and diffusion into Zircaloy-4 getter

Tritium (T) occurs only in trace amounts in the Earth’s environment. To make T in abundance, nuclear reactions are needed. In tritium-producing burnable absorber rods (TPBARs), γ-LiAlO₂ pellets enriched with ⁶Li isotope are used to produce T. When irradiated in a pressurized water reactor, the LiAlO₂ pellets absorb neutrons, simulating the nuclear characteristics of a burnable absorber rod, and produce T through ⁶Li + n à --> T + α. The T reacts with the Ni-coated Zr-base getter where it is captured and leads to formation of metal hydrides. However, accurate analysis of the T transport through the ceramic pellets and the barrier/cladding system is hampered by the lack of fundamental data about T solubility and diffusivity. In this presentation, using first-principles density functional theory, we will elucidate the formation and diffusion pathways of T species (T, OT, T₂, T₂O, CT₄ etc.) in γ-LiAlO₂ depending on the surface structure, vacancy types and different kinds of impurities. We will also demonstrate how these T species diffuse from surface of γ-LiAlO₂ through the Ni layer into the Zircaloy-4 getter to form hydrides. Our results provide a better understanding of T transport properties within TPBARs to improve performance and increase T production with high confidence.