Theoretical investigations of the tritium diffusion pathways in γ-LiAlO₂ pellets

In tritium-producing burnable absorber rods (TPBAR), γ-LiAlO₂ is used in the form of an annular ceramic pellet enriched with ⁶Li isotope and is located between the zircaloy-4 liner and nickel-plated zircaloy-4 tritium getter with a gas gap in between. When irradiated in a pressurized water reactor (PWR), the ⁶Li pellets absorb neutrons and produce tritium (³H) through ⁶Li+ n → ³H + α. However, accurate analysis of the ³H transport through the ceramic pellets and the barrier/cladding system is hampered by the lack of fundamental data about the hydrogen isotope solubility and diffusivity. For TPBARs to enable effective tritium production in PWRs and to improve the performances of these components, we are investigating the ³H solubility and diffusion pathways in the bulk and surface of γ-LiAlO₂ with different concentrations of lithium defects. The calculated results for bulk and low-index surfaces properties, thermal conductivity, ³H activation energy barriers, and the diffusion coefficients in γ-LiAlO₂ are in good agreement with the available experimental values. With a better knowledge of ³H transport properties within γ-LiAlO₂ pellets through our modeling, its performances and higher ³H production rate can be further evaluated experimentally with a higher confidence.