Study of Tritium Diffusivity in Pure and Sn-Defective Zr: A First-Principles Density Functional Theory Approach

Zirconium alloys (e.g., zircaloy-4) are used as tritium(H-3) getter materials in tritium-producing burnable absorberrods (TPBARs)owing to their ability to capture H-3 and chemically convertthem into metal hydrides. Understanding of H-3 diffusionmechanisms in zircaloy is crucial for the optimal design of materialperformance in nuclear technology. Here, we perform first-principlesdensity functional theory calculations to study the (3)Hdiffusion mechanism in pure and impure Zr with a low concentrationof tin (Sn) atoms to determine the impact of the presence of Sn onthe movement of H-3 atoms through the material. First, wecalculated the diffusion barriers for H-3 in pure Zr bytaking different migration pathways. We then introduced a low concentrationof Sn impurity and systematically explored the impurity effect onthe diffusion barriers for H-3. Using our calculated diffusionenergy barriers, we further obtained the diffusion coefficients andanalyzed the results by comparing them with the experimental and previouslycalculated values. A diffusion coefficient of the order of 10(-8) m(2)/s is predicted. We also found thatthe presence of a Sn impurity could reduce the diffusivity up to 4orders of magnitude. Our results could serve as guidelines for furtherexperimental investigations.