PNNL

Abstract

Zirconium alloys (e.g., Zircaloy-4) are used as tritium (3H) getter materials in tritium-producing burnable absorber rods (TPBARs) owing to their ability to capture 3H, and chemically convert them into metal hydrides. Understanding of 3H diffusion mechanisms in zircaloy is crucial for optimal design of material performance in nuclear technology. Here we perform first-principles density functional theory calculations to study 3H diffusion mechanism in pure and impure Zr with a low concentration of tin (Sn) atoms to determine the impact of the presence of Sn atoms on the movement of 3H atoms through the material. First, we calculated the diffusion barriers for 3H in pure Zr by taking different migration pathways. We then introduced a low concentrations of Sn impurity and systematically explored the impurity effect on the diffusion barriers for 3H. Using our calculated diffusion energy barriers, we further obtained the diffusion coefficients and analyzed the results by comparing them with the experimental and previously calculated values. A diffusion coefficient of the order 10-8 m2/s is predicted. We also found that the presence of a Sn impurity could reduce the diffusivity up to four orders of magnitude. Our results could serve as guidelines for further experimental investigation.