Tritium adsorption and absorption on (100) and (001) surfaces of pure and tin defective zirconium

Abstract

Zirconium alloys such as zircaloy-4 are used as tritium (T) getter materials in tritium-producing burnable absorber rods (TPBARs) due to their ability to capture T, thereby forming metal hydrides. Developing an understanding of T adsorption onto zircaloy prior to diffusion into the subsurface is relevant for rational tritium getter and TPBAR design, to improve material properties for nuclear applications. Herein, density functional theory calculations revealed the preferred binding sites for T adsorption on Zr(001) and Zr(100). The energy barriers of T transfer, along the surface and from the surface to the subsurface were computed. The adsorption properties of Zr(001) were found to be superior to those of Zr(100). Surface tin impurities were found to strongly repel T. The presence of subsurface and surface tin resulted in higher absorption energy barriers for both the forward and reverse processes. Based on the calculated energy barriers, a surface to surface T diffusion coefficient of 9.53 × 10⁻¹⁰ m² s⁻¹ is expected for pristine Zr(001). A surface to subsurface T diffusion coefficient on the order of 10⁻¹³ m² s⁻¹ is predicted in pristine Zr, decreasing to 10⁻¹⁹ m² s⁻¹ for the transfer with a subsurface tin impurity.