Influence of Ta and Nb on the hydrogen absorption kinetics in Zr-based alloys

• Influence of tantalum and niobium on hydrogen absorption in zirconium is studied.
• Alloying Zr with Ta and Nb decreases activation energy for hydrogen diffusion.
• Tantalum has major influence on the surface reactivity of studied alloys.
• Niobium has major influence on the improvement of hydrogen diffusivity.

The kinetics of hydrogen absorption in Zr alloys containing Nb and Ta admixtures (10 wt%Nb, 12 wt%Ta and 10 wt%Nb&12 wt%Ta) is addressed. Hydrogen absorption is measured in the temperature range 400–700 °C at hydrogen pressure 1 bar using the volumetric method, and a kinetic analysis is performed to determine the mechanisms and rates of hydrogen absorption. To get further insight into hydrogen diffusivity in zirconium hydride, 1H NMR spectroscopy is used to provide the activation energies for proton jumping in the studied samples. The tantalum is found to dominantly influence the surface reactivity, while niobium influences large decrease of the activation energy for hydrogen diffusion in the bulk of zirconium hydride. This behavior is linked to the information on the structure of the alloys obtained by XRD.