Oxidation properties of Zr-Nb alloys at 973-1273 K in air

In order to investigate the oxidation behavior of LWR cladding materials under the condition of reactor accidents, e.g. LOCA, Zr-Nb alloys with 1-10 wt%Nb and Zircaloy-4 (0 wt%Nb) were oxidized at 973-1273 K in dry air. The weight gain due to oxidation increased with Nb content at 973 and 1073 K was the smallest for 2.5 wt%Nb at 1173 and 1273 K. The oxidation kinetics obeyed the parabolic rate law without a few cases, e.g. 6-10 wt%Nb and 1273 K. The parabolic rate constant at high temperatures had the somewhat low activation energy compared to that at low temperatures. These results implied that such oxidation behaviors of Zr-Nb alloys related to the lattice structures of oxide films as well as underlying metal during oxidation. Especially at high temperatures, 6ZrO₂-Nb₂O₅ compound might promote the oxidation of Zr-Nb alloys with high content of Nb.