Nb speciation and microstructural characterization of the oxide layer formed on neutron-irradiated Zr-2.5 Nb alloy in high-temperature water

It is crucial to understand the degradation mechanisms of the alloy Zr-2.5 Nb, which make the pressure boundary in Canada Deuterium Uranium reactors. In the present study, Zr-2.5 Nb coupons were exposed for 567 days at 325 °C with and without neutron-irradiation in simulated primary water chemistry. A combination of scanning/transmission electron microscopy with energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy was used to investigate the base metal and oxide. The obtained results suggest that the distribution of nanopores and the variation in Nb oxidation state likely create a gradient in the oxygen concentration and electrochemical potential through the film.