Comparative high-temperature oxidation tests with Zircaloy-4 in various atmospheres

This study presents results of overall 124 oxidation tests of Zircaloy-4 at 900°C, 1000°C and 1100°C in different nitrogen-containing atmospheres, namely air (oxygen-nitrogen), steam-nitrogen, steam-air, and, for comparison, pure steam under comparable boundary conditions. The experiments were conducted in a tube furnace coupled with a sophisticated gas/steam inlet system and a mass spectrometer to analyse the composition of the off-gases. The experiments confirmed the strong effect of nitrogen on the oxidation of zirconium alloys. Metallographic post-test examinations were conducted mainly using optical microscopy. The oxidation kinetics of Zircaloy-4 in atmospheres containing nitrogen was similar to each other, but was much faster compared to reference tests in pure steam. Initial local attack of nitrogen was observed for all gas mixtures containing nitrogen, whereas the oxide scale formed under steam atmosphere developed homogeneously.