This presentation is about the oxidation of zirconium alloys at high temperatures in
various atmospheres with special focus on the time dependence of the oxide/nitride
formation to show which reactions could happen during an air ingress scenario in
reactors or in spent fuel pools.
Therefore test series were made with 2 cm Zircaloy-4 cladding tube segments at
three different temperatures, 900 °C, 1000 °C and 1100 °C and in four different
atmospheres: Steam, synthetic air, nitrogen with steam and synthetic air with steam.
These tests were made in a tube furnace coupled to a mass spectrometer.
The mass gain of the samples is shown in three diagrams. Nitrogen is significantly
accelerating the oxidation of zirconium.
For the temperature 1000 °C macro- and micrographs of the samples in all
atmospheres are shown. They prove that the nitrogen attack starts locally on the
oxide scale surface.
Another diagram shows the gas release during the reaction of Zircaloy-4 with a
nitrogen and steam atmosphere. It can be observed that there is a significant
hydrogen formation after the transition time, which is caused by the nitrogen effect.
All results are finally summarized in the 19th slide.