Corrosion behaviour of physical vapour deposited coatings on nuclear components and Fe-Cr-Al alloy under normal operation and accident scenarios

As a result of a loss of coolant accident, temperatures within the fuel cladding can reach in excess of 1000 °C, resulting in thermal energy release and hydrogen generation. To combat this, candidate accident tolerant fuel cladding (ATFC) materials and coatings are being investigated. Physical vapour deposited (PVD) CrN and TiAlN coatings have shown promising results to act as protective barriers for zirconium alloys. Fe-Cr-Al alloys are also considered as potential ATFC candidate materials due to the formation of alumina at high temperatures, which acts as a protective oxide and has slow growth kinetics. PVD CrN and TiAlN coatings on a Zircaloy-2 substrate were exposed to reactor primary-side conditions (300 °C and pH25°C 10.2) for up to 180 days to assess their corrosion resistance under normal operating conditions. To evaluate the oxidation resistance of these coatings and a Fe-Cr-Al alloy under accident conditions, samples were exposed to high temperature steam (1000 °C) for up to 24 hours. Based upon the current results, it was found that CrN coatings acted as a barrier to corrosion under normal operating conditions and a temporary barrier under accident scenarios due to the formation of a Cr-rich oxide. The Fe-Cr-Al alloy was found to have decreased corrosion rates in comparison with stainless steels and zirconium alloys when exposed to accident scenarios due to the protective nature of the formed Al2O3 layer.