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In an effort to develop coatings to increase the oxidation resistance of nuclear fuel cladding during a loss-of-coolant-accident (LOCA), undoped and ytterbium-doped titanium aluminum nitride (Ti x Al 1-x N) coatings were deposited onto ZIRLO® and grade-5 titanium substrates using a hybrid coating technique incorporating both resistance evaporation and cathodic arc physical vapor deposition (CA-PVD). The coating systems consisted of a titanium bond layer, an undoped TiAlN layer, and an outer TiAlN layer doped with varying levels of ytterbium (0.44 to 33.24 at.%). The coated materials were subjected to high temperature atmospheric oxidation testing and differential scanning calorimetry (DSC) to evaluate the effect of different Yb dopant concentrations on the Ti x Al 1-x N coating oxidation resistance. The results showed that the coatings evaluated in this study protected the tubular ZIRLO® cladding material from oxidation when exposed to air at temperatures up to 1200 °C. DSC data showed that the corrosion resistance of coatings with Yb dopant concentrations of 0.44 and 0.64 at.% was better than that of undoped Ti x Al 1-x N coatings and of Ti x Al 1-x N coatings with Yb concentrations ≥ 4.78 at.%. Yb doping and the 0.44 and 0.64 at.% level also resulted in a lower rate of oxide scale growth and improved scale adherence, which further slowed oxidation kinetics. Peak oxidation resistance was observed in the TiAlN coating with a 0.44 at.% ytterbium dopant concentration. Ytterbium concentrations of 4.78 at.% and greater led to accelerated oxidation rates for the testing conditions studied compared to undoped TiAlN. These results show that ytterbium doped coatings are possible candidates for high temperature resistance of accident tolerant fuel coatings. [ABSTRACT FROM AUTHOR]

In an attempt to develop a nuclear fuel cladding that is more tolerant to loss-of-coolant-accidents (LOCA), ceramic coatings were deposited onto a ZIRLO™ 1 1 ZIRLO is a trademark of Westinghouse Electric Co. substrate by cathodic arc physical vapor deposition (CA-PVD). The coatings consisted of either Ti 1 – x Al x N or TiN ceramic monolithic layers with a titanium bond coating layer as the interlayer between the ceramic coating and the ZIRLO™ substrate to improve coating adhesion. Several coating deposition trials were performed investigating the effects of bond coating thickness (200–800 nm), ceramic coating thickness (4, 8 and 12 μm), substrate surface roughness prior to deposition, and select coating deposition processing parameters, such as nitrogen partial pressure and substrate bias, in order to optimize the coating durability in a corrosion environment. Corrosion tests were performed in static pure water at 360 °C and saturation pressure (18.7 MPa) for 3 days. The optimized nitride-based ceramic coatings survived the autoclave test exposure showing very low weight gain of 1–5 mg/dm 2 compared to the uncoated ZIRLO™ samples which showed an average weight gain of 14.4 mg/dm 2 . Post-corrosion exposure analytical characterization showed that aluminum depletion occurred in the TiAlN coated samples during the autoclave corrosion test, which led to the formation of the boehmite phase that degraded the corrosion durability of some of the TiAlN samples. However, by eliminating the aluminum content and depositing TiN, the boehmite phase was prevented from forming. Best results in TiAlN coated samples were obtained with 600 nm Ti bond coating thickness, 12 µm coating thickness and 0.25 µm substrate surface roughness (E14). Results are discussed in terms of the capability of TiN and Ti 1 – x Al x N coatings to improve the high temperature corrosion resistance and oxidation resistance of zirconium alloy cladding. [ABSTRACT FROM AUTHOR]