In an attempt to develop an accident-tolerant fuel (ATF) that can delay the deleterious consequences of loss-of-coolant-accidents (LOCA), multilayer coatings were deposited onto ZIRLO ® 1 coupon substrates by cathodic arc physical vapor deposition (CA-PVD). Coatings were composed of alternating TiN (top) and Ti 1-x Al x N (2-layer, 4-layer, 8-layer and 16-layer) layers. The minimum TiN top coating thickness and coating architecture were optimized for good corrosion and oxidation resistance. Corrosion tests were performed in static pure water at 360º C and 18.7 MPa for up to 90 days. The optimized coatings had no spallation/delamination and had a maximum of 6 mg/dm² weight gain, which is 6 times smaller than that of a control sample of uncoated ZIRLO ® which showed a weight gain of 40.2 mg/dm². The optimized architecture features a ~1µm TiN top layer to prevent boehmite phase formation during corrosion and a TiN/TiAlN 8-layer architecture which provides the best corrosion performance.

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 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

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Recent concern with fuel safety in accident scenarios has motivated research into accident tolerant fuels (ATF), which are defined as fuels that could increase coping time in case of an accident. This study is an attempt to develop an ATF by improving the corrosion performance of nuclear fuel cladding during a high-temperature excursion through the application of a ceramic coating using physical vapor deposition. In this study, ceramic coatings constituted of single-layer and multi-layer TiN/TiAlN coatings with a titanium bond coat layer to improve adhesion were applied onto ZIRLO sheets using cathodic arc physical vapor deposition. The coating architecture and deposition parameters were systematically optimized to achieve good adhesion and corrosion performance, and an initial evaluation was performed for resistance to radiation damage. The coating performance was highly dependent on coating design architecture, and the best coating architecture was found to be that of eight-layer TiN/TiAlN coatings deposited with optimized parameters. The optimized coatings were corrosion tested in 360°C water for up to 90 days, showing essentially no oxygen penetration, very low weight gain, and no spallation or debonding. The samples were also examined in microscopy and X-ray diffraction after corrosion testing, and little change was observed. To evaluate the coating performance under irradiation, cross-sectional transmission electron microscopy samples of the coating were subjected to in situ ion irradiation to a dose of 20 dpa with 1 MeV Kr ions at 300°C, followed by further annealing to 800°C. Little interlayer mixing and overall damage accumulation was observed. Coating adhesion was investigated through scratch testing and post-scratched sample failure mode characterization to determine a critical load value for spallation. The coating layers are found to require a high load for debonding and spallation. The results suggest that this optimized coating system is a promising path for developing an ATF.

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