Corrosion and Ion Irradiation Behavior of Ceramic-Coated Nuclear Fuel Cladding

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.