Mechanical properties of CrN coatings on Zircaloy substrates for the development of accident-tolerant fuel cladding

Abstract

The cladding is an important structural component of fuel rods which serves as the first engineered barrier against the release of fission products into coolant water during reactor operation and into the surroundings in case of an accident. Zirconium alloys are adopted to be used for this purpose due to their unique high-temperature mechanical properties and low neutron absorption cross-section. However, during a loss of coolant accident, the fuel cladding undergoes extreme temperature increases (up to 1200°C), leading to thermal energy release and hydrogen generation from cladding oxidation. The development of accident-tolerant fuel cladding (ATFC) has been pursued as one of the possible solutions to overcome the inherent technical shortcomings of standard claddings. Physical vapor deposited (PVD) nitride-based coatings have shown promising results to act as protective barriers for Zircaloys. Mechanical properties of CrN-coated Zircaly-2 cladding material are investigated in this study, using micro- tensile testing. Different configurations of samples made of pure coating material and the mixture of coating and substrate material are tested to investigate the adhesion of the coated layer to the substrate and its effect on the cladding material properties. The effect of neutron irradiation is emulated by preparing and testing samples irradiated by a proton accelerator. Results of irradiated samples show that the tensile properties do not change as a result of irradiation.