Thermochemical Compatibility and Oxidation Resistance of Advanced LWR Fuel Cladding

The thermochemical compatibility of potential replacement fuel rod cladding materials for zirconium alloys in light water reactors was assessed. Considered were the family of FeCrAl alloys, Nb-1%Zr (similar to PWC-11), and a hybrid SiC-composite with a metallic barrier layer. The niobium alloy was also seen as requiring an oxidation protective layer, and a diffusion silicide was investigated. Metallic barrier layers for the SiC-composite reviewed included an FeCrAl alloy, Nb-1%Zr, and chromium. Thermochemical calculations were performed to determine oxidation behavior of the materials in steam and for hybrid SiC-composites to determine possible interactions between the metallic layer and SiC. In addition, experimental exposures of SiC-FeCrAl alloy reaction couples at 673, 1073, and 1273 K for 168 h in an inert atmosphere were made, and microanalysis was performed. Whereas all materials were determined to oxidize under higher oxygen partial pressures in the steam environment, these varied by material. The computed and experimental results indicate the formation of liquid phase eutectic in the FeCrAl-SiC system at the higher temperatures.