Effect of lithium hydroxide on stability of fuel cladding oxide film in simulated pressurized water reactor primary water environments

The trend in pressurized water reactors (PWR) toward higher burnups, increasing lithium concentrations, and higher coolant temperatures imposes a demand for better fuel cladding corrosion and hydriding properties. There is a lack of reliable and fast in-situ techniques to investigate zirconium alloys in high-temperature water environments. The contact electric resistance (CER) technique was used to measure the electric resistance of the oxide growing on a zirconium-based fuel cladding material. Lithium hydroxide (LiOH) decreased electric resistance of the oxide when LiOH was in excess of ∼ 70 ppm in PWR water at 300°C. Electric resistance of the oxide was dependent upon LiOH concentration and was shown to correlate inversely with the effect of LiOH on weight gain. Kinetics of the decrease of electric resistance indicated the mechanism of degradation was a phase transformation rather than a diffusion-limited process.