Characterization of oxides formed on model zirconium alloys in 360°C water using micro-beam synchrotron radiation

Uniform oxidation by the primary circuit water may limit the service of Zr alloy fuel cladding in Light Water Reactors, especially under more severe fuel duty cycles. Understanding the impact of alloy chemistry and micro structure on corrosion performance may allow us to design better alloys for severe duty cycle applications. To undertake such research, model zirconium alloys (Zr-xCr-yFe, Zr-xCu-yMo, Zr-xSn and ZrxNb, with various values of x and y) were corroded at 360°C in pure water to help isolate the role of individual alloying elements on the oxide formation process. The structure of the protective oxide, believed to be the cause for the different corrosion behavior of different zirconium alloys, was investigated using microbeam synchrotron radiation diffraction. Experiments were conducted at both the Advanced Photon Source in the USA using a 0.25 micron beam, and in the Pohang Light Source, Korea, using a 1.25 micron beam. Such micro-diffraction experiments allow the determination of phases present, oxide texture, grain size and accumulated stress, as a function of distance from the oxide-metal interface. Additional examinations were performed using cross-sectional transmission electron microscopy (TEM). The results of this examination show heretofore unobserved details of the oxide-metal interface and of the variation of phase content with distance from oxide-metal interface and overall oxide thickness. We focus in this paper on the evolution of oxide texture and phase content, between the different model alloys to help elucidate the role of individual alloying elements on the oxide formation process.