The structures of oxides formed in water and lithiated water on three Zr-based alloys with varied corrosion behavior were studied with micro-beam synchrotron radiation and optical microscopy. Micro-beam synchrotron radiation (0.2 µm spot) has a unique combination of high elemental sensitivity (ppm level) and fine spatial resolution that allowed the determination of various oxide characteristics such as phase content, texture, grain size, and composition as a function of distance from the oxide-metal interface. Micro-beam X-ray fluorescence shows that the oxides formed in lithiated water have increased levels of Fe absorbed from the autoclave environment indicating greater oxide porosity in these oxides. The phase content, texture, and grain size of oxides were studied in detail using synchrotron radiation micro-beam diffraction for samples corroded in water and lithiated water. A remarkable periodicity was observed in the oxide structures using various techniques including X-ray peak intensities for both monoclinic and tetragonal zirconia, texture, and optical microscopy. The periods were similar to the transition period and were less visible in the oxides that behaved worse in lithiated water. These results are discussed in terms of models of oxide growth and of the differences between alloys.

Microstructure and growth mechanism of oxide layers formed on Zr alloys studied with micro-beam synchrotron radiation

https://www.research.manchester.ac.uk/portal/files/48465324/1_s2.0_S1359645415005698_main.pdf

The effect of Sn concentration on oxide texture and microstructure formation in zirconium alloys

Barrier oxide chemistry and hydrogen pick-up mechanisms in zirconium alloys

An X-ray absorption near-edge structure (XANES) study of the Sn L3 edge in zirconium alloy oxide films formed during autoclave corrosion

The pre-transition oxides formed on five different types of Zircaloy-2 alloys have been characterized in-situ using electrochemical impedance spectroscopy (EIS) in high-temperature water simulating BWR conditions at 300°C. The contribution of the oxide film properties to the impedance spectra has been distinguished from the contribution of the corrosion reaction by performing additional EIS measurements in a gas atmosphere. To obtain a correlation between the oxide film thickness, the oxide growth rate, and the impedance parameters, the EIS data have been fitted to the transfer functions derived from the Mixed Conduction Model for oxide films. As a result, the oxide growth rate of each alloy has been calculated assuming that the growth rate is proportional to the flux of oxygen vacancies through the film. The values of the oxide film thickness based on the model calculations have proved to be in good agreement with the values measured from the cross-section micrographs of the specimens using scanning electron microscopy (SEM). The measured corrosion properties have been qualitatively correlated to the secondary phase particle distributions of the five fuel cladding materials. However, to establish a quantitative correlation between the corrosion rates and the second phase particle distributions of these alloys, more data on the microstructure of the metal-oxide interface are needed.

VP Filippov

Papers

Mössbauer Investigations of the Chemical States of Tin and Iron Atoms in Zirconium Alloy Oxide Film