Low temperature (< 300 ° c) oxidation of Zircaloy-2 in water

Abstract

Measurements of the oxidation of two batches of Zircaloy-2 at 200, 250, 275 and 300 °C in demineralised water, combined with earlier unpublished data at intermediate temperatures, have shown that published extrapolations of the oxidation rate downward in temperature gave inaccurate predictions. Neither the kinetic rate law, nor the temperature coefficient was regular, the latter being low for temperatures between 260 and 290 °C, and for exposure times below ~ 50 days. The irregularities indicated successive changes in the balance between a series of oxidation controlling processes. Interferometer measurements, optical and electron microscopy have shown that up to 40% of the weight gain resulted from the formation of local regions of thicker oxide (together with some oxygen dissolution in the metal). Nucleation of spinel-like crystals (possibly of magnetite) on the oxide surface also contributed to the weight gain. Their deposition was probably controlled by the local electrical properties of the oxide film.