Measurements of Zirconium Alloy Oxide Layers

Abstract

Introduction - This is an overview of results, presented at APCOM workshops since 2001, achieved at systematic measurements on samples of oxide films on tubes of Zr1Nb, ZIRLO and Zry-4W, used for fuel cladding in light water reactors, which had been grown in the Research Institute UJP [1] at VVER conditions in water of 360°C with various times from one day up to 4 years. In a high temperature aqueous environment oxides are formed by diffusion of oxygen ions through the built-up layer, combining with zirconium ionized by electron emission [2]. The corrosion of the zirconium is due to oxide formation by the transfer of electrons from the metal to the water, whereby oxygen ions flow in the opposite direction. Thus the corrosion rate depends largely on the electron motion, which is governed by the conductivity of the oxide layer. The investigation of the electrical properties of the oxide is therefore of interest for the understanding of the corrosion resistance of the Zircaloys. It is well known [2,3,4] that ZrO2 is predominantly an electronic high-resistivity semiconductor with a low amount of ionic conduction (over room temperature). The band gap is approximately 5 eV, the work function 4.0 eV and the relative permittivity 22.