In situ measurement of electrical conductivity of Zircaloy oxides and their formation mechanism under electron irradiation

Abstract

Insitu electrical conductivity of Zircaloy-2, improved Zircaloy-2 and Zircaloy-4 oxide films has been measured with 1 MeV electron irradiation using gold, copper and zirconium electrodes during beam-on and -off in the temperature range of 296–680 K in order to find the rate controlling factor of oxidation of the alloy. Current–voltage characteristics of all oxides during irradiation show almost ohmic behavior for Zircaloy-2 and Zircaloy-4 oxides, and non-ohmic for improved Zircaloy-2 oxide where the current is electronic in nature and may be associated with ohmic and Schottky and/or Poole–Frenkel processes, respectively. The electrical conductivity of such films under irradiation, called radiation induced conductivity (RIC), is proportional to the irradiation flux and it is predominantly due to electronic excitation. Subsequent subjection of the specimens under irradiation with beam-on and -off shows RIC by electron excitation from the valence to conduction band and annealing of the conductivity at temperature, respectively. It is concluded that the electron motion dominates the electrical conductivity of Zircaloy oxides. Therefore, the slow-diffusing negative oxygen ions control the oxidation process of Zircaloys.