Influence of Simulated LOCA on the Properties of Zircaloy Oxide Layers

Abstract

Specimens of Zr1Nb and Zry-4W were pre-oxidized first for 360 days in steam at 425 °C and were then exposed for 3 min to 1200 °C in steam, simulating loss of coolant conditions. In this way, the oxide thickness was more than doubled. The I-V characteristics, measured up to 90 V at temperatures up to 180 °C, revealed the formation of double layers, consisting of dark monoclinic oxide with 1.3 eV activation energy near the metal, and of a whitish surface phase with only 0.5 eV, for both samples. The I-V characteristics of Zr1Nb showed normal behavior, whereas Zry-4W changed from an unusual sub-linear form at low temperatures and voltages to normal space-charge limited currents at higher temperatures and voltages. Observation of the injection and extraction currents in the Zry-4W sample showed abnormally high negative zero voltages produced by extraction after former injection.