The temperature dependence of the in-reactor oxidation of zirconium alloys in moist CO2 atmospheres from 573–868 k

Abstract

The temperature dependence of the in-reactor oxidation of three zirconium alloys was determined using a sweep-gas oxidation rig in the HIFAR reactor, extending the previous range of data to 868 K, and providing new data for the inreactor oxidation of Ozhennite-0.5 in moist gas atmosphere.At the lowest temperature of 573 K, the in-reactor weight gains for Zircaloy-2 and Ozhennite-0.5 were up to twice those of out-of-reactor control samples, which is equivalent to an increase of six times in the cubic rate constant. The activation energies for the in-reactor oxidation were about one third of those for out-of-reactor oxidation, indicating a mechanism involving radiation-enhanced diffusion in the oxide layer. At higher temperatures some radiation-induced suppression of oxidation occurred, the largest effects being for the zirconium +2.5 wt% niobium alloy. The effects were generally smaller than those found in previous studies of the corrosion of zirconium alloys in aqueous solution using the same reactor.