Zircaloy-4 oxidation at 1300 to 2400/sup 0/C

The oxidation kinetics of Zircaloy-4 in steam have been extended to 2400/sup 0/C. The ZrO/sub 2/ and ..cap alpha..-Zr layers display parabolic growth behavior over the entire temperature range studied. A discontinuity in the oxidation kinetics at 1510/sup 0/C causes rates to increase above those previously established by the Baker-Just relationship. This increase coincides with the tetragonal-to-cubic phase transformation in ZrO/sub 2-x/. No additional discontinuity in the oxide growth rate was observed when the metal phase melted. The effects of temperature gradients were taken into account, and corrected values representative of near-isothermal conditions were computed. Oxide growth was also measured in various steam-hydrogen mixtures at 1565/sup 0/C and 1815/sup 0/C. Hydrogen concentrations up to 90 mol% had no effect on oxidation kinetics. The rate-controlling factor appears to be diffusion through the oxide layer. Finally, the oxidation kinetics of prereacted Zircaloy-15 mol% UO/sub 2/ were measured at 1400 to 2150/sup 0/C. The rates were comparable to those obtained for Zircaloy above 1500/sup 0/C.