The oxidation kinetics of Zircaloy-4 in steam have been extended to 2400°C. Growth of the ZrO₂ and α-Zr(O) layers display parabolic behavior over the entire temperature range studied; however, a discontinuity in the oxidation kinetics above 1510°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_2−x. No additional discontinuity in the oxide-growth rate is observed upon melting of Zr(O). The effects of temperature gradients have also been taken into account, and corrected values representative of near-isothermal conditions have been computed.

Experiments have been performed in steam-hydrogen mixtures at 1565 and 1815°C. Concentrations of hydrogen up to 90 mol% have no effect on the oxidation kinetics. The rate-controlling factor appears to be the available flux of oxygen atoms incident to the reaction surface and is not dependent upon hydrogen content.