As a part of a broader program designed to consider oxidation-related phenomena important during the high temperature reaction of Zircaloy in steam under conditions anticipated for a hypothetical loss-of-coolant accident in a light water reactor, the diffusivity of oxygen in beta-Zircaloy-4 and the isothermal oxidation rates of Zircaloy-4 in steam were determined. Both sets of measurements were made in the temperature range 900 to 1500°C (1652 to 2732°F), and considerable care was exercised to ensure the accuracy of temperature determinations.

Diffusivity determinations were made using an ¹⁸O radioactivation technique; supplemental measurements were made by Auger electron spectroscopy and by observations of the movement of (α + β)/β boundaries during diffusion anneals. We observed no differences between tracer and chemical diffusivity values or among oxygen diffusivities determined in zirconium, Zircaloy-2, and Zircaloy-4. Between 1000 and 1500°C (1832-and 2732°F) the combined data set for the diffusion of ¹⁶O (corrected for mass effects from the ¹⁸O data) was represented by Dβ=0.0263 exp(−28200/RT) cm2/s

Oxidation rate curves were determined at 50°C (90°F) intervals, ten specimens being used to define the curve at each temperature. Above 1000°C (1832°F) parabolic oxidation behavior was observed; below that temperature, the curves for the rate of growth of the oxide layer were not parabolic. For this reason, statistical evaluation of the data based on parabolic kinetics was limited to temperatures above 1000°C except for alpha-layer growth, which followed parabolic kinetics over the entire temperature range. The rate constants were well represented between 1000 and 1500°C by Arrhenius relationships given by δ2φ2=0.01126 exp(−35890/RT) cm2/s δ2φ2=0.7615 exp(−48140/RT) cm2/s δ2ξ2=0.3412 exp(−41700/RT)cm2/sδ2τ2=0.1811 exp(−39940/RT) (g/cm2)2/s where δ2/2 are the rate constants (defined by dK/dt=1/Kδ2/2 K) for oxide layer growth, ϕ alpha layer growth, αXI layer growth (oxide + alpha), ξ; and total oxygen consumption, τ.