Zirconium metal--water oxidation kinetics. II. Oxygen-18 diffusion in. beta. -Zircaloy

Abstract

The diffusion of oxygen-18 in ..beta..-Zircaloy-4 was measured from 900 to 1500/sup 0/C and survey measurements were made for ..beta..-zirconium and ..beta..-Zircaloy-2. The tracer diffusivity was measured over the entire temperature range and the chemical diffusivity from 1100 to 1500/sup 0/C. The experiments were performed by using oxygen-18 as the tracer and activating it by proton bombardment. Complementary measurements were also made using Auger Electron Spectroscopy. Results indicated that the tracer and chemical diffusivity of oxygen in ..beta..-Zircaloy-4 are statistically identical, and there is no oxygen concentration dependence over the oxygen concentration range studied, 0.1 to 0.6 wt percent. The temperature dependence of the diffusivity from 1000 to 1500/sup 0/C is D = 2.48 x 10/sup -2/ exp (-28200/RT) cm/sup 2//s. Below 1000/sup 0/C, the diffusivity dropped sharply because a two-phase ..cap alpha.. + ..beta.. mixture was present. Results for the ..beta..-Zircaloy-2 and ..beta..-zirconium indicated that the alloying additions have no influence upon the oxygen diffusivity. Combination of three sets of boundary conditions (thin-film tracer diffusion, single-phase chemical diffusion couple, and phase-boundary-movement chemical diffusion couple) and two methods of oxygen profiling (oxygen-18 radioactivation and Auger Electron Spectroscopy) were used to increase the confidence in the results. Current results are aboutmore » 50 percent lower than the previous results of Mallett, Albrecht, and Wilson. The diffusivity of oxygen-16 is expected to be 6 percent greater than that for oxygen-18. (auth)« less