High-Temperature Oxidation of Zirconium and Zircaloy-2 in Oxygen and Water Vapor

Abstract

Zirconium and Zircaloy-2 were found to gain more weight in oxygen than in water vapor at low pressures. The pretransition oxidation kinetics of Zircaloy-2 are comparable with those of pure zirconium, both following a cubic rate law. The pretransition oxidation kinetics of Zircaloy-2 are sensitive to water vapor pressure in the range of 5-25 mm, but are not sensitive to oxygen pressure. The post-transition oxidation kinetics of Zircaloy-2 are notably dependent on the pressure of either gas, indicating a gaseous diffusion rate control. Zirconium exhibited no transition in rate from the cubic over the duration of the exposure. It is shown that the rate-controlling mechanism which results in the cubic rate law is not directly dependent on the total thickness of the oxide layer. Activation energies for the rate-controlling mechanism of the cubic rate law lie in the range 50-63 kcal/mole, indicating that similar mechanisms are operative, regardless of material or atmosphere.

Metallurgy Research Operation Quarterly Progress Report, April-June 1965

“…Thi s (1) effect was observed in both beta formed from gamma, By, and beta formed from alpha, Ba' Similarly, plastic deformation of the beta phase by tension decreases the B=a transformation rate. Tensile specimens were transformed to beta from alpha at 150 'C and strained 50% in tension.…”

“…Comparison of results for this exposure (1) shows the lattice parameter increase to be the same for crystals irradiated in the as-grown and in the annealed condition. Length changes, however, are significantly greater for the annealed crystals.…”

“…It will be recalled that low burnup data (0.03 at. % burnup) on high purity uranium revealed very little swel- (1) ling at 700 'C. The limited swelling that was observed was primarily due to fission gas porosity.…”

“…Averbach, and Cohen found that plastic strains up to 2% (1) elongation favored the austenite = martensite transformation; whereas, plastic strains above 2% elongation hindered the subsequent transformation. concerned with the preliminary results of a study of the beta phase of plutonium as it is affected by the phase from which it originates.…”

“…Again the beta phase formed from gamma was deformed only by compression since the ductility of B was very low. The influence (1) Plastic deformation of the stable alpha phase accelerated the a = B transformation at slow transformation rates. This effect is similar to the effect of beta plastic deformation on the B --' Y transformation.…”