Multiple Rate Transitions in the Aqueous Corrosion of Zircaloy

Abstract

The weight gain of Zircaloy-2, -3, and low nickel Zircaloy-2 during water and steam corrosion is shown to go through two or more repetitive cycles. The evidence indicates these weight gain curves truly represnt the corrosion kinetics. Several corrosion mechanisms are considered in the light of these kinetics. While no definite mechanism can be established, a supposition that stresses in the film periodically cause it to crack at or near the oxide-metal interface appears consistent with the data. Preliminary micrographic evidence supporting the existence of a cyclic corrosion process also is shown. 1021 Zircaloy-2 ZH Zircaloy-2 L or H Low nickel Zirca]oy-2 KE-46 Low nickel Zircaloy-2 Rolled sheet (30 mils) produced from ingot 5Y-HO-9. Analysis below. Rolled sheet (62 mils) produced from ingot SA-11857. Analysis below. Rolled sheet (25 mils) produced from ingot 28260-4-6V. Analysis below. Rolled sheet (30 mils) produced from ingot KE-46. Analysis below.

3D Visualisation of Crack Distributions in Oxidised Zirconium Alloys by FIB-Slicing

“…There is no indication in any of our data to show a sudden burst of cracking at the kinetic transition, as has frequently been assumed from observation of the characteristic layered crack morphology in thicker oxides [4,5,7,14]. It is only the last sample (180 days) that appears to show a faster cracking rate.…”

“…Oxidation of zirconium alloys proceeds by the inward diffusion of oxygen ions from the oxidizing media to the metal/oxide interface, resulting in a diffusion-limited initial oxidation rate and cubic or parabolic kinetics [1]. The final breakaway is often preceded by repeated stages of parabolic kinetics where first slowing and then acceleration of the oxidation rate occurs [4][5][6]. The final breakaway is often preceded by repeated stages of parabolic kinetics where first slowing and then acceleration of the oxidation rate occurs [4][5][6].…”

Structure of zirconium alloy oxides formed in pure water studied with synchrotron radiation and optical microscopy: relation to corrosion rate

“…On individual samples, the cyclic nature of the kinetics can be easily distinguished through several repetitions. The cyclic nature of post-transition corrosion has been observed and noted for some time [16,17] and observations [8,9,18,19] of stratification in the oxide films have been correlated with the cyclic kinetics.…”

Phase transformation of oxide film in zirconium alloy in high temperature hydrogenated water

“…Fax: +82 52 217 3009. pre-transition and post-transition. In the pre-transition period, the rate of oxidation can be parabolic or cubic, and a cyclic growth of the oxide is observed [22,23]. Then, after breakaway phenomena, the oxide growth rate assumes a linear shape due to reduced oxygen diffusion.…”