SEDL / STP / STP633-EB / STP35569S

Oxidation of Zirconium During a High-Temperature Transient

Sawatzky, A
Senior scientist and technologists, Materials and Component Development Branch, Atomic Energy of Canada Limited, Whiteshell Nuclear Research Establishment, Pinawa, Manitoba, Canada

Ledoux, GA
Senior scientist and technologists, Materials and Component Development Branch, Atomic Energy of Canada Limited, Whiteshell Nuclear Research Establishment, Pinawa, Manitoba, Canada

Jones, S
Senior scientist and technologists, Materials and Component Development Branch, Atomic Energy of Canada Limited, Whiteshell Nuclear Research Establishment, Pinawa, Manitoba, Canada

Pages: 16    Published: Jan 1977

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Abstract

A physical model describing oxidation and oxygen diffusion under non-isothermal conditions is presented. It assumes (a) equilibrium at phase interfaces, as is usual in the treatment of diffusion, and (b) oxygen supersaturation of the β-zirconium to precipitate α-zirconium on cooling. An important consideration, not required in isothermal diffusion, is that the equilibrium oxygen concentrations in the α- and β-phases decrease with temperature.

During isothermal oxidation at temperatures above 850°C, the phase distribution is zirconium dioxide (ZrO²/α/β. This model predicts that on slow cooling, oxygen in the β-region diffuses to the α/β interface leading to a depletion of oxygen in this region with a corresponding increase in the thickness of the α-layer. With more rapid cooling, α-zirconium is precipitated in the β-region near the α/β interface. The oxygen concentration of the β-region is determined not by the maximum temperature in the transient but by the lowest temperature at which appreciable diffusion is still possible.