Influence of stress developed due to oxide layer formation on the oxidation kinetics of Zr–2.5%Nb alloy

Abstract

Knowledge of oxidation kinetics of Zr alloys is extremely important because it helps to evaluate the lifetime of pressure tubes, which constitute an integral part of the heat transfer system of many nuclear power stations. The presented diffusion model describes oxidation kinetics of zirconium alloy (Zr–2.5%Nb) under stress at the oxide/metal interface. A major assumption of this model is that the gas/oxide interface moves inwards into the oxide scale by creating a continuous network of internal defects (cracks, voids, etc.). A linear relation coupling the equations describing the evolution in the movement of the gas/oxide and oxide/metal interfaces was used as a first approach. After a certain period of time, the diffusion process obeys a pseudo-steady-state solution. A distance between gas/oxide and oxide/metal represents a thickness of the non-porous layer that remains constant during the pseudo-steady-state growth. An explanation of a possible transition between the parabolic and the cubic character of the oxidation kinetics is presented.