Model to simulate high temperature oxidation kinetics of zircaloy-4: Parabolic and linear behaviour

Abstract

A calculation code to simulate parabolic and linear behaviour of Zircaloy-4 oxidation between 600 and 862°C in water vapour was developed. This code consists of solving the diffusion equations by the finite-difference method. This method in its explicit version was employed previously, but this type of calculation becomes impracticable with present-day computers when attempts are made to simulate long-term experiments (24 h). This is why the implicit finite-difference method is proposed here: this method has the advantage of drastically reducing the calculation time. The code allowed us to calculate the relationship between the oxygen mass in theα-phase to the total oxygen mass, the oxide thickness and the diffusion profile of oxygen in the α-phase. The results obtained with the model are compared with experimental data existing in the literature for Zircaloy-4, although it could be applied to pure zirconium or other zirconium alloys if more experimental data were available. The singular behaviour of the diffusion profiles in the α-phase during linear kinetics is particularly analyzed. This work is part of a programme to study the oxide-metal interface movement during vapour oxidation of Zircaloy-4 subjected to temperature transients. Knowledge of this is of vital importance for evaluating mechanical properties of fuel claddings during possible loss of coolant accidents in nuclear power reactors.