Models for hydrogen uptake and release kinetics by zirconium alloys at high temperatures

The authors’ models on hydrogen uptake and release kinetics by Zr alloys in pure hydrogen and steam atmospheres are overviewed and refined. On this base, a more general model considering the hydrogen uptake kinetics in various hydrogen–steam–argon mixtures, typical for experimental conditions, and including two mechanisms (first, direct reaction with molecular hydrogen, and second, absorption of hydrogen liberated by the decomposition of water or steam during the oxidation process and absorbed as part of the oxidation mechanism) as the limiting cases, is developed. The new model is implemented in the mechanistic single fuel rod code SVECHA/QUENCH and applied to analysis of recent experimental data on hydrogen uptake and release kinetics in various atmospheres.