We present a numerical model to predict oxide scale growth and failure in zirconium clad exposed to
water in out-of-pile conditions. The model includes the formation of two oxide sublayers on top of the
metal clad, whose interfaces are tracked using a Stefan model coupled to diffusion kinetics. The kinetics
is coupled to a thermal model that accounts for temperature gradient effects via thermo-migration inside
the clad. The model also includes a mechanical failure criterion based on the accumulation of
compressive stresses in the oxide near the interface with the metal. We present results of oxygen
diffusion into the clad, oxide formation as a function of time, and oxide fragmentation by mechanical
failure. We find that the growth of the oxide scale as the cubic root of time is recovered for a special
charge distribution near the oxide interface. This charge distribution can be suppressed via alloying,
which explains the square root scaling for certain Zr alloys. A sensitivity study has been conducted,
showing that variations of ± 15% in selected model parameters result in approximately ± 5% changes in
model predictions.