Modeling sub-parabolic oxidation kinetics of Zr–Sn–Nb alloy by numerically solving the space charge effect

Zr–Sn–Nb alloy, widely used as fuel cladding in light water reactors, exhibits sub-parabolic oxidation kinetics distinct from the parabolic behavior of Nb-solute-strengthened Zr–Nb alloys. This difference arises because abundant (Nb, Fe)-rich second-phase particles in Zr–Sn–Nb alloy drastically reduce Nb solid solubility, invalidating the charge-neutrality. Here, we retain the space charge density and numerically solve the built-in electric field evolution without invoking charge neutrality. The electrochemical model for the corrosion of zirconium alloys accurately reproduces Zr–Sn–Nb alloy’s oxidation kinetics at 360 ∘ C, yielding a power-law exponent of [Formula: see text] and a mean absolute percentage error of 4.86%. This work demonstrates that explicitly solving the space charge effect numerically is essential for predicting corrosion behavior of the zirconium alloy where solute compensation is limited.