A mechanism for in-reactor oxidation of zirconium alloys from oxide electrical characteristics: (III). Zr-2.5 wt % Nb

A molten nitrate/nitrite eutectic has been used for studying the electrical characteristics of oxides on heat-treated Zr-2.5 wt % Nb in two conditions: quenched from 850°C or quenched, cold-worked and aged at 500°C. Oxides were grown in either water or steam, with or without oxygen, out-of- or in-reactor (fast flux $\text{1.5 × 10}{}^{13}\text{n · cm}{}^{\mathrm{?2}}\text{· s}{}^{\mathrm{?1}}$). Tafel analysis of current-voltage curves yielded oxide growth rates that were generally in reasonable agreement with weight gain data. Radiation suppressed the oxidation rate and the ionic and electronic oxide conductances, by inducing oxide recrystallisation and precipitating niobium from solid solution in the metal. The latter was not a factor for quenched, cold-worked and aged material whose most important corrosion resistant property was that its oxide did not become highly water permeable in reactor environments containing free oxygen. In this the alloy's behaviour was in sharp contrast to that of Zircaloy-2 and other alloys.