Electrochemical properties and dissolution of U-5 wt % Zr Alloy in HNO3 solutions

The main parameters of dissolution of U-5 wt % Zr alloy in HNO₃ solutions were determined by linear voltammetry. Without applying external potential, the electrode potential E ⁰ in 0.5–6.0 M HNO₃ solutions increases. Its value is determined by the formation of a film containing hydrated Zr(IV) and U(IV) oxides and by the cathodic reduction of the acid. The reduction of NO₃ — ions on the surface of U-5 wt % Zr alloy in 0.5–6.0 M HNO₃ occurs with high overvoltage. In experiments without applying external potential, an increase in the HNO₂ yield in accordance with this reaction leads to an increase in the alloy dissolution rate with an increase in the HNO₃ concentration in the electrolyte from 0.5 to 6.0 M. At potentials higher than 450 mV vs. Ag/AgCl electrode, the U-5 wt % Zr electrode undergoes transpassivation. Data on the electrolysis at controlled potential in the region close to the transpassivation potential showed that an increase in the electrode potential at the given HNO₃ concentration leads to an increase in the alloy dissolution rate.