Uranium and U–Zr and U–Ru alloy corrosion rates in the transpassive state

Electrochemical studies of reactor-grade uranium metal and its alloys with Zr and Ru in neutral electrolyte (0.1 M NaClO4, pH 3.0–9.0) in the potential region close to uranium's transpassivation threshold were performed. Transpassivation potentials from 320 mV/Ag/AgCl (U–1.3 at.% Zr) to 470 mV (U–10.5 at.% Ru) were found to be weakly affected by added alloying element concentration and electrolyte pH. Comparison of I–t curves registered on U metal, U–1.3 at.% Zr, and –1.2 at.% Ru electrodes indicate that the electrochemical oxidation rate of alloyed uranium was lower than that of pure U metal. The difference of the electrochemical oxidation rates was dependent on electrolyte pH. The calculated corrosion rates of uranium metal and alloy increased from 0.89 mg cm−2 h−1 (U–1.3 at.% Zr, E = 300 mV/Ag/AgCl) to 40.4 mg cm−2 h−1 (U metal, E = 600 mV/Ag/AgCl) and were found to be independent of alloy addition and electrolyte pH. The contribution of spallation of non-oxidized uranium species from the electrode surface to the observed corrosion rates was made.