PNNL

Abstract

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 – 12.0 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 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-2h-1 (U – 1.3 at.% Zr, E=300 mV / Ag/AgCl) to 40.4 mg•cm-2h-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.