High-level radioactive wastes are stored in large underground storage tanks made of low-carbon steel. The wastes consist of concentrated solutions of sodium nitrate (NaNO_3) and sodium hydroxide (NaOH), and the radionuclides (137)~Cs, (99)~Tc, and (90)Sr. The corroding steel microenvironment may produce localized reducing or oxidizing conditions that affect the solubilities of the species such as Tc(VII) and Tc(IV), which in turn modifies the kinetics of corrosion of the storage tank. To understand the influence of technetate ions on the corrosion of steel, electrochemical polarization studies of A 537 steel samples were carried out in 1 M NaNO_3 + 0.05 M Sr(NO_3)_2 + 0.1 M NaOH with and without addition of HReO_4 at different temperatures (24 - 85 °C). The concentration of HReO_4 was varied from 0.014 - 0.04 M.
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