Corrosion Behavior of Borated and Non-Borated 304L SS in Nitric Acid Media Containing Chloride Impurities

Borated 304L stainless steel, widely used for storing and transporting spent nuclear fuel, was studied to assess its corrosion behavior in nitric acid solutions of varying concentrations (1 M, 3 M, 6 M HNO₃) containing 0.06 and 0.3 wt.% chloride, and compared with non-borated 304L SS. An increase in nitric acid concentration shifted the open-circuit potential and corrosion potential to more noble values, indicating stronger passive film formation and improved corrosion resistance. However, passive current density and pitting potential showed minimal variation with nitric acid or chloride concentration. Heat treatment at 1450 K for 4 hours dissolved boride particles, homogenizing the surface and reducing passivation current density. Confocal microscopy revealed a slight increase in pit density with increasing chloride concentration in 1 M nitric acid. Laser Raman spectroscopy identified magnetite as the primary corrosion product across all nitric acid concentrations, with Fe₃O₄ and FeOOH dominant in 3 M and 6 M nitric acid, while borate and chromic oxides were also detected in 1 M nitric acid, suggesting weaker passive film formation and enhanced pitting in the latter medium. This study highlights the interplay of acid and chloride concentration, passive film behaviour, and heat treatment in influencing the corrosion resistance of borated 304L SS.