Effect of Metallic Ion Species on Nitric Acid Corrosion of Type 304L Stainless Steel

Abstract

AbstractDuring nuclear reprocessing and waste storage conditions in highly oxidizing nitric acid media, trans-passive corrosion attacks occur, i.e., corrosion potential is shifted to noble direction near or over the passive region, and stainless steel (SS) suffers severe intergranular corrosion (IGC) even if the steel is not sensitized. In this work, corrosion behavior in simulated non-radioactive PUREX environment with different oxidizing species (Nd3+, Mo6+ and Cs+, corrosion product Fe3+, and surrogate element V5+, etc.) on AISI type 304L SS in different concentrations (2, 6, and 8 M) of nitric acid has been evaluated. The electrochemical corrosion behavior was evaluated by open circuit potential (OCP) and potentiodynamic anodic polarization methods. The electrochemical corrosion test results indicated a shift in the corrosion potential with the metallic ions concentration to a more noble potential towards the trans-passive region. No significant change in the breakdown potential was observed. The composition of the surface film has been evaluated by X-ray Photoelectron Spectroscopy (XPS). The three-phase corrosion test in boiling liquid, vapor, and condensate phases (similar to the ASTM A-262 Practice-C test) in simulated dissolver conditions in 2, 6, and 8 M nitric acid solution with or without oxidizing ions have also been studied. Surface morphology of the corrosion tested samples were examined by an optical microscope, which indicated severe intergranular corrosion (IGC) attack in the boiling liquid phase. In summary, oxidizing species and higher nitric acid concentration enhance the IGC attack in type 304L SS. The role of metallic ion species on IGC of type 304LSS is also highlighted.KeywordsStainless steelIGCMetallic redox ionsPolarizationXPS