Corrosion Testing of Nickel and Titanium Alloys for Nuclear Waste Disposition

Extensive testing has been performed at the Lawrence Livermore National Laboratory (LLNL, Livermore, California) to determine the corrosion characteristics of nickel-based alloys such as Alloy 22 (UNS N06022) and three titanium alloys. The studies focused on three major areas: immersion tests at the long-term corrosion test facility (LTCTF), the determination of the corrosion potential (E_corr), and the measurement of the repassivation potential. A review summary of the previously published results from LLNL in the three mentioned areas is presented. Examination of specimens removed from the LTCTF yielded significant information regarding the general, localized, and stress corrosion cracking resistance of Alloy 22, four other nickel-based alloys, and three titanium alloys. Results from the E_corr studies were significant but not conclusive. Current E_corr results mainly opened areas for future research. Repassivation potential studies helped in understanding the role of temperature, chloride concentration, and inhibitive effect of nitrate, but other areas such as fabrication effects still need to be investigated in more detail. A list of suggested future studies in the three areas mentioned above is also offered.