Electrochemical corrosion behavior of low carbon steel in concentrated geologic vadose waters

The corrosion performance of type 1016 (UNS G10160) low-carbon steel (LCS) was evaluated by direct current (DC) polarization techniques in waters with concentrated solutes expected in the vadose waters of the proposed Yucca Mountain (YM) geologic nuclear waste storage repository. Solute concentration simulated the expected effects of boiling and evaporation in the vadose waters surrounding the YM waste packages. LCS, a candidate material for the outer layer in current multibarrier waste-package designs, corroded at low general rates with no localized corrosion in deaerated waters at 25 C concentrated to 10 times (X), 100X, and 1,000X the reference water-well concentrations. Higher water temperatures (up to 90 C) and concentrations (100X and 1,000X) favored precipitation of silicate surface layers that further decreased corrosion rates and significantly increased apparent pitting potentials in deaerated water. Aeration increased corrosion rates significantly in 10X water at 25 C, but had lesser effects at 100X and 1,000X. Aeration and chloride additions also significantly degraded the protectiveness of inhibitive precipitate surface films. Added soluble Fe3+ in aerated 10X waters increased general corrosion at 25 C and initiated pitting at still higher concentrations and temperatures