Nuclear Technology / Volume 182 / Number 1 / April 2013 / Pages 111-122
Technical Paper / Materials for Nuclear Systems
Crevice corrosion is the predominant mode of localized corrosion of Alloy 22 in concentrated chloride solutions at near-boiling temperatures. A literature review was performed to assess the electrochemical criteria for the long-term initiation of stable crevice corrosion of nickel-based or passive alloys, such as Alloy 22, in terms of likelihood, timing, and magnitude of potential damage due to crevice corrosion. The assessment in this study intends to predict the long-term performance of the waste package in nuclear waste management. Specifically, the areas of review included (a) environments (e.g., solution chemistry and electrochemical polarized condition) and crevice corrosion initiation criteria, (b) data and models for Alloy 22 crevice corrosion, and (c) induction times for crevice corrosion initiation. The assessment of the criteria for crevice corrosion initiation indicates that without externally applied current (i.e., at the open-circuit corrosion potential), initiation of crevice corrosion could be more difficult compared to the case when external current is applied. Without external current, crevice corrosion may not be initiated and sustained until the corrosion potential reaches the breakdown potential. Because the breakdown potential is typically more anodic than the repassivation potential, it is likely that the use of repassivation potential as the initiation criterion can overestimate a localized corrosion susceptibility. A short-term laboratory polarization test of Alloy 22 investigated whether any pits developed under the crevice were unstable for growth and if they could be stifled (i.e., suppressed). The long-term immersion tests of Alloy 22 exhibited a trend of continuous decrease of corrosion rate with time while the corrosion potential increased with time. An assessment of the theoretical models appeared to adequately scale induction time for crevice corrosion initiation to extrapolated long time periods.