Understanding long-term corrosion of Alloy 22 container in the potential Yucca Mountain repository for high-level nuclear waste disposal

A Case for Molecular Recognition in Nuclear Separations: Sulfate Separation from Nuclear Wastes

“…The effectiveness of waste containers in this regard depends upon the robustness of passive surface oxide films, and any chemical species that can disturb such films will therefore have an impact on the corrosion rates. Sulfur is thought to play such a role, as considered at length in a recent review of the long-term corrosion of Alloy 22, the corrosion-resistant Ni-22Cr-13Mo-3W-4Fe alloy that has been intensively examined for use in the proposed Yucca Mountain repository . Impurity sulfur atoms within the metal itself can form a surface layer, displacing the passivating oxide layer over many years.…”

“…Experimental evidence for this process, called anodic sulfur segregation, has been presented in which the accumulated sulfur was found to be in its zero oxidation state . During anodic sulfur segregation, corrosion may accelerate, although taking into account factors that could lead to repassivation and subsequent depassivation–repassivation cycles led to the conclusion that the waste-package lifetime was unlikely to be significantly reduced. , Nevertheless, this proposed complex corrosion mechanism and uncertainty in its conclusion remain to be demonstrated and experimentally validated for Alloy 22 under repository-relevant conditions. In view of the uncertainty, it was noted that the risk of anodic sulfur segregation could be reduced by decreasing the sulfur content of the alloy from its value of ca.…”

“…In view of the uncertainty, it was noted that the risk of anodic sulfur segregation could be reduced by decreasing the sulfur content of the alloy from its value of ca. 5 ppm …”

“…Other corrosion mechanisms related to Alloy 22 waste packages for Yucca Mountain disposal have been considered. , These can potentially involve sulfur as sulfate in the groundwater. It should at first be noted that the composition of Yucca Mountain water is considered to be relatively benign and is unlikely to cause localized corrosion of Alloy 22 .…”

“…Other corrosion mechanisms related to Alloy 22 waste packages for Yucca Mountain disposal have been considered. , These can potentially involve sulfur as sulfate in the groundwater. It should at first be noted that the composition of Yucca Mountain water is considered to be relatively benign and is unlikely to cause localized corrosion of Alloy 22 . Further, sulfate was found to confer an inhibitory effect on localized corrosion on Alloy 22. , However, the variable behavior of sulfate under different conditions, where in some cases sulfate has been found to induce corrosion, led to the observation that there is no consensus yet on the role of sulfate in localized corrosion .…”