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The proposed waste packages for the disposal of high-level radioactive waste at the potential repository at Yucca Mountain, Nevada, consist of an outer container and inner container. The outer container is made of alloy 22, a corrosion-resistant Ni-Cr-Mo-W alloy, while the inner container is made of type 316 nuclear-grade stainless steel. Fabrication processes such as welding and postweld heat treatments can induce changes to the microstructure of alloy 22. Such microstructural changes can reduce ductility and impact strength and promote localized corrosion. Environmental conditions within the emplacement drifts, such as composition of solutions contacting the waste packages, can also affect localized corrosion susceptibility. In this study, the effects of fabrication processes on impact strength, fracture toughness, and crevice-corrosion resistance of alloy 22 were investigated.

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Alloy 22 (UNS N06022) is a Ni-Cr-Mo-W alloy developed for corrosion resistance in a variety of aggressive environments.Because of its excellent corrosion resistance, Alloy 22 was selected as a candidate container material for the disposal of high-level nuclear waste at the proposed repository at Yucca Mountain, Nevada. The localized corrosion susceptibility of mill-annealed Alloy 22 was assessed in chloride-containing solutions at temperatures ranging from 60°C to 150°C by comparing the crevice corrosion repassivation potentials with corrosion potentials measured in separate tests. Crevice corrosion repassivation potentials were found to be strongly dependent on temperature, chloride concentration, and nitrateto-chloride molar concentration ratio. Corrosion potentials were dependent on solution pH but independent of chloride concentration.

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