Probabilistic methodology to estimate environmental conditions for localized corrosion and stress corrosion cracking of Alloy 22 in a high-level radioactive waste repository setting

The US Department of Energy (DOE) has indicated that it may use Alloy 22 (Ni–22Cr–13Mo–4Fe–3W) as the waste package outer container material for the potential high-level waste repository at Yucca Mountain, Nevada. This alloy could be susceptible to localized corrosion, in the form of crevice corrosion, and stress corrosion cracking if environmental conditions and material requirements (e.g., existence of crevices or high enough tensile stresses) are met. An approach is proposed to assess the likelihood of environmental conditions capable of inducing crevice corrosion or stress corrosion cracking in Alloy 22. The approach is based on thermodynamic simulations of evaporation of porewaters and published equations to compute corrosion potential and critical potentials for crevice corrosion and stress corrosion cracking as functions of pH, ionic concentration, temperature, and metallurgical states from fabrication processes. Examples are presented to show how the approach can be used in system-level assessment of repository performance.