Corrosion of relevant metals and alloys in mild and near-neutral pH environments

This section presents the general corrosion behaviour of passive and non­passive metal and alloys in mild and near-neutral pH environments such as tuff or granite hostrock sets. Both tuff and granite will have reducing groundwater, whereas tuff can also have oxidizing groundwater. Over a long period of geological time (e. g., several thousand years), a container of a finite thickness is expected to fail even at very slow general corrosion rates. Under more aggressive aqueous environmental conditions that may evolve during the disposal, localized corrosion (e. g., crevice corrosion or pitting corrosion) may occur, decreasing the container lifetime in a very short time (e. g., months to years). The first case to be discussed is long-term integrity of a protective passive film in nickel-based alloy, resulting in very low general corrosion rates. The second case is corrosion-allowance, carbon steel in reducing aqueous environments resulting in very low general cor­rosion rates. These two cases are discussed further regarding susceptibility to localized corrosion. Finally, risk insights of the general corrosion and localized corrosion in a disposal system are discussed with respect to this type of container with low general corrosion rate or possible susceptibility to localized corrosion.

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