Titanium alloy degradation modes are reviewed in relation to their performance in repository environments. General corrosion, localized corrosion, stress corrosion cracking, hydrogen-induced cracking, microbiologically influenced corrosion, and radiation-assisted corrosion of Ti alloys are considered. With respect to the Ti Grade 7 drip shields selected for emplacement in the repository at Yucca Mountain, general corrosion, hydrogen-induced cracking, and radiation-assisted corrosion either do not initiate or propagate sufficiently fast over a 10,000-year time frame in likely repository environments to cause penetration of the drip shield. Stress corrosion cracking (in the absence of disruptive events) is of no consequence to barrier performance; and localized corrosion and microbiologically influenced corrosion are not expected to occur. To facilitate the discussion, Ti Grades 2, 5, 7, 9, 11, 12, 16, 17, 18, and 24 are included in this review.

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