Materials performance issues for high-level radioactive waste packages

The disposal of spent nuclear fuel and high-level radioactive waste in a geologic repository requires materials performance over time periods unprecedented in any previous engineering application. Corrosion-resistant barriers of nickel-based and titanium alloys are currently proposed for the engineered barrier system of a repository that may be located at Yucca Mountain, Nevada, where a site 305 m underground (but still well above the water table) is being studied for its potential suitability to host a respository. Prediction of the performance of these materials over the 10 000 year regulatory period in an evolving, high-humidity, moderate-temperature, mildly oxidizing environment poses great challenges.