Waste package design and container materials evaluation for the Yucca Mountain repository

Container material concerns for the long-term containment of high-level reprocessed nuclear waste and spent nuclear fuel in a potential repository at Yucca Mountain, Nevada are discussed. The current container design focuses on a thin corrosion resistant inner barrier surrounded by a thick corrosion allowance outer barrier. Carbon steel is the principal candidate material for the outer barrier, while Ni-Cr-Mo alloys are the main focus for the inner barrier. The repository is initially expected to be hot and dry, but as the temperature decreases, the possibility of a humid environment and liquid water entry into the repository zone increases. Gradual wastage of the outer barrier delays access of water to the inner barrier, which is expected to be resistant to most forms of corrosion. The creviced region between the two barriers, however, may provide an area of localized corrosion on the inner barrier. Galvanic effects between the two barrier materials introduce some complexities in the same creviced region. A testing program has been initiated to measure corrosion rates, determine the kinds of corrosion attack, and provide input for the long-term performance modeling of the container.