Publications
Evolution of repository, container, waste form characterization and design at the proposed us disposal system in volcanic tuff
Over 25 years, scientists and engineers designed engineered features to complement attributes of the natural barrier of volcanic tuff at Yucca Mountain in southern Nevada such that a proposed repository in the unsaturated zone would safely isolate spent nuclear fuel and highlevel radioactive waste over 106 years. Initially in 1983, an engineered barrier design applicable to several geologic media was used. With the Congressional direction to characterize Yucca Mountain, the engineered design gradually adapted to conditions in unsaturated tuff in the 1990s. The repository switched from floor emplacement of waste in small, single-walled stainless steel canisters to in-drift emplacement in large, double-layered containers. By 2000, the outer layer was high-nickel alloy to resist corrosion and the inner layer was stainless steel for strength. To avoid localized corrosion during the ∼1000-yr thermal period, titanium drip shields were also added above the containers. By 2008, a modular design of the repository was used for flexibility. In general, flexibility in accommodating various waste forms has been an intended attribute of geologic disposal system designs, rather than tuning the disposal system to specific characteristics of waste durability. The degradation rate of the radioactive waste matrix was an important parameter of the source-term in early modeling analysis. However, by the mid 1990s, analyses used fairly rapid degradation rates within the oxygenated environment of the unsaturated zone. Other components of the multiple barrier disposal system compensated for high degradation rates.