Analytic models for assessing the performance of engineered barriers in a basalt repository

Analytic models have been developed and used to study the performance of engineered barriers in a basalt repository with waste packages vertically emplaced below the storage room floors. Models have been developed for the ground water flow field and for waste transport through the waste package backfill and up to the top of the storage room. The lowest release rates at the top of the storage room occur for a room backfill with high hydraulic conductivity (greater than the surrounding rock), high porosity and good sorption. Such a room backfill is much more effective than waste package backfill at delaying releases from the engineered system, especially for short-lived nuclides. A repository design with horizontal emplacement of waste packages has also been studied and found to have higher release rates, owing to a larger cross-section to ground water flow and the absence of an overlying storage room. 5 references, 2 figures, 2 tables