Groundwater flux, travel time, and radionuclide transport

Lawrence Livermore National Laboratory (LLNL) provides the scientific and engineering bases for design and performance analyses of the waste package and other components of the engineered barrier system (EBS) for a potential repository at Yucca Mountain, Nevada. The EBS is an important component of a multi-barrier system designed to isolate radioactive waste until it decays to the point that it is no longer radiologically hazardous to humans or other species. Its performance depends strongly upon the amount, chemical composition, and temperature of liquid water in the ''near field'' region immediately surrounding the waste packages. For this reason, much of LLNL's Yucca Mountain research has been directed toward understanding flow, transport, and chemical processes in fractured rock under both preemplacement and post-emplacement conditions. Because the radioactive decay heat from a potential repository at Yucca Mountain would dominate the movement of water for thousands of years within the entire repository block and possibly even beyond, the spatial domain of our investigations ranges from the scale of individual fracture apertures (micrometers) to a few kilometers