Three-dimensional simulations of radionuclide transport at Yucca Mountain

This paper presents preliminary transport calculations for radionuclide movement at Yucca Mountain. The simulations were run with TRACRN using approximately 30 000 finite-difference zones to represent the unsaturated and saturated zones underlying the potential repository in three dimensions. The results are used to study the sensitivity of radionuclide migration to uncertainties in several factors that affect transport through porous media. These factors include recharge rate, dispersivity length scale, radionuclide species, and source term. The calculations show that the transport of weakly sorbing species like 99Tc and 129I is highly sensitive to all of these factors. The transport of strongly sorbing species like 135Cs is limited by retardation and is therefore fairly insensitive to these factors. In addition to showing the sensitivity of transport to physical processes, the results show that the calculations themselves are sensitive to problem dimensionality. The calculations indicate that modeling in three dimensions provides faster breakthrough than modeling in one or two dimensions. (author) 30 figs., 2 tabs., 13 refs