Parametric Analyses of Alternative Flow Models at Yucca Mountain, Nevada Calibrations and Controls - State of Nevada-Funded Research

The controls on the potentiometric surface and temperature distribution at Yucca Mountain have long been thought to be related to major fault zones. The exact way the faults influence these distributions has been somewhat elusive. The parametric studies discussed in this paper show that the fault zone x, y and z permeability tensors, as well as the alignment of the fault zone in relation to the flow field (1), are major contributing factors in the pressure and temperature distributions. A series of runs were conducted for the State of Nevada with a 3-dimensional model utilizing the AT2VOC version of the A-TOUGH code (2),(3). The runs were conducted under steady state conditions and utilized fully coupled heat and flow conditions. The model setup and boundary conditions are fully described. Comparisons were done with varying degrees of anisotropic permeability ratios in the fault zones. The resulting temperature and pressure profiles are compared. The model, while simple, allowed us to examine the relationship of the head and temperature distributions to the position and permeability of major fault zones. It is our conclusion that the major faults included in this model do significantly affect the observed head and temperature distributions. Performance Assessments currently may not reflect actual doses at the Compliance boundary due to the potential for radionuclide flow to be captured in the Ghost Dance Fault and be transported primarily south with little dilution and dispersion