Further modeling studies of gas movement and moisture migration of Yucca Mountain, Nevada.

摘要

In this report we present modeling studies on moisture redistribution processes that are mediated by gas-phase flow and diffusion. Knowledge of the physical processes and parameter sensitivity studies show that moisture removal from Yucca Mountain arising from a lowered humidity of the soil gas at the land surface is controlled by vapor diffusion. Both the presence of realistic stratigraphy of alternate layers of nonwelded and welded units, and the choice of characteristics curves, have only minor effects on the magnitude of moisture removal, though characteristic curves play a dominant role in defining the equilibrium liquid-saturation profiles of the layered formation. We are therefore able to conclude from our calculations that the rate of moisture removal from vapor transport has an upper limit of about 0.1 mm/yr. Our calculations for stratigraphic columns with alternate layers of nonwelded and welded units show that order-of-magnitude discontinuities in absolute and relative permeabilities at a lithologic contact give rise to artificially large resistance to flow if the usual numerical scheme of harmonic weighting of absolute permeability and upstream weighting of relative permeability is used. We have resolved the numerical difficulty by invoking a physics-based intuitive model of a ''fuzzy lithologic contact,'' and employing a complete 100% upstream weighting of the effective permeability at all interfaces. 33 refs., 22 figs., 2 tabs.