Potential releases of gaseous 14C from Yucca Mountain: A limited role for buoyancy as compared to other flow inducing phenomena

The issue of gas flow and contaminant transport out of the potential high-level waste (HLW) and spent nuclear fuel repository site at Yucca Mountain, NV, has recently received much attention. An important concern exists over whether or not heating of the rock mass by the waste may generate convective currents resulting from buoyancy. This could significantly reduce (relative to the half-life of the element) the travel time of gaseous contaminants, such as {sup 14}CO{sub 2} (g), to the surface of the mountain. The studies that rely on a full-fledged analysis of the system of coupled equations representing nonisothermal flow in porous media discount the effect of buoyancy; the more simplified analyses do not. To reconcile the contradictory results, the authors have performed a review of the general literature, including studies not directly concerned with flow at Yucca Mountain. The authors conclude that there is convincing theoretical and experimental indications to exclude net mass flows of air to the surface of the mountain resulting only from buoyancy. Therefore, the buoyancy effect, alone, would not cause {sup 14}C releases. On the other hand, the authors identify barometric pumping and topographically assisted flow as the most relevant mechanisms for the release of thismore » radionuclide. Coupling between these effects and buoyancy may enhance these surface-driven processes.« less