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Gas-Phase Transport of Carbon-14 Released from Nuclear Waste into the Unsaturated Zone

Published online by Cambridge University Press:  28 February 2011

Benjamin Ross
Benjamin Ross*
Affiliation:
Disposal Safety Inc., 1629 K Street NW, Suite 600, Washington DC 20006
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Abstract

Gas-phase carbon-14 dioxide released from spent fuel buried in unsaturated rocks will move upward by molecular diffusion and advection. The flux resulting from molecular diffusion will be determined by the concentration gradient of gaseous carbon-14 dioxide. Advection will be caused by density-driven flow of the pore gas. Such flow occurs under present conditions as a result of annual and diurnal temperature changes and differences in chemical composition between pore gas and air, and it will be enhanced when the spent fuel heats the rock. The advective flux will be determined by the gas-phase concentration of carbon-14 and by the velocity of convective flow of the pore gas. Gas-phase concentrations of carbon-14 dioxide will be strongly influenced by isotopic exchange with bicarbonate dissolved in water that is retained in the unsaturated zone by capillary forces. Isotopic equilibrium between these two phases will be attained very rapidly on repository time scales. If the liquid phase is saturated with calcium carbonate, precipitation of calcite may provide a sink for removal of carbon-14 from the mobile phases.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 112: Symposium P – Scientific Basis for Nuclear Waste Management XI , 1987 , 273
Copyright
Copyright © Materials Research Society 1988

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