Preliminary 3-D site-scale studies of radioactive colloid transortin the unsaturated zone at Yucca Mountain, Nevada

The U.S: Department of Energy is actively investigating the technical feasibility of permanent disposal of high-level nuclear waste in a repository to be situated in the unsaturated zone at Yucca Mountain, Nevada. In this study we investigate, by means of numerical simulation, the transport of radio...

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Bibliographic Details
Published in:Journal of contaminant hydrology 2001-09, Vol.60 (3-4)
Main Authors: Moridis, G.J., Hu, Q., Wu, Y.-S., Bodvarsson, G.S.
Format: Article
Language:English
Subjects:
ADVECTION
COLLOIDS
DECAY
DIFFUSION
FILTRATION
FRACTURES
GEOLOGY
GEOSCIENCES
HYDRAULICS
HYDRODYNAMICS
HYDROLOGY
KINETICS
MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
RADIOACTIVE WASTES
SPATIAL DISTRIBUTION
WATER TABLES
YUCCA MOUNTAIN
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Summary:The U.S: Department of Energy is actively investigating the technical feasibility of permanent disposal of high-level nuclear waste in a repository to be situated in the unsaturated zone at Yucca Mountain, Nevada. In this study we investigate, by means of numerical simulation, the transport of radioactive colloids under ambient conditions from the potential repository horizon to the water table. The site hydrology and the effects of the spatial distribution of hydraulic and transport properties in the Yucca Mountain subsurface are considered. The study of migration and retardation of colloids accounts for the complex processes in the unsaturated zone of Yucca Mountain, and includes advection, diffusion, hydrodynamic dispersion, kinetic colloid filtration, colloid straining, and radioactive decay. The results of the study indicate that the most important factors affecting colloid transport are the subsurface geology and site hydrology, i.e., the presence of faults (they dominate and control transport), fractures (the main migration pathways), and the relative distribution of zeolitic and vitric tuffs. The transport of colloids is strongly influenced by their size (as it affects diffusion into the matrix, straining at hydrogeologic unit interfaces, and transport velocity) and by the parameters of the kinetic-filtration model used for the simulations. Arrival times at the water table decrease with an increasing colloid size because of smaller diffusion, increased straining, and higher transport velocities. The importance of diffusion as a retardation mechanism increases with a decreasing colloid size, but appears to be minimal in large colloids.
ISSN:0169-7722
1873-6009