Tracer transport in fractures

Conference · Tue Jun 01 04:00:00 EDT 1993

OSTI ID:139505

Tsang, Y W ^[1]

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1. Lawrence Berkeley Lab., CA (United States)

A fractured medium represents a strongly heterogeneous system. If the matrix permeability is negligibly small compared to the fracture permeability, the flow and transport approximately take place in 2D fractures in a highly heterogeneous 3D space. However, the whole fracture plane is not uniformly conductive to water, rather, flow channeling occurs, that is, the majority of flow concentrates in flow paths of least resistance as demonstrated in recent experimental studies. These features specific to fluid flow in a fractured medium imply that tracer transport is such a medium cannot usually be interpreted by theories which assume flow in a homogeneous porous medium. In the following I describe a new approach to study tracer transport in fractured media. The approach is based on the concept of the variable aperture channel model, in which transport through fractured rocks is controlled by a number of channels, each of which has variable aperture along its length. These variable apertures sample the aperture probability distribution function which characterize a single fracture. The flow channels are not physical pipes in the fracture plane, but rather preferred paths of least resistance in the sense of potential theory. Flow and transport through a system of fractures is then envisioned as occurring through these tortuous channels of flow paths from fracture to fracture in the 3D space. Advective dispersion arises then from the possibility of different channels available for transport, and hence the dispersion displayed in tracer breakthrough measurements can be correlated to the geometric parameters of the fractures. This approach is applied to the analysis of Stripa 3D field data. 16 refs.

• Research Organization: Nuclear Regulatory Commission, Washington, DC (United States). Div. of Regulatory Applications; Southwest Research Inst., San Antonio, TX (United States). Center for Nuclear Waste Regulatory Analyses; Arizona Univ., Tucson, AZ (United States). Dept. of Hydrology and Water Resources
• OSTI ID: 139505
• Report Number(s): NUREG/CP--0040; CONF-9101106--; ON: TI93016989
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
54 ENVIRONMENTAL SCIENCES
CHANNELING
FLUID FLOW
GEOLOGIC FRACTURES
HIGH-LEVEL RADIOACTIVE WASTES
PERMEABILITY
RADIOACTIVE WASTE DISPOSAL
RADIONUCLIDE MIGRATION
ROCKS