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Convection of radionuclides with water flow through fractures in rocks may be retarded temporarily by diffusion first into and later back from the porosity of the adjacent rock. Statistical models to predict flow and convection through inter-connected fractures, assuming these to be parallel walled, have been derived and experimental methods of measuring the fracture statistics needed by these models have been developed. More recently attention has been turned to channelling of the flow by areas of contact between the faces of fractures which decreases their area in contact with the flow. This phenomenon may substantially reduce diffusion into the rock and, consequently, the hoped for- retardation. A method of mapping channelling has been developed. Results obtained with it for a fracture in Cornish granite show that channelling could have a major effect in reducing retardation because the flow takes place over about only 20% of the area of the fracture face. Channelling of the flow will also control dispersion of the radionuclides in larger volumes of water. This dispersion will occur at intersections of channels both in the fractures and at intersections of fractures.

Additional information

Bibliographic Reference: EUR 11455 EN (1988) FS, 10 PP., ECU 4.50, AVAILABILITY: EUROFFICE, LUXEMBOURG, POB 1003
Availability: Can be ordered online
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