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This report concerns the safe long-term disposal of radioactive waste by deep burial in stable fractured rock formations. Radio-nuclides from waste could return to the biosphere by leaching and dissolution of the waste-form, then transport by ground water. Two experiments were conducted, using 82Br as a conservative tracer, on a discrete fracture identified by hydraulic interference tests at approximately 100 m depth in moderately-fractured monzonitic gneiss. The selected fracture intersects two boreholes in a relatively horizontal attitude over a distance of about 10 m. Approximately dipole flow fields were used. The experiments were designed to minimise the mixing effects in both the injection and sampling intervals. A numerical model was developed including the effects of a dipole flow field with unequal injection and withdrawal flowrates and hydrodynamic dispersion within the fracture, modelled by a dispersion length. The wide variation of travel times in the dipole field was a major dispersal mechanism in these experiments, masking the effects of pure hydrodynamic dispersion and diffusion of tracer into stagnant water in pores in the rock surrounding the fracture.

Additional information

Authors: LEVER D A, Theoretical Physics Division, Harwell Laboratory, Oxfordshire (GB)
Bibliographic Reference: EUR 11454 EN (1988)
Availability: (2)
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