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Radionuclide migration experiments in quarried blocks of granite under in-situ conditions at the 240-m level in AECL's Underground Research Laboratory (URL) were performed under a five-year cooperative research program between Japan Atomic Energy Research Institute (JAERI, reorganized to Japan Atomic Energy Agency, JAEA) and Atomic Energy of Canada Ltd. (AECL). Migration experiments with Br, 3 H, 85 Sr, 237 Np, 238 Pu, 95m Tc and synthetic colloids, and post-experimental alpha and gamma scanning of the fracture surfaces were performed using 1m 3 granite blocks, containing a single fracture, excavated from a water-bearing fracture zone. The transport of the radionuclides was affected by macroscopic mechanical dispersion, matrix diffusion and element-specific sorption on fracture surfaces. Colloid transport exhibited a complicated process that may include sedimentation and diffusion into stagnant zones.

Results are presented from a migration experiment carried out in a natural fracture in a 1 m × 1 m × 0.6 m quarried granite block. Near-uniform flow in the fracture was achieved by controlling the groundwater flow from the fracture laterally across the exit face of the fracture. The longitudinal dispersion was determined from the elution profile of uranine, a non-sorbing tracer. The effect of matrix diffusion was determined by reducing the linear velocity of the transport solution from approximately 3 to 0.75 cm/h. The velocity of a sorbing tracer, Cs-137, was compared to that of non-sorbing I-131 and with that calculated from data obtained for Cs-137 in static sorption experiments on similar fracture surfaces. Information on channeling in the fracture was obtained by autoradiographing the fracture surface of the separated block after the termination of the experiment. Quantitative information on the sorbed Cs-137 inventory by two-dimensional gamma scanning of the fracture surfaces is underway.