Radionuclide and colloid migration experiments in quarried block of granite under in-situ conditions at a depth of 240 m

Yamaguchi, Tetsuji ; Nakayama, Shinichi ; Vandergraaf, T. T.*; Drew, D. J.*; Vilks, P.*

In safety assessments of the geologic disposal of high-level radioactive wastes, the possibility that long-lived radionuclides may be leached from the wastes and may subsequently be transported through surrounding rock masses must be considered. It is therefore necessary to understand the transport of radionuclides through water-bearing fractures in rocks surrounding the repository. For this purpose, 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, synthetic colloids, H, Sr, Tc, Np and Pu, and post-experimental alpha and scanning of the fracture surfaces were performed using 1 m granite blocks, each 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.