Radionuclide migration experiments in a natural fracture in a quarried block of granite

A radionuclide migration experiment was performed over a distance of 1 m in a natural fracture in a quarried block of granite. The fracture in the block was characterized hydraulically by measuring the pressure drop in borehole-to-borehole pump tests. The effective fracture volume in the block was similar to 100 mL. A silicone coating was applied to the exterior, and the block was immersed in a tank of water to which hydrazine was added to provide a chemically reducing barrier. Migration experiments were performed at a flow rate of 2.2 mL h(-1) using Sr-85, I-131, Cs-137, Ce-144, Eu-152, Np-237 and Pu-238. A total of 9.5 L of groundwater was pumped through the fracture, corresponding to similar to 95 fracture volumes. only Sr-85, I-131, Cs-137, Np-237 and Pu-238 were observed in the eluent. Scanning of the fracture surface at the end of the migration experiment showed limited mobility of alpha-emitting radionuclides and of the rare-earth elements, consistent with static sorption data obtained on representative fracture surface material. The mobility of Cs-137 was higher than that of the rare-earth elements, but it was lower than that of Sr-85. When samples of fracture-coating material were separated into fractions with different specific gravity, there was a clear indication of radionuclide association with mineral groups.