The role of colloids and suspended particles in radionuclide transport in the Canadian concept for nuclear fuel waste disposal

AECL Research is developing a concept for the permanent disposal of nuclear fuel waste in a deep engineered vault in plutonic rock of the Canadian Shield and is preparing an Environmental Impact Statement (EIS) to document its case for the acceptability of the disposal concept. This report, one in a series of supporting documents for the EIS, addresses the role of particles in radionuclide transport. It summarizes our studies of natural particles in groundwater and presents the arguments used to justify the omission of particle-facilitated transport in the geosphere model that is based on the Whiteshell Research Area (WRA) and used in the postclosure assessment study case. Because radiocolloids formed in the vault will not be able to migrate through the clay buffer, radiocolloid formation in the geosphere will be determined by the sorption of radionuclides onto particles in groundwater. These particles consist of typical fracture-lining minerals, such as clays, micas and quartz; precipitated particles, such as colloidal silica and Fe-Si oxyhydroxides; and organic particles. In groundwater from the WRA, the average concentrations of colloids and suspended particles are 0.34 and 1.4 mg/L respectively. Particle-facilitated transport is not included in the geosphere model because the concentrations of particles in groundwater from the WRA are too low to have a significant impact on radionuclide transport. (author). 92 refs., 11 tabs., 13 figs