The engineered barrier system of a repository may completely contain the waste for a long period, but will slowly degrade, eventually releasing small quantities of radionuclides.
It is expected that most of these radionuclides will be retarded in the host rock surrounding the repository, principally by sorption onto and diffusion into the rock matrix (see also LTD).
However, failure of the engineered barriers may also produce colloids, which could sorb some of the radionuclides and transport them "piggy back" through the host rock to the biosphere with less retardation
Relative size of colloids
- Generation of inorganic colloids.
- Dissolved radionuclides in ground water.
- Sorption/de-sorption of colloids onto/from rock surface.
- Sorption of radionuclides onto colloids.
- Filtration of colloids.
- Colloid size prevents penetration into pore space of rock.
- Diffusion of radionuclides into the pore space of the rock.
- Sorption of radionuclides onto organic colloids or incorporation of radionuclides into organic colloids.
Such radionuclide-colloid associated transport is extremely difficult to examine under laboratory conditions and so Nagra, in partnership with Andra (France), ENRESA (Spain), FZK (Germany), JNC (now JAEA) (Japan) and Sandia (USA), have been carrying out a complex, in situ study of the coupling of radionuclide retardation and colloid transport processes.
The experience and know-how needed to carry out the Colloid and Radionuclide Retardation experiment (CRR) is based on 15 years of examining mechanisms of radionuclide migration in fractured rock at the same site in the GTS. To find out about the radionuclide migration experiment, downloadable datasets and for a selected bibliography (1984 - 2001) follow the links in the CRR menu above.
Colloid and Radionuclide Retardation Experiment
RMP Video