RD&D-Programme 2004 - SKB

18.2.18 Radiation-induced montmorillonite transformation
The process is judged to be negligible in the buffer and therefore also in the backfill.
18.2.19 Radiolysis of pore water
The process is judged to be negligible in the buffer and therefore also in the backfill.
18.2.20 Microbial processes
The potential for bacterial activity increases in the backfill material with decreasing density and
increasing water content. Many bacteria consume oxygen as they break down organic material,
methane, iron(II) and sulphur.
Conclusions in RD&D 2001 and its review
The conclusion is unchanged that bacterial activity in the backfill can be advantageous, since it
will make a significant contribution to oxygen reduction there.
Newfound knowledge since RD&D 2001
No new knowledge has been forthcoming.
Programme
See section 17.2.22.
18.2.21 Radionuclide transport – advection
The backfill has a hydraulic conductivity and a diffusivity that lie in a range where both
diffusion and advection can be important transport mechanisms.
Conclusions in RD&D 2001 and its review
In Kasam’s view, SKB should conduct performance assessments of the buffer-backfillgeosphere
system in order to clarify advantages and disadvantages of different types of
backfill (natural clays, mixtures of crushed rock and clay, and only crushed rock with a size
distribution that best withstands the expansion of the buffer). The performance assessment
should also include long-term evolution in environments with various salinities.
Newfound knowledge since RD&D 2001
No new knowledge has been forthcoming.
Programme
A thorough study of radionuclide transport in the backfill under different conditions and
assumptions will be conducted within SR-Can.
18.2.22 Radionuclide transport – diffusion
Diffusion of radionuclides in the backfill is of subordinate importance for repository safety.
RD&D-Programme 2004 239