RD&D-Programme 2004 - SKB

19.2.23 Methane ice formation
Conclusions in RD&D 2001 and its review
At low temperature and high pressure, water and methane form a solid phase called methane
ice. Methane ice can form under permafrost, for example.
Newfound knowledge since RD&D 2001
Together with researchers from Finland and Canada, SKB has studied a gold mine in the
permafrost area in Canada (the Lupin Mine). No methane ice was found.
Programme
Studies around the mine in Canada will continue.
19.2.24 Salt exclusion
Conclusions in RD&D 2001 and its review
When saline water freezes slowly, the solutes (salts) present in the water are forced out into
solution. This process can be of importance in a cold climate, for example during a period with
permafrost.
Newfound knowledge since RD&D 2001
Investigations in the Lupin Mine in the permafrost area in Canada have not been able to
demonstrate the effect of salt exclusion.
Programme
The investigations in the Lupin Mine will continue. If salt exclusion occurs, the saline waters
will move towards greater depth due to their greater density and be added to the saline groundwaters
that already exist at greater depths. It is therefore not likely that accumulations of saline
groundwater will be found beneath layers of permafrost. See also section 19.2.23 above.
19.2.25 Integrated modelling – hydrogeochemical evolution
In combination with groundwater flow, groundwater composition is of great importance for the
performance of the final repository, in both the short and long term. The interaction between the
engineered barriers and the groundwater determines how long the spent nuclear fuel will remain
isolated. Even in a situation when this isolation has been breached, the groundwater is of crucial
importance for dissolution and transport of radionuclides in the fuel.
The groundwater chemistry programme aims at describing the chemistry of the groundwater
in the deep repository volume and its environs from a safety assessment perspective and
producing the body of chemical data required for design of the deep repository. In general, the
geochemistry programme contributes towards a general understanding of how the groundwater
system works at repository depth. Hydrogeochemical and hydrogeological data together provide
a description of the water flux within the repository area and its influence on groundwater
composition, as well as how this composition varies in the repository volume.
The simplest hydrochemical model is a spatial distribution of the concentrations of the most
important solutes in the rock volume. Normally the distribution of the main components sodium,
potassium, calcium, manganese, chlorine, sulphate and hydrogen carbonate, including pH, is
investigated, but it is also of great value to include the stable and radioactive isotopes deuterium,
oxygen-18, sulphur-34, carbon-14, carbon-13, tritium and strontium-87. The distributions
268 RD&D-Programme 2004