RD&D-Programme 2004 - SKB

important parameter. However, the values of this parameter are in principle unknown. This
study shows that relevant processes can be incorporated in models of radionuclide transport, but
that the uncertainty in parameter selection is great. This uncertainty is largely due to inadequate
process knowledge.
Scoping calculations have been performed in preparation for a possible field-scale tracer test
with colloids /19-94/. The test, if it takes place, would be included in the Colloid Project and
be conducted on the site down in the Äspö HRL where True-1 is situated. The calculations
show what parameter combinations would then be appropriate for detecting colloid-facilitated
transport /19-94/. The work also shows how colloid transport can be incorporated into models
for radionuclide transport.
A numerical variant of SKB’s code for radionuclide transport in the geosphere, Farf31, has been
developed to handle colloid-facilitated radionuclide transport /19-95/. The same conceptualization
of colloid transport has been used as in SKI’s study /19-96/. This concept implies that
nuclide transport takes place on a separate colloid phase, and that the uptake of nuclides on the
colloids is described by a sorption-desorption model. The numerical Farf model can reproduce
the results in SKI’s study and also handle chain decay.
Programme
If tracer tests with colloids are conducted in the Colloid Project, see section 19.2.20, then
modelling of the experiments will also be carried out. This modelling will be based on the
experience and code development described in /19-94/.
The newly developed numerical version of Farf31 will be utilized to study the impact of
colloids on radionuclide transport in greater detail for different scenarios and parameter variations.
Based on these studies, a strategy will be formulated for how colloids are to be handled in
the safety assessment.
19.2.22 Gas formation/dissolution
Conclusions in RD&D 2001 and its review
Gases that occur dissolved in the groundwater are of varying composition. The main components
are usually the following, in order of decreasing concentration: nitrogen, methane, argon,
helium, carbon dioxide, hydrogen and carbon monoxide. Traces of ethane, ethene, acetylene,
propane and propene also occur. The total quantity of dissolved gas per litre of analyzed
Swedish groundwater varies from about 30 millilitres to about 100 millilitres, down to a
kilometre beneath the surface. These quantities are well below the solubility limits for the
encountered gases at the pressure prevailing at the depth in question. Larger quantities of gas
of differing composition have been encountered in Finnish groundwaters, up to 0.3–0.4 dm 3 gas
per litre of groundwater /19-97/. No issues for further research were identified in RD&D 2001.
Newfound knowledge since RD&D 2001
The database of dissolved gases in groundwater is being added to continuously /19-86/, both
with data from groundwater around the Äspö HRL and with data from groundwater at the site
investigations.
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Systems for gas analysis and research on gases have been installed under ground at the Äspö
HRL and at a laboratory at Göteborg University. New methods have been developed for extraction
and analysis of all occurring gases. Research is being conducted on the impact of the gases
on the occurrence and activity of microorganisms, and on the impact of microorganisms on gas
content and composition. The results of these investigations are reported in section 19.2.18.
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