RD&D-Programme 2004 - SKB

17.2.22 Microbial processes
Conclusions in RD&D 2001 and its review
SKB concluded that microbial processes can under certain conditions result in the formation
of gas and sulphide. Gas formation can give rise to disrupting mechanical effects on the buffer,
and sulphide can corrode the copper canister. Sulphide formation must take place in the buffer,
near the canister, and be of considerable scope for corrosion to be possible, mainly due to the
fact that the solubility of sulphide, and thereby its diffusive transport capacity, is very low. It
is also known that bacteria can bind and transport metals in ionic form. In order for the abovedescribed
processes to take place, however, the bacteria must be active and have access to water,
nutrients and space.
Newfound knowledge since RD&D 2001
Nothing new has been learned since the previous study in conjunction with the Lot project at
Äspö /17-20/, see also section 16.2.12.
Programme
Termination of ongoing five-year test with microbes in bentonite within the Lot project during
2005.
17.2.23 Integrated studies – evolution under saturated conditions
Integrated model studies for the buffer under saturated conditions are being conducted for the
integrated chemical evolution.
Conclusions in RD&D 2001 and its review
In SKI’s opinion, SKB should update the THMC couplings – especially the chemical aspects
– with the results of the most recent temperature calculations.
Newfound knowledge since RD&D 2001
The THM studies of integrated processes that have been carried out on unsaturated buffer since
RD&D 2001 are as follows:
• Influence of rapid pressure pulses on the buffer, see section 17.2.5.
• Effect of earthquake-induced rock shear through deposition holes, see section 17.2.9.
No further development has been done of the THM material model for saturated conditions.
Programme
The mechanical part of the THM model for water-saturated bentonite is complex and has certain
remaining questions as regards both parameter values and model. It actually consists of two
models: One that handles the relationships between stresses and deformations, and a creep
model that handles the time dependence. The models are used to model:
• The interaction between buffer and backfill.
• Homogenization of the buffer.
• The canister’s movement in the buffer with time.
The work with these questions and follow-up of model development will continue.
Tests for studying the influence of pressure pulses will continue, see also sections 17.2.5 and
17.2.9.
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