RD&D-Programme 2004 - SKB

In parallel with the field tests, the tests will be modelled in an attempt to understand the flow
paths in the backfill and the connection with the properties of the rock. Furthermore, supplementary
laboratory tests will be conducted to gain a better understanding of the influence of test
technique and inhomogeneities in the backfill.
Monitoring of wetting and swelling pressure will continue in the Prototype Repository. Valuable
information can be obtained about the hydraulic interaction between rock and backfill by modelling
of the processes and comparisons with the measurement results. Supplementary laboratory
investigations will also be conducted. Dismantling of the outer section is planned to take place
in 2008.
The project “Backfill and Closure of Tunnels and Rock Caverns” is continuing with the next
phase, whereby the selected alternatives and materials will be studied more closely. Laboratory
tests will be performed on alternative materials such as Milos calcium bentonite and Ashapura
bentonite (Indian) in order to determine hydraulic and mechanical properties as well as compaction
properties. Technology for in situ compaction in the tunnel, block pressing (concept D)
and block emplacement will be studied. The hydraulic interaction of the backfill with the rock,
as well as possible problems with piping and erosion, will also be studied. Phase two will
continue until 2005, after which pilot tests with prototype equipment will be carried out to
verify and improve the emplacement and compaction techniques with some selected materials
and concepts. A large-scale field test aimed at verifying the function of the backfill is planned
in phase four.
18.2.3 Radiation attenuation/heat generation
The process can be neglected in the backfill.
18.2.4 Heat transport
Conclusions in RD&D 2001 and its review
The unchanged conclusion is that the temperature of the backfill is determined by the surrounding
rock, which has a higher thermal conductivity. The backfill’s inherent heat transport capacity
is only a factor insofar as the average effective heat transport resistance of the near field will be
slightly greater if the heat transport capacity is low. However, the tunnel’s volume fraction of
the near field is so small that changes in the backfill’s contribution to the heat transport resistance
have insignificant effects on the temperature, both in the backfill itself and in the buffer.
Newfound knowledge since RD&D 2001
The temperature evolution in the backfill in the Prototype Repository will be measured and
monitored in many points. These measurement results, together with the temperature evolution
in the upper part of the buffer in the deposition holes, can be used to verify that heat transport in
the backfill is being accurately modelled.
Programme
The measurements and evaluations of the temperature evolution in the Prototype Repository
continue. The thermal conductivity can be calculated theoretically. These calculations should
also be done for the new backfilling concepts and verified by some laboratory measurements.
18.2.5 Water transport under unsaturated conditions
It is possible that the backfill will be the primary source of water to the buffer in certain
deposition holes.
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