RD&D-Programme 2004 - SKB

have been performed for some ten consignments, representing 20 years’ production. According
to the results, the montmorillonite content is around 85 percent, with a few percent’s variation.
Previous determinations have found about 75 percent /17-3/, while the manufacturer of MX-80
has stated that the montmorillonite content is over 90 percent. The examined bentonite from
Milos has a montmorillonite content of 80 to 85 percent.
Programme
SKB intends to continue to develop testing and analysis methods, and to conduct investigations
of swellable minerals in potential buffer materials, as described in section 17.1.2.
17.1.7 Water content
In KBS-3V in SR-Can, the compacted bentonite blocks are assumed to have an initial degree of
water saturation of between 70 and 85 percent. It is further assumed that the buffer-rock gaps
can be reduced to three centimetres. The buffer-canister and buffer-rock gaps may be filled with
water, but in SR-Can it is assumed that they are dry. The water content may be slightly lower in
KBS-3H.
Conclusions in RD&D 2001 and its review
Not dealt with.
Newfound knowledge since RD&D 2001
No work has been done on isostatic block pressing since RD&D 2001. Full-sized blocks with
a high degree of water saturation have been compacted by uniaxial technique for Lasgit in the
Äspö HRL. Rings with 99 percent water saturation and cylindrical blocks with 96 percent water
saturation have been made.
Programme
Development of technology for fabrication of blocks with a greater height is under way and will
continue. The goal is to optimize the pressing procedure in order to obtain the best quality and
the most rational deposition. Since blocks larger than 50–100 cm in height cannot be produced
by uniaxial compression, development work is being focused on isostatic pressing. There is no
isostatic press in Sweden today that is big enough to press full-scale blocks, but tests of isostatic
pressing of blocks with a diameter of about 100 cm are planned.
Large complex blocks with bottom and rings as a unit can entail problems with cracking and
disintegration during the wetting/drying process after deposition. Furthermore, in such blocks
mean density and swelling pressure are higher in the bottom than around the canister, since the
difference in density between rings and cylindrical blocks made for Äspö cannot be achieved in
a composite block. These two potential problems will be studied.
17.1.8 Gas contents
The bentonite blocks have a degree of water saturation of 70–85 percent, which means that
70–85 percent of the pore volume is filled with water and the remainder with air. The outer gap
is left unfilled. The air in a deposition hole occupies approximately six percent of the volume.
The uncertainties in gas contents are not important for long-term safety.
The initial gas content follows from the water content and the porosity, see above.
198 RD&D-Programme 2004