RD&D-Programme 2004 - SKB

was observed on the simulated copper canister and in the innermost one to two millimetres of
the bentonite. Geochemical modelling of redistribution of minerals in a MX-80 material as a
consequence of exposure to Äspö groundwater was done in the Lot project /17-18/.
Programme
The ongoing laboratory tests within the Lot project are expected to provide an answer to the
question of whether the precipitations are due to vaporization of incoming water during the
water saturation phase, or whether the process continues even after full water saturation. The
latter is conceivable, since e.g. gypsum and calcite exhibit declining solubility at increasing
temperature.
At present, four long-term tests are being conducted within the Lot project. According to the
original plan, a high-temperature test will be terminated in the spring of 2005, entailing an
exposure time of five years. A five-year test with KBS-3 temperature is planned to be terminated
in 2006. According to the current plan, the remaining two tests will be conducted for a much
longer time.
Continued geochemical modelling is planned within the Lot project, partly with respect to
redistribution of minerals and partly with respect to transformation of montmorillonite.
17.2.19 Colloid release/erosion
The estimates in SR 97 suggest that there is little risk of erosion, whether chemical or
mechanical, of large quantities of bentonite. However, the process should be further studied.
One remaining question concerns the importance of very low ionic strengths in the groundwater.
Conclusions in RD&D 2001 and its review
SKI notes that erosion of the buffer material is not mentioned in the RD&D-Programme, but is
of the opinion that SKB has taken the necessary initiatives to move forward in the colloid issue
(for example by means of the Colloid Project in the Äspö HRL).
Newfound knowledge since RD&D 2001
Tests conducted in conjunction with KBS-3H studies have shown that piping from waterconducting
fractures accompanied by erosion could be a problem before the buffer has become
water-saturated. These phenomena are particularly serious for KBS-3H, since they can affect all
canister parcels that have been installed downstream of the water-conducting fracture. But this
could also conceivably affect certain deposition holes in KBS-3V. The following description
pertains primarily to KBS-3H, however.
If the inflowing water causes piping and erosion in the buffer, the buffer may be unable to seal
properly before closure, which means the flow of water must be stopped in some other way. The
base scenario is that 0.1 litre of water per minute runs into a section with a deposition parcel
in a KBS-3H tunnel and that the build-up of water pressure in the rock is about 100 kPa/hour
if the inflow is stopped. No matter how this inflow occurs, it is likely that the bentonite inside
the perforated container will be unable to stop the inflow before all gaps are first filled out from
the bottom at the same rate as the distance block swells and prevents further outward transport.
After at least ten days the gaps have been filled and the distance block has swollen (mainly as
gel) out against the rock. The last part expected to swell is at the roof. When this part has also
become impervious, the water cannot escape and the pressure in the fracture then builds up. If
the pressure builds up too quickly, the bentonite will not have time to swell fast enough without
piping occurring in the gel and erosion can start if the flow is heavy.
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