RD&D-Programme 2004 - SKB

external forces are required in the case of highly compacted bentonite. The phenomenon has
been observed in connection with compaction of bentonite blocks with a high water ratio if the
compaction pressure has been so high that the bentonite has become fully water-saturated.
Conclusions in RD&D 2001 and its review
SKI does not believe that liquefaction due to earthquake is a problem either, but the issue needs
to be monitored. They also emphasize the importance of SKB’s continued work on the development
of a THM model for water-saturated conditions.
Newfound knowledge since RD&D 2001
Extensive laboratory tests with different salinities and ionic species have been conducted,
mainly on bentonite from Wyoming and Milos, for the purpose of determining its hydraulic
conductivity.
Some laboratory tests have been performed to show how liquefaction can occur and what the
effects are. They have shown that while a rapid increase in the water pressure cannot cause
liquefaction of the buffer, a rapid increase in the total pressure can. The effects of liquefaction
have not yet been investigated.
Programme
Laboratory tests with different salinities and ionic species will be conducted for other potential
buffer materials. A smaller test series will be carried out at elevated temperatures.
Flow tests with measurement of hydraulic conductivity and investigation of the influence of
density and pore water composition – in addition to those already done on MX-80 and the Milos
bentonite – also need to be done for other buffer candidates, for example Indian bentonites.
The development of the THM models for water-saturated buffer will continue, see section
17.2.23.
The effects of a (highly improbable) liquefaction of the buffer may possibly be studied in a
simulated deposition hole with a loaded canister on a scale of about 1:40.
17.2.6 Gas transport/dissolution
In the case when a copper canister is damaged and water can come into contact with an iron
insert, hydrogen gas will be formed inside the canister. Dissolved gas is transported slowly
through the bentonite buffer, and it is very probable that a gas phase and a gas pressure will be
built up in the canister. It is important to be able to show that this pressure will not lead to any
negative consequences for the performance of the repository. This means that the gas must be
able to escape without damaging buffer or rock.
Conclusions in RD&D 2001 and its review
Kasam considers it positive that SKB is prioritizing gas transport in buffer material.
In SKI’s opinion, the Äspö HRL could be used to demonstrate gas transport through the buffer
on a full scale.
Regarding gas transport in saturated buffer, it is particularly urgent according to SKI that
full-scale tests and tests on other scales be started and evaluated in a shorter period of time
than three years if SKB is to keep to its timetable. SKI considers it doubtful whether there will
be time to finish the remaining work by the scheduled time for repository licensing and points
out that validated models for gas transport in saturated buffer remain to be developed, which
requires experiments on different scales and even some long-term tests.
RD&D-Programme 2004 205