RD&D-Programme 2004 - SKB

10.6.1 Requirements and premises
In Sweden there is no formal requirement that retrieval of a deposited canister must be possible,
and retrieval requires the permission of the authorities. The principle that retrieval should not be
impossible is a logical consequence of the stepwise build-out of the repository with intervening
evaluation that is planned. The design requirements are such that retrieval of canisters must be
possible and that any measures adopted to facilitate retrieval may not affect the safety performance
of the deep repository.
10.6.2 Freeing of canister
Conclusions in RD&D 2001 and its review
A number of methods for removing bentonite have been studied. They can be divided into four
main categories: mechanical, hydrodynamic, thermal and electrotechnical. The hydrodynamic
method has shown the best results and has been recommended for further study.
In RD&D 2001, SKB concludes that technology and methods for retrieval as well as a facility
for interim storage of the fuel must be available if, on evaluation of the initial operating phase
of the deep repository, it is found necessary to retrieve deposited canisters.
Newfound knowledge since RD&D 2001
Freeing of a full-sized canister surrounded by non-water-saturated bentonite has been demonstrated
at the Äspö HRL. The purpose of the test, which was carried out with improvised
equipment, was to clarify whether freeing of canisters is possible by slurrying of the buffer with
salt solution and dewatering with a decanter in a continuous process /10-13/, see Figure 10-4.
The tests show positive results and confirm that the hydrodynamic method used is a method
which SKB should continue to develop and test.
Programme
Further demonstrations of technology and equipment for freeing of a deposited canister will be
provided when the Canister Retrieval Test and the Prototype Repository at the Äspö HRL are
dismantled. These demonstrations will only include parts of the buffer, since the buffer material
will also be used and investigated in the framework of other studies.
Figure 10-4. The photo at the left shows the experimental set-up used in the slurrying test
– slurrying is done in the tank in the middle. The photo at the right shows how the bentonite is
slurried by means of a salt solution.
126 RD&D-Programme 2004