Development of Bentonite Buffer

The applicability of bentonite as a release barrier in the final disposal of nuclear waste has been investigated since 1970s. Research has focused on e.g. the effects of different conditions and on the fabrication of the bentonite blocks.

The reactions of bentonite with saline solutions have been studied, as the salinity of water increases with depth. The increased salinity decreases the swelling of bentonite and increases its permeability to water. Current knowledge suggests that the expected salinity of water will not prevent the use of bentonite as a sealing material, but needs to be taken into account in the sizing of the material.

The bentonite block fabrication process has also been tested. The tests have produced information about the factors that influence the properties of compressed bentonite and about the behaviour of bentonite under compression.

The behaviour of bentonite in actual disposal conditions has been studied at a depth of 460 metres in SKB's hard rock laboratory in Sweden. Heated copper canisters have been embedded in deposition holes with a diameter of almost two metres, drilled at the bottom of tunnels that correspond in size to the tunnels in the final disposal repository. The canisters, which do not contain spent nuclear fuel, however, have then been enclosed in bentonite clay. The parameters studied in the test include e.g. temperatures, saturation of water and pressure variations. This test has started in the early part of the decade and the test tunnel will be dismantled in two phases. The first part of the experiment will be dismantled at the beginning of 2010s while the second part, tunnels inner part, will be available for further follow-up studies until actual final disposal starts.