Scale-tests in the laboratory

Bentonite clay is an important part of the Swedish KBS-3V design for final repositories of spent nuclear fuel. The spent nuclear fuel, encapsulated in copper canisters, will be deposited in vertical deposition holes in crystalline rock at a depth of 400-700 meters. Between the canisters and the rock, compacted bentonite blocks are emplaced as buffer material to protect the canisters and limit the flow of water. The bentonite absorbs water and develops a swelling pressure that will keep the canister in place and the microbiological activity low. The plasticity of the clay should be high enough to minimize any force from the rock to the canister in case of rock displacements. 

An important part of the research and development work of the concept for a final repository is to perform scale tests in laboratory. Clay Technology has long experience from this kind of work e.g. regarding design and construction of the test equipment, preparation of bentonite components, measurement technology and data acquisition.  

Examples of bentonite components are compacted cylindrical blocks with different diameters (often between 50 and 300 mm in laboratory scales), bentonite pellets or granulated bentonite fillings. The left photo in Figure 1 shows a simulated deposition hole in scale 1:10. In conjunction with the water saturation of the buffer, the development of swelling pressure is registered at several levels. The high swelling pressure of compacted bentonite often requires test equipment of steel, but also acrylic plastic is sometimes used when phenomena as piping and erosion are to be observed, right photo in Figure 1

Figure 2.

Figure 1 Left: Deposition hole in scale 1:10. Measurement of swelling pressure development in conjunction with the water saturation (SKB report TR-20-04). Right: Example of test equipment used to study piping and erosion phenomena in a pellet filling (SKB report TR-14-22).