Compaction of large buffer block for disposal of high-level radioactive waste

The concept model of high-level radioactive waste (HLW) repositories in deep geological media is based on a multi-barrier system. In accordance with this concept for the storage of spent nuclear fuel, the canister with the fuel should be surrounded by bentonite blocks. A useful technique for producing compacted blocks of bentonite is described in this work. These blocks were uniaxially compacted with a mold that yielded blocks with an outer diameter of 1200 mm, inner diameter of 600 mm, and angle of 45 degrees. A technique has been developed for manufacturing blocks from GMZ-Na bentonite using a large press machine. During these tests, blocks were compacted for studying different factors that affect the quality of the blocks. The blocks were also examined with respect to damage and cracks. The results from these tests revealed that the natural water content of the bentonite powder leads to several problems that affect the quality of the blocks. In the subsequent test, the blocks were manufactured with different compaction rates using powders with high water content. Samples (nine cylindrical samples in total) were taken from the two examined blocks, and the water content and the density were determined. The results revealed that the solid block is rather homogenous. This indicates that the technique of compacting bentonite blocks established in the present study is suitable for manufacturing buffer blocks.