Abstract
Abstract
In the current concept for disposal of high-level radioactive waste (HLW) in China, a barrier composed of blocks of highly compacted bentonite is constructed around the waste canisters. To develop this technique, uniaxial compaction of full-sized bentonite blocks has been initiated. Many factors affect the quality of bentonite blocks, including water ratio and granule size distribution of the bentonite, compaction pressure and rate, and form geometry. In the present study, compaction tests were conducted using powdered, pelleted, and mixed GMZ bentonite to evaluate the effects of granule size distribution on the integrity and uniformity of the block samples. Results show that high-quality blocks can be manufactured by adjusting the water content of the bentonite to 17%, in spite of different granule size distributions. The compaction in the mixed bentonite was better than that in the powdered and pelleted samples. However, the difference in final density was negligible when compacting at the same pressure. The block uniformity was not improved by adopting different granule size distributions when the height:diameter ratio of the bentonite samples reached 2. Blocks produced by powdered and mixed bentonite were prone to radial cracks when subjected to moisture loss; however, the cracks were healed after moisture redistribution.