Investigation on the packing and hydration homogeneity of bentonite pellet mixtures

Abstract

Bentonite pellets are commonly regarded as an excellent sealing/backfilling material for high-level nuclear waste repositories. This study investigated the particle motion characteristics and segregation degree in bentonite pellet mixtures during a vibration process. Results showed that the packing homogeneity of mixtures with multi-size classes was always higher than that of mixtures with binary-size classes during vibration. The mixtures with binary-size classes achieve structural stability more quickly due to the percolation, while the mixtures with multi-size classes remain in motion. Additionally, hydration tests were conducted to analyze the water injection rate and pore-structure distribution evolution in mixtures. Uniformly mixed specimens exhibit faster injected water rates during the hydration process. After long-term hydration, the specimens achieved macroscopic homogeneity, but significant heterogeneity still exists in microstructure. The uniformly mixed method caused higher homogeneity in specimens with binary-size classes, and the layered filling achieved higher homogeneity in specimens with multi-size classes.