Inhibition of groundwater salt content on the healing of HLW buffer block joints
ZHANG Huyuan1，2，ZHU Fei1，2，WANG Zhaoming1，2
(1. Key Laboratory of Mechanics on Disaster and Environment in Western China，Ministry of Education，Lanzhou University，
Lanzhou，Gansu 730000，China；2. School of Civil Engineering and Mechanics，Lanzhou University，
Lanzhou，Gansu 730000，China)
Abstract：Construction joints between compacted bentonite blocks in buffer barrier will be closed due to bentonite hydration and swell during the long-term operation of underground HLW repositories. While this self-healing of joints tends to be inhibited，because the swelling of bentonite will be restricted by salts in groundwater. This work studies the effect of permeat salt content on joint healing performance by permeability，thermal conductivity and microstructure tests. The bentonite-sand mixture is compacted into cake-shaped sample with a joint，in which pellet bentonite with a particle rate of 70% was filled. Chemical solutions simulating the groundwater of Beishan area in Gansu is used to conduct permeability tests by rigid-wall permeameter，followed by thermal conductivity and microstructure tests，in comparison with the tests by distilled water. The results show that the hydraulic conductivity of block joint system is the smallest in case that distilled water is used as permeating fluid. With the increase of total dissolved solid，TDS，from zero to 10 g/ L，the hydraulic conductivity increased from 3×10－10 cm/s to 8.5×10－9 cm/s，more than one order of magnitude，indicating an increased inhibition to joint healing by higher salt content. After permeation test，the dry density in the joint area was increased，while the dry density outside the joint was decreased. This certificates that joint is healed by a process that bentonite swells towards the space where low stress conditions exist. Detailed analysis shows that higher TDS corresponds to lower increment in dry density within joint compared with distilled water，indicating again the salt inhibition effect. When permeat TDS is increased，thermal conductivity，in general，tends to be decreased slowly with a larger variation，indicating a reduction in thermal stability.
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2020, Vol. 39 
