Increasing thermal conductivity of buffer materials makes the disposal tunnel and hole spacings in high-level radioactive waste (HLW) repositories decrease, so that the area of the HLW repository decreases, which gives more choices to choose the HLW repository site and economical cost savings to construct HLW repositories. Thus, developing enhanced buffer materials with improved thermal conductivity is needed. One of the methods to develop enhanced buffer materials is to add additives to the bentonite which is main material for buffer materials. Most additives have high thermal conductivity, but most additives do not swell or less swell than bentonite, so that the swelling pressure of the enhanced buffer materials by additives decreases compared to the swelling pressure of pure bentonite buffer materials. Swelling pressure is an important performance criterion to design buffer materials. Thus, it is important to confirm the swelling pressure of the enhanced bentonite. However, it is not simple to measure the swelling pressure of the buffer materials and furthermore, it takes several days to measure the swelling pressure of the buffer materials. For these reasons, swelling index can be considered to predict the swelling pressure of the enhanced buffer materials relatively. In this study, it was investigated through tests how the swelling index of bentonite-sand mixtures change according to the amount of sand and it was found that the linear relationship between swelling index and sand amount in the bentonite-sand mixtures.

• Gi-Jun Lee(Korea Atomic Energy Research Institute, 111, Daedeok-daero 989beon-gil, Yuseong gu, Daejeon) Corresponding author
• Seok Yoon(Korea Atomic Energy Research Institute, 111, Daedeok-daero 989beon-gil, Yuseong gu, Daejeon)