The swelling capacity of bentonite buffers is vital in high-level radioactive waste (HLW) repositories, as it minimizes groundwater infiltration, prevents nuclides from reaching the biosphere, and stabilizes the HLW canisters. As swelling capacity is a function of temperature, understanding bentonite’s behavior at approximately 100°C (its presumed upper limit) is essential. However, research on this subject has been scarce. Hence, this study explored the effects of thermal treatment of Ca-bentonite at 105°C under injected water pressures. The results suggest a 19% reduction in “swell index” and a 35%–36% decrease in the total pressure in thermally treated bentonite. The heated samples demonstrated higher hydraulic conductivity than the non-heated ones, indicating potential performance deterioration in controlling the fluid movement. Furthermore, the injected water pressure (base pressure) was not fully transmitted to the sample owing to the difference between the base and back pressures, leading to variations in the total pressure despite maintaining a constant differential pressure. Thus, the results demonstrated a degradation in bentonite’s swelling capacity and its compromised role in safe HLW disposal, when subjected to treatment at 105°C. The insights from this research can assist in HLW repository design, while highlighting the need for further research into bentonite’s performance.

1. Introduction
2. Sample and Experimental Procedure
    2.1 Sample
    2.2 Measurement of Swell Index
    2.3 Measurement of Swelling Pressure
    2.4 Measurement of Hydraulic Conductivity
3. Results
    3.1 Swell Index
    3.2 Swelling Pressure
    3.3 Hydraulic Conductivity
4. Discussion
    4.1 Reduction of Swelling by ThermalTreatment
    4.2 Swelling Pressure With Injected WaterPressure Conditions
5. Conclusions
Conflict of Interest
Acknowledgements
REFERENCES

• Gi-Jun Lee(Korea Institute of Civil Engineering and Building Technology, 283, Goyang-daero, Ilsanseo-gu, Goyang-si, Gyeonggi-do 10223, Republic of Korea)
• Seong-Won Lee(Korea Institute of Civil Engineering and Building Technology, 283, Goyang-daero, Ilsanseo-gu, Goyang-si, Gyeonggi-do 10223, Republic of Korea)
• Seok Yoon(Korea Atomic Energy Research Institute, 111, Daedeok-daero 989beon-gil, Yuseong-gu, Daejeon 34057, Republic of Korea) Corresponding author
• Gyu-Hyun Go(Kumoh National Institute of Technology, 61, Daehak-ro, Gumi-si, Gyeongsangbuk-do 39177, Republic of Korea)