Pressure evaluation of a gap space in the engineered barrier system in a high-level radioactive waste repository

Disposal canisters and buffer materials are main components in an engineered barrier system designed for high-level radioactive waste disposal. The design temperature of the buffer material is below 100 °C in most countries, and many studies have been conducted to increase the design temperature of the buffer material to increase the disposal density of the repository. A 1-cm air gap exists between the canister and buffer material that can cause several variations in the thermal–hydraulic–mechanical performance of the compacted bentonite buffer material. Therefore, considering the air-gap effect under high-temperature conditions is necessary because high temperatures can cause pressure variations in the air gap and compacted bentonites. Therefore, an experimental system was developed to measure the pressure variations in a confined cell, which contained air and compacted bentonites from room temperature to 150 °C. The pressure of the confined cell increased with increasing water content of the compacted bentonite, and the pressure changes were similar up to 100 °C irrespective of the presence of the 1-cm air gaps. Moreover, the pressure values at 150 °C were 10–15% higher in samples without gaps.