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 degrees 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 degrees 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 degrees C irrespective of the presence of the 1-cm air gaps. Moreover, the pressure values at 150 degrees C were 10-15% higher in samples without gaps.