Evaluation of changes in buffer properties from an in-situ engineered barrier experiment

The In-situ Demonstration of Engineering Barrier System (In-DEBS), a field test in Korea, commenced operations in July 2016 to showcase the complex thermal-hydraulic-mechanical behavior of the engineering barrier in a high-level radioactive waste repository. To emulate the actual repository, the In-DEBS test utilized a heater and buffer material comprised of compacted bentonite blocks. From January to October 2022, the In-DEBS buffer was sequentially dismantled, and the buffer samples were collected and analyzed for physical properties such as dry density and water content based on the sample location. The findings indicated that the physical properties of the In-DEBS buffer material showed variations, which may have been caused by various factors such as technical gaps, the dismantling process, and temperature gradient caused by heaters. This study also presents several experiments conducted on the samples obtained from the In-DEBS field test and compared with laboratory experimental data of untreated samples. The thermal conductivity and the hydraulic conductivity of the field-collected samples were lower than those of the untreated samples and the swelling properties of the samples were found to be influenced by their respective locations within the buffer, Although the empirical correlation based on laboratory data on untreated samples demonstrated high accuracy, some discrepancies were observed between the properties of field samples and the predicted values, highlighting the importance of field tests.