Impact of γ irradiation and thermal aging on the swelling pressure of GMZ bentonite

To investigate the combined effects of gamma irradiation and thermal aging on the swelling pressure of buffer materials used in the geological disposal of high-level radioactive waste, Gaomiaozi (GMZ) bentonite from Inner Mongolia was herein selected. Samples were irradiated by gamma rays and exposed to a combination of gamma irradiation followed by thermal aging at 90 degrees C. Swelling pressure tests were then conducted. Results showed that irradiation and thermal aging reduced the swelling pressure of GMZ bentonite. Notably, after irradiating and storing at (25 +/- 3)degrees C for 360 d, the swelling pressure increased by 51.59 % compared with that of the gamma-irradiated sample; the swelling pressure decreased by 75.9 % for the gamma irradiation-thermal sequentially aged sample (heated for 180 d). Partial chemical-bond destruction, the transformation of structure trivalent to divalent iron, and the water redistribution in the bentonite were the primary drivers of the decrease in the swelling pressure of GMZ bentonite.