The Effect of Porosity Change in Bentonite Caused by Decay Heat on Radionuclide Transport through Buffer Material

Bentonite is used as a buffer material in most high-level radioactive waste (HLW) repository designs. Smectite clay is the main mineral component of bentonite and plays a key role in controlling the buffer’s physical and chemical behaviors. Moreover, the long-term functions of buffer clay could be lost through smectite dehydration under the prevailing temperature stemming from the heat of waste decay. Therefore, the influence of waste decay temperatures on bentonite performance needs to be studied. However, seldom addressed is the influence of the thermo-hydro-chemical (T-H-C) processes on buffer material degradation in the engineered barrier system (EBS) of HLW disposal repositories as related to smectite clay dehydration. This study adopts a chemical kinetic model of smectite dehydration and hydration of compacted bentonite to analyze the impact of temperature changes due to radionuclide decay heat on the porosity and transport properties of the buffer material. Results demonstrate significant changes in porosity correlate with enhanced radionuclide transport, emphasizing the necessity of incorporating T-H-C processes in HLW repository design for improved safety assessments.