Effect of Elevated Temperature on Mechanical and Structural Properties of Bentonite from Barmer, Rajasthan

ABSTRACT The disposal of high-level nuclear waste (HLW) deep underground is based on a system of multiple natural and artificial barriers. In recent decades, compacted bentonite has been considered a potential buffer material for nuclear waste repositories due to its low permeability and high swelling property. The bentonite buffer is expected to be exposed to high temperatures for an extended period due to the heat released from the nuclear waste container and the geothermal gradient within the deep geological repository. The temperature of the waste container can reach up to 200°C and eventually drop to a lower temperature as the waste material decomposes. This more extended temperature change puts the bentonite buffer under thermal stress, which affects its physico-mechanical properties. In this study, bentonite collected from Barmer district of Rajasthan was constantly exposed to different temperature levels of 25°C, 65°C, 110°C, 125°C and 160°C for 72 hours (3 days). Effects of elevated temperatures on the mechanical and structural behavior of bentonite were observed. The experiments evaluated the change in different properties such as UCS, Poisson’s ratio, cohesion, friction angle, X-ray diffraction and swelling pressure. The result showed that with increasing temperature, UCS, Poisson’s ratio, cohesion and swelling pressure decreased while the internal friction angle increased. X-ray diffraction analysis of thermally loaded bentonite samples of Barmer revealed no potential mineralogical transformations upon heat exposure upto 160°C, which could significantly impact the buffer’s engineering performance under deep geological repository (DGR) conditions.