Assessment of thermal performance of engineered barrier system made up of barmer bentonite, India

Abstract

The concept of deep geological repository for safe and long term disposal of high level nuclear waste is based on the multi-barrier system. Buffer material (bentonite clay) is key component of EBS and plays a critical role to minimize the flow of groundwater, provides mechanical stability of waste container, to prevent the canister from possible degradation and eliminate the chances of migration of radionuclides. One of the critical design parameter for designing the engineered barrier system could be the temperature evolved in near field area of geological repository. A small scale (centimeter scale) physical model has been developed to assess the temperature distribution within the engineered barrier system. Bentonite supplied by a supplier has been compacted with low saturation condition. Cylindrical confining structure having 155 mm diameter and made by low carbon steel has been used to compact the bentonite clay to represent the pit for nuclear waste. A heater of 500-watt capacity has been placed to represent the nuclear waste canister. Confining structure has been insulated using rock wool and sealed to prevent heat loss. Test has been conducted for 3 weeks and temperature at various locations have been recorded until the temperature at each point becomes steady.The objective of the study was to monitor the temperature change at different location in longitudinal direction within the compacted bentonite. The experiment has been carried out to assess the thermal behavior of engineered barrier made of compacted bentonite. The moisture content has been maintained at 10% by weight. A 3-dimensional numerical model has been developed using commercially available software package, COMSOL multi physics based on finite element method. The experimental result shows that maximum temperature evolved in longitudinal direction reaches up to 53°C, at monitoring point T1 within bentonite having moisture content of 10% respectively. © 2020 ISRM.