Experiment on Thermal Conduction of Compacted Bentonite Blocks

Abstract

Bentonite has been regarded as buffer material for high-level radioactive waste (HLW) disposal all over the world, plenty of decay heat released from HLW is conducted through butter material, therefore, thermal conduction of compacted bentonite is very important. This study presents compacted GMZ Na-bentonite(with 8.9% water content, 1.8 g/cm3 compacting density) temperature and relative humidity change pattern with time and position variation taking intermittent warming method and using thermal conduction equipment, it is designed according to the conceptual model of HLW geological disposal repository. The results show that the temperature achieve a balance quickly, the temperature of compacted bentonite block which the distance is 2 cm to heat source reaches the first about 55°C balance stage after about 40 hours, radial temperature gradient (GT) increases with the temperature rising, average of GT during the first stage is 0.85°C/cm, average of GT during the second balance stage about 82°C is 1.57°C/cm; Affected by temperature, relative humidity increase rapidly at the beginning with the temperature rising, when the temperature reaches equilibrium, the relative humidity decreases slowly, the higher temperature of the compacted bentonite block is, the lower relative humidity is, the radial gradient of relative humidity (GHR) increase with heating time, average of GHR during the first stage about 55 °C is 1.32%/cm, average of GHR during the second stage about 82°C is 1.89 %/cm.