Study On The Thermal Conductivity Of Crushed Granite And Bentonite Mixture

With the rapid development and widely used of nuclear technology, how to safely dispose nuclear waste has become an important research topic. At present, the geological disposal is widely regarded as the most feasible method of high-level waste (HLW) disposal, using multiple barrier system (engineering barrier and natural barrier). Buffer material is a part of engineering barrier. Bentonites were selected as buffer materials because of its good thermal conductivity, low permeability, high expansibility etc. Inner Mongolia GMZ bentonites were pre-selected as Chinese HLW geological disposal bentonite. Many studies have found that adding silica sand, crushed granite and graphite in the bentonite can improve the thermal properties of bentonite.This paper focuses on the mixture of crushed granite and GMZ bentonite (hereafter referred to as granite-bentonite), using the transient plane heat source method to study the thermal properties of the meterials.The main research contents and achievements include:(1)The thermal properties of bentonites and granite-bentonite were studied under different temperature conditions.In the results we find that temperature have little influence on their thermal conductivity.(2)Premised on the water content of bentonite in mixed materials (hereafter referred to as matrix water content), we used Hot Disk thermal constants analyser to measure the thermal propertied of soil samples (different dry density, different content of granite and different granite size).Results show that the thermal conductivity of granite-bentonite increases with the increase of dry density and decreases with the increase of granite content.(3)The thermal conductivities of sand-bentonite and graphite-bentontie were studied.Under the condition of the matrix water content is constant, graphite can significantly improve the thermal conductivity of bentonites, while granite and silica reduce the thermal conductivity of bentonites.(4)Self-Consistent model, Differential model and De Vries and Campbell model was used to predict the thermal conductivity of granite-bentonite. We find Differential model can well predict the thermal conductivity of granite- bentonite.(5)A research of the thermal conductivity of granite-bentonite from the microscopic view was done in this paper. Soil porosity and pore radius distribution were obtained by mercury intrusion experiment. Results show that the thermal conductivity of granite-bentonite and the volumetric fraction of air (va/v) have a linear relationship.