Study On Thermal Conductivity Of Compacted Bentonite Block As HLW Buffer

Satisfactory thermal conductivity property is essential to buffer block as high-level radioactive waste(HLW)barrier.By using semi-automatic pressing apparatus,buffer blocks with the mixtures of GMZ bentonite and standard quartz sand were prepared to study the effect of water content and dry density on the thermal performance of buffer block and so to evaluate the uniformity of thermal performance and the feasibility of predicting model.Test results show that: the mean value and extreme values(both maximum and minimum)of thermal conductivity of buffer blocks increase linearly with increase in water contents and dry densities.The mean value of thermal conductivity satisfies the requirement,which is more than 0.8 W/m?K recommended by IAEA.The maximal relative errors of thermal conductivity decrease as water contents and dry densities increase.It means that thermal conductivity of buffer blocks tends to be homogeneous,especially at a more dense and wet condition.The mean value and extreme values of thermal diffusion coefficient increase nonlinearly as water contents and dry densities increase.No obvious change was found on mean value and extreme values of mass specific heat capacity for blocks with water contents and dry densities increase.The thermal conductivity of buffer blocks exhibits a good homogeneity in the directions along R,(?)and Z axis.Test results are in agreement with results of t test in statistics,and that proves t test can be successfully used to check the thermal conductivity data of buffer blocks in the future.Data analysis shows that Johansen model can predict thermal conductivity of buffer block with an error less than ±10% compared with the experimental values.Johansen model was used to a supposed barrier,which is to be constructed with blocks whether the block joints are sealed or not in case that contact with water to predict the thermal conductivity of buffer blocks of 1.50g/cm3~1.90g/cm3 in dry densities.The results show that the thermal conductivity of “practical” buffer block barrier increase as initial dry densities increase and the sealed situation has a better thermal conductivity than that of the un-sealed situation.This tendency is much more obvious as initial dry densities increase.Generally,the values of thermal conductivity are among 1.5~2.2W/m·K,which is a good reference for multi-field coupling simulation of depository barrier.