Influence Of Thermal Treatment On The Thermal Conductivity Characteristics Of Beishan Granite

Deep geological disposal is internationally accepted as a feasible and safe way to dispose of high-level radioactive waste(HLW).As a natual barrier,the host rock is the last line of defense in the whole diposal system.Among all the engineering properties of the host rock,the thermal conductivity is a key parameter to describe the heat transfer capability,and has a significant influence on layout of a HLW repository and optimization of distance between disposal elements.Hence,a better understanding of the thermal conductivity of the host rock is essential to design HLW repositories.The Beishan area in Gansu Province of northwestern China is the first priority area for the HLW repository.This work aims at investigating the thermal conductivity characteristics of Beishan granite after different temperature treatments.The following summarizes the major achievements obtained from this study.(1)The thermal conductivities of the specimens treated with different temperatures(200,300,400,550,650,and 800 °C)were obtained using the Transient Plane Source(TPS)method.Based on scanning electron microscope(SEM)observations,microstructural characteristics of the specimens before and after thermal treatment were characterized.The influence of the thermally induced microcracks on the thermal conductivity was revealed.(2)The relationships between conventional physical properties(i.e.,porosity,bulk density,and P-wave velocity)and the thermal conductivity were analyzed.Empirical equations were established to predict the thermal conductivity of thermally treated specimens using the conventional physical parameters.(3)The variations of the thermal conductivity of the thermally treated specimens under water-saturated,increased ambient temperature and compression stress condtions were obtained.The relations between rock porosity and water saturation,ambient temperature and compression stress dependent thermal conductivity were discussed.A series of models considering the effect of porosity were established for describing the effects of water saturation,ambient temperature,and compression stress on the thermal conductivity of thermally treated rock.(4)The variations of the lateral thermal conductivity of the thermally treated speicmens in the process of failure under uniaxial compression were obtained.The influence of the thermal treatment temperature on the strength,deformation and acoustic emission characteristics was analyzed.The thermal conductivity characteristics of the specimens were revealed at different deformation stages.