Experimental investigations on the thermal conductivity characteristics of Beishan granitic rocks for China's HLW disposal

Abstract

Crystalline rocks are potential host rock types for the construction of high-level radioactive waste (HLW) repositories. A better understanding of thermal conductivity of rocks is essential to safe evaluation and engineering optimization of a HLW disposal system in the rock at depth. In the present study, experimental investigations on the thermal conductivity characteristics of 47 pairs of granitic rock specimens were conducted using the Transient Plane Source (TPS) method. The specimens were collected from borehole cores in the Beishan area, which is being considered as the most potential candidate area for China's HLW repository. To evaluate geological nature of the rocks, mineralogical compositions of the rocks were identified, and porosity of the specimens was measured. The thermal conductivities of the specimens under dry and water-saturated conditions were determined, and the effect of water saturation on the thermal conductivity was investigated. In addition, the influence of temperature and axial compression stress on the thermal conductivity of dry specimens was studied. The results revealed that the thermal conductivity of tested rocks was dependent on water saturation, temperature and compression stress. Based on the obtained data, some models considering porosity were established for describing the thermal conductivity characteristics of the tested rocks. Furthermore, when the rocks have a similar porosity, the quartz content dominates the thermal conductivity, and there exists an obvious increase of the thermal conductivity with increasing quartz content. The test results constitute the first systematic measurements on the Beishan granitic rocks and can further be used for the development of thermal models for predicting thermal response near the underground excavations for HLW disposal.