Damage Characteristics of Jalore Granitic Rocks After Thermal Cycling Effect for Nuclear Waste Repository

Abstract

Crystalline rocks are the best-suited rock type for the nuclear waste repository. A deeper understanding of the thermomechanical stability of rocks plays a crucial role in the selection of suitable host rock for this purpose. To investigate the feasibility of different types of jalore granitoid rocks (red, pink, golden, and white granites) in this application. The main objective of this study is devoted to damage characteristics when selecting the potential rock, while little work has been done in the field of rock mechanical behaviors in particular nuclear waste disposal. Where rock needs to stable after undergoing increases in the number of the thermal cycle in the treatment if a below damage threshold temperature is applied as in this study (i.e., 250 °c). The rock specimens were heated till 250 °c for 12 h, with constant heating rate 5 °c/min and constant cooling rate 0.364 °c/min, up to nine cycles. In this paper, the stress–strain curve under tension (brazilian disc test) was plotted for jalore granitoid rocks after different thermal cycle treatment. Using lemaitre’s strain equivalent principle along with statistics and damage theory, a model for damage caused due to thermal cycles under indirect tension condition is established. We have also measured the microscopic observation (thin section), mineral characterization (xrd), and surface morphology (sem) of different thermal cycles treated. Thermogravimetric analysis (tga) and differential thermal analysis (dt) have also been used to identify the changes in thermal and kinetic behaviors. It is found that the increase of the thermal cycle leads to an accumulation in strains and a reduction in the p-wave velocity and rock strength. We have found that the thermal damage incurred on the rock, in the form of mass loss and p-wave velocity decrease, due to thermal cracks and nonuniform expansion of grains along the grain boundary were developed on the surface. Increasing thermal cycles lead to a reduction in tensile strength and elastic modulus. Fracturing within the rock is more severe, as compared to three cycles, after being subjected to five thermal cycles. It is interesting to note that beyond five cycles of thermal treatment, the thermal damage and stability of the granitoid have remained mostly unchanged. © 2020, springer-verlag gmbh austria, part of springer nature.