The waste in a nuclear repository generates heat for hundreds to thousands of years and the stability, deformation and water flow characteristics of the rock mass is influenced by the introduced thermal pulse. The storage of the waste in rock caverns essentially introduces stress, due to excavation (mechanical stress), due to the temperature generated by radioactive wastes (thermal stress) and due to the pore water pressure generated by the change in the temperature (hydro-thermal). Therefore, an analysis of the stability conditions of the surrounding rock, through the estimation of resulting stress and displacements around the openings is of great significance. In this paper, three-dimensional analysis of a KBS3 type repository in granite rock is carried out using the software FLAC3D. The dimension and properties of different materials is taken for a typical Indian rock. In this study mechanical (M), thermo-mechanical (TM) and thermo-hydro-mechanical (THM) analyses are carried out assuming linearly elastic model.
Nuclear waste storage structures are completely encased and housed into the existing host ground medium. Unlike a surface structure, interaction of the host medium with the underground structure plays an important role in the proper design of an underground structure. Nuclear waste consists of radionuclides which have extremely long half life and high heat generation capacity. Therefore, long term performance is very important for the host ground medium of repository structure. Different countries are following different storage concepts according to in-situ stress characteristics, rock structure, tectonic settings and ground water flow conditions. These concepts for high-level waste disposal are [1]-
KBS3 Concept
VLH (Very Long Hole) Concept
VDH (Very Deep Hole) Concept Rutqvist and Tsang [2] conducted coupled thermal, hydrologic and mechanical analysis to evaluate the impact of coupled THM processes on the performance of a potential nuclear waste repository at Yucca Mountain.
Chijimatsu et al. [3] studied the implications of coupled thermohydro- mechanical (THM) processes on the safety of a hypothetical nuclear waste repository at the near-field. Hudson et al. [4] have reviewed coupled thermo-hydro-mechanical issues relating to nuclear waste repository design and performance and stated that the heat generated by the waste is transferred generally due to conduction, and through movement of fluid particles can be neglected. Rutqvist et al. [5] have predicted coupled thermo-hydromechanical responses during an insitu heater experiment which simulates a nuclear waste deposition hole with a waste over-pack and bentonite buffer, surrounded by fractured rock. Chijimatsu et al. [6] conducted large-scale insitu experiment at the Kamaishi mine, Japan. The objectives of this thermo-hydro-mechanical (THM) test were to evaluate the applicability of the engineered barrier technology, to observe near field-coupled THM phenomena insitu and 1168 to increase confidence in coupled THM models. Hsiung et al. [7] investigated coupled processes associated with (i) temperature effects on mechanical deformation and (ii) effect of thermal–mechanical processes on rock-mass permeability.
