Thermal-Hydrological-Mechanical Characterization of the Ghareb Formation at Conditions of High-Level Nuclear Waste Disposal

Abstract

ABSTRACT: The Ghareb Formation in the Yasmin Plain of Israel is under investigation as a potential disposal rock for nuclear waste disposal. Triaxial deformation tests and hydrostatic water-permeability tests were conducted with samples of the Ghareb to assess relevant thermal, hydrological, and mechanical properties. Axial deformation tests were performed on dry and water-saturated samples at effective pressures ranging from 0.7 to 19.6 MPa and temperatures of 23 °C and 100 °C, while permeability tests were conducted at ambient temperatures and effective pressures ranging from 0.7 to 20 MPa. Strength and elastic moduli increase with increasing effective pressure for the triaxial tests. Dry room temperature tests are generally the strongest, while the samples deformed at 100 °C exhibit large permanent compaction even at low effective pressures. Water permeability decreases by 1-2 orders of magnitude under hydrostatic conditions while experiencing permanent volume loss of 4-5%. Permeability loss is retained after unloading, resulting from permanent compaction. A 3-D compaction model was used to demonstrate that compaction in one direction is associated with de-compaction in the orthogonal directions. The model accurately reproduces the measured axial and transverse strain components. The experimentally constrained deformational properties of the Ghareb will be used for 3-D thermal-hydrological-mechanical modelling of borehole stability. 1. INTRODUCTION The disposal of high-level nuclear waste is a top concern worldwide (Faybishenko et al., 2017). With increasing interest in nuclear power as an alternative to carbon-based fuels, the problem of safely storing nuclear waste is expected to grow (Kim et al., 2011). One solution for disposal is geological disposal of nuclear waste, where waste is isolated within subsurface geologic formations to be contained and isolated from the surrounding environment (Birkholzer et al., 2012). Given the risks associated with nuclear waste, any potential disposal site must be demonstrably capable of isolating the material from the surface environment for large time scales (Krauskopf, 1988).