scholarly journals FEM Analyses for T-H-M-M Coupling Processes in Dual-Porosity Rock Mass under Stress Corrosion and Pressure Solution

2012 ◽  
Vol 2012 ◽  
pp. 1-21 ◽  
Author(s):  
Yu-Jun Zhang ◽  
Chao-Shuai Yang ◽  
Gang Xu
Keyword(s):  
Rock Mass ◽  
Stress Corrosion ◽  
Nuclear Waste ◽  
Near Field ◽  
Dual Porosity ◽  
Pressure Solution ◽  
Fracture Aperture ◽  
Hypothetical Model ◽  
Coupling Processes ◽  
Aperture Closure

The models of stress corrosion and pressure solution established by Yasuhara et al. were introduced into the 2D FEM code of thermo-hydro-mechanical-migratory coupling analysis for dual-porosity medium developed by the authors. Aiming at a hypothetical model for geological disposal of nuclear waste in an unsaturated rock mass from which there is a nuclide leak, two computation conditions were designed. Then the corresponding two-dimensional numerical simulation for the coupled thermo-hydro-mechanical-migratory processes were carried out, and the states of temperatures, rates and magnitudes of aperture closure, pore and fracture pressures, flow velocities, nuclide concentrations and stresses in the rock mass were investigated. The results show: the aperture closure rates caused by stress corrosion are almost six orders higher than those caused by pressure solution, and the two kinds of closure rates climb up and then decline, furthermore tend towards stability; when the effects of stress corrosion and pressure solution are considered, the negative fracture pressures in near field rise very highly; the fracture aperture and porosity are decreases in the case 1, so the relative permeability coefficients reduce, therefore the nuclide concentrations in pore and fracture in this case are higher than those in case 2.

Modelling of thermal rock mass properties at the potential sites of a Swedish nuclear waste repository

2009 ◽  
Vol 46 (6) ◽  
pp. 1042-1054 ◽  
Author(s):  
Jan Sundberg ◽  
Pär-Erik Back ◽  
Rolf Christiansson ◽  
Harald Hökmark ◽  
Märta Ländell ◽  
...  
Keyword(s):  
Rock Mass ◽  
Nuclear Waste ◽  
Nuclear Waste Repository ◽  
Rock Mass Properties ◽  
Mass Properties ◽  
Waste Repository

scholarly journals Radiation Effects on Materials in the Near-Field of a Nuclear Waste Repository

2000 ◽  
Vol 663 ◽  
Author(s):  
B.X. Gu ◽  
L.M. Wang ◽  
S.X. Wang ◽  
R.C. Ewing
Keyword(s):  
Ion Exchange ◽  
Nuclear Waste ◽  
Radiation Effects ◽  
Ion Beam ◽  
Near Field ◽  
Energetic Electron ◽  
Layered Silicates ◽  
Nuclear Waste Repository ◽  
Layer Spacing ◽  
Waste Repository

ABSTRACTThe long-term radiation effects on materials in the near-field of a nuclear waste repository have been evaluated using accelerated laboratory experiments with energetic electron or ion beam irradiation. The materials studied include: zeolites, layered silicates (smectite clay and mica), as well as crystalline silicotitanate (CST) which is an important ion exchange material for the chemical separation of high-level liquid radioactive wastes.In situ transmission electron microscopy (TEM) during irradiation by energetic electrons and ions has shown that all of the studied materials are susceptible to irradiation-induced amorphization. At room temperature, complete amorphization was observed after ionizing doses of 1010 ∼ 1012 Gy or displacement doses on the order of 0.1 dpa (equivalent to doses received in 400-1,000 years for a high-loading nuclear waste form). Amorphization may be preceded or accompanied by dehydration, layer spacing reduction and gas bubble formation. In the case of zeolites, CST and some layered silicates, radiation effects are significantly enhanced at higher temperatures. Our experiments have shown that amorphization or even partial amorphization will cause a dramatic reduction in ion exchange and sorption/desorption capacities for radionuclides, such as Cs and Sr. Because the near-field or chemical processing materials (e.g. zeolites or CST) will receive a substantial radiation dose after they have incorporated radionuclides, our results suggest that radiation effects may, in some cases, retard the release of sorbed or ion-exchanged radionuclides.

Stress corrosion cracking of copper in swollen bentonite simulating nuclear waste disposal environment

2020 ◽  
Vol 72 (1-2) ◽  
pp. 333-338
Author(s):  
Shinji Fujimoto ◽  
Hiroaki Tsuchiya ◽  
Soma Ogawa ◽  
Yoshihisa Iida ◽  
Naoki Taniguchi
Keyword(s):  
Stress Corrosion ◽  
Nuclear Waste ◽  
Waste Disposal ◽  
Stress Corrosion Cracking ◽  
Nuclear Waste Disposal ◽  
Corrosion Cracking

scholarly journals Evolution of Fracture Aperture in Quartz Sandstone under Hydrothermal Conditions: Mechanical and Chemical Effects

Minerals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 657
Author(s):  
Chaojie Cheng ◽  
Harald Milsch
Keyword(s):  
Fluid Flow ◽  
Hydraulic Fracture ◽  
Chemical Equilibrium ◽  
Pore Fluid ◽  
Pressure Solution ◽  
Fracture Aperture ◽  
Hydraulic Aperture ◽  
Mechanical Aperture ◽  
Stagnant Flow

Fractures efficiently affect fluid flow in geological formations, and thereby determine mass and energy transport in reservoirs, which are not least exploited for economic resources. In this context, their response to mechanical and thermal changes, as well as fluid–rock interactions, is of paramount importance. In this study, a two-stage flow-through experiment was conducted on a pure quartz sandstone core of low matrix permeability, containing one single macroscopic tensile fracture. In the first short-term stage, the effects of mechanical and hydraulic aperture on pressure and temperature cycles were investigated. The purpose of the subsequent intermittent-flow long-term (140 days) stage was to constrain the evolution of the geometrical and hydraulic fracture properties resulting from pressure solution. Deionized water was used as the pore fluid, and permeability, as well as the effluent Si concentrations, were systematically measured. Overall, hydraulic aperture was shown to be significantly less affected by pressure, temperature and time, in comparison to mechanical aperture. During the long-term part of the experiment at 140 °C, the effluent Si concentrations likely reached a chemical equilibrium state within less than 8 days of stagnant flow, and exceeded the corresponding hydrostatic quartz solubility at this temperature. This implies that the pressure solution was active at the contacting fracture asperities, both at 140 °C and after cooling to 33 °C. The higher temperature yielded a higher dissolution rate and, consequently, a faster attainment of chemical equilibrium within the contact fluid. X-ray µCT observations evidenced a noticeable increase in fracture contact area ratio, which, in combination with theoretical considerations, implies a significant decrease in mechanical aperture. In contrast, the sample permeability, and thus the hydraulic fracture aperture, virtually did not vary. In conclusion, pressure solution-induced fracture aperture changes are affected by the degree of time-dependent variations in pore fluid composition. In contrast to the present case of a quasi-closed system with mostly stagnant flow, in an open system with continuous once-through fluid flow, the activity of the pressure solution may be amplified due to the persistent fluid-chemical nonequilibrium state, thus possibly enhancing aperture and fracture permeability changes.

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