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Author: R.P. Shaw Publisher: Geological Society of London ISBN: 1862397228 Category : Science Languages : en Pages : 260
Book Description
Understanding the behaviour of gases in the context of radioactive waste disposal is a fundamental requirement in developing a safety case for the disposal of radioactive waste. Of particular importance are the long-term performance of bentonite buffers and cement-based backfill materials that may be used to encapsulate and surround the waste in a repository, and the behaviour of plastic clays, indurated mudrocks and crystalline formations that may be the host rocks for a repository. The EC Euratom programme funded project, FORGE, has provided new insights into the processes and mechanisms governing gas generation and migration with the aim of reducing uncertainty. This volume brings together papers on aspects of this topic arising from both the FORGE project and work undertaken elsewhere. This has been achieved by the acquisition of new experimental data coupled with modelling, through a series of laboratory and field-scale experiments performed at a number of underground research laboratories throughout Europe.
Author: R.P. Shaw Publisher: Geological Society of London ISBN: 1862397228 Category : Science Languages : en Pages : 260
Book Description
Understanding the behaviour of gases in the context of radioactive waste disposal is a fundamental requirement in developing a safety case for the disposal of radioactive waste. Of particular importance are the long-term performance of bentonite buffers and cement-based backfill materials that may be used to encapsulate and surround the waste in a repository, and the behaviour of plastic clays, indurated mudrocks and crystalline formations that may be the host rocks for a repository. The EC Euratom programme funded project, FORGE, has provided new insights into the processes and mechanisms governing gas generation and migration with the aim of reducing uncertainty. This volume brings together papers on aspects of this topic arising from both the FORGE project and work undertaken elsewhere. This has been achieved by the acquisition of new experimental data coupled with modelling, through a series of laboratory and field-scale experiments performed at a number of underground research laboratories throughout Europe.
Author: Nuclear Energy Agency Publisher: Nuclear Energy Agency, Organisation for Economic Co-operation and Development ISBN: Category : Technology & Engineering Languages : en Pages : 200
Book Description
These conference proceedings examine gas generation, accumulation and migration in underground repository systems for radioactive waste: safety-relevant issues.
Author: Xue Wei Publisher: ISBN: Category : Languages : en Pages :
Book Description
With the widening and increasing use of nuclear energy, it is very important to design and build long-term deep geological repositories (DGRs) to manage radioactive waste. The disposal of nuclear waste in deep rock formations is currently being investigated in several countries (e.g., Canada, China, France, Germany, India, Japan and Switzerland). In Canada, a repository for low and intermediate level radioactive waste is being proposed in Ontario's sedimentary rock formations. During the post-closure phase of a repository, significant quantities of gas will be generated from several processes, such as corrosion of metal containers or microbial degradation of organic waste. The gas pressure could influence the engineered barrier system and host rock and might disturb the pressure-head gradients and groundwater flows near the repository. An increasing gas pressure could also cause damage to the host rock by inducing the development of micro-/macro-cracks. This will further cause perturbation to the hydrogeological properties of the host rock such as desiccation of the porous media, change in degree of saturation and hydraulic conductivity. In this regard, gas generation and migration may affect the stability or integrity of the integrate barriers and threaten the biosphere through the transmitting gaseous radionuclides as long-term contaminants. Thus, from the safety perspective of DGRs, gas generation and migration should be considered in their design and construction. The understanding and modelling of gas migration within the host rock (natural barrier) and the associated potential impacts on the integrity of the natural barrier are important for the safety assessment of a DGR. Therefore, the key objectives of this Ph.D. study include (i) the development of a simulator for coupled modelling of gas migration in the host rock of a DGR for nuclear waste; and (ii) the numerical investigation of gas migration in the host rock of a DGR for nuclear waste in Ontario by using the developed simulator. Firstly, a new thermo-hydro-mechanical-chemical (THMC) simulator (TOUGHREACT-COMSOL) has been developed to address these objectives. This simulator results from the coupling of the well-established numerical codes, TOUGHREACT and COMSOL. A series of mathematical models, which include an elastoplastic-damage model have been developed and then implemented into the simulator. Then, the predictive ability of the simulator is validated against laboratory and field tests on gas migration in host rocks. The validation results have shown that the developed simulator can predict well the gas migration in host rocks. This agreement between the predicted results and the experimental data indicates that the developed simulator can reasonably predict gas migration in DGR systems. The new simulator is used to predict gas migration and its effects in a potential DGR site in Ontario. Valuable results regarding gas migration in a potential DGR located in Ontario have been obtained. The research conducted in this Ph.D. study will provide a useful tool and information for the understanding and prediction of gas migration and its effect in a DGR, particularly in Ontario.
Author: Royal Society (Great Britain) Publisher: ISBN: Category : Conservation of natural resources Languages : en Pages : 220
Book Description
How can it be demonstrated, within reasonable bounds, that radionuclides from radioactive waste buried in a repository deep underground will not make their way back to the surface over the next million years and endanger human beings then living there? That is the challenge facing Nirex, the company owned by the main producers of radioactive waste and charged with defining and implementing an acceptable disposal strategy. In order to address it, Nirex is conducting a major research programme involving scientists and engineers from many disciplines. Nirex also invited the Royal Society to conduct an independent review of this programme.
Author: Jianxiong Yang Publisher: ISBN: Category : Languages : en Pages :
Book Description
As a safe long-term management of nuclear wastes, deep geological repositories (DGRs) have been proposed or currently being constructed in several countries. The host rocks in DGRs are saturated with water after the geological disposal facilities (GDFs) are closed and sealed. Significant gas can be generated due to several processes, e.g., the metal corrosion, water radiolysis or microbial reaction of organic materials, etc. The generated gas is anticipated to span throughout the long-term disposal of waste, which may jeopardize the stability of host rocks. Correspondingly, the performance of GDF will be affected since the host rocks provide a final impediment to the radionuclide transport. As gas migration in saturated host rocks is a highly coupled hydro-mechanical (HM) process, either gas-induced micro-fracturing or macro-fracturing may contribute to the development of preferential gas pathways, which needs to be concerned to ensure the feasibility and safety of geological disposal. Current numerical studies on the gas migration behavior devoted to explaining the experimental phenomena in the gas injection tests conducted on the rock materials, in which some behaviors still cannot be well represented, i.e., gas induced fracturing, volulme dilation, anisotropic radial deformation. Therefore, to better represent the actual physical process of preferential gas flow, two modelling frameworks, i.e., macroscopic HM framework and two-scale HM framework, are proposed in the PhD study. For the macroscopic HM framework, a double porosity model is firstly developed based on the dual continuum method, in which the volumetric strains of the porous continuum (PC) and fractured continuum (FC) are work-conjugated to the respective effective stress level. The treatment in two types of porosity allows us to capture that the opening/closure of the fractures is caused by the interaction between the dilation of the PC and the dilation of the FPM, which is beneficial to describe the gas induced fracturing in an implicit way. Then, an enriched embedded fracture model (EFM) is proposed to address the mechanical behavior of fractures. A hyperbolic relation of fracture deformability is incorporated into the rock matrix, as a result the fractured rock shows a nonlinear elastic behavior, which can capture the stiffness degradation due to fracture opening. The equivalent continuum method is provided to derive the effective compliance tensor, which includes the transverse isotropic matrix and two fracture sets. Using the enriched EFM with a three-dimensional (3D) geometry is able to capture the anisotropic radial deformation during gas migration. Although the macroscopic HM framework is able to capture the major HM behaviors related to preferential gas flow, the development of gas dilatant pathways is still represented in an implicit way. Therefore, a two-scale HM framework is developed to explicitly simulate the development of preferential gas pathways. Initiating from the periodically distributed microstructures with microcracks, the asymptotic homogenization method is used to derive the macroscopic governing equations coupled with the normalized damage variable. The time-dependent damage evolution law is obtained from the microscopic mechanical energy analysis for evolving microcracks. Both time effect and size effect are incorporated in the damage model that will affect the overall HM behavior of rocks. The developed two-scale HM framework with single gas flow can qualitatively capture important behaviors, such as the discrete pathways, localized gas flow, unstabilized fracture branching. More specifically, the simulated results demonstrates that the inter-connection of fractures from gas inlet to outlet is a prerequisite for gas breakthrough, accompanied by large amounts of gas flowing out of the sample and a rapid drop in gas injection pressure. Incorporating water flow in the two-scale framework allows the model to quantitatively reproduce the experimental phenomena observed in the laboratory air injection tests, such as gas pressure evolution and mechanical deformation. More importantly, the model exlpaines that the significant differences in controlling gas breakthrough and mechanical deformation are resulting from the arbitrary nature of microstructural heterogeneities. To account for the gas-water interaction in the two-scale HM framework, a fully coupled two-phase flow and elaso-damage model is developed to simulate the laboratory and in-situ gas injection experiments. The model can quantitatively capture the experimental behaviors, e.g., gas pressure evolution and non-desaturation phenomenon. Furthermore, model results show that the highly localized fracture pathways are the major places where gas and water interacts each other, and as a result the rock is still kept fully saturated. As a whole, the obtained numerical results are synthesized and analyzed, the pros and cons of the developed models are discussed. To better improve the model performance, some recommendations are proposed for the future studies.
Author: R.P. Shaw 
Author: R.P. Shaw 
Author: R. M. Jeffries
Author: R. M. Jeffries
Author: W. R. Rodwell
Author: R. M. Jeffries
Author: Nuclear Energy Agency
Author: 
Author: Xue Wei
Author: Royal Society (Great Britain)
Author: Jianxiong Yang