A Parametric Study of Gas Migration From an Underground Nuclear Waste Repository (original) (raw)
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Modelling and Numerical Simulation of Gas Migration in a Nuclear Waste Repository
We present a compositional compressible two-phase, liquid and gas, flow model for numerical simulations of hydrogen migration in deep geological radioactive waste repository. This model includes capillary effects and the gas diffusivity. The choice of the main variables in this model, Total or Dissolved Hydrogen Mass Concentration and Liquid Pressure, leads to a unique and consistent formulation of the gas phase appearance and disappearance. After introducing this model, we show computational evidences of its adequacy to simulate gas phase appearance and disappearance in different situations typical of underground radioactive waste repository.
Engineering Geology, 2014
In a deep geological repository (DGR) for nuclear wastes, several mechanisms such as waste form degradation and corrosion could lead to gas generation. The produced gas can potentially overpressurize the repository, alter the hydraulic and mechanical properties of the host rock and affect the long term containment function of the natural (host rock) and engineered barriers. Thus, the understanding of the gas migration within the host rock and engineered barriers and the associated potential impacts on their integrity is important for the safety assessment of a DGR. In this paper, a coupled hydro-mechanical model for predicting and simulating the gas migration in sedimentary host rock is presented. A detailed formulation coupling moisture (liquid water and water vapor) and gas transfer in a deformable porous medium is given. The model takes into account the damage-controlled fluid (gas, water) flow as well as the coupling of hydraulic and mechanical processes (e.g., stress, deformation). The model also considers the coupling of the diffusion coefficient with mechanical deformation as well as considers the modification of capillary pressure due to the variation of permeability and porosity. The prediction capability of the developed model is tested against laboratory scale and in situ experiments conducted on potential host sedimentary rocks for nuclear waste disposal. The model predictions are in good agreement with the experimental results. The numerical simulations of the laboratory and field gas injection tests provide a better understanding of the mechanisms of gas migration and the potential effects of excessive gas pressure on the host sedimentary rocks. This research work has allowed us to identify key features related to gas generation and migration that are considered important in the long term safety assessment of a DGR in sedimentary host formations.
2013
This paper presents the results of a benchmark study that compares a number of numerical models applied to a specific problem in the context of hydrogen flow and transport in a nuclear waste repository. The processes modeled are two-phase (water and hydrogen) immiscible compressible two-component transient flow in a heterogeneous porous medium under isothermal conditions. The three-dimensional model represents a module of a repository for high level waste in a clay host rock. An upscaling technique and a vertex-centred finite volume method are employed to yield very accurate solutions. Since the full range of results required in the benchmark is too large to be displayed in this paper, we focus on the evolution of the pressures, the saturations, the fluxes and the comparison of the numerical results with the other participants. A homemade C++ upscaling code and the parallel multiphase flow simulator DuMuX have been adopted for this study.
Transport in Porous Media, 2011
In low/intermediate-level waste (L/ILW) repositories, anaerobic corrosion of metals and degradation of organic materials produce mainly hydrogen, methane, and carbon dioxide. The Swiss reference concept for the L/ILW repository consists of parallel caverns sealed off from a single access tunnel in a deep low-permeability claystone formation. The potential buildup of excess gas pressures in the backfilled emplacement caverns was investigated in a series of two-phase flow models. In the first step, a large-scale model was constructed, implementing the 3D radial tunnel and cavern geometry with a simplified rectangular geometry. In the second step, the potential impact of the detailed geometry of the engineered barrier system (EBS) and the associated heterogeneity inside the cavern was examined using detailed models of the repository caverns, tunnel seals, access tunnel, and surrounding host rock. The simulation results from the large-scale 3D repository model show that during the early post-closure period simulated pressures can vary significantly between different parts of the repository. The simulated pressure increase in the emplacement caverns
Computational Geosciences, 2009
We derive a compositional compressible two-phase, liquid and gas, flow model for numerical simulations of hydrogen migration in deep geological repository for radioactive waste. This model includes capillary effects and the gas high diffusivity. Moreover, it is written in variables (total hydrogen mass density and liquid pressure) chosen in order to be consistent with gas appearance or disappearance. We discuss the well possedness of this model and give some computational evidences of its adequacy to simulate gas generation in a water-saturated repository.
1990
Preface This report is one of a series documenting the results of the Nagra-DOE Cooperative (NDC-I) research program in which the cooperating scientists explore the geological, geophysical, hydrological, geochemical, and structural effects anticipated from the use of a rock mass as a geologic repository for nuclear waste. This program was sponsored by the U. S. Department of Energy (DOE) through the Lawrence Berkeley Laboratory (LBL) and the Swiss Nationale Genossenschaft flir die Lagerung radioaktiver AbflUla (Nagra) and concluded in September 1989. The principal investigators are
2003
Radioactive wastes conditioned for final disposal in repositories in deep, low permeability formations will produce a significant amount of gas due to corrosion and microbiological degradation processes. This paper addresses the process of gas release from disposal tunnels for spent fuel (SF) and long-lived intermediate level wastes (ILW) in a clay-shale formation. For the SF the impact of additional heat transfer is considered. The issues under consideration are the interference of the repository resaturation process by the build-up of gas pressures in the disposal tunnels and the impact of waste-generated thermal loads on fluid and gas flow. Numerical simulations were conducted, representing the backfilled disposal tunnels (SF and ILW, respectively) and the surrounding host rock formation by a two-dimensional cross-section. The simulations were carried out with the TOUGH2 EOS5 module. The paper gives results of a sensitivity study, aimed at investigating the impact of repository-i...
Computational Geosciences, 2012
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Gas transport across the low-permeability containment zone of an underground nuclear explosion
Scientific Reports, 2020
Understanding the nature of gas transport from an underground nuclear explosion (Une) is required for evaluating the ability to detect and interpret either on-site or atmospheric signatures of noble gas radionuclides resulting from the event. We performed a pressure and chemical tracer monitoring experiment at the site of an underground nuclear test that occurred in a tunnel in nevada to evaluate the possible modes of gas transport to the surface. the site represents a very well-contained, low gaspermeability end member for past Unes at the nevada national Security Site. However, there is very strong evidence that gases detected at the surface during a period of low atmospheric pressure resulted from fractures of extremely small aperture that are essentially invisible. our analyses also suggest that gases would have easily migrated to the top of the high-permeability collapse zone following the detonation minimizing the final distance required for migration along these narrow fractures to the surface. this indicates that on-site detection of gases emanating from such low-permeability sites is feasible while standoff detection of atmospheric plumes may also be possible at local distances for sufficiently high fracture densities. Finally, our results show that gas leakage into the atmosphere also occurred directly from the tunnel portal and should be monitored in future tunnel gas sampling experiments for the purpose of better understanding relative contributions to detection of radioxenon releases via both fracture network and tunnel transport.