The Experts below are selected from a list of 3009 Experts worldwide ranked by ideXlab platform
Frederic Skoczylas - One of the best experts on this subject based on the ideXlab platform.
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research on gas migration properties in a saturated bentonite sand mixture under flexible boundary conditions
Soils and Foundations, 2018Co-Authors: Shuaibing Song, Hongyang Ni, Hai Pu, Frederic SkoczylasAbstract:Abstract Gas migration/breakthrough in saturated bentonite is an important issue for the evolution of the sealing ability of the engineered barrier in deep Geological Repositories. The main contribution of our study is to provide insights into the water and gas transport properties in a compacted bentonite/sand mixture, which was wrapped by a flexible Viton™ membrane directly before being put into a triaxial cell. The experimental results indicate that the water permeability is very low and the magnitude is in the order of 10−20 m2. Gas breakthrough tests show that no continuous gas flow was detected during the entire gas breakthrough test (until the gas pressure of 10 MPa), which indicates that the compacted bentonite/sand mixture has a good sealing ability after full saturation. Another important finding is that the gas migration properties are closely related to the stress state around the sample, the internal pore fluid pressure, and the creep effects caused by the two factors.
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gas permeability of a compacted bentonite sand mixture coupled effects of water content dry density and confining pressure
Canadian Geotechnical Journal, 2015Co-Authors: Frederic Skoczylas, Jiangfeng Liu, Jean TalandierAbstract:The gas-tightness of compacted bentonite–sand mixtures is important to the total sealing efficiency of Geological Repositories. The initial aim of this work was to determine whether the combination of a high confining pressure (Pc) and incomplete saturation could cause a bentonite–sand mixture to become gas-tight. The results show that the physical characteristics of the materials (degree of saturation, Sr; porosity, ϕ; and dry density, ρd) are very sensitive to changes in the applied confining pressures and their own swelling deformation (or shrinkage). The combination of these changes affects the sample’s effective gas permeability (Keff). For materials prepared at a relative humidity (RH) of 98%, Keff decreased from 10−16 to 10−20 m2 when Pc increased from 1 to 7 MPa. This means that gas-tightness can be obtained for a compacted bentonite–sand mixture when the materials experience a series of changes (e.g., w, Sr, ϕ, and ρd). In addition, larger irreversible deformation (or hysteresis) was observed dur...
Davide Costa - One of the best experts on this subject based on the ideXlab platform.
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fundamentals of the nea thermochemical database and its influence over national nuclear programs on the performance assessment of deep Geological Repositories
Journal of Environmental Radioactivity, 2019Co-Authors: Mariaeleni Ragoussi, Davide CostaAbstract:For the last 30 years, the NEA Thermochemical Database (TDB) Project (www.oecd-nea.org/dbtdb/) has been developing a chemical thermodynamic database for elements relevant to the safety of radioactive waste Repositories, providing data that are vital to support the geochemical modeling of such systems. The recommended data are selected on the basis of strict review procedures and are characterized by their consistency. The results of these efforts are freely available, and have become an international point of reference in the field. As a result, a number of important national initiatives with regard to waste management programs have used the NEA TDB as their basis, both in terms of recommended data and guidelines. In this article we describe the fundamentals and achievements of the project together with the characteristics of some databases developed in national nuclear waste disposal programs that have been influenced by the NEA TDB. We also give some insights on how this work could be seen as an approach to be used in broader areas of environmental interest.
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selection of reference thermodynamic data for modelling of deep Geological Repositories present and future of the nea thermochemical database project
Journal of Solution Chemistry, 2017Co-Authors: Davide Costa, Mariaeleni RagoussiAbstract:The OECD Nuclear Energy Agency (NEA) works as a forum for sharing and analyzing information and experience among member countries, fostering international co-operation in the nuclear field, helping member countries to pool and maintain their technical expertise and human infrastructure, and supporting nuclear activities by providing member countries with nuclear policy analyses as stated in its Strategic Plan 2011–2016. Under this umbrella, the Thermochemical Database project emerged with the aim of defining an internationally recognized set of recommended thermochemical data to support the geochemical modelling of high-level radioactive waste disposal. Such data are selected on the basis of a well-defined review procedure which is coordinated by the NEA and are freely available. These efforts have resulted in the publication of thirteen major reviews containing selected values for around 1500 species, out of which more than 700 aqueous species, 650 solids and 150 gases. Additionally, six publications are currently under preparation. The key aspects of the Project, its accomplishments and future actions are outlined herein.
Trevor Taborowski - One of the best experts on this subject based on the ideXlab platform.
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mobility and reactivity of sulphide in bentonite clays implications for engineered bentonite barriers in Geological Repositories for radioactive wastes
Applied Clay Science, 2017Co-Authors: Karsten Pedersen, Andreas Bengtsson, Anders Blom, Linda Johansson, Trevor TaborowskiAbstract:Abstract Bentonite clays will be used as barriers in Geological Repositories for radioactive wastes. Anoxic conditions will prevail in such Repositories, and the presence of sulphide-producing bacteria in commercial bentonites and deep groundwater environments is well established. In this study, sulphide was found to reduce ferric iron in bentonites denoted Asha, MX-80 and Calcigel under the formation of elemental sulphur, ferrous iron and iron sulphide. These reactions rendered an immobilisation capacity of the clays that was 40 μmole sulphide (g clay) − 1 or more, depending on the load of sulphide, and type of clay. In addition, the effective diffusion coefficients for sulphide in Asha bentonite, compacted to saturated wet densities of 1750 kg m − 3 and 2000 kg m − 3 , were determined to 2.74 × 10 − 11 m 2 s − 1 and 6.60 × 10 − 12 m 2 s − 1 , respectively. The found immobilisation effect can reduce the mass of sulphide that corrode metal canisters over repository life times, but the concomitant reduction of ferric iron may be problematic due to the destabilizing effect of ferrous iron on dioctahedral smectites such as montmorillonites.
Mariaeleni Ragoussi - One of the best experts on this subject based on the ideXlab platform.
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fundamentals of the nea thermochemical database and its influence over national nuclear programs on the performance assessment of deep Geological Repositories
Journal of Environmental Radioactivity, 2019Co-Authors: Mariaeleni Ragoussi, Davide CostaAbstract:For the last 30 years, the NEA Thermochemical Database (TDB) Project (www.oecd-nea.org/dbtdb/) has been developing a chemical thermodynamic database for elements relevant to the safety of radioactive waste Repositories, providing data that are vital to support the geochemical modeling of such systems. The recommended data are selected on the basis of strict review procedures and are characterized by their consistency. The results of these efforts are freely available, and have become an international point of reference in the field. As a result, a number of important national initiatives with regard to waste management programs have used the NEA TDB as their basis, both in terms of recommended data and guidelines. In this article we describe the fundamentals and achievements of the project together with the characteristics of some databases developed in national nuclear waste disposal programs that have been influenced by the NEA TDB. We also give some insights on how this work could be seen as an approach to be used in broader areas of environmental interest.
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selection of reference thermodynamic data for modelling of deep Geological Repositories present and future of the nea thermochemical database project
Journal of Solution Chemistry, 2017Co-Authors: Davide Costa, Mariaeleni RagoussiAbstract:The OECD Nuclear Energy Agency (NEA) works as a forum for sharing and analyzing information and experience among member countries, fostering international co-operation in the nuclear field, helping member countries to pool and maintain their technical expertise and human infrastructure, and supporting nuclear activities by providing member countries with nuclear policy analyses as stated in its Strategic Plan 2011–2016. Under this umbrella, the Thermochemical Database project emerged with the aim of defining an internationally recognized set of recommended thermochemical data to support the geochemical modelling of high-level radioactive waste disposal. Such data are selected on the basis of a well-defined review procedure which is coordinated by the NEA and are freely available. These efforts have resulted in the publication of thirteen major reviews containing selected values for around 1500 species, out of which more than 700 aqueous species, 650 solids and 150 gases. Additionally, six publications are currently under preparation. The key aspects of the Project, its accomplishments and future actions are outlined herein.
Cinzia Miracapillo - One of the best experts on this subject based on the ideXlab platform.
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radionuclides migration in the far field of Geological Repositories a numerical example
Energy Procedia, 2014Co-Authors: Luisa Ferroni, Cinzia MiracapilloAbstract:Abstract Radioactive wastes can be classified according to their activities and their half-life period: high activity and/or long half-life may cause severe hazards to people and environment for thousands and thousands of years. For Repositories of such dangerous wastes classified as Category III by Italian law and as High Level Waste (HLW) by IAEA - the Geological repository technology is the preferred technology. As one can imagine, most of the volume of these wastes are spent nuclear fuel and products of nuclear reprocessing plants. To permanently isolate HLW from the biosphere, the segregation of wastes in Geological Repositories, several hundred meters below the surface, is now under way in many countries where large, compact and impermeable Geological formations, not exposed to the seismic risk, exist. Safety conditions associated with these Repositories must be guaranteed also in the case that the secular contact of the waste canisters with the groundwater allows the radionuclides to migrate to the external environment. In the present article the first results of a numerical simulation made using PMWIN (Processing Modflow), one of the most complete groundwater simulation codes, are presented to assess the migration process of radionuclides in the far-field of a Geological repository to study the influence of two important parameters, the distribution coefficient and the hydraulic gradient, on the numerical results.
