Computing the drainage discharge and assessing the impacts of tunnels drilled in Hard Rocks

International audienceMost Hard Rocks (HR) are or were exposed to deep weathering processes. It turns out that the hydraulic conductivity of HR is mostly inherited from these weathering processes (Lachassagne et al., 2011): (i) within their permeable Stratiform Fissured Layer (SFL) located below the low hydraulic conductivity unconsolidated weathered layer (saprolite). The thickness of both layers often reaches more than 100 m (Dewandel et al., 2006), (ii) and within the permeable vertical fissured layer developed at the periphery of or within preexisting geological discontinuities (joints, dykes, veins, lithological discontinuities, etc.) (Dewandel et al., 2011, Roques et al., 2012). From this conceptual model, the drainage discharge and the surface hydrogeological (piezometry in wells) and hydrological (discharge of streams) impacts of shallow highway tunnels drilled in a metamorphic series (metasedimentary and metavolcanic rocks) intruded by granitic bodies have been forecasted. These tunnels belong to the A89 highway recently opened (2012) in France between Balbigny and La Tour de Salvagny (Monts du Lyonnais, 50 km West of Lyon city). They are up to 4 km long, and their depth below ground level ranges between 0 and 300 m. The method is based on

Waste Minimization Study on Pyrochemical Reprocessing Processes

International audienceIdeally a new pyro-process should not generate more waste, and should be at least as safe and cost effective as the hydrometallurgical processes currently implemented at industrial scale. This paper describes the thought process, the methodology and some results obtained by process integration studies to devise potential pyro-processes and to assess their capability of achieving this challenging objective. As example the assessment of a process based on salt/metal reductive extraction, designed for the reprocessing of Generation IV carbide spent fuels, is developed. Salt/metal reductive extraction uses the capability of some metals, aluminum in this case, to selectively reduce actinide fluorides previously dissolved in a fluoride salt bath. The reduced actinides enter the metal phase from which they are subsequently recovered; the fission products remain in the salt phase. In fact, the process is not so simple, as it requires upstream and downstream subsidiary steps. All these process steps generate secondary waste flows representing sources of actinide leakage and/or FP discharge. In aqueous processes the main solvent (nitric acid solution) has a low boiling point and evaporate easily or can be removed by distillation, thereby leaving limited flow containing the dissolved substance behind to be incorporated in a confinement matrix. From the point of view of waste generation, one main handicap of molten salt processes, is that the saline phase (fluoride in our case) used as solvent is of same nature than the solutes (radionuclides fluorides) and has a quite high boiling point. So it is not so easy, than it is with aqueous solutions, to separate solvent and solutes in order to confine only radioactive material and limit the final waste flows. Starting from the initial block diagram devised two years ago, the paper shows how process integration studies were able to propose process fittings which lead to a reduction of the waste variety and flows leading at an 'ideal' new block diagram allowing internal solvent recycling, and self eliminating reactants. This new flowsheet minimizes the quantity of inactive inlet flows that would have inevitably to be incorporated in a final waste form. The study identifies all knowledge gaps to be filled and suggest some possible R and D issues to confirm or infirm the feasibility of the proposed process fittings

Waste Minimization Study on Pyrochemical Reprocessing Processes

International audienceIdeally a new pyro-process should not generate more waste, and should be at least as safe and cost effective as the hydrometallurgical processes currently implemented at industrial scale. This paper describes the thought process, the methodology and some results obtained by process integration studies to devise potential pyro-processes and to assess their capability of achieving this challenging objective. As example the assessment of a process based on salt/metal reductive extraction, designed for the reprocessing of Generation IV carbide spent fuels, is developed. Salt/metal reductive extraction uses the capability of some metals, aluminum in this case, to selectively reduce actinide fluorides previously dissolved in a fluoride salt bath. The reduced actinides enter the metal phase from which they are subsequently recovered; the fission products remain in the salt phase. In fact, the process is not so simple, as it requires upstream and downstream subsidiary steps. All these process steps generate secondary waste flows representing sources of actinide leakage and/or FP discharge. In aqueous processes the main solvent (nitric acid solution) has a low boiling point and evaporate easily or can be removed by distillation, thereby leaving limited flow containing the dissolved substance behind to be incorporated in a confinement matrix. From the point of view of waste generation, one main handicap of molten salt processes, is that the saline phase (fluoride in our case) used as solvent is of same nature than the solutes (radionuclides fluorides) and has a quite high boiling point. So it is not so easy, than it is with aqueous solutions, to separate solvent and solutes in order to confine only radioactive material and limit the final waste flows. Starting from the initial block diagram devised two years ago, the paper shows how process integration studies were able to propose process fittings which lead to a reduction of the waste variety and flows leading at an 'ideal' new block diagram allowing internal solvent recycling, and self eliminating reactants. This new flowsheet minimizes the quantity of inactive inlet flows that would have inevitably to be incorporated in a final waste form. The study identifies all knowledge gaps to be filled and suggest some possible R and D issues to confirm or infirm the feasibility of the proposed process fittings

Aspects of fabrication of curium-based fuels and targets

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Status on the development of an electrolytic device based on liquid metallic drops in molten salt media

paper 9376International audienceThis article describes the progress made recently at CEA-Marcoule on the conception of an innovative electrolytic pyroprocess dedicated to the quantitative actinides recovery. The results of this work can be seen as a breakthrough in the electrolytic methods carried out in molten salt media, when the electrodeposition occurs at a dispersed phase cathode consisting of a liquid metal

Cerium and neodymium co-precipitation in molten chloride by wet argon sparging

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Geometry and kinematics of the Boulonnais fold-and-thrust belt (N France) : implications for the dynamics of the Northern Variscan thrust front

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Electrochemical determination of gadolinium and plutonium solvation propertiesin liquid gallium at high temperature.

International audiencePyrochemical separation processes are considered to treat spent nuclear fuel and particularly to separate fission products from actinides. In order to estimate the efficiency and selectivity for various extraction processes based on a molten salt/solvent metal separation technique, we have to know the properties of the elements to be extracted in each solvent, notably their activity coefficients in the two phases. The classical way to measure the activity coefficient of an element in a liquid metal is to use a concentration cell whose the electromotive force is measured. This type of cell involves two electrodes: (a) the element investigated in its pure metallic form and (b) the element solvated in the solvent metal. The electrolyte used for this study is a chloride melt that contains the element under consideration as a solute. In this paper, an effort was made to measure activity coefficients in liquid metals by means of electrochemical techniques rather than a potentiometric technique. The experimental protocol was optimized by measuring the activity coefficient of gadolinium in liquid gallium (solvent metal) $\gamma$(Gd/Ga) at 530°C for several amounts of gadolinium in gallium, and log $\gamma$(Gd/Ga) was determined to be equal to −10.17 (mole fraction scale). Then, the temperature dependence of the activity coefficient was determined in the range of 535 to 630°C. It appears that log $\gamma$(Gd/Ga) varies linearly with the reciprocal value of T, thus following the theoretical variation. The electrochemical method was also performed to determine the activity coefficient of plutonium in liquid gallium at 560°C. The value of log $\gamma$(Pu/Ga) so obtained is equal to −8.04 (mole fraction scale). This value was confirmed using electrochemical and potentiometric measurements with a plutonium-saturated gallium electrode

Promising Pyrochemical Actinides / Lanthanides Separation Processes Using Aluminium

Thermodynamic calculations have shown that aluminum is the most promising metallic solvent or support for the separation of actinides (An) from lanthanides (Ln). In molten fluoride salt, the technique of reductive extraction is under development in which the separation is based on different distributions of An and Ln between the salt and metallic Al phases. In this process molten aluminum alloy acts as both a reductant and a solvent into which the actinides are selectively extracted. It was demonstrated that a one-stage reductive extraction process, using a concentrated solution, allows a recovery of more than 99.3% of Pu and Am. In addition excellent separation factors between Pu and Ln well above 103 were obtained. In molten chloride media similar separations are developed by constant current electrorefining between a metallic alloy fuel (U60Pu20-Zr10 Am2Nd3.5Y0.5Ce0.5Gd0.5) and an Al solid cathode. In a series of demonstration experiments, almost 25 g of metallic fuel was reprocessed and actinides collected as An-Al alloys on the cathode. Analysis of the An-Al deposits confirmed that an excellent An/Ln separation (An/Ln mass ratio_ 2400) had been obtained. These results show that Al is a very promising material to be used in pyrochemical reprocessing of actinides.JRC.E.4-Nuclear fuel