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

A Potentiometric Study of the Interaction of Zr(IV) and O(II) Ions in the LiCl-KCl Eutectic Molten Salt

International audienceThe physical and chemical properties of zirconium chlorides have been studied in fused LiCl-KCl eutectic at 823 K using anelectrochemical cell containing two platinum-oxygen electrodes with a solid electrolyte membrane. The first is used as pO22indicator electrode and the second as an oxygen pump which allows us to vary the pO22 of the ionic melt by electrolysis. Titrationof Zr~IV! chlorocomplex by O22 ions demonstrated the precipitation of ZrOCl2 and ZrO2 . The solubility constants of thesecompounds were calculated. A Pourbaix type diagram, which summarizes the properties of zirconium species in the melt, wasdetermined

Aspects of fabrication of curium-based fuels and targets

International audienc

Determination of the activity coefficient of Am in liquid Al by electrochemical methods

International audienceThe activity coefficient of americium in liquid aluminium has been determined by electrochemical methods. To the author’s knowledge, this is the first time this value is published in the open literature. For radiation safety reasons only 100 mg of this highly radioactive element were permitted to be manipulated inside the glove-box. Hence an “ad hoc” experimental set-up, which allows working with small amounts of solvent, has been designed. The Am(III) solution has been prepared by direct AmO2 dissolution into CaCl2–NaCl; the conversion into its chloride form has been achieved by carbochlorination (Cl2 + C) at 600 °C. Cyclic voltammetry technique, performed in the obtained CaCl2–NaCl–AmCl3 solution, has allowed a first estimation for the logarithm of the activity coefficient, being equal to -6.7 +/- 1 at 700 °C

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

Electrochemical Behavior of Np in the Molten LiCl–KCl Eutectic

International audienceThis work presents a study on the electrochemical behavior of neptunium, and in particular of the NpIII/Np0 redox system, inthe molten LiCl–KCl eutectic. Neptunium solutions have been prepared by two different methods: from NpO2 dissolution intoLiCl–KCl by carbochlorination Cl2g + Cs at 550°C and from metal Np oxidation from an Al–Cu–Np alloy by CuCl2. Theseneptunium solutions were investigated by cyclic voltammetry. A mixture of NpIII, NpIV species, and NpV soluble oxychloride was obtained from NpO2 dissolution by carbochlorination. In order to remove any oxygenated species from the melt, thissolution was contacted with metal Zr, leading in our experimental conditions to a mixture of stable NpIV and NpIII species.The second method used by Np oxidation from an Al–Cu–Np alloy gave a stable NpIII solution. The study of the reductionreaction NpIII/Np0 has been performed by different electrochemical techniques. Apparent standard potentials of theNpIII/Np0 system at different temperatures were determined by chronopotentiometry at zero current techniqueENpIII/Np0 o = −2.68 vs Cl2g1 atm/Cl−at 450°C. Standard free energy, enthalpy, and entropy of formation, as well as theactivity coefficient of NpIII in LiCl–KCl, were also obtained

Electrodeposition of Uranium and Transuranics Metals (Pu) on Solid Cathode

International audienceThe results from a study of U and Pu metal electrodeposition from molten eutectic LiCl-KCl on a solid inert cathode are presented. This study has been conducted using ;50 g of U-Pu together with rare earths (mostly Nd) and 1.5 kg of salt. The introduction of a three electrode probe with an Ag/AgCl reference electrode has allowed voltammetric measurement during electrolysis and control of the cathode potential versus the reference.Cyclic and square-wave voltammetric measurements proved to be very useful tools for monitoring the electrolysis as well as selecting the cathode versus reference potential to maximize the separation between actinides and rare earths. The voltammetric data also highlighted the occurrence of back reactions between the cathode deposit and oxidizing equivalents formed at the anode that remained in the molten salt electrolyte. Any furtherelectrolysis test needs to be conducted continuously and followed by immediate removal of the cathode to minimize those back reactions