Numerical simulations in the development of the French radioactive waste vitrification processes using induction furnace

International audienceFor many years, the CEA (Commissariat à l’Énergie Atomique et aux Énergies Alternatives) Marcoule France has developed various processes dedicated to radioactive waste confinement, especially vitrification processes for HLLW. For 15 years now, the numerical simulation has become an important tool for research and developement projects held in the CEA-AREVA Joint Vitrification Laboratory (LCV). Induction heating, fluid mechanics and thermal simulations take part of all new R&D projects. The apports of such simulations are, first, the enhancement of the working knowledge of existing process. Those data are very useful to define optimisation choices, for example upgrades made on the hot metallic melter used since the 90s at LaHague facility. Second, the simulations are, of course, also used at the conception stage of new processes as a tool allowing wide ranges parametric tests. This has been extensively used in the design of the cold crucible inductive melter (CCIM) commissioned in 2010 at La Hague plant. Finally, it is a powerful and relatively cheap tool for prospective studies for processes of the future. Whatever the purpose, the potential benefits are gains on the reliability, the output capacity and the life time

2D and 3D reconstructions in acousto-electric tomography

We propose and test stable algorithms for the reconstruction of the internal conductivity of a biological object using acousto-electric measurements. Namely, the conventional impedance tomography scheme is supplemented by scanning the object with acoustic waves that slightly perturb the conductivity and cause the change in the electric potential measured on the boundary of the object. These perturbations of the potential are then used as the data for the reconstruction of the conductivity. The present method does not rely on "perfectly focused" acoustic beams. Instead, more realistic propagating spherical fronts are utilized, and then the measurements that would correspond to perfect focusing are synthesized. In other words, we use \emph{synthetic focusing}. Numerical experiments with simulated data show that our techniques produce high quality images, both in 2D and 3D, and that they remain accurate in the presence of high-level noise in the data. Local uniqueness and stability for the problem also hold

Gas bubbling modeling in vitrification processes

International audienceA direct induction process using the cold crucible technology has been developed by the French Alternative Energies and Atomic Energy Commission and AREVA-NC for 25 years. In this process, walls of the crucible are cooled by internal water circulation which protects them from the corrosion and allow higher temperature of the molten glass. Moreover, a mechanical stirrer and air bubbling system promote a good homogeneity of the melt. In results, the lifetime of the crucible as the incorporation rate of the nuclear waste is increased.The 3D numerical simulation of glass elaboration by induction in cold crucible needs a coupled approach of the different phenomena induction, thermal and hydrodynamic. Indeed, those three phenomena are strongly coupled because of the temperature dependence of the glass properties.This presentation describes how the air bubbling in the glass is modelled in our simulation and enlightens its important role in the homogenisation of the glass during its elaboration. Air bubbling in liquids as viscous as the glass (viscosity up to 10 Pa.s) is not common and specific models have to be built. Two different models are used. The first one is a semi-empirical based model and the second is a two phase model (VOF). In order to model air bubbling in the molten glass, specific experiments have been performed based on the principle of hydraulic similarity. They consist in replacing the glass by silicon oil of equivalent viscosity in a tank of the same size. Non-dimensional Reynolds number as Galilee numbers are well respected between the two configurations. Only the Morton number differs, but it reflects tension surface effect which has been proven to have a weak effect on the formation of air bubbles in a very viscous liquid. This experiment facility allows us to acquire data as bubbles size, bubbles velocity and their behaviour. These data are used to build specific correlations for the semi-empirical model and also to validate the two phase model.The importance of air bubbling is quantified in simulations of the cold crucible process in a case with thermal convection forces only compared with a case with the air bubbling.Thanks to this numerical simulation new capability, the internal design of the crucible can be optimized and the comprehension of glass elaboration can be improved

Analysis of a one-dimensional variational model of the equilibrium shapel of a deformable crystal

The equilibrium configurations of a one-dimensional variational model that combines terms expressing the bulk energy of a deformable crystal and its surface energy are studied. After elimination of the displacement, the problem reduces to the minimization of a nonconvex and nonlocal functional of a single function, the thickness. Depending on a parameter which strengthens one of the terms comprising the energy at the expense of the other, it is shown that this functional may have a stable absolute minimum or only a minimizing sequence in which the term corresponding to the bulk energy is forced to zero by the production of a crack in the material

3D Magneto-thermal modeling of cold crucible inductive melters

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Couplage magneto-thermo-hydraulique 3D d'un creuset froid

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