Modelling and experimental study of sizes and shell thickness of polyurea microcapsules on UV absorption of octyl salicylate

International audienc

Tritium trapping by metal oxides in radioactive wastes

International audienceITER (International Tokamak Experimental Reactor) is a fusion machine which should demonstrate scientific and technological feasibility of fusion energy by means of D-T fusion reaction. Therefore, most of the solid radioactive waste produced during operation and dismantling phase (around 34 000 tons) will result not only from activation by 14 MeV neutrons, but also from contamination by tritium. One of the main issues in tritiated waste management is the confinement of tritium which presents a good ability to diffusion. One of the solutions is to trap the tritium directly in waste drums. In containers tritium is under gaseous form (HT and T$_2$), tritiated water vapor (HTO and T$_2$O) and organic bounded tritium species (OBT). As a hydrogen isotope, HT and T2 conversion is possible thanks to a reaction with a mix of metal oxides MnO$_2$ and Ag$_2$O, which can be used for hydrogen hazards mitigation. Associated to a molecular sieve, trapping of tritiated hydrogen and water is workable. This paper will describe a methodology to develop a trapper. An experimental study will enable to test different formulation of oxidation powders (with or without catalyser Pt, Pd, Cu, salts). It will enable to obtain the most efficient mix of powder to convert tritiated hydrogen in tritiated water. After determined reaction kinetics with the best trapper, tests will be focused on tritiated water adsorption phenomenon. Then, a modelling part will aim to analyse the influence of trapper on diffusion of tritiated hydrogen outside radioactive waste drum, with obtaining firstly tritium release rate without trapper and secondly this rate for tritiated waste drum with trapper inside

Simulation of Micromixing in a T-mixer under Laminar Flow Conditions

International audienceThe CFD simulation of fast reactions in laminar flows can be computationally challenging due to the lack of appropriate sub-grid micromixing models in this flow regime. In this work, simulations of micromixing via the implementation of the competitive-parallel Villermaux/Dushman reactions in a T-micromixer with square bends for Reynolds numbers in the range 60–300 are performed using both a conventional CFD approach and a novel lamellae-based model. In the first, both the hydrodynamics and the concentration fields of the reaction species are determined directly using a finite volume approach. In the second, the hydrodynamic field from the CFD calculations is coupled with a Lagrangian model that is used to perform the chemical reactions indirectly. Both sets of results are compared with previously published experimental data and show very good agreement. The lamellar model has the advantage of being much less computationally intensive than the conventional CFD approach, which requires extremely fine computational grids to resolve sharp concentration gradients. It is a promising solution to model fast chemical reactions in reactors with complex geometries in the laminar regime and for industrial applications

Comparative study of semi-solid liposome purification by different separation methods

International audienc

Modelling of heat transfer and hydrodynamic with two kinetics approaches during supercritical water oxidation process

International audienceSupercritical water oxidation is an innovative and very efficient process to treat hazardous organic waste. In order to better understand the complex physic phenomena involved in this process, and to design more efficient reactors or to insure future efficient scale-up, a simulation with the Computational Fluid Dynamics software FLUENT was carried out for a simple tubular reactor. The turbulent non-reactive flow is well-represented using the $\kappa-\epsilon$ model. Nevertheless, the $\kappa-\epsilon$ model gives better results when a source term is added to take into account the chemical reaction. Two approaches are used to model the reaction rate: an Arrhenius law and the Eddy Dissipation Concept (EDC) generally used to describe combustion reactions. The results of this simulation using Arrhenius law, are in good agreement with experimental data although a simple thermohydraulic model was used. Moreover, the sensitiveness to the inlet temperature has been demonstrated. It influences the reaction start-up and the shape of the measured wall temperature peak. Equally, the simulated temperature profiles using Eddy Dissipation Concept model are in good agreement with experimental ones. Hence, the two approaches give similar results. Nevertheless, the EDC model predicts more precisely the thermal peak location at the reactor wall