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Développement d’un procédé super-absorbant pour la décontamination nucléaire en profondeur de matériaux poreux

Abstract : Within the framework of decommissioning of nuclear facilities, various decontamination operations are required. One of the main issues is the decontamination of cementitious materials due to the incorporation of contaminants into their porous structures. Throughout this project, we study the possibility of using a process for decontaminating cementitious materials based on the "poultice" method, which is mainly used nowadays for desalination of buildings. Such a technical adaptation first requires a meticulous study of physical mechanisms that control the different phases of the process. For that aim, we use model systems, composed of poultices (based on kaolin or cellulose fibers) applied to the surface of a model substrate (glass beads packing) in order to understand the whole process, and in particular the water transfers involved. Magnetic Resonance Imaging techniques are therefore used to monitor water distribution within these systems, and provide complete original information. Our approach consists in breaking down our study into three axes. First, we study substrate imbibition from a wet poultice. We show that liquid can invade the substrate even if it has a larger pore size than the poultice. The imbibition process stops when the capillary pressure in the substrate balances the stress needed to further contract the poultice. This in particular means that the liquid penetration in a porous medium from a poultice may be controlled by adjusting the poultice characteristics. Then, we provide the detailed drying mechanisms of initially saturated systems depending on their pore size distribution. We show that poultice can extract a large part (~ 85 %) of substrate liquid thanks to capillary equilibration processes that allow both media to desaturate homogeneously and simultaneously up to the very last stages of drying. Finally, decontamination efficiency of substrates initially contaminated by inactive cesium is evaluated. We show that salt crystals (cesium nitrate) growing during the system poultice/substrate drying can, in some configurations, limit contaminants transport from the substrate to the poultice and thus reduce the decontamination efficiency.
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Submitted on : Friday, August 14, 2020 - 9:56:28 AM
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Mohamed Nidal Ben Abdelouahab. Développement d’un procédé super-absorbant pour la décontamination nucléaire en profondeur de matériaux poreux. Mécanique des fluides [physics.class-ph]. Université Paris-Est, 2019. Français. ⟨NNT : 2019PESC1026⟩. ⟨tel-02915305⟩

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