Modélisation du transfert des aérosols dans un local ventilé

La protection des opérateurs et la surveillance des ambiances de travail en cas de mise en suspension d’aérosols radioactifs, dans un local ventilé d’une installation nucléaire, requièrent la connaissance de l’évolution spatio-temporelle de la concentration en particules, en tout point du local considéré. L’estimation précise de cette concentration a fait l’objet du développement de modèles spécifiques de transport et de dépôt d’aérosols dans un local ventilé, dans le cadre d’une thèse cofinancée par l’IRSN et EDF, en collaboration avec l’IMFT. Un formalisme eulérien de glissement est utilisé pour modéliser le transport des aérosols. Celui-ci est basé sur une unique équation de transport des concentrations en particules (« Diffusion-Inertia model »). L’étude spécifique du dépôt d’aérosols en parois a permis de développer un modèle de couche limite, qui consiste à déterminer précisément le flux de dépôt de particules en parois, quels que soient le régime de dépôt et l’orientation de la surface considérée. Les modèles de transport et de dépôt finalement retenus ont été implantés dans Code_Saturne, un logiciel de mécanique des fluides. La validation de ces modèles a été effectuée à partir de données de la littérature en géométries simples, puis sur la base de campagnes expérimentales de traçage dans des locaux ventilés d’environ 30 m\ub3 et 1500 m\ub3. ABSTRACT : When particulate radioactive contamination is likely to become airborne in a ventilated room, assessment of aerosol concentration in every point of this room is important, in order to ensure protection of operators and supervision of workspaces. Thus, a model of aerosol transport and deposition has been developed as part of a project started with IRSN, EDF and IMFT. A simplified eulerian model, called “diffusion-inertia model” is used for particle transport. It contains a single transport equation of aerosol concentration. The specific study of deposition on walls has permitted to develop a boundary condition approach, which determines precisely the particle flux towards the wall in the boundary layer, for any deposition regime and surface orientation.The final transport and deposition models retained have been implemented in a CFD code called Code_Saturne. These models have been validated according to literature data in simple geometries and tracing experiments in ventilated rooms, which have been carried out in 30 m\ub3 and 1500 m\ub3 laboratory rooms

Modelling aerosol transfer in a ventilated room

La protection des opérateurs et la surveillance des ambiances de travail en cas de mise en suspension d’aérosols radioactifs, dans un local ventilé d’une installation nucléaire, requièrent la connaissance de l’évolution spatio-temporelle de la concentration en particules, en tout point du local considéré. L’estimation précise de cette concentration a fait l’objet du développement de modèles spécifiques de transport et de dépôt d’aérosols dans un local ventilé, dans le cadre d’une thèse cofinancée par l’IRSN et EDF, en collaboration avec l’IMFT. Un formalisme eulérien de glissement est utilisé pour modéliser le transport des aérosols. Celui-ci est basé sur une unique équation de transport des concentrations en particules (« Diffusion-Inertia model »). L’étude spécifique du dépôt d’aérosols en parois a permis de développer un modèle de couche limite, qui consiste à déterminer précisément le flux de dépôt de particules en parois, quels que soient le régime de dépôt et l’orientation de la surface considérée. Les modèles de transport et de dépôt finalement retenus ont été implantés dans Code_Saturne, un logiciel de mécanique des fluides. La validation de ces modèles a été effectuée à partir de données de la littérature en géométries simples, puis sur la base de campagnes expérimentales de traçage dans des locaux ventilés d’environ 30 m³ et 1500 m³.When particulate radioactive contamination is likely to become airborne in a ventilated room, assessment of aerosol concentration in every point of this room is important, in order to ensure protection of operators and supervision of workspaces. Thus, a model of aerosol transport and deposition has been developed as part of a project started with IRSN, EDF and IMFT. A simplified eulerian model, called “diffusion-inertia model” is used for particle transport. It contains a single transport equation of aerosol concentration. The specific study of deposition on walls has permitted to develop a boundary condition approach, which determines precisely the particle flux towards the wall in the boundary layer, for any deposition regime and surface orientation.The final transport and deposition models retained have been implemented in a CFD code called Code_Saturne. These models have been validated according to literature data in simple geometries and tracing experiments in ventilated rooms, which have been carried out in 30 m³ and 1500 m³ laboratory rooms

Modélisation du transfert des aérosols dans un local ventilé

La protection des opérateurs et la surveillance des ambiances de travail en cas de mise en suspension d aérosols radioactifs, dans un local ventilé d une installation nucléaire, requièrent la connaissance de l évolution spatio-temporelle de la concentration en particules, en tout point du local considéré. L estimation précise de cette concentration a fait l objet du développement de modèles spécifiques de transport et de dépôt d aérosols dans un local ventilé, dans le cadre d une thèse cofinancée par l IRSN et EDF, en collaboration avec l IMFT. Un formalisme eulérien de glissement est utilisé pour modéliser le transport des aérosols. Celui-ci est basé sur une unique équation de transport des concentrations en particules ( Diffusion-Inertia model ). L étude spécifique du dépôt d aérosols en parois a permis de développer un modèle de couche limite, qui consiste à déterminer précisément le flux de dépôt de particules en parois, quels que soient le régime de dépôt et l orientation de la surface considérée. Les modèles de transport et de dépôt finalement retenus ont été implantés dans Code_Saturne, un logiciel de mécanique des fluides. La validation de ces modèles a été effectuée à partir de données de la littérature en géométries simples, puis sur la base de campagnes expérimentales de traçage dans des locaux ventilés d environ 30 m³ et 1500 m³.When particulate radioactive contamination is likely to become airborne in a ventilated room, assessment of aerosol concentration in every point of this room is important, in order to ensure protection of operators and supervision of workspaces. Thus, a model of aerosol transport and deposition has been developed as part of a project started with IRSN, EDF and IMFT. A simplified eulerian model, called diffusion-inertia model is used for particle transport. It contains a single transport equation of aerosol concentration. The specific study of deposition on walls has permitted to develop a boundary condition approach, which determines precisely the particle flux towards the wall in the boundary layer, for any deposition regime and surface orientation.The final transport and deposition models retained have been implemented in a CFD code called Code_Saturne. These models have been validated according to literature data in simple geometries and tracing experiments in ventilated rooms, which have been carried out in 30 m³ and 1500 m³ laboratory rooms.TOULOUSE-INP (315552154) / SudocSudocFranceF

Etude expérimentale de la faisabilité de piégeage des gaz rares (Xe, Kr) par des matériaux poreux innovants de type Metal-Organic Framework (MOF)

International audienc

Etude expérimentale de la faisabilité de piégeage des gaz rares (Xe, Kr) par des matériaux poreux innovants de type Metal-Organic Framework (MOF)

International audienc

Volatilization and trapping of ruthenium under a loss of cooling accident on high level liquid waste (HLLW) storage tanks in reprocessing plants

International audienceThe reprocessing of spent nuclear fuel produces high level liquid waste (HLLW). Due to the decay heat, these concentrated nitric solutions containing fission products are stored in cooled tanks to prevent the solution from boiling, evaporating and drying out. In case of a total loss of cooling, potential large releases of radioactive materials into the environment, especially volatile species derived from ruthenium, can happen. The loss-of-cooling accident on HLLW storage tanks is one of the accident scenarios identified as a very dreaded situation. Besides, an extensive literature review performed at IRSN confirms the lack of reliable data on the behaviour of ruthenium in nitric acid solutions and concerning mechanism of releases. It highlights that research works on this topic can be classified in several categories: ruthenium chemistry in a nitric medium characterized by the formation of nitrosyl ruthenium ion RuNO3+; behaviour of volatile forms of ruthenium in presence of steam, nitric acid vapour and nitrogen oxides (recombination, decomposition, etc.); transfer phenomena and stability of the different gaseous species containing ruthenium through the ventilation network. Subsequently, the efficiency and the performance of various trapping systems that can be used for mitigation of ruthenium release (gas/liquid absorbers/traps, steel filters, porous media such as zeolites etc.), or even various means of preventing its volatilization (recombination, addition of reducing agents in situ, etc.) have been investigated by different authors. Previous experimental work performed at IRSN on severe accident scenarios in nuclear facilities allowed to characterize usual filtration devices such as active charcoals or metallic filters, with respect to gaseous RuO4. It showed that these latter do not trap efficiently RuO4(g).From these findings, IRSN started a research program aiming at improving the knowledge on this topic. A specific test bench has been developed in order to study the volatilization of a nitric acid solution containing Ru nitrosyl, simulating a real HLLW in terms of acidity and ruthenium concentration, and to investigate the possible inhibition of Ru volatilization by addition of specific reducing compounds (nitrogen oxides, sucrose, etc). A first series of tests showed that the quantities of released ruthenium obtained for different temperature levels are consistent with the literature, before testing inhibitors. The experimental setup mentioned before dedicated to gaseous RuO4 is also used to study trapping of RuO4(g) by different porous materials: zeolites, rare earth oxides, etc. Decontamination factors (DF) and RuO4(g) retention capacity have been determined for several of these compounds

Trapping of iodine compounds by pool scrubbing: Hydrodynamic aspects

International audienceIn the nuclear industry, pool scrubbing is one of the retention mechanisms capable of reducing the release of fission products during a severe nuclear accident. It relies on a set of physical and chemical processes that are governed by the behavior of bubbles. The efficiency of this filtration process will depend on the different flow conditions and hydrodynamic parameters. Experimental work has been carried out, for which an optical measurement technique has been implemented in order to characterize different parameters related to bubble hydrodynamics such as frequency, shape, bubble volume and void fraction. Two approaches to characterize bubble formation are implemented. A classical approach has been conducted, based on the assumptions usually considered in the main models of the literature, namely a unique regime of bubbles and a spherical shape. The comparison of the bubble characteristics (volume and diameter), which are obtained after determining the frequency of bubble detachment shows good agreement with these models. However, the comparison with the observed bubble morphology (coalescence, non-sphericity) shows the limits of these assumptions. This led us to introduce, via a more phenomenological approach, the concept of globule, i.e. a structure of larger volume, generated after coalescence of several bubbles in the injection zone. This approach appears more relevant for further studies. These volumes are generally higher than those predicted by the usual approaches, highlighting the limits of existing models for high Weber numbers. This phenomenological approach is confirmed by comparing the flow rate calculated experimentally (thanks to the determined volumes and frequencies of the globules formed) with the actual flow rate injected. In the long term, this will make it possible to improve the modelling of such phenomena, in particular in the ASTEC calculation code developed by the IRSN to simulate a serious nuclear accident and its consequences

Etude de matériaux poreux de type Metal-Organic Framework (MOF) pour le piégeage du tetroxid de ruthénium (RuO4)

National audienc

Trapping of iodine compounds by pool scrubbing: Hydrodynamic aspects

International audienceIn the nuclear industry, pool scrubbing is one of the retention mechanisms capable of reducing the release of fission products during a severe nuclear accident. It relies on a set of physical and chemical processes that are governed by the behavior of bubbles. The efficiency of this filtration process will depend on the different flow conditions and hydrodynamic parameters. Experimental work has been carried out, for which an optical measurement technique has been implemented in order to characterize different parameters related to bubble hydrodynamics such as frequency, shape, bubble volume and void fraction. Two approaches to characterize bubble formation are implemented. A classical approach has been conducted, based on the assumptions usually considered in the main models of the literature, namely a unique regime of bubbles and a spherical shape. The comparison of the bubble characteristics (volume and diameter), which are obtained after determining the frequency of bubble detachment shows good agreement with these models. However, the comparison with the observed bubble morphology (coalescence, non-sphericity) shows the limits of these assumptions. This led us to introduce, via a more phenomenological approach, the concept of globule, i.e. a structure of larger volume, generated after coalescence of several bubbles in the injection zone. This approach appears more relevant for further studies. These volumes are generally higher than those predicted by the usual approaches, highlighting the limits of existing models for high Weber numbers. This phenomenological approach is confirmed by comparing the flow rate calculated experimentally (thanks to the determined volumes and frequencies of the globules formed) with the actual flow rate injected. In the long term, this will make it possible to improve the modelling of such phenomena, in particular in the ASTEC calculation code developed by the IRSN to simulate a serious nuclear accident and its consequences

Bubbles dynamics under pool scrubbing conditions for iodine compounds trapping applications

International audienceAccident management systems are highly regarded in the designing of nuclear power plants, in order to mitigate as much as possible the radiological consequences of accidents. Wet FCVS is one of these systems that aims to trap fission products in liquid bath by pool scrubbing as well as suppression pool in BWR. Relying on set of bubble dynamics and retention mechanisms, it is essential to characterize the relevant hydrodynamics in pool scrubbing conditions, for the development and assessment of models. Injecting air induces bubble-bubble interactions which provoke, depending on the flow rate, random formation of bubbles affecting their size, shape, and frequency of bubbling. Experimental work is carried out to reveal the impact of these interactions on the formation of bubbles at a submerged orifice. Based on the different bubble's morphologies that have been observed, we first investigated the bubble-bubble interactions and then classified different bubbling regimes depending on the position of bubbles' coalescence. The biggest bubble formed above the orifice, after the coalescence of bubbles, is referred by a globule. On the basis of the morphological description of bubbles throughout our experiments, two approaches in characterizing the bubbles sizes were developed. The first conventional approach is based on the assumption of single bubbling formation and spherical shape of bubbles. Upon this approach, the comparison of characteristic bubble size Vb, which is computed after determining the bubble departure frequency fb, shows a good agreement with literature models. However, this approach is not consistent with flow morphology experimentally observed. Therefore, and through a proposed phenomenological approach, we aimed to characterize experimentally the globule formation frequency fa and its volume Va, by tracking the globules formation through image processing and reconstructing bubble shape with axisymmetric assumption. Experimental work characterizing bubble dynamics in the injection zone for different flow conditions (orifice diameter, injection flowrate, and submergence) is presented. In parallel, decontamination factors (DF) for iodine compounds are experimentally determined, in order to be able in the long term to correlate iodine trapping with hydrodynamics considerations