Contribution of IRSN R&D to reducing the risks of airborne pollutants dispersion during the dismantling of nuclear facilities

International audienceThis paper presents a general overview of IRSN research activities for assessing and reducing the risksof airborne dispersion of radioactive contamination during the dismantling operations of nuclearfacilities. Four main topic areas are addressed: aerosol source term, contamination transfers, behaviorof containment equipment and contamination metrology. Firstly, the various experimental and numericalmeans involved are presented

Simulations of filter media performances from microtomography-based computational domain. Experimental and analytical comparison

International audienceIn this work, synchrotron X-ray microtomography was used to produce high spatial resolution images of one fibrous filter, made of binderless monodispersed fiberglass. Based on these images, representative computational domains were created using the import interface of the GeoDict software. Both flow and collection efficiency simulations were then carried out using the CFD modules of GeoDict. In parallel, permeability and collection efficiency measurements were performed on the same media, to provide an experimental comparison. A very good agreement was found between the experimental and simulated permeability values. However, simulated efficiency values tend to underestimate the experimental ones. In the second part of the paper, an image analysis program based on Matlab (R) was used to determine the structural properties of the fibrous structures, namely the thickness, the solid volume fraction and the fiber size distribution. These data were introduced into analytical models that successfully predict the permeability and collection efficiency values

Modelling the pressure drop across HEPA filters during cake filtration in the presence of humidity

International audienceThe modelling of the variation in the pressure drop across a HEPA filter during cake filtration in the presence of humidity was studied. A semi-empirical model was developed that considers the pressure drop across the clogged filter as the sum of the pressure drops across the clean filter and across the cake, which is itself decomposed into several successive layers. The pressure drop across each layer of particles depends on its state of equilibrium with the air humidity. The model includes the specific resistance of each layer of particles and its variation when the cake is exposed to a flow of moist air. This model applies for relative humidity below the deliquescent point of the aerosol if it is hygroscopic. The results show good agreement between the calculated values and experimental values for flat filters clogged with aluminium oxide and sodium chloride test aerosols. The model also revealed the influence of filtration time on the evolution of the pressure drop across a clogged filter in the presence of humidity, especially with a hygroscopic aerosol

Pressure drop model for nanostructured deposits

International audienceThis study presents a new pressure drop model developed for cakes composed of nanostructured particles. The cake structure is understood as a tangle of chains composed by juxtaposed primary particles with (aggregates) or without (agglomerates) a partial overlap. Since cake porosity is one of the main parameters determining aeraulic resistance, an experiment protocol based on the changes in deposit thickness as a function of the cake mass per surface area has been developed to accurately determine this parameter. To this end, the pressure drop and the porosity of the cakes created by the filtration of carbon nanoparticles aggregates and agglomerates on PTFE membrane were measured. The aggregate and agglomerate count median mobility diameters range from 91 nm to 170 nm and from 48 nm to 62 nm, respectively. The associated Peclet numbers range from 0.19 to 53 for filtration velocities of 0.01, 0.05 and 0.09 m/s. Initial experimental results indicate that the porosity of the cakes ranges from 0.94 to 0.984 in correlation with the Peclet number of the aggregates or agglomerates. The agreement between experimental results and the pressure drop model is fairly good. Of the experimental values, 95% are within plus or minus 25% of the theoretical value

Influence de l'humidité sur le colmatage de filtres THE à petits plis par des aérosols hygroscopique et non-hygroscopique

National audienceCette étude a permis d'acquérir une base de données expérimentales sur l'évolution de la perte de charge d'un filtre plissé à Très Haute Efficacité (THE), pendant son colmatage en présence d'humidité par un aérosol micronique non-hygroscopique d'oxyde d'aluminium et un aérosol submicronique hygroscopique de chlorure de sodium. Les résultats obtenus avec l'aérosol non-hygroscopique ont montré que la fermeture des plis est d'autant plus rapide que l'humidité de l'air est grande ; ainsi, pour une même masse d'aérosol déposée, la perte de charge du filtre est plus importante lorsque l'humidité de l'air est proche de la saturation. Avec l'aérosol hygroscopique étudié et pour des taux d'humidité relative en dessous de son point de déliquescence, les résultats montrent qu'en début de colmatage, l'accroissement de la perte de charge du filtre est d'autant plus faible que l'humidité de l'air est grande, comme pour les filtres plans ; puis, lorsque la réduction de la surface de filtration devient importante, il semble que l'accroissement de la perte de charge augmente avec l'humidité. Pour des taux d'humidité relative supérieurs au point de déliquescence de l'aérosol, les résultats indiquent une évolution de la perte de charge caractéristique d'un colmatage avec un aérosol liquide, entraînant la formation d'un film liquide à la surface du medium

Influence of Humidity on Clogging of Flat and Pleated HEPA Filters

International audienceThe influence of humidity on changes to the pressure drop of flat and pleated HEPA filters clogged by polydisperse hygroscopic and non-hygroscopic aerosols has been studied. For flat filters, the results confirm the observations reported by Gupta et al. (1993) that with a hygroscopic aerosol at humidity below the deliquescent point, or with a non-hygroscopic aerosol, the particulate specific cake resistance decreases as relative humidity increases. For pleated filters as for flat filters, the results reveal that during the formation of the particulate cake, the increase in relative humidity leads to a decrease in the specific cake resistance. When the reduction in filtration area, specific to pleated filters, becomes large, the presence of humidity accelerates the filling of pleats causing a greater pressure drop for a same aerosol mass loading. With a hygroscopic aerosol at a humidity above its deliquescent point, the change in pressure drop through flat or pleated filters is not linear but characteristic of liquid aerosol filtration. The influence of humidity on the efficiency of pleated filters, measured by a soda fluorescein aerosol, has also been studied. For clean filters, the efficiency decreases with increasing relative humidity above 90%. For filters clogged with solid aerosol, change in efficiency versus collected surface mass reaches a maximum whose value depends on the relative humidity; when the aerosol is liquid, the efficiency decreases throughout the clogging

An experimental protocol to analyze the structure of nanoparticles deposit in pleats of industrial HEPA filters.

International audienceFire is one of the most probable hazards of internal aggression in a nuclear facility. For many years, IRSN is conducting research programs dealing with the impact of a fire on the behaviour of containment devices of radioactive materials such as High Efficiency Particulate Air (HEPA) filters. It has been already observed, in addition to the well-known regimes of in depth and surface filtration, that for a high deposited mass of nanometrics aerosols (mainly soot particles emitted in case of fire) and low filtration velocity, an additional pressure drop increase occurs for pleated HEPA filters used in the French nuclear industry (Mocho and Ouf 2011). Up to now, little information is available in the literature about this last regime of filtration. The most probable phenomenon is an unbalance in the aerosol repartition along the pleat which causes a reduction of the filtration surface (Del Fabbro et al., 2002). This paper deals with an experimental method to measure the repartition of deposited nanoparticles in the depth of a pleat using embedded samples and electronic microscopy. In this study, HEPA filters were clogged at various controlled filtration velocities on a test bench generating nanoparticles aggregates of Zinc/Aluminium denoting similarities in terms of size and morphology to soot particles emitted in case of fire (Mocho et al., 2011). A pleat of 20 mm in depth of the pleated filter was stabilized in a polymer resin (Schmidt et al., 1990) and deposited mass along the pleat was measured using electronic microscopy. Results show an influence of the filtration velocity on the deposit

An experimental protocol to analyze the structure of nanoparticles deposit in pleats of industrial HEPA filters.

International audienceFire is one of the most probable hazards of internal aggression in a nuclear facility. For many years, IRSN is conducting research programs dealing with the impact of a fire on the behaviour of containment devices of radioactive materials such as High Efficiency Particulate Air (HEPA) filters. It has been already observed, in addition to the well-known regimes of in depth and surface filtration, that for a high deposited mass of nanometrics aerosols (mainly soot particles emitted in case of fire) and low filtration velocity, an additional pressure drop increase occurs for pleated HEPA filters used in the French nuclear industry (Mocho and Ouf 2011). Up to now, little information is available in the literature about this last regime of filtration. The most probable phenomenon is an unbalance in the aerosol repartition along the pleat which causes a reduction of the filtration surface (Del Fabbro et al., 2002). This paper deals with an experimental method to measure the repartition of deposited nanoparticles in the depth of a pleat using embedded samples and electronic microscopy. In this study, HEPA filters were clogged at various controlled filtration velocities on a test bench generating nanoparticles aggregates of Zinc/Aluminium denoting similarities in terms of size and morphology to soot particles emitted in case of fire (Mocho et al., 2011). A pleat of 20 mm in depth of the pleated filter was stabilized in a polymer resin (Schmidt et al., 1990) and deposited mass along the pleat was measured using electronic microscopy. Results show an influence of the filtration velocity on the deposit

Etude du colmatage des filtres THE à petits plis

National audienceLa purification de l'air revêt une grande importance dans de nombreux secteurs tels que les industries nucléaires, pharmaceutiques, agroalimentaires et électroniques. Cette étape de filtration est fréquemment réalisée en utilisant un medium filtrant à base de fibres de verre. Le plissage du medium filtrant, qui augmente la surface de filtration pour un même encombrement de l'équipement, permet d'accroître la capacité de collecte des particules. Les performances du médium filtrant se caractérisent par la probabilité de pénétration des particules (fonction de la taille des particules) et par la perte de charge au travers du medium au débit et conditions du procédé. A ce jour, les études réalisées sur les performances des filtres concernent essentiellement l'évolution de l'efficacité et de la perte de charge sur des media plans. Les paramètres étudiés portent sur la structure du medium (densité des fibres, diamètre des fibres), sur les conditions de fonctionnement (vitesse de filtration, température, pression de gaz) et sur les caractéristiques des aérosols (nature, densité, distribution granulométrique). Ainsi, de nombreux auteurs ont étudié l'évolution de la perte de charge et de l'efficacité de filtration au cours du colmatage par des particules microniques ou submicroniques principalement sur des filtres plans. Au cours de cette étude, nous nous sommes intéressés au colmatage de filtres plissés à petits plis, très répandus dans l'industrie nucléaire française. Préalablement, une caractérisation aéraulique de l'évolution de la perte de charge des filtres en fonction de la vitesse de filtration a été réalisée. Dans un premier temps, des filtres, dont la géométrie des plis correspond à celle des filtres employés dans les installations nucléaires, ont été colmatés, sur un banc d'essais à petite échelle, par des particules microniques pour différentes vitesses de filtration. Les courbes de colmatage obtenues sur le banc d'essais à petite échelle, ont ensuite été confrontées aux résultats obtenus avec l'installation CATFISH qui permet d'étudier, dans des conditions identiques, le colmatage de filtres de dimensions supérieures

Ситуации запрета в аспекте повседневности

Запрет – одно из первых общекультурных понятий в истории человечества, которое может трактоваться как организующее начало, поскольку момент структурирования содержит в себе и функцию ограничения. Современному обществу приписываются че-тыре базовые ситуации запрета (запреты на секс, власть, агрессию и творчество