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International audience; This paper addresses the problem of false positive alarm when using a continuous air monitor (CAM) in decommissioning sites of nuclear facilities. CAMs are used to measure airborne activity and play an important role in the radiation protection of workers likely to be exposed to radioactive aerosols. Monitors usually sample aerosols on a membrane filter. Radioactive particles sampled are detected through the alpha and beta decays that they emit. These latter ionizing particles are measured online by spectrometry thanks to a Passivated Implanted Planar Silicon detector (PIPS). Alpha and beta decays, in this context, come mainly from the natural radon progeny (218Po, 214Pb, and so on) and, in the case of radioactive contamination, also from artificial radionuclides such as 239Pu or 137Cs. The aim of the CAM is to alert the workers when the artificial airborne activity occurs, always considering the presence of a variable background due to the natural particulate airborne activity. The CAM-specific algorithm considers this background dynamically and continuously, often by using a constant parameter. However, non-radioactive aerosols are also sampled on the membrane filter. These latter make the discrimination more difficult as they lead to the deterioration of the alpha-energy spectrum. In this paper, the effect of coarse non-radioactive aerosols on the CAM response is highlighted with four aerosol size-distributions. The evolution of the background is characterized as a function of the aerosol mass sampled, with the example of a simple algorithm. Thus, in this paper, results show a positive correlation of the background with the aerosol mass sampled by the CAM. In addition, results highlight at least two different evolutionary trends according to the aerosol size distribution. An explanation of these evolutions is given by considering the penetration profile of the natural radioactive aerosols in the granular deposit above the CAM filter. The main consequence of these results is that the background could not be considered as proportional to radon progeny as it is currently used.

Errors in the paper [1] are corrected here. As a result, particle trajectories are quite different.

During a loss of vacuum accident (LOVA), dust particles that will be present in the future tokamak ITER are likely to be resuspended, inducing a risk for explosion and airborne contamination. Evaluating the particle resuspension/deposition and resulting airborne concentration in case of a LOVA is therefore a major issue and it can be investigated by using a CFD code. To this end, this article presents the implementation of a resuspension model in a CFD code (ANSYS CFX) and its application to an air ingress in a vacuum toroidal vessel with a volume comparable to ITER one. In the first part of the article, the Rock’n Roll model and its operational version with the Biasi’s correlation is presented. The second part of the article will be devoted to the implementation of the Rock’n’Roll model in ANSYS CFX for constant friction velocities and its adaptation to non-constant friction velocities. Finally, the paper presents the simulations obtained on the particle resuspension for an air ingress scenario in a large vacuum vessel. This case is particularly interesting and non-intuitive because as the initial pressure is reduced, the particle behavior is different from that at atmospheric pressure. Further, a competition between airflow forces and gravitational force occurs, due to the low pressure environment, potentially restricting the resuspension, and the pressure influence also has to be taken into account in the particle transport and deposition (Nerisson, 2011). Three particle diameters were studied allowing to show the evolution of the resuspension with this parameter and to calculate dust resuspension rates and airborne fractions during the air ingress.

This article focuses on the mean charge per particle of monodisperse submicron aerosols charged by the diffusion of unipolar ions in post-corona discharge. It aims to confirm and discuss the limits of considering a single value of Ni·t to describe aerosol charging and then to present methods to control the size-charge relation. Three aerosol chargers with different mixings of ion and aerosol flows are investigated. Despite comparable ion sources with discharge currents of a few tens of µA, the size-charge relations differ from one charger to another due to different ion-aerosol mixing conditions and subsequent differences in ion density along the particles’ trajectories. Discrepancies are even more noticeable as the particle size increases. Discharge current, velocities of ion and aerosol flows and the electric field control post-discharge ion density at each point of the charging zone. The control of particle trajectory in expanding unipolar ion clouds leads to tuneable size-charge relations. Aerosol inertia and charging dynamics both depend on particle size, affect the Ni·t experienced by the particle and thus the final charge of the particle. Operating conditions to reach a constant mean charge for particles larger than 200 nm are reported. Conclusions provide a basis to design aerosol chargers devoted to electric mobility selection for aerosol deposition, separation or electrical measurements, especially to overcome the limits of mobility-to-size data inversion due to the multiple charge ambiguity inherent to diffusion chargers. Copyright © 2020 American Association for Aerosol Research

Poly-dispersed particle resuspension by turbulent airflow was experimentally studied in a wind tunnel called BISE. The set-up was carefully validated to produce reference airflows with three absolute pressures and friction velocities values. Monolayer deposits of poly-dispersed tungsten particles on tungsten surfaces were used for the experiments. The fraction of detached particles by size bin from 1 μm to 50 μm was quantified to analyze the effects of friction velocity, absolute pressure and particles concentration on surface. Comparison of the results with Rock'n Roll and Monte-Carlo resuspension modeling revealed discrepancies for particles behavior with diameter below 4.5 μm. These discrepancies could not be understood by assessment of particle-surface adhesion force distribution carried out with Atomic Force Microscopy analysis. For particle surface concentrations ranging from 35 to 100 mm−2, a collision effect was identified due to the concentration and poly-dispersion of particles deposited on the surface. Indeed, when analyzing the experimental data, a good linear correlation is obtained between the fraction of the small particles detached and a collision parameter, demonstrating that collisions could be responsible for the unexpectedly high resuspended fraction observed for particle size below 4.5 μm in diameter. The experimental data and the analysis presented in the paper show that particle surface concentration and collision effects are clearly relevant and should be considered in the above-mentioned resuspension models, especially for poly-dispersed particles assessment.

International audience; Adhesion forces between tungsten spherical microparticles and tungsten substrates with different roughnesses have been measured using the Atomic Force Microscopy (AFM) colloidal probe technique. Mean roughnesses of the tungsten substrates were measured by AFM and were ranked in three categories i.e. nanoscale, sub-microscale and microscale roughnesses. Experimental Hamaker constant of 37 ± 3.5 × 10 −20 J has been obtained using a spherical tungsten particle of 10.5 µm in radius and a tungsten substrate with nanoscale root-mean-square roughness of rms = 11.5 nm. It was shown that larger roughness of the order rms = 712 nm induces a two order of magnitude decrease on the adhesion of tungsten microparticles compared to a smooth tungsten surface with nanoscale roughness. Comparison with the van der Waals-based adhesion force model of Rabinovich which integrates the roughness of surfaces showed good agreement with experimental pull-off forces even when roughness of the substrate is close to the micrometer range. In such case, measurements have shown that dependency of adhesion force with particle size (in the micrometer range) has a secondary influence compared to the roughness of surfaces.

Background: Health-risk issues are raised concerning inhalation of particulate pollutants that are thought to have potential hazardous effects on the central nervous system. The brain is presented as a direct target of particulate matter (PM) exposure because of the nose-to-brain pathway involvement. The main cause of contamination in nuclear occupational activities is related to exposure to aerosols containing radionuclides, particularly uranium dust. It has been previously demonstrated that instilled solubilized uranium in the rat nasal cavity is conveyed to the brain via the olfactory nerve. Objective: The aim of this study was to analyze the anatomical localization of uranium compounds in the olfactory system after in vivo exposure to a polydisperse aerosol of uranium tetraoxide (UO4) particles. Methods: The olfactory neuroepithelium (OE) and selected brain structures—olfactory bulbs (OB), frontal cortex (FC), hippocampus (HIP), cerebellum (Cer), and brainstem (BS)—were microdissected 4 h after aerosol inhalation via a nose-only system in adult rats. Tissues were subjected to complementary analytical techniques. Results: Uranium concentrations measured by inductively coupled plasma mass spectrometry (ICP-MS) were significantly higher in all brain structures from exposed animals compared with their respective controls. We observed that cerebral uranium concentrations followed an anteroposterior gradient with typical accumulation in the OB, characteristic of a direct olfactory transfer of inhaled compounds. Secondary ion mass spectrometry (SIMS) microscopy and transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (TEM-EDX) were used in order to track elemental uranium in situ in the olfactory epithelium. Elemental uranium was detected in precise anatomical regions: olfactory neuron dendrites, paracellular junctions of neuroepithelial cells, and olfactory nerve tracts (around axons and endoneural spaces). Conclusion: These neuroanatomical observations in a rat model are consistent with the transport of elemental uranium in different physicochemical forms (solubilized, nanoparticles) along olfactory nerve bundles after inhalation of UO4 microparticles. This work contributes to knowledge of the mechanistic actions of particulate pollutants on the brain. https://doi.org/10.1289/EHP4927

The electrostatic self-charging rate of tokamak dust is investigated using Geant4, a toolkit for the simulation of the passage of particles through matter. To do so, the particles geometrical characteristics, the β disintegration energy spectrum and the deepness of tritium infusion are taken into account. The investigated materials are tungsten and beryllium, the plasma facing components (PFC) of ITER, considered as spherical particles from 20 nm to 200 μm in diameter, both tritiated. Two cases of tritium distribution in the particles are examined. On the one hand, tritium is homogeneously distributed over the whole sphere; on the other hand, tritium is homogeneously distributed within the external 100 nm layer of the sphere. The self-charging rate is assessed through the calculation of the particle exiting electron rate. Based on a tritium inventory of 10 GBq/g, relevant for ITER tokamak environment, our results show that, for a single tungsten or beryllium particle of 10 μm in diameter, the self-charging rate when the tritium is homogeneously distributed within the whole sphere is respectively 2.4 and 1.9 positive elementary charges per second. In the configuration where the tritium absorption is confined in the external 100 nm layer, the charge magnitude raises up to 37.1 and 8.4 respectively.

International audience; Background: Health risk issues are raised concerning inhalation of particulate pollutants that are thought to have potential hazardous effects in the central nervous system. The brain is presented as a direct target of particulate matter exposure because of the “nose-to-brain” pathway involvement. The main cause of contamination in nuclear occupational activities is related to exposure to aerosols containing radionuclides, in particular uranium dust. It has been previously demonstrated that instilled solubilized uranium in the rat nasal cavity is conveyed to the brain via the olfactory nerve. Objective: The aim of this study was to analyze the anatomical localization of uranium compounds in the olfactory system after in vivo exposure to a polydisperse aerosol of uranium tetraoxide (UO4) particles.Methods: The olfactory neuroepithelium and selected brain structuresolfactory bulbs, frontal cortex, hippocampus, cerebellum and brainstemwere microdissected four hours after aerosol inhalation via a nose-only system in adult rats. Tissues were subjected to complementary analytical techniques.Results: Uranium concentrations measured by ICP-MS were significantly higher in all brain structures from exposed animals compared to their respective controls. We observed that cerebral uranium concentrations followed an antero-posterior gradient with typical accumulation in the olfactory bulbs, characteristic of a direct olfactory transfer of inhaled compounds. Secondary Ion Mass Spectrometry microscopy and Transmission Electron Microscopy coupled to Energy Dispersive X-Ray spectroscopy were used in order to track elemental uranium in situ in the olfactory epithelium. Elemental uranium was detected in precise anatomical regions: olfactory neuron dendrites, paracellular junctions of neuroepithelial cells, olfactory nerve tracts (around axons and endoneural spaces).Conclusion: These neuroanatomical observations in a rat model are consistent with the transport of elemental uranium in different physico-chemical forms (solubilized, nanoparticles) along olfactory nerve bundles after inhalation of UO4 microparticles. This work contributes to knowledge of the mechanistic actions of particulate pollutants on the brain.

International audience; During ITER operation, it is expected that the large panel of plasma-wall interactions triggers the production of dust particles from the tungsten and beryllium first wall. These particles can be loaded with tritium (T) used as a fuel for the fusion reaction; T inventory is of prime importance for the safety assessment, particularly when considering dispersible matters that could be released in case of a Loss Of Vacuum Accident (LOVA),. The impact of accidental inhalation of such particles has therefore to be evaluated. Yet, particles properties in terms of tritium inventory and general behaviour are strongly dependent on their physical and chemical characteristics, and large uncertainties remain on those parameters; It is therefore important to obtain and characterize relevant W dust samples for toxicity studies before ITER operation starts. We produced model tungsten (W) Nano-Particles (NPs) by two different methods with characteristics closer to the plasma-wall interaction processes than grinding (usually used to produce commercial NPs): (i) magnetron plasma sputtering followed by gas condensation as well as (ii) laser ablation. The two types of tungsten NPs obtained exhibit very different properties investigated by a large characterization techniques panel; but both sets show similarities with samples collected in tokamak or observed in dusty plasmas setups, therefore could potentially be expected in ITER. Producing samples with strong differences is an asset to lead a first global study, highlighting which parameters are key, whether it affects the tritium inventory or the toxicity for lung cells during in vitro studies. In a second phase, it will help precise the impact of ITER particles when their definition will clarify. The aim of this paper is therefore to study and describe the characteristics of different types of W dusts, this knowledge being mandatory for the next steps of the project dealing with tritium inventory in the described W dusts and their suspension in various liquid media for cell exposure for toxicity studies.

International audience; During International Thermonuclear Experimental Reactor operation, due to plasma-wall interaction, particles/dust will be created in sizes ranging from nanometers to tens of microns. The dust properties, especially their ability to be covered by a thin oxide electrostatic insulating layer, and surface topology deeply affect their tritium inventory. Consequently, physico-chemical properties specific to tritiated tungsten particles and consequence on particle behavior in the facility and environment must be carefully assessed. For size-relevant tungsten particles, the measured tritium inventory is similar to 10 GBq g(-1). However, it varies with the particle specific surface area. Due to tritium beta decay and the oxide-insulating layer, dust exhibits a positive electrostatic self-charging. For a 5 mu m particle in diameter with a 10 GBq g(-1) tritium inventory, self-charging rate could lead to 5.5 10(4) elementary electric charges per day. These electrostatic properties could change the adhesion of dust on walls. In the case of a single particle, the adhesion will be reinforced due to image and dielectric forces. However, if the tritiated particle is part of an aggregate, the adhesion remains unknown. Due to the limited free path of the beta emission in material, the tritium inventory carried by airborne particles cannot be measured in real time by conventional continuous radioactive aerosols monitors, and a new measurement strategy is needed for atmospheric surveillance in the workplace and of facility exhaust. Toxicity studies dealing with exposure to untritiated/tritiated tungsten particles of 100 nm have been undertaken. It was shown that these particles are rapidly dissolved in biologic media. Finally, after collection, dust must be confined to avoid its spreading into the environment. Different technical solutions are presented in this paper.

International audience; Exposure assessment is a key step in the evaluation of the risk induced by the handling of engineered nanomaterials. It is a very complex task, because several properties of nanoparticles are assumed to have an effect on their hazards. For exposure monitoring at the workplace, real-time onsite measurements are commonly implemented to measure the particles size and number density, whereas the sampled material is subsequently analysed by electron microscopy. A complementary approach would consist in doing onsite chemical analysis of the filter samples, in order to routinely monitor a potential chronic exposure. Laser-induced breakdown spectroscopy (LIBS) has distinctive advantages for this purpose. Therefore, this work aims at evaluating the performances of LIBS to assess the exposure to airborne carbon nanotubes (CNTs) at the workplace. As carbon is a ubiquitous element in the environment, our strategy was to target metal impurities in CNTs, aluminum and iron in our case. Then, we proceeded in three steps. First, we optimized the choice of the filter type to get the lowest detection limit for both elements. Secondly, this filter was used to quantitatively measure deposited CNTs. Eventually, we conducted an onsite measurement campaign in an industrial CNT production plant to evaluate the exposure in a real situation. We demonstrated that we could reach a detection limit for CNTs compliant with the current NIOSH recommendation of 1 μg m$^{−3}$, and that the detected CNTs during the onsite campaign in areas accessible to workers were at an extremely low concentration, several orders of magnitude lower than this recommendation.

International audience; In the companion (Part I) paper, we have described and evaluated a new versatile optical particle counter/sizer named LOAC (Light Optical Aerosol Counter), based on scattering measurements at angles of 12 and 60 •. That allows for some typology identification of particles (droplets, carbonaceous, salts, and mineral dust) in addition to size-segregated counting in a large diameter range from 0.2 µm up to possibly more than 100 µm depending on sampling conditions (Renard et al., 2016). Its capabilities overpass those of preceding optical particle counters (OPCs) allowing the characterization of all kind of aerosols from submicronic-sized absorbing carbonaceous particles in polluted air to very coarse particles (> 10–20 µm in diameter) in desert dust plumes or fog and clouds. LOAC's light and compact design allows measurements under all kinds of balloons , on-board unmanned aerial vehicles (UAVs) and at Published by Copernicus Publications on behalf of the European Geosciences Union. 3674 J.-B. Renard et al.: LOAC: a counter/sizer for ground-based and balloon measurements – Part 2 ground level. We illustrate here the first LOAC airborne results obtained from a UAV and a variety of scientific balloons. The UAV was deployed in a peri-urban environment near Bordeaux in France. Balloon operations include (i) tethered balloons deployed in urban environments in Vi-enna (Austria) and Paris (France), (ii) pressurized balloons drifting in the lower troposphere over the western Mediter-ranean (during the Chemistry-Aerosol Mediterranean Experiment – ChArMEx campaigns), (iii) meteorological sounding balloons launched in the western Mediterranean region (ChArMEx) and from Aire-sur-l'Adour in southwestern France (VOLTAIRE-LOAC campaign). More focus is put on measurements performed in the Mediterranean during (ChArMEx) and especially during African dust transport events to illustrate the original capability of balloon-borne LOAC to monitor in situ coarse mineral dust particles. In particular, LOAC has detected unexpected large particles in desert sand plumes.

The sanitation of concrete structures through dismantling of nuclear buildings is complicated by the radiological threat associated with the airborne release of fine dust. This is the reason why the aerosol release fraction (ARF) associated with mechanical removal of concrete structure containing radioactivity needs to be accurately evaluated to implement efficient radiological survey. We characterize experimentally the ARF resulting from milling operations on a standard concrete slab in a confined experimental chamber using an industrial scarifying machine. Our results reveal a significant production of fine aerosol particles with a mass median aerodynamic diameter close to 4 µm and which mineralogical composition is dominated by calcium and silica compounds. The ARF measured when a vacuum suction device is used to confine the dust production close to the source is on the order of 5×10-4; the maximum ARF estimated when no suction device is used is on the order of 0.5.

International audience; This article presents an experimental study that encompasses a need for nuclear safety on the consequences of a leakage of fission products (FP) concentrates in a failed vessel during spent fuel reprocessing operations. Particulate airborne release fractions (ARFs), as the result of liquid FP simulants impacting a rigid surface, were assessed for two circular leakage geometries of 1 and 2 mm diameter. The detailed analysis of these ARFs which are between 2.7 × 10−5 and 5.2 × 10−5 for the different experimental configurations revealed their dependence on the surface tension and the viscosity of the solutions, as well as on the impacting jet diameter. The study also makes it possible to develop an empirical correlation that links the ARFs with the dimensionless Ohnesorge and Weber numbers in the considered surface tension and viscosity range.

International audience; The behavior of tungsten and beryllium particles close to the wall of a tokamak type geometry (i.e. a toroidal vacuum vessel) during a loss of vacuum accident (LOVA) is explored in this paper.Values of the flow field and temperature of the air surging into the torus were calculated by Computational Fluid Dynamics (CFD) simulations from an initial low pressure of 1000 Pa by Gelain et al., Fusion Engineering and Design, 100:87–99, 2015. A new CFD calculation is performed here for an initial low pressure of 500 Pa. The aerodynamic forces on particles in rarefied flow are derived from the calculated friction velocity and temperature in the lowest wall region. The focus is on spherical particles, but these values of forces are complemented for comparison with an estimate of the force on an elongated particle following Sentman (1961). Typical particles with diameters of 1, 2, 5, 10, 20 μm are considered. The possibility for particles which are detached from the lower wall to be entrained away the wall is explored. A particle may be detached by the flow field provided it escapes the adhesion force with the wall, which occurs only for a rough wall and large particles. It is then entrained away from the lower part of the wall provided its weight is smaller than the aerodynamic force, which occurs even at low pressure for all sizes of studied beryllium particles and only for specific sizes and a pressure above 1500 Pa for tungsten particles. This key influence of particle weight on the particle dynamics in rarefied gas flow is the focus of the paper. As a result, only particles of intermediate diameters may be resuspended and transferred away from the wall during the whole pressurisation sequence of the vessel. Using the data for the initial low pressure of 500 Pa, these particle diameters are 5, 10 μm for tungsten and 5, 10, 20 μm for beryllium.

During a loss of vacuum accident (LOVA), dusts that will be present in the future tokamak ITER are likely to be resuspended. Such dusts may present a risk of explosion and airborne contamination. Hence, an assessment of the amount of particles which may be resuspended in case of LOVA is a major safety issue in ITER and more widely for all the fusion reactors. This article presents the implementation of the Rock’n’Roll model for the particle resuspension in ANSYS CFX and its coupling with a validated particles transport and deposition model. After reminding the main phenomena contributing to the particle resuspension and their equations, this article proposes in a first time a checking of the good implementation of the resuspension model in ANSYS CFX. To do that, numerical results are compared to analytical calculations and experimental results acquired on facilities dedicated to the study of the resuspension. After this first step, this article proposes an application for a LOVA scenario in a toroidal vessel in order to demonstrate the feasibility of this kind of calculation in conditions similar to those encountered in a tokamak type geometry and the robustness of the coupling between the particle transport model and the resuspension model. The final application for modelling a LOVA in a toroidal geometry with different particle sizes shows a good behaviour of the coupled resuspension and transport models and a good agreement of the results with the expected physics. However, it must be reminded that this numerical application is a first step towards the analysis of dust resuspension and transport in a tokamak like ITER and the interpretation of quantitative results presented here should remain in this specific context.

The ability of tungsten (W) dust to be remobilized from rough tokamak plasma-facing surfaces is investigated in this study. Atomic Force Microscopy is used to evaluate the adhesion force distribution between W spheroids of ∼ 1 − 10 µm radius and a rough W substrate. Our results confirm that the Rabinovich model describes reasonably well the mean adhesion force in tokamak-relevant surface roughness regimes. The external (electric and ion drag) forces are estimated as well using a simplified sheath model. The results reveal that micron-size dust can be resuspended by attainable electric fields in tokamak conditions.

International audience; A scanning mobility particle sizer (SMPS) is a high resolution nanoparticle sizing system that is widely used as the standard method to measure airborne particle size distributions (PSD) in the size range 1 nm–1 μm. This paper addresses the problem to assess the uncertainty associated with PSD when a differential mobility analyzer (DMA) operates under scanning mode. The sources of uncertainty are described and then modeled either through experiments or knowledge extracted from the literature. Special care is brought to model the physics and to account for competing theories. Indeed, it appears that the modeling errors resulting from approximations of the physics can largely affect the final estimate of this indirect measurement, especially for quantities that are not measured during day-to-day experiments. The Monte Carlo method is used to compute the uncertainty associated with PSD. The method is tested against real data sets that are monosize polystyrene latex spheres (PSL) with nominal diameters of 100 nm, 200 nm and 450 nm. The median diameters and associated standard uncertainty of the aerosol particles are estimated as 101.22 nm ± 0.18 nm, 204.39 nm ± 1.71 nm and 443.87 nm ± 1.52 nm with the new approach. Other statistical parameters, such as the mean diameter, the mode and the geometric mean and associated standard uncertainty, are also computed. These results are then compared with the results obtained by SMPS embedded software.

International audience; During a loss of vacuum accident (LOVA), dusts that will be present in the future tokamak ITER are likely to be re-suspended. Such aerosols formed may present a risk for explosion and airborne contamination. This article presents parameters that govern the forces affecting particles deposited on a wall and subject to airflow. It is shown the influence of three parameters in the dust mobilization mechanism, i.e. the particles diameter, the fluid density and the friction velocity. From numerical simulations, it is determined the evolution of wall friction velocities in the vacuum vessel (VV) of ITER during a LOVA. The numerical calculations performed with ANSYS CFX code provide average friction velocities in the lower part of the tokamak between 12 m s-1 at a pressure of 150 Pa, and 0.5 m s-1 at a pressure of 105 Pa. © 2015 Elsevier B.V. All rights reserved.

International audience; Experimental investigations on the electric field strength required to overcome the adhesion forces of micron size tungsten metallic dust as well as silver and aluminum oxide in powdery form deposited on a conductive surface are presented. The results reveal a strong influence of particulate surface properties on the detachment threshold, especially for tungsten particles which exhibit a thin surface oxide layer that screens their electrical conductivity. Such tungsten particles makes possible that electrostatic self-charging occurs when tritiated because of their dielectric properties even if there are deposited on a conductive grounded surface. © 2017 Elsevier B.V.

Understanding the mobilization of dust in tokamaks is essential for proper machine operation and occupational worker exposure during maintenance operations. It is also a key issue for the safety assessment of ITER in Loss of Vacuum Accident (LOVA) scenario. Dust mobilization by airflow is strongly dependent on particle size and shape, and these characteristics are related to the specific process of erosion of the plasma facing components. Accordingly, it is important to develop techniques for in situ analysis of wall dustiness and potential dust mobilization by airflow. We propose a device, called DUSTER BOX, allowing to study dustiness of Tore Supra surfaces and to collect dust sample without mechanical stresses. This device consists in a simple airflow channel box and allows injecting a filtered airflow tangentially to the surface. The flow velocity parallel to the plasma facing components is 10 m/s and the friction velocity is 0.7 m/s which is the value needed to tear off particles greater than few microns from surfaces. After being resuspended, carbon dusts are collected on a membrane filter for weight analysis, size distribution analysis and electron microscope imaging. DUSTER BOX has been successfully used to realize a mapping of particles deposit in Tore Supra and to collect samples for size distribution analysis.

International audience; This paper deals with the electric and hydrodynamic confinement of negative ions in a point-to-plane corona discharge gap. Radial ion current density profiles have been measured on the earthed planar electrode, drilled in the axis of the point. The experimental setup is first validated by comparison with the Warburg's law without injected gas flow rate. The gas injected in the gap and blown from the discharge gap through the hole located at the centre of the plane affects neither the electric field close to the point nor the subsequent electric wind. However, it leads to the confinement of ions flux towards the central symmetry axis in the low electric field region up to a critical gas velocity, which for no more effect is measurable. Hence, electro hydro-dynamics confinement of ions can be achieved by limiting the outward radial expansion of ions to increase ion current densities on specific locations close to the low field planar electrode. © 2015 Elsevier B.V.

Corrigendum to “Three-dimensional motion of particles in a shear flow near a rough wall” (Three-dimensional motion of particles in a shear flow near a rough wall (2016) 96 (69–95), (S0021850215001664), (10.1016/j.jaerosci.2015.10.004)); International audience; A model is proposed for the three-dimensional motion of a small spherical particle entrained by the shear flow of a gas near a rough wall. On the basis of experimental results, the wall is modeled by an average small roughness and some much larger isolated peaks, which are yet smaller than the sphere radius. When encountering a high peak of roughness, the particle may be lifted if the aerodynamic force and torque take over the force and torque due to adhesion on the wall. The aerodynamics is treated using previous analytical results for the creeping flow around a particle near a wall. Values of the adhesion forces of a particle near a rough wall are obtained experimentally. When lifted from the wall, the particle follows a three-dimensional trajectory while rotating around the peak of roughness. Examples of calculated trajectories show that the particle may or may not reach the top of the peak, depending on the various physical parameters. Since the velocity of the particle when leaving the peak grows with its final distance from the wall, that velocity is essential for the subsequent particle resuspension by the ambient shear flow. © 2015 Elsevier Ltd.

International audience; Surface probes, based on airflow particle detachment coupled with optical particle counter, are actually available to measure the particle cleanliness of surfaces in cleanroom. No reliable data exits dealing with the performance assessment of these probes in unstuck and counting particles deposited on surfaces. This work presents a method for determining the efficiency of instruments dedicated to particle surface cleanliness measurements. The method is based on the realisation of standard particle deposits by sedimentation and analysis of whole of the contaminated surface by microscopy combined with a micrometric displacement bench. The method is used to assess a trial surface probe with 30 μm and 80 μm glass beads deposited on transparent (glass) or opaque (aluminium) surfaces at concentrations ranging from 1 particle·cm-2 to 50 particles·cm -2. The results obtained show that the overall efficiency of the instrument tested is less than 5 %. The detailed analysis of results shows that this low value is mainly due to poor efficiency of sampling and detection of particles in the optical counter. When analysed in terms of particle detachment efficiency, the results agree qualitatively with a force balance analysis taking into account the friction by airflow and the distribution of adhesion forces of glass particles to glass substrates or rough aluminium substrates. Such result shows that airflow based surface probes for particle cleanliness measurements should be systematically qualified for representative conditions of operations whereas analytical microscopy measurements could be considered as reference. Copyright © 2012 WILEY-VCH Verlag GmbH andamp; Co. KGaA, Weinheim.

The objective of this work is to carry out an experimental investigation on the influence of different parameters such as liquid properties (viscosity and liquid-gas surface tension), impacting droplet properties (velocity vi and diameter di) and the thickness of liquid film on the emission of airborne particles produced by the impact of millimetre-size droplets onto a liquid film. Our results show that in the variation range studied, the increase of vi and di or the decrease in liquid film thickness produces an increase in the mean number of microdroplets emitted by impact in the size range 2-50 μm. Furthermore, it was also observed that an increase in viscosity involves a steep decrease in the mean number of microdroplets emitted. These microdroplets may be produced by the fingers pinching of the crown formed during impact. In the case of low surface tension liquid, the formation of bubbles involves high production of droplets smaller than 15 μm. The results presented here constitute a database of the micro-droplets produced to validate models of droplet impact outcomes. © 2009 Elsevier Ltd. All rights reserved.

The study of aerosols in the troposphere and in the stratosphere is of major importance both for climate and air quality studies. Among the numerous instruments available, optical aerosol particles counters (OPCs) provide the size distribution in diameter range from about 100 nm to a few tens of µm. Most of them are very sensitive to the nature of aerosols, and this can result in significant biases in the retrieved size distribution. We describe here a new versatile optical particle/sizer counter named LOAC (Light Optical Aerosol Counter), which is light and compact enough to perform measurements not only at the surface but under all kinds of balloons in the troposphere and in the stratosphere. LOAC is an original OPC performing observations at two scattering angles. The first one is around 12°, and is almost insensitive to the refractive index of the particles; the second one is around 60° and is strongly sensitive to the refractive index of the particles. By combining measurement at the two angles, it is possible to retrieve the size distribution between 0.2 and 100 µm and to estimate the nature of the dominant particles (droplets, carbonaceous, salts and mineral particles) when the aerosol is relatively homogeneous. This typology is based on calibration charts obtained in the laboratory. The uncertainty for total concentrations measurements is ±20 % when concentrations are higher than 1 particle cm−3 (for a 10 min integration time). For lower concentrations, the uncertainty is up to about ±60 % for concentrations smaller than 10−2 particle cm−3. Also, the uncertainties in size calibration are ±0.025 µm for particles smaller than 0.6 µm, 5 % for particles in the 0.7–2 µm range, and 10 % for particles greater than 2 µm. The measurement accuracy of submicronic particles could be reduced in a strongly turbid case when concentration of particles > 3 µm exceeds a few particles cm−3. Several campaigns of cross-comparison of LOAC with other particle counting instruments and remote sensing photometers have been conducted to validate both the size distribution derived by LOAC and the retrieved particle number density. The typology of the aerosols has been validated in well-defined conditions including urban pollution, desert dust episodes, sea spray, fog, and cloud. Comparison with reference aerosol mass monitoring instruments also shows that the LOAC measurements can be successfully converted to mass concentrations.

International audience; Abstract Tritium adsorption and desorption from well characterized tungsten dust are presented. The dust used are of different types prepared by planetary milling and by aggregation technique in plasma. For the milled powder, the surface specific area (SSA) is 15.5 m2/g. The particles are poly-disperse with a maximum size of 200 nm for the milled powder and 100 nm for the aggregation one. Prior to tritiation the particles are carefully de-oxidized. Both samples are experiencing a high tritium inventory from 5 GBq/g to 35 GBq/g. From comparison with massive samples and considering that tritium inventory increases with SSA, it is shown that surface effects are predominant in the tritium trapping process. Extrapolation to the ITER environment is undertaken with the help of a Macroscopic Rate Equation model. It is shown that, during the life time of ITER, these particles can exceed rapidly 1 GBq/g. © 2014 Elsevier B.V.

Generally, particles dispersed in air arise, comparatively to gaseous pollutants, specific metrological problems because of the influence of various parameters of their own, such as particle size, shape, electric charge, concentration in the air, etc. The physical behavior of the particles changes drastically depending on these parameters, the most important of them being the size. For these reasons, the characterization of particles dispersed in air is more complex than the characterization of gases or vapors. In this section, we present the concepts of equivalent diameters of the particles (aerodynamic, thermodynamic, electrical mobility) and their suitability to describe the different behaviors of particles according to their nanometer or micrometric size when dispersed in air. We show later the basic principles used in aerosol metrology to characterize these equivalent diameters and quantify particles with different metrics (number, surface, mass).

International audience; At the starting of the shutdown of the AUG (ASDEX Upgrade: Axially Symmetric Divertor EXperiment) German tokamak, we collected particles deposited on the divertor surfaces by means of a dedicated device called “Duster Box”. This device allows to collect the particles using a controlled airflow with a defined shear stress. Consequently, the particles collected correspond to a potentially mobilizable fraction, by an airflow, of deposited dust. A total of more than 70,000 tungsten particles was, analysed showing a bimodal particle size distribution with a mode composed of flakes at 0.6 μm and a mode composed of spherical particles at 1.8 μm.

International audience; This work presents the results of experiments conducted with carbon microparticles collected in the tokamak Tore Supra in order to characterize their resuspension behaviour from a stainless-steel substrate when exposed to turbulent airflow. Experiments were conducted in a wind tunnel with controlled velocity profiles and monitored environmental conditions. A consequent amount of dust has been collected in the vessel of the tokamak and a bimodal particle size distribution of samples is first demonstrated. Comparison with resuspension of alumina powders with equivalent particle size distributions under turbulent airflow is also discussed. Results for both carbon and alumina microparticles are then compared to a theoretical resuspension model. Data reveal that exposing multilayer deposits with bimodal particle size distributions to low-speed flows (i.e. 3-10 m/s) induces a significant reduction of the mobilized fractions compared to what was predicted by the model. In addition, results helped to highlight some limitations in the model to physically describe changes in the adhesive strength that can occur with a polydisperse deposit. © 2014 Published by Elsevier B.V.

WOS:000342541100008; International audience; The Radial Flow Thermophoretic Analyser developed by Brugiere et al. (2013) is used to measure the thermophoretic velocity of carbon nanoparticle aggregates produced by combustion with a propane/air diffusion flame. This work is carried out within the scope of the evaluation of aerosol deposition by thermophoresis for nuclear power plant fire risk assessment purposes. Thermophoretic velocity measurements are performed on monodisperse particles with electrical mobility diameters ranging from 30 nm to 600 nm and for a temperature gradient equal to 50 750 K/m. The results obtained show an increase in thermophoretic velocity as a function of the mobility diameter, contrary to what is observed for spherical particles in the transition regime. When the thermophoretic velocity is expressed as a function of the number of primary particles making up the aggregates, a good agreement is found with the experimental results of Messerer et al. (2003). Measurements performed with the Radial Flow Thermophoretic Analyser show, for the first time, an increase in the thermophoretic velocity of carbon aggregates as a function of the number of primary particles, in qualitative agreement with the Monte Carlo simulation results of Mackowski (2006). (C) 2014 Elsevier Ltd. All rights reserved.

International audience; Due to the increasing use of nanomaterials in research and product development, it is probable that the number of situations of occupational exposure to them is also rising. The same is true for the number of workers. Although current research in nanotoxicology is far from conclusive, it is clear that relying on mass concentration and chemical composition alone is not appropriate in all cases and alternative measurement methods and approaches need to be developed. In this work, we propose a method based on simultaneous size-integrated measurements of two particle concentrations (number and lung-deposited surface area, CNC/NSAM), and on the estimation of the average size of potentially inhaled particles from the combination of these measurements. The proposed method could be part of a measurement strategy that is practical as it would use field-portable, commercially available aerosol instruments. In the absence of instruments providing real-time size-resolved measurements, this original approach can be carried out as considering that the ratio of these concentrations is a monotonous function of particle size. Indeed, the latter function depends only on the geometric standard deviation of airborne particle number size distribution, assumed to be lognormal. Compared to SMPS data for polydisperse aerosols having three chemical natures with count median diameters ranging from 64 to 177 nm, experimental results were obtained with acceptable relative discrepancies of ±30 %. Though the method proposed is less accurate than traditional instruments like SMPS, it can be used for workplace air monitoring or as a screening tool to detect the presence of airborne nanoparticles

Results of an interlaboratory comparison on size characterization of SiO2 airborne nanoparticles using on-line and off-line measurement techniques are discussed. This study was performed in the framework of Technical Working Area (TWA) 34 - "Properties of Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS) in the project no. 3 "Techniques for characterizing size distribution of airborne nanoparticles". Two types of nano-aerosols, consisting of (1) one population of nanoparticles with a mean diameter between 30.3 and 39.0 nm and (2) two populations of non-agglomerated nanoparticles with mean diameters between, respectively, 36.2-46.6 nm and 80.2-89.8 nm, were generated for characterization measurements. Scanning mobility particle size spectrometers (SMPS) were used for on-line measurements of size distributions of the produced nano-aerosols. Transmission electron microscopy, scanning electron microscopy, and atomic force microscopy were used as off-line measurement techniques for nanoparticles characterization. Samples were deposited on appropriate supports such as grids, filters, and mica plates by electrostatic precipitation and a filtration technique using SMPS controlled generation upstream. The results of the main size distribution parameters (mean and mode diameters), obtained from several laboratories, were compared based on metrological approaches including metrological traceability, calibration, and evaluation of the measurement uncertainty. Internationally harmonized measurement procedures for airborne SiO2 nanoparticles characterization are proposed. © 2013 Springer Science+Business Media Dordrecht.

International audience; Segregation and radioactive analysis of aerosols according to their aerodynamic size were performed in France, Austria, the Czech Republic, Poland, Germany, and Greece after the arrival of contaminated air masses following the nuclear accident at the Fukushima Dai-ichi nuclear power plant in March 2011. On the whole and regardless of the location, the highest activity levels correspond either to the finest particle fraction or to the upper size class. Regarding anthropogenic radionuclides, the activity median aerodynamic diameter (AMAD) ranged between 0.25 and 0.71 μm for 137Cs, from 0.17 to 0.69 μm for 134Cs, and from 0.30 to 0.53 μm for 131I, thus in the "accumulation mode" of the ambient aerosol (0.1-1 μm). AMAD obtained for the naturally occurring radionuclides 7Be and 210Pb ranged from 0.20 to 0.53 μm and 0.29 to 0.52 μm, respectively. Regarding spatial variations, AMADs did not show large differences from place to place compared with what was observed concerning bulk airborne levels registered on the European scale. When air masses arrived in Europe, AMADs for 131I were about half those for cesium isotopes. Higher AMAD for cesium probably results from higher AMAD observed at the early stage of the accident in Japan. Lower AMAD for 131I can be explained by the adsorption of gaseous iodine on particles of all sizes met during transport, especially for small particles. Additionally, weathering conditions (rain) encountered during transport and in Europe in March and April contributed to the equilibrium of the gaseous to total 131I ratio. AMAD slightly increased with time for 131I whereas a clear decreasing trend was observed with the AMADs for 137Cs and 134Cs. On average, the associated geometric standard deviation (GSD) appeared to be higher for iodine than for cesium isotopes. These statements also bear out a gaseous 131I transfer on ambient particles of a broad size range during transport. Highest weighted activity levels were found on the 0.49-0.95 μm and on the 0.18-0.36 μm size ranges in France and in Poland, respectively. The contribution from resuspension of old deposited 137Cs was assessed for the coarse particle fractions only for the first sampling week. © 2013 American Chemical Society.

A new device to study the thermophoresis of particles is presented in this paper. The instrument, called a radial flow thermophoretic analyser, is based on the geometry of the radial flow differential mobility analyser RF-DMA or SMEC (Spectrometre de Mobilite Electrique Circulaire). The device uses two circular plates, each with hot and cold temperature imposed. The instrument was designed with computational fluid dynamic software in order to check uniformity of the temperature field in the selection area after an establishment length. The transfer function of the instrument is then established and determines the effective thermophoretic velocity of particles selected in the temperature field imposed in the apparatus. For the experimental validation, effective thermophoretic velocities of monodispersed spherical latex particles for diameters ranging from 64 nm to 500 nm and a temperature gradient equal to 50,750 K/m are measured and compared with theoretical values. The results show good repeatability and discrepancies with theoretical values less than 7%.

International audience; Uranium nanoparticles (

Experimental results are reported on the resuspension of particles deposited on polymer samples representative of glove boxes used in the nuclear industry, under thermal degradation. A parametric study was carried out on the effects of heat flux, air flow rate, fuel type and particle size distribution. Small-scale experiments were conducted on 10 cm × 10 cm PolyMethyl MethAcrylate (PMMA) and PolyCarbonate (PC) samples covered with aluminium oxide particles with physical geometric diameters of 0.7 and 3.6 μm. It was observed for both polymer (fuel) samples that heat flux has no effect on the airborne release fraction (ARF), whereas particle size is a significant parameter. In the case of the PMMA sample, ARF values for 0.7 and 3.6 μm diameter particles range from 12.2% (± 6.2%) to 2.1% (± 0.6%), respectively, whereas the respective values for the PC sample range from 3.2% (± 0.8%) to 6.9% (± 3.9%). As the particle diameter increases, a significant decrease in particle release is observed for the PMMA sample, whereas an increase is observed for the PC sample. Furthermore, a peak airborne release rate is observed during the first instants of PMMA exposure to thermal stress. An empirical relationship has been proposed between the duration of this peak release and the external heat flux.

International audience; A model to simulate SMPS (Scanning Mobility Particle Sizer) measurement and the associated uncertainty analysis when axial DMA (Di erential Mobility Analyser) classi er operates under scanning mode conditions is de- scribed. Starting from simulated SMPS raw data, a fast estimation of aerosol size distribution measurement using regularization technique is performed. Then, global sensi- tivity analysis is used to discriminate signi cant parameters of the system and, as a preliminary result, a 95% con dence region is obtained by Monte Carlo simulations on an atmo- spheric aerosol size distribution.

Many toxicology studies on insoluble and poorly soluble nanoparticles point out surface area as an indicator of inhalation exposure. Measuring this criterion thus constitutes an important challenge. Instruments exist which can measure particle surface area concentration in real-time, but it is not known how well they perform when faced with polydisperse nanostructured aerosols. In this study, the response functions of three commercially available instruments based on diffusion charging (LQ1-DC, Matter Engineering; NSAM, TSI model 3550; AeroTrak™ 9000, TSI) were measured for monodisperse aerosols of four different chemical natures with particles ranging in size from 15 to 520 nm. Our results show good agreement between the experimental and theoretical response functions for the three instruments studied. In addition, no significant effect of the chemical nature, density or particle morphology was revealed. Instrument response was also tested with polydisperse aerosols. For these aerosols, discrepancies were observed between measurements and calculated concentrations based on response function and particle number size distribution. Relative differences varied between −60 and +55 % with an average value of −20 %. These differences may be explained by different factors; among them, the existence of a distribution of electrical charges on particles can lead to identical signals measured, and differential diffusion charging performance might lead to concentration-dependent response.

International audience; Impingement of droplets on surfaces occurs in many industrial and natural processes. The study of droplet break-up is fundamental in order to determine the potential sources of airborne contamination for scenarios of hazardous liquid falls such as dripping. There are very few data in the literature describing the case of impact of millimetre-size droplets. The purposes of this work were to study experimentally particle emission during the impact of droplets on a liquid film and to assess the use of coalescence/splash relations to predict airborne particle release. The results are described using dimensionless numbers taking into account the inertial, viscosity and surface tension forces. Experiments were carried out for Weber numbers between 62 and 1754 and for Ohnesorge numbers between 2.0×10 -3 and 1.5×10 -2. New results on coalescence/splash thresholds are obtained using highly sensitive aerosol measurement and allow a prediction concerning the presence or absence of airborne particles according to a threshold relation. Moreover, we propose a modification of the Cossali et al.'s [1] relation in order to describe the coalescence/prompt splash threshold. © 2011 Elsevier Inc.

International audience; nanoparticle generator based on the principle of electrical discharge (PALAS GFG-1000) was used to produce nanoparticles of different chemical natures. The fractions of electrically neutral particles were then measured by means of a Spectromètre de Mobilité Electrique Circulaire (SMEC, i.e. radial-flow mobility analyzer) for different operating conditions. The experimental results were compared with the theoretical values calculated from the Fuchs extended charge equilibrium model for spherical particles and agglomerates. For the smallest particles (below 20 nm), the deviations observed remain below 10%, and tend towards 20% for larger particles (over 35 nm).

At the present time, no stabilised method exists allowing an estimation of the specific surface area for airborne nanostructured particles (nanoaerosols). Recent toxicological studies have, however, revealed biological effects linked to the surface area of these particles. Only the BET method, which can determine the specific mass surface area of a powder, constitutes a reference both in toxicology and in the materials domain. However, this technique is not applicable to nanostructured aerosols given the mass quantities of particles required (between approximately some mg to hundreds of mg taking into account the limit of quantification of existing BET instruments). To characterise the specific surface area of airborne nanostructured particles, a method based on analysing transmission electron microscopy (TEM) images is proposed. This has recourse in particular to previous work carried out in the area of nanoparticles originating from combustion (soot), and takes into account structural parameters of nanostructured particles including the number distribution of primary particles, their overlap coefficient and the fractal dimension of agglomerates and aggregates. The approach proposed in this work was applied to five commercially-available nanostructured powders of differing natures (SiO 2 , ZrO 2 , Al 2 O 3 , Fe 2 O 3 and Fe 3 O 4 ). This first involved their prior analysis by the BET method and then being placed in suspension in aerosol form using a vortex-type shaker system. The procedure to calculate the specific surface area using image analysis was then applied to the sampled aerosols and compared to the BET measurements. The experimental results obtained on the five nanostructured powders cover a range of specific surface areas from 20 to 200 m 2 /g, the primary particles having mean diameters varying from 7 to 47 nm. Close agreement was observed between the two approaches which, taking into account measurement uncertainties, are statistically equivalent at significance level α = 0.05.

International audience; Measuring linear polarization of light scattered by a cloud of particles can help retrieve their physical properties. We present an extensive study of polarimetric measurements of sand grains that can be found on the surface and in the atmosphere of the Earth. Different techniques of measurements are compared using the Laboratoire de Météorologie Physique nephelometer on the ground and the Propriétés Optiques des Grains Astronomiques et Atmosphériques on the ground and in microgravity during parabolic flights. The techniques used on the ground bias the measurements. When the grains are lifted by an air draft, differentiation is produced in the size distribution and the nature of the floating particles. When the grains are carried along with the airflow, some grains become oriented along the flow direction at air speeds greater than a few meters per second, producing abnormal negative polarization. On the other hand, measurements conducted under microgravity permit the retrieval of the representative optical properties of the lifted sand grains with sizes greater than tens of micrometers.

Scanning Mobility Particle Sizer (SMPS) is a high resolution nanoparticle sizing system that has long been hailed as the researcher's choice for airborne nanoparticle size characterization for nano applications including nanotechnology research and development. SMPS is widely used as the standard method to measure airborne particle size distributions below 1 m. It is composed of two devices: a Dierential Mobility Analyzer (DMA) selects particle sizes thanks to their electrical mobility and a Condensation Particle Counter (CPC) enlarges particles to make them detectable by common optical counters. System raw data represent the number of particles counted over several classes of mobility diameters. Then, common inversion procedures lead to the estimation of the aerosol size distribution. In this paper, we develop a methodology to compute the uncertainties associated with the estimation of the size distribution when several experiences have been carried out. The requirement to repeat the measure ensures a realistic variability on the simulated data to be generated. The work we present consists in considering both the uncertainties coming from the experimental dispersion and the uncertainties induced by the lack of knowledge on physical phenomena. Experimental dispersion is quantied with the experimental data while the lack of knowledge is modelled via the existing physical theories and the judgements of experts in the eld of aerosol science. Thus, running Monte-Carlo simulations give an estimation of the size distribution and its corresponding condence region.