Institute for Radiation Protection and Nuclear Safety (IRSN)
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Living among blacksmiths ? Preliminary archaeological results of the 2023 campaign at the Kpeta 2 settlement (Benin)
No full textInternational audienc
Modélisation des contributions des retombées atmosphériques et des rejets des installations à la contamination des rivières depuis les années 60
No full textInternational audienceLe 137Cs est un radionucléide artificiel introduit dans l’environnement par les rejets des installations nucléaires et par les retombées atmosphériques des essais nucléaires réalisés entre les années 1950 et 1980 et de l’accident nucléaire de Tchernobyl en 1986. Ainsi, des années 1960 à aujourd’hui, la contamination radioactive des cours d’eau a essentiellement résulté des rejets liquides des installations et de l’érosion/lessivage des différentes retombées atmosphériques sur les bassins versants. Pour reconstruire les trajectoires temporelles du 137Cs au cours du siècle dernier, le projet ANR-TRAJECTOIRE a collecté et daté des archives sédimentaires dans les zones aval des rivières françaises nucléarisées (Eyrolle et al., 2024) : le Rhin, la Meuse, la Moselle, le Rhône, la Seine et la Loire. Dans ce contexte, cette communication présente un travail de complétion de ces trajectoires afin d’évaluer, des années 1960 à nos jours et en fonction des chroniques de débit des rivières, les contributions de ces différentes sources de contamination aux activités dissoutes et particulaires de 137Cs.Ce travail a été mené en deux phases. Pour chaque bassin versant, une première étape a consisté à effectuer une calibration par approche bayésienne d’un modèle de lessivage/érosion en fonction des archives sédimentaires, des chroniques de dépôts atmosphériques et des données de l’AIEA sur les rejets liquides annuels des installations.Les chroniques d’exports de 137Cs ainsi modélisées pour chaque bassin versant sont ensuite injectées avec les chroniques de rejet annuels des installations et de débit des rivières dans le code CASTEAURx de l’ASNR. Sur l’ensemble de la période, et pour chaque rivière, celui-ci peut alors évaluer les évolutions journalières des transferts et du fractionnement solide-liquide du 137Cs ainsi que les contributions des différentes sources de contaminations.En pratique, cette démarche apporte de nouvelles informations sur l’évolution depuis les années 1960 des poids respectifs des différentes sources à la contamination des rivières en 137Cs dissous et particulaire. Plus globalement, elle permet aussi d’affiner l’évaluation des contributions de ces sources aux doses engagées via les usages de l’eau des rivières françaises nucléarisées. RéférenceEyrolle F., Chaboche P. A., Lepage H, Nicoulaud Gouin V., Boyer P. et al., Evrad O. Temporal trajectories of artificial radiocaesium 137Cs in French rivers over the nuclear era reconstructed from sediment cores, Sci. Rep., 14, 14213 (2024)
Développement d'un réacteur d'écoulement à train de gouttelettes pour la détermination de l'absorption d'iode moléculaire gazeux par les aérosols atmosphériques.
No full textInternational audienceThe fate of gaseous species in the atmosphere are influenced by the interaction between the gas and the condensed phase. In the event of an accident at a nuclear facility, radioactive iodine in its gaseous form may be released in the atmosphere. It is essential to understand its fate in the environment and its reactivity in order to predict its dispersion and implement appropriate actions to protect the population. However, a significant gap exists in experimental data on the uptake of gaseous molecular iodine (I₂) by aqueous surfaces of atmospheric aerosols, which is important in refining the radioiodine dispersion tool. In this work, a droplet train flow reactor was constructed to investigate the uptake of gaseous molecular iodine (I₂) by atmospheric aerosols. This experimental setup, widely used for assessing gas uptake by liquid surfaces, is undergoing several validation steps. These validations are necessary to ensure the reliability of the system for performing the uptake experimentsLe devenir des espèces gazeuses dans l'atmosphère est influencé par l'interaction entre le gaz et la phase condensée. En cas d'accident dans une installation nucléaire, de l'iode radioactif sous forme gazeuse peut être rejeté dans l'atmosphère. Il est essentiel de comprendre son devenir dans l'environnement et sa réactivité pour prévoir sa dispersion et mettre en œuvre les actions appropriées de protection des populations. Cependant, les données expérimentales sur l'absorption de l'iode moléculaire gazeux (I₂) par les surfaces aqueuses des aérosols atmosphériques présentent deslacunes considérables, qui sont importantes pour affiner l'outil de dispersion de l'iode radioactif. Dans cette étude, un réacteur d'écoulement à train de gouttelettes a été construit pour étudier l'absorption de l'iode moléculaire gazeux (I₂) par les aérosols atmosphériques. Ce dispositif expérimental, largement utilisé pour évaluer l'absorption de gaz par des surfaces liquides, fait l'objet de plusieurs étapes de validation. Ces validations sont nécessaires pour garantir la fiabilité du système pour la réalisation des expériences d'absorption
Evidence of Alveolar Macrophage Metabolic Shift Following Stereotactic Body Radiation Therapy -Induced Lung Fibrosis in Mice
No full textInternational audienceRadiation-induced pneumopathy is the main dose-limiting factor in cases of chest radiation therapy. Macrophage infiltration is frequently observed in irradiated lung tissues and may participate in lung damage development. Radiationinduced lung fibrosis can be reproduced in rodent models using whole thorax irradiation but suffers from limits concerning the role played by unexposed lung volumes in damage development. Methods and Materials: Here, we used an accurate stereotactic body radiation therapy preclinical model irradiating 4% of the mouse lung. Tissue damage development and macrophage populations were followed by histology, flow cytometry, and single-cell RNA sequencing. Wild-type and CCR2 KO mice, in which monocyte recruitment is abrogated, were exposed to single doses of radiation, inducing progressive (60 Gy) or rapid (80 Gy) lung fibrosis. Results: Numerous clusters of macrophages were observed around the injured area, during progressive as well as rapid fibrosis.The results indicate that probably CCR2-independent recruitment and/or in situ proliferation may be responsible for macrophage invasion. Alveolar macrophages experience a metabolic shift from fatty acid metabolism to cholesterol biosynthesis, directing them through a possible profibrotic phenotype. Depicted data revealed that the origin and phenotype of macrophages present in the injured area may differ from what has been previously described in preclinical models exposing large lung volumes, representing a potentially interesting trail in the deciphering of radiation-induced lung damage processes. Conclusions: Our study brings new possible clues to the understanding of macrophage implications in radiation-induced lung damage, representing an interesting area for exploration in future studies.</p
Local-scale experimental investigation of a two-phase cross-flow in a tube bundle and flow-induced vibration; Bubbly flow regime
No full textInternational audienceTwo-phase cross-flows can induce vibrations in several industrial situations. This is especially the case in nuclear power plant U-tube Steam Generator (SG) tube bundles. With the purpose of gathering high quality data for the validation of multiphase CFD simulation tools, a new experimental apparatus was designed and put in operation. The facility is instrumented for the two-phase air–water flow and tube vibration characterization. The two-phase flow was investigated starting from the bubble generation at the gas injection, to inside the tube bundle. Bubble sizes, shapes and velocities were measured by means of high speed camera image post-processing in the region comprised from the gas injection to the inlet of the tube bundle: the bubbles are generated with unstable size and shape, this results in promoting their breakup before reaching the tube bundle. The local behavior of the two-phase flow within the tube bundle was studied through an optical dual-tip probe, placed in different positions in order to obtain profiles of void fraction, bubble diameter and gas velocity. To study the flow-induced vibrations, the central tube of the bundle was designed to be flexible, and its vibrational response was studied by accelerometers. The root mean square displacements could be derived and the variation of the added mass with the void fraction could be observed. This paper represents the first part of two papers and focuses on bubbly flow experimental tests; the second part focuses on experimental tests performed at the so-called intermittent flow-regime conditions
Flamelet modelling of turbulent reactive flows with non-premixed reactants and multiple inlets
No full textInternational audienceThe present work describes an extension of the standard (i.e., two-inlet) mixture-fraction-based flamelet model, that is aimed at accommodating an arbitrary number of inlets. The corresponding framework relies on the consideration of inlet tracers, which allow to retrieve the fresh mixture composition, used in conjunction with a single mixture fraction variable that discriminates oxidizer inlets from fuel inlets contributions. This mixture fraction variable is also retained as a mapping variable to parameterize a chemical manifold generated from diluted one-dimensional non-premixed flamelets, with corresponding levels of dilution set from the knowledge of inlet tracers values. The resulting turbulent combustion model is presented in detail and subsequently applied to the Reynolds-averaged Navier–Stokes (RANS) and large-eddy simulation of an experimental benchmark featuring three distinct inlets. The detailed comparisons between computational results and experimental data together with ternary plots in the inlet tracers space confirm the relevance of the proposed modelling framework
First wheat certified reference material for organically bound tritium measurement in the environment
No full textInternational audienceMeasuring the radioactivity of organically bound tritium in environmental samples is difficult. For the past twenty years, many laboratories have been working on the development of reliable tritium measurement methods. In this context, several interlaboratory comparisons have been organised to develop these methods and enable laboratories to compare themselves. However, the trueness of the measurement methods has never been estimated due to the lack of certified reference materials available for use during the analyses. This document presents the production of the first certified reference material for the measurement of organically bound tritium radioactivity in environmental samples
Trapline foraging by nectar-collecting hornets
No full textInternational audienceCentral place foraging bees, butterflies, birds and bats are known to develop routes in order to visit familiar plant resources in a stable and repeatable order called “traplines”. Here we report a similar behaviour in a social wasp, the Japanese yellow hornet Vespa simillima . We monitored the foraging movements of individually marked wild hornets collecting sucrose solution on four artificial flowers placed in the field. After thirty foraging bouts, all the hornets had developed a repeatable flower visitation sequence. Using two different arrays of flowers, we show how hornets increase their foraging efficiency through time but do not always use the shortest path to visit all flowers, often favoring movements between nearest neighbor flowers over global path optimization. Our study adds nectar-foraging wasps to the growing list of animals developing traplines thereby opening new perspectives for comparative cognition research
Analysis of the long term interaction between molten core and dry concrete at Fukushima Daiichi Unit 1
No full textInternational audienceThe latest investigations of Fukushima Daiichi Uni 1 have demonstrated that corium attack to the pedestal walls and pedestal floor has occurred in Fukushima Daiichi Unit 1 to a certain extent. The results of past analytical benchmarks such as the OECD/NEA BSAF project were in agreement with this finding. However, the latest investigation do not show evidence of unlimited MCCI which is one of the main discrepancies from the BSAF project. More recently a MCCI benchmark as been launched in the context of the OECD/NEA ARC-F project. In the benchmark common geometry, boundary and initial conditions have been selected among all the participants. The results show an improved agreement among different codes for what concerns overall erosion, corium temperature and hydrogen generation, however the unlimited erosion is still predicted by all codes. It is considered that this behavior might be the result of improper boundary conditions or modeling (e.g. interfacial temperature and effective heat transfer coefficients) In this paper a summary of the overall results and a discussion of modeling and boundary conditions is done to disclose the results of the activity and the future steps to be taken in the OECD/NEA FACE project
Augmented Quantization: Mixture Models for Risk-Oriented Sensitivity Analysis
No full textA central question in risk analysis is to identify the factors that drive the system toward a specific hazardous outcome, such as the exceedance of a given threshold. When relying on numerical simulators, we propose to study the distribution of the inputs, transformed into uniform variables via their cumulative distributions, conditionally on the occurrence of the hazardous event. To represent this multivariate conditional distribution for sensitivity analysis, we introduce an original quantization approach based on estimating a mixture of Dirac and local uniform distributions. For each marginal of this mixture, a Dirac component indicates a strong influence of the corresponding variable, whereas a uniform component with wide support reflects weak influence. A notable advantage of this method is its ability to identify the regions of the input space that most strongly influence the occurrence of the risk event, while also capturing the joint effects of multiple variables. However, learning mixture models typically relies on likelihood-based methods, which are not well suited to mixtures involving singular or Dirac components. To address this, we propose an \emph{Augmented Quantization} method, a reformulation of the classical quantization problem based on the -Wasserstein distance, which can be computed in very general distribution spaces. The performance of Augmented Quantization in estimating such mixture models is first demonstrated on analytical toy problems, and then applied to sensitivity analysis of both an analytical function and a practical flooding case study on a section of the Loire River