Institute for Radiation Protection and Nuclear Safety (IRSN)
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Influence d'une source interne sur la température de Leidenfrost – application à un écoulement de type DFFB
No full textInternational audienceLors d'un accident de perte de réfrigérant primaire (APRP), le cœur du réacteur perd son inventaire en eau et malgré l'arrêt automatique du réacteur par chute des barres de contrôle (qui provoque l'arrêt de la réaction en chaine), la température des assemblages va augmenter rapidement du fait de la puissance résiduelle produite par le cœur ; cette puissance est due à la désintégration des produits de fission. Cette source thermique représente environ 7 \% de la puissance nominale du réacteur et elle décroit de façon exponentielle. Ainsi, même à l'arrêt, l'existence de cette puissance résiduelle explique qu'il faille refroidir le réacteur et que la température des assemblages puisse augmenter très rapidement dans les premiers instants suivant l'arrêt car ils ne sont plus refroidis. Ce refroidissement va s'opérer par une injection d'eau « froide » par le bas des assemblages et il va donner lieu à un écoulement dispersé de vapeur d'eau et de gouttes (en anglais, dispersed film flow boiling ou DFFB) qui se propage dans tout l'assemblage assez rapidement car même si la vitesse de renoyage est faible, le débit de vapeur générée au front de trempe donnera lieu à des vitesses importantes de la vapeur et des gouttes entrainées. Par conséquent, cet écoulement joue un rôle primordial dans le refroidissement initial des crayons combustibles qui ne sont pas encore immergés dans l'eau. Dans cet article, on va s'intéresser à l'influence de la puissance résiduelle sur la température de remouillage de la paroi. En effet, les assemblages se refroidissant en aval de la zone de trempe, on va passer d'un écoulement de type DFFB sans mouillage de la paroi à un écoulement mouillant si la température de paroi passe en deçà du point de Leidenfrost. Des expériences ont montré que cette température est influencée par plusieurs paramètres dont la puissance résiduelle. C'est ce que nous allons montrer et analyser dans cet article
Archaeomagnetism study of iron metallurgy archaeological sites in Togo and Benin
No full textInternational audienc
AFRICA Archéométallurgie du Fer : Ressources, Identités et Commerce en Afrique Rapport des missions et des analyses archéologiques et archéo-sous-marines francobénino-togolaise effectuées entre octobre 2023 et septembre 2024 Présenté par
No full textFormation et valorisation du patrimoine sidérurgique au Togo et au Bénin (C. Robion-Brunner) .</div
Effects of ground heating on atmospheric gravity current fronts velocity
No full textInternational audienceWe present an experimental study of atmospheric gravity currents advancing over a heating ground. The study aims at identifying the processes that characterize this flow, to gain better insight into atmospheric phenomena like the inland penetration of sea-breeze fronts or the evolution of thunderstorm outflows. Particular attention is given to the advancing velocity of the current front, as a function of the nondimensional parameters that characterize the problem.The experimental setup consists of a 4-meter-long channel in which the bottom wall can be heated by resistive fabrics generating a homogeneous heat flux. A sustained dense gravity current, created by a mixture of air and carbon dioxide, is injected at the channel inlet and visualized through laser tomography.The different heating intensities are characterized by a non-dimensional parameter, referred to as B, and defined as the ratio between the vertical buoyancy flux, induced by the imposed heat flux per unit area φ, and the horizontal buoyancy flux that generates the current.We find that, regardless of the Richardson number at the inlet, the advancement velocity is reduced in the heated-ground case compared to the adiabatic experiment (see Figure). The slowdown of the front in the heated case is due to i) the interaction between the current front and the vertical hot plumes created by natural convection and ii) the heating of the current flow, causing a reduction of the density difference between the current and the ambient. Intense heating can cancel out the density differences between the current head and the ambient, which can eventually stop the current and induce the liftoff of the current head. For different initial conditions and heating intensities, the stopping position xstop follows the relation xstop /hs =5/B, where hs is the height of the channel inlet
Meta-modelling of atmospheric dispersion simulations for emergency response in case of nuclear accident
No full textInternational audienceIn the event of a nuclear accident, numerical simulations of atmospheric dispersion are used to predict the territories potentially impacted by radioactive releases. The French institute of radiation protection and nuclear safety (IRSN) develops and uses atmospheric dispersion models to perform these calculations. For its evaluations, IRSN uses its local-scale Gaussian puff atmospheric dispersion model called pX, along with an estimated source term and simple meteorological data provided by on-site observations. These simulations are used to infer zones where a dose threshold will be exceeded. These estimations are provided to decision-makers who may trigger protective actions such as population evacuation, sheltering, stable iodine prophylaxis or food restrictions. Such evaluations are subject to uncertainties due to lack of information on the installation's status, meteorological forecast uncertainties, and models' approximations. A better quantification of uncertainties may help refine the hypotheses and potentially reduce the margins of the conservative assumptions, while ensuring a sufficient population protection. An emulator is a substitution model built to run much faster than the original. It approximates the function linking the inputs with one of its scalar outputs, often built by interpolation from a sample of simulations. Emulators have previously been built on a severe accident scenario, based on a database of simulations generated with pX model (Périllat et al., 2020). However, these were only able to predict the maximum distance of threshold exceedance, not a two-dimensional dose map. To emulate dose maps, an additional dimension reduction step is necessary. The Auto-Associative Models (AAM) is an extension of Principal Component Analysis that allows to capture nonlinear structures (Girard and Iovleff, 2005). AAM has been used once to analyse a set of maps simulated with a dispersion model (Girard et al., 2020). The method allows to parameterize a dataset by only few parameters, which can be seen as coordinates. The present study is the first combination of AAM with emulation, applied to the prediction of dose maps in case of an accidental release of radioactive materials in the atmosphere.We simulated the result of a primary breach leading to a total core meltdown in one hour of a 1300 MWe Pressurized Water Reactor. The pX Gaussian puff dispersion model with the Doury diffusion model in neutral atmospheric stability was used to build the simulations database. We considered five sources of uncertainty as inputs of the model: the wind module and rainfall rate; a multiplicative factor applied to the source term computed for the chosen accidental scenario; the release height; and the meandering wind coefficient which accounts for wind direction variability. We performed 1024 simulations uniformly sampling the input space. The AAM reduced the dimension of the resulting dose maps to eight coordinates. Kriging, or Gaussian Process, was then used to create emulators. Once these emulators built, the emulator combined with dimension reduction can then be used to predict an output map for any new input vector. We then evaluated separately the two steps: dimension reduction by AAM and kriging, using a test sample of 1000 new simulations. Finally, we validated the meta-model combining dimension reduction and kriging and compared its performance to other methods, including the emulation of distance from Périllat et al (2020). The results are very satisfactory in terms of Figure of Merit in Space (FMS), which measures the proportion of surface of threshold exceedance predicted by both the reference model and the meta-model. The FMS is over 0.8 in more than 80% of the cases (a “perfect model” having an FMS equal to 1). The guide-level dose exceedance isoline obtained with the emulator is very close to the one obtained with the original model. AAM coupled with kriging allows the creation of emulators that can reproduce the model output in approximately 0.004 seconds, whereas the original dispersion model, pX, takes about 1 minute. This increased speed of calculation enables the use of the emulator in various applications where the use of the original model is not feasible, such as uncertainty quantification.Girard, S., Armand, P., Duchenne, C., Yalamas, T., 2020. Stochastic perturbations and dimension reduction for modelling uncertainty of atmospheric dispersion simulations. Atmos. Environ. 224, 117313. https://doi.org/10.1016/j.atmosenv.2020.117313Girard, S., Iovleff, S., 2005. Auto-Associative Models and Generalized Principal Component Analysis. J. Multivar. Anal. 93, 21–39. https://doi.org/10.1016/j.jmva.2004.01.006Périllat, R., Girard, S., Korsakissok, I., Quentric, E., 2020. Emulators for the rapid prediction of consequences in case of nuclear hazards. Presented at the 20th International Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes, Tartu, Estonia
Les micro-ARN comme biomarqueurs des lésions radio-induites
No full textNational audienceIn the event of a radiological or nuclear emergency following an accident or malicious act, potentially involving many victims, medical care requires the identification and diagnosis of individuals exposed to high doses of ionizing radiation as quickly as possible. While an initial screening can be carried out directly in the field, additional biological in-lab analyses are required to refine the diagnosis and optimize the therapeutic management of victims. The fast and simultaneous management of many patients is limited by currently established techniques. To overcome these constraints, the use of new biomarkers to predict the risk and severity of radiation-induced injuries is under investigation. This synthesis summarizes the latest scientific advances demonstrating the potential of microRNAs as biomarkers of radiationinduced injuries, highlighting their relevance for human health care and radioprotection.En cas d’urgence radiologique ou nucléaire résultant d’un accident ou d’un acte de malveillance, la prise en charge médicale requiert l’identification et le diagnostic des individus exposés à de fortes doses de rayonnements ionisants le plus rapidement possible. Bien qu’un triage préliminaire puisse être effectué directement sur le terrain, une analyse complémentaire en laboratoire est nécessaire pour affiner le diagnostic. Les techniques actuellement utilisées limitent la prise en charge rapide et simultanée de nombreux patients. Afin de pallier ces contraintes, l’utilisation de nouveaux biomarqueurs pour prédire le risque et la gravité des lésions radio-induites est à l’étude. Dans cette revue, nous abordons le potentiel des micro-ARN comme biomarqueurs pour le pronostic des lésions radio-induites et leur pertinence pour une utilisation en radioprotection chez l’homme
Simulation of Crack Growth in Mini-C(T) Fracture Tests in the Ductile-to-Brittle Transition Using a Cohesive Zone Model: Application to Reactor Pressure Vessel Steels
No full textInternational audienceThe goal of this study is to simulate crack growth in mini-C(T) fracture tests using a Cohesive Zone Model (CZM) in order to derive the evolution of the toughness in the Ductile-to-Brittle Transition (DBT) region. The calibration method used is adapted from [1] and only requires low-temperature experiments. For a given temperature, it is assumed that the cohesive energy increases with the fracture probability, and that the shape of the CZM traction-separation law varies from a triangle to a trapezoid when the cohesive energy is greater than a value identified using elasto-plastic simulations. The cohesive parameters are determined using two calibration procedures. The first is performed using two experimental load-displacement curves. The second involves finding the cohesive energy leading to the right fracture toughness value given by the master curve for three different temperatures and two fracture probabilities. An exponential evolution of the cohesive energy with temperature is proposed. Cohesive energy is also assumed to depend on fracture probability. Simulations of mini-C(T) toughness tests are then performed for cumulative failure probabilities of 2%, 50% and 98% at different temperatures. A good agreement is observed between the toughness computed from the simulations and the master curve approach
Métamorphose des systèmes de gouvernance des risques à l'ère des poly-crises : les voies de la performativité
No full textInternational audienceThis paper examines the quest for effective risk governance in a context of poly-crises. It highlights the importance of governance performativity in public decision-making processes, particularly in the context of complex crises such as climate disruption and resource scarcity. Whereas centralized approaches led by a charismatic leader were historically favored, participatory and deliberative models are now seen as more effective and legitimate ways of making decisions in the face of complex issues. However, the choice between representative and participative models remains open to debate, and there is a lack of research on their effectiveness and performativity. The paper also highlights the importance of evaluating decisions and processes to understand their real impact. By adopting a holistic and ecosystemic approach, risk governance aims to transcend anthropocentrism and take into account spatiality and temporality to ensure both the effectiveness and robustness of governance systems in the face of contemporary challenges.L'article examine la quête d'une gouvernance des risques efficace dans un contexte de poly-crises. Il souligne l'importance de la performativité de la gouvernance dans les processus de décision publique, en particulier dans le contexte de crises complexes telles que le dérèglement climatique et la raréfaction des ressources. Alors que les approches centralisées dirigées par un leader charismatique étaient historiquement privilégiées, les modèles participatifs et délibératifs sont désormais considérés comme des moyens plus efficaces et légitimes de prendre des décisions face à des enjeux complexes. Cependant, le choix entre les modèles représentatifs et participatifs reste sujet à débat, et il y a un manque de recherche sur leur efficacité et leur performativité. L'article souligne également l'importance de l'évaluation des décisions et des processus pour comprendre leur impact réel. En adoptant une approche holistique et écosystémique, la gouvernance des risques vise à transcender l'anthropocentrisme et à prendre en compte la spatialité et la temporalité pour assurer à la fois l'efficacité et la robustesse des systèmes de gouvernance face aux défis contemporains
Dating the Egyptian Old Kingdom: The reign of Djedkare (5th dynasty)
No full textInternational audienceThis study aims to discuss the chronology of the Egyptian 5th dynasty of the Old Kingdom and the tentative date of accession of king Djedkare based on material from his royal necropolis at South Saqqara and non-royal cemetery of Abusir South, Egypt. A series of radiocarbon ( 14 C) dates were established through analysis of archaeological material from several monuments at the necropolis, including the king's pyramid complex, pyramid complex of his queen, and two elite tombs (Isesiankh and Khuwy). In addition, two samples from non-royal tombs in the Abusir South cemetery, were taken into consideration for further precision during the modeling, associated with king Huni (end 3rd dynasty) and king Niuserre (5th dynasty). The contextualized 14 C dates together with re-evaluation of historical evidence on Djedkare's rule, results in a new model of temporal probability density which can be further refined with any new data from archaeological research. It shows that Djedkare's reign can be currently modelled between 2503 and 2449 BCE (95.4%), thus slightly older than expected by literature. This presented model provides a more precise chronological frame for the late 5th dynasty period of Egyptian history, which was period of a significant socio-economic transformation
PROPOSAL OF A NEW GRAIN BOUNDARY RUPTURE MODEL FOR UO2 FUEL IN THE SCANAIR SOFTWARE
No full textInternational audienceFission Gas Release (FGR) is a key phenomenon that shall be correctly modelled to accurately predict the behaviour of a fuel rod during a Reactivity-Initiated Accident (RIA). Indeed, the quantity of fission gas released from the fuel, the timeat which the release occurs, and the location of the released gas in the fuel rod are of importance to determine the clad deformations, if the clad will fail, how, and when it will fail.In the IRSN FUEL+ software platform, the SCANAIR code simulates the thermomechanical behaviour of a fuel rod during an RIA transient. Three strongly coupled modules control respectively the thermal, mechanical and gases behaviour aspects in the fuel rod. The FGR is mainly driven by the fuel Grain Boundaries (GB) decohesion. The GB rupture model is based on a local strength equilibrium. Despites its simplicity, it gives reasonable results in terms of fission gas releasedcompared with experimental reference tests. Nevertheless, three limitations have been recently identified.First, the fuel stress modelling is unable to represent accurately the local stress state in the pellets. It is proposed to replace it with a simpler but more physics-based expression, that depends on the hydrostatic pressure and the radial thermal gradient in the pellets. Then, the local GB rupture stress value is a user-defined parameter. The proposition is to make it dependent on the local fuel temperature and cavity radii. Finally, the GB rupture model for UO2 fuel in the non-restructured zone is indistinguishable from the High Burnup Structure (HBS). It is proposed to reformulate the model to account for the pore pressures and the fuel porosity in the HBS.The proposed GB rupture model generally improves the gas-related results compared with the origin model, both in terms of transient FGR and pores behaviour