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Evidence of nanocavity diffusion in irradiated tungsten by combining experiments and multiscale modelling
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Method For Estimating A Future Value Of The Axial Power Imbalance In A Nuclear Reactor.
No full textMethod for estimating an axial power imbalance in a nuclear reactor, comprising the following steps:obtaining a reactor power setpoint,for each variable of a plurality of variables of the reactor, determining a sequence of the variable, the sequence representing estimated future variations of the variable,determining a sequence of the axial power imbalance, by taking into account the sequences of the plurality of variables of the reactor, the determination of the sequence of the axial power imbalance using a machine learning module that is trained beforehand on historic reactor data
Interaction entre le polyacrylate de sodium et le transport des sédiments dans une configuration simplifiée d'un tronçon de rivière
No full textInternational audienceSodium polyacrylate is well known for its use as a chelating agent in many detergents. When released into a river, usually at low concentrations, it can be adsorbed onto the surface of suspended mineral solid particulate matter, such as kaolin, found in the water body. The capacity of this polymer to be adsorbed makes sediment dynamics a major factor in its transport, as sediments act as a vehicle for the adsorbed fraction. Accurate and efficient prediction of the distribution and fate of this polymer, eventually deposited on the riverbed, is of primary importance.A mathematical model that simulates the transport and fate of the polymer by accounting for its interactions within the river system is proposed. The numerical solution of the five coupled governing equations is performed using the MICROPOL submodule of the WAQTEL module of the openTELEMAC system. This module allows for the simulation of the exchanges of this polymer between three compartments of the river reach: the water body (dissolved form), the suspended sediment (adsorbed form), and the bed sediments (eroded and/or deposited).In this study, we compare numerical results with our original one-dimensional analytical solutions applied to simulate a 1000meter reach of the Seine River, represented by a channel-like configuration. A sensitivity analysis is then performed to assess the impact of the model's input parameters on the accumulation of polymers in the riverbed near the discharge point. A fixed inlet concentration for the suspended sediment and the free (dissolved) polymer is imposed as the upstream boundary condition. The adsorption kinetics and equilibrium parameters are based on laboratory experiments of the adsorption of sodium polyacrylate on kaolin under controlled conditions similar to those found in the Seine River.</div
Etude spatiale des congestions sur le réseau de sub-transmission français à partir de données publiques
No full textInternational audienceForecasts of strong growth in the penetration of variable renewable energies, connected for the most part to the sub-transmission and distribution networks, encourage us to take into account the network impact of the sub-transmission part (between main transmission and distribution) in the European load flow simulations. Congestion has been observed in some European countries, but explicit modelling of the European sub-transmission network remains too complex and limited by the available data. With the objective of a granularity descent on chosen parts of the sub-transmission network, this study proposes a method for identifying areas at risk of congestion based on public data. Although the lack of availability of certain data limits the accuracy of the results, in France, a high level of wind power installation is the factor most correlated with RTE congestion (observed for many in sub-transmission in 2022). In addition, there is a threshold effect on the meshing density, beyond which zones are no longer congested.Les prévisions de forte croissance de la pénétration des EnR variables, raccordées en grande partie sur les réseaux de répartition et de distribution, nous incitent à prendre en compte l'impact réseau de la partie sub-transmission (entre grand transport et distribution), dans les simulations de load flow européennes. Des congestions y sont observées dans certains pays européens, mais une modélisation explicite du réseau de sub-transmission européen reste trop complexe et limitée par les données disponibles. Dans l'optique d'une descente en granularité ponctuelle sur certaines partie du réseau de sub-transmission, cette étude propose une méthode d'identification des zones à risques de congestion à partir de données publiques. Si le manque de disponibilité de certaines données limite la précision des résultats, en France métropolitaine, une forte installation éolienne est le facteur le plus corrélé aux congestions RTE (observées pour beaucoup en sub-transmission en 2022). De plus, on observe sur la densité de maillage un effet de seuil, au-delà duquel les zones ne sont plus congestionnées
Quantification of extrapolation performances of extreme quantile estimators
No full textInternational audienceThe analysis of the extreme data helps regulate the norms of installation of energy sites such as nuclear plants and hydraulic dams in accordance with the adaptation to floods, storms, droughts and meteorological aggression coming with climate change. A specific model for extreme values needs to be designed, and confidence intervals need to be established to capture a quantile of a selected probability. It is important to refine the confidence intervals to help in decision-making. Standard confidence intervals are established in common libraries in R language, but the results obtained on simulated data and real data cannot properly fit the theoretical objectives. The goal is to present new ways to construct confidence intervals on large quantiles using extreme-value theory in the special case of heavy-tailed distributions and study the efficiency of the newly-built intervals
Observation morphodynamique à long terme pour l'étude des évènements extrêmes dans l'évolution et la projection morphologiques des côtes
No full textInternational audienceDepuis plus de 20 ans, des suivis topomorphologiques sont réalisés sur plusieurs sites littoraux de Bretagne caractérisés par des morphologies très variées comme des systèmes de plage/dune, des cordons de galets, ou des falaises rocheuses. Ces observations ont été facilitées par le développement et la généralisation de techniques de mesures pertinentes dès les années 2000 (GPS, TLS, drone, LiDAR, imageries satellitaires, etc.). Pour chacune de ces morphologies, le choix d’un indicateur permettant d’enregistrer les changements morphologiques liés à la variation des conditions météo-marines (évènements extrêmes vs temps calme) est observé à des fréquences mensuelle à annuelle. La compilation de ces données permet de proposer un inventaire des évènements extrêmes ayant eu un impact significatif sur la morphologie des côtes en terme d’érosion et/ou de submersion au cours des deux dernières décennies. Ces données permettent également d’estimer les périodes de retour de ces épisodes morphogènes et/ou de faire des projections à plus ou moins long terme de l’évolution du littoral, notamment pour l’érosion
Bilan d’activités sur la modélisation et la simulation numérique des écoulements multiphasiques
No full textCette note fournit une synthèse d'actions, menées sur la période 2001-2024 dans le lot de RD numérique du projet quadripartite -CEA-EDF-Framatome-IRSN- NEPTUNE, ainsi que dans d’autres projets d’EDF R&D, concernant la modélisation et la simulation numérique des écoulements transitoires diphasiques et multiphasiques. Une première partie décrit le développement de modèles hors-équilibre (EDP) et de lois de fermeture pour la représentation des écoulements multi-phasiques, à composants miscibles ou non miscibles, en milieu libre ou poreux, et pour des lois d’état thermodynamique quelconques par phase, en s’appuyant sur un cahier des charges strict.Les modèles totalement hors-équilibre sont associés au cadre :- diphasique eau-vapeur en milieu libre ;- diphasique eau-vapeur en milieu poreux ;- diphasique gaz-solide ;- diphasique hybride à trois champs (eau liquide, vapeur d’eau et gaz incondensable) ;- triphasique immiscible à trois champs (métal liquide, eau liquide et vapeur d’eau) ;- triphasique hybride à quatre champs (métal liquide, eau liquide, vapeur d’eau et gaz incondensable).Une seconde partie des actions a concerné la construction, le développement et la vérification de schémas d’approximation des solutions de ces modèles d’EDP en situation hors-équilibre, et d’éléments de validation des modèles
Impact of Welding Residual Stresses on the risk of fracture in the brittle to ductile transition of ferritic steels
No full textInternational audienceThis paper describes a test campaign initiated by EDF and FRAMATOME on the topic of the Welding Residual Stress consideration within the Fracture Mechanics Assessment of components. For that purpose, pipes mock-ups with a non-post-weld heat-treated weld at its centre part and containing an initial crack are submitted to 4 points bending load tests at low temperature up to failure.The paper describes the material used for this campaign, the Welding Residual Stresses characterisation, and the post-test interpretation of the first test achieved today. Despite a non-expected failure during the test, this first test illustrates the large conservatism of the design approach relying on glob al approach and a consideration of the Welding Residual Stress contribution through an envelope membrane stress throughthickness stress distribution
A Systematic Approach of Global Sensitivity Analysis and Its Application to a Model for the Quantification of Resilience of Interconnected Critical Infrastructures
No full textInternational audienceWe consider a model for the resilience analysis of interconnected critical infrastructures (ICIs) that describes the dependencies among the subsystems within the ICIs and their time-varying behavior. The model response is a function of uncertain inputs comprising ICIs design parameters and failure magnitudes of vulnerable elements in the system, etc. In this methodological paper, we present a systematic approach based on an innovative blend of methods to perform a sensitivity analysis for identifying the most relevant variables affecting the system resilience at different stages, during a disruptive event. The methods considered include the following: the use of the graphical representation of Cusunoro curves for a visualization of the impact of an input on the resilience metric and an understanding of whether the associated dependence is monotonic, increasing, or decreasing; the introduction of an ensemble of indicators related to different properties of the resilience metric to allow the prioritization of variable importance and avoid false negatives, meaning to regard a variable as non-influential when, instead, it plays a relevant role in the determination of the model response; the calculation of first-order variance-based sensitivity indices to have an appreciation on the relevance of interactions when inputs are independent; and a data approach to visually identify relevant second-order interactions. All the sensitivity methods considered are performed on a provided sample, and do not require additional model evaluations. They allow the analyst to post-process the data to extract, simultaneously, several desirable insights. The systematic approach proposed to apply these methods allows us to identify the model input variables and parameters that are not very relevant, while it enables the identification of the relevant ones which allows prioritizing interventions on the vulnerable elements of the system for its resilience at different stages during a disruptive event. Given the methodological nature of the work, a simplified infrastructure model describing an interconnected gas network and electric power grid is taken as case study: this allows us to show that the approach is straightforward to understand and implement, and the results obtained show the usefulness of the approach in providing meaningful insights that can be used by stakeholders and decision makers to inform strategies for the improvement of system resilience. By the application of the simplified ICIs model to the case study, it is shown that the approach can be straightforwardly implemented to identify the most relevant variables on system resilience and obtain the most important subsystems. The key factors which affect system resilience in multiple initial failures scenarios are found; this allows us to identify the key resilience improvement measurements, and their priorities
Optimization and metamodeling of functions defined over clouds of points
No full textInternational audienceThis presentation explores innovative methods for the optimization and metamodeling of complex functions defined over sets of vectors (or "clouds of points"), with various applications such as wind-farm layout or experimental design optimization. Unlike more common functions defined over vectors, functions defined over sets vectors have the specificity of being invariant with respect to the vectors permutations. Additionally, the size of the sets varies. Finally, in this work, the functions are considered as "black-boxes", meaning that no information regarding their regularity and derivates is known.The first part of this work addresses the optimization of such functions using evolutionary algorithms, focusing on stochastic perturbation operators, such as crossovers and mutations, which are developed using the Wasserstein metric. By representing sets of points as discrete measures, we leverage the Wasserstein barycenter for designing these evolutionary operators. This approach enables a precise representation of the functions’ geometric information, balancing contraction and expansion effects to enhance optimization.In order to handle cases in which the functions are computationally costly, the metamodeling of functions defined over sets of points is also studied, with a focus on Gaussian processes. We employ substitution kernels based on Euclidean, sliced-Wasserstein, and Maximum Mean Discrepancy (MMD) distances to model complex inter-point relationships, with MMD kernels yielding particularly promising results in wind-farm simulations by adapting to the predominant wind direction.The presentation concludes by discussing cases where the vectors belong to a non-convex domain. We also briefly show how all this work can come together to carry out Bayesian optimization over sets of vectors