Nouvelle approche pour étudier le phénomène d'hydruration secondaire sur les gaines M5Framatome dans des conditions d'APRP

International audienceThe focus of this study is about a new experimental approach for a separate effects study of the secondary hydriding phenomenon under LOCA conditions. Many nuclear institutes perform semi–integrals tests to study the cladding behaviour during a LOCA transient. Those tests combined several phenomena and performing a detailed analysis of the secondary hydriding phenomenon using these tests can be challenging. A dedicated experimental protocol aiming at simulating secondary hydriding has been set up. Separate effects tests (SETs) were then carried out using this protocol to study the effects of both oxidation duration and temperature, on the hydrogen absorption during the oxidation stage of the LOCA transient on M5Framatome1 cladding. The effects of gap size were also investigated. Metallographic analysis has been used to characterise the M5Framatome clad metallurgical transformation after the high–temperature (HT) oxidation

Effets de la gestion sédimentaire du barrage du Chambon sur le comportement de déplacement de la truite (Salmo trutta) sur la Romanche (Isère, F).

International audienceTo maintain the efficiency of the production chain at the St-Guillerme plant (Romanche) while ensuring the safety of the facilities, the quantity of fine sediment stored in the reservoirs has been managed. Over the period 2019-2022, several flushing operations (short-term events with potentially high turbidity) per year and one dragging operation (long-term event with moderate turbidity) have been carried out. During three-year, radiotelemetry was used to monitor the mobility of 97 adult brown trout (Salmo trutta) downstream of the dam in order to assess the consequences of sediment management events and natural hydrological events. Two radiotelemetry protocols were used. A “complete” protocol (positioning every two weeks) and an “hourly” protocol (positioning a few selected individuals hourly over the course of a day) allowed to link the individual movement observed with the Suspended Sediment Concentrations (SSC) and hydrology. Preliminary analyses suggest moderate trout mobility on this river. Suspended sediments, whether anthropogenic or natural in origin, appear to have little impact on trout mobility, whatever the radio positioning time step. However, natural hydrological factors, particularly floods, seem to have a greater effect on mobility.Pour maintenir l’efficacité de la chaîne de production de l'usine de St-Guillerme (Romanche) tout en assurant la sûreté des aménagements, une gestion de la quantité de sédiments fins stockés dans les retenues a été mise en place sur les ouvrages du Ferrand, du Chambon et du Clapier. Sur la période 2019-2022, plusieurs chasses (évènements de courte durée occasionnant une turbidité potentiellement élevée) par an et un curage (évènement long avec une turbidité modérée) ont été réalisés. Pendant trois ans, un suivi par radio-télémétrie de la mobilité de 97 truites fario (Salmo trutta) adultes à l’aval des barrages a permis d’évaluer les conséquences des évènements de gestion sédimentaire et des évènements hydrologiques naturels. Deux protocoles de radio-télémétrie ont été mis en œuvre. Un protocole dit « complet » (positionnement toutes les deux semaines) et un protocole « horaire » (positionnement de quelques individus toutes les heures sur une journée) permettent de relier les déplacements individuels observés avec les concentrations en Matières en Suspension (MES) et l’hydrologie. Les analyses préliminaires suggèrent une mobilité des truites modérée sur ce cours d’eau. Les MES, d’origine anthropique ou naturelle, semblent peu perturber la mobilité des truites quel que soit le pas de temps du positionnement radio. L’hydrologie naturelle, notamment les crues, semble cependant avoir des effets un plus importants sur la mobilité

Influence des conditions estuariennes sur la dynamique temporelle de la migration de la grande alose (Alosa alosa)

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CONFORMAL APPROACH TO GAUSSIAN PROCESS SURROGATE EVALUATION WITH COVERAGE GUARANTEES

International audienceGaussian processes (GPs) are a Bayesian machine learning (ML) approach widely used to construct surrogate models for the uncertainty quantification (UQ) of computer simulation codes in industrial applications. It provides both a mean predictor and an estimate of the posterior prediction variance, the latter being used to produce Bayesian credibility intervals. Interpreting these intervals relies on the Gaussianity of the simulation model and the well-specification of the priors, which may not be appropriate. We propose to address this issue with the help of conformal prediction (CP), which is a finite-sample and distribution-free technique for estimating prediction intervals with marginal coverage guarantees. In the present work, a method for building adaptive cross-conformal prediction intervals is proposed by weighting the nonconformity score with the posterior standard deviation of the GP. The resulting CP intervals exhibit a level of adaptivity akin to Bayesian credibility sets and display a significant correlation with surrogate model local approximation error while being free from the underlying model assumptions and having marginal frequentist coverage guarantees. These estimators can be used to evaluate the quality of a GP surrogate model and can assist a decisionmaker in choosing the best prior to the specific application of the GP. We illustrate the proposed method's performance through a panel of numerical examples based on various computer experiments, including the GP metamodeling of analytical functions and an expensive-to-evaluate simulator of the clogging phenomenon in steam generators of nuclear reactors

Investigations méthodologiques et compréhension des dynamiques de transport des microplastiques dans la SeineRencontres 2025 du GDR Plastiques Environnement Santé, Juin 2025.

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An innovative method based on CFD to simulate the influence of photovoltaic panels on the microclimate in agrivoltaic conditions

International audienceAssessing the impact of photovoltaic panels on solar and infrared radiation, wind speed, and turbulence is essential for understanding how these panels may affect crops or livestock in agrivoltaic (APV) systems, as well as water reservoirs in floating photovoltaic (FPV) installations. However, state-of-the-art numerical methods require huge computing resources and rarely account for many physical phenomena at the same time. This study suggests the implementation of source and sink terms within the Computational Fluid Dynamics (CFD) solver code_saturne, specifically in the Unsteady Reynolds-Averaged Navier-Stokes (U-RANS) equations and the Discrete Ordinate Radiation Model (DOM). It enables time-efficient simulations of solar and infrared radiation, wind speed, and turbulence in the presence of obstacles. First, this method is compared to wind tunnel measurements of velocity and turbulence fields for a downsized ground-mounted photovoltaic plant, RMSEvel<0.12 m/s, and RMSEturb<0.05 m(2)/s(2 ), for a flow with a wind speed of 2.5 m/s and a turbulent kinetic energy of 0.05 m(2)/s(2 )at the PV panel height. Then, it has been applied to an actual APV power plant to validate solar and infrared radiation simulations, on average RMSEsolar<61.0 W/m(2), and RMSEir<14.0 W/m(2), for a solar radiation reaching 500 W/m2 and an IR radiation of about 350 W/m(2). This innovative method allows for the examination of how obstacles affect the microclimate, and subsequently, key parameters such as evapotranspiration. It paves the way for comprehensive numerical studies of the influence of photovoltaic panels on their environment, with a particular focus on APV and FPV configurations

Resolved DEM-CFD coupling for wave-armour blocks interactions

The present work aims to tackle breakwater stability challenges through an innovative numerical deterministic method using a resolved DEM-CFD (Discrete Element Method—Computational Fluid Dynamics) strategy, which simulates the individual motions of armour units within a fluid solver. To achieve this, a coupling between a DEM code and a CFD code is implemented and validated. The fluids (air and water) are solved using a Eulerian–Eulerian CFD solver, and the contacts between blocks are solved using a DEM code. The solids are defined within the fluid solver using a discrete forcing approach and are therefore fully resolved. In this way, the fluid solver enables the prediction of object motions with complex shapes such as tetrapods. To couple the codes, forces exerted on the solids are calculated in the fluid solver and sent to the DEM solver. Then, contact and gravity forces are computed and added to the fluid forces. The DEM solver then computes the new positions and velocities of the bodies, which are retrieved by the fluid solver. An experimental study is performed on a fixed and instrumented idealized breakwater to evaluate the wave forces acting on a coastal structure. The experiments are then numerically reproduced to validate the numerical model. Simulations of the impact of solitary waves on a row of mobile isolated tetrapods laid on a horizontal berm are then performed using the DEM-CFD coupling. The importance of initial placement and friction parameters is investigated to show the sensitivity to these parameters

Concevoir une IA explicable, appropriable et de confiance : approche située par et pour les métiers

International audienceLes récents progrès de l'intelligence artificielle (IA) ont permis des innovations dans de nombreux domaines, notamment grâce aux techniques de machine learning et de deep learning. Cependant, ces techniques, souvent perçues comme opaques, soulèvent d'importants défis en matière de transparence et d'explicabilité, en particulier dans les contextes de prise de décision. Pour y répondre, un courant appelé intelligence artificielle explicable (Explainable AI ou XAI) a émergé, visant à améliorer la compréhension de ces technologies. Toutefois, les recherches actuelles en XAI restent majoritairement technocentrées, en négligeant le contexte d'usage et l'activité des utilisateurs. Ce projet de thèse propose donc une approche anthropocentrée, cherchant à comprendre et à transformer l'activité humaine à travers la co-conception d'un dispositif d'aide au diagnostic

Implémentation d’un contrôleur non-linéaire dans la méthode Boucle de Phase Asservie (PLL) pour l’identification expérimentale de structures non-linéaires

International audienceExperimental continuation methods are used to retrieve and identify nonlinear characteristics of vibrating structures. Among the available methods, Phase-Locked Loop (PLL) allows for an easy-to-implement yet efficient method to continue nonlinear solutions such as backbone curves or frequency response functions. The PLL automatically locks onto the prescribed phase and thanks to a linear (proportional-integral) controller, can stabilize unstable periodic orbits. However, the tuning of the different parameters to be used in such a loop are seldomly documented in the literature, which in turn might lead to long duration tests. To ease the tuning effort and reduce the experimenting time, a nonlinear controller is here proposed as a way to improve the efficacy of Phase-Locked Loop testing. Thanks to the proposed design, named NCPLL (Nonlinear Controller PLL), most of the parameters are tuned easily, while a rapid locking to the prescribed state is at hand. The nonlinear gain can be easily adapted to reach a locked state rapidly. The efficacy of the NCPLL is first demonstrated on simple numerical examples including nonlinear oscillators with smooth restoring forces and Coulomb friction, and a finite element beam model with localized nonlinearities. Then the method is deployed on two different experimental test rigs. First, the case of smooth nonlinearity is tackled thanks to a cantilever beam vibrating in the magnetic field created by two magnets. Finally, the case of friction is addressed by considering an assembled beam with friction joints. In all the tested cases, the NCPLL shows excellent performance, requiring minimal tuning efforts whilst leading to fast measurements.Les méthodes de continuation expérimentales sont utilisées pour extraire et identifier les caractéristiques non linéaires des structures vibrantes. Parmi les méthodes disponibles, la méthode de Boucle de Phase Asservie (Phase-Locked Loop - PLL) constitue une approche simple à mettre en œuvre et efficace pour poursuivre des solutions non linéaires telles que des "backbone curves" ou des fonctions de réponse en fréquence, étendant ainsi le champ d’application des méthodes de résonance de phase (PRM). La PLL se verrouille automatiquement sur la phase prescrite et, grâce à un contrôleur linéaire (proportionnel-intégral), elle peut stabiliser des orbites périodiques instables. Cependant, le réglage des différents paramètres à utiliser dans une telle boucle est rarement documenté dans la littérature, ce qui peut entraîner des essais de longue durée. Afin de faciliter le réglage et de réduire le temps d’expérimentation, un contrôleur non linéaire est proposé ici pour améliorer l’efficacité des tests basés sur la PLL. Grâce à ce design, nommée NCPLL (Nonlinear Controller PLL), le nombre de paramètres à ajuster est réduit, tout en assurant un verrouillage rapide sur l’état prescrit. Une borne supérieure pour le gain du contrôleur non linéaire est déduite à partir de développements théoriques. L’efficacité du NCPLL est d’abord démontrée sur des exemples numériques simples, incluant des oscillateurs non linéaires avec des forces de rappel régulières et des forces de frottement de type Coulomb, ainsi qu’un modèle éléments finis de poutre avec des non-linéarités localisées. Ensuite, la méthode est appliquée à deux bancs d’essais expérimentaux distincts. Dans un premier temps, le cas d’une non-linéarité régulière est étudié avec une poutre cantilever vibrant dans le champ magnétique créé par deux aimants. Enfin, le cas du frottement est abordé à travers une poutre assemblée comportant des joints frottants. Dans tous les cas testés, le NCPLL démontre d’excellentes performances, nécessitant un réglage minimal tout en permettant des mesures rapides