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International audience; Nd-based (Nd-Fe-B) permanent magnets are widely used in the field of new energies. However, the worldwide pressure on their supply is pushing manufacturers to develop new magnets with reduced Nd content, replaced by other less critical rare earths (RE), typically Ce and La. The complexity induced by the multitude of elements involved in the production of this new set of magnets requires a numerical approach. The overall objective of this study is to better predict the manufacturing conditions of these substituted magnets of global composition (Nd,RE)$_2$Fe$_{14}$B.This work focuses on the effect of the addition of Ce to the Nd-Fe-B base system, which may lead to the formation of the CeFe$_2$ intermetallic with poor magnetic properties. This phase may dissolve a significant amount of Nd and has an impact on the efficiency of the magnets.In parallel to the experimental approach on the interactions between rare earths within the (RE)$_2$Fe$_{14}$B composition, a thermodynamic database related to these new magnets is being developed with the CALPHAD method. Experimental results on this quaternary system and thermodynamic properties reinforced by ab-initio calculations on some constitutive phases will be presented. Some application calculations will also illustrate the usefulness of the CALPHAD approach to improve the control of the compositions and microstructures of magnets during the manufacturing processes of such complex materials.

International audience; Oxide glasses have many advantageous properties, including optical transparency, low thermal expansion coefficients, thermally insulating, etc. As such, they have a number of applications in the world today (windows in buildings, dishes, protection panels for plasma screens and solar panels, etc.). Optimizing a wide range of physical, thermodynamic and mechanical properties is necessary to ensure their best performance in each use. However, literature focuses on a select number of compositions; making optimization of the glass as a whole unreachable. This is in part due to sample lost between different tests, multiple batches, expense of sample fabrication, etc.Recently, the development of complex interatomic empirical potentials modeling simultaneously multiple oxides makes way for capturing various physical, thermodynamic and mechanical properties. Hence, a systematic approach to capture a large numbers of different chemical compositions is feasible. This work concerns molecular dynamics simulations based on two simple and reliable empirical potentials. This presentation will focus on select physical, thermodynamic and mechanical properties presented in [1].[1] M. B. Mama Toulou, P. C. M. Fossati, C. L. Rountree, “Systematic approach to thermophysical and mechanical properties of SiO2–B2O3–Na2O glasses using molecular dynamics simulations,” Journal of Non-Crystalline Solids, 603(2023):122099.

International audience; We present a stochastic three dimensional cellular automata model of aqueous corrosion. We consider the cathodic reaction with dissolved oxygen and different concentrations of the oxidizer. We study the role and the stability of the passive layer and its effect on the kinetics, surface morphology and roughness of the metallic surface. The model considers balanced spatially separated anodic and cathodic reactions and is capable of illustrating the cathodic control of the corrosion rate. Besides the electrochemical reactions, we take into account ionic diffusion, acido/basic neutralization. Results are compared to aqueous corrosion of Fe in near neutral solution.

International audience

For the past decade, an increasing interest have been showed to molten chloride salts in the field of energy production and storage. Their physico-chemical properties, associated with the development of liquid-fuelled fourth-generation nuclear reactors, may be relied on to design efficient systems in terms of resource sustainability, actinide waste elimination and safety.The Oak Ridge National Laboratory (ORNL) program on the molten salt reactor experiment led to the development of the Hastelloy N alloy, a nickel alloy containing 7wt% of Cr and 16wt% of Mo. The composition of the alloy was optimized for corrosion resistance (both in low oxygen gas atmosphere and in molten fluorides), irradiation resistance and high temperature mechanical properties. Nevertheless, no notably resistant materials in molten chlorides have been identified and optimized so far, due to a less advanced research around nuclear systems exploiting chloride-based fuel salt.The main studies conducted in these environments have revealed the complexity of the corrosion mechanisms of materials in contact with molten chloride salts, which is due to the interaction between the dissolved species in the salt and the immersed materials, but also the interaction between atmospheric gases and the melted salt. The oxide ions activity (oxoacidity) in the salt is, for example, one of the key parameters regarding the behavior of materials in molten chloride salts. However, the determination of the oxoacidity is not frequently addressed among corrosion studies in molten chloride salt media.In the first part of the present study, various electrochemical techniques in molten salts were exploited and compared in order to quantify in the best way the oxoacidity of the NaCl-CaCl₂ binary salt molten at 600 °C. The obtained results demonstrated the good complementarity between the two main techniques for in-situ quantification of oxide ions in molten salts which are cyclic voltammetry and the yttria zirconia probe. Their use subsequently made it possible to monitor the enrichment in oxide ions of the NaCl-CaCl₂ mixture, by addition of CaO, as well as their depletion by separate addition of MgCl₂ and ZrCl₄. Obtaining these different oxoacidity conditions allowed to set the conditions for the immersion tests aimed at better understanding the impact of the oxide ion content on the corrosion of the immersed materials.The three selected test materials for the immersions are the 304 stainless steel, the nickel-based C276 alloy, and the ceramic Cr₂AlC. The corroded samples are characterized by gravimetric measurements, as well as by SEM-EDS observations and XRD analyses. The results obtained after static immersion for 336 h in NaCl-CaCl₂ at 600°C demonstrated that the corrosion resistance of the materials considered increased in the order: SS304 < C276 < Cr₂AlC, but also that the corrosion mechanisms for the two alloys differed according to the oxoacidity and the presence of reactive element in the salt. The Cr₂AlC ceramic behavior differs from the two alloys, by presenting a corrosion mechanism that is not significantly disturbed by the oxoacidity conditions, however the corrosion kinetics of the Cr₂AlC depend on the oxoacidity conditions.A third part was dedicated to the impact of the oxidizing species contained in the sweep gas, on the corrosion of the nickel-based alloy C276 immersed in the liquid salt NaCl-CaCl₂. These immersion studies, associated with gas chromatography analyses, revealed the role of O₂ and H₂O on the corrosion of the C276 alloy. These results, brought together with those concerning the influence of oxoacidity, have made it possible to outline a global mechanism of corrosion in NaCl-CaCl₂ at 600 °C.; Depuis plusieurs années, l'étude des sels chlorures fondus s'est amplifiée dans le domaine de la production et du stockage énergétique. Leurs propriétés physico-chimiques, associées au développement de réacteurs nucléaires de quatrième génération à combustible liquide, permettraient de concevoir des systèmes plus performants en termes de sécurité intrinsèque, de durabilité des ressources et d'élimination des déchets d'actinides.Le programme de recherche du laboratoire national d'Oak Ridge (ORNL) sur le MSRE (Molten salt Reactor Experiment) a conduit au développement de l'alliage Hastelloy N, un alliage à base de nickel contenant 7 mass.% de Cr et 16 mass.% de Mo. La composition de cet alliage fut optimisée pour une meilleure résistance à la corrosion (à la fois dans une atmosphère d'oxygène et dans les fluorures fondus), à l'irradiation et pour ses propriétés mécaniques à haute température. Néanmoins, aucun matériau spécifiquement résistant dans les chlorures fondus n'a été identifié ni optimisé jusqu'à présent, en raison d'une recherche antérieure moins avancée autour des systèmes nucléaires exploitant ce type de sel.Les principales études menées dans ces milieux ont révélé la complexité des mécanismes de corrosion, qui impliquent l'interaction entre les espèces dissoutes dans le sel et les matériaux immergés mais également l'interaction entre le ciel gazeux et le sel fondu. La teneur en ions oxyde (oxoacidité) dans le sel est, par exemple, un des paramètres clés vis-à-vis de la tenue des matériaux en sels chlorures fondus. La détermination et le suivi de l'oxoacidité du sel n'est pourtant que très peu réalisée dans les études de corrosion en milieux sels fondus chlorures.La première partie des travaux présente les diverses techniques électrochimiques en sels fondus qui ont été exploitées et comparées afin de pouvoir quantifier l'oxoacidité du sel binaire NaCl-CaCl₂ fondu à 600 °C. Les résultats obtenus montrent la bonne complémentarité entre les deux principales techniques de quantification in-situ des ions oxydes en sels fondus, à savoir la voltammétrie cyclique et la sonde de zircone yttriée. Leur utilisation a par la suite permis de suivre l'enrichissement en ions oxyde du mélange NaCl-CaCl₂, par ajout de CaO, ainsi que son appauvrissement par ajouts de MgCl₂ ou ZrCl₄ . L'obtention de ces différentes conditions d'oxoacidité a permis de fixer les conditions des essais d'immersion visant à comprendre l'impact de la teneur en ions oxyde sur la corrosion des matériaux immergés.Les trois matériaux d'étude retenus pour les immersions menées sont l'acier inoxydable 304, l'alliage C276 à base de nickel et la céramique Cr₂AlC. Les échantillons ont été caractérisés par mesures gravimétriques ainsi que par observations MEB-EDS et analyses DRX. Les résultats obtenus après immersions statiques de 336 h dans NaCl-CaCl₂ à 600 °C ont mis en évidence d'une part que la résistance à la corrosion des matériaux étudiés augmente dans l'ordre : 304 < C276 < Cr₂AlC, et d'autre part que les mécanismes de corrosion pour les deux alliages varient selon l'oxoacidité et la présence d'élément réactif dans le sel. La phase Cr₂AlC se distingue des deux alliages, en présentant un mécanisme de corrosion indépendant des conditions d'oxoacidité mais dont la vitesse de corrosion en dépend.Une troisième partie est consacrée à l'impact des espèces oxydantes contenues dans le gaz de balayage, sur la corrosion de l'alliage à base de nickel C276 immergé dans le sel liquide NaCl-CaCl₂. Ces études d'immersion, associées à des analyses par chromatographie gazeuse ont révélé le rôle de O₂ et H₂O sur la corrosion de l'alliage C276. Ces résultats, associés à ceux concernant l'influence de l'oxoacidité ont permis de proposer un mécanisme global de corrosion des matériaux dans NaCl-CaCl₂ à 600 °C.

International audience; Calculations of dislocation-defect interactions are essential to model metallic strength, but the required system sizes are at or beyond ab initio limits. Current estimates thus have extrapolation or finite size errors that are very challenging to quantify. Hybrid methods offer a solution, embedding small ab initio simulations in an empirical medium. However, current implementations can only match mild elastic deformations at the ab initio boundary. We describe a robust method to employ linear-in-descriptor machine learning potentials as a highly flexible embedding medium, precisely matching dislocation migration pathways whilst keeping at least the elastic properties constant. This advanced coupling allows dislocations to cross the ab initio boundary in fully three dimensional defect geometries. Investigating helium and vacancy segregation to edge and screw dislocations in tungsten, we find long-range relaxations qualitatively change impurity-induced core reconstructions compared to those in short periodic supercells, even when multiple helium atoms are present. We also show that helium-vacancy complexes, considered to be the dominant configuration at low temperatures, have only a very weak binding to screw dislocations. These results are discussed in the context of recent experimental and theoretical studies. More generally, our approach opens a vast range of mechanisms to ab initio investigation and provides new reference data to both validate and improve interatomic potentials.

It is generally considered that the elementary building blocks of defects in face-centred cubic (fcc) metals, e.g., interstitial dumbbells, coalesce directly into ever larger 2D dislocation loops, implying a continuous coarsening process. Here, we reveal that, prior to the formation of dislocation loops, interstitial atoms in fcc metals cluster into compact 3D inclusions of A15 Frank-Kasper phase. After reaching the critical size, A15 nano-phase inclusions act as a source of prismatic or faulted dislocation loops, dependent on the energy landscape of the host material. Using cutting-edge atomistic simulations we demonstrate this scenario in Al, Cu, and Ni. Our results explain the enigmatic 3D cluster structures observed in experiments combining diffuse X-ray scattering and resistivity recovery. Formation of compact nano-phase inclusions in fcc structure, along with previous observations in bcc structure, suggests that the fundamental mechanisms of interstitial defect formation are more complex than historically assumed and require a general revision. Interstitial-mediated formation of compact 3D precipitates can be a generic phenomenon, which should be further explored in systems with different crystallographic lattices.

Phase separation in sodium borosilicate glasses containing molybdenum oxide has been studied in a compositional range of interest for nuclear glasses. Two series of quaternary compositions (63.5SiO$_{2-}$19.6Na$_2$O-16.9B$_2$O$_3$)$_{1-x}$ (MoO$_3$)x with 0 $\le$ x $\le$ 3 mol.% MoO$_3$ have been synthesized and characterized, by a range of complementary experimental techniques both in situ in temperature, by viscometry and hot stage SEM, and ex-situ, by HRTEM, PXRD, EPMA and dissolution calorimetry. The phase separation temperatures between silicate and molybdenum oxide rich liquids were determined for each composition. Molybdenum oxide solubility limits were established for quenched and annealed glasses.For molybdenum oxide contents exceeding these limits, crystalline sodium mono-molybdates precipitate in the glasses as shown by XRD results and the fractions of precipitates were indirectly quantified by MoO$_3$ mole balance and enthalpy balance relying on solution calorimetry experiments. The experimental results were compared with thermodynamic calculations performed with Thermo-Calc software and a CALPHAD database of the SiO$_2$-Na$_2$O-MoO$_3$ ternary system. The ternary model allows the calculation of the nature and quantity of the precipitated phases in reasonable agreement with the experiments, even if, in the current state of development of the thermodynamic database, the absence of boron restricts the relevance of the calculations. Thus, for the construction of a predictive thermodynamic calculation tool, the addition of boron to the database is the most promising prospect.

In situ XANES is a powerful method to collect new experimental data in the U–O phase diagram., The U–O phase diagram is of paramount interest for nuclear-related applications and has therefore been extensively studied. Experimental data have been gathered to feed the thermodynamic calculations and achieve an optimization of the U–O system modelling. Although considered as well established, a critical assessment of this large body of experimental data is necessary, especially in light of the recent development of new techniques applicable to actinide materials. Here we show how in situ X-ray absorption near-edge structure (XANES) is suitable and relevant for phase diagram determination. New experimental data points have been collected using this method and discussed in regard to the available data. Comparing our experimental data with thermodynamic calculations, we observe that the current version of the U–O phase diagram misses some experimental data in specific domains. This lack of experimental data generates inaccuracy in the model, which can be overcome using in situ XANES. Indeed, as shown in the paper, this method is suitable for collecting experimental data in non-ambient conditions and for multiphasic systems.

During a severe accident involving the meltdown of the core of a pressurized water nuclear reactor, the nuclear fuel will react with the zircalloy cladding around it and the structural materials of the core to make a high temperature magma called corium. Depending on its composition and its temperature, the corium can stratify because of two non-miscible metallic and oxidic liquids. For some stratification configurations, the heat flow can focus on the vessel’s wall, threatening its integrity with a corium flowing outside of it. The aim of this thesis is to collect thermodynamic and thermophysic data on a prototypical corium, the U-Zr-Fe-O system. The thermodynamic data collected in this thesis are related to the definition of the liquid miscibility gap and the compositions of the liquids in the U-Zr-Fe-O system and its sub-systems, depending on the composition and the temperature. Compositions of interest were selected after performing thermodynamic calculation by the CALPHAD method with the TAF-ID V13 database. The corresponding samples underwent heat treatments and post-treatment analyses to measure the compositions of the liquids and to compare them to thermodynamic calculations. An iron rich liquid miscibility gap and a zirconium rich one were highlighted in the Fe-Zr-O system. Although calculations were in agreement with data from the first miscibility gap at 1990 °C, measurements in the zirconium rich miscibility gap at 2420 °C and 2650 °C reveal an underestimation of the zirconium quantity in the metallic liquid and its overestimation in the oxidic liquid by the model. Studies on the UO2-Zr-Fe system at 2423 °C show that the liquid miscibility gap definition and the compositions of the liquids depend on the quantity of iron in the system, the U/Zr ratio and corium oxidation degree. Furthermore, the zirconium molar fraction is underestimated by the model in the metallic liquid to the benefit of iron, and is overestimated in the oxidic liquid. Finally, the oxygen solubility in the metallic liquid is underestimated by the model. Thermophysic data were collected thanks to the improvement of the ATTILHA experimental setup, allowing the study of oxygen sensitive or radioactive liquids at high temperature by using a laser heating. Experimental values on liquidus and eutectic transformation temperatures of the oxygen-rich domain of the Zr-O system were acquired with this setup. Furthermore, the development of the aerodynamic levitation allows us the investigation liquids’densities for the Zr-Fe2O3 and the Zr-UO2 systems between 1884 °C and 2268 °C for different zirconium molar fractions. Densities of liquids from the Zr-Fe2O3 system were used to refine surface tension values acquired on the VITI-MBP setup at CEA Cadarache. These values confirmed the surfacting properties of the oxygen on these liquids. The experimental data collected during this thesis will be used to feed the databases and to improve the forecast of the corium’s behavior during a severe accident.; Lors d’un accident grave impliquant la fusion du cœur d’un réacteur nucléaire à eau pressurisée, le combustible nucléaire va réagir avec la gaine en zircalloy qui l’enrobe et les matériaux de structure présents dans le cœur pour former un magma à haute température appelé corium. Suivant sa composition et sa température, le corium peut se stratifier dû à la présence d’un liquide métallique et d’un liquide oxyde non-miscibles. Selon la configuration de cette stratification, une concentration du flux de chaleur peut avoir lieu sur la paroi de la cuve, menaçant son intégrité et risquant un écoulement du corium hors de celle-ci. L’objectif de cette thèse est d’obtenir des données thermodynamiques et thermophysiques sur un corium prototypique, le système U-Zr-Fe-O. Les données thermodynamiques recueillies dans cette thèse sont liées à la définition de la lacune de miscibilité liquide et à la composition des liquides dans le système U-Zr-Fe-O et de ses sous-systèmes, en fonction de la composition et de la température. Des compositions d’intérêt sont sélectionnées suite à des calculs thermodynamiques réalisés par la méthode CALPHAD grâce à la base de données TAF-ID V13. Les échantillons relatifs à ces compositions ont subi des traitements thermiques et des analyses post-opératoires afin de mesurer les compositions des liquides et de les comparer aux calculs thermodynamiques. Une lacune de miscibilité liquide riche en fer et une autre riche en zirconium ont été mises en évidence dans le système Fe-Zr-O. Alors que les données obtenues sur la première lacune à 1990 °C et 2614 °C montrent un bon accord entre le calcul et l’expérience, les mesures sur la lacune riche en zirconium à 2420 °C et 2650 °C indiquent que le modèle sous-estime la quantité de zirconium dans le liquide métallique et, à l’inverse, la surestime dans le liquide oxyde. Les études réalisées sur le système UO2-Zr-Fe à 2423 °C montrent que la présence de la lacune de miscibilité liquide et la composition des liquides dépendent grandement de la quantité de fer dans le système, du rapport U/Zr et du degré d’oxydation du corium. De plus, le modèle tend à sous-estimer la fraction molaire de zirconium dans le liquide métallique au profit du fer, et à la surestimer dans le liquide oxyde. Enfin, le modèle sous-estime grandement la solubilité de l’oxygène dans le liquide métallique. L’obtention de données thermophysiques a pu être réalisée grâce à l’amélioration du banc expérimental ATTILHA, rendant possible l’étude de liquides sensibles à l’oxygène ou radioactifs à hautes températures via un chauffage laser. Ce banc a permis de mesurer des valeurs expérimentales de température de liquidus et de transition eutectique sur le système Zr-O dans le domaine riche en oxygène. De plus, le développement de la lévitation aérodynamique sur ce banc permit l’étude de la masse volumique de liquides Zr-Fe2O3 et Zr-UO2 entre 1884 °C et 2268 °C pour différentes fractions molaires de zirconium. Les résultats de masse volumique des liquides Zr-Fe2O3 ont permis d’affiner des mesures de tension de surface réalisées sur le banc VITI-MBP au CEA Cadarache. Ces mesures confirmèrent les propriétés surfactantes de l’oxygène sur ces liquides. Les données expérimentales recueillies durant cette thèse pourront servir à alimenter les codes de calcul afin de mieux prédire le comportement du corium et le déroulement des accidents graves.

1. Kinetics and Oxidation Mechanisms 1.1 Experimental Devices that Produce Water Vapor1.2 Using the Jump Method to Understand Oxidation Mechanisms and Kinetics1.3 Detection of Breakaway Oxidation with Acoustic Emission during Thermal Oxide Scale Growth 1.4 Stress Analysis during and after Oxidation 2. Characterization 2.1 Use and Potential of Environmental SEM (ESEM) in High-Temperature Oxidation and Corrosion Studies in Wet Air 2.2 In Situ X-Ray Diffraction for Water Vapor Analyses2.3 Use of Synchrotron Beam for Evaluating the Influence of Water Vapor on the Corrosion of Metallic Materials 2.4 Raman Spectrometry2.5 In Situ Steam Oxidation Chamber Coupled to XPS 2.6 Hydrogen Profiling in Oxide Layers by GDOES and ERDA 2.7 Photoelectrochemical Technique 3. Modeling and Numerical Simulations3.1. Molecular Dynamics Study of Oxidation Mechanisms 3.2. CIN3 Software; International audience; Many papers deal with the effect of water vapor on the high-temperature corrosion behavior of metallic materials. Experimental procedures are an essential consideration in the study of oxidation in steam, O2-H2O or air-H2O atmospheres, H2-H2O atmospheres, etc. The influence of various laboratory-controlled experimental parameters on the steam oxidation response of materials has been reviewed, and best practice recommendations are proposed in many papers. There are two main ways of enriching a gas in water vapor. The first consists in bubbling a gas (H2, air, N2, Ar, etc.) through a water bath held at a fixed temperature (thermostat). For example, synthetic air bubbled through a water bath held at 46°C gives a 10% H2O enrichment of the gas. The SiMap laboratory in Grenoble uses two successive water baths to obtain the desired water vapor content. The first bath is used to pre-enrich the gas by bubbling at a temperature below the target temperature. The second bath is heated to the temperature required for water vapor enrichment. The LICB team in Dijon and the LVVEEM team at Le Puy en Velay use a slightly different setup that involves a cooling tower: the gas is made to flow through a distilled water bath held at 70-80°C, and the H2O fraction is controlled and adjusted by passing the gas through a cooling tower heated to the correct temperature. Hayashi et al. use the same process to perform water vapor experiments. The experimental setup presented in Figure 1 possesses three water sources, which makes it very convenient for conducting long-term experiments as it is possible to switch from the first to the second or third bath, as many times as needed. Successive experiments in H216O, H218O and D2O can also be carried out by placing each isotope in a separate bath.

International audience; Le cobalt constitue une grande partie des déchets radioactifs du circuit primaire des réacteurs nucléaires. Le remplacement des revêtements durs à base de cobalt fait l'objet de recherches depuis des années dans les applications nucléaires. A ce jour, il n'existe pas d'alliage capable de résister à l'abrasion et à la corrosion à 350°C et 150bar de pression pendant des cycles longs. Les alliages complexes concentrés constitués de Cr-Fe-Mo-Ni-Ti ont montré des propriétés prometteuses pour ces applications [1].La méthode CALPHAD (CALculation of PHAse Diagram) a été choisie pour déterminer les compositions les plus intéressantes de ce système. Pour cela, une évaluation critique de tous les sous-systèmes constitutifs a été réalisée. Comme ce système présente plusieurs phases de Frank-Kasper (σ, µ, χ, R, Laves), les modèles ont été discutés et choisis en fonction de la structure cristalline. La stabilité du réseau (lattice stability) et l'enthalpie de formation des composés stables et métastables ont été calculées par DFT (Density Functional Theory). Il a également été constaté que certains systèmes manquent de données fiables ou que des contradictions existent parmi différentes études. Par conséquent, la détermination expérimentale des équilibres de phase dans ces systèmes a été effectuée. Des échantillons du système Cr-Mo-Ti ont été synthétisés pour déterminer les limites de phase des phases de Laves et l'extension de la lacune de miscibilité Cr-Mo au système ternaire. Le système binaire Cr-Ti a été réoptimisé, et les systèmes ternaires où il est présent seront réévalués.

International audience

International audience; Corrosion of titanium alloys in pressurized water at 300 °C, 15 MPa, pH300 °C = 7.2 follows a flow acceleration corrosion mechanism between 0 m.s-1 and 8 m.s-1. At low water velocity (0 m.s-1 or 10-3 m.s-1), the evacuation rate of titanium hydroxides away from the samples is low, the concentration of titanium hydroxides in the vicinity of the TiO2 layer is high, which limits the dissolution rate. The increase in the water velocity up to 8 m.s-1 increases both the corrosion rate (from ~1 µm/yr to ~10 µm/yr) and the fraction of oxidized titanium that is moved away from the samples (from ~0.3 to ~0.8). When titanium alloys are used in association with stainless steel, the increase of water velocity also accelerates the coverage of the TiO2 layer by FeTiO3 ilmenite crystallites, which protect the titanium alloys from further corrosion as long as the corresponding product of solubility is maintained in the water.

International audience; Les alliages de titane sont largement utilisés dans les domaines aéronautique, biomédical et l'industrie chimique car ils possèdent une bonne résistance à la corrosion dans de nombreux milieux. Leur utilisation dans l'industrie nucléaire est envisagée ; une étude de leur durabilité dans l'eau sous pression à 300 °C a donc été engagée au CEA (commissariat à l'énergie atomique et aux énergies alternatives) en collaboration avec l'Université Grenoble Alpes.Trois matériaux ont été étudiés : du titane commercialement pur, du Ti-6Al-4V et du Ti-10V-2Fe-3Al. Ils ont été exposés à un milieu représentatif du milieu primaire des réacteurs nucléaires à eau sous pression (REP) : de l'eau désaérée, hydrogénée, contenant de la lithine, à 300 °C entre 110 et 150 bars, jusqu'à 15 mois, dans des dispositifs en acier inoxydable.Cette exposition conduit à la croissance et à la dissolution simultanées d'une couche nanométrique continue de TiO2 en surface des échantillons ainsi qu'à son recouvrement progressif par des cristallites micrométriques de TiO2 anatase et de FeTiO3 ilménite formées par la précipitation des hydroxydes de fer et de titane en solution issus de la corrosion des échantillons et du dispositif expérimental. Après un premier stade transitoire, la couche continue atteint une épaisseur stationnaire. La vitesse de corrosion est alors constante (quelques µm/an) et augmente avec la vitesse du fluide. Lorsque l'on conserve une teneur suffisante en hydroxydes dans le milieu, la totalité de la surface des échantillons finit par être recouverte d'ilménite, ce qui ralentit très fortement la corrosion et l'absorption d'hydrogène associée.

International audience; A French R&D program (CEA, CNRS, Orano) has been launched on molten salts cooled reactors which aims at assessing the feasibility of fast MSRs and confirm their potential assets. Chloride salts have been selected and in the French context (closed cycle, transmutation, Pu multirecycling), we focus on chlorides fast MSR with a focus on actinides conversion (reducing ultimate wastes). One of the major constraints on the use of molten chlorides is the corrosion behaviour of structural materials. To overcome this constraint, different approaches are performed with different time scales:- Evaluation of already available and /or qualified materials such as nickel base alloys but also high entropy alloys or ceramics.- Evaluation of different corrosion protection strategies: protective coatings, electrochemical potential control, chemistry control…- Evaluation of more innovative solutions: advanced manufacturing processes, smart materials, architectured materials…In the same time a large French research program has been launched together with CEA and CNRS to work on the global acceleration of materials discovery, the DIADEM (DIscovery Acceleration for the Deployment of Emerging Materials) project. In the frame of this large project which will be launched in 2022 for 8 years, shorter targeted projects have been already selected (duration of 3 years), as the A-DREAM project which is dedicated to the acceleration of the development of corrosion resistant materials in molten chlorides. For this, the A-DREAM project proposes an integrated approach implementing: (i) the digital design of materials/coatings, (ii) the high throughput synthesis of these materials and (iii) the implementation of an accelerated corrosion methodology. In this presentation, the French corrosion strategy for MSR will be presented together with results obtained.

International audience; Corrosion experiments were performed on a ferrito-pearlitic (P285-NH) and a ferritic steel (Armco) in a synthetic solution representing the Callovo-Oxfordian porewater during a month at 120°C. Corrosion product layers (CPLs) were characterized from micro to nanoscale in terms of morphology (electron microscopies), composition (energy dispersive X-ray spectroscopy), and structure (µ-Raman, selected area electron diffraction). Both systems present a Ca-siderite bilayer which interface locates the metal original surface, and nano to micrometric magnetite islets on the internal carbonated layer and at the M/CPL interface. The impact of cementite is highlighted in terms of morphology of the CPL and corrosion mechanism.

We investigate the impact of the oxidizing character of the nitric medium on the evolution of the intergranular corrosion of a stainless steel. In two different oxidizing conditions ("severe" and "soft"), the corroded surface of the steel reaches a different steady state: the oxide is thicker, the intergranular grooves are thinner and the surface area is larger in the "severe" conditions than in the "soft" ones. Then we investigate the effect of an alternative "severe then soft" corrosion sequence. We show that the system re-adapts to the "soft" conditions without memory effect from the previous "severe" ones. bstra, Accepted version

International audience; To investigate the fate of nuclear waste in geologic repositories, corrosion experiments were performed on a ferrito‐pearlitic (P285‐NH) and a ferritic steel (Armco) in a synthetic solution representing the Callovo-Oxfordian porewater for 3-months at 120°C. Corrosion product layers (CPL) were characterized from micro to nanoscale. Local corrosion areas of higher thicknesses were composed of siderite layers with different nano-morphologies, iron silicate, iron sulphate and magnetite. Their formation could be due to local pH variation, but also on metal microstructure (phases location and morphology). Differences in corrosion progress are suggested to be mainly related to differences in porewater chemistry and cathodic sites

International audience; Ti-stabilized austenitic stainless steel was carburized in sodium containing a high carbon activity at three different temperatures, 500 °C, 600 °C, and 650 °C during 1000 hours and 5000 hours. The carbon profile, the carbide volume fraction, and the lattice parameter evolution as function of depth were determined using high-energy X-ray diffraction and electron probe microanalysis. At 650 °C and 600 °C, the carbon precipitated as M23C6 and M7C3 carbides in the sample. The volume fraction of M7C3 carbides was lower than predicted by thermodynamic equilibrium using Thermo-Calc software®. At 500 °C, carbides almost did not form in the steel. Instead, high carbon supersaturation of the austenitic matrix occurred. Both results demonstrate that the carburization profile was strongly influenced by the kinetics of carbide formation at temperatures lower than 650 °C. High-energy X-ray diffraction measurements demonstrated that the austenite and carbide lattice parameters evolved along the carbon profile. Both measured lattice parameter profiles of austenite and M23C6 carbide were compared to the ones predicted from chemical changes of austenite and carbides.

Uranium-plutonium mixed oxide U1-yPuyO2-x is the reference fuel for future sodium fast reactors (Generation IV). The plutonium content considered for this fuel ranges between 0.20 and 0.40 and its oxygen stoichiometry or Oxygen/Metal ratio (M = U+Pu+Am) must be between 1.94 and 2.00. Furthermore, a multi-recycling of the plutonium is envisaged, which will induce a change in the initial isotopic composition with a decrease in the 239Pu content and an increase in the proportions of 238Pu and 241Pu. Due to the half-life of 241Pu (λ1/2 = 14 years) and the elapsed time between fabrication and irradiation, up to 5 mol.% of 241Am could be present in the fuel due to the β-decay of 241Pu. The influence of the presence of Am on the thermodynamic and structural properties of U1-yPuyO2-x has to be determined and predicted. The objective of this work is the thermodynamic modelling of the U-Pu-Am O using the CALPHAD method, which is based on the extrapolation of the binary and ternary sub-systems. The first step consisted in performing a critical review of the experimental available data on the different sub-systems, highlighting the lack of data on americium-bearing systems. For the Pu-Am-O system, experimental data were obtained on phase equilibria, oxygen potential and solid/liquid phase transitions for PuyAmzO2-x mixed oxides with z = 0.20, 0.50 and 0.80. Structural (phases, cationic distribution, lattice expansion) and thermodynamic (enthalpy increment, heat capacity, melting behaviour) properties of various U1 y zPuyAmzO2±x (0.235 < y < 0.39 and 0.005 < z < 0.02) were also investigated. During the laser heating experiments, the variation of the O/M ratio of the samples was quantified thanks to oxygen gauges. Based on these new sets of data, the models of the Pu-O, U-Pu-O and Pu-Am-O systems were re-assessed using the CALPHAD method to better reproduce the experimental data. The melting behaviour of the U-Pu-O system was investigated and highlighted a shift of the congruent melting composition towards the hypo-stoichiometric range. Thermodynamic calculations explained this observation by the stabilisation of the solid solution in this domain due to the formation of defects at high temperature. The thermodynamic modelling of the quaternary U-Pu-Am-O was also compared to the experimental data. The oxidation or reduction behaviour of the samples evidenced in the experiments was explained by thermodynamic calculations evidencing an oxidation favoured in the case of initially hypo-stoichiometric samples and a reduction enhanced for initially hyper- or near-stoichiometric oxides. Based on the thermodynamic calculations and the experimental results obtained for the U-Pu-Am-O system, a small influence of the presence of up to 2 % americium on the structural and thermodynamic properties of U1 y zPuyAmzO2±x was highlighted., L’oxyde mixte d’uranium et de plutonium U1-yPuyO2-x est le combustible de référence pour la future génération de réacteurs à neutrons rapides à caloporteur sodium (Génération IV). La teneur en plutonium de ce combustible sera comprise entre 0,20 et 0,40 et leur stœchiométrie en oxygène ou rapport Oxygène/Métal (M = U+Pu+Am) devra être entre 1.94 et 2.00. De plus, pour ce combustible, le multi-recyclage du plutonium est envisagé. Cette étape induit des changements dans la composition isotopique initiale du plutonium, avec une diminution de la teneur en 239Pu et une augmentation de celles en 238Pu et 241Pu. Avec une demi-vie de 14 ans, la désintégration bêta du 241Pu entraine la formation de 241Am dans le combustible avec une teneur Am/M pouvant aller jusqu’à 5 mol%. L’influence de l’américium sur les propriétés thermodynamiques et structurales de l’oxyde mixte doit donc être étudiée et prédite. L’objectif de cette thèse est la modélisation thermodynamique du système U-Pu-Am-O par la méthode CALPHAD, qui repose sur l’extrapolation des modèles des sous-systèmes binaires et ternaires. La première étape a consisté en l’analyse critique des données expérimentales disponibles dans la littérature sur les différents systèmes, qui a mis en évidence le manque de données sur les systèmes contenant de l’américium. Dans le système Pu-Am-O, des nouvelles données expérimentales ont été obtenues sur les équilibres de phases, les potentiels d’oxygène et les températures de transition solide/liquide pour des oxydes mixtes PuyAmzO2-x avec z=0,23, 0,51 et 0,80. Les propriétés structurales (phases en présence, distribution cationique, expansion thermique) et thermodynamiques (incrément enthalpique, température de solidus) de différents oxydes mixtes U1 y zPuyAmzO2±x (avec 0,235 < y < 0,39 et 0,005 < z < 0,02) ont ensuite été étudiées. Lors des mesures de températures de solidus par chauffage laser, grâce à l’utilisation de sondes à oxygène, la variation du rapport O/M des échantillons a pu être quantifiée pour la première fois. Sur la base de ces mesures, les modèles des systèmes Pu-O, U-Pu-O et Pu-Am-O ont été réévalués par la méthode CALPHAD pour mieux reproduire les données expérimentales. Le comportement à la fusion du système U-Pu-O a été étudié et a révélé un décalage de la température de fusion congruente des oxydes mixtes dans le domaine sous-stœchiométrique en oxygène. Les calculs thermodynamiques ont permis d’expliquer ce phénomène par la stabilisation de la solution solide dans ce domaine liée à la formation de défauts à haute température. La modélisation thermodynamique du système U-Pu-Am-O a également été comparée aux données expérimentales. L’oxydation ou la réduction des échantillons observées expérimentalement lors du chauffage laser a pu être expliquée par les calculs montrant une oxydation favorisée dans le cas d’échantillons initialement sous-stœchiométriques et une réduction favorisée pour des échantillons initialement sur- ou stœchiométriques. Sur la base des calculs d’applications et des résultats expérimentaux obtenus sur le système U-Pu-Am-O, une faible influence de la présence d’américium sur les propriétés thermodynamiques et structurales des oxydes U1 y zPuyAmzO2±x, pour des teneurs en Am jusqu’à z = 0,02, a été établie.

A clean and defect-free substrate/coating interface is required to guarantee good adhesion of coatings under service conditions. For this purpose, an etching pre-treatment using High-Power Impulse Magnetron Sputtering (HiPIMS) was performed to modify the surface of 304L stainless steel. The effect of three etching procedures on the substrate properties, such as corrosion resistance and adhesion, was investigated with unprecedented spatial resolution and spectroscopic details. Glancing angle X-ray diffraction showed modification in phase content but no neoformation after steel etching. X-ray photoelectron spectroscopy confirmed the presence of etchant species (6–7 at.%) on the extreme surface of the substrate. Transmission Electron Microscopy and Atomic Probe Tomography showed that the interface was less than a few nanometers wide. Polarization curves in a nitric acid solution at boiling temperature showed, for the first time, that the Ti+ and Zr+ etchings decreased the corrosion current density compared to the untreated original surface. Scratch-test measurements indicated better substrate/coating adhesion using HiPIMS metal ion etching. Electrochemical characterization revealed that Zr etching and thin coating improve the anti-corrosion properties of stainless steel in strong nitric acid conditions.

International audience; This article synthesizes all the results obtained to establish a global corrosion mechanism when a Pb–Sn coating deposited on low carbon steel is corroded in an HCl-polluted wet environment. The successive stages of the process are shown. In HCl-polluted environment, coupled with water, acid chlorides provide an aggressive electrolyte particularly favorable to corrosion. In contact with this electrolyte, lead products are created as PbCO3 and PbCl2, showing the impact of the surrounding atmosphere. In parallel, the electrolyte concentrates in Sn2+ until saturation, and tin precipitates under different forms. Due to the lead consumption, the lead corrosion products layer breaks, and the coating thins, diffusion pathways are created and the steel oxidizes. Iron corrosion products are similar with or without a coating except for the presence of a tin-rich filament. Lead is no longer present. The different stages of the mechanism are compared to corrosion phenomena observed during the use of Pb–Sn alloys to provide effective solutions to minimize or even avoid the phenomenon of corrosion.

International audience; During 2022, the global market for flat glass is estimated to exceed 100 billion metric tons. Moreover, the glass industry concerns many sectors of our daily lives (buildings, cars, dishes…) along with being integral parts of heat resistant technologies, protection panels (smart phones, plasma screens…), low-carbon energies (protection for solar panels) and satellites in outer space to name a few. Making them less reactive to Stress Corrosion Cracking (SCC), tougher (increasing their fracture toughness, K_c) and lighter, while maintaining other properties, is a fundamental issue plaguing glass scientists and researchers. This presentation will take a closer look on how the chemical composition of SiO2-B2O3-Na2O ternary glass systems alters the physical, mechanical and fracture properties of these systems. These changes lead to mesoscale changes as revealed by a novel parameter coined the depolymerization index. This parameter reveals surprising trends with the stress corrosion cracking behavior in Region I. The presentation will focus on stress corrosion cracking and how it varies with chemical composition and the depolymerization index.

Atomic-scale simulations, and in particular molecular dynamics (MD), are key assets to model the behavior of the structure of materials under the action of external stimuli, say temperature, strain or stress, irradiation, etc. Despite the widespread use of MD in condensed matter science, some basic material characteristics remain difficult to determine. This is, for instance, the case for the long-range strain tensor, and its root-mean-squared fluctuations, in disordered materials. In this work, computational diffraction is introduced as a fast and reliable structural characterization tool of atomic-scale simulation cells in the case of irradiated single crystals. In contrast to direct-space methods, computational diffraction operates in the reciprocal space and is therefore highly sensitive to long-range spatial correlations. With the example of irradiated UO2 single crystals, it is demonstrated that the normal strains, shear strains and rotations, as well as their root-mean-squared fluctuations (microstrain) and the atomic disorder, are straightforwardly and unambiguously determined. The methodology presented here has been developed with efficiency in mind, in order to be able to provide simple and reliable characterizations either operating in real time, in parallel with other analysis tools, or operating on very large data sets.

International audience; The irradiation-induced defects in stainless steel internal components of pressurized water reactors com- bined with hydrogen uptake during the oxidation process could be a key parameter in the mechanism for Irradiation-Assisted Stress Corrosion Cracking (IASCC). A heat-treated 316 L SS containing a low amount of defects was Fe 3 + ions-implanted; irradiation-induced defects types and depth distributions were charac- terized by Transmission electron microscopy (TEM). Deuterium was then inserted in the specimens either by cathodic charging or by sample exposure to deuterated primary water. Secondary Ions Mass Spectrom- etry –SIMS –permitted to access the deuterium distribution at the implanted stainless steel surface. A finite difference numerical solver accounting for hydrogen diffusion/trapping coupling was used to simu- late the hydrogen transport in the implanted material, taken into consideration the specific heterogeneous character of the irradiation-induced defects distribution in matter. Taking as input data the experimen- tal defects distribution associated with Frank loops or voids, the main trapping sites for hydrogen were assigned to voids, not Frank loops. Such numerical approach was able to deal accurately with the prob- lem of hydrogen transport in a heterogeneous material as well as to differentiate two potential trap sites contributions to the experimental deuterium distribution. In addition, according to results obtained after primary water exposure, trapping at voids was still effective at 320 °C, signature of a high binding energy of hydrogen in voids.

From corrosion layers to high-performance storage devices, the Fe-Cr-O ternary system contains typical “old” materials with widespread applications. In this PhD thesis, the macroscopic behavior of this multifaceted system is analyzed in the light of their microscopic properties. To do so, a comprehensive investigation of high-purity, epitaxial Fe-Cr-O thin films is performed in combination with theoretical calculations. Focus is placed on two stable structures of the Fe-Cr-O system: ∝-Cr₂O₃ and (Fe,Cr)₃O₄ series. The first part of this thesis holds a discussion about the effects of lattice strain in the electronic structure of ∝-Cr₂O₃ thin films. Here epitaxial ∝-Cr₂O₃(0001) thin films were synthetized in three model strain scenarios: completely relaxed, under compressive or under tensile in-plane strain. For each scenario, Cr 2p X-ray photoemission (XPS) spectra were recorded and their features were analyzed by crystal field multiplet (CFM) calculations. According to this approach, the lattice strains introduce distortions in the Cr local environment that split the 3d valence orbitals triplet t2g into a1 + e orbitals. For relaxed thin films, the XPS spectroscopic signatures were well reproduced by CFM calculations when the t2g subset was fully degenerated. Meanwhile, spectra of films under tensile (or compression) in-plane strain were simulated properly when a1 orbitals was stabilized (or destabilized) with respect to e orbitals. Therefore, one proved that subtle changes observed in the lines-shape of the Cr 2p XPS spectrum can be used to identify stress states on complex oxides. This convenient methodology (XPS+CFM), which was first optimized using model samples, was then used to successfully identify stress states on polycrystalline ∝-Cr₂O₃ layers grown during the oxidation of a commercial chromia-forming alloy. The second part of this thesis holds a discussion about the effects of composition, cation disorder and microstructure on the physical properties of (Fe,Cr)₃O₄ thin films. Here stoichiometric series of epitaxial (Fe,Cr)₃O₄(111) thin films were prepared by molecular beam epitaxy (MBE) and their structural, chemical and physical properties were studied by a number of characterization methods. These thin films are composed by Cr³⁺ ions sitting exclusively at octahedral (Oh) interstices and Fe²⁺ and Fe³⁺ ions distributed at Oh and tetrahedral (Td) interstices of the spinel structure. Once again, spectroscopic signatures (here from X-ray magnetic circular dichroism or XMCD) of Cr and Fe were explored by CFM calculations in order to obtain their valence and local environment. More importantly, we were able to determine the cation site distribution, i.e. the relative concentration of each specie on each interstice of the spinel structure. This information is crucial in the analysis of physical properties. In general, we observed that increasing Cr content steadily decreases the magnetic moment and increases the resistivity of the (Fe,Cr)₃O₄ thin films, which is consistent with previous studies in bulk samples. However, unlike bulk structures, the thin films kept an intermediate spinel structure (i.e. Fe²⁺ and Fe³⁺ ions in both Oh and Td-sites) for high Cr content. Because of that, all thin films presented Curie temperatures (Tc) above the room temperature, which is further proved using another theoretical model: the atomistic spin simulations. Furthermore, three possible conductive paths (involving electron hopping between Fe²⁺ and Fe³⁺ sites) were analyzed for the (Fe,Cr)₃O₄( thin films. Because both Fe²⁺ and Fe³⁺ ions sit at Oh-sites (even at high Cr content), these films are less resistive than the bulk as the favored Oh-to-Oh electron-hopping path is still available. In conclusion, we showed that tuning the physical properties of the (Fe,Cr)₃O₄ series can be achieved through the composition and size modulation., Les spinelles fer – chrome et la chromine sont des composés du système ternaire Fe-Cr-O qui sont présents aussi bien dans les couches de corrosion des aciers inoxydables que dans les dispositifs de stockage haute performance. L’enjeu de cette thèse est de lier des observations à l’échelle microscopique (par exemple, la structure électronique ou l’occupation des sites cationiques) à des grandeurs physiques macroscopiques (par exemple, la résistivité ou l’aimantation) sur ces matériaux sous forme de couches minces « modèle » épitaxiées. L’utilisation ciblée de calculs théoriques a permis d’apporter une interprétation fine de certaines mesures expérimentales. La première partie de la thèse est dédiée à l’étude de l’effet de la déformation de films minces de chromine ∝-Cr₂O₃ sur ses propriétés électroniques. Les couches minces de chromine ∝-Cr₂O₃(0001) sont d’abord synthétisées par jets moléculaires (MBE) suivant trois états de contrainte : tension, compression dans le plan ou parfaitement relaxé. Pour chaque cas, les spectres des niveaux 2p du chrome ont été mesurés par photoémission de rayons X (XPS) et analysés à l’aide de calculs de multiplets (méthode CFM). Les résultats montrent que les distorsions de l’environnement local du chrome, lié à la déformation, lèvent la dégénérescence du triplet t2g des orbitales 3d en une orbitale et deux orbitales dégénérées a1 + e. On remarque ainsi que la signature XPS de la chromine complètement relaxée correspond à une dégénérescence des orbitales t2g. La tension (ou compression) dans le plan induit quant-à-elle une stabilisation (ou déstabilisation) de l’orbitale a1 par rapport aux orbitales e. L’analyse des spectres XPS des niveaux 2p du chrome apparaît dès lors être un outil pour identifier l’état de contrainte de la chromine. Au-delà du cas des couches minces épitaxiées utilisées pour mettre au point la démarche, il a été ensuite possible de suivre l’évolution de l’état de contrainte de la couche de ∝-Cr₂O₃ polycrystalline obtenue durant l’oxydation in situ d’un alliage commercial nickel-chrome. La seconde partie de cette thèse est consacrée aux effets de composition, de désordre et de microstructure sur les propriétés physiques de films minces de spinelles (Fe,Cr)₃O₄. A nouveau, la première étape a consisté à synthétiser par MBE des films minces épitaxiés de (Fe,Cr)₃O₄(111) de haute qualité structurale et chimique. L’analyse des mesures obtenues par dichroisme magnétique circulaire (XMCD) à l’aide de calculs CFM a permis d’extraire l’environnement local (i.e. valence et occupation des sites cationiques) du fer et du chrome dans ces spinelles, en fonction de la teneur en chrome. Les résultats montrent (i) que le chrome est dans l’état Cr³⁺ et se substitue au fer en position octaédrique (Oh) exclusivement, (ii) que les cations Fe²⁺ et Fe³⁺ sont redistribués dans les deux sites tétraédrique (Td) et octaédrique (Oh) et (iii) que l’évolution du taux d’inversion dans les films est plus faible que pour les composés massifs à mesure que la concentration en chrome augmente. La quantification de cette redistribution s’est révélée cruciale pour interpréter les mesures macroscopiques. Ainsi, il a été possible de relier l’évolution de l’aimantation en fonction de la concentration en chrome au taux d’inversion. De plus, l’augmentation de la résistivité avec la teneur en chrome a pu être associée à la disponibilité des chemins de sauts d’électrons Oh–Oh, c’est-à-dire à la concentration en fer dans les sites octaédriques.

Conducting experiments in an inert shielding-gas environment limits the likelihood for experiencing significant mass loss or compositional shifts due to differential relative evaporation. Species-specific evaporation is proven to be below prescribed limits and near-real time monitoring of the potential for exposure is shown to be an effective tool to ensure astronaut safety. The activity coefficients for key constituents in the alloy are defined as a function of temperature for inclusion in next-generation toxicity tracking software.

During a severe accident in a Sodium Fast Reactor (SFR), nuclear fuel may react with steel cladding and absorbing materials (B₄C) to form a molten mixture, called "corium". The project aims to investigate chemical reactions involved in corium formation through a thermodynamic approach on the prototypical system (Pu – U – O – Fe – Cr – Ni – B – C). The approach is based on the CALPHAD method, predicting properties of multicomponent systems using those from binary and ternary subsystems. The TAF-ID database has been used.High temperature chemical interactions in the (U,Pu)O₂ – steel – B₄C and UO₂ – steel – B₄C systems have been studied through heat treatments at 1923 K and 2173 K. In this temperature range, the oxide fuel interacts with a metallic liquid phase that results from the melting of the steel – (B₄C mixture. A carbo-reduction of the oxide from the dissolved carbon then occurs. This reaction leads to CO(g) vaporisation and minor U and Pu dissolution in metallic liquid phase. High temperature mass spectrometry measurements on (U,Pu)O₂ – Fe – (B₄C and PuO₂ – Fe - B₄C systems confirmed the CO(g) release, as well as CO₂(g) and BO(g), as predicted by thermodynamic calculations. These trials also showed an effect of the fuel Pu content on the carbo-reduction. Higher Pu content increases the fuel oxygen potential and thus supports carbo-reduction. Finally, laser heating experiment on (U,Pu)O₂ – B₄C system revealed that the carbo-reduction even occurs under very fast kinetic conditions.The detailed analysis of sample microstructures showed the formation of numerous phases during the liquid phase solidification. Formation of mixed borides (Fe,Cr)Bx and U(Fe,Ni)yBx was not predicted by the TAF-ID calculations as Cr – Fe – B and U – Fe – B systems were not modelled. Therefore, Cr – Fe – B and U – Fe – B modelling was carried out with the CALPHAD method. For this purpose, each system went through a specific study to complete the literature data. Thermal analysis and heat treatments permitted to acquire phase diagram data on the B – Cr – Fe system. DFT calculations coupled with a quasi-harmonic model allowed to define thermodynamic properties of B – Fe – U ternary compounds. By considering these two models, the calculated solidification paths very well agree with the observed microstructures.Finally, based on experimental and computational results, a carbo-reduction mechanism was proposed to explain the different reaction steps.This work shows that an approach through thermodynamic computation is essential to describe chemical reactions involved in SFR reactors severe accidents. Combining Open Calphad code, TAF-ID database and severe accident simulation codes, such as SIMMER, should allow improvement of the physicochemical description of the corium.; Lors d’un accident grave dans un réacteur à neutrons rapides refroidi au sodium (RNR-Na), le combustible nucléaire (U,Pu)O₂ peut réagir avec la gaine en acier et le matériau absorbant (B₄C) pour former un mélange partiellement ou totalement fondu, appelé « corium ». L’objectif de la thèse est d’étudier les réactions chimiques menant et les mécanismes de formation du corium par une approche thermodynamique sur le système prototypique (Pu – U – O – Fe – Cr – Ni – B – C). La démarche utilisée dans la thèse est basée sur la méthode CALPHAD qui permet de modéliser les propriétés thermodynamiques et les équilibres de phase de ce système complexe à partir de données expérimentales et de calcul. La base de données TAF-ID a été utilisée.Les interactions chimiques à haute température dans les systèmes (U,Pu)O₂ – acier – B₄C et UO₂ – acier – B₄C ont été étudiées par des traitements thermiques à 1923 K et 2173 K. Dans cette gamme de température le combustible oxyde est en contact avec une phase liquide métallique issue de la fusion du mélange acier-B₄C. Une réaction de carbo-réduction de l’oxyde par le carbone dissout dans la phase liquide se produit. Cette réaction mène à la production de CO(g) et à la dissolution d’une faible fraction d’U et de Pu dans la phase liquide métallique. Des mesures de spectrométrie de masse à haute température sur les systèmes (U,Pu)O₂ – Fe – B₄C et PuO₂ – Fe – B₄C ont confirmé le relâchement de principalement CO(g), mais aussi de CO₂ (g) et BO(g), pendant la réaction, prédit par le calcul thermodynamique. Ces essais ont aussi montré une influence de la teneur en Pu du combustible sur la réaction de carbo-réduction. L’augmentation de la teneur en Pu tend à augmenter le potentiel d’oxygène du combustible et donc à favoriser la réduction de l’oxyde par carbo-réduction. Enfin, un essai par chauffage laser sur le système (U,Pu)O₂ – B₄C dans le dispositif RADES a montré que la réaction de carbo-réduction se produit même dans ces conditions de cinétique très rapide.L’analyse détaillée de la microstructure des échantillons a montré la formation de nombreuses phases lors de la solidification de la phase liquide métallique. La présence des borures mixtes du type (Fe,Cr)Bx et U(Fe,Ni)yBx n’était pas prédite par les calculs avec la TAF-ID car les systèmes ternaires Cr – Fe – B et U – Fe – B n’étaient pas modélisés. La modélisation des systèmes ternaires B – Cr – Fe et B – Fe – U a donc été effectuée avec la méthode CALPHAD. Pour cela, chaque système a fait l’objet d’une étude spécifique pour compléter les données de la littérature. Des données de diagramme de phase ont été mesurées sur le système B – Cr – Fe par des essais d’analyse thermique et des traitements thermiques. Pour le système B – Fe – U, les propriétés thermodynamiques des composés ternaires ont été déterminées par des calculs DFT couplés à un modèle quasi-harmonique. Avec la prise en compte de ces deux modèles sur les ternaires B – Cr – Fe et B – Fe – U, les chemins de solidification calculés sont en très bon accord avec les microstructures observées.Finalement, sur la base des résultats expérimentaux et de calcul, un mécanisme a été proposé pour expliquer les différentes étapes de la réaction de carbo-réduction.Ce travail montre que l’approche par le calcul thermodynamique est indispensable pour décrire les réactions chimiques à haute température se produisant dans le corium lors d’un accident grave dans un réacteur RNR-Na. Un couplage pourrait être envisagé entre le code Open Calphad, la TAF-ID et les codes de simulation d’accident grave comme SIMMER pour améliorer la description physico-chimique du corium dans ces codes.

International audience; The ternary Cr-Mo-Ti system is a constitutive alloying system for steels and titanium alloys. Ferritic alloys with Cr, Mo and Ti contents have been studied, achieving good mechanical properties, corrosion resistance and microstructural stability to 550°C. Beta titanium alloys are nowadays largely employed in biomedical applications, and aviation and aerospace industries. The system is also interesting for the development of new high-entropy alloys with a body-centered cubic structure. The Calphad method is a useful tool to explore and study all these alloy systems.Nevertheless, the experimental data about this ternary system remains scarce and no recent data was published. Thermodynamical assessments were carried out by Lee et al.[1] and recently by Hu et al. [2]. The first assessment was based on the solid phase boundaries in the Ti-rich region published by Elliot et al. [3]. In the respective re-assessment, they added with a low weight data from Grum-Grizhimailo and Gromova [4].Therefore, we will study the Laves phase extension in the ternary Cr-Mo-Ti system. DFT calculation will be used in order to obtain the enthalpy of formation of the metastable end-members. Cumulate data will be evaluated and used to re-assess the ternary system.References[1] J. Y. Lee, J. H. Kim, et H. M. Lee, « Effect of Mo and Nb on the phase equilibrium of the Ti-Cr-V ternary system in the non-burning β-Ti alloy region », J. Alloys Compd., vol. 297, n 1, p. 231-239, févr. 2000, doi: 10.1016/S0925-8388(99)00557-5.[2] B. Hu, J. Wang, C. Wang, Y. Du, et J. Zhu, « CALPHAD-type thermodynamic assessment of the Ti-Mo-Cr-V quaternary system », Calphad, vol. 55, p. 103-112, déc. 2016, doi: 10.1016/j.calphad.2016.08.003.[3] R. Elliott, B. Levinger, et W. Rostoker, « System Titanium-Chromium-Molybdenum », Trans. Am. Inst. Min. Metall. Eng., vol. 197, n 11, p. 1544-1548, 1953.[4] N. B. Grum-Grzhimaylo et V. G. Gromova, « Phase diagram of the Ti-Cr-Mo-system at 1200, 900 and 600°C », Akad Nauk SSSR, vol. 7, p. 35-42, 1962.

Slow strain rate tensile tests (SSRT) and oxidation tests were performed on a 316L stainless steel in Pressurized Water Reactors (PWR) primary water. The tests were performed under transient conditions (hydrogenated-oxygenated water cycling). The present results indicate stress corrosion cracking (SCC) susceptibility dependence of SSRT samples on cumulated time exposure to hydrogenated water. After short-time exposure under hydrogenated conditions, most of the crack-like defects are shorter than 2 µm and crack mean depth is around 5 µm. In contrast, after long-time exposure, most SCC crack-like defects are longer than 2 µm and the crack mean depth increases linearly with the cumulated time spent under hydrogenated conditions.

International audience; Molten corium is considered to form in a severe accident at the Fukushima Daiichi Nuclear Power Station (FDNPS). Investigation of the primary containment vessel (PCV) inside at the FDNPS showed that a significant amount of the molten corium reached the bottom of the pedestal region. The molten corium and concrete likely caused a complex interaction called Molten Corium Concrete Interaction (MCCI). Then, ex-vessel debris was formed after the solidification of the MCCI products and accumulated in the pedestal region. The solidification hysteresis of ex-vessel debris significantly influences its properties. Although many studies on the MCCI behavior were previously carried out, the solidification path analysis was hardly attempted. We performed a thermodynamic analysis using the TAF-ID database to infer the solidification path of U-Zr-Al-Ca-Si-O molten corium, which was chosen for a prototypic system of ex-vessel debris. The solidification path for the CaO-rich sim-corium showed the following sequence: (i) melting as a single liquid phase at temperatures higher than 2430 K, (ii) selective solidification of the oxide-rich corium mainly consisted of fuel materials, and (iii) solidification of the remaining materials as a silicate matrix. In contrast, the solidification path for the SiO2-rich corium indicated that (i) formation of liquid miscibility gap above 2200 K, (ii) individual precipitation of solid phases in each liquid phase. Identified features of these solidification paths were in good agreement with the experimental data for the solidified sim-corium.

Under irradiation, the formation of fission products in the (U,Pu)O2 fuel with time has a substantial effect on its chemistry. In particular, migration of the most volatile fission products (Cs, Te, I, Mo) from the center to the periphery of the fuel pellet is induced by the large radial thermal gradient. To predict the thermodynamic properties of the irradiated fuel, thermodynamic modeling of the complex multi-component (Cs-I-Te-Mo)–(U-Pu)–O system is performed using the CALPHAD method. In this work, the thermodynamic assessment of the U–Te sub-system is performed. The literature review reveals a lack of experimental data as well as scattering and inconsistency of some of the data. In particular, no thermodynamic data exist on the liquid. From this review, input thermodynamic and phase diagram data are carefully selected. The Gibbs energy functions are then adjusted by fitting these data. An overall good agreement is obtained with all the selected data except for the enthalpy of formation for UTe which is underestimated by 13% by our model. This could be due to an inconsistency between the enthalpy of formation and vapor pressure data. In a second step, the uncertainties on the thermodynamic parameters and their propagation on the calculated thermodynamic and phase diagram data are estimated using a Bayesian approach. The analysis shows that there are too many parameters (22) for too few data points (120 points). The uncertainties are thus large on some of the calculated data. Moreover the inconsistency of some of the data and the lack of thermodynamic data for the liquid makes the model uncertain. New experimental data such as heat capacity, enthalpy of formation for the compounds, and chemical potentials or activities for the liquid phase would improve the reliability of our model. Measurements of phase diagram data in the U–UTe2 region are also required. However this work provides the first detailed uncertainty analysis of the U–Te CALPHAD model. Moreover our approach, contrary to other Bayesian methods, provides an analytical posterior probability distribution and analytical credible intervals for the calculated thermodynamic quantities. It also speeds up the simulation of the uncertainty estimations on the phase diagram.

International audience; Molecular dynamics simulations of microstructural evolution under irradiation of (U,Pu)O2 solid solutions have been carried out with the Frenkel pair accumulation method with two empirical potentials. Simulated X-Ray diffraction patterns have been systematically generated along the irradiation pathway from the computed atomistic configurations. Description of the X-Ray diffraction patterns with increasing irradiation dose is discussed. Attempt to correlate the features of the X-Ray diffraction peaks with the microstructural evolution is also provided. Special attention is dedicated to the swelling effect.

International audience; Precipitation of radial hydrides in zirconium-based cladding concomitant with the cooling of spent nuclear fuel can potentially compromise cladding integrity during its subsequent handling and transportation. Complementary experimental programs on unirradiated and irradiated cladding were performed to assess the conditions leading to the precipitation of radial hydrides and their detrimental effects on mechanical properties. This sequel paper to a previous publication [1] presents results for cold-worked, stress-relieved Zircaloy-4 and ZirloTM cladding used in pressurized water reactors. Cold-worked, stress-relieved Zircaloy-4 and ZirloTM behave very similarly, although irradiated ZirloTM was found to be slightly more prone to hydride reorientation (HRO) than irradiated Zircaloy-4. No distinct irradiation-induced effect on the HRO critical stress was detected. Depending on the initial high temperature that varied from 350 to 450 °C, HRO may cause a ductile-to-brittle transition when the cladding hoop stress, created by internal pressurization of the specimen, ranges from 70 MPa to 120 MPa. Cracking of the oxide layer caused local preferential radial hydride precipitation. The impact of the decreasing temperature and internal pressure during cool-down was also investigated: it has been found that samples undergoing decreasing temperature and pressure cycles are less prone to hydride reorientation.

Euratom Research and Training in 2022: the Awards collection; International audience; CHICADE (CHimie CAractérisation DEchets – Chemistry CAracterization Wastes) is one of the nuclear facilities of the Energy Division of the French Alternative Energies and Atomic Energy Commission (CEA/DES). The CEA/DES is responsible for structuring and piloting the research programmes on energy at CEA. It involves its own institutes of research and those of other divisions. CHICADE is part of the Directorate for Nuclear Dismantling, Services and Waste Management. The Laboratory of Expertise and Destructive characterization is set up in the Basic Nuclear Facility – N° 156 called “CHICADE” where heavy equipment is used. The laboratory brings together both skills and means of characterization, using destructive methods on nuclear waste packages. It also carries out measurements on the whole waste package (gas release measurements, leaching tests). After a short presentation of the CEA and the Cadarache Centre, this publication aims to present the CHICADE facility and present the types of expertise on nuclear waste that are conducted there, i.e., measurement of the diffusion coefficient, inventories, leaching test, permeability measurement, gas measurements, radiochemistry, imaging. In conclusion, CHICADE is a nuclear facility with unique equipment, allowing exhaustive expertise to be carried out in a single location, benefiting from cross and complementary methods.

International audience; Radiation damage in materials is a space and time multi-scale process, ranging from the atomic scale up to the macroscopic scale, and from the femtosecond up to several years. The prediction of the long term evolution of materials subjected to radiative environments (in the nuclear or in the space industry, as well as in the field of microelectronics) therefore requires the combination of several simulation and experimental techniques able to cover the different space and time scales involved. X-ray diffraction (XRD) is highly sensitive to atomic displacements while probing macroscopic volumes of material. In this respect it is perfectly suited for the study of radiation damage. In this work it is shown how XRD can be quantitatively and qualitatively used in combination with numerical simulations, like molecular dynamics and rate-equation cluster dynamics, to analyze damage build-up in irradiated SiC and ZrC single crystals. Particular emphasis is laid on the methodological aspects of XRD data treatment in order to extract parameters such as damage-induced strain and disorder.

International audience; In the frame of severe accident studies, the overheated nuclear MOX fuel may interact with the steel alloy cladding leading to the formation of a liquid phase at temperature well below the melting temperature of the fuel itself. Moreover, the presence of a miscibility gap in the liquid phase in the U-O, Pu-O and Fe-O binary sub-systems that extends in the U-Fe-O, Pu-Fe-O and U-Pu-O ternary systems may induce an accumulation of fissile elements in a specific region of the damaged reactor, with the risk of re-criticality. This work reports the experimental results obtained at JRC on the PuO2-Fe3O4 system (liquidus and solidus) and at CEA on the Fe-U-O system (miscibility gap in the liquid phase). The JRC laser heating setup was improved to account for oxygen potential effects on liquidus/solidus transitions. At CEA, a novel experimental setup was developed to obtain new data in the Fe-U-O liquid miscibility gap.These experimental results have been used to check on the quality of the existing thermodynamic description of the Fe-U-O system and to assess the thermodynamic model of the Pu-Fe-O system using the CALPHAD method. Thermodynamic calculation performed using the U-Pu-Fe-O thermodynamic database will allow to predict the formation of the liquid phases during a severe accident.

International audience; Red lead and lead white are some of the most ancient and common pigments in mural paintings. However, they tend to blacken with time due to their oxidation to plattnerite (β-PbO2). The possibility to induce the reconversion reactions by CW laser heating is hereby discussed. A thermodynamic study by TGA showed that direct cerussite or hydrocerussite formation from plattnerite are not suitable reconversion routes, which was confirmed by laser irradiation trials under CO2 and CO2/H2O fluxes. Minium (Pb3O4) and subsequent massicot (β-PbO) formation from plattnerite were achieved (confirmed by SEM-EDS, XRD and micro-Raman) under Ar + , 810 nm diode and Nd:YAG lasers. The latter appears to be the most suited for restauration purposes, given the broad minium reconversion irradiance range. This is confirmed by successful trials on macroscopic areas of naturally darkened red lead containing samples.

International audience; The relaxation volume ( rel), here determined per extra-atom or vacant site, of common crystalline defects in bcc iron (Fe) was calculated from molecular dynamics simulation (MD) cells containing defects of varying size and/or density. To this end, we used both real and reciprocal space data: for the former, the change in the MD cell volume was calculated, while for the latter, we computed X-ray diffraction reciprocal space maps to evaluate the change in the lattice parameter. We show that dumbbell self-interstitial atoms have the largest  rel , ~1.5 atomic volume (~1.5 0). C15 clusters of size 12 and 48 atoms show  rel of ~0.91 0 and ~0.98 0, respectively, and similar values are found for ½ and interstitial dislocation loops, with  rel ~0.905 0 and  rel ~0.873 0, respectively. Single vacancies are characterized by a negative  rel , ~-0.11 0. For cavities,  rel rapidly increases to approach zero as the clusters grow. Using these values, we managed to predict (with an accuracy better than 2 %) the lattice strain in MD cells containing several types of defects, which indicates that the relaxation volumes can be summed up to estimate the microscopic (i.e., lattice) volume change.

International audience; Some AX2 binary compounds with the fluorite structure (space group Fm-3m) are well-known examples of materials exhibiting transitions to ionic superconducting phases at high temperatures but below their melting points. This transition is characterised by lambda-shaped peaks in constant-volume heat capacity and linear thermal expansion coefficients , as well as more gradual changes in enthalpy and entropy.The high-temperature superionic states have been described before as either highly defective crystals or part-crystal, part-liquid states where the A ions retain their crystalline order whilst the B ions undergo partial melting. However, no detailed description of the structure of these phases exists.We present here the results of our investigation of the structural changes that occur during superionic transitions and the structural characteristics of the resulting superionic materials. This work is based on atomic-scale molecular dynamics modelling methods as well as computational diffraction techniques. We employed a set of empirical potentials representing several compounds with the fluorite structure to investigate any potential-dependent effect.We show the limitations of our current understanding of the superionic transition in fluorites, as well as the importance of small-scale structure changes and how they are crucial to explain the thermodynamical properties of these materials at high temperatures.

International audience; This paper describes air pressure, relative humidity (RH), temperature and oxygen molar fraction (xO$_2$) measurements that have been carried out over several years in a hundred meter long and 75 centimeters diameter micro-tunnel (MT) at the Andra Meuse/Haute-Marne underground research laboratory (MHM URL). Sensors were placed all along, every twenty meters inside the MT, and in the access drift. RH and xO$_2$ time evolutions exhibit very complicated profiles, showing many singularities. These features can be well explained by taking into account mainly the corrosion of the steel casings, the water evaporation from the surrounding saturated clay and a leak between the head of the MT excavation and the access drift. Airflow through the leak is driven by the drift pressure seasonal and short time fluctuations. A simple model involving coupled infinite and finite reservoirs made it possible to reproduce xO$_2$ evolution and to calculate the air fluxes associated. Drift pressure variations induce longitudinal compression-dilatation processes in the system that are closely estimated using suitable analytical formulas. By taking into account diffusion driven leaks at the casings interfaces, it was possible to build a global model from which the results compare very well with experimental data.

International audience; Stress corrosion cracking is a well-known phenomenon in oxide glasses. However, how amorphous phase separation (APS) alters stress corrosion cracking, and the overall mechanical response of an oxide glass is less known in literature. APS is a dominant feature concerning many multicomponent systems, particularly the ternary sodium borosilicate (SBN) glass systems. Its three constituent oxides have significant industrial relevance, as they are the principal components of many industrial oxide glasses. Simulations and experimental studies demonstrate the existence of a two-phase metastable miscibility gap. Furthermore, theory suggests the possibility of three-phase APS in these oxide glasses. Literature already details the mechanisms of phase separation and characterizes SBN microstructures. Realizing that glasses are structurally sensitive materials opens a number of other questions concerning how the mesoscopic APS affects the continuum behavior of glasses, including dynamic fracture and stress corrosion cracking. This paper reviews current literature and provides a synthetic viewpoint on how APS structures of oxide glasses alter physical, mechanical, dynamic fracture, and stress corrosion cracking properties

International audience; Ultra-fast diffusion rates were largely reported in ultrafine-grained (UFG) materials procuded by severe plastic deformation (SPD) and were explained by the formation of specific non-relaxed high-angle "deformation-modified" grain boundaries exhibiting an increased free energy density, higher diffusion rates and a significant residual microstrain [1]. The increase of the grain boundary (GB) diffusion coefficients accounts for one to several orders of magnitude with respect to relaxed interfaces with similar misorientation characteristics [1]. In this work, using both radiotracer and SIMS techniques [2] Cr diffusion in UFG Ni was investigated at low temperatures ranging from 403 to 603 K and a whole spectrum of possible grain boundary states was addressed. The combination of the two methods provided unprecedented insights into structure properties relationships in severely deformed Ni. Abnormally high diffusion rates of Cr are measured and the presence of the deformation-modified state of a fraction of the high-angle GBs is verified. For the first time, a co-existence of relaxed and deformation-modified high-angle GBs in UFG Ni is unambiguously established, addressing the different interfaces by different techniques on the same samples. The temperature/time evolution of the deformation-modified state of high-angle GBs is followed by dedicated measurements of the atomic transport and the microstructure characteristics. The combination of the two complementary techniques allows a unique cross-scale multi-level characterization of the grain boundary diffusion properties spread over a large number of orders of magnitude in the same material.References[1] X. Sauvage, G. Wilde, S.V. Divinski, Z. Horita, R.Z. Valiev, Materials Science and Engineering: A. 540 (2012) pp. 1-12. [2] D. Gärtner, L. Belkacemi, V.A. Esin, F. Jomard, A.A. Fedotov, J. Schell, J.V. Osinskaya, A.V. Pokoev, C. Duhamel, A. Paul, S.V. Divinski, Diffusion Foundations. 29 (2021) pp. 31-73.

International audience

RAPPORT CEA-R-6580; Natural and complex, the corrosion phenomenon is an industrial problem that can take various forms, ranging from a simple loss of uniform material to more complex aspects. In atmospheric corrosion, the presence of pollutants plays a key role in the corrosion phenomenon, particularly chloride-based pollutants. If, in the first place, we think of the seaside with the presence of sodium chloride NaCl, chloride ions are also widely used in industry. What makes the difference is the cation with which the anion is associated. The objective of the study is to understand the corrosion phenomenathat can appear when a material is exposed to a humid environment in the presence of chlorinated pollutants such as HCl or NaCl. If corrosion phenomena are at the heart of the problem, the study of the electrolyte is an essential point. From its creation to its disappearance, including its finite size, the electrolyte plays a key role in atmospheric corrosion phenomena because its presence ensures the transport of ionic species, and therefore of current. This HDR shows how factors inherent in the medium such as aeration, acidity, or salinity of the medium, can influence the course of electrochemical processes ; and how external parameters such as temperature or hydrodynamics of the solution can also be a source of significant variations in corrosion phenomena.; Naturel et complexe, le phénomène de corrosion est un problème industriel pouvant revêtir des formes variées allant d’une simple perte de matière uniforme à des aspects plus complexes. En corrosion atmosphérique, la présence de polluants joue un rôle clé dans le phénomène de corrosion et particulièrement les polluants à base de chlorures. Si en tout premier lieu, on pense au bord de mer avec la présence de chlorure de sodium NaCl, les ions chlorures sont aussi très utilisés dans l’industrie. Ce qui fait la différence c’est le cation avec lequel l’anion est associé. L’objectif de l’étude est de comprendre les phénomènes de corrosion qui peuvent apparaître lorsqu’un matériau est exposé à un environnement humide en présence de polluants chlorurés tels que HCl ou NaCl. Si les phénomènes de corrosion sont au coeur de la problématique, l’étude de l’électrolyte est un point essentiel. De sa création à sa disparition en passant par sa taille finie, l’électrolyte joue un rôle clé dans les phénomènes de corrosion atmosphérique car sa présence assure le transport des espèces ioniques, et donc du courant. Cette Habilitation à Diriger des Recherches (HDR) montre comment des facteurs inhérents au milieu comme l’aération, l’acidité, ou la salinité du milieu, peuvent influer le déroulement des processus électrochimiques ; et comment les paramètres externes tels que la température ou l’hydrodynamique de la solution peuvent également être une source de variations importantes des phénomènes de corrosion.

The Nuclear Energy Agency (NEA) Expert Group on Innovative Structural Materials (EGISM) was established in 2008 under the guidance of the Nuclear Science Committee (NSC). Its objectives are to conduct joint and comparative studies to support the development, selection and characterisation of innovative structural materials that can be implemented in advanced nuclear fuel cycles, under long service lifetime and extreme conditions, such as high temperature, high dose/dose rate and corrosive chemical environments. In this context of growing interest and initiatives, the EGISM initiated at the beginning of 2018 an activity among its members to: • Identify, in a non-exhaustive way, the currently existing programs on innovative materials and fabrication processes in NEA member countries and China; • Establish a first cartography of the activities that are underway on these topics and identify common subjects and thematic; • Propose a Technology Readiness Level scale to estimate the maturity of both innovative materials and fabrication processes; • Carry out a reflection on what the enablers are to quickly climb this TRL scale, as well as the obstacles, in order to identify solutions to overcome them. This paper first gives definitions shared between the EGISM members on what are considered as advanced structural materials solutions. Next, some international initiatives for the accelerated development of high performance materials are presented both in non-nuclear and nuclear fields. Then, the methodology adopted for technology readiness assessment is explained. A non-exhaustive synthesis of the projects identified among the EGISM members on innovative structural materials and advanced manufacturing solutions such as additive manufacturing is presented. The TRL level of these projects is evaluated. A focus is also made on some of these projects to illustrate and explain the TRLs chosen as well as highlighting enablers or obstacles identified to climbing up the TRL scale.

International audience; 316L austenitic stainless steel was carburized in sodium containing a high-carbon activity at two different temperatures, 500 °C and 600 °C for 1000 h. The carbon profile, carbide mass fraction and residual stress tensor profile were determined using electron probe microanalysis and high-energy X-ray diffraction. The carbon profile and carbides mass fractions were also predicted using a thermodynamic and kinetic modeling tool (DICTRA). At 600 °C, the experimental results and predictions suggested that the carbon absorbed by the sample was mainly trapped to form M23C6 and M7C3 carbides. The residual stress profile in austenite was strongly dependent on the M23C6 precipitation and the induced modification of the substrate chemical composition. At 500 °C, results and predictions suggested that the carbon was mainly dissolved in austenite. The residual stress profile was governed by the formation of expanded austenite at the sample surface.

International audience; Under normal operating conditions in PWRs, the external surface of the zirconium alloys cladding is oxidized, process during which the alloy absorbs a fraction of the hydrogen produced by water reduction. During the transport of spent fuel, hydrogen may desorb from the cladding, which implies safety concerns. The aim of the present study is to identify and quantify the rate-limiting step in the desorption process of hydrogen initially present in the alloys. To better understand the desorption process, the Thermal Desorption Spectrometry (TDS) was extensively used in association with X-ray Photoelectron Spectroscopy analyses. The TDS results were analyzed thanks to simulations by finite elements (F.E.) using the Cast3M code and the optimization of the kinetic constants of hydrogen desorption has been performed with URANIE tool developed at CEA. Results showed the hydrogen desorption kinetics from the metal is limited by the surface molecular recombination. Arrhenius-type temperature dependence of rate constants allowed to simulate with a good agreement experimental data. The optimized activation energy and the pre-exponential factor for desorption processes were in the range of 290 ± 10 kJ.mol-1 and exp(23 ± 1) m.s-1 respectively.

Lead carbonates were used as cosmetic and pigment since Antiquity. The pigment, known as lead white, was generally composed of cerussite and hydrocerussite. Unlike most ancient pigments, lead white was obtained by a synthetic route involving metallic lead, vinegar and organic matter. Fermentation of organic matter produces heat and CO2 emission, leading to the formation of carbonates. As lead white is formed by trapping CO2, radiocarbon (14C) dating can thus be considered. We have developed a protocol to prepare lead white. We selected modern pigments for the experiment implementation and ancient cosmetic and paintings for dating. After characterization of the samples by XRD, thermal decomposition of cerussite at various temperatures was explored in order to select the appropriate conditions for painting samples. CO2 extraction yield, SEM and XPS were used to characterize the process. Thermal decomposition at 400°C was successfully applied to mixtures of lead white with other paint components (oil as binder, calcite as filler/extender) and to historical samples. We obtained radiocarbon measurements in agreement with the expected dates, demonstrating that thermal decomposition at 400°C is efficient for a selective decomposition of lead white and that paintings can be directly 14C-dated by dating lead white pigment.