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International audience; In the core of a nuclear reactor, irradiation defects created by the fast neutron flux can have a detrimental effect on the corrosion of aluminium alloys. In order to better understand the effect of irradiation on aluminium corrosion, a hydroxide obtained by corrosion of an Al-Mg-Si alloy is irradiated with Al ions. The damage created is 2.5 dpa (displacement per atom) on average in the aluminium hydroxide (Stopping and Range of Ions in Matter (SRIM) calculation). The ion irradiation seems to cause an amorphization of the hydroxide. Voids and nano-crystallites can also be observed.After re-corrosion of the irradiated hydroxide, an increase of the thickness of the oxide layer can be observed compared to the non-irradiated oxide.

International audience; As many components of the core of water-cooled nuclear research reactors (NRR) are composed of aluminium alloys, the corrosion study of these alloys is important for their safe and efficient operation. In particular, in the reactor core, irradiation defects created by the rapid neutron flux can have a detrimental effect on corrosion of aluminium alloys increasing thickness of corrosion layers.In order to better understand the effect of irradiation defects on aluminium corrosion, a hydroxide obtained by corrosion of an Al-Mg-Si alloy is irradiated with Al ions at the JANNuS facility at CEA (French Atomic Energy Commission) of Saclay. Al ions with successive energies of 1.2 and 5 MeV are used in order to have a homogenous damage profile in the hydroxide. A TRIM calculation indicates the damage is on average 2.5 dpa (displacement per atom) in the aluminium hydroxide. Various characterization techniques are used to study the impact of ion-irradiation on morphology and crystallography of the aluminum hydroxide. Before ion irradiation, grazing incidence X-ray diffraction and Raman analysis indicate the corrosion product are composed of bayerite (α-Al(OH3)) and pseudo-boehmite (AlOOH). An observation of the aluminium hydroxide with a Scanning Electron Microscopy (SEM) suggests a hydroxide grain size between 1 and 4 µm. After irradiation, X-rays diffraction indicates bayerite is still present but an amorphization of this crystalline phase can be observed. In addition, an observation of a cross section of the irradiated hydroxide with a Transmission Electron Microscopy (TEM) suggests the irradiated hydroxide contains nano-sized crystallites and bubbles. Identifying the phase of these crystallites and the amorphisation process will enable a better prediction of the expected hydroxide thicknesses in core. The results from this work are compared to those obtained after neutron irradiation in order to assess the relevance of ion-irradiation in understanding corrosion behavior of aluminum components in NRRs.

International audience; Aluminum alloys have been widely used in nuclear research reactors since 1960. Even though many data on their mechanical behavior are available, few studies focus on the understanding of void swelling. Indeed, the density measurements of aluminum samples before and after irradiation allow to assess the total swelling but don't discriminate the contributions of thermal and fast neutrons. In the material testing reactors, the higher fast neutron flux (E>1MeV) is expected to impact the relative contributions to total swelling. Therefore, this study aims to reproduce reactor irradiation conditions using a simultaneous triple beam irradiation to simulate the materials damage observed in aluminum components. Aluminum specimens were irradiated with different ions helium ions, simulating the production of alpha particles inside the reactor, silicon ions to reproduce the aluminum transmutation and tungsten ions to enhance the DPA rate. Using the proper energy and flux conditions, a 200 nm wide area of interest was obtained (figure 1a) and TEM specimens were prepared in this specific zone. TEM examinations show multiple defects and a unique microstructure. A wide area with helium bubbles (figure 1b) is present, thus modifying the initial microstructure (precipitates and dispersoids). Comparing the current results with previous single beam studies using gold ions, we strive to explain and understand the peculiar role of helium and silicon in the void swelling process.

International audience; Austenitic stainless steels are foreseen as cladding and structural materials for future generation IV reactors. However, their swelling under irradiation favored by their Face Centered Cubic (FCC) structure limits their lifetime in reactors and therefore the fuel burn-up. Austenitic steel swelling is a complex phenomenon. It starts with an incubation regime with no macroscopic deformation and is followed by a steady state regime where the swelling rate is about 1%/displacement per atom (dpa). The steel composition does not influence the swelling rate in the steady state regime but thermomechanical treatments, major and minor elements, such as chromium (Cr) and titanium (Ti), play a major role on the incubation dose. In order to increase the incubation time of austenitic steels, it is utmost important to get a better understanding of the mechanisms involved. This study focuses on the effect of Ti and Cr on the microstructure evolution of FCC structure on the incubation period during irradiation. Pure nickel and two binary alloys (Ni-0.4wt%Ti and Ni-0.4wt%Cr) were studied as FCC model alloys of austenitic steels. In a first step, the effect of an addition of Ti or Cr on the nature, size and density of dislocation loops was studied with an ex-situ irradiation experiment on JANNuS-Saclay platform. The samples were irradiated at 450 °C with Ni ions up to 0.5 dpa and characterized by Transmission Electron Microscopy (TEM). Microstructures after irradiation are showed in Fig.1. It suggested that Ti and Cr could delay the transition from Frank loops to perfect loops either by increasing the stacking fault energy or by reducing the defect mobility or the dislocation bias. Therefore, in a second step, the influence of Ti and Cr on the dislocation bias and the loop growth was investigated by electron and ion in-situ experiments at 450°C. Electron irradiations were performed on the High Tension TEM of CEA/SRMA and the Ni ion irradiation on JANNuS-Orsay platform. Results will be presented and discussed during the presentation.

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International audience; Nanostructuration has opened the way for designing materials with improved properties by taking advantage of multiple interfaces providing enhanced local physical properties. In this frame, nanostructured materials are envisioned for nuclear applications owing to severe environmental conditions (radiation, temperature, corrosion…). Here we report a study based on IBA (RBS and NRA) of a nanometric Cr/Ta multilayer coating demonstrating an extremely high radiation tolerance. TEM and X-ray diffraction were also performed to confirm RBS results and reveal crystallographic structures. Multilayer coated samples were firstly submitted to helium ion implantation, and NRA analyses have revealed that optimized geometry can accommodate up to 20 at. % of gas without noticeable damage, implanted atoms being probably stored at the Cr/Ta interfaces. Heavy ion irradiation was also performed at room temperature (RT), mimicking nuclear reactor neutron bombardment. Although we detected the growing upon irradiation of mixing layers at the Cr/Ta interfaces, these newly created layers remain many fold thinner than that produced at a single interface, preserving the initial multilayer arrangement. Currently the study is extended to high temperature irradiation, and preliminary results are encouraging, confirming that the nanometric Cr/Ta multilayer coating can tolerate up to 100 dpa irradiation dose.

International audience; Oxide dispersion strengthened (ODS) steels are promising materials as fuel claddings for future nuclear reactors. Indeed, they exhibit a good swelling resistance under irradiation thanks to their metallic body-centered cubic matrix FeCrW [1]. Beside, their titanium and yttrium nano-oxides dispersion increases their mechanical properties at high temperature [2] and under irradiation [1]. The usual way to produce an ODS material is a high energy milling of powders FeCrWTi and Y2O3 followed by thermo-mechanical treatments. Nevertheless, the process seems to be rather hard to control since the huge variations of mechanical properties observed in the literature.Previously, a new elaboration route inspired of reactive ball milling was developed on a very small milling device (FeCrW+YFe3+Fe2Ti+Fe2O3) where the crucial role of the milling parameters was highlighted [3, 4]. Two powders revealed different after milling remained different despite any post-milling heat treatment [4]. The goal of the actual study is to elaborate hot extruded ODS steels with the new method and determine the influence of milling parameters on the microstructure and the mechanical properties. This study proves the efficiency of the new procedure at large scale to elaborate ODS steels and highlights the role of carbon and nitrogen on the mechanical properties.[1]R.L. Klueh et al., Journal of Nuclear Materials. 341 (2005) 103.[2]T.R. Allen et al., Journal of Nuclear Materials. 375 (2008) 26.[3]M. Brocq et al. , Journal of Nuclear Materials. 409 (2011) 80.[4]M. Laurent-Brocq et al., Acta Mater. 60 (2012) 7150.

The present contribution approaches the theme of international law as a profession by focusing on the relationship between professionals and the(ir) law. It argues that understanding international law as a practice can plausibly articulate how it is both true that professionals make their law and that the law makes its professionals. It places its argument between the twin dangers of intentionalism, which reduces the language of international law to the will of its speakers and, of objectivism, which reifies international law or reduces it to an undistorted mirror image of structural forces. On the one hand, the contribution draws attention to the professionals as agents and speakers. It emphasises the variety of their roles, explores their respective engagement with international law, and it flashes out the drawbacks of intentionalism. On the other hand, it highlights the study of social conditions that influence professionals, and of biographies as a medium to approach these forces. It shows the drawbacks of objectivism. Setting out a road between these two sides with a refined understanding of international practice, then, also helps to better locate the autonomy of international law. The contribution closes with an outlook on the appeal of formalism and a note on the anxieties about inter-disciplinarity.