Molten salt setup analysis

International audienceThe CEA is developing safer and more modular next-generation reactors. Among the diversity of new reactors considered, there is a family that would use molten salts as coolant (MSR). This solution offers many advantages but requires solving some problems related to the corrosion of metals by salts.The corrosion study can be quite long and would be considerably accelerated if an in-situ measurement of the chemical composition of the salts was available. Because LIBS technic is an all optical sensor, it would make it possible to achieve this. However, the constraints related to temperature, inertness of the salts, narrowness of access make accessibility non-trivial. The work will present the optical study that has been done as well as the stability study of the signal obtained with the selected setup on a simulating liquid medium

Electrochemical behavior of plutonium in nitric acid media

International audienceThe first step of the spent nuclear fuel reprocessing is a dissolution of actinides and fission products in hot nitric acid at high concentration. Among all these species, the knowledge of redox plutonium equilibria with discerning between their oxidation states is essential to understand and depended on many chemical conditions. Nevertheless, the knowledge of speciation in this media is a challenge especially for a better understanding of corrosion mechanism in the dissolution medium. Thus this paper proposes to determine the electrochemical behaviour of plutonium and especially the Pu(IV)/Pu(III), Pu(VI)/Pu(V) and Pu(V)/Pu(IV) redox couple in nitric acid media and acquire thermodynamic and kinetic constants at higher temperatures than 25C and higher nitric concentration than 1 mol L−1

Pêcher, préparer et consommer les ressources animales de l’estran et au-delà

National audienceSince prehistoric times, coastal populations exploited animal resources from the seashore. They are found alive or dead in the tide marks; or at low tide in the emerged areas. Thus, the archaeozoologist is confronted with a variety of possible acquisition techniques that he can sometimes describe through a detailed analysis of the parts of the animal skeletal discovered in an archaeological context. For each period of our history, the archaeozoologist adapts his expertise according to the socio-economic systems of human populations. While some exploitations of these animal resources remain local, others are linked to exportation as soon as they are acquired. Whether they are shellfish or fish, some of these resources will leave the shoreline after they have been processed. These high value-added products play an important role in the coastal economic fabric. Thus, thanks to these activities, the coastline becomes sometimes an export platform. Other materials of animal origin, such as empty shells or marine mammal bones collected from sometimes distant beaches, will be used to make decor or means of expression to allow some people to display their status. Thus, the possible thematic developments in archaeology, based on the animal resources provided by the seashore, are varied. However, they remain very dependent on the requirements and techniques of excavation.Dès la préhistoire, les populations littorales ont su exploiter les ressources animales provenant de l’estran. Elles sont trouvées vivantes ou mortes dans les laisses de haute mer ou à chaque marée basse dans les zones émergées. Ainsi, l’archéozoologue est confronté à une diversité de techniques d’acquisitions qu’il peut parfois décrire grâce à l’analyse fine des parties squelettiques animales découvertes en contexte archéologique. Pour chaque période de notre histoire, l’archéozoologue adapte son expertise en fonction des systèmes socio-économiques des populations humaines concernées. Si certaines exploitations de ces ressources restent locales, d’autres sont destinées dès leur acquisition à l’exportation. Qu’elles consistent en coquillages ou en poissons, certaines de ces ressources quitteront le littoral après avoir été transformées en produits de haute valeur ajoutée. Leur place non négligeable dans le tissu économique côtier fait parfois du littoral une véritable plateforme d’exportation. D’autres matières animales, comme les coquilles vides ou des ossements de mammifères marins ramassés sur des plages parfois lointaines, permettront à certaines personnes d’afficher leur statut par des parures ou même des décors d’habitats. Ainsi, les développements thématiques possibles en archéologie, à partir des ressources animales fournies par les estrans, sont variés. Ils restent cependant très dépendants des prescriptions et des techniques de fouille

Redox Potential Evolution of Nitric Species and Plutonium in HNO3

International audienceIn France, the reprocessing process of spent fuel is carried out using the Purex process. The first chemical step of this process is the dissolution of the spent fuel in aqueous concentrated nitric acid. This dissolution solution is composed of many oxidizing species and it is necessary to understand the chemistry of these species to apprehend the behavior of structural materials. The redox potential is a useful discriminate variable to differentiate the effect of each species. In this framework, only the effect of NO 3-/HNO 2 couple and PuO 2 2+ /Pu 4+ couple were investigated. These species were chosen because one is the main couple of medium and the other has a high standard potential. Their influence was investigated from the Nernst's equation

Dans les Limbes du corps : du golem au robot et retour

Gruet Brice, Berque Augustin, Boutry-Stadelmann Britta, Frogneux Nathalie, Sadami Suzuki. Dans les Limbes du corps : du golem au robot et retour. In: Ebisu, n°40-41, 2008. Actes du colloque de Cerisy. "Être vers la vie. Ontologie, biologie, éthique de l'existence humaine" pp. 165-174

Dissolution and Passivation of a Silicon-Rich Austenitic Stainless Steel during Active-Passive Cycles in Sulfuric and Nitric Acid

International audienceThe high Si containing X1CrNiSi18-15-4 stainless steel (SS) spontaneously forms a protective oxide film that is mostly composed of mixed chromium and silicon oxides. This film ensures a good durability of the industrial facilities the alloy was designed for, containing very acidic electrolytes such as hot and concentrated nitric acid, HNO$_3$ , in presence of oxidizing species. In the present work, the chemistry of the oxide formed and the passivation kinetics of the alloy in sulfuric acid, H$_2$SO$_4$, and for the first time in HNO$_3$ , were monitored by atomic emission spectroelectrochemistry (AESEC) over successive activation and passivation cycles of the material. X1CrNiSi18-15-4 SS was compared to a low Si containing SS, the X2CrNiN18-10 SS. It was found that a similar quantity and rate of passive film was formed during passivation, and dissolved during activation. Reproducible results were obtained over several active-passive cycles. The excess Cr was correlated with the dissolution rate decay during passivation. The Si/Cr ratio of the passive film was determined by X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy (performed using transmission electron microscopy), and AESEC giving similar results within experimental error. The EDX profile suggest that the passive film consists of a Si rich outer and Cr rich inner layer

Effect of the oxidizing power of the medium on intergranular corrosion: influence of diffusion

International audienceThe intergranular corrosion behavior of a stainless steel is studied as a function of the oxidizing power of the medium. It is shown that the evolution of the mass loss and the shape of the intergranular corrosion morphology both vary with the oxidizing power. Electrochemical measurements (corrosion potential monitoring, linear sweep voltammetry, electrochemical impedance spectroscopy) and COMSOL Multiphysics modelling show that these observations are due to a change of limiting step of corrosion. In a moderately oxidizing medium, the limiting step is the dissolution reaction at the stainless steel / solution interface. In a strongly oxidizing medium, the limiting step becomes (at least partially) the diffusion of the oxidizing species in solution towards to stainless steel surface. Consequently, the local concentration of the oxidizing species becomes not any more homogenous all along the surface, especially inside the grooves formed by intergranular corrosion. Thus, the local dissolution rate in the intergranular grooves evolves spatially and temporally, contrary to the case of moderately oxidizing medium

Silicon enrichment of an austenitic stainless steel – Impact on electrochemical behavior in concentrated nitric acid with oxidizing ions

International audienceThe effect of a 3.5 wt % addition of Si on the corrosion resistance of an 18Cr–15Ni stainless steel (SS) in 100 °C nitric acid, HNO3 was investigated using transmission electron spectroscopy, X-ray photoelectrons spectroscopy, linear scan voltammetry and electrochemical impedance spectroscopy. The X1CrNiSi18-15-4 SS was compared to the X2CrNiN18-10 SS in various types of conditions: pure concentrated HNO$_3$ with or without oxidizing species (V(V) and Cr(VI)). In pure HNO$_3$, both SS are passive and the X1CrNiSi18-15-4 SS dissolves spontaneously faster than the X2CrNiN18-10 SS. The addition of oxidizing species V(V) or Cr(VI) in the electrolyte leads to the opposite result: the X1CrNiSi18-15-4 SS remains in the passive state, whereas the 18Cr–10Ni SS is polarized in the transpassive state. As a consequence, the X1CrNiSi18-15-4 SS corrodes slower than the X2CrNiN18-10 SS. All these observations demonstrate that the presence of Si in the oxide film slightly deteriorates the passivity of the SS but also moderates the reduction processes. It keeps the corrosion potential of the X1CrNiSi18-15-4 SS low enough for the alloy to remain passive even if oxidizing species are present in the electrolyte. A specific impact of the addition of Cr(VI) is also shown, as Cr(VI) seems to play a role on both cathodic and anodic processes, whereas V(V) mainly impacts the cathodic kinetics

A step towards a better understanding of corrosion of zirconium in nitric acid with additions of fluorine: focus on the role of the presence of an initial oxide film

International audienceThe presence of fluorine is known to drastically reduce the corrosion resistance of zirconium in nitric acid. Nevertheless corrosion processes involved for this system appear controversial, especially concerning the role played by the initial oxide film (ZrO2) that can naturally be formed in nitric acid. To study the contribution of the initial oxide film, zirconium samples were pre-oxidized in several ways so as to obtain different thicknesses of the initial oxide film. Then, the corrosion evolution of these samples was studied in nitric acid with fluorine additions. It appears that the initial oxide film present on surface plays a protective role for corrosion. But as the oxide film slowly dissolves, this protective role may only be transitory (depending on the thickness of the initial oxide film). When the oxide film has been sufficiently dissolved, it breaks by a process of initiation, growth and coalescence of pits. Zirconium is then directly attacked by fluorine and its corrosion rate increases largely. After the complete vanishing of the initial oxide film, corrosion becomes uniform and the corrosion rate decreases slowly: the corrosion process is limited by the diffusion and the consumption of fluorine