Carburization of austenitic and ferritic steels in carbon-saturated sodium: preliminary results on the diffusion coefficient of carbon at 873 K

Three commercial steels were exposed to carbon-saturated sodium at 873 K for durations up to 5000 h. Analyses by optical microscopy, infrared-inductive carbon combustion, electron probe microanalysis and glow discharge optical emission spectrometry revealed important carburization of the steels. The carbon concentration at the metal–sodium interface reached equilibrium, and the carbon uptake varied with the square root of time. The carburization kinetics was well described by assuming that diffusion of carbon was coupled with rapid carbide precipitation and equilibrium partitioning of carbon between the metal and precipitates phases

Chemical Interaction of Austenitic and Ferritic Steels with B4C Powder in Liquid Sodium at 600°C

In the framework of studies on the control rods’ lifetime for Sodium Fast Reactor, three commercial steels were exposed to B4C powder in liquid sodium at 600°C for durations up to 3,000 h. Analyses by optical and secondary electron microscopy, x-ray diffraction, electron microprobe, and glow discharge optical emission spectrometry revealed the formation of boride layers at the surface of the steels and slight carburization underneath. The growth of the boride layers followed parabolic kinetics. The nature of the formed boride layers was in good agreement with thermodynamic equilibrium predicted by software. The carburization depths were much lower than the ones obtained in carburizing liquid sodium at 600°C. Finally, the carbon penetration depth did not grow with time revealing a transient carburization phenomenon and possible protective character of the boride layers against carbon penetration

Corrosion mechanism of a Ni-based alloy in supercritical water: Impact of surface plastic deformation

Ni–Fe–Cr alloys are expected to be a candidate material for the generation IV nuclear reactors that use supercritical water at temperatures up to 600 °C and pressures of 25 MPa. The corrosion resistance of Alloy 690 in these extreme conditions was studied considering the surface finish of the alloy. The oxide scale could suffer from dissolution or from internal oxidation. The presence of a work-hardened zone reveals the competition between the selective oxidation of chromium with respect to the oxidation of nickel and iron. Finally, corrosion mechanisms for Ni based alloys are proposed considering the effects of plastically deformed surfaces and the dissolution

Corrosion mechanisms of 316L stainless steel in supercritical water: The significant effect of work hardening induced by surface finishes

The oxidation of 316 L stainless steel in hydrogenated supercritical water at 600 °C is strongly dependent on the effects of work hardening induced by surface finishes. The oxide scale formed under these conditions is always double-layered with an external layer of Fe-rich oxides. However, when a hardening threshold is reached, a switch in oxidation mechanisms leads to a considerable thinning of the oxide scale. This thinning results from the formation of a Cr-rich internal oxide layer that acts as a diffusion barrier against ionic species responsible for its growth but also against Fe cations implied in the external layer growth

Taxonomic units, civilization, volcanism: Their influence on the chemical composition of ostracod carapaces (Kagoshima Bay, Kyushu Island, Japan)

International audienceTo test the influence of both civilization and volcanism on the chemical composition of ostracod carapaces, 32 wellpreserved valves from Kagoshima Bay (Kyushu Island, South Japan) were analysed by means of spark source mass spectrometry. In Kagoshima Bay, the extent of pollution corresponds to human activities. Kagoshima Bay is also an area of important volcanic activity: emissions from Sakurajima volcano are very frequent. The species analysed were Argilloecia hanaii , Callistocythere undulatifacialis , Pontocythere subjaponica and Loxoconcha tosaensis . Twenty-three chemical elements were detected. Among them, 11 were always above the limit of detection: Al, B, Cl, F, Fe, K, Na, P, S, Si and Zn. The correlation between Zn and Fe was characteristic of the volcanic environment. Two discriminant analyses were performed using either the location area or the species as grouping variables. An association between Zn and S is possible; it could be related to volcanic activity. The chemical composition of carapaces is ascribed to taxonomic units rather than the environment

Alternative dissolution and oxidation behavior of 316LN steel at 550°C in liquid sodium containing low concentration of oxygen

International audienc

Growth of micrometric oxide layers for the study of metallic surfaces decontamination by laser

The nuclear industry produces a wide range of radioactive waste in term of level of hazard, contaminants and material. For metallic equipment like steam generators, the radioactivity is mainly located in the oxide surface. In order to study and develop techniques for dismantling and for decontamination in a safe way, it is important to have access to oxide layers with a representative distribution of non-radioactive contaminants. We propose a method of formation of oxide layer on stainless steel 304L with europium (Eu) as contaminant marker. In this method, an Eu-solution is sprayed on the stainless steel samples. The specimen are firstly treated with a pulsed nanosecond laser and secondly the steel samples are exposed to a 600°C furnace for various durations in order to grow an oxide layer. The oxide structure and in-depth distribution of Eu in the oxide layer are analysed by scanning electron microscopy coupled with energy dispersive X-ray microanalyzer, and by glow discharge optical emission or mass spectrometry. The oxide layers were grown to thicknesses in the range of 200 nm to 4.5 μm regarding to the laser treatment parameters and the heating duration. These contaminated oxides have a ‘duplex structure’ with a mean weight percentage of 0.5% of europium in the volume of the oxide layer. It appears that europium implementation prevents the oxide growth by furnace but has no impact on laser heating. These oxide layers are used to study the decontamination of metallic surfaces such as stainless steel 304L using a nanosecond pulsed laser

Oxidation of 316L(N) stainless steel in liquid sodium

International audienc