Laser surface melting of nickel-based alloy reduces nickel release in the primary cooling system of a nuclear power plant

The surface of Ni-based alloy 690 was treated using a sub-microsecond pulsed laser in order to reduce the amount of nickel released when the surface is exposed to the primary cooling system of pressurized water nuclear reactors. A 2D array of laser treatment parameter sets was investigated. The results on sample surfaces was characterized using interferometric microscopy, Scanning Electron Microscopy (SEM), Glow Discharge Optical Emission Spectrometry (GDOES) and X-ray Photoelectron Spectrometry (XPS). The treatment leading to a continuous and defect-free chromine surface having the minimum nickel content over about the first two nanometers and no subsurface chromium depletion was selected for the nickel release test. This selection criterion proved to be very efficient as the total amount of nickel released in a standard qualification test using a simulated primary coolant was reduced, compared to a non-treated surface, by a factor of 7 during the heating phase and by a factor of 3.7 on average over the whole month-long test

Cas de gale sarcoptique chez des renards en Belgique

Eight cases of sarcoptic mange in foxes were reported during summer 2014 (n=3) and winter 2015 (n= 5) in Belgium. All animals came from the same restricted forest zones near urbanized areas and some of them were discovered in private gardens (Forest District of Thuin, Hainaut, Belgium). Three of them were found dead, the others were shot for sanitary reasons. At necropsy, all of them presented large areas of alopecia and extensive skin lesions such as hyperkeratosis and suppurative lacerations. Animals presented poor body condition and some of them were severely emaciated (absence of visceral fat). Mange has profound influences on population since, if untreated, death follows in four to six months. In the present cases, cutaneous scrapings and histopathological examinations were systematically performed. Numerous parasites were observed in skin scrapings and marked dermo-epidermatitis with several parasites was observed in histopathological sections. These results suggest an outbreak of sarcoptic mange in red foxes in a limited area of the country. This is a first record for the country. Furthermore, investigations on lungs and digestive tracts performed on 3 of these foxes revealed they were also infected by parasites transmissible to pets and/or humans: Angiostrongylus vasorum was observed in the respiratory tract of one fox whereas Toxocara canis, Uncinaria stenocephala, Taenia spp. and Echinococcus multilocularis worms were detected in the digestive tract. In conclusion, urban foxes represent a source of parasites of public health and veterinary importance and foxes surveillance should be strengthened in these areas

T Cells Contribute to Tumor Progression by Favoring Pro-Tumoral Properties of Intra-Tumoral Myeloid Cells in a Mouse Model for Spontaneous Melanoma

Tumors affect myelopoeisis and induce the expansion of myeloid cells with immunosuppressive activity. In the MT/ret model of spontaneous metastatic melanoma, myeloid cells are the most abundant tumor infiltrating hematopoietic population and their proportion is highest in the most aggressive cutaneous metastasis. Our data suggest that the tumor microenvironment favors polarization of myeloid cells into type 2 cells characterized by F4/80 expression, a weak capacity to secrete IL-12 and a high production of arginase. Myeloid cells from tumor and spleen of MT/ret mice inhibit T cell proliferation and IFNγ secretion. Interestingly, T cells play a role in type 2 polarization of myeloid cells. Indeed, intra-tumoral myeloid cells from MT/ret mice lacking T cells are not only less suppressive towards T cells than corresponding cells from wild-type MT/ret mice, but they also inhibit more efficiently melanoma cell proliferation. Thus, our data support the existence of a vicious circle, in which T cells may favor cancer development by establishing an environment that is likely to skew myeloid cell immunity toward a tumor promoting response that, in turn, suppresses immune effector cell functions

Contribution à l'étude des propriétés physico-chimiques des surfaces modifiées par traitement laser (application à l'amélioration de la résistance à la corrosion localisée des aciers inoxydables)

Les matériaux métalliques sont utilisés dans des conditions de plus en plus sévères et doivent présenter une parfaite intégrité sur des périodes de plus en plus longues. L objectif de ce travail de thèse est d évaluer le potentiel d'un traitement de refusion laser pour améliorer la résistance à la corrosion d'un acier inoxydable de type 304L ; l utilisation du laser dans le domaine des traitements de surface constituant un procédé en pleine évolution à cause des changements récents dans la technologie des lasers. Dans le cadre de ce travail, le choix du laser s est porté sur un laser nano-impulsionnel à fibre dopée ytterbium dont les caractéristiques permettent la fusion quasi-instantanée sur quelques microns de la surface traitée, immédiatement suivie d'une solidification ultra-rapide avec des vitesses de refroidissement pouvant atteindre 1011 K/s. La combinaison de ces processus favorise l'élimination des défauts surfaciques, la formation de phases hors équilibre, la ségrégation d éléments chimiques et la formation d une nouvelle couche d oxyde dont les propriétés sont gouvernées par les paramètres laser. Afin de les corréler avec la réactivité électrochimique de la surface, l influence de deux paramètres laser sur les propriétés physico-chimiques de la surface a été étudiée : la puissance du laser et le taux de recouvrement des impacts laser. Pour clarifier ces relations, la résistance à la corrosion par piqûration des surfaces traitées a été déterminée par des tests électrochimiques. Pour des paramètres laser spécifiques, le potentiel de piqûration d'un acier inoxydable de type 304L augmente de plus de 500 mV traduisant ainsi une meilleure tenue à la corrosion localisée en milieu chloruré. L interdépendance des différents phénomènes résultant du traitement laser a rendu complexe la hiérarchisation de leur effet sur la sensibilité de l alliage testé. Cependant, il a été montré que la nature de l oxyde thermique formé au cours de la refusion laser et ses défauts sont du premier ordre pour l amorçage des piqûres.Metallic materials are more and more used in severe conditions with particularly strong request for improving their behavior in aggressive environment and especially over long periods. The objective of this PhD work is to estimate the potentiality of a laser surface melting treatment on the improvement of the stainless steel 304L corrosion resistance, surface treatments by laser can be revisited on the basis of a recent change in the laser technology. In the frame of this work, a nano-pulsed laser fiber was chosen : it allows the treated surface to be melted for few microns in depth, followed by an ultra-fast solidification occuring with cooling rates up to 1011 K/s. The combination of these processes leads to the elimination of the surface defects, the formation (trapping) of metastable phases, the segregation of chemical elements and the growth of a new oxide layer which properties are governed by the laser parameters. To correlate these latter to the electrochemical reactivity of the surface, the influence of two laser parameters on the physico-chemical properties of the surface was studied : the laser power and the overlap of the laser impacts. To support this approach, the pitting corrosion resistance of the samples was determined by standard electrochemical tests. For specific laser parameters, the pitting potential of a 304L stainless steel was increased by more than 500 mV corresponding to an important enhancement in localized corrosion resistance in chloride environment. The interdependence of the different phenomena resulting from the laser treatment lead to a quite complex prioritization of their role on the sensibility of the 304L. However, it was demonstrated that the nature of the thermal oxide formed during the laser surface melting and the induced defects are first-order parameters for the initiation of pits.DIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Les matériaux du centre industriel de stockage géologique Cigéo

L'exploitation du centre de stockage Cigéo s'étendra sur une centaine d'années. Durant cette période et bien au-delà de celle-ci - sur plusieurs siècles -, la sûreté de l'installation devra être maintenue et la radioactivité confinée pour protéger l'homme et l'environnement. Des ouvrages aux matrices de conditionnement des déchets, les matériaux forment la clé de voûte du projet. Les travaux de R&D menés depuis plusieurs années par les équipes françaises ont permis de connaître les processus de corrosion des aciers et d'identifier les matériaux disposant des propriétés les plus robustes et les plus durables pour pallier ces difficultés. Si la conception de Cigéo repose aujourd'hui sur l'utilisation de matériaux éprouvés faisant l'objet d'un important retour d'expérience, la R&D doit se poursuivre, y compris pendant la phase d'exploitation de l'installation, pour optimiser la conception du stockage et des colis de déchets

Nanosecond laser surface modification of AISI 304L stainless steel: Influence the beam overlap on pitting corrosion resistance

International audienc

Fretting and wear behaviors of Ni/nano-WC composite coatings in dry and wet conditions

The fretting and wear behaviors of Ni/nano-WC composite coatings were studied by considering the effect of fretting frequency of 1 Hz during 10,000 cycles, at different applied loads in dry or wet conditions. The studies were performed on a ball-on-disk tribometer and the results were compared with pure Ni coating. The nanohardness of pure Ni and Ni/nano-WC composite coatings was tested by nanoindentation technique. To evaluate the wet wear (tribocorrosion) behavior the open circuit potential (OCP) was measured before, during and after the fretting tests at room temperature in the solution that simulates the primary water circuit of Pressurized Water Reactors (PWRs). The results show that Ni/nano-WC composite coatings exhibited a low friction coefficient, high nanohardness and wear resistance compared with pure Ni coatings under similar experimental conditions. Ni/nano-WC composite coatings were obtained on stainless steel support by electrochemical codeposition of nano-sized WC particles (diameter size of ~60 nm) with nickel, from a standard nickel Watts plating bath. The surface morphology and the composition of the coatings were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX) respectively.status: publishe

Recombination of silica and zirconia into zircon by means of laser treatment of plasma-sprayed coatings

International audienceSelf-supported zircon (ZrSiO 4) coatings have been deposited by means of atmospheric pressure plasma spraying, a high growth rate deposition method. However, it is well known that ZrSiO 4 dissociates into ZrO 2 and SiO 2 in the high-temperature plasma torch during plasma spraying, the rapid quenching preventing reverse combination of both components into ZrSiO 4. Usually, high-temperature annealing (1,600–1,900 K) is applied to recombine SiO 2 and ZrO 2 into ZrSiO 4. In this contribution, we investigate an attractive technological alternative to recombine SiO 2 and ZrO 2 into ZrSiO 4 by laser treatment with a scanning continuous wave CO 2 laser. By carefully adjusting the CO 2 laser treatment parameters (laser power density and scanning velocity), we show that the SiO 2 and ZrO 2 phases indeed recombine into ZrSiO 4 , however, with a very low recombination rate. Thus, we have investigated the addition of SiO 2-rich glassy particles to the plasma spray powders to facilitate the recombination of ZrO 2 , and SiO 2 into ZrSiO 4 during the laser treatment. Furthermore, the beneficial role of the glassy particles addition to substantially lower the annealing temperature during classical heat treatments has been studied. Available evidence indicates that the glassy particles melt during heat treatment , and thus favor the mobility and availability of silica at the ZrO 2 grains, which results in a lowering of the reaction temperature and an enhancement of the reaction kinetics

Analysis of liquid sodium purity by laser-induced breakdown spectroscopy. Modeling and correction of signal fluctuation prior to quantitation of trace elements

International audienceLiquid sodium is used as coolant in sodium-cooled fast nuclear reactors. Among many parameters to monitor to ensure the safe operation of the reactor, the coolant chemical purity is a relevant indicator of several undesirable situations, like corrosion of structural materials or sodium contamination, which may release different elements in the coolant. Several techniques have already been implemented to measure the sodium purity, but their response time is long and not suited for continuous monitoring. Therefore, as a complement to them, Laser-Induced Breakdown Spectroscopy (LIBS) is considered as a promising technique for real-time analysis of the coolant purity. In this paper we report on the first LIBS quantitative measurements performed in liquid sodium at 150℃. Calibration curves were traced for lead and indium using the standard addition method. Important intensity drifts and fluctuations were observed, mostly due to pressure variations in the sodium oven. Background subtraction and/or normalization was used to compensate for those intensity fluctuations. To describe the effect of these corrections on the analytical signal noise, a simple model was proposed and its results were found to satisfactorily fit the experimental data. Using this approach, the best detection limits were obtained for the background-subtracted and normalized data, and were found to be 6 ppm for lead and 5 ppm for indium