A flow microdevice for studying the initiation and propagation of a single pit

International audienceA novel experimental setup in which a glass microcapillary can be precisely positioned close to a metallic electrode has been developed to locally inject aggressive solutions at will. It has been used for studying the pitting corrosion of a 316L stainless steel in 0.5 M H2SO4 medium. The amount of chloride ions released by the capillary could be controlled and the analysis of the corrosion products by scanning electron microscopy and energy dispersive X-ray spectroscopy showed there was no selective dissolution of the 316L stainless steel. This device was shown to be an efficient tool for understanding localized corrosion. (c) 2012 Elsevier Ltd. All rights reserved

Corrosion of metallic materials in flowing liquid lead-bismuth

Corrosion tests of martensitic and austenitic steels were performed in a forced liquid eutectic Ph-Bi circulation loop. Experiments were carried out at 470°C and 600°C. Two oxygen concentrations in Pb-Bi were studied: $10^{-6}$ wt% and $10^{-7}-10^{-8}$ wt%. The results showed that at 470°C, all the tested steels have a satisfying corrosion behaviour for both oxygen contents. An oxide layer is formed on martensitic steels (T91 and EM10); its thickness depends on the oxygen content. It is constituted of an outer layer of magnetite and an inner (Fe, Cr)$_3$O$_4$ spinel layer. Austenitic steel 316L is protected by a very thin oxide layer ($<$ 1 $\mu$m). At 600°C, martensitic steels (T91 and EM10) undergo an important oxidation for both oxygen contents (after 1000h, the thickness of the oxide layer varies from 10-15 $\mu$m to 20-25 $\mu$m depending on the oxygen content). The oxide layer is constituted of (Fe, Cr)$_3$O$_4$ spinel and appears porous. Austenitic 316L undergoes severe dissolution at the lowest oxygen content in Ph-Bi and partial dissolution and oxidation at the highest oxygen concentration. Erosion phenomena were observed on all the steels

Thermomechanical compatibility of SiC/SiC composites as structural materials for Sodium-cooled Fast Reactors

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Evaluation of the chemical compatibility of SiC/SiC composite materials in nuclear environments

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Traitements de surface avec et sans apport de matiere pour le nucleaire - Modification de surface par laser, PVD et CVD

International audienceDans le contexte actuel d'optimisation du parc actuel et futur et de l'allongement de la duree de vie des centrales et des installations du cycle, la problematique de duree de vie des materiaux est cruciale. Les problematiques de vieillissement et de reactivite (corrosion) constituent un defi majeur dans l'industrie nucleaire. Pour relever l'ensemble de ces defis, les technologies innovantes dans le domaine des procedes de traitements de surfaces avec ou sans apport de matiere sont des solutions prometteuses d'autant plus que ces dernieres ont connu un developpement significatif ces dernieres annees.Parmi les technologies de traitement de surface etudiees au Service d'Etudes Analytiques et de Reactivite des Surfaces (SEARS) de la DEN (Division de l'Energie Nucleaire), les techniques par laser sont historiquement presentes grace aux competences du LISL (Laboratoire d'Ingenierie des Surfaces et Lasers). Une premiere appartient a la famille des traitements sans apport de matiere. Elle consiste a venir frapper une surface avec un laser dont les proprietes sont judicieusement choisies pour que la matiere presente soit fondue voire ejectee. En pilotant les caracteristiques du faisceau laser incident les proprietes de surface peuvent etre modifiees. Il est par exemple possible de former une couche barriere d'oxydes, d'homogeneiser des phases et d'augmenter la teneur en certains elements chimiques voire de modifier la structure cristallographique ce qui peut conduire a une augmentation de la durete. Les applications de ce procede sont le renforcement de la resistance a la corrosion par piquration d'aciers 304L ou la limitation du relachement de nickel en milieu primaire au niveau des generateurs de vapeur. Enfin, l'ejection de matiere provenant de la surface traitee peut etre maximisee pour utiliser ce traitement comme une technique d'ablation surfacique pour le demantelement ou la maintenance d'installations, son point fort etant la possibilite de decontaminer des composants a distance.Les autres traitements de surface concernent des methodes avec apport de matiere. Parmi les technologies etudiees, certaines passent par un etat gazeux de la matiere. Suivant si la phase gazeuse se condense ou se decompose a la surface du composant a revetir, on parlera de PVD (condensation) ou de CVD (decomposition avec reaction chimique). Ces techniques sous vide sont majoritairement employees pour deposer des revetements protecteurs afin d'augmenter les performances et les durees de vie de composants en milieux extremes (haute temperature, irradiation, oxydation, corrosion ou encore usure abrasive). On peut citer les developpements actuels avec Areva pour les EATFs (Enhanced Accident Tolerant Fuels) concernant les gaines de combustible nucleaire qui, avec un revetement protecteur, resisteraient bien mieux a des hypothetiques conditions accidentelles de perte de refrigerant primaire

Determination of mass transfer coefficient in flow assisted corrosion of steel in liquid Pb Bi. Rotating cylinder geometry

International audienceThe aim of this experimental and numerical work is to determine the mass transfer at the wall of a steel cylinder rotating within liquid Lead-Bismuth blend. This is a crucial parameter for the analysis of corrosion tests performed in the CICLAD experimental setup for the investigation of flow assisted corrosion of steel by liquid metals. As a reliable numerical modelling must rely on experimental validation, and since no direct wall mass transfer measurement is possible in CICLAD, a scaled electrochemical model has been achieved. Modelling the turbulence in this rotating configuration is shown to require the use of a Reynolds-Stress Model. A sensitivity to the Schmidt number is observed in the numerical simulations representing the measured mass transfer in the electrochemical model. Simulations dedicated to liquid Pb-Bi are thus presented in addition to those dedicated to the aqueous solution used in the electrochemical model. Following correlations are proposed for the prediction of Fe mass transfer at the wall of a steel rotating cylinder in liquid Pb-Bi: Sh=1.9x10-1 (Re 2 Sc) 0.31 for 2x10 9 <Re 2 Sc<5.3x10 10 ; Sh=1.4x10-3 (Re 2 Sc) 0.51 for 5.3x10 10 <Re 2 Sc<8.5x10 11

Corrosion of Fe-9Cr Steels in Sodium Fast Reactors Environments

The sodium cooled fast reactor is selected by France as the most mature GEN IV concept to be industrially developed by the year 2040. A collaborative research program has been established together with EDF and Areva NP. In this program, different innovations are being considered in the design of the reactor leading to the use of various environments apart from liquid sodium and water vapor encountered in the “classical” sodium fast reactors. As a matter of fact, considerations on the suppression of the water-sodium reaction risk led to the proposal of the use of alternative coolants such as Pb-Bi involving an intermediate circuit between the primary sodium and the steam generator. Other concepts involve the use of supercritical CO2 instead of water vapor in the energy conversion system. In all cases, structural materials encounter severe conditions regarding corrosion concerns: high temperatures and possibly aggressive chemical environments. In this paper, status of the research performed in CEA on the corrosion behavior of the structural material and especially Fe-9Cr steels is presented in the various environments: sodium (see paper by JL Courouau), Pb-Bi, water vapor and CO2. The materials studied are metallic materials: austenitic and ferrito-martensitic steels as well as ODS steels as an option for the cladding material. In the different environments studied, the scientific approach is identical, the objective being in all cases the understanding of the corrosion processes to establish recommendations on the chemistry control of the coolant and to predict the long term behavior of the materials by the development of corrosion models. First, the corrosion mechanisms are analyzed using dedicated experimental devices. As a matter of fact, the complex environments require also controlled, safe and precise experimental systems to perform long duration corrosion tests (several thousands of hours). Therefore, specific experiments, adapted to each corrosive medium, are carried out in the laboratory. For example: - laboratory scale loops are used for liquid metals corrosion studies (use of rotating cylinders to simulate high turbulent conditions), - thermogravimetric analyses are also used to perform gas corrosion studies in representative temperature and environmental conditions,… Then, multi-scale characterization of the materials studied is performed (FEG-SEM, EDX, XRD, GD-OES…), together with precise analyses of the environments tested (in situ measurements with specific probes, gas chromatography…). Corrosion mechanisms are then proposed and models developed, depending on the advancement and the maturity of the program

Liquid metal embrittlement of an austenitic stainless steel in liquid sodium

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