Papers by Loïc Marchetti
Journal of Materials Science, 2015
ABSTRACT This paper presents an extensive set of measurements from complementary surface analysis... more ABSTRACT This paper presents an extensive set of measurements from complementary surface analysis techniques performed for characterizing deuterium retention in carbon fiber composite Sepcarb®NB31 subsequently to a deuterium beam exposition: adsorption isotherm measurements and Hg porosimetry to characterize the porous network, coupled deuterium beam exposure and in situ µ-NRA analysis to follow the dynamics of the penetration of the retained deuterium in the material, TEM and Raman microscopy to investigate the change in the material structure induced by ion irradiation, and finally TPD to estimate the respective proportion of deuterium retained in the surface layer and in the bulk material. The parameters extracted from this set of characterizations are introduced in a 2D Monte Carlo model which couples the propagation of deuterium and eroded carbon atoms in a network of rectilinear pores and plasma–surface interaction parameters from the SRIM code. The simulations reproduce satisfactorily the main features of the measured deuterium concentration profile and behavior of the retained deuterium amount with incident fluence, validating the physical picture of deuterium retention in CFC as due to the simultaneous implantation of the incident ions in the few 10-nm-depth layer the closest to the surface and penetration of atoms deeper in the material (several tens of microns) through the pore network.
SSRN Electronic Journal, 2022
Matériaux & Techniques, 2011
Les alliages base nickel sont les principaux materiaux constitutifs des tubes de generateurs de v... more Les alliages base nickel sont les principaux materiaux constitutifs des tubes de generateurs de vapeur des reacteurs a eau pressurisee (REP). Leur etat de surface, en termes notamment de defauts metallurgiques, est un parametre cle pour l’oxydation car il influence aussi bien la structure du film d’oxyde forme que sa cinetique de croissance. Dans ce contexte, l’implantation d’ions est une technique adaptee pour preparer des surfaces modeles, dont l’etat plus ou moins defectueux (densites de lacunes et dislocations maitrisees) est parfaitement caracterise. Les premiers resultats concernant l’implantation de Xe+ ont mis en evidence le double effet du taux de defauts en sub-surface : il influence a la fois la densite de courts-circuits de diffusion au sein de l’oxyde mais egalement la vitesse de formation des nodules de chromine a l’interface entre l’alliage et la chromite mixte de nickel et de fer. Le travail actuellement en cours sur l’implantation d’ions Nix + a pour objectif d’integrer le parametre densite de defauts de surface dans une approche de modelisation mecanistique du processus de corrosion.
Corrosion Science, 2016
316L samples were implanted with xenon ions in order to generate defects (characterised as caviti... more 316L samples were implanted with xenon ions in order to generate defects (characterised as cavities) in the alloy subsurface region. Their oxidation kinetics in pressurized water reactor primary water at 325 °C were determined using ion beam analyses. After a 24 h exposure, the internal oxide layer reaches a thickness equivalent to the implanted affected depth (90 nm) which does not change much for longer exposure duration. Two-stages corrosion experiments followed by secondary ion mass spectrometry analyses have revealed two oxygen diffusion regimes in the internal oxide layer, which seems to be linked with the distribution of implanted defects.
Journal of Nuclear Materials, 2015
This study aims at characterizing the interactions of hydrogen with point defects and their clust... more This study aims at characterizing the interactions of hydrogen with point defects and their clusters in nickel-based superalloys. For this, nickel ion implantation was used to create defects in the sub-surface of alloy 690 coupons. The interaction of hydrogen with these defects was studied thanks to SIMS depth profile analysis performed after deuterium cathodic charging, and different annealing treatment. In parallel, TEM observations were carried out in order to qualify and quantify the defects responsible for the trapping, and to observe their evolution in the presence of hydrogen. All the results exhibit a strong interaction of hydrogen with implantation-defects, up to high temperatures (325 C). Also, hydrogen is shown to assist defects reorganisation, in a way similar to the effect of temperature. The effect of hydrogen on the alloy atoms as explored by SIMS, combined with the TEM investigation of defects evolution in the presence of hydrogen, allows to suggest that the main mechanism for hydrogen-assisted motion of defects is by lowering the lattice friction, thus decreasing the activation volume for the unfaulting or motion of point defect clusters, up to dislocation loops.
Corrosion Science, 2016
Abstract The generalised corrosion of Ni-base alloys exposed to pressurized water reactors primar... more Abstract The generalised corrosion of Ni-base alloys exposed to pressurized water reactors primary coolant leads both to the growth of a protective oxide scale and to the release of cations. Based on experimental results previously published, a mechanistic description of this phenomenon is proposed. Then, from a simplified view of theses mechanisms, a kinetic model is proposed, focusing on the link between the alloy subsurface defects density and the shape of oxidation kinetic curves. Comparing calculated curves and experimental data shows this first approach is promising. Nevertheless a better knowledge of some kinetic parameters is necessary to improve the model.
Conférence les 6 et 7 Avril 2006. Communication par affiche.
Materials Science Forum, 2008
Oxidation mechanism of Alloy 690 has been investigated in Pressurised Water Reactor (PWR) primary... more Oxidation mechanism of Alloy 690 has been investigated in Pressurised Water Reactor (PWR) primary coolant conditions (325°C, aqueous hydrogenated media). Experiments performed with gold marker and RBS technique reveal that the passive film formation is the consequence of an anionic mechanism. This result is confirmed by experiments achieved with two sequences of corrosion in a H2 16O media and in a mixed H2 16O/ H2 18O media. The localisation of 18O by SIMS analysis in the thin passive layer underlines an oxidation mechanism due to oxygen diffusion by short circuits (like grain boundaries) in the oxide scale. Moreover grain boundary diffusion coefficient in chromite like oxide was estimated to be in the range 2 10-18 – 1 10-17 cm2.s-1 and compared to values extrapolated from higher temperature.
Oxidation of Metals, 2013
Oxidation of stainless steel in PWR primary water at 325°C was studied by investigating the influ... more Oxidation of stainless steel in PWR primary water at 325°C was studied by investigating the influence of defects created at the alloy subsurface by proton irradiation before corrosion exposure. Corrosion experiments were conducted by sequentially exposing samples, with H 2 18 O used for the second exposure. The oxide layer, formed in these conditions was studied by SEM and TEM and could be divided in two parts: an external discontinuous layer composed of crystallites rich in iron and an internal continuous layer richer in chromium. Tracer experiments revealed that the growth of this protective scale was due to oxygen diffusion in the grain boundary of the oxide layer. Defects created by irradiation have an effect on the two oxide layers. They are a preferential nucleation site for the external layer and so increase the density of the crystallites. They also induce a slower diffusion of oxygen in the internal layer.
Journal of Nuclear Materials, 2014
ABSTRACT Tritium adsorption and desorption from well characterized tungsten dust are presented. T... more ABSTRACT Tritium adsorption and desorption from well characterized tungsten dust are presented. The dust used are of different types prepared by planetary milling and by aggregation technique in plasma. For the milled powder, the surface specific area (SSA) is 15.5 m2/g. The particles are poly-disperse with a maximum size of 200 nm for the milled powder and 100 nm for the aggregation one. Prior to tritiation the particles are carefully de-oxidized. Both samples are experiencing a high tritium inventory from 5 GBq/g to 35 GBq/g. From comparison with massive samples and considering that tritium inventory increases with SSA, it is shown that surface effects are predominant in the tritium trapping process. Extrapolation to the ITER environment is undertaken with the help of a Macroscopic Rate Equation model. It is shown that, during the life time of ITER, these particles can exceed rapidly 1 GBq/g.
Journal of Nuclear Materials
Oxygen stoichiometry in (U,Pu)O 2-x nuclear fuels, while of prime interest, is still difficult to... more Oxygen stoichiometry in (U,Pu)O 2-x nuclear fuels, while of prime interest, is still difficult to be determined at the micrometric scale. It has been recently evidenced that Raman microscopy is a promising tool to characterize (U,Pu)O 2-x samples at a microscopic scale by probing the oxygen sublattice. Its use for determining the local O/M ratio was studied in this work on mixed oxide samples mostly containing 239 Pu and natural uranium, in addition to minor traces of other isotopes, including decay products and 241 Am. The first step was to dissociate the influence of the Pu/(U + Pu + Am) content, self-irradiation and O/M ratio on Raman spectra and especially on the main Raman band position in fluorite structure, the T 2g. In this aim, freshly annealed and aged U 1-y Pu y O 2-x samples, with 0.19 < y < 0.46 and different O/M ratios, were analyzed by XRD and Raman spectroscopy. After figuring out that self-irradiation alone had no significant impact on the T 2g position, two mathematical relations were determined, linking the T 2g position to the Pu/(U + Pu + Am) content and to the lattice parameter. Finally, the oxygen hypostoichiometry direct impact on (U,Pu)O 2-x Raman spectra was determined for the first time. In agreement with past results observed in CeO 2-x , a O/M ratio decrease induces a T 2g shift towards lower frequencies in (U,Pu)O 2-x. Combining the whole results, an equation allowing to determine the T 2g position according to the O/M ratio and Pu/(U + Pu + Am) content was established. Raman spectrometer associated to a confocal optical microscope can then be used to determine locally (≈1 μm) either the Pu/(U + Pu + Am) content or the O/M ratio. This study proves the relevance of such method to characterize the fuel pellets in an industrial way.
Advances in Materials Sciences, 2007
Uploads
Papers by Loïc Marchetti