Fluage en flexion du dioxyde d'uranium après irradiation aux ions

International audienceCette communication concerne les propriétés mécaniques des combustibles nucléaires. Le travail réalisé a pour but d'améliorer les connaissances sur les propriétés viscoplastiques de l'UO2, afin de permettre une meilleure maîtrise des interactions pastille – gaine. Pour cela, le Centre des Matériaux a développé un système de flexion trois points, à haute température, sous atmosphère contrôlée, spécialement adapté à la réalisation d'essais de fluage sur des éprouvettes de très petites dimensions (entraxe de sollicitation 10 mm, épaisseur 500 μm). Des spécimens ont été irradiés aux ions lourds dans l'accélérateur du GANIL de Caen, dans le but d'obtenir des défauts d'irradiation équivalents à ceux générés dans les réacteurs industriels. Les premiers essais sur ces échantillons révèlent un fluage thermique très nettement accéléré par cette irradiation : les éprouvettes se déforment en fluage en dessous de 800°C, alors que le matériau vierge ne présente une déformation viscoplastique significative qu'au-delà de 1100°C. Ici sont présentés les premiers résultats expérimentaux de fluage sur éprouvettes vierges ou irradiées. Ces premiers résultats obtenus sur UO2 démontrent l'intérêt d'un tel dispositif pour caractériser le comportement mécanique à haute température (notamment le fluage) de matériaux irradiés aux ions. Ce dispositif pourra entre autre permettre de caractériser les différents matériaux céramiques envisagés pour les « réacteurs du futur »

Characterization of aluminum nitride material under swift heavy ion irradiations

International audienceFor Generation IV reactors, and more particularly the Gas Fast Reactor, aluminum nitride is an interesting candidate for the application as fuel coating; actually, its great thermal conductivity should allow efficient thermal transfer between the fuel pellets and the coolant. Unfortunately, few data are available on its behavior under irradiation. In this study, we attempted to understand the effect of irradiation parameters on the defect creation thanks to thermally-stimulated luminescence and optical absorption spectrophotometry. Thus, we didn't note any new defect created by the irradiation and the fact that these techniques complement each other allowed to know the influence of each irradiation parameter on the defects concentration

Heavy ion induced damages in Ti3SiC2: study of the swelling

International audienceFor Generation IV reactors, and more particularly the Gas Fast Reactor, ternary carbide Ti3SiC2 is an interesting candidate for the application as fuel coating; actually, it has the advantage to combine some properties of metals with those generally attributed to ceramics. Unfortunately, few data are available on its behavior under irradiation. In this study, we attempted to measure and to understand the origin of the swelling induced by nuclear collisions. Thus, it seems that Ti3SiC2 irradiated at room temperature swell less than silicon carbide and that critical amorphization temperature is less than room temperature

Heavy ions induced damages in Ti3SiC2: effect of irradiation temperature

International audienceThanks to their refractoriness, carbides are sensed as fuel coating for the IVth generation of reactors. Among those studied, the Ti3SiC2 ternary compound can be distinguished for its noteworthy mechanical properties: the nanolamellar structure imparts to this material some softness as well as better toughness than other classical carbides such as SiC or TiC. However, under irradiation, its behaviour is still unknown. In order to understand this behaviour, specimens were irradiated with heavy ions of different energies, then characterised. The choice of energies used allowed separation of the effects of nuclear interactions from those of electronic ones. Thus, AFM, SEM and XRD techniques allowed to note an important spoiling due to nuclear collision whereas electronic interactions would induce the formation of hills and the expansion of the unit cell. Irradiations at higher temperatures allowed to study the effect of temperature on these results

Formation of nanosized hills on Ti3SiC2 oxide layer irradiated with swift heavy ions

International audienceThe Ti3SiC2 refractory compound that combines properties of both metals and ceramics is a fuel cladding candidate under investigation for Gas-cooled Fast Reactor. Its behavior under swift heavy ion irradiation (Xe ions, 92 MeV, 1019 m−2) was investigated. Significant and unexpected surface changes have been highlighted: hills have been observed by AFM on the surface of Ti3SiC2. Such a topographic modification has never been observed in other materials irradiated in similar conditions. The characterization of these hills by both XPS and X-TEM has highlighted that the surface modifications do not appear in Ti3SiC2 but in the amorphous oxide layer located on the sample surface before irradiation. Moreover, the thickness of this oxide layer grew under irradiation dose. The comparison with previous irradiations has led to the conclusion that this surface modification stems from electronic interactions in this amorphous layer, and that there is a threshold in the electronic stopping power to overcome to form hills

Dommages d'irradiation dans Ti3SiC2 : Effets des interactions nucléaires et électroniques

Comme pour tout système nucléaire, le concept du combustible pour les réacteurs de IVème génération consiste en des pastilles de combustible conditionnées dans une matrice qui doit contenir les produits de fission. De par leur excellente réfractarité, les carbures sont pressentis pour constituer cette barrière de confinement. Parmi ceux étudiés, le ternaire Ti3SiC2 se distingue par ses propriétés mécaniques particulières : en effet, sa structure nanolamellaire lui confère une certaine plasticité ainsi qu'une ténacité supérieure aux carbures classiques tels que SiC ou TiC. Cependant, son comportement sous irradiation n'est pas connu. Afin d'appréhender ce comportement, des échantillons ont été irradiés aux ions lourds de différentes énergies puis caractérisés. Le panel d'énergies utilisé a permis de discriminer l'effet des interactions nucléaires – pulvérisation – des interactions électroniques – apparition de monticules et dilatation de la maille cristalline

Irradiation damages in Ti3SiC2: formation and characterisation of the oxide layer

International audienceThe concept of the fuel for the IVth generation reactors should consist of fuel pellets surrounded with a matrix that must contain fission products. Thanks to their interesting thermo-mechanical properties, carbides are sensed to become this matrix. Among the studied carbides, Ti3SiC2 can be distinguished; actually, its nano-laminated structure confers to it some softness as well as a better toughness than classical carbides like SiC or TiC. However, before to use this remarkable carbide, a study of its behaviour under irradiation must be led. Thus, some characterisations were performed on 75 MeV Kr irradiated specimens. They allowed to underline that TiO2 (formed on the surface of Ti3SiC2 during the surface preparation) seems to be sputtered by irradiation, and that the unit cell of Ti3SiC2 is dilated along c axis

Dommages d'irradiation dans Ti3SiC2

Les carbures, de par leurs propriétés remarquables, sont pressentis comme matériau de structure autour du combustible du réacteur de génération IV. Parmi ceux étudiés, Ti3SiC2 se distingue car il associe les propriétés des céramiques à celles des métaux. Cependant, son comportement sous irradiation n'est pas connu. Des caractérisations ont été réalisées sur des échantillons irradiés aux ions Kr à 75 MeV. Elles ont permis de mettre en exergue que TiO2 (formé en surface de Ti3SiC2) est pulvérisé par l'irradiation et que la maille cristalline de Ti3SiC2 se dilate suivant c

Damages induced by heavy ions in titanium silicon carbide: effects of nuclear and electronic interactions at room temperature

International audienceThanks to their refractoriness, carbides are sensed as fuel coating for the IVth generation of reactors. Among those studied, the Ti3SiC2 ternary compound can be distinguished for its noteworthy mechanical properties: the nanolamellar structure imparts to this material some softness as well as better toughness than other classical carbides such as SiC or TiC. However, under irradiation, its behaviour is still unknown. In order to understand this behaviour, specimens were irradiated with heavy ions of different energies, then characterised. The choice of energies used allowed separation of the effects of nuclear interactions from those of electronic ones

Microstructural changes induced by low energy heavy ion irradiation in titanium silicon carbide

International audienceLow energy ion irradiation was used to investigate the microstructural modifications induced in Ti3SiC2 by nuclear collisions. Characterization of the microstructure of the pristine sample by electron back-scatter diffraction (EBSD) shows a strong texturing of TiSi2, which is a common secondary phase present in Ti3SiC2. A methodology based on atomic force microscopy (AFM) was developed to measure the volume swelling induced by ion irradiation, and it was validated on irradiated silicon carbide. The swelling of Ti3SiC2 was estimated to 2.2 ± 0.8% for an irradiation dose of 4.3 dpa at room temperature. Results obtained by both EBSD and AFM analyses showed that nuclear collisions induce an anisotropic swelling in Ti3SiC2