19 research outputs found
Thermal conductivity and emissivity measurements of uranium carbides
Thermal conductivity and emissivity measurements on different types of uranium carbide are presented, in the context of the ActiLab Work Package in ENSAR, a project within the 7th Framework Program of the European Commission. Two specific techniques were used to carry out the measurements, both taking place in a laboratory dedicated to the research and development of materials for the SPES (Selective Production of Exotic Species) target. In the case of thermal conductivity, estimation of the dependence of this property on temperature was obtained using the inverse parameter estimation method, taking as a reference temperature and emissivity measurements. Emissivity at different temperatures was obtained for several types of uranium carbide using a dual frequency infrared pyrometer. Differences between the analyzed materials are discussed according to their compositional and microstructural properties. The obtainment of this type of information can help to carefully design materials to be capable of working under extreme conditions in next-generation ISOL (Isotope Separation On-Line) facilities for the generation of radioactive ion beams
Influence of density and release properties of UC targets on the fission product yields at ALTO
International audienceTo study the influence of the structural properties of UC targets on their release properties, several types of targets using different precursors (carbon and uranium) were synthesized, characterized, irradiated and heated leading to the determination of the released fractions of eight elements. In this article, the production rates of these targets are estimated under the use conditions at ALTO, i.e. with targets bombarded by an electron beam (10 μA, 50 MeV). We have simulated the fission number produced using the FLUKA code. Then, we have determined the release efficiency as a function of the half-life of the isotopes using average diffusion coefficients deduced for the elements studied previously. Finally, we compare the production rates obtained from the various targets and conclude that the target must be adapted to the element studied. It is crucial to find in each case the best compromise between the target density and the release efficiency
Combustibles de substitution dans les fours de cimenteries : effet du phosphore sur la phase majoritaire du ciment Portland
Le ciment anhydre Portland est obtenu par broyage du clinker (roche artificielle issue de la cuisson à 1450 °C d'un mélange de calcaire et d'argile) et de gypse. Pour des raisons économiques et environnementales, les cimentiers recyclent de plus en plus de combustibles alternatifs à l'origine d'impuretés supplémentaires dans le clinker, tel le phosphore dans le cas de la combustion des farines animales. Il est donc important de contrôler voire de prédire l'effet de ces impuretés sur les performances du matériau hydraté. Cette étude expérimentale traite de l'effet du phosphore (0 à 0,9 % massique P2O5) sur la phase majoritaire du clinker, le silicate tricalcique, avec une analyse systématique de la localisation du phosphore dans le composé anhydre et de la résistance mécanique du composé hydraté. La seconde partie s'inscrit dans une démarche thermodynamique prédictive, avec la mise au point d'une approche calculatoire des diagrammes de phases majoritaires du clinker
BST ceramics: Effect of attrition milling on dielectric properties
The effect of grain size on the dielectric properties of Ba0.6Sr0.4TiO3 (BST) ceramics is investigated. Attrition milling is chosen to obtain nanometre particle size from micrometre particle size powders. Fine grained ceramics are obtained by hot uniaxial pressing (HUP)..
Study of uranium oxide milling in order to obtain nanostructured UCx target
International audienceA R&D program is developed at the ALTO facility to provide new beams of exotic neutron-rich nuclei, as intense as possible. In the framework of European projects, it has been shown that the use of refractory targets with nanometric structure allows us to obtain beams of nuclei unreachable until now. The first parameter to be controlled in the processing to obtain targets with a homogeneous nanostructure is the grinding of uranium dioxide, down to 100 nm grain size. In this study, dry and wet grinding routes are studied and the powders are analyzed in terms of phase stabilization, specific surface area and grain morphology. It appears that the grinding, as well dry as wet, leads to the decrease of the particle size. The oxidation of UO2 is observed whatever the grinding. However, the dry grinding is the most efficient and leads to the oxidation of UO2 into U4O9 and U3O7 whose quantities increase with the grinding time while crystallite sizes decrease
Development of radioactive beams at ALTO: Part 2. Influence of the UC target microstructure on the release properties of fission products
International audienceProducing intense radioactive beams, in particular those consisting of short-lived isotopes requires the control of the release efficiency. The released fractions of 11 elements were measured on 14 samples that were characterized by various physicochemical analyses in a correlated paper (Part 1). A multivariate statistical approach, using the principal component analysis, was performed to highlight the impact of the microstructure on the release properties. Samples that best release fission products consist of grains and aggregates with small size and display a high porosity distributed on small diameter pores. They were obtained applying a mixing of ground uranium dioxide and carbon nanotubes powders leading to homogeneous uranium carbide samples with a porous nanostructure. A modelling under on-line ALTO conditions was carried out using the FLUKA code to compare the yields released by an optimized and a conventional target
An off-line method to characterize the fission product release from uranium carbide-target prototypes developed for SPIRAL2 project
International audienceIn the context of radioactive ion beams, fission targets, often based on uranium compounds, have been used for more than 50 years at isotope separator on line facilities. The development of several projects of second generation facilities aiming at intensities two or three orders of magnitude higher than today puts an emphasis on the properties of the uranium fission targets. A study, driven by Institut de Physique Nucléaire d'Orsay (IPNO), has been started within the SPIRAL2 project to try and fully understand the behavior of these targets. In this paper, we have focused on five uranium carbide based targets. We present an off-line method to characterize their fission product release and the results are examined in conjunction with physical characteristics of each material such as the microstructure, the porosity and the chemical composition