Systeme mixte de goniometrie a haute resolution et de rejection adaptative de brouilleurs dans la gamme HF

Le propos de cet article est de présenter les résultats expérimentaux obtenus, dans la gamme HF, avec un système mixte de goniométrie et de filtrage spatial adaptatif. Une goniométrie à haute-résolution par la méthode MUSIC fournit une estimée des vecteurs directeurs des sources présentes, que le filtrage adaptatif utilise pour mettre en oeuvre le Filtre Adapté Spatial (FAS) à l'une des sources détectées. Après une présentation des techniques utilisées et du système expérimental, les résultats obtenus sont décrits. Ceux-ci sont généralement satisfaisants, aussi bien en ondes de sol qu'en ondes ionosphériques, et dans certains cas approchent même les performances théoriques

Thermal diffusion of lithium implanted in small and large grain boron carbide

International audienceBoron carbide (B4C) is used as a neutron absorber for nuclear reactor control and installation protection in most types of reactors. When the B4C is irradiated in the reactor, large quantities of lithium and helium (up to about 1022 /cm3) are produced due to the neutron absorption reaction 10B (n, α) 7Li. This work aims at studying the Li diffusion in large grain size (20–50 µm) or small grain size (0.2 – 5 µm) B4C in the temperature range of 500–800 °C. Lithium was implanted in B4C samples at a fluence of 1014 ions/cm2 (maximum concentration of 54 at. ppm). The Li concentration profiles as a function of depth were obtained before and after each heat treatment by Time-Of-Flight Secondary Ionization Mass Spectrometry technique. A heterogeneous diffusion process was observed depending on the implantation depth. Considering diffusion in the non-damaged, bulk material beyond the implanted zone, the thermal diffusion of lithium into the grain boundaries was found to be about four orders of magnitude higher than into the grains. •TOF-SIMS analyses of Li have been performed in implanted and annealed high density, large grain boron carbide.•The diffusion coefficient of Li in boron carbide has been determined in the 500 – 800 °C range, the obtained activation energy, about 2 eV, is close to ab initio estimations.•Li diffusion is highly enhanced in the gain boundaries

Influence of the Oxygen content on the thermal migration of Xenon in ZrCxO1−x

International audienceZirconium carbide (ZrC) is a refractory ceramic presenting interesting properties such as a high melting point, a very high hardness and a good thermal stability. For these reasons, this material is considered as a candidate for fuel coating for fourth-generation reactors in particular for the Gas cooled Fast Reactors (GFR). The ceramic temperature could reach 1200 °C in normal reactor operation and reach 1700 °C in accidental conditions. It is therefore important to assess the ZrC thermal retention capacity regarding abundant and/or volatile fission products. This paper deals with the behavior of Xenon which is the major gaseous fission product created during fission. Previous studies have shown that Xenon remained motionless in an "Oxygen-poor" matrix such as ZrC0.95O0.05, up to temperatures of 1800 °C. However, Zirconium oxycarbides are known to be very sensitive to oxidation. This study aims therefore at studying the behavior of Xenon in Zirconium oxycarbide samples with different Oxygen contents. Xenon is introduced by ion implantation and the samples are annealed in secondary vacuum in the temperature range 1400 °C-1800 °C. The Oxygen profiles are determined by using the 16O(4He, 4He)16O nuclear reaction at 7.5 MeV and the concentration profiles of Xenon are measured by Rutherford Backscattering Spectrometry at each step of the treatment. The results show that the behavior of the material during annealing with respect to oxidation is strongly related to its initial Oxygen content. More generally, the higher the initial Oxygen content, the more important is the oxidation. Consequently, the Xenon migration is enhanced in Oxygen rich Zirconium carbides

Comparaison de techniques d'analyse par faisceau d'ions ERDA, NRA et SIMS pour profiler le deutérium dans le carbure de bore B4_4C

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Structural modifications of boron carbide irradiated by swift heavy ions

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Xe-implanted zirconium oxycarbide studied by variable energy positron beam

The effect of annealing on defects and the formation of Xe bubbles were investigated in zirconium oxycarbide implanted with 800-keV136Xe2+ ions at two fluences 1 × 1015 and 1 × 1016 Xe/cm2. Doppler broadening technique combined with slow positron beam was used. The analysis of the S depth profiles and S-W maps revealed that in the as-implanted samples at both fluences Xe bubbles are not formed. The post-implantation annealing of the samples implanted at 1 × 1016 Xe/cm2 caused formation of Xe bubbles. The response of the lower implantation dose samples to this post implantation annealing was found rather complicated and is discussed

Thermal diffusion of chlorine in uranium dioxide studied by secondary ion mass spectrometry and X-ray adsorption spectroscopy

In a nuclear reactor, 35Cl present as an impurity in the nuclear fuel is activated by thermal neutron capture. During interim storage or geological disposal of the nuclear fuel, 36Cl may be released from the fuel to the geo/biosphere and contribute significantly to the ‘instant release fraction'. In order to elucidate the diffusion mechanisms, both irradiation and thermal effects must be assessed. This paper deals with the thermal diffusion of chlorine in depleted UO2. For this purpose, sintered UO2 pellets were implanted with 37Cl at an ion fluence of 1013 cm−2 and successively annealed in the 1175–1475 K temperature range. The implanted chlorine is used to simulate the behaviour of the displaced one due to recoil and to interactions with the fission fragments during reactor operation. The behaviour of the pristine and the implanted chlorine was investigated during thermal annealing. SIMS and μ-XAS (at the Cl–K edge) analyses show that: (1) the thermal migration of implanted chlorine becomes significant at 1275 K; this temperature and the calculated activation energy of 4.3 eV points out the great ability of chlorine to migrate in UO2 at relatively low temperatures, (2) the behaviour of the implanted chlorine which aggregates into ‘hot spots' during annealing before its effusion is clearly different from that of the pristine one which remains homogenously distributed after annealing, (3) the ‘hot spot' and the pristine chlorine seem to be in different structural environments. Both types of chlorine are assumed to have a valence state of −I, (4) the comparison between an U2O2Cl5 reference compound and the pristine chlorine environment shows a contribution of the U2O2Cl5 to the pristine chlorine