Deuterium migration in nuclear graphite : consequences for the behavior of tritium in CO2 cooled reactors and for purification of irradiated graphite

International audienc

Migration du Deuterium dans le graphite nucleaire : conséquences sur le comportement du Tritium dans des réacteurs de type UNGG et sur la décontamination des graphites irradiés

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Thermal behavior of deuterium implanted into nuclear graphite studied by NRA

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Reactive gas pulsing sputtering process, a promising technique to elaborate silicon oxynitride multilayer nanometric antireflective coatings

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Effects of helium irradiation on fine grained β-SiC synthesized by spark plasma sintering

International audienceSilicon carbide has a high resistance to irradiation making it a material of choice for use in the nuclear reactors. In this work, we focus on experiments involving implantation of 30 keV 3He ions at room temperature (RT) in sintered β-SiC. Helium is produced in large quantities in fission and fusion reactors, and its accumulation in materials can lead to the formation of bubbles. The irradiation induces structural modifications within the material that can be coupled with changes in composition, especially at high fluence. Three ion fluencies are used here: 5 × 1015, 1 × 1017and 1 × 1018at. cm−2. Structural damages are studied by electron microscopy and helium profiles are measured by nuclear reaction analysis (NRA). At 1 × 1018 at. cm−2, helium bubbles are formed in the implanted zone, which also undergoes strong oxidation. Surface blisters are also observed and helium concentration threshold for bubble formation is estimated to about 4 at. % by correlating the MET observations with the results obtained by ion beam analysis. For the highest fluence, a residual concentration of 3.6 × 1017 at. cm−2 was measured just after implantation (instead of 1 × 1018 at. cm−2), which indicates a significant release of helium by the material during the process. The link between the microstructural evolution of the material, its progressive oxidation under beam and the release of helium is discussed. The very likely role played by the porosity on the oxidation of the material under irradiation at RT is underlined. Finally, the results obtained here on silicon carbide are compared with those obtained on another ceramic (TiC) which does not amorphize in similar conditions

Influence of grain size and microstructure on oxidation rate and mechanism in sintered titanium carbide under high temperature and low oxygen partial pressure

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Surface damage on polycrystalline β\beta-SiC by xenon ion irradiation at high fluence

International audienceNano-grained $\beta$-silicon carbide ($\beta$-SiC) pellets were prepared by Spark Plasma Sintering (SPS). These were implanted at room temperature with 800 keV xenon at ion fluences of 5.10$^{15}$ and 1.10$^{17}$ cm$^{-2}$. Microstructural modifications were studied by electronic microscopy (TEM and SEM) and xenon profiles were determined by Rutherford Backscattering Spectroscopy (RBS). A complete amorphization of the implanted area associated with a significant oxidation is observed for the highest fluence. Large xenon bubbles formed in the oxide phase are responsible of surface swelling. No significant gas release has been measured up to 10$^{17}$ at.cm$^{-2}$. A model is proposed to explain the different steps of the oxidation process and xenon bubbles formation as a function of ion fluence