Impact de la radiolyse alpha sur la corrosion d'alliages de magnesium en solution alcaline

National audienceLe retraitement des combustibles nucleaires de la filiere UNGG (Uranium Naturel Graphite Gaz) requiere le conditionnement du materiau de gainage de ces assemblages combustible a base d'alliages de magnesium. L'immobilisation de ces gaines dans des matrices de blocage de type cimentaires necessite l'etude la corrosion de ces alliages de magnesium dans ces milieux fortement alcalins (pH > 12,5). Par ailleurs, ces gaines peuvent etre accompagnees de graphite, d'acier ou d'inox qui peuvent induire un couplage galvanique et ainsi augmenter la vitesse de corrosion. Suite a leur passage en reacteur, ces gaines irradiees ont ete activees et contaminees et presentent donc un spectre radiologique mixte et61537;et61538;et61543;. La radiolyse de la solution porale des matrices cimentaires pourrait alors modifier les mecanismes de corrosion de ces alliages de magnesium dans ces milieux alcalins.L'objectif de ce travail est d'etudier l'impact de la radiolyse et61537; a l'interface metal/solution par des mesures electrochimiques de la cible metallique sous irradiation. Pour ce faire, une cellule d'irradiation d'interfaces cible/solution (developpee au CEMHTI a Orleans (UPR3079 CNRS) [Cannizares, 2012]), a ete mise en oeuvre, apres modifications, sur le cyclotron du CEMHTI. L'irradiation et61537; des interfaces metal/solution visait a reproduire la radiolyse et61537; induite dans la solution porale d'une matrice cimentaire, par les emetteurs et61537; que sont les actinides qui composent le combustible (U, Pu). Il s'agissait de reproduire l'effet d'une contamination surfacique de la gaine de Mg par un fragment de combustible. Des irradiations et61537; d'interfaces (alliage de Mg/solutions alcalines) ont ete realisees en faisant varier les flux et61537;, la nature des alliages de Mg, la solution alcaline ou encore la nature du materiau en couplage galvanique. Au cours des irradiations, des mesures de potentiels de corrosion et de courants de corrosion ont pu etre realises in situ, permettant d'apprehender directement l'impact de la radiolyse et61537; sur la corrosion du metal. Ces premiers resultats ont mis en evidence plusieurs phenomenes, comme une relation entre courant de corrosion et flux et61537;, l'existence d'un seuil en flux et61537; a partir duquel un effet sur le courant de corrosion est observe, ainsi que l'importance du couplage galvanique

Inhomogeneous magnetism studied by ESR in La 1-x Sr x MnO 3 (0.45 ≤ x ≤ 0.62)

International audienceThe influence of strontium substitution on lanthanum site in La1-xSrxMnO3 manganites has been investigated with x ranging from 0.55 to 0.62 in the 130–400 K temperature range. Powder X-ray diffraction reveals structural changes from rhomboedral to tetragonal and to orthorhombic structures upon increasing Sr substitution. Magnetic properties also show a rich variety of phases and behaviors, including coexistence of phases above Curie temperature. The electron spin resonance measurements allow quantifying paramagnetic phases and properties with randomly distributed spins and ferromagnetic phases or inclusions with oriented spins giving rise to a local magnetic field. When x = 0.55, 0.57, the ferromagnetic state is the minor phase embedded in a paramagnetic matrix. Conversely, when x increases, the ferromagnetic phase grows and becomes the only phase observed for x = 0.62

Temperature dependence of phase separation and magnetic anisotropy by electron spin resonance in Pr

Electron spin resonance (ESR) measurements have been performed on polycrystalline samples of Pr0.6Ca0.4Mn1-xRuxO3 (x = 0, 0.1). The substitution of Ru in the Mn-site strengthens ferromagnetic interactions due to the double exchange between the Mn3+ and Mn4+ species and super-exchange between the Ru5+ and Mn3+ species. The temperature dependence of the ESR spectra indicates development of magnetic phase separation in Pr0.6Ca0.4Mn0.9Ru0.1O3 in contrast with the un-doped sample

Irradiation Defects in UO2 Leached in Oxidizing Water: An in-situ Raman Study

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In situ Raman spectroscopy for characterization of irradiation induced defects in graphite

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High temperatures and Raman scattering through pulsed spectroscopy and CCD detection

International audienceA Raman scattering system devoted to high temperatures is presented. It is based on a pulsed system to remove thermal emission with retaining charge-coupled device (CCD) detection. Two types of optical gating are used: a Pockels switch or an intensified CCD (ICCD), combining in this case the optical gate and the CCD detection. The performances of both systems are presented and their respective advantages are discussed and compared. The ICCD device allows recording of spectra in the 2000°C range, and typical results obtained on alumina and zirconia ceramics are shown

RAMAN STUDY OF SECONDARY MINERALS IN A RECENT LAVA TUBE

International audienceIn this paper, we present first the technical adaptations made for a field use of the laboratory in situ spectrometer, its capabilities and limits as well.Secondly, we present identification of secondary mineral phases growing in the lava tube with a particular emphasis on the study of white speleothems and dendrites by mean of XRD, SEM-EDX and Raman spectroscopy

Raman spectroscopy as suitable tool for the field study of recent volcanic environments

International audienceIn 2013, a portable Raman setup was implemented for on-site and rear-base characterization of volcanic products. Silica and rutile rock coatings, sulfate incrustations and speleothems, plagioclase, clinopyroxene, and (Fe, Ti, Cr) oxides lava minerals were identified on the young lava flows of Piton de la Fournaise volcano. These analytical abilities opens the way of in situ study of the first aging and weathering steps of recent lava flows. This paper relates the preliminary results of the field campaign. Three months after the investigation, all the speleothems have naturally disappeared. Copyright © 2016 John Wiley & Sons, Ltd

Combined synchrotron XRD and ì-Raman for following in situ the growth of solution deposited YBa2Cu3O7 thin films

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