Nkou-Bouala, Galy-Ingrid
Universite de Montpellier, Faculte des Sciences, Campus Triolet Place Eugene Bataillon - CC437 34095 Montpellier cedex 5 (France); CEA, DEN-ICSM (France)2016
Universite de Montpellier, Faculte des Sciences, Campus Triolet Place Eugene Bataillon - CC437 34095 Montpellier cedex 5 (France); CEA, DEN-ICSM (France)2016
AbstractAbstract
[en] Sintering is a key step in the elaboration of UOx and MOx (U/Pu mixed oxide) nuclear fuels pellets used in the pressurized water reactors. The first step of this process, which consists in the elaboration of a neck between the grains and led to the consolidation of the material, is generally described through numerical simulation. The models used for the theoretical description of this step are generally constituted by two spherical grains in contact. In order to perform the first experimental observations of the initial stage of sintering of ceramics materials of interest for electronuclear fuel cycle and to complement the numerical approaches, samples of lanthanide (CeO2) and actinides (ThO2 and UO2) dioxides with controlled morphology were examined by environmental scanning electron microscopy during heat treatment at high temperature (HT-ESEM).First, the protocols leading to the synthesis of lanthanides and actinides oxides microspheres were developed, and the powders obtained characterized. It was thus possible to obtain, for all the compounds studied, systems similar to those generally modeled. HT-ESEM was then used as the main investigation tool for the in situ study of the first stage of sintering of these compounds. The study of the morphological modifications occurring in isolated microspheres first confirmed their polycrystalline character. Indeed, heat treatment led to a progressive decrease of the crystallites number included inside the grains through different mechanisms (oriented attachment, diffusion), whose activation energy was evaluated. For the systems constituted by two CeO2 or ThO2 microspheres in contact, the ESEM micrographs allowed to observe the evolution of several parameters during heat treatment, such as neck size and grain size as well as distance between the grains center. Images processing methods using custom software were then applied in order to determine the quantitative kinetic data. The mechanisms involved, such as the rearrangement of crystalline planes and the matter diffusion, and the corresponding activation energies, were also identified. Furthermore, the law of neck growth, which allows one to describe the evolution of sintering degree, was used to determine the prevailing diffusion mechanism during heat treatment. The influence of various parameters on the sintering degree was also highlighted. For example, the influence of grains poly-crystallinity on sintering mechanisms and kinetics was particularly investigated study by working in parallel with polycrystalline and single crystal grains, then by comparing the experimental results with data coming from modeling. Finally, the methodology developed for the study of CeO2 and ThO2 was transposed to the compound of interest UO2. In this case, the data previously described were complemented by a first approach of the influence of atmosphere used during the heat treatment. (author)
[fr]
Le frittage est une etape cle de l'elaboration des pastilles de combustible nucleaire de type UOx et MOx (oxyde mixte (U,Pu)O2) utilisees dans les reacteurs a eau pressurisee. Le premier stade de ce procede, qui consiste en l'elaboration de ponts entre les grains et conduit a la consolidation des materiaux, est jusqu'a present principalement aborde par simulation numerique. Les modeles utilises pour la description theorique de cette etape du frittage sont alors generalement constitues de deux grains spheriques en contact. Afin de realiser les premieres observations experimentales du stade initial du frittage de materiaux ceramiques d'interet pour le cycle du combustible electronucleaire et d'en completer les approches numeriques, des poudres d'oxydes de lanthanides (CeO2) et d'actinides (ThO2 et d'UO2) de morphologie controlee ont ete etudiees par microscopie electronique a balayage en mode environnemental lors de traitements thermiques a haute temperature (MEBE-HT). Dans un premier temps, des protocoles conduisant a la synthese de microspheres d'oxydes de lanthanides ou d'actinides ont ete developpes, et les poudres obtenues entierement caracterisees. Il a ainsi ete possible d'obtenir pour l'ensemble des composes etudies des systemes similaires a ceux modelises. Par la suite, le MEBE-HT a ete utilise comme principal outil d'investigation pour le suivi in situ de ces composes. Ainsi, l'etude de l'evolution morphologique de microspheres isolees a tout d'abord confirme leur caractere polycristallin. Le traitement thermique conduit alors a une diminution progressive du nombre de cristallites sous l'effet de differents mecanismes (rearrangement mecanique, diffusion) dont l'energie d'activation a ete evaluee. Pour les systemes constitues de deux microspheres de CeO2 ou de ThO2 en contact, les micrographies collectees ont permis d'observer l'evolution de parametres tels que la taille du pont, la taille des grains et la distance entre leur centre au cours du traitement thermique. Des procedures de traitement d'images ont ensuite ete appliquees pour aboutir a des donnees cinetiques quantitatives. Les mecanismes mis en jeu, tels que le rearrangement des plans cristallins et la diffusion de matiere, ainsi que les energies d'activation correspondantes, ont en outre ete identifies. De plus, la loi de croissance des ponts, qui permet de decrire les cinetiques d'avancement du frittage, a ete utilisee pour determiner le mecanisme de diffusion preponderant lors du traitement thermique. L'influence de differents parametres sur l'avancement du frittage a enfin pu etre mise en evidence. A titre d'exemple, l'effet de la polycristallinite des grains sur les mecanismes et les cinetiques de frittage a ete etudie en travaillant en parallele sur des grains poly- et monocristallins, puis en comparant les donnees experimentales avec celles issues de modelisation. Enfin, la methodologie developpee pour l'etude de CeO2 et ThO2 a ete transposee au compose d'interet UO2. Dans ce cas, les donnees precedemment decrites ont egalement ete completees par une premiere approche de l'influence de l'atmosphere utilisee lors du traitement thermique. (l'auteur)Original Title
Premier stade du frittage des dioxydes de lanthanides et d'actinides: Une etude in situ par MEBE a haute temperature
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7 Nov 2016; 202 p; 330 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; Also available from Service commun de documentation Universite de Montpellier Institut de biologie - 2e etage, bureau 212, 4, Boulevard Henri IV 34000 Montpellier (France); Sciences des Materiaux
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AbstractAbstract
[en] Sintering is one of the key-points of the processing of ceramic materials. It is then of primary interest for the nuclear fuel cycle, in which it constitutes an important step in the fabrication of either UO2 or (U,Pu)O2 pellets used in current PWR reactors. The sintering of actinides oxides not only drives the final density and microstructure of the fuels, but also several characteristics that can impact significantly their behavior in the reactor. Dedicated tools are then needed to monitor the microstructure of such materials and forecast their evolution. In this frame, this paper presents the new potentialities offered by the use of environmental scanning electron microscope at high temperature (HT-ESEM) for the study of nuclear ceramics sintering. First, the results obtained from bulk pellets are detailed, either regarding original fundamental data at the grain level (such as grain boundaries and pores motion), or design of dedicated microstructures through the assessment of grain growth kinetics. Acquisition of sintering maps thanks to the combination of HT-ESEM observations and classical dilatometric measurements are also addressed. In a second part, observations undertaken at the 2-grain scale to monitor the first stage of sintering, dedicated to neck elaboration, are presented, and compared to the results currently provided by numerical models.
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Special issue: Nuclear materials
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Journal Article
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ACTIVATION ENERGY, CERAMICS, CERIUM OXIDES, COMPARATIVE EVALUATIONS, DENSITY, FUEL PELLETS, GRAIN BOUNDARIES, GRAIN GROWTH, IMAGE PROCESSING, NUCLEAR FUELS, NUMERICAL ANALYSIS, PLUTONIUM DIOXIDE, PWR TYPE REACTORS, SCANNING ELECTRON MICROSCOPY, SINTERED MATERIALS, SINTERING, THORIUM OXIDES, TIME DEPENDENCE, URANIUM DIOXIDE
ACTINIDE COMPOUNDS, CERIUM COMPOUNDS, CHALCOGENIDES, ELECTRON MICROSCOPY, ENERGY, ENERGY SOURCES, ENRICHED URANIUM REACTORS, EVALUATION, FABRICATION, FUELS, MATERIALS, MATHEMATICS, MICROSCOPY, MICROSTRUCTURE, OXIDES, OXYGEN COMPOUNDS, PELLETS, PHYSICAL PROPERTIES, PLUTONIUM COMPOUNDS, PLUTONIUM OXIDES, POWER REACTORS, PROCESSING, RARE EARTH COMPOUNDS, REACTOR MATERIALS, REACTORS, THERMAL REACTORS, THORIUM COMPOUNDS, TRANSURANIUM COMPOUNDS, URANIUM COMPOUNDS, URANIUM OXIDES, WATER COOLED REACTORS, WATER MODERATED REACTORS
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Guillaumont, Robert; Nkou Bouala, Galy Ingrid; Smith, Anna; Martinez, Julien; Rodrigues, Davide; Lopez-Leon, Servando; Bahri, Mohamed Ali; Georgette, Selim; Autillo, Matthieu; Audras, Matthieu; Costagliola, Amaury; Suzuki-Muresan, Tomo; Fleury, Guillaume; Brunel, Benoit; Benamrane, Yasmine; Cagniant, Antoine; Villard, Arnaud; Maloubier, Melody; Brulfert, Florian; Davantes, Athenais; Maurice, Remi; Vandenborre, Johan; Le Guillou, Mael; Leoni, Elisa; Solari, Pier Lorenzo; Fichet, Pascal; Bacri, Charles-Olivier
Institut de Physique Nucleaire d'Orsay - IPN Orsay, 15 rue Georges Clemenceau, 91406 Orsay (France)2014
Institut de Physique Nucleaire d'Orsay - IPN Orsay, 15 rue Georges Clemenceau, 91406 Orsay (France)2014
AbstractAbstract
[en] The first session of this colloquium concerned the nuclear fuel: elaboration of nanoparticles of actinide oxides, study of Na-U-O and Na-Np-O phase diagrams, relationships between precursors and sintering behaviour, study of uranium IV and thorium IV speciation. The second session addressed fuel processing: semi-quantitative analysis of metallic cations in organic phase, cathodic reduction of plutonium IV solutions, study of paramagnetism of actinide complexes, complexing of actinides III and IV, behaviour under alpha radiation of oximes and influence on redox properties of actinides. The third session addressed radionuclides and geosphere: study of the reactivity of surfaces of clayey phases, study of alpha-Al2O3/fulvic acid/Eu III interactions, determination of microscopic interactions between actinides and humic substances. Then, after a contribution of the evolution of the use of modelling tools of atmospheric dispersion and of the health and environmental impact in the support to the management of radiological emergencies, a fourth session addressed the relationship between radiochemistry and health: bio-accumulation and speciation of europium, mechanisms of interaction between actinides and a protein, speciation of (poly)molybdate and (poly)tungstate ions, study of astatine chemistry by means of quantum molecular modelling. The fifth session addressed storage safety: C14 diffusion in used fuel claddings, migration of deuterium in nuclear graphite, quantification of the production of radiolysis gas in radioactive waste parcels. The sixth session addressed tools for radiochemistry: advances on MARS (the beamline dedicated to radioactive materials at synchrotron SOLEIL), from radiolysis to radiochemistry (speciation of radio-elements under alpha and gamma radiation), presentation of γ3 (an electron/photon spectrometer with a high resolution and low background noise for the detection of ultra-traces of fission and activation products in the environment), analysis of wastes coming from the nuclear industry. Posters addressed the following issues: EF hand affins and uranium specific patterns engineering, Production of 64Cu radionuclides, Plutonium electrochemical kinetics in nitric acid, Study of the self-radiolysis of tritiated water, Study of uranium complexing by phenylphosphonate, Synthesis, structure and solubility of Rhabophane as a monazite precursor, Determination of 93Zr in radioactive effluents, Study of Tc redox in carbonate environment induced by radiolysis, Behaviour of rare gases in uranium-based nuclear fuels, Redox properties of Samarium in ionic liquids, Some chemical separations by chromatography developed for analytic purposes, Apatite composition effect (U-Th)/He thermo-chronometer, Coordination chemistry of uranium VI, In-situ Raman spectroscopy for the study of nuclear fuel salts, Dissolution of Thorium oxides, BDD/Si-PIN detector for direct spectrometry of actinides, Competition between chelating agents and identified target proteins of actinides, Nano-size metallic oxide cluster formation in Fe alloy by ion implantation.
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XIVes Journees nationales de radiochimie et de chimie nucleaire
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Sep 2014; 114 p; Colloquium 14. National days of radiochemistry and nuclear chemistry; Colloque 14. Journees nationales de radiochimie et de chimie nucleaire; Orsay (France); 11-12 Sep 2014; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses
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Miscellaneous
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Conference
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ACTINIDES, ASTATINE, FUEL CYCLE, IONIZING RADIATIONS, MEASURING INSTRUMENTS, MEASURING METHODS, MEETINGS, NANOPARTICLES, NUCLEAR CHEMISTRY, NUCLEAR FUELS, NUCLEAR PROPERTIES, NUCLEAR REACTIONS, RADIATION PROTECTION, RADIOACTIVE WASTE PROCESSING, RADIOCHEMICAL ANALYSIS, RADIOCHEMISTRY, REPROCESSING, SOLVENT EXTRACTION, SYNCHROTRONS
ACCELERATORS, CHEMICAL ANALYSIS, CHEMISTRY, CYCLIC ACCELERATORS, ELEMENTS, ENERGY SOURCES, EXTRACTION, FUELS, HALOGENS, MANAGEMENT, MATERIALS, METALS, NONMETALS, PARTICLES, PROCESSING, QUANTITATIVE CHEMICAL ANALYSIS, RADIATIONS, RADIOACTIVE WASTE MANAGEMENT, REACTOR MATERIALS, SEPARATION PROCESSES, WASTE MANAGEMENT, WASTE PROCESSING
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