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The conversion of minor actinides to fuel starting materials for transmutation in a closed nuclear cycle is a big challenge for the next decades and the development of Gen(IV) nuclear systems. Conversion routes are numerous, but one needs to prove that they can be adapted to handle minor actinides. One of them is called the resin process and is par...
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... morphology of the micro-spheres remains constant after the heat treatment as is shown in figure 8 for the mineralization of uranium-americium loaded resin microspheres. As one can see in figure 9, the radius of a micro-sphere of neodymium loaded resin decreases by a factor of 2. The homogeneity of the material obtained after thermal conversion under argon has been checked by electron probe microanalysis for a uranium-neodymium resin and shows that the repartitioning of U, Nd and C is homogeneous up to the core of the microsphere. ...
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Citations
... Microsphere synthesis is carried out from metal loaded ion exchange resin beads [13,15,20] that are mineralised by thermal treatment under air to obtain regular-shaped oxide microspheres. The ion exchange resin used for the fixation was a gel-type IMAC HP333 carboxylic resin supplied by Dow Chemicals Company (Dow Chemical Company, Chauny, France). ...
Actinide oxide microspheres are considered as promising substituents to powder precursors for the production of ceramic pellets of nuclear fuel or targets. Porous microspheres of sub-millimetric size are synthesised using the Weak Acid Resin process. Controlling their microstructure and their mechanical properties is essential to predict the microstructure of green compacts and sintered pellets. Here, cerium and gadolinium are used to mimic actinides as metal cation. Single microspheres are crushed experimentally using a micropress in a Scanning Electron Microscope (SEM) to investigate their mechanical properties and visualise their fracture behaviour. The results are compared to numerical simulations based on the Discrete Element Method (DEM). In DEM, a microsphere is modelled as an assembly of bonded spheres representing aggregates. Bonds may fracture in tension or shear. A limited number of material parameters (aggregate elastic modulus, bond strength) are sufficient for the accurate simulation of the fracture behaviour of a microsphere.
... In this aim, the development of an innovative route using micrometric spherical precursors is studied. Through an adaptation of the weak acid resin (WAR) process [21][22][23][24][25], the general approach consists of elaborating micrometric and brittle spherical mixed-oxide precursors. This geometry was chosen to facilitate the filling of the compaction chamber and subsequent pelletizing. ...
... 20 As with the sphere-cal or the SGMP programme, our study deals with the development of a spherule route which is called the calcined resin microsphere pelletization (CRMP) process. It consists of the synthesis of mixed oxide precursors of spherical form and millimetric size obtained by an adaptation of the weak acid resin (WAR) process [21][22][23][24] and their compaction into pellets before sintering. The microsphere synthesis is based on the fixation of cerium cations into beads of ion exchange resin (IER) and their mineralization in air to form the oxide. ...
This study deals with the preliminary development of a powder-free process called calcined resin microsphere pelletization (CRMP) used for the fabrication of metallic oxide pellets. This dustless process could be used for the fabrication of mixed U1−yAmyO2±x pellets dedicated to the transmutation of Am in fast neutron reactors. In this study, porous CeO2 microspheres, used as a surrogate of AmO2, were obtained after mineralization of cerium loaded ion exchange resin beads. These millimetric oxide microspheres were die-pressed into pellets which were then sintered under air to form ceramic pellets. Their densities approached 95% of theoretical density of CeO2 and a homogeneous microstructure was obtained by using optimized microspheres. The influence of calcination parameters on the characteristics of microspheres and on the properties of sintered pellets is discussed.
Mixed uranium-americium oxides are one of the materials envisaged for Americium Bearing Blankets dedicated to transmutation in fast neutron reactors. Conversion and fabrication processes are currently developed to make those materials in the form of dense and homogeneous oxide ceramic pellets or dense granulates incorporating uranium and americium. Their development points out the need of a simplified and optimized process which could lower hazards linked to dust generation of highly contaminating and irradiating compounds and facilitate material transfer in remote handling operations. This reason motivated the development of innovative “dustless” route such as the Weak Acid Resin route (WAR) which provides the oxide precursors in the form of sub-millimeter-sized microspheres with optimal flowability and limits dust generation during conversion and fabrication steps. This study is thus devoted to the synthesis of mixed uranium-americium oxide microspheres by the WAR process and to the characterization of such precursors. This work also deals with their application to the fabrication of dense or porous pellets and with their potential use as dense spherules to make Sphere-Pac fuel.
This chapter summarizes different innovative fuel production techniques using the product streams from an aqueous reprocessing route with a focus on the well-known sol-gel conversion method. There is also reference to additional steps, post sol-gel conversion; for example, in order to load the sample matrix with minor actinides or to introduce a barrier for fission products.
This study is devoted to the synthesis and the characterization of porous metal oxide microsphere from metal loaded ion exchange resin. Their application concerns the fabrication of uranium-americium oxide pellets using the powder-free process called Calcined Resin Microsphere Pelletization (CRMP). Those mixed oxide ceramics are one of the materials envisaged for americium transmutation in sodium fast neutron reactors. The advantage of such microsphere precursor compared to classical oxide powder is the diminution of the risk of fine dissemination which can be critical for the handling of highly radioactive powders such as americium based oxides and the improvement of flowability for the filling of compaction chamber. Those millimetric oxide microspheres incorporating uranium and americium were synthesized and characterizations showed a very porous microstructure very brittle in nature which occurred to be adapted to shaping by compaction. Studies allowed to determine an optimal heat treatment with calcination temperature comprised between 700–800 °C and temperature rate lower than 2 °C/min. Oxide Precursors were die-pressed into pellets and then sintered under air to form regular ceramic pellets of 95% of theoretical density (TD) and of homogeneous microstructure. This study validated thus the scientific feasibility of the CRMP process to prepare bearing americium target in a powder free manner.
Transmutation of americium in heterogeneous mode through the use of U1-xAmxO2±δ ceramic pellets, also known as Americium Bearing Blankets (AmBB), has become a major research axis. Nevertheless, in order to consider future large-scale deployment, processes involved in the AmBB fabrication have to minimize fine particles dissemination, due to americium presence, which considerably increases the risk of contamination. New synthesis routes avoiding the use of pulverulent precursors are thus currently under development, such as the Calcined Resin Microsphere Pelletization (CRMP) process. It is based on the use of weak-acid resin (WAR) microspheres as precursors, loaded with actinide cations. After two specific calcinations under control atmospheres, resin microspheres are converted into oxide microspheres composed of a monophasic U1-xAmxO2±δ phase. Understanding the different mechanisms implied during thermal conversion, leading to the release of organic matter and the formation of a solid solution, appeared essential. By combining in-situ technics such as XRD and XAS, it has become possible to identify the key temperatures for oxide formation, and the corresponding oxidation states taken by uranium and americium during mineralization. This paper thus presents the first results on the mineralization of (U,Am) loaded resin microspheres into a solid solution, through in-situ XAS analysis correlated with HT-XRD.
