Application of Weak Acid Resin process to the production of spherical and calibrated oxide precursor bearing uranium and americium overview of 10 years research at CEA
Résumé
Mixed uranium-americium oxides are one of the materials envisaged for Americium Bearing Blankets dedicated to americium transmutation in fast neutron reactor. Recently, several processes have been developed in order to improve and validate fabrication in terms of material specifications such as density and homogeneity. The challenge is also to propose simplifications for lowering industrial costs and hazards linked to dust generation of highly contaminating and irradiating compounds such as Am based oxides which presence complicates grinding and milling operations commonly encountered in conventional powder metallurgy processes. Our goal was then to develop an innovative and dust-free process for synthetizing uranium-americium mixed oxide in the form of spherules of the size of hundreds microns in order to facilitate remote handling operations and reduce fine dust dispersion. In this way, the Weak Acid Resin route (WAR), originally dedicated to uranium carbide kernel synthesis, was selected and adapted to mixed oxide fabrication incorporating uranium and americium. This process is based on the fixation of actinide cations in acrylic resin beads and the subsequent mineralization in air of the metal loaded resin into oxide microspheres. A final reducing thermal treatment is then necessary to adjust oxygen stoichiometry and form the mixed oxide phase. This process has been tested and validated for many oxide compounds such as single lanthanide or uranium oxide but also for mixed uranium and lanthanides or americium compounds. Therefore, this contribution aims at describing the development of WAR process for oxide synthesis during recent years at CEA Marcoule and will detail particularly the synthesis and characterization of U0.9Am0.1O2±x mixed oxide precursor. The current study of pelletization and sintering of such precursors, known as Calcined Resin Microsphere Pelletization process (CRMP), will be also presented and will illustrate the application of WAR spherule metallurgy to the fabrication of uranium and americium containing materials.