Partitioning and transmutation processes are being researched for isolating longlasting radioactive elements from nuclear spent fuel and recycling them with appropriate strategies, in order to enhance atomic energy sustainability. Transmutation targets are needed, for which inert matrices, having specific characteristics and requirements, are under development. Although use of yttria stabilized zirconia (YSZ) shows promising results; however, the classical manufacturing strategy by powder metallurgy is not feasible, due to hazards derived by radioactive dust formation. Therefore, production by wet routes (using liquid precursors), is preferred. One promising method is external gelation (EG), a sol-gel approach that can be combined with infiltration of an MA solution, minimizing time and processes performed in a shielded environment. The purpose of the present work was the investigation of the external gelation method, followed by infiltration, to produce transmutation targets. 4 mol% yttria-stabilized zirconia microspheres were firstly produced via EG, analyzed by thermogravimetry and then calcined. Mechanical stabilization and pore formation following the calcination were evaluated by immersion density measurements, optical microscopy and pycnometry. XRD analysis and BET surface analysis provided additional information about the stabilization of the cubic zirconia phase and specific surface area. Microspheres were then infiltrated with different amounts (10, 20 or 30 mol%) of Nd3+, used as a surrogate for Am3+ and sintered to high density. A final characterization consisting of optical microscopy, XRD analysis and SEM analysis was performed, in order to assess product quality (in terms of single-phase compliance, geometricity and mechanical stability) as a function of the production parameters. Despite the initial trial-and-error approach, several microspheres’ batches were spherical after calcination and sintering. A 10 mol% Nd3+ eventually proved to be the best dopant concentration for EG produced YSZ microspheres. Finally, the scientific validity of the method was verified, and key parameters for further optimization were highlighted.
|Qualification||Master of Science|
|Date of Award||25 Aug 2022|
|State||Published - 25 Aug 2022|