PREPARATION AND CHARACTER IZATION OF SPENT NUCLEAR FUEL SURROGATES TO MIMIC POROSITY. (IONMAT PROJECT. SUBTASK 1.2)

Abstract

One of the most relevant microstructural changes occurring in irradiated UO2 fuel at high burnup is the development of the rim region, characterized by significant porosity and the formation of submicrometric grains. Understanding the influence of porosity on fuel behavior is essential for modelling spent fuel performance during storage and disposal. Within the framework of the IONMAT project, one of the goals was to fabricate UO2 pellets with distinct porosities using U3O8 as a pore-forming precursor. Pellets containing 0, 5, 12 and 19 wt.% U3O8 were produced, sintered under reducing atmosphere and characterized by XRD, pycnometry, BET specific surface area method and SEM. The objective was to reproduce porosity levels comparable to those observed in spent nuclear fuel while maintaining a UO2 matrix. The results demonstrate that the addition of different U3O8 quantities slightly modifies the microstructure and density of the sintered pellets. The highest porosity levels, as well as the greatest lattice parameter and specific surface area values, were obtained for the pellets initially containing around 5 wt.% U3O8, while the highest density corresponded to those where 19 wt.% U3O8 was added. XRD confirmed in all cases the preservation of the fluorite UO2 structure after sintering. These materials constitute suitable surrogates for future studies focused on the role of porosity in spent nuclear fuel behavior.