Examination of possible mitigation of MOX pellet in-reactor behaviors by means of its microstructure control during manufacturing with surrogate CeO2 for PuO2

Simulated MOX pellet microstructures with various pore size distributions and grain sizes were attempted to investigate the pellet in-pile behavior by relating between the their microstructural features and thermal resintering behavior. For fuel specimens, UO2-5wt%CeO2 was used, with CeO2 being as a surrogate for PuO2. In order to realize the various distributions of pore size and structure, an organic poreformer was added during powder preparation step. Also, Cr2O3, a known as an effective grain growth additive for UO2 fuel, for the grain growth of UO2-5wt%CeO2 pellet was admixed up to 0.3wt% in the powder preparation step in order to elucidate the interaction between the pore formation and matrix grain growth, and consequent variations in pore size distribution. Sintered density decreased linearly as a function of AZB content and its slope of density change on the AZB content was about -4. Not only the pellets with mono-modal pore distribution but also the pellets with bimodal pore showed the large densification during the resintering. It is confirmed that the pores with the size of below 10μm principally shrank by moving grain boundary. (author)