Produção de pastilhas cerâmicas combustíveis de UO2 dopadas para aplicação nuclear /

Abstract

The performance of UO2 fuel pellets is mainly limited by the fission gas release. A fuel that retain more of these fission gases lead to a decrease in the internal rod pressure at the end of its life cycle, improving the safety and operational margins. In order to overcoming the limitation mentioned, pellets with high average grain sizes (≥ 30 µm) and sintered densities (≥ 10.53 g/cm3 ) have been manufactured using doping technology. Considering the exposed scenario, the goal of this study was to manufacture doped UO2 fuel ceramic pellets using 0.05, 0.10, 0.20 and 0.30 wt% of alumina, niobia and chromia as additives to the standard fuel. The results showed that the alumina decreased the densities almost linearly and did not promoted any significant changes in average grain sizes. The niobia provided an increase in densities close to linear (≥ 0,10 wt%) and, for the grains sizes, the highest value of this study was obtained (52.31 µm; 0.30 wt%). Using chromia as additive, the sintered densities were improved (10,60 g/cm3 ; 0,10 %p) and then diminished until the minimum for the system (10.56 g/cm3 ; 0.30 %p). The grains grew till 0.20 wt% (37.51 µm), with a slight decrease in 0.30 %p (34.83 µm). To sum up, chromia is the most promising dopant because, with the lowest amount (≤ 0.20 wt%), it promoted the highest densification and grain growth.