An innovative nuclear fuel for pressurized water reactors (PWR) is under study in order to gain margins during power transients. Indeed, the frequent use of power transients in nuclear reactors can lead to fuel element embrittlement phenomena. During irradiation, the combination of the pellet-cladding interaction (PCI) and the formation of fission products (FP), some of which, such as iodine, have corrosive forms (TeI₂, I₂) for the cladding can lead to its rupture by stress corrosion cracking (SCC) [1]. It has been shown that the speciation of these corrosive forms depends on the oxygen potential. It is therefore possible to control the FP speciation by doping the fuel with a redox buffer couple which allows fixing the oxygen potential during reactor operation.
Previous studies were carried out in the framework of PhD theses of V. Pennisi (2015) [2] and M. Khair (2018) [3]. The Nb₂O₅/NbO₂ couple was identified as candidate to form a redox buffer within UO₂. This work allowed to define a process that leads to the elaboration of doped UO₂ pellets and it was shown that the couple’s composition evolves during sintering. Moreover, the obtained pellets did not present a homogeneous doping, nor a sufficient final density.
An optimization of the sintering process of the doped fuel is carried out through the study of the influence of various parameters on the composition of the dopant, the densification and the microstructure of the studied fuel. The sintering atmosphere is controlled to enable the conservation of the redox buffer. The dopant concentration varies between 0.5 and 4 wt%. Moreover, the dopant was pre-treated by cryo-grinding in order to reduce the particle size of the powder. The effects of these parameters were characterized by density measurements and SEM observations, completed by EDS analysis.

[1]           K. Une, « Stress Corrosion Cracking of Zircaloy-2 Cladding in Iodine Vapor », Journal of Nuclear Science and Technology, vol. 14, no 6, p. 443?451, juin 1977, doi: 10.1080/18811248.1977.9730783.
[2]           V. Pennisi, « Contribution à l’identification et à l’évaluation d’un combustible UO2 dopé à potentiel oxygène maîtrisé », PhD thesis, Université de Bordeaux, 2015.
[3]           M. Khair, « Oxydo-réduction et spéciation des produits de fission corrosifs dans les combustibles oxydes : évaluation des bénéfices d’un combustible tamponné en pO2 »,PhD thesis, Université de Bordeaux, 2019.