Dilatometric study of U1−xAmxO2±δ and U1−xCexO2±δ reactive sintering

In order to reduce the radiotoxicity of nuclear fuel waste, the transmutation of americium in U1−xAmxO2±δ dedicated fuels is considered. A convenient route to produce such fuels is reactive sintering from a UO2+δ/AmO2−δ green pellet, i.e., a single heat treatment during which both the densification and the formation of the U1−xAmxO2±δ solid solution occur. The mechanisms of such sintering are however barely known and require experimental data. In this aim, the densification through reactive sintering of a UO2+δ/AmO2−δ sample was monitored by dilatometry. The obtained results were compared to those reported for the formation of the U1−xAmxO2±δ solid solution monitored by in situ high-temperature X-ray diffraction. To assess the use of Ce as a substitute of Am, similar dilatometric studies were also carried out on UO2+δ/CeO2 pellets. Obtained results show that the use of a reactive sintering causes a delay in the densification process associated to the competition between solid solution formation and densification, which yields limitations in pellet final densities. The importance of redox behavior of Am (or Ce) on the achievement of solid solution formation and densification are also discussed, especially based on discrepancies in densification behavior between UO2+δ/AmO2−δ and UO2+δ/CeO2.