Résumé
Sintering is one of the key-point of the processing of ceramic materials. It is then ofprimary interest for the nuclear fuel cycle, in which it constitutes an important step in thefabrication of either UO2 or (U,Pu)O2 pellets used in current PWR reactors. The sintering ofactinides oxides not only drives the final density and microstructure of the fuels, but alsoseveral characteristics that can impact significantly their behavior in the reactor. Dedicatedtools are then needed to monitor the microstructure of such materials and forecast theirevolution. In this frame, this paper presents the new potentialities offered by the use ofenvironmental scanning electron microscope at high temperature (HT-ESEM) for the study ofnuclear ceramics sintering.First, the results obtained from bulk pellets are detailed, either regarding originalfundamental data at the grain level (such as grain boundaries and pores motion), or design ofdedicated microstructures through the assessment of grain growth kinetics. Acquisition ofsintering maps thanks to the combination of HT-ESEM observations and classicaldilatometric measurements are also addressed. In a second part, observations undertaken atthe 2-grain scale to monitor the first stage of sintering, dedicated to neck elaboration, arepresented, and compared to the results currently provided by numerical models.