Densification of UO2 pellets by microwave sintering using an instrumented multimode cavity

Abstract A study of microwave sintering of uranium dioxide pellets has been performed with the aim to densify the material. Microwave sintering heating has been carried out in a 2.45 GHz multimode cavity, designed to fit the different requirements linked to sintering of nuclear ceramics. Hybrid and direct microwave heating (i.e., with and without susceptor) conditions were carried out. In the hybrid condition, thermal cycles at temperatures up to 1700°C, with a heating rate of 20 °C/min and dwell times of 10–60 min could be applied to the samples. The sintered specimens exhibited high values of densities (92.6–94.6% of theoretical density) with a grain size range of 9.1–11.8 μm, which is close to the results obtained with conventional sintering with longer thermal cycles. The pellet tested in the direct configuration only heated until 950°C, showing the impossibility to heat UO2 in a microwave furnace without the help of a susceptor.