Microwave process for sintering of uranium dioxide

Sintering of UO2 pellets by microwave was studied using a multi-mode-type cubic applicator (2.45 GHz). The quasi-steady-state temperature distribution in the cylindrical UO2 pellet under microwave heating was measured. If the heating rate was as high as 20–30 K/min, local sintering occurred and a large crack was formed around the circumference of the sintered pellet. An optimum condition to have intact crack-free pellets was to heat at a rate 7 K/min up to 1550 °C and then 3 K/min to final sintering temperature. The effect of sintering temperature and time on the density and grain size of UO2 pellets was investigated for the microwave sintering process where the heating rate was properly controlled. The results were compared with those obtained by conventional sintering method. The microwave processing produced an enhancement in both densification and grain growth. The UO2 pellet without any cracks having more than 95% theoretical density and 5 μm grain size was obtained by the present microwave sintering in H2 at 1600 °C for 1 h.