Abstract ThO 2 containing around 2–3% 233UO 2 is the proposed fuel for the forthcoming Indian Advanced Heavy Water Reactor (AHWR). This fuel is prepared by powder metallurgy technique using ThO 2 and U 3O 8 powders as the starting material. The densification behaviour of the fuel was evaluated using a high temperature dilatometer in four different atmospheres Ar, Ar–8%H 2, CO 2 and air. Air was found to be the best medium for sintering among them. For Ar and Ar–8%H 2 atmospheres, the former gave a slightly higher densification. Thermogravimetric studies carried out on ThO 2–2%U 3O 8 granules in air showed a continuous decrease in weight up to 1500 °C. The effectiveness of U 3O 8 in enhancing the sintering of ThO 2 has been established.