A process for producing sintered mixed metal oxide nuclear fuel pellets containing UO.sub.2 and the oxide of at least one other fissile or fertile or rare earth element M, said pellets being directly soluble in nitric acid without nitric acid additives or prior treatment of the pellets, comprising the steps of:
- (a) mixing together aqueous solutions of uranium nitrate and the nitrate of said at least one other element M;
- (b) concentrating the mixture of solutions;
- (c) thermally denitrating said concentrated mixture, without additives, to obtain an at least partially denitrated intermediate mixed oxide powder of high reactivity, with the uranium in valence VI;
- (d) optionally calcining said intermediate mixed oxide powder to the extent necessary to convert uranium oxide to U.sub.3 O.sub.8 and to complete the conversion of difficult to decompose nitrates into oxides;
- (e) directly reducing, without grinding, the resulting mixed oxide powder to bring the uranium to valence IV;
- (f) optionally stabilizing the uranium oxide UO.sub.2 in the reduced oxide mixture;
- (g) shaping and pressing the resulting reduced oxide mixture to obtain pellets of green material suitable for manufacturing the mixed oxide fuel;
- (h) sintering said pellets of green material at high or low temperature in a reducing and/or gently oxidizing atmosphere;
- (i) grinding said sintered pellets,
- said process providing as a result of steps (c), (d), (e) and (f) mixed oxide powders of high flowability and good sinterability without crushing, whereby no troublesome effluent or dangerous aerosol of solids is produced as a result of crushing.