Density control method for nuclear fuel pellet

In a density control for nuclear fuel pellets produced from a raw material powder containing dioxides of uranium or plutonium and oxides of rare earth elements, trimetal octoxides formed from dioxides or the raw material powder not undergoing thermal hysteresis at higher than 1,000degC are added to the raw material powder. Further, trimetal octoxides obtained by calcining a sintering product of the raw material powder is added in addition the trimetal octoxides of the elements. Furthermore, the density of the nuclear fuel pellet is controlled by two kinds of trimetal octoxides obtained by calcining the sintering products of the dioxides, the raw material powder or the nuclear fuel sintering materials at 350 to 800degC. Since trimetal octoxides powder derived from the raw material powder is used as a density increasing additive for the nuclear fuel pellets, it is advantageous in view of stable operation, different from a conventional method of controlling molding condition and sintering condition, and since the trimetal octoxides powder derived from the sintering product is also used, various kinds of density control for nuclear fuel pellets can be conducted. (N.H.)