Method of manufacturing nuclear fuel lumps containing gadolinium oxides

Purpose: To enable to easily control the upper-limit of pellet density, and obtain thermally stable sintered lumps of low porosity. Method: Powder of organic acid salts of gadolinium, preferably, at least one of oxalate and carbonate, or a mixture incorporated with gadolinium oxide is admixed as additives for nuclear fuel material. In this case, while the addition amount of the additives is determined by the calculation for the nuclear fuel design, since the carbonate and the organic acid salt of gadolinium is heat-decomposed into gadolinium oxide at a temperature of about 100 0C or less much lower than one thousand and several hundred 0C as the pellet sintering temperature, the addition amount may also be determined being converted as the resultant gadolinium oxide. Then, the mixed powder is melted in a press followed by sintering. In this case, the pellet can easily be adjusted for a predetermined sintering density and the porosity of the sintered lumps can be reduced to obtain thermally stable pellets. (Seki, T.)