Manufacturing method of niobia(Nb2O5)-added oxide nuclear fuel pellet

Niobium oxides, as a sintering promoter, are applied with reducing heat treatment, in hydrogen or a gas stream of a mixture of hydrogen and nitrogen at 800degC for an appropriate period of time. Then, pentavalent Nb2O3 is converted into tetravalent NbO2 powders. 0.2 to 1.0% by weight of the NbO2 powders is added to a starting powder of uranium oxides or the mixture of uranium oxides and plutonium oxide, and then mixed and molded into green pellets. The pellets are applied with reducing heat treatment in hydrogen or a gas stream of a mixture of hydrogen and nitrogen. Further, in a sintering atmosphere, it is sintered in a gas stream within such a range of the flow rate ratio of carbon dioxide and carbon monoxide that the relationship between the logarithm of the flow rate ratio of carbon dioxide and carbon monoxide and the reciprocal of the absolute temperature of the sintering temperature is enveloped by a substantial linear line. This can reduce the cost for molding and fabrication. (T.M.)