Method of manufacturing sintered oxide nuclear fuel

Purpose: To reduce the increase in PCI due to increase in swelling, as well as reduce the releasing rate of FP gases. Method: UO2 powder and 15 wt% GD2O3- powder at the maximum are mixed, at the material ratio of Gd2O3-incorporated UO2 pellet, within a range of greater than 2.10 for O/M (M = U + Gd) and within a range from 2.10 to 2.20 for O/U ratio of UO2 powder, molded and then sintered. In this case, sintering is at first proceeded in a CO2 gas atmosphere mixed with air to such a degree as the crystal grain size is from 2 to 3 mm. Then, at the second step, the atmosphere is switched to H2 and the temperature is increased abruptly up to a temperature higher than 1700degC at such an rising rate as not causing cracking. This enables to obtain a sintering product in which the average crystal grain size at the outer circumferential portion is smaller than that in the inner side, thereby obtain the intended purpose. (Takahashi, M.)