Patent Number: 
Section: claims

1. A method for fabricating a sintered duplex nuclear fuel pellet, comprising the steps of:preparing a first powder composed of a material selected from the group consisting of UO2 and UO2—Er2O3, and a second powder composed of UO2—Gd2O3 and a sintering additive;producing a duplex compact consisting of an annular outer portion composed of the first powder and a cylindrical inner portion composed of the second powder; andsintering the duplex compact under a reducing gas atmosphere,wherein the sintering additive is manganese oxide of from 0.001% to 2% by weight based on the total weight of the cylindrical inner portion, and the density of the sintered duplex nuclear fuel pellet is more than 94% of theoretical value,wherein the sintering additive is added only to the second powder. 2. The method according to claim 1, wherein the Er2O3 content in the mixture UO2—Er2O3 constituting the first powder is 4% by weight or less. 3. The method according to claim 1, wherein the Gd2O3 content in the mixture UO2—Gd2O3 constituting the second powder is in the range of 4% to 15% by weight. 4. The method according to claim 1, wherein the reducing gas is hydrogen gas, or a mixed gas of hydrogen gas with at least one gas selected from water vapor, inert gases and carbon dioxide. 5. The method according to claim 1, wherein the duplex compact is sintered in the temperature range of between 1,600° C. and 1800° C. 6. The method according to claim 1, wherein at least part of the UO2 constituting the annular outer portion and the cylindrical inner portion is replaced by PuO2.