Sintering of mixed UO2 and U3O8 powder compacts

U3O8 powder made by oxidation of defective UO2 pellets was mixed with UO2 p owder, and Nb2O5 was then added. Powder mixtures including various U3O8 con tents were pressed into compacts and sintered at 1680 degrees C in a reduci ng atmosphere. Without Nb2O5 addition, the U3O8 content of a mixed UO2-U3O8 compact is allowed only within about 15 wt%, since higher U3O8 contents ma ke the UO2 pellet density unacceptable. Using more than 0.3 wt% Nb2O5, howe ver, the UO2 pellet density is higher than 94% TD under any U3O8 content of the mixed compact. The grain size of the UO2 pellets increases with the Nb 2O5 content of the mixed compact but is not influenced by the U3O8 content. Therefore, the U3O8 powder can be reused without any limit in the UO2 pell et fabrication by sintering with Nb2O5. It is supposed that NbO2, a reduced product of Nb2O5, is dissolved in UO2 to form uranium vacancies. The enhan cement of densification and grain growth may be attributed to the increase of the uranium vacancy concentration. (C) 2000 Elsevier Science B.V. All ri ghts reserved.