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Gao J.-C.,Chongqing University | Wu S.-F.,Chongqing University | Yang X.-D.,Yibin Nuclear Fuel Corporation | Chang X.,Yibin Nuclear Fuel Corporation
Yuanzineng Kexue Jishu/Atomic Energy Science and Technology | Year: 2010

Oxidation mechanism and kinetics in static air at 513 K of uranium dioxide powder was investigated on purpose to obtain surface pre-oxidation treated active uranium dioxide powder whose O/U ratio in outer layer was approximately 2.25 while whose phase in core was still uranium dioxide so as to carry out low temperature sintering test. Oxidation process of uranium dioxide powder oxidized at 513 K is divided into the earlier period and the later period. The limitation of absolute increased mass ratio of uranium dioxide powder at 513 K in the later period is 0.489%. The reaction rate is controlled by interface chemical reaction in the earlier period and by diffusion in the later period. Oxidation mechanism of uranium dioxide powder oxidized at 513 K in the earlier period conforms to scaled core model. The functional relationship between increased mass in unit area of single uranium dioxide particle and oxidation time t can be expressed by equation Δw/Sn=0.1041t-2.14667, oxidation rate constant kc in the earlier period of uranium dioxide powder is 3.49×106exp(-73919.39/RT).

Gao J.,Chongqing University | Wu S.,Chongqing University | Yang X.,Yibin Nuclear Fuel Company | Chang X.,Yibin Nuclear Fuel Company
Cailiao Yanjiu Xuebao/Chinese Journal of Materials Research | Year: 2012

The relationship between surface pre-oxidation and low-temperature sintering of uranium dioxide powders was studied. The oxidation processess of uranium dioxide powders in air were analysed by DSC-TG. The morphology, phase constitution and properties of modified powders were tested by SEM, XRD and BET. The sintering behavior of uranium dioxide powders before and after modification was researched and compared by thermal expansion instrument. The results show that a process of 240°C×8 h in air is the optimum process conditions for surface modify uranium dioxide powders. There are UO 2+x and a little U 3O 7 phases in surface layer of the powders after modification. The beginning shrinkage temperature of modified powder pellets in Ar decreased from 1096-1171°C to 572-576°C, average line shrinking rate increased from 151×10 -6/K to 308×10 -6/K, density of the uranium dioxide pellets increased also from 8.52 g/cm 3 to 9.44 g/cm 3. Density and O/U of the modified powders sintered pellets at 1300°C×5 h/N 2 + 5%CO 2-1500°C×1 h/H 2 is 10.26 g/cm 3 and 2.013. © right.

Gao J.,Chongqing University | Wu S.,Chongqing University | Yang X.,Yibin Nuclear Fuel Corporation | Li R.,Chongqing University | Wang Y.,Chongqing University
Fenmo Yejin Jishu/Powder Metallurgy Technology | Year: 2010

Preparation and properties of the uranium dioxide powders with active surface layer for low temperature sintering were studied in this paper. Effect factors on specific surface area of uranium dioxide powders were determined by orthogonal experiment. Oxidation process and phases and properties of the powders were analyzed by DSC-TG, XRD, BET. The results show that 330°C × 8h and 18%O2+N2 is better process for pre-oxidation of uranium dioxide powders. Main effect factors on specific surface area of uranium oxide powders in pre-oxidation are oxidation atmosphere and oxidation temperature. DSC analysis shows that there is a little of U3O7 in uranium dioxide powders by pre-oxidation treatment at 240°C for 8h in air, all UO2 powders will become U3O8 at 382°C or 815°C for 8h in air. Therefore the powders with optimal O/U ratio for low temperature sintering will be obtained by pre-oxidation of powders at 240-370°C in air.

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