• Journal of the Korean Ceramic Society
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• v.29 no.8
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• pp.609-616
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• 1992

This study has been investigated on the milling of Aluminium Distearate (ADS) powder and characteristics of the ADS-doped UO2 pellets. As-received ADS powder of the agglomerated particles has not shown any milling effect because of heat generated during planetary milling. But the use of coolant to effectively remove heat generated during milling has been found an effective way in breaking up the agglomerates of ADS powder. The green density of the UO2 pellet decreases with the amount of ADS powder doped. Therefore, in order to get the sintered density of 95% pellet decreases with the amount of ADS powder doped. Therefore, in order to get the sintered density of 95% theoretical density, the 200 ppm ADS-doped UO2 pellet has to be pressed under higher compacting pressure of 3500~4000 kgf/$\textrm{cm}^2$ compared with the ADS-undoped UO2 pellet pressed under around 3000 kgf/$\textrm{cm}^2$. The ADS-dpoed UO2 pellet with even relatively low sintered density of 10.27 g/㎤ exhibits open porosity of 1% while open porosity of the ADS-undoped UO2 pellet is reduced to around 1% only after its sintered density increases to 10.43g/㎤. It is, therefore, concluded that doping of ADS powder significantly contributes to the decrease in open porosity of the UO2 pellet. The dilatometry of the ADS doped UO2 pellet shows the sintering rate curve with the bimodal mode, which could be attributed to a phase reaction between UO2 and ADS. The X-ray diffraction analysis indicates that there occurs not any new phase formed but the shift of the peaks. It would be expected that a phase reaction resulting in solid solution would happen in the temperature range of 130$0^{\circ}C$ to 150$0^{\circ}C$ between UO2 and ADS.

• Journal of Energy Engineering
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• v.15 no.1 s.45
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• pp.8-13
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• 2006

The oxidation behavior of $UO_2$, pellet was studied using an XRD and a thermogravimetric analyzer in the temperature range from 573 to 873 K and in the density range from 94.64 to 99.10% of theoretical density in air. It was found from the XRD study that $UO_2$ was completely converted to $U_3O_8$ in this experimental temperature range. The formation of $U_3O_8$ displays sigmoidal reaction kinetics. The oxidation rate was reduced with density. Induction time for the oxidation of $UO_2$ was delayed with density because of open pore formed in surface of $UO_2$ pellet. The activation energy for oxidation of $UO_2$ was determined to be 89.54 kJ/mol and 34.40 kJ/mol in the temperature range from 573 to 723 K and from 723 to 873 K, respectively.

• Applied Microscopy
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• v.29 no.3
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• pp.323-329
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• 1999

Synthesis of inorganic nanophase particles was performed to verify and understand the binding of non-ferrous metal ions including Al and $UO_2$ to the apoferritin molecules. Reconstituted inorganic particles of Al or $UO_2$ were identified by TEM as discrete electron dense cores encapsulated within the protein shell. The corresponding EDXA spectra confirm the presence of metal ions in the reconstituted ferritin. The Al cores of ferritin has been studied by TEM for the first time. Bimetallic cores with Al/Fe and $UO_2/Al$ were also produced and examined under TEM. Mixed metal cores encapsulated in the protein shell are well formed and its corresponding EDXA spectra also confirm the presence of metal ions in the mineral cores. Therefore, the present study proves that ferritin can be used to synthesize inorganic nanophase particles of Al and $UO_2$.

• Journal of the Korean Chemical Society
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• v.29 no.2
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• pp.121-128
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• 1985

The electrochemical reduction of uranyl ion in aqueous basic media has been examined by d. c. polarography, differential pulsed polarography and cyclic voltammetry. From voltammograms obtained in uranyl solutions containing 0.1M sodium bicarbonate, either with or without the same amounts of sodium tripolyphosphate it is concluded that the first wave corresponds to the reduction of $UO_2^{2+}$ to $UO_2^+$. It is assumed that the uranyl ion undergoes appreciable hydrolysis in these media. The hydrolysis product $UO_2OH^+$ from $UO_2^{2+}$ is not reduced at the first wave, but is reduced at the second wave together with $UO_2^+$. The diffusion current was found proportional to the uranyl concentration in a range between $7.5 {\times} 10^{-4}$ and $3.75 {\times}10^{-3}$M.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.171-176
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• 1997

UO$_2$-Gd$_2$O$_3$fuel has been sintered to study the effect of powder property and sintering atmospheres on densification and microstructure. Three types of powders have been used; AUC-UO$_2$ powder and ADU-UO$_2$ powder were mixed with Gd$_2$O$_3$ Powder, and co-milled AUC-UO$_2$ and Gd$_2$O$_3$ powder. UO$_2$-(2, 5, 10)wt% Gd$_2$O$_3$pellets have been sintered at 168$0^{\circ}C$ for 4 hours in the mixture of H$_2$ and $CO_2$ gases, of which oxygen potential has been controlled by the ratio of $CO_2$ to H$_2$ gas. Densities of UO$_2$-Gd$_2$O$_3$ fuel pellets are quite dependent on powder types, and UO$_2$-Gd$_2$O$_3$ fuel using co-milled UO$_2$ powder yields the highest density. A long range homogeneity of Gd is determined by powder mixing. As the oxygen potential of sintered atmosphere increases, the sintered densities of UO$_2$-Gd$_2$O$_3$ pellets decrease but grain size increases. In addition, (U, Gd)O$_2$ solid solution becomes more homogeneous. The UO$_2$-Gd$_2$O$_3$fuel having adequate density and homogeneous microstructure can be fabricated by co-milling powder and by high oxygen potential.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2880-2886
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• 2020

A small leak occurring on the surface of a fuel rod due to damage exposes UO₂ to a steam atmosphere. During this time, fission gas trapped inside the fuel rod leaks out, and the gas leakage can be increased due to UO₂ oxidation. Numerous studies have focused on the steam oxidation and its thermodynamic calculation in UO₂. However, the thermodynamic calculation of the UO₂ oxidation in a pressurized water reactor (PWR) environment has not been studied extensively. Moreover, the kinetics of the oxidation of UO₂ pellet also has not been investigated. Therefore, in this study, the thermodynamics of UO₂ oxidation under steam injection due to a damaged fuel rod in a PWR environment is studied. In addition, the diminishing radius of the UO₂ pellet with time in the PWR environment was calculated through an experiment simulating the initial time of steam injection at the puncture.

• Nuclear Engineering and Technology
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• v.50 no.2
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• pp.253-258
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• 2018

A microcell $UO_2$ pellet, as an accident-tolerant fuel pellet, is being developed to enhance the accident tolerance of nuclear fuels under accident conditions as well as the fuel performance under normal operation conditions. Improved capture-ability for highly radioactive and corrosive fission product (Cs and I) is the distinct feature of a ceramic microcell $UO_2$ pellet, and the enhanced pellet thermal conductivity is that of a metallic microcell $UO_2$ pellet. The fuel temperature can be effectively decreased by enhanced thermal conductivity. In this study, the material concepts of metallic and ceramic microcell $UO_2$ pellets were designed, and the fabrication process of microcell $UO_2$ pellets embodying the designed concept was developed. We successfully implemented the microcell $UO_2$ pellets and produced microcell $UO_2$ pellets. In addition, an assessment of the out-of-pile properties of a microcell $UO_2$ pellet was performed, and the in-reactor performance and behavior of the developed microcell pellets were evaluated through a Halden irradiation test. According to the expectations, the excellent performance of the microcell $UO_2$ pellets was confirmed by the online measurement data of the Halden irradiation test.

• Nuclear Engineering and Technology
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• v.4 no.2
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• pp.132-136
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• 1972

The mechanism for activated sintering of UO$_2$by an addition of 0.05 w/o TiO$_2$was investigated using a high temperature X-ray diffractometer. The diffraction pattern of UO$_2$pellets was studied in a temperature range from room temperature to 120$0^{\circ}C$ in hydrogen atmosphere. At 120$0^{\circ}C$, the expansion of UO$_2$lattice were 1.448% and 1.354% greater when it was compared with those at room temperature for pellets with and without the 0.05 w/o TiO$_2$addition, respectively-The effect of the TiO$_2$addition is to increase the lattice constant of UO$_2$by 0.094% at 120$0^{\circ}C$. The lattice constant at 120$0^{\circ}C$without the TiO$_2$addition is equal to that at 108$0^{\circ}C$ with the 0.05 w/o TiO$_2$addition. This temperature difference could be well compared with the suppression of sintering temperature by TiO$_2$hat had been observed Previously. It is believed that the increase in lattice expansion due to the TiO$_2$addition would give rise to the activated sintering of UO$_2$by the lattice-expansion-induced-enhancement of self diffusion.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.05a
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• pp.269-269
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• 1999

• Proceedings of the Korean Nuclear Society Conference
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• 2002.05a
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• pp.230.1-230
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• 2002