• Journal of the Korean Ceramic Society
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• v.40 no.5
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• pp.410-414
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• 2003

Characteristics of $UO_{2+x}$ powders oxidized at different temperatures were examined. Pellets were fabricated by adding these oxidation powders and their properties were also investigated. Particle size of the $UO_{2+x}$ powders decreased with increasing oxidation temperature while surface area increased. Only the powders oxidized at 35$0^{\circ}C$ enhanced the strength of green pellet. However, 35$0^{\circ}C$ oxidized powders added pellet had many surface defects. The difference of shrinkage rate between the oxidized and UO$_2$ powders was thought to be the cause of them.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2016.05a
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• pp.167-168
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• 2016

• Journal of Powder Materials
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• v.16 no.4
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• pp.254-261
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• 2009

In this study, we investigated the unit process parameters in spherical $UO_2$ kernel preparation. Nearly perfect spherical $UO_3$ microspheres were obtained from the 0.6M of U-concentration in the broth solution, and the microstructure of the $UO_2$ kernel appeared the good results in the calcining, reducing, and sintering processes. For good sphericity, high density, suitable microstructure, and no-crack final $UO_2$ microspheres, the temperature control range in calcination process was $300{\sim}450^{\circ}C$, and the microstructure, the pore structure, and the density of $UO_2$ kernel could be controlled in this temperature range. Also, the concentration changes of the ageing solution in aging step were not effective factor in the gelation of the liquid droplets, but the temperature change of the ageing solution was very sensitive for the final ADU gel particles.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.4
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• pp.411-420
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• 2018

This study presents a revised crackling core model for the description of $UO_2$ sphere oxidation in air atmosphere. For close reproduction of the sigmoid behavior exhibited in $UO_2$ to $U_3O_8$ conversion, the fragmentation effect contributing to the increased reactive surface area and the concept of variable grain conversion time were considered in the model development. Under the assumptions of two-step successive reaction of $UO_2{\rightarrow}U_3O_7{\rightarrow}U_3O_8$ and final grain conversion time equivalent to ten times the initial grain conversion time, the revised model showed good agreement with the experimental data measured at 599 - 674 K and a lowest deviation when compared with Nucleation and Growth model and AutoCatalytic Reaction model. The evaluated activation energy at 100% conversion to $U_3O_8$, $57.6kJ{\cdot}mol^{-1}$, was found to be closer to the experimentally extrapolated value than to the value determined in AutoCatalytic Reaction model, $48.6kJ{\cdot}mol^{-1}$.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2019.05a
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• pp.393-394
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• 2019

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.4
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• pp.343-353
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• 2017

Processing and equipment were tailored for engineering scale fabrication of $UO_2$ porous pellets, a feed material for the electrolytic reduction process in the PRIDE (PyRoprocessing Integrated DEmonstration) facility at KAERI (Korea Atomic Energy Research Institute). The starting materials, $UO_2$ powder and pre-milled surrogate oxide powders, were proportioned to simulate the chemical composition of spent fuel (so-called Simfuel). The Simfuel powders were homogenized by mixing, compacted into a pellet shape, and finally heat treated using a tumbling mixer, rotary press, and sintering furnace. After sintering at $1450^{\circ}C$ for 24 h in $4%\;H_2-Ar$, the average bulk density of the $UO_2$ Simfuel pellets was $6.89g{\cdot}cm^{-3}$, which meets the standard of the following electrolytic reduction process. In addition, the results of a microstructural analysis demonstrated that the sintered Simfuel $UO_2$ porous pellets accurately simulate the properties of spent fuel in terms of the formation of second phases. These results provide essential information for the massive fabrication of $UO_2$ porous pellets for engineering scale pyroprocessing research.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2012.10a
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• pp.93-94
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• 2012

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2012.05a
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• pp.57-58
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• 2012

• Journal of the Korean Ceramic Society
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• v.42 no.11 s.282
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• pp.729-736
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• 2005

HTGR (High Temperature Gas-cooled Reactor) is spotlighted to next generation nuclear power plant for producing the clean hydrogen gas and the electricity. In this study, the spherical $UO_3$ gel particles were prepared by the external gelation process, and the characteristics of these particles were analyzed the particle shape, composition of precipitate, and thermal decomposition characteristics with the Streoscope, FT-IR, and X-ray diffractometer. Raw material of the ADUN (Acid Deficient Uranyl Nitrate) solution, which has [$NO_3$]/[U] mole ratio = 1.75, was obtained from dissolution of the $U_{3}O_{8}$ powder with concentrated $HNO_3$, and its concentration is 3.5 M-U/l. The broth solution is prepared with the ADUN, urea, PVA, and THFA solution. The droplets of the broth solution was made through a nozzle system. From this study, we obtained the following results; 1) an externel chemical gelation process is a suitable method in the spherical $UO_3$ particle production, 2) the particle shape are changed by an urea mixing time, THFA volume, and the viscosity of the broth solution, 3) the amorphous $UO_3$ particles obtained from these experiments was converted to $U_{3}O_{8}$ and then $UO_2$ by heat treatment in hydrogen atmosphere at $600^{\circ}C$.

• Bulletin of the Korean Chemical Society
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• v.25 no.5
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• pp.629-633
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• 2004

A new PVC membrane electrode for $UO_2^{2+}$ ion based on 2,2'-[1,2-ethanediyl bis (nitriloethylidene)]bis(1-naphthalene) as a suitable ionophore was prepared. The electrode exhibites a Nernstian response for $UO_2^{2+}$ ion over a wide concentration range ($1.0{\times}10^{-1}-1.0{\times}10^{-7}$M) with a slope of 28.5 ${\pm}$ 0.8 mV/decade. The limit of detection is $7.0{\times}10^{-8}$M. The electrode has a response time of < 20 s and a useful working pH range of 3-4. The proposed membrane sensor shows good discriminating abilities towards $UO_2^{2+}$ ion with regard to several alkali, alkaline earth transition and heavy metal ions. It was successfully used to the recovery of uranyl ion from, tap water and, as an indicator electrode, in potentiometric titration of $UO_2^{2+}$ ion with Piroxycam.