• Journal of the Korean Ceramic Society
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• v.35 no.8
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• pp.783-790
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• 1998

The characterization of the complexation reaction of PVA and Al(III) ion at different pH and the sint-ering behaviour of UO2 containing the PVA-Al(III) complexes were investigated. Compared with pure PVA powder the complexed PVA-Al(III) powder had compacter shape and lower decomposition temperature The major phase of PVA-Al(III) complex decomposed at 90$0^{\circ}C$ was $\alpha$-Al2O3 The PVA-Al(III) complex formed at pH 9 had the lowest relative viscosity the highest Al content of 36% and the smallest particle size of 19${\mu}{\textrm}{m}$ While the pure UO2 pellet appeared with bimodal one. The grain size of the pure UO2 pellet was 7${\mu}{\textrm}{m}$ but that of the PVA-Al(III) complex added UO2 pellet was increased up to 36${\mu}{\textrm}{m}$ The largest grain size was ob-tained when the PVA-Al(III) complex formed at pH9 was added and the PVA-Al(III) complex formed at pH 11 had the greatest effect on increasing pore size.

• Journal of the Korean Ceramic Society
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• v.42 no.9 s.280
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• pp.618-623
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• 2005

HTGR (High Temperature Gas-Cooled Reactor) is highlighted to next generation power plant for producing the clean hydrogen gas. In this study, the spherical $UO_2$ kernel via $UO_3$ gel particles was prepared by the sol-gel process. Raw material of slightly Acid Deficient Uranyl Nitrate (ADUN) solution, which has pH = 1.10 and $[NO_3]/[U]$ mole ratio = 1.93, was obtained from dissolution of $U_3O_8$ powder with conc.-$HNO_3$. The surface of these spherical $UO_3$ gel particles, which was prepared from the broth solution, consisted of 1 M-uranium, 1 M-HMTA, and urea, were covered with the fine crystallite aggregates, and these particles were so hard that crushed well. But the other $UO_3$ gel particles prepared with the broth solution, consisted of 2 M-uranium, 2 M-HMTA, and urea, have soft surface characteristics and an amorphous phase. This type of $UO_3$ gel particles is some chance of doing possibility of high density from the compaction. The amorphous $UO_3$ gel particles was converted to $U_3O_8$ and then $UO_2$ by calcination at $600^{\circ}C\;in\;4\%\;-\;H_2\;+\;N2$ atmosphere.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.590-597
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• 2010

HTGR using a TRISO coated particles as nuclear raw fuel material can be used to produce clean hydrogen gas and process heat for a next-generation energy source. For these purposes, a TRISO coated particle was prepared with 3 pyro-carbon (buffer, IPyC, and OPyC) layers and 1 silicone carbide (SiC) layer using a CVD technique on a spherical $UO_2$ kernel surface as a fissile material. In this study, a spherical $UO_2$ particle was prepared using a modified sol-gel method with a vibrating nozzle system, and TRISO coating fabrication was carried out using a fluidized bed reactor with coating gases, such as acetylene, propylene, and methyltrichlorosilane (MTS). As the results of this study, a spherical $UO_2$ kernel with a sphericity of 1+0.06 was obtained, and the main process parameters in the $UO_2$ kernel preparation were the well-formed nature of the spherical ADU liquid droplets and the suitable temperature control in the thermal treatment of intermediate compounds in the ADU, $UO_3$, and $UO_2$ conversions. Also, the important parameters for the TRISO coating procedure were the coating temperature and feed rate of the feeding gas in the PyC layer coating, the coating temperature, and the volume fraction of the reactant and inert gases in the SiC deposition.

• Journal of the Korean Chemical Society
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• v.28 no.5
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• pp.309-314
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• 1984

The species and equilibria of uranium and vanadium have been investigated in the various concentration of perchloric, hydrochloric and sulfuric acid by anion exchange chromatography. In the concentration range of $0.01\;{\sim}\;0.5M$ hydrochloric and $0.01\;{\sim}\;0.5M$ perchloric acid, uranium seems to be $UO_2^{2+}$species and in higher concentration than 0.5M hydrochloric acid $UO_2^{2+}$seems to form the chloride complex ion as $UO_2Cl^+$, $UO_2Cl_2$, $UO_2Cl_3^-$ and $UO_2Cl_4^{2-}$ according to the increase of the hydrochloric acid concentration. In the dilute(0.01N) sulfuric acid the adsorbability of uranium on anion exchange resin is strong and then decreases with increasing the sulfuric acid concentration. From this result we conclude that $UO_26{2+}$ formed the complex ion as $UO_2(SO_4)_2^{2-}$. In the perchloric acid of $0.01\;{\sim}\;0.5N$ concentration the existing equilibrium of vanadium and its constant calculated at $20^{\circ}C$ is $1.9{\times}108$ for $H_2V_{10}O_{28}^{4-}$ + $14H^+$ = $10VO_2^+ + 8H_2O$. The elution behaviors of vanadium in the hydrochloric and sulfuric acid are smiliar to those in perchloric acid.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05a
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• pp.630-635
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• 1995

장차 우리나라에서 미래형 핵연료의 한 종류로서 사용될 가능성이 있는 경수로용 혼합핵연료가 기존의 $UO_2$ 핵연료와 노내거동에서 어떤 차이를 야기시키는가를 물리적 성질변화 및 반경방향 출력변화의 관점에서 예비적으로 분석하였다. 분석 결과 혼합핵연료는 $UO_2$ 핵연료에 비해 (1) 열전도도가 작아 핵연료 온도가 높았고 (2)증가된 핵연료 온도로 인해 핵분열기체 방출률도 증가하여 핵연료봉 내압의 관점에서는 불리하였으나 (9)증가된 핵연료 내압으로 인해 냉각수 압력과 핵연료봉 내압의 차이가 감소하여 피복관 변형도가 감소하므로써, PCI 판점에서는 $UO_2$ 핵연료에 비해 유리하였다.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.7 no.3
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• pp.133-141
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• 2009

Study on the chemical speciation of uranium(VI) species, ${UO_2}^{2+}$, $UO_2(OH)^+$, ${(UO_2)}_2{(OH)_2}^{2+}$, ${(UO_2)}_3{(OH)_5}^+$, has been peformed by using time-resolved laser-induced fluorescence spectroscopy. Speciation sensitivity which depends on the excitation wavelength was investigated. We obtained the speciation sensitivity in the order of $10^{-9}$ M concentration of U(VI) compounds at the excitation wavelength of 266 nm. The fluorescence spectrum and lifetime of ${UO_2}^{2+}$ were carefully measured at pH 1 and ion strength of 0.1 M. The spectrum showed the four characteristic peaks located around 488, 509, 533, 559nm and the fluorescence lifetime of $1.92{\pm}0.17{\mu}s$. The wavelength shifts of fluorescence peaks and the change of lifetimes for uranium hydrolysis compounds were compared with those of ${UO_2}^{2+}$. We report on the characteristic features, the shifts of peaks to the longer wavelength direction and the prolonged lifetimes, in the fluorescence of the U(VI) hydrolysis compounds.

• Nuclear Engineering and Technology
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• v.31 no.5
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• pp.455-464
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• 1999

The effect of TiO$_2$ on the sintering behavior of mixed UO$_2$-U$_3$O$_{8}$ Powder compacts has been investigated using the U$_{3}$O$_{8}$ powder made tv oxidation of defective UO$_{2}$ pellets. Without TiO$_2$, UO$_2$ pellet density is inversely proportional to U$_3$O$_{8}$ content and is below 94 %TD in the U$_3$O$_{8}$ range above 15 wt%. Using more than 0.1 wt % TiO$_2$, however, the density decreases slightly with U$_3$O$_{8}$ content and thus is higher than about 94% TD in the whole range of U$_3$O$_{8}$ content. The grain sizes of UO$_2$ pellets with more than 0.1 wt % TiO$_2$are larger than about 30${\mu}{\textrm}{m}$. Therefore, the U$_3$O$_{8}$ Powder can be reused without any restriction on its amount in UO$_2$ pellet fabrication by sintering the mixed UO$_2$-U$_3$O$_{8}$ compact with the aid of TiO$_2$. Mechanisms for densification and grain growth are proposed and discussed, based on a dilatometry study and an examination of microstructure. microstructure.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.11a
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• pp.443-444
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• 2007

• Journal of the Korean Ceramic Society
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• v.37 no.7
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• pp.660-664
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• 2000

Effect of various kinds of additive such as AlOOH, Al(OH)3, Al2Si2O5(OH)4, Nb2O5, TiO2 and MgO on the properties and microstructures of UO2 pellet has been examined. All the tested dopants had played a role to reduce sintered density and open porosity. It was revealed that the addition of TiO2 made pellet more stable thermally. UO2 pellet doped with 0.2wt% TiO2 was swelled rather than densified after annealing for 24 hrs at 1$700^{\circ}C$. It was attributed to large pore with spherical shape. Titinia and silicon coexisted with Al element were more effective to increase grain size than other additives. It could be also revealed that the formation of liquid phase was the main cause of grain growth.

• 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.