• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.170-170
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• 2012

• Journal of Energy Engineering
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• v.5 no.2
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• pp.193-197
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• 1996

A study was conducted on the oxidation behavior of U-0.75 wt% Ti chips (Depleted Uranium, DU chips) using an XRD and a thermogravimetric analyzer in the temperature range from 250 to 500$^{\circ}C$ in air. At the temperature lower than 400$^{\circ}C$, DU chips were converted to UO$_2$, U$_3$O$\_$7/, and U$_3$O$\_$8/ whereas at the temperature higher than 400$^{\circ}C$, DU chips were completely converted to U$_3$O$\_$8/, the most stable form of uranium oxide. The activation energy for the oxidation of DU chips is found, 44.9 kJ/mol and the oxidation rate in terms of weight gain (%) can be expressed as; dW/dt8.4${\times}$10$^2$e(equation omitted) wt%/min (250$\leq$T($^{\circ}C$) $\leq$ 500) where W=weight gain (%), t=time and T=temperature.

• Nuclear Engineering and Technology
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• v.52 no.5
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• pp.1013-1021
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• 2020

A combination of simultaneous thermal analysis, evolved gas analysis and non-ambient XRD techniques was used to characterise and investigate the conversion reactions of ammonium uranates into uranium oxides. Two solid phases of the ternary system NH₃ - UO₃ - H₂O were synthesised under specified conditions. Microspheres prepared by the sol-gel method via internal gelation were identified as 3UO₃·2NH₃·4H₂O, whereas the product of a typical ammonium diuranate precipitation reaction was associated to the composition 3UO₃·NH₃·5H₂O. The thermal decomposition profile of both compounds in air feature distinct reaction steps towards the conversion to U₃O₈, owing to the successive release of water and ammonia molecules. Both compounds are converted into α-U₃O₈ above 550 ℃, but the crystallographic transition occurs differently. In compound 3UO₃·NH₃·5H₂O (ADU) the transformation occurs via the crystalline β-UO₃ phase, whereas in compound 3UO₃·2NH₃·4H₂O (microspheres) an amorphous UO₃ intermediate was observed. The new insights obtained on these uranate systems improve the information base for designing and synthesising minor actinide-containing target materials in future applications.

• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.967-972
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• 2001

The crystal and defect structures of U $O_{x}$(x=2.0, 2.03, 2.14, 2.19, 2.20 and 2.26) were analysed by rietveld refinement and the results were compared to the U-O phase diagram. Neutron diffraction data were collected in the temperature range of RT~100$0^{\circ}C$. The specimens of x=2.14, 2.19, and 2.20 consisted of two phase: $UO_{2+x}$(Fm3m, a≒5.4$\AA$) and $U_4$$O_{9}$(I43d, a≒21.8$\AA$). The proportion of the $UO_{2+x}$(Fm3m) phase increased with increasing the temperature. The variation of the proportion of the two phases with temperature in the U $O_{2.2}$ and U $O_{2.18}$ samples showed some deviation from the expected values from the phase diagram especially at the high temperature range. The phase transitions ${\gamma}$longrightarrow$\beta$longrightarrow$\alpha$ of $U_4$$O_{9}$ were discussed in relation with the phase separation.eparation.ion.

• Korean Journal of Materials Research
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• v.5 no.6
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• pp.723-731
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• 1995

P $b_2$S $r_2$( $Y_{1-x}$ C $a_{x}$)C $u_3$ $O_{8+}$$\delta$/ samples were prepared with x=0.4~0.6 and small $\delta$. To minimize the extent of oxidative decomposition reaction which occurs during the preparation of this phase, two annealing steps were adopted : First, sintered samples of P $b_2$S $r_2$( $Y_{1-x}$ C $a_{x}$)C $u_3$ $O_{8+}$$\delta$/ are oxygenated under 100% $O_2$, which leads to a large $\delta$(e.g., $\delta$=1.8). Second, the resulting samples are deoxygenated under 0.1~1.0% $O_2$in $N_2$, lowering $\delta$ to desired values. This two-step annealing procedure minimized the extent of oxidative decomposition. However, even with the two-step annealing procedure, the oxidative decomposition of P $b_2$S $r_2$( $Y_{1-x}$ C $a_{x}$)C $u_3$ $O_{8+}$$\delta$/ cannot be completely suppressed if $\delta$ is to be reduced to maximize $T_{c}$. Electrical resistivity data show that $T_{c}$(onset) is a function of hole concentration in the Cu $O_2$layer, and the optimum hole concentration for the maximum $T_{c}$ is achieved when $Ca^{2+}$is substituted for $Y^{3+}$between 0.5 and 0.6 A $T_{c}$(onset)=80K has been observed for one such sample, and this is the highest $T_{c}$(onset) yet reported for this compound.ed for this compound.nd.

• Nuclear Engineering and Technology
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• v.13 no.1
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• pp.22-35
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• 1981

The U$_3$O$_{8}$ requirements are estimated for the high, intermediate, and low growth projections of nuclear power in Korea. To each projection, four illustrative reactor-mix strategies and four fuel cycle options are applied for estimating the requirements. The reactor types considered are PWR, PHWR. and FBR. The fuel cycles considered are once-through cycle, U/Pu recycle, and improved once-through cycle. Also the amount of Pu-fissile recovered from U recycle is estimated. The maximum cumulative (to the year 2000) requirements of U$_3$O$_{8}$ occupy about 4 to 5 percent of the WOCA requirements and are about 23 times larger than the U$_3$O$_{8}$ resources in Korea. For the high nuclear power growth projection, the cumulative amount of Pu-fissile recovered from U recycle is sufficient for the startup of 2 units of 1200 MWe fast reactors by the year 2000. 2000.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.4
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• pp.613-619
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• 1994

Dielectric properties of Ba(ZnS11/3TTaS12/3T)OS13T+x ZnO(x=0, 0.4, 0.8, 1.0 wt%) ceramics have been investigated at microwave frequencies. With excess ZnO, the sinterability was improved and the dielectric constant($\varepsilon$S1rT) and the unloaded quality factor(QS1UT) were increased. The structure changed into hexagonal from pseudocubic as being annealed at 140$0^{\circ}C$ in excess ZnO composition. Also, the temperature coefficient of the resonant frequency ($\tau$S1fT) turned into (-)ppm/$^{\circ}C$ when sintered at 155$0^{\circ}C$ for 2 hours. But the specimen sintered in ZnO muffling showed increased density and $\varepsilon$S1rT but lowerde QS1uT. Among the specimen investigated, expecially the composition added with 0.4wt% excess ZnO showed the most optimum dielectric values ($\varepsilon$S1rT=28, QS1uT x f=120000GHz) better than those of original Ba(ZnS11/2T TaS12/3T)OS13T ceramics.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.10a
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• pp.293-294
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• 2006

• 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.

• Proceedings of the Materials Research Society of Korea Conference
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• 1992.05a
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• pp.16-16
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• 1992

We have studied the effect of platinum addition on the supercon ducting properties of YB $a_2$C $u_3$$O_{7-x}$ (123) compound and elucidated the mechanism of fine dispersion of $Y_2$BaCu $O_{5}$(211) particles in YB $a_2$C $u_3$$O_{7-x}$ superconductor prepared by melting method from the metallurgical point of view. In this study, BaCu $O_2$ and CuO-rich phase unreacted during the peritecitc reaction markedly decreased by the 211 powder addition. The 211 particle of Pt-fee sintered samples exhibited 8~10$\mu$m in size, but in 1wt%Pt-added sample, 211 particles were finely dispersed in 123 matrix and the size of 211 particle was about 1~2$\mu$m. And, the critical temperature( $T_{c. zero}$) of Pt doped samples was 91.5K and the transport critical current density ( $J_{c}$) of Pt-doped samples was much more than 10$^4$A/$\textrm{cm}^2$. The high $J_{c}$ and fine dispersion of 211 particles of Pt doped YB $a_2$C $u_3$$O_{7-x}$ superconductor are attributed to $Ba_4$CuP $t_2$ $O_{8}$ compounds formed during the partial melting, which were considered als nucleation sites of 211 particles, rather than Pt inself.han Pt inself.