• 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.

• 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 Nuclear Society Conference
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• 1996.05c
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• pp.470-475
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• 1996

사용후핵연료 장기 건식저장시 여러가지 저장조건에서 사용후핵연료 피복관 및 사용후핵연료 ($UO_2$)에 대한 장기 건전성을 종합적으로 평가할 수 있는 SIECO 코드를 개발하였다. 건식저장 시스템은 사용후핵연료를 헬륨 및 공기분위기하에서 TN-24P 건식 저장용기에 장기 저장할 경우로 하였으며 피복관의 최대 표면온도는 COBRA-SFS코드를 사용하여 계산하였고, 열유동 해석결과를 바탕으로 SIECO코드를 이용하여 핵연료 연소도 및 냉각기간, 냉각매체에 따른 최대 건식저장 허용온도를 피복관의 열화 및 $UO_2$ 산화의 관점에서 계산하였다.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1099-1109
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• 2020

The performance of gadolinium burnable absorber (GdBA) for reactivity control in UO₂ and (U, Th)O₂ fuels and its impact on spent fuel characteristics was performed. Five fuel assemblies: one without GdBA fuel rod and four each containing 16, 24, 34 and 44 GdBA fuel rods in both fuels were investigated. Reactivity swing in all the FAs with GdBA rods in UO₂ fuel was higher than their counterparts with similar GdBA fuel rods in (U, Th)O₂ fuel. The excess reactivity in all FAs with (U, Th)O₂ fuel was higher than UO₂ fuel. At the end of single discharge burn-up (~ 49.64 GWd/tHM), the excess reactivity of (U, Th) O₂ fuel remained positive (16,000 pcm) while UO₂ fuel shows a negative value (-6,000 pcm), which suggest a longer discharge burn-up in (U, Th)O₂ fuel. The concentration of plutonium isotopes and minor actinides were significantly higher in UO₂ fuel than in (U, Th)O₂ fuel except for ²³⁶Np. However, the concentration of non-actinides (gadolinium and iodine isotopes) except for ¹³⁵Xe were respectively smaller in (U, Th)O₂ fuel than in UO₂ fuel but may be two times higher in (U, Th)O₂ fuel due to its potential longer discharge burn-up.

• Nuclear Engineering and Technology
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• v.28 no.5
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• pp.458-466
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• 1996

The effects of dopants on the modification of microstructure of UO$_2$ and UO$_2$-4wt%CeO$_2$ sintered pellets have been studied in hydrogen and $CO_2$/CO mixture atmospheres by using $Ta_2O_5$, TiO$_2$ and $Nb_2O_5$ as sintering additives. The dopant were added as oxide powders and homogenized by attrition milling. The mixed powders were pressed, and then sintered in hydrogen at 1$700^{\circ}C$ , or in oxidizing atmosphere using Controlled $CO_2$/CO mixtures at 125$0^{\circ}C$. Both density and microstructure of UO$_2$ are modified by the addition of dopants in reducing atmosphere. The sintered density is increased with $Ta_2O_5$ addition up to 0.33wt% and subsequently decreased with higher content of the additive. The effect on the densification and the gain growth are apparent with the addition of 0.24wt% $Nb_2O_5$. With 0.lwt% titania and 0.6wt% $Ta_2O_5$, the sintered density is decreased, but the grain size is increased. In oxidizing atmosphere, the grain sizes for UO$_2$ doped with the above additives are smaller than that for pure UO$_2$. The grain size of Ta or Nb-doped UO$_2$ is decreased with increasing $CO_2$/CO ratio, but that of pure UO$_2$or T-doped UO$_2$ is increased. A large portion of second phases is observed in UO$_2$ doped with 0.lwt% TiO$_2$ sintered in hydrogen atmosphere, while, in $CO_2$/CO atmospheres, the second phases or dopant agglomerates are not observed. For UO$_2$-4wt%CeO$_2$ mixed oxide, the effect of additives on the gain growth is not so much as that for the pure UO$_2$. This is attributed to the formation of clusters by dopant cations and Ce ions, so that the additives contribute to a lesser exent to the grain growth for the mixed oxide.

• Journal of the Korean Ceramic Society
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• v.41 no.8
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• pp.567-572
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• 2004

The variation of the sintered density and grain size of UO$_2$ as a function of the Li$_2$O amount and sintering atmosphere was observed. Li$_2$O enhanced the grain growth of the UO$_2$ pellet in H$_2$, but rather hindered it in $CO_2$ atmosphere. Grain size of the UO$_2$ and UO$_2$-0.1 wt%Li$_2$O pellets was, respectively, 8 $\mu$m and 100 $\mu$m at 168$0^{\circ}C$ in the H$_2$ atmosphere, and that of each pellet was, respectively, 24 $\mu$m and 17 $\mu$m at the same temperature in the $CO_2$ atmosphere. As-received Li$_2$O powder, which had been composed of Li$_2$O and LiOH, was converted to the Li$_2$CO$_3$ phase after heating to 80$0^{\circ}C$ in $CO_2$. On the other hand, the Li$_2$O and LiOH phases remained unchanged in H$_2$ atmosphere. In the H$_2$, the as-received Li$_2$O powder began to evaporate at about 105$0^{\circ}C$ and then about 20 wt% residue was left at 150$0^{\circ}C$. But, most of the Li elements evaporated at 150$0^{\circ}C$ in the $CO_2$ atmosphere.

• Nuclear Engineering and Technology
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• v.35 no.1
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• pp.14-24
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• 2003

This work investigates the effects of Cr$_2$O$_3$ and oxygen potential on grain growth and densification of UO$_2$ pellets. Powder mixtures of UO$_2$ and 0.03-0.4wt% Cr$_2$O$_3$ were pressed and sintered in 3 different gas atmospheres: the $H_2O$-to-H$_2$ ratios were 5$\times$10$^{-4}$ , 1$\times$10$^{-2}$ and 3$\times$10$^{-2}$ In the first gas atmosphere the Cr$_2$O$_3$ contents below 0.2 wt% have an insignificant effect on grain size, but the Cr$_2$O$_3$ contents more than 0.3 wt% promote grain growth in the inner zone of a pellet but not in the outer zone. In both the second and third atmospheres, the grain size increases with the Cr$_2$O$_3$ content. With the same level of Cr$_2$O$_3$ content the grain size is larger in the second atmosphere than in the third. Sintering behavior and developed microstructure are discussed in terms of the reduction of C$r^2$O$^3$ to Cr, the dissolution of C$r^2$O$^3$ in UO$_2$, and liquid phase sintering.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2002.11a
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• pp.71-79
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• 2002

Nuclear design characteristics of duplex burnable poison rod were evaluated based on 24 month cycle fuel for Korean Standard Nuclear Plant. A fuel assembly with duplex burnable poison rod was designed for an equivalent assembly to 16 gadolinia BPs. Duplex BP is composed of inner region of natural U-12wt%Gd$_2$O$_3$ and outer shell of 4.95wt%UO$_2$-2wt%Er$_2$O$_3$. In order to compare this duplex option, assemblies with 140 erbia pins were designed as an alternative option. The variation of k-infinitive, rod worth, pin peaking and MTC were compared. Duplex BP had the better neutronic performance than gadolinia BP in all parameters. However, Duplex BP was worse than erbia BP in the aspect of safety.

• Advances in environmental research
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• v.4 no.2
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• pp.135-142
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• 2015

In this study, we evaluated the adsorption/desorption of uranium (U) in pure soil environment using continuous column reactor. We additionally investigated the adsorption/desorption mechanism of U on vivianite surface in molecular scale using quantum calculation. We observed that below $0.1{\mu}M$ of U was detected after 20 d from U injection ($1{\mu}M$) in adsorption test. However, all of absorbed U was detached from vivianite surface in 24 h by injection of CARB solution ($1.44{\times}10^{-2}M\;NaHCO_3$ and $2.8{\times}10^{-3}M\;Na_2CO_3$). Based on exchange energy calculation, we found that $UO_2(CO_3)_2{^{2-}}$ and $UO_2(CO_3)_3{^{4-}}$ species have higher repulsive energy than $UO_2(OH)_2$ species. The results obtained from this study could be applied to predict the behavior of uranium in contaminated and remediation sites.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.674-680
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• 2020

We used MCNP6 computer code to model HTR-10 core reactor. We used two types of fuel; UO₂ and (Th+Pu)O₂ mixture. We determined the critical height at which the reactor approached criticality in both two cases. The neutronic and burnup parameters were investigated. The results indicated that the core fueled with mixed (Th+Pu)O₂, achieved about 24% higher fuel cycle length than the UO₂ case. It also enhanced safeguard security by burning Pu isotopes. The results were compared with previously published papers and good agreements were found.