• 한국세라믹학회지
• /
• 제35권6호
• /
• pp.559-568
• /
• 1998

Studies of preparation condition and characteristics of AUC(ammonium uranyl carbonate) were carried out to optimize AUC process with different reactor sizes and precipitation methos. As results four types of precipitates with different chemical compositions and morphologies were obtained from the reaction of {{{{ {(NH }_{4 }) { }_{2 } {CO }_{3 } }} with {{{{ {UO }_{2 }( {NO }_{3 }) { }_{2 } }} solution. A phase diagram has been made and crystal structure and chemical composition of each phase have been characterized by using SEM X-ray IR and thermal analysis. It was found that ammonium uranyl carbonate {{{{ {(NH }_{4 }) { }_{4 } {UO }_{2 } {(CO }_{3 }) { }_{3 } }} with monoclinic crystal morphology could be syn-thesized when the mole ratio of in {{{{ {(NH }_{4 }) { }_{2 } {CO }_{3 }/ {UO }_{2 } {(NO }_{3 }) { }_{2 } }} in the solution was higher than 5 Also a mechanism and a precipitating condition on rounding of the AUC particle were examined in the course of the AUC pre-cipitation. The rounding of the AUC particle was possible only by external circulation using pump not by internal circulation using agitator.

• 한국세라믹학회지
• /
• 제42권9호
• /
• pp.618-623
• /
• 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.

• 한국분말재료학회지
• /
• 제16권4호
• /
• pp.254-261
• /
• 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.

• Bulletin of the Korean Chemical Society
• /
• 제12권2호
• /
• pp.130-137
• /
• 1991

The following new cryptand 221 complexes of lanthanides(Ⅲ) and dioxouranium(Ⅵ) nitrate have been synthesized: $(Ln(C_{16}H_{32}N_2O_5)(H_2O)_2(NO_3)_3\ and \((UO_2)_2(C_{16}H_{32}N_2O_5)(H_2O)_4(NO_3)_4$. These complexes have been identified by elemental analysis, moisture titration, conductivity measurements and various spectroscopic techniques. The proton and carbon-13 NMR as well as calorimetric measurements were used to study the interaction of cryptand 221 with La(Ⅲ), Pr(Ⅲ ), Ho(Ⅲ) and $UO_2(Ⅱ)$ ions in nonaqueous solvents. The bands of metal-oxygen atoms, metal-nitrogen atoms and O-U-O in the IR spectra shift upon complexation to lower frequencies, and the vibrational spectra ({\delta}NMN$) of metal-amide complexes in the crystalline state exhibit lattice vibrations below 300 $cm^{-1}$. The NMR spectra of the lanthanides(Ⅲ) and dioxouranium(Ⅵ) nitrate complexes in nonaqueous solvents are quite different, indicating that the ligand exists in different conformation, and also the $^1H$ and $^{13}C-NMR$ studies indicated that the nitrogen atom of the ring has greater affinity to metal ions than does the oxygen atom, and the planalities of the ring are lost by complexation with metal ions. Calorimetric measurements show that cryptand 221 forms more stable complexes with $La^{3+}$ and $Pr^{3+}$ ions than with $UO^{22+}$ ion, and $La^{3+}/Pr^{3+}$ and $UO^{22+}/Pr^{3+}$ selectivity depends on the solvents. These changes on the stabilities are dependent on the basicity of the ligand and the size of the metal ions. The absorption band (230-260 nm) of the complex which arises from the direct interaction of macrocyclic donor atoms with the metal ion is due to n-{\delta}*$ transition and also that (640-675 nm) of $UO^{22+}$-cryptand 221 complex, which arises from interaction between two-dioxouranium(Ⅵ) ions in being out of cavity of the ligand ring is due to d-d* transition.

• Nuclear Engineering and Technology
• /
• 제50권2호
• /
• pp.259-267
• /
• 2018

Focused ion beam-scanning electron microscope and electron backscattered diffraction examinations were conducted in the center of a $73\;GWd/t_U\;UO_2$ fuel. They showed the formation of subdomains within the initial grains. The local crystal orientations in these domains were close to that of the original grain. Most of the fission gas bubbles were located on the boundaries. Their shapes were far from spherical and far from lenticular. No interlinked bubble network was found. These observations shed light on previous unexplained observations. They plead for a revision of the classical description of fission gas release mechanisms for the center of high burn-up $UO_2$. Yet, complementary detailed observations are needed to better understand the mechanisms involved.

• 한국세라믹학회지
• /
• 제46권6호
• /
• pp.574-582
• /
• 2009

$UO_2$ microsphere particles, core material of HTGR(High Temperature Gas Reactor) nuclear fuel, were prepared using by the GSP(Gel Supported Precipitation) method which is a modified-method of the wet sol-gel process. The spherical shape of initial liquid ADU droplets from the vibration nozzle system was continuously kept till the conversion to the final $UO_2$ microsphere. But the size of a final $UO_2$ microsphere was shrunken to about 25% of an initial ADU droplet size. Also, we found that the composition of dried-ADU gel particles was constituted of the very complicated phases, coexisted the U=O, C-H, N-H, N-O, and O-H functional groups by FT-IR. The important factors for obtain the no-crack $UO_2$ microsphere during the thermal treatment processes must perfectly wash out the remained-$NH_4NO_3$ within the ADU gel particle in washing process and the selections of an appropriate heating rate at a suitable gas atmosphere, during the calcining of ADU gel particles, the reducing of $UO_3$ particles, and the sintering of $UO_2$ particles, respectively.

• 공업화학
• /
• 제3권2호
• /
• pp.312-317
• /
• 1992

디옥소우라늄(VI) (우라닐) 이온과 질산 이온과의 상호작용을 산소-17 핵자기공명분광법으로 연구하였다. $UO_2NO_3{^+}$의 우라닐 산소 원자(이후 우라닐 산소)의 산소-17 공명신호는 우라닐 이온의 그것보다 낮은 자기장에서 나타났다. $UO_2NO_3{^+}$의 안정도상수를 5, 15, 25, $35^{\circ}C$에서 질산 이온 농도에 따른 산소-17 화학적 이동의 변화로부터 구했으며, 그 값은 이온강도에 따라 달랐다. 안정도상수의 온도 의존성으로부터 계산한 열역학적 파라미터는 다음과 같다: ${\Delta}H=-(27.2{\pm}1.7)kJ\;mol^{-1}$와 ${\Delta}S=-(110{\pm}7)JK^{-1}mol^{-1}$. 우라닐 이온과 여러가지 음이온의 배위자와의 1:1 착물형성 반응에 대한 엔탈퍼와 엔트로피 사이에는 직선관계가 있었다.

• 방사성폐기물학회지
• /
• 제13권3호
• /
• pp.229-233
• /
• 2015

파이로프로세싱 전해환원 공정에서 현재 사용 중인 Pt 양극을 대체하기 위한 소재 개발은 매우 중요하다. 이 연구에서는 전기화학 반응시 산소를 발생시키는 전도성 세라믹 양극으로서 TiN의 전기화학적 거동을 알아보았다. UO₂의 전해환원이 일어나는 동안 TiN 양극의 적합성과 안정성에 대한 평가를 진행하였다. LiCl-Li₂O 용융염에서 TiN 양극을 이용하여 UO₂를 전기화학적으로 금속 U로 변환시킬 수 있었다. 반응 도중 TiN의 산화 반응은 관찰되지 않았다. 하지만 TiN 내부에서 공공이 생기는 것을 확인하였으며, 이에 따라 소재 수명에 제한이 있을 것으로 판단된다.

• 대한화학회지
• /
• 제54권4호
• /
• pp.395-401
• /
• 2010

[M(L/L')$(NO_3)_n$].$mH_2O$ 및 [VO(L/L')($SO_4)$].$2H_2O$ (여기서 L/L'는 Schiff 염기로 thiocarbohydrazide (TCH), benzilmonohydrazone (BMH)/diacetylmonohydrazone (DMH) 및 carbon disulphide에서 유도된 "3,4,10,11-tetraphenyl/tetramethyl-1,2,5,6,8,9,12,13-octaazacyclotetradeca-2,4,9,11-tetraene-7,14-dithione")의 분자식을 갖는 일련의 거대고리 착물을 (M = $UO_2$(VI), Th(IV) and ZrO(IV), n = 2, 4, m = 2, 3)을 금속이온 주형법으로 합성하였다. 이들 착물의 특성을 원소분석, 열분석, 몰 전기전도도, 자기모멘트 그리고 전자, 적외선 및 $^1H$-NMR로 조사하였다. 바나딜 착물의 경우 ESR 및 순환 전압전류법을 사용하였다. 그 결과, VO(IV) 이온은 5배위의 상자기성 착물을 이루며, $UO_2$(VI) 및 ZrO(IV)는 6배위 그리고 Th(IV)는 8배위를 가지나 공통적으로 위의 조성을 갖는 반자기성임을 알았다.

• 한국세라믹학회지
• /
• 제42권11호
• /
• pp.729-736
• /
• 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 $600^{\circ}C$.