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유동층 화학기상증착법을 이용하여 제조된 열분해 탄화규소의 특성에 미치는 증착온도의 영향
김연구,김원주,여승환,조문성,Kim, Yeon-Ku,Kim, Weon-Ju,Yeo, SungHwan,Cho, Moon-Sung 한국분말야금학회 2014 한국분말재료학회지 (KPMI) Vol.21 No.6
Silicon carbide(SiC) layer is particularly important tri-isotropic (TRISO) coating layers because it acts as a miniature pressure vessel and a diffusion barrier to gaseous and metallic fission products in the TRISO coated particle. The high temperature deposition of SiC layer normally performed at $1500-1650^{\circ}C$ has a negative effect on the property of IPyC layer by increasing its anisotropy. To investigate the feasibility of lower temperature SiC deposition, the influence of deposition temperature on the property of SiC layer are examined in this study. While the SiC layer coated at $1500^{\circ}C$ obtains nearly stoichiometric composition, the composition of the SiC layer coated at $1300-1400^{\circ}C$ shows discrepancy from stoichiometric ratio(1:1). $3-7{\mu}m$ grain size of SiC layer coated at $1500^{\circ}C$ is decreased to sub-micrometer (< $1{\mu}m$) $-2{\mu}m$ grain size when coated at $1400^{\circ}C$, and further decreased to nano grain size when coated at $1300-1350^{\circ}C$. Moreover, the high density of SiC layer (${\geq}3.19g/cm^3$) which is easily obtained at $1500^{\circ}C$ coating is difficult to achieve at lower temperature owing to nano size pores. the density is remarkably decreased with decreasing SiC deposition temperature.
Sol-Gel법을 이용한 구형 UO<sub>2</sub> Kernel 제조에 관한 기초연구
김연구,정경채,오승철,조문성,나상호,이영우,장종화,Kim, Yeon-Ku,Jeong, Kyung-Chai,Oh, Seung-Chul,Cho, Moon-Sung,Na, Sang-Ho,Lee, Young-Woo,Chang, Jong-Wha 한국세라믹학회 2005 한국세라믹학회지 Vol.42 No.9
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.
피복입자핵연료에서 증착조건이 탄화규소층의 특성에 미치는 영향
김연구,김원주,여승환,조문성,Kim, Yeon-Ku,Kim, Weon-Ju,Yeo, SungHwan,Cho, Moon Sung 한국분말야금학회 2016 한국분말재료학회지 (KPMI) Vol.23 No.5
Tri-isotropic (TRISO) coatings on zirconia surrogate beads are deposited using a fluidized-bed vapor deposition (FB-CVD) method. The silicon carbide layer is particularly important among the coated layers because it acts as a miniature pressure vessel and a diffusion barrier to gaseous and metallic fission products in the TRISO-coated particles. In this study, we obtain a nearly stoichiometric composition in the SiC layer coated at $1400^{\circ}C$, $1500^{\circ}C$, and $1400^{\circ}C$ with 20 vol.% methyltrichlorosilane (MTS), However, the composition of the SiC layer coated at $1300-1350^{\circ}C$ shows a difference from the stoichiometric ratio (1:1). The density decreases remarkably with decreasing SiC deposition temperature because of the nanosized pores. The high density of the SiC layer (${\geq}3.19g/cm^2$) easily obtained at $1500^{\circ}C$ and $1400^{\circ}C$ with 20 vol.% MTS did not change at an annealing temperature of $1900^{\circ}C$, simulating the reactor operating temperature. The evaluation of the mechanical properties is limited because of the inaccurate values of hardness and Young's modulus measured by the nano-indentation method.
졸-겔 방법으로 제조된 Ammonium Diuranate 핵연료 분말의 공정장치 변수에 따른 특성
김연구,정경채,엄성호,조문성,Kim, Yeon-Ku,Jeong, Kyung-Chai,Ueom, Sung-Ho,Cho, Moon Sung 한국분말야금학회 2012 한국분말재료학회지 (KPMI) Vol.19 No.6
This paper describes the spherical ammonium diuranate gel particles which are the intermediated material of the $UO_2$ microsphere for an VHTR(very high temperature reactor) nuclear fuel. The characteristics of the intermediate-ADU gel particles prepared by AWD(ageing, washing, and drying) and FB(fluidized-bed) apparatus were examined and compared in a sol-gel fabrication process. The electrical conductivity of washing filtrate from the FB treating and the surface area of dried-ADU gel particles were higher than those of AWD treating. Also, an internal pore volume in dried-ADU gel particles showed a more decrease in AWD treatment than FB treatment because of decomposition of PVA affected by the washing time. However, the internal microstructures of ADU gel particles were similar regardless of the process variation.
김연구,서동수,정경채,오승철,조문성,Kim, Yeon-Ku,Suhr, Dong-Soo,Jeong, Kyung-Chai,Oh, Seung-Chul,Cho, Moon-Sung 한국세라믹학회 2008 한국세라믹학회지 Vol.45 No.11
In this study the preparation method of the spherical ADU droplets, intermediate compound of a HTGR nuclear fuel, was detailed-reviewed and then, the characteristics on an ageing and a washing steps among the wet process and the thermal treatment process on the died-ADU${\rightarrow}UO_3$ conversion with the high temperature furnaces were studied. The key parameters for spherical droplets forming are a precise control of feed rate and a suitable viscosity value selection of a broth solution. Also, a harmony of vibrating frequency and amplitude of a vibration dropping system are important factor. In our case, an uranium concentration is $0.5{\sim}0.7mol/l$, viscosity is $50{\sim}80$ centi-Poise, vibration frequency is about 100Hz. In thermal treatment for no crack spherical $UO_3$ particle, the heating rate in the calcination must be operated below $2^{\circ}C$/min, in air atmosphere.
고온가스로용 핵연료 제조에서 열처리 조건이 우라늄산화물 입자 특성에 미치는 영향
김연구,정경채,오승철,서동수,조문성,Kim, Yeon-Ku,Jeong, Kyung-Chai,Oh, Seung-Chul,Suhr, Dong-Soo,Cho, Moon-Sung 한국분말야금학회 2009 한국분말재료학회지 (KPMI) Vol.16 No.2
The effects of thermal treatment conditions on ADU (ammonium diuranate) prepared by SOL-GEL method, so-called GSP (Gel supported precipitation) process, were investigated for $UO_2$ kernel preparation. In this study, ADU compound particles were calcined to $UO_3$ particles in air and Ar atmospheres, and these $UO_3$ particles were reduced and sintered in 4%-$H_2$/Ar. During the thermal calcining treatment in air, ADU compound was slightly decomposed, and then converted to $UO_3$ phases at $500^{\circ}C$. At $600^{\circ}C$, the $U_3O_8$ phase appeared together with $UO_3$. After sintering of theses particles, the uranium oxide phases were reduced to a stoichiometric $UO_2$. As a result of the calcining treatment in Ar, more reduced-form of uranium oxide was observed than that treated in air atmosphere by XRD analysis. The final phases of these particles were estimated as a mixture of $U_3O_7$ and $U_4O_9$.
Sol-gel 공정을 이용한 UO<sub>2</sub> kernel 제조에서 공정변수가 입자특성에 미치는 영향
김연구,정경채,오승철,서동수,조문성,Kim, Yeon-Ku,Jeong, Kyung-Chai,Oh, Seung-Chul,Suhr, Dong-Soo,Cho, Moon-Sung 한국분말야금학회 2009 한국분말재료학회지 (KPMI) Vol.16 No.4
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.
김연구,사인진,김응선,Kim, Yeon-Ku,Sah, Injin,Kim, Eung Seon 한국재료학회 2020 한국재료학회지 Vol.30 No.10
UO<sub>2</sub> kernels, a key component of fuel elements for high temperature gas cooled reactors, have usually been prepared by sol-gel methods. Sol-gel processes have a number of advantages, such as simple processes and facilities, and higher sphericity and density. In this study, to produce 900 ㎛-sized UO<sub>2</sub> particles using an external gelation process, contact length extension of the NH<sub>3</sub> gas of the broth droplets pass and the improvement of the gelation device capable of spraying 14 M-NH<sub>4</sub>OH solution are used to form 3,000 ㎛-sized liquid droplets. To produce high-sphericity and high-density UO<sub>2</sub> particles, HMTA, which promotes the gelation reaction in the uranium broth solution, is added to diffuse ammonium ions from the outside of the gelation solution during the aging process and generate ammonium ions from the inside of the ADU gel particles. Sufficient gelation inside of ADU gel particles is achieved, and the density of the UO<sub>2</sub> spheres that undergo the subsequent treatment is 10.78 g/㎤; the sphericity is analyzed and found to be 0.948, indicating good experimental results.
고온가스로용 핵연료 UO<sub>2</sub> Kernel 입자제조
정경채,김연구,오승철,조문성,Jeong, Kyung-Chai,Kim, Yeon-Ku,Oh, Seung-Chul,Cho, Moon-Sung 한국세라믹학회 2007 한국세라믹학회지 Vol.44 No.8
The broth solution was prepared by the mixing of an uranyl nitrate, THFA, PVA, and water. The uranium concentration of the broth solution was $0.5{\sim}0.8$ mole-U/L and the viscosity of it was $30{\sim}80cSt$. The droplets of this broth solution were farmed in air and ammonia by the vibrating nozzle with the frequency of 100 Hz at the amplitude of $100{\sim}130V$. The diameter of the droplet was about $1900{\mu}m$ from using the nozzle diameter of 1 mm. The diameter of the aged gel was about $1400{\mu}m$ after aging in ammonia solution at $60{\sim}80^{\circ}C$, and the dried gel with the diameter of about $900{\mu}m$ was obtained after drying at room temperature or partially vacuum condition. The diameter of the calcined $UO_3$ microsphere after calcination at $600^{\circ}C$ appeared about $800{\mu}m$ in air atmosphere. Although the droplets of the same sizes were formed, the calcined microspheres of different sizes were manufactured in the case of the broth solutions of the different uranium concentration. The droplets of the desired diameters were obtained by the change of the nozzle diameters and the broth flow rates.