• Nuclear Engineering and Technology
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• v.40 no.1
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• pp.21-36
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• 2008

High bum-up fuel technology has been developed through a national R&D program, which covers key technology areas such as claddings, $UO_2$ pellets, spacer grids, performance code, and fuel assembly tests. New cladding alloys were developed through alloy designs, tube fabrication, out-of-pile test and in-reactor test. The new Zr-Nb tubes are found to be much better in their corrosion resistance and creep strength than the Zircaloy-4 tube, owing to an optimized composition and heat treatment of the new Zr-Nb alloys. A new fabrication technology for large grain $UO_2$ pellets was developed using various uranium oxide seeds and a micro-doping of Al. The uranium oxide seeds, which were added to $UO_2$ powder, were prepared by oxidizing and heat-treating scrap $UO_2$ pellets. A $UO_2$ pellet containing tungsten channels was fabricated for a thermal conductivity enhancement. For the fuel performance analysis, new high burnup models were developed and implemented in a code. This code was verified by an international database and our own database. The developed spacer grid has two features of contoured contact spring and hybrid mixing vanes. Mechanical and hydraulic tests showed that the spacer grid is superior in its rodsupporting, wear resistance and CHF performance. Finally, fuel assembly test technology was also developed. Facilities for mechanical and thermal hydraulic tests were constructed and are now in operation. Several achievements are to be utilized soon by the Korea Nuclear Fuel and thereby contribute to the economy and safety of PWR fuel in Korea

• Journal of Integrative Natural Science
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• v.14 no.1
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• pp.1-5
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• 2021

A zinc oxide thin film was made by varying the deposition time on the silicon(110) substrate by using a radio frequency sputtering time of 60 minutes, 120 minutes and 180 minutes. As a result of analyzing the grain growth surface of the ZnO₂ thin film using an X-ray diffraction apparatus, the directions of the main growth plane (002) and (103) planes of the thin film were significantly affected by the deposition time. As a result of observing the particle growth of the ZnO₂ thin film through an electron scanning microscope, it was observed that in the initial stage of deposition of the ZnO₂ thin film, an incubation time was required during which growth was stagnant, and then particle growth occurred again after a certain period of time. As a result of chemical analysis of the ZnO₂ thin film, the increase in the deposition time did not change with the amount of oxygen in the ZnO₂ thin film, but a change in the composition of Zn was observed, indicating that the deposition time of the thin film had an effect on the Zn component in the thin film.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2019.04a
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• pp.107-107
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• 2019

Millets are provided considerable amounts of nutrients and gluten-free cereal products and their rich non-nutritional compounds having proven health benefits, especially phenolic compounds. The aim of present investigation was to determine phenolic composition and antioxidant and SOD activity of three different millet of genetic resources namely, foxtail, proso and finger millet. Phenolic compounds were extracted from dehulled grain of genetic resources using methanol and examined for their total phenolic content (TPC), antioxidant activities and superoxide dismutase (SOD)-like activity. The TPC range of hog millet, finger millet and finger millet range from 3.3 to 25.1, 11.1 to 29.0 and 3.8 to 94.3 gallic acid equivalent (GAE)mg/g, respectively. Most of TCP content in dehulled millet grains was distributed from 10 to 20 gallic acid equivalent (GAE)/g, but two accessions of finger millet (IT235690 and 235689) were showed over than 90. The antioxidant activities were measured by 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity. Finger millet and hog millet showed 26.4% and 26.7% in the mean of DPPH scavenging activity percentage, but foxtail millet was 13%. The finger millet showed the higher value than hog and foxtail millet in superoxide dismutase (SOD)-like activity. Particularly, two accessions of finger millet (IT235690 and 235689) showed the highest phenolic content and antioxidant activities among the used millet genetic resources and will be primary resources for finger millet breeding to develop the appropriate breeding strategies.

• Corrosion Science and Technology
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• v.18 no.1
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• pp.1-7
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• 2019

To find proper lathe machining parameters for SA182 Grade 304 stainless steel (SS), six kinds of samples with different machining surface states were prepared using a lathe. Surface morphologies and microstructures of near surface deformed layers on different samples were analysed. Surface morphologies and chemical composition of oxide films formed on different samples in simulated primary water with $100{\mu}g/L\;O_2$ at $310^{\circ}C$ were characterized. Results showed that surface roughness was mainly affected by lathe feed. Surface machining caused grain refinement at the top layer. A severely deformed layer with different thicknesses formed on all samples. In addition to high defect density caused by surface deformation, phase transformation, residual stress, and strain also affected the oxidation behaviour of SA182 Grade 304 SS in the test solution. Machining parameters used for # 4 (feed, 0.15 mm/r; back engagement, 2 mm; cutting speed, 114.86 m/min) and # 6 (feed,0.20 mm/r; back engagement, 1 mm; cutting speed, 73.01 m/min) samples were found to be proper for lathe machining of SA182 Grade 304 SS.

• Korean Journal of Materials Research
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• v.29 no.2
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• pp.129-135
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• 2019

A powder mixture of 70 wt% $Al_2O_3$ and 30 wt% hydroxyapatite (HA) is sintered at $1300^{\circ}C$ or $1350^{\circ}C$ for 2 h at normal pressure. An $MgF_2$-added composition to make HA into fluorapatite (FA) is also prepared for comparison. The samples without $MgF_2$ show ${\alpha}$ & ${\beta}$-tricalcium phosphates (TCPs) and $Al_2O_3$ phases with no HA at either of the sintering temperatures. In the case of $1,350^{\circ}C$, a $CaAl_4O_7$ phase is also found. Densification values are 69 and 78 %, and strengths are 156 and 104 MPa for 1,300 and $1,350^{\circ}C$, respectively. Because the decomposition of HA produces a $H_2O$ vapor, fewer large pores of $5-6{\mu}m$ form at $1,300^{\circ}C$. The $MgF_2$-added samples show FA and $Al_2O_3$ phases with no TCP. Densification values are 79 and 87 %, and strengths are 104 and 143 MPa for 1,300 and $1,350^{\circ}C$, respectively. No large pores are observed, and the grain size of FA ($1-2{\mu}m$) is bigger than that of TCP ($0.7{\mu}m{\geq}$) in the samples without $MgF_2$. The resulting $TCP/Al_2O_3$ and $FA/Al_2O_3$ composites fabricated in situ exhibit strengths 6-10 times higher than monolithic TCP and HA.

• Journal of Powder Materials
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• v.25 no.6
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• pp.487-493
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• 2018

The impact of different mixing methods and sintering temperatures on the microstructure and piezoelectric properties of PZNN-PZT ceramics is investigated. To improve the sinterability and piezoelectric properties of these ceramics, the composition of $0.13Pb((Zn_{0.8}Ni_{0.2})_{1/3}Nb_{2/3})O_3-0.87Pb(Zr_{0.5}Ti_{0.5})O_3$ (PZNN-PZT) containing a Pb-based relaxor component is selected. Two methods are used to create the powder for the PZNN-PZT ceramics. The first involves blending all source powders at once, followed by calcination. The second involves the preferential creation of columbite as a precursor, by reacting NiO with $Nb_2O_5$ powder. Subsequently, PZNN-PZT powder can be prepared by mixing the columbite powder, PbO, and other components, followed by an additional calcination step. All the PZNN-PZT powder samples in this study show a nearly-pure perovskite phase. High-density PZNN-PZT ceramics can be fabricated using powders prepared by a two-step calcination process, with the addition of 0.3 wt% MnO2 at even relatively low sintering temperatures from $800^{\circ}C$ to $1000^{\circ}C$. The grain size of the ceramics at sintering temperatures above $900^{\circ}C$ is increased to approximately $3{\mu}m$. The optimized PZNN-PZT piezoelectric ceramics show a piezoelectric constant ($d_{33}$) of 360 pC/N, an electromechanical coupling factor ($k_p$) of 0.61, and a quality factor ($Q_m$) of 275.

• Korean Chemical Engineering Research
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• v.57 no.3
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• pp.425-431
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• 2019

As rechargeable metal-air batteries will be ideal energy storage devices in the future, an active cathode electrocatalyst is required with bi-functionality on both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during discharge and charge, respectively. Here, a class of perovskite cathode catalyst with a micro-tubular structure has been developed by controlling bi-functionality from different Ru and Ni dopant ratios. A micro-tubular structure is achieved by the activated carbon fiber (ACF) templating method, which provides uniform size and shape. At the perovskite formula of $LaCrO_3$, the dual dopant system is successfully synthesized with a perfect incorporation into the single perovskite structure. The chemical oxidation states for each Ni and Ru also confirm the partial substitution to B-site of Cr without any changes in the major perovskite structure. From the electrochemical measurements, the micro-tubular feature reveals much more efficient catalytic activity on ORR and OER, comparing to the grain catalyst with same perovskite composition. By changing the Ru and Ni ratio, the $LaCr_{0.8}Ru_{0.1}Ni_{0.1}O_3$ micro-tubular catalyst exhibits great bi-functionality, especially on ORR, with low metal loading, which is comparable to the commercial catalyst of Pt and Ir. This advanced catalytic property on the micro-tubular structure and Ru/Ni synergy effect at the perovskite material may provide a new direction for the next-generation cathode catalyst in metal-air battery system.

• Korean Journal of Metals and Materials
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• v.49 no.7
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• pp.583-588
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• 2011

$Cd_xZn_{1-x}O$ thin films were grown on quartz substrates by using the sol-gel spin-coating method. The mole fraction, x, of the $Cd_xZn_{1-x}O$ thin films was controlled from 0 to 1 by changes in the content ratio of the cadmium acetate dehydrate [$Cd{(CH_3COO)}_2{\cdot}2H_2O$] and zinc acetate dehydrate [$Zn{(CH_3COO)}_2{\cdot}2H_2O$]. The effects of the mole fraction on the morphological, structural, and optical properties of the $Cd_xZn_{1-x}O$ thin films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-visible spectroscopy. The $Cd_xZn_{1-x}O$ thin films exhibited the polygonal surface morphology and their grain size was increased ranging from 42.1 to 63.9 nm with the increase in the mole fraction. It was observed that the absorption bandgap of the $Cd_xZn_{1-x}O$ thin films decreased from 3.25 to 2.16 eV as the mole fraction increased and the Urbach energy ($E_U$) values changed inversely to the optical bandgap of the $Cd_xZn_{1-x}O$ thin films.

• Nuclear Engineering and Technology
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• v.54 no.8
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• pp.3051-3058
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• 2022

In the present work, untreated Iraqi sand with grain sizes varied between 100 and 200 ㎛ was used to produce a colored glass sample that has shielding features against the low gamma-ray energy. Therefore, a weight of 70-60 wt % sand was mixed with 9-14 wt% B₂O₃, 8-10 wt% Na₂O, 4-6 wt% of CaO, 3-6 wt% Al₂O₃, in addition to 0.3% of Co₂O₃. After melting and annealing the glass sample, the X-ray diffraction spectrometry was applied to affirm the amorphous phase of the fabricated glass samples. Moreover, the X-ray dispersive energy spectrometry was used to measure the chemical composition, and the MH-300A densimeter was applied to measure the fabricated sample's density. The Makishima-Makinzie model was applied to predict the mechanical properties of the fabricated glass. Besides, the Monte Carlo simulation was used to estimate the fabricated glass sample's radiation shielding capacity in the low-energy region between 22.1 and 160.6 keV. Therefore, the simulated linear attenuation coefficient changed between 10.725 and 0.484 cm^-1, raising the gamma-ray energy between 22.1 and 160.6 keV. Also, other shielding parameters such as a half-value layer, pure lead equivalent thickness, and buildup factors were calculated.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2582-2590
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• 2021

The high-energy milling is one of the most extended techniques to produce Oxide dispersion strengthened (ODS) powder steels for nuclear applications. The consequences of the high energy mill process on the final powders can be measured by means of deformation level, size, morphology and alloying degree. In this work, an ODS ferritic steel, Fe-14Cr-5Al-3W-0.4Ti-0.25Y₂O₃-0.6Zr, was fabricated using two different mechanical alloying (MA) conditions (M_std and M_act) and subsequently consolidated by Spark Plasma Sintering (SPS). Milling conditions were set to evidence the effectivity of milling by changing the revolutions per minute (rpm) and dwell milling time. Differences on the particle size distribution as well as on the stored plastic deformation were observed, determining the consolidation ability of the material and the achieved microstructure. Since recrystallization depends on the plastic deformation degree, the composition of each particle and the promoted oxide dispersion, a dual grain size distribution was attained after SPS consolidation. M_act showed the highest areas of ultrafine regions when the material is consolidated at 1100 ℃. Microhardness and small punch tests were used to evaluate the material under room temperature and up to 500 ℃. The produced materials have attained remarkable mechanical properties under high temperature conditions.