• Nuclear Engineering and Technology
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• v.53 no.10
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• pp.3217-3228
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• 2021

Flow blockage of the fuel assembly in the lead-based fast reactor (LFR) may produce critical local spots, which will result in cladding failure and threaten reactor safety. In this study, the flow blockage characteristics were analyzed with the sub-channel analysis method, and the circumferentially-varied method was employed for considering the non-uniform distribution of circumferential temperature. The developed sub-channel analysis code SACOS-PB was validated by a heat transfer experiment in a blocked 19-rod bundle cooled by lead-bismuth eutectic. The deviations between the predicted coolant temperature and experimental values are within ±5%, including small and large flow blockage scenarios. And the temperature distributions of the fuel rod could be better simulated by the circumferentially-varied method for the small blockage scenario. Based on the validated code, the analysis of blockage characteristics was conducted. It could be seen from the temperature and flow distributions that a large blockage accident is more destructive compared with a small one. The sensitivity analysis shows that the closer the blockage location is to the exit, the more dangerous the accident is. Similarly, a larger blockage length will lead to a more serious case. And a higher exit temperature will be generated resulting from a higher peak coolant temperature of the blocked region. This work could provide a reference for the future design and development of the LFR.

• Journal of Korea Foundry Society
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• v.41 no.6
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• pp.505-515
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• 2021

Creep properties of directionally solidified Ni-based superalloy CM247LC under various temperature and stress conditions have been investigated. In the heat-treated specimen, some portion of eutectic γ-γ' remained, and uniform cubic γ' was observed in the dendrites. At low temperature (750℃) and high stress condition, a large amount of deformation occurred during the primary creep, while the tertiary creep region accounted for most of the creep deformation under high temperature and low stress condition. γ' particles are sheared by dislocation dissociated into super lattice partial dislocations separated by stacking faults at 750℃. No stacking faults in γ' were found at and above 850℃ due to the temperature dependence of the stacking fault energy. Raft structure of γ' was found after creep test at high temperature of 950℃ and 1000℃. At 850℃, the deformation mechanism was shown to be dependent on the stress condition, and so rafting was observed only under low stress condition.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.86-86
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• 2012

The new approaches for silicon solar cell of new concept have been actively conducted. Especially, solar cells with wire array structured radial p-n junctions has attracted considerable attention due to the unique advantages of orthogonalizing the direction of light absorption and charge separation while allowing for improved light scattering and trapping. One-dimenstional semiconductor nano/micro structures should be fabricated for radial p-n junction solar cell. Most of silicon wire and/or pillar arrays have been fabricated by vapour-liquid-solid (VLS) growth because of its simple and cheap process. In the case of the VLS method has some weak points, that is, the incorporation of heavy metal catalysts into the growing silicon wire, the high temperature procedure. We have tried new approaches; one is electrochemical etching, the other is noble metal catalytic etching method to overcome those problems. In this talk, the silicon pillar formation will be characterized by investigating the parameters of the electrochemical etching process such as HF concentration ratio of electrolyte, current density, back contact material, temperature of the solution, and large pre-pattern size and pitch. In the noble metal catalytic etching processes, the effect of solution composition and thickness of metal catalyst on the etching rate and morphologies of silicon was investigated. Finally, radial p-n junction wire arrays were fabricated by spin on doping (phosphor), starting from chemical etched p-Si wire arrays. In/Ga eutectic metal was used for contact metal. The energy conversion efficiency of radial p-n junction solar cell is discussed.

• Journal of the Korea Institute of Military Science and Technology
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• v.19 no.4
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• pp.469-475
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• 2016

Thermal batteries are primary reserve power sources, which are activated upon the melting of eutectic electrolytes by the ignition of heat sources. Therefore, sufficient thermal insulation is absolutely needed for the stable operation of thermal batteries. Currently, excessive amount of heat sources is being used to compensate the heat loss in the cell stack along with the insertion of metal plates and thermal insulators to reserve heat at the both ends of cell stack. However, there is a possibility that the excessive heat flows into the cell stack, causing a thermal runaway at the early stage of discharge. At the same time, the internal temperature of thermal batteries cannot be maintained above the battery operating temperature at the later stage of discharge because of the insufficient insulation. Therefore, the effects of Phase Changing Material(PCM) plates were demonstrated in this study, which can replace the metal and insulating plates, to improve the thermal insulation performance and safety of thermal batteries.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.726-731
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• 2002

Reaction synthesis is a process to form ceramics, intermetallics and their composites from elemental powder mixture. Application of this process to a surface modification techniques has a possibilities to enable the process at a lower temperature or for a shorter time, although synthesized materials are likely to include voids and unreacted elements. This paper intend to examine the effect of Si addition to the mixture of Al and Ni on the densification of synthesized Ni-Al intermetallic compounds and to evaluate the surface properties of obtained coatings. By the Si addition, exothermic reaction temperature to form Ni-Al intermetallic was lowered to be below the melting point of Al. Si soluted $Al_3$Ni$_2$, $Al_3$Ni and $Al_{6}$Ni$_3$Si were mainly formed in the coating layer when powder mixture was heated to 973K for 300s. Besides, densification was enhanced by increasing hot press pressure, Si additions and heating rate. When the composition of eutectic Al-Si reaches 78%, void ratio of sintered compact reduced to 0.4%. It is caused by higher flowability of Al-Si liquid phase generated and its infiltration into the void. Since the hardness of NiAl(Si) compound (about 600HV) formed in the coating layer is higher than that of Ni-Al compound (about 400HV), coating layer with high density and superior wear property is obtained by hot press using reaction synthesis from Al-Ni-Si powder mixture.

• Journal of Korea Foundry Society
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• v.36 no.1
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• pp.1-9
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• 2016

Improvement of the mechanical properties of a commercial aluminium casting alloy, A356, was achieved through an optimised combination of alloying elements, modification, and heat treatment. 0.7 wt.% Cu and an additional 0.2 wt.% Mg were added to an Al-7Si-0.35Mg alloy for strengthening at both room and elevated temperatures, whilst a subsequent decrease in the ductility was compensated for by the modification of eutectic Si by Sr addition at a level of up to 110 ppm. It was found that the dissolution of Cu-rich or Mg-rich phases could be maximised by solid-solutionising an alloy with 40 ppm Sr at $530^{\circ}C$, increasing the tensile and yield strengths to 350 MPa and 297 MPa, respectively, with a reasonably high strain of 5% after peak-aging at $210^{\circ}C$. Further addition of Sr up to 110 ppm is, however, more likely to interfere with the dissolution of the Cu-rich or Mg-rich phases during solid solution treatment, resulting in a slight decrease in both tensile and yield strengths at room temperature. Besides the Cu addition, such undissolved phases, on the other hand, may contribute to elevated temperature strength at $200^{\circ}C$.

• Journal of the Korean Vacuum Society
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• v.13 no.3
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• pp.127-131
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• 2004

Package reliability test was conducted to investigate the effect of solder composition on the ball fatigue strength for BGA (Ball Grid Array) packaging. The test pieces are assembled using eutectic composition 63Sn/37Pb, 62Sn/36Pb/2Ag, and 63Sn/34.4Pb/2Ag/0.5Sb solder after pre-conditioning at MRT Lv 3 (Moisture Resistance Test Level) and then conducted under T/C (Temperature Cycle test). For each case, the ball shear strength was obtained and micro structure photos were taken. SEM (scanning electron microscope) and EDX (Energy Dispersive X-ray) were used to the analyze failure mechanism. The growth rate of Au-Sn intermetallic compound in Sn63Pb34.5Ag2Sb0.5 solder was slow when compared to 63Sn/37Pb solder and 62Sn/36Pb/2Ag solder. The degradation of shear strength of solder balls caused by solder composition was discussed.

• Korean Journal of Materials Research
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• v.28 no.9
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• pp.499-505
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• 2018

This investigates the microstructure and mechanical properties of Al hybrid material prepared by electromagnetic duo-casting to determine the effect of heat treatment. The hybrid material is composed of an Al-Mg-Si alloy, pure Al and the interface between the Al-Mg-Si alloy and pure Al. It is heat-treated at 373, 573 and 773K for 1h and T6 treated (solution treatment at 773K for 1h and aging at 433K for 5h). As the temperature increases, the grain size of the Al-Mg-Si alloy in the hybrid material increases. The grain size of the T6 treated Al-Mg-Si alloy is similar to that of one heat-treated at 773K for 1h. The interface region where the micro-hardness becomes large from the pure Al to the Al-Mg-Si alloy widens with an increasing heat temperature. The hybrid material with a macro-interface parallel to the tensile direction experiences increased tensile strength, 0.2 % proof stress and the decreased elongation after T6 heat treatment. On the other hand, in the vertical direction to the tensile direction, there is no great difference with heat treatment. The bending strength of the hybrid material with a long macro-interface to the bending direction is higher than that with a short macro-interface, which is improved by heat treatment. The hybrid material with a long macro-interface to the bending direction is fractured by cracking through the eutectic structure in the Al-Mg-Si alloy. However, in the hybrid material with a short macro-interface, the bending deformation is observed only in the limited pure Al.

• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1056-1063
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• 2010

We present a new joining method for Pd-Cu membrane foils used as permeation tubes to collect $CO_2$. Since foils have poor mechanical strength, joining should be done at low temperatures to reduce residual stresses and without joining pressure. This contradicts the well known conditions for good contact between base materials that determines joint qualities. We selected Sn-Ag-Cu alloys that are highly reactive with Pd and Cu as a filler metal. As the filler melts at joining temperatures as low as $220{\sim}280^{\circ}C$, Pd and Cu are dissolved into the melt and react with the filler elements, which raises the melting temperature of the filler based on eutectic structures among the elements. Then, isothermal solidification progresses for the rest of the joining time. Intermetallic compounds (IMC) in the joints, one of the main factors for brittle joints, are inevitably formed. However, by optimizing both joining time and temperature, we balanced the wettability with IMC. Sealing test results confirmed that the joints are mechanically reliable during operation.

• Journal of Powder Materials
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• v.29 no.4
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• pp.283-290
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• 2022

A Cu-15Ag-5P filler metal (BCuP-5) is fabricated on a Ag substrate using a high-velocity oxygen fuel (HVOF) thermal spray process, followed by post-heat treatment (300℃ for 1 h and 400℃ for 1 h) of the HVOF coating layers to control its microstructure and mechanical properties. Additionally, the microstructure and mechanical properties are evaluated according to the post-heat treatment conditions. The porosity of the heat-treated coating layers are significantly reduced to less than half those of the as-sprayed coating layer, and the pore shape changes to a spherical shape. The constituent phases of the coating layers are Cu, Ag, and Cu-Ag-Cu3P eutectic, which is identical to the initial powder feedstock. A more uniform microstructure is obtained as the heat-treatment temperature increases. The hardness of the coating layer is 154.6 Hv (as-sprayed), 161.2 Hv (300℃ for 1 h), and 167.0 Hv (400℃ for 1 h), which increases with increasing heat-treatment temperature, and is 2.35 times higher than that of the conventional cast alloy. As a result of the pull-out test, loss or separation of the coating layer rarely occurs in the heat-treated coating layer.