• Nuclear Engineering and Technology
• /
• v.55 no.8
• /
• pp.2835-2843
• /
• 2023

After an emergency shutdown of a lead-bismuth fast reactor, thermal stratification occurs in the upper Plenum, which negatively impacts the integrity of the reactor structure and the residual heat removal capacity of natural circulation flow. The research on thermal stratification of reactors has mainly been conducted using an experimental method, a system program, and computational fluid dynamics (CFD). However, the equipment required for the experimental method is expensive, accuracy of the system program is unpredictable, and resources and time required for the CFD approach are extensive. To overcome the defects of thermal stratification analysis, a high-precision full-order thermal stratification model based on CFD technology is prepared in this study. Furthermore, a reduced-order model has been developed by combining proper orthogonal decomposition (POD) with Galerkin projection. A comparative analysis of thermal stratification with the proposed full-order model reveals that the reduced-order thermal stratification model can well simulate the temperature distribution in the upper plenum and rapidly elucidate the thermal stratification interface characteristics during the lead-bismuth fast reactor accident. Overall, this study provides an analytical tool for determining the thermal stratification mechanism and reducing thermal stratification.

• Nuclear Engineering and Technology
• /
• v.55 no.3
• /
• pp.1125-1139
• /
• 2023

The system-integrated modular advanced reactor 100 (SMART100), an integral-type pressurized water small modular reactor, is based on a novel design concept for containment cooling and radioactive material reduction; it is known as the containment pressure and radioactivity suppression system (CPRSS). There is a passive cooling system using a condensation with non-condensable gas in the SMART CPRSS. When a design basis accident such as a small break loss of coolant accident (SBLOCA) occurs, the pressurized low containment area (LCA) of the SMART CPRSS leads to steam condensation in an incontainment refuelling water storage tank (IRWST). Additionally, the steam and non-condensable gas mixture passes through the CPRSS heat exchanger (CHX) submerged in the emergency cooldown tank (ECT) that can partially remove the residual heat. When the steam and non-condensable gas mixture passes through the CHX, the non-condensable gas can interrupt the condensation heat transfer in the CHX and it degrades CHX performance. In this study, condensation heat transfer experiments of steam and non-condensable gas mixture in the natural circulation loop were conducted. The pressure, temperature, and effects of the non-condensable gas were investigated according to the constant inlet steam flow rate with non-condensable gas injections in the loop.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2021.06a
• /
• pp.57-57
• /
• 2021

최근 급격한 도시화와 기후변화로 인해 도시의 홍수피해가 증가하고 있으며, 복합적인 재난으로 악화되는 경우가 많아졌다. 복합재난으로 인한 피해를 줄이기 위해 재해발생 전·후 대응이 중요하며, 이를 위해 복원력 개념을 도입할 필요가 있다. 도시 배수 시스템의 복원력은 대상유역의 면적과 절대적인 침수량에 따라 좌우된다. 따라서 지역의 도시 배수 시스템의 복원력을 정확하게 평가하기 위해 대상유역의 정보를 반영한 지역 맞춤형 복원력 지수의 개발이 필요하다. 대상유역의 정보를 반영하기 위해 도시 배수 시스템의 배수능력을 복원력 지수에 적용하였다. 도시 배수 시스템의 배수능력을 나타내기 위해 시스템 잔류유량을 분모로, 침수량을 분자로 하여 복원력 지수를 계산하였다. 본 연구에서는 제안된 새로운 복원력 지수를 대구 비산 빗물펌프장에 적용하였다. 강우자료는 재현기간이 100년, 200년 그리고 300년 빈도의 확률강우량을 사용하였으며, 지속시간은 30분, 60분 그리고 90분으로 설정하였다. 침수량과 시스템 잔류 유량은 1분 단위로 EPA SWMM을 통해 값을 구하였다. 시스템 잔류 유량을 기반으로 하는 복원력 지수는 최소 0.995029에서 최대 0.998662로 나타났다. 본 연구에서 제안한 도시 배수 시스템 잔류 유량 기반 복원력 지수는 배수 시스템의 처리 능력을 반영한 지수라고 할 수 있으며 배수 시설의 설치, 교체 및 재건 등 수해 방재 계획 평가에 활용될 수 있다.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2022.11a
• /
• pp.149-150
• /
• 2022

In Korea, there is no clearly established technology for diagnosing and evaluating the damage depth of concrete structures created by fire. There have been cases of repairing, reinforcing, and demolishing degraded structures without diagnosing the damage depth. The commonly used phenolphthalein-based carbonate thickness measurement does not satisfy the complete disappearance condition of Ca(OH)₂ in the interval where the relatively stationary flow declines after exposure to high temperatures. Even a small amount of Portlandite[Ca(OH)₂] reacts with a red color, and the damage depth is misjudged. It was confirmed by X-ray diffraction and scanning electron microscope that Ca(OH)₂ existed from 300℃ to 500℃ where the residual compressive strength decreased.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.37 no.1
• /
• pp.56-62
• /
• 2024

By introducing curing kinetics and chemo-rheology for the epoxy resin formulation for ultra-high voltage gas insulated switchgear (GIS) Insulating Spacers, a study was conducted to simulate the curing behavior, flow and warpage analysis for optimization of the molding process in automatic pressure gelation. The curing rate equation and chemo-rheology equation were set as fixed values for various factors and other physical property values, and the APG molding process conditions were entered into the Moldflow software to perform optimization numerical simulations of the three-phase insulating spacer. Changes in curing shrinkage according to pack pressure were observed under the optimized process conditions. As a result, it was confirmed that the residence time in the solid state was shortened due to the lowest curing reaction when the curing holding pressure was 3 bar, and the occurrence of deformation due to internal residual stress was minimized.

• Korean Journal of Radiology
• /
• v.22 no.4
• /
• pp.568-576
• /
• 2021

Arteriovenous malformations (AVMs) are direct communications between primitive reticular networks of dysplastic vessels that have failed to mature into capillary vessels. Based on angiographic findings, peripheral AVMs can be classified into six types: type I, type IIa, type IIb, type IIc, type IIIa, and type IIIb. Treatment strategies vary with the types. Type I is treated by embolizing the fistula between the artery and the vein with coils. Type II (IIa, IIb, and IIc) AVM is treated as follows: first, reduce the blood flow velocity in the venous segment of the AVM with coils; second, perform ethanol embolotherapy of the residual shunts. Type IIIa is treated by transarterial catheterization of the feeding arteries and injection of diluted ethanol. Type IIIb is treated by transarterial or direct puncture approaches. A high concentration of ethanol is injected through the transarterial catheter or direct puncture needle. When the fistula is large, coil insertion is required to reduce the amount of ethanol. Type I and type II AVMs showed the best clinical results; type IIIb showed a satisfactory response rate. However, type IIIa showed the poorest response rate, either alone or in combination with other types. Clinical success can be achieved by using different treatment strategies for different angiographic AVM types.

• Journal of IKEEE
• /
• v.28 no.2
• /
• pp.158-167
• /
• 2024

In this study, U-net model based on electrical capacitance is applied to monitor the condition inside the pipeline of semiconductor rear end process implemented in the numerical simulation. Capacitance values measured from electrodes attached to the pipeline is used as input data for the U-net network model and estimated permittivity distribution by the U-net model is used to reconstructed cross-sectional image at the pipeline. In the numerical simulation, images reconstructed by U-net model, Fully-connected neural network (FCNN) model and Newton-Raphson method are compared for evaluation. U-net model shows good results as compared to other models.

• Journal of Chest Surgery
• /
• v.37 no.2
• /
• pp.131-138
• /
• 2004

High-flow gas insufflation to get a bloodless field during off-pump coronary artery bypass may have adverse effects on the coronary endothelium. This study was designed (1) to elucidate the effect of carbon dioxide gas insufflations on the coronary endothelium at different flow rates and (2) to assess the protective effect of humidifcation against the coronary endothelial damage. Material and Method: In nine pigs, the left anterior descending coronary artery (LAD) was exposed after a median sternotomy. The LAD was divided into 4 segments and a coronary arteriotomy was made in each LAD segment in the beating heart. The far distal arteriotomy was exposed to room air for 10 minutes and was harvested as a control. Non-humidified carbon dioxide gas at a continuous flow rate of 5 L/min (Group I), humidified carbon dioxide gas at a continuous flow rate of 5 L/min (Group II), and humidified carbon dioxide gas at a continuous flow rate of 10 L/min (Group III) were insufflated for 10 minutes on each coronary arteriotomy site, respectively. After harvesting the coronary segments, hematoxylin-eosin staining, elastic fiber staining, and immunostaining with a CD34 monoclonal antibody were performed to evaluate the depth of endothelial damage and to count the residual endothelial cells, Result: In all three groups (Group I, II, and III), internal elastic laminae were preserved, however, the endothelial layers were significantly damaged by carbon dioxide gas insufflation. The mean percentages of remaining endothelial cells were 20,9$\pm$16.7%, 39.3$\pm$19.6%, and 6.8$\pm$5.3%, in groups I, II, and III, respectively. The percentages of remaining cells were significantly higher in group II than in groups I and III (p=0.008). The percentages of remaining cells were significantly higher in group I than in group III (p=0.008). Conclusions: The harmful effect of carbon dioxide gas insufflation on the coronary endothelium was dependent on the flow rate. The addition of humidification did not protect the coronary endothelium from denudation injury caused by high flow carbon dioxide gas insufflations.

• Polymer(Korea)
• /
• v.36 no.6
• /
• pp.677-684
• /
• 2012

Injection molding process is a popular polymer processing involving plasticizing and enforcing the material flow into the mold. A polymer material shrinks according to temperature variations during the shaping process, and subsequently molding shrinkage developed. Developed deflections or warpages after molding process in part are caused by residual stress relaxation contained in the part. Adding inorganic materials or fibers such as glass and carbon to control shrinkage and enhance warpage resistance are common. In this study, warpages according to part design have been investigated through experiment. Warpages for molding conditions and mold designs such as gate locations were measured. Warpages along flow direction and perpendicular to the flow direction were also measured. Warpages near gate and far from gate were compared. Glass fiber reinforced crystalline polymers, PP and PA66 have been used in this experiment. Glass fiber reinforced crystalline polymers showed large warpage compared with glass reinforced amorphous polymers. Warpages in crystalline polymers were less influenced by molding conditions compared with amorphous polymers, however warpages of crystalline polymers significantly depend on part design.

• Journal of the Korean Geotechnical Society
• /
• v.22 no.5
• /
• pp.83-91
• /
• 2006

Recently, the intensive rainstorm possibly induced by global warming plays a key role on the instability of railway adjacent slopes. The instability of slopes results as covering and loss of railway lines induced by slided soil mass. According to the site investigation on the failed slopes triggered by rainfall, low types of slope failure were observed: shallow, intermediate, gully erosion, and soil-rock interface failures. The observation reveals the different characteristics of slope failure depending on the thickness of soil layer, morphological features of slope, etc. Based upon the observations, flume tests were conducted to analyze the sliding mechanism of each failure. The variables of flume test are soil layer thickness, rainfall intensity, and morphology of slope under the constant condition of the percentage of fine, initial soil moisture content, slope angle and compaction energy. Test results show that shallow failure was mostly observed from the surface of the slope and caused by the soil erosion; in addition, compared to the other types of failure, the occurrence of initial erosion is late, however, the development of erosion is fast. In gully erosion failure, the collected water from the water catchment area helps erosion of the upper soil layer and transfer of residual corestone, which impedes the erosion process once the upper soil layers are eroded and corestone are exposed. The soil-rock interface failure shows the most fast initial erosion process among the failure types. Interestingly, the common feature observed from the different types of failure was the occurrence of the initial deformation near the toe of slopes which implies the existence of surbsurface flow along the downslope direction.