Material balance evaluation is an important measure to determine whether or not nuclear material is diverted. A prototype code to evaluate material balance has been developed for uranium fuel fabrication facility. However, it is difficult to analyze the code’s functionality and performance because the utilization of real facility data related to material balance evaluation is very limited. It is also restricted to deliberately implement various abnormal situations based on real facility data, such as nuclear diversion condition. In this study, process flow simulator of uranium fuel fabrication facility has been developed to produce various process data required for material balance evaluation. The process flow simulator was developed on the basis of the Simulink-SimEvents framework of the MathWorks. This framework is suitable for batch-based process modeling like uranium fuel fabrication facility. It dynamically simulates the movement of nuclear material according to the time function and provides process data such as nuclear material amount at inputs, outputs, and inventories required for Material Unaccounted For (MUF) and MUF uncertainty calculation. The process flow simulator code provides these data to the material balance evaluation code. And then the material balance evaluation code calculates MUF and MUF uncertainty to evaluate whether or not nuclear material is diverted. The process flow simulator code can simulate the movement of nuclear material for any abnormal situation which is difficult to implement with real process data. This code is expected to contribute to checking and improving the functionality and performance of the prototype code of material balance evaluation by simulating process data for various operation scenarios.

국제해사기구(IMO)의 온실가스(GHG) 감축 전략과 같은 환경규제를 강화함에 따라 친환경 선박 및 대체 연료 등 기술 개발이 확대되고 있다. 그의 일환으로 해운사와 조선사를 중심으로 에너지 저감과 풍력 추진 기술을 활용한 선박 추진 기술이 대두되고 있다. 풍 력 추진 기술의 확보와 실증 연구를 조선 및 해운 분야에 도입함으로써 친환경 기술을 활용한 고부가가치 시장을 창출할 수 있으며, 운항 선박의 연료 소비율을 줄임으로써 연비를 약 6~8 % 정도 향상시켜 GHG의 감축을 기대할 수 있다. 로터 세일(Rotor Sail, RS) 기술은 원형 실린더가 일정한 속도로 회전하여 유체를 통과할 때 실린더의 수직 방향으로 유체역학적 힘을 발생시키는 기술이다. 이를 마그누스 효과 (Magnus Effect)라고 하며, 본 연구에서는 선박에 설치된 풍력보조추진 시스템인 RS 주위의 난류 유동특성에 관한 수치해석적 연구를 통하 여 추진효율을 높일 수 있는 방안을 제시하고자 하였다. 그래서 RS의 공기 역학적 힘에 영향을 미치는 매개변수로써 속도비(Spin Ratio, SR)와 종횡비(Aspect Ratio, AR) 변화에 따른 양력계수( )와 항력계수( )를 도출하였고, RS 끝단 플레이트(End Plate, EP) 적용에 따른 RS 주변 유동특성을 비교하였다.

The design of the high-level radioactive waste (HLW) repository is made for isolating the HLW from the groundwater system by using artificial and natural barriers. Granite is usually considered to be a great natural barrier for the HLW repository in various countries including Sweden, Canada, and Korea due to its low hydraulic permeability. However, many fractures that can act as conduits for groundwater and radionuclides exist in granite. Furthermore, the decay heat generated by the HLW can induce groundwater acceleration through the fracture. Since the direction, magnitude, and lasting time of the heat-induced groundwater flow can be differed depending on the fracture geometry, the effect of fracture geometry on the groundwater flow around the repository should be carefully analyzed. In this study, groundwater models were conducted with various fracture geometries to quantify the effect of various properties of fractures (or fracture networks) on the heat-induced groundwater flow. In all models, the pressure around the repository only lasted for a short period after it peaked at 0.1 years. In contrast, the temperature lasted for 10,000 years after the disposal inducing the convective groundwater flow. Single fracture models with different orientations were conducted to evaluate the variations in groundwater velocities around the repository depending on the fracture slope. According to the results, the groundwater velocity on the fracture was the fastest when the regional groundwater flow direction and the fracture direction coincided. In double fracture models, various inclined fractures were added to the horizontal fracture. Due to the intersecting, the groundwater flow velocity showed a discontinuous change at the intersecting point. Lastly, the discrete fracture network models were conducted with different fracture densities, length distributions, and orientations. According to the modeling results, the groundwater flow was significantly accelerated when the fracture network density increased, or the average fracture length increased. However, the effect of the fracture orientation was not significant compared to the other two network properties.

Among the various causes of the vibration problem of the radial sluice gate used in Saemangeum, the effect of flow-induced vibration was studied by the method of computational fluid analysis. In this study, the effect on the flow-induced vibration of the Saemangeum radial sluice gate was evaluated by 2D unsteady flow numerical analysis using ANSYS Fluent. Gate opening cases of 0.2m, 0.3m, 0.4m, 0.5m, and 1.0m were analyzed. As a result, the flow-induced vibration characteristics due to the instability of turbulent flow were observed through FFT analysis. As the gate opening increases, the frequency of the maximum amplitude moves gradually to a lower frequency region with the reduction of the magnitude. Therefore the flow-induced vibration effects can be considered as small with the gate opening increase.

Numerical analysis has been carried out to investigate the characteristics of seawater flow fields and turbine output in a compact double current tidal power generation system for various level differences. There are growing concerns for the development of efficient tidal power generation which is stable and less affected by environmental circumstances as ocean energy. Especially the flow field characteristics in the compact tidal power generation system have a large influence on the system power generation performance. Flow velocity, pressure, and streamline distributions are compared including vertical type turbine out, and it can be predicted that seawater is accelerated by vortex flow in front of the turbine and there is severe turbine output variation due to the water level difference with pressure difference. These results can be applied as basic data for the effective development of compact tidal power generation system.

Small-sized heater is usually used to make the hot water in resting place, factory, household affairs and so on. One of methods to obtain hot water in short time is known as using instantaneous electric water heater. In this study, numerical analysis for small-sized hot water heater with straight double tube-type was tried to achieve the basic design data. This study aims to investigate the characteristics of thermal flow, for instance, such as pressure difference, outlet mean temperature and velocity, due to clearance. As the clearance is decreased, outlet mean temperature and pressure difference(Pmax.-Pmin.) are increased. Therefore appropriate relations between area of heat source and pressure difference should be set up. Further small-sized hot water heater in this study must be equipped with electric device capable of heating over 90℃.

In this study, gas flow pattern and temperature distribution in a laboratory scale low temperature furnace for carbonization were numerically analyzed. The furnace was designed for testing carbonization process of carbon fibers made from polyimide(PI) precursor. Nitrogen gas was used as a working gas and it was treated as an ideal gas. Three-dimensional computational fluid dynamics analysis for steady state turbulent flow was used to analyze flow pattern and temperature field in the furnace. The results showed that more uniform velocity profile and axisymmetric temperature distribution could be obtained by varying mass flow rate at the inlets.

Chemical decontamination of primary systems in a nuclear power plant (NPP) prior to commencing the main decommissioning activities is required to reduce radiation exposure during its process. The entire process is repeated until the desired decontamination factor is obtained. To achieve improved decontamination factors over a shorter time with fewer cycles, the appropriate flow characteristics are required. In addition, to prepare an operating procedure that is adaptable to various conditions and situations, the transient analysis results would be required for operator action and system impact assessment. In this study, the flow characteristics in the steady-state and transient conditions for the chemical decontamination operations of the Kori-1 NPP were analyzed and compared via the MARS-KS code simulation. Loss of residual heat removal (RHR) and steam generator tube rupture (SGTR) simulations were conducted for the postulated abnormal events. Loss of RHR results showed the reactor coolant system (RCS) temperature increase, which can damage the reactor coolant pump (RCP)s by its cavitation. The SGTR results indicated a void formation in the RCS interior by the decrease in pressurizer (PZR) pressure, which can cause surface exposure and tripping of the RCPs unless proper actions are taken before the required pressure limit is achieved.

이 연구는 지속가능한 수자원 이용 및 관리대책을 수립하는 데에 필요한 수문학적 자료를 제공할 목적으로 2017~2020년 홍수기 (6~9월)에 발생한 총 59회의 강우 사상에 대한 강우-유출 특성을 파악하였다. 그 결과, 강우량은 5.0~400.8 mm, 유출고는 0.1~176.5 mm, 유출률은 0.1~242.9%의 범위로 나타났다. 그리고 유출수문곡선에서 직접유출과 기저유출을 분리한 결과, 홍수기의 총 유출일 대비 기저유출 (139.3일)이 직접유출 (78.3일)보다 유출기간이 길었지만, 총 유출고에 대한 기여도는 직접유출 (54.2%)이 기저유출 (45.8%)보다 높게 나타났다. 또한, 유출에 영향을 미치는 강우조건을 분석한 결과, 직접 유출과 기저유출의 유출고 및 첨두유출고에 높은 유의성 (p<0.05)을 보이는 강우조건은 강우량과 강우지속시간으로 나타났다. 특히, 유출고와 첨두유출고의 강우량은 각각 5.0~200.4, 10.5~110.5 mm의 범위에서는 기저유출이 우세한 강우사상이 나타났지만, 유출고와 첨두유출고의 강우량이 각각 267.4~400.8, 169.0~400.8 mm의 범위에서는 직접유출이 우세한 강우사상이 나타났다. 앞으로 극한 기후현상에 따른 물 부족이 심화할 것으로 예상되는 가운 데, 산지계류의 직접유출 및 기저유출에 대한 장기적이고도 지속적인 분석이 이루어진다면 지표수-지하수의 이용 및 관리 측면에서의 활용과 자료의 신뢰성을 높일 수 있을 것으로 판단된다.

This paper presents a Raman spectroscopy study of the influence of methane flow on the micro-tribological behavior of diamond-like carbon coatings deposited with an industrial plasma-enhanced chemical vapor deposition system. Results have shown a direct relationship between the methane flow and thickness of the coatings. The analysis of the Raman spectra and deposition parameters allowed establishing the influence of H content with the methane flow, the disorder level and estimation of the sp3 fraction on the carbon coatings. The micro-tribology tests showed a strong dependence of the wear resistance and hardness with Raman parameters. The coating deposited at 72-sccm methane flow presented a thickness of 1.7 μm and a sp3 fraction of 0.33. This sp3 fraction gave rise to a hardness of 24 GPa and an excellent wear resistance of 3.3 × 10–6 mm3 N−1 mm−1 for this DLC coating. Wear tests showed a swelling in the wear profiles on this coating, which was associated with the occurrence of a re-hybridization process.

This study was performed to analyze the effect on driving performance by identifying the flow characteristics of the rear diffuser such as drag coefficient, lift coefficient, velocity vector, velocity streamlines, turbulence kinetic energy and vortex-core region according to the angle of the sedan rear diffuser and the shape of the divider. The angle of the diffuser was analyzed at 2° intervals from 0° to 18°, and the divider was analyzed by changing from one to five. The three-dimensional modeling was performed using CATIA V5 and the vehicle model was selected as a sedan car in the form of an LF Sonata. The CFD analysis was performed in order to identify the flow characteristics of rear diffuser using ANSYS CFX 14.5.7. For each model, the analysis was performed under each condition with speeds of 80km/h, 100km/h, 120km/h, 140km/h. The results of the flow analysis showed that the rear diffuser angle was the best result in driving stability at 6°. The results of the study on the number of dividers showed the best result value in driving stability when the rear diffuser angle was 6° and the divider was 3 and selected as the optimal shape.

Numerical analysis has been carried out to investigate the flow field characteristics for exhaust gas in automobile engine DPF system. The DPF system performance is largely affected by exhaust gas flow while it passes through the complicated geometry of DOC/DPF system, fan shape structure, and perforated can with air for fuel combustion. Hence the characteristics of fluid velocity, pressure, and streamline are analyzed with velocity uniformity in front of DOC and swirl flow near the fan. It can be seen that the velocity uniformity increases with the gas flow rate including flow acceleration near the lower area of the fan. The air flow also influences the gas flow distribution close to the impeller and fan structure with complicated swirl flow. These results are expected to be applicable as fundamental design data for automobile engine exhaust system.

In this study, the flow analyses were carried out on three kinds of front wing models. The down forces of front wings which influence the stability, cornering at driving were investigated with three models. At model 1, the maximum pressure shown on the main plate of front wing is 3177.539Pa. The maximum pressures at models 2 and 3 are shown to be 3429.677Pa and 3506.494Pa, respectively. The higher the pressure, the more resistance. So, the lower the pressure, the less resistance the model gets. At model 1, the maximum velocity of stream that flows under the front wing was shown to be the smallest among three models. In case of all three models, the pressure at which the air passes through the front wing is high in the upper part of the front wing. Among three models, model 1 is thought to be the most appropriate model to give the effect of the down force while reducing the flow resistance at driving. By utilizing this study result, the flow velocity and pressure are investigated without the flow experiment at driving due to the configuration of automotive front wing, and the flow resistance can be seen.