• Journal of Korean Society of Environmental Engineers
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• v.34 no.11
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• pp.772-779
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• 2012

For improving performance of conical air diffuser generating fine bubble, both experimental and numerical simulation method were used. After adapting diffusers inner real scale bubble column, suitable for various diffuser submergence, the effect of diffuser submergence on oxygen transfer performance such as Oxygen Transfer Coefficient ($K_{L}a_{20}$) and Standard Oxygen Transfer Efficiency (SOTE) was investigated empirically. As flow patterns for various diffuser number and submergence were revealed throughout hydrodynamic simulation for 2-phase fluid flow of air-water, the cause of the change for oxygen transfer performance was cleared up. As results of experimental performance, $K_{L}a_{20}$ was increased slightly by 7% and SOTE was increased drastically by 39~72%, 5.6% per meter. As results of numerical analysis, air volume fraction, air and water velocity in bioreactor were increased with analogous flow tendency by increasing diffuser number. As diffuser submergence increased, air volume fraction, air and water velocity were decreased slightly. Because circulative co-flow is determinant factor for bubble diffusion and rising velocity, excessive circulation intensity can result to worsen oxygen transfer by shortening bubble retention time and amount.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.1
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• pp.54-60
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• 2004

Experimental study on combustion characteristics of double swirl coaxial injectors has been conducted for the assessment of critical injector design parameters. A reusable, subscale thrust chamber has been fabricated with a water-cooled copper nozzle. Two different configurations of injectors have been tested for the understanding of the effects of recess length on high pressure combustion. Clearly, the recess length drastically affects the combustion efficiency and hydraulic characteristics of an injector. Internal mixing of propellants in an injector with recess number of two increases a combustion efficiency and reveals sound combustion although a pressure drop required for the same amount of mass flow rates increases compared with an injector of recess number of one.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.2
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• pp.85-94
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• 2004

Experimental study on combustion characteristics of double swirl coaxial injectors has been conducted for the assessment of critical injector design parameters. A reusable, unielement thrust chamber has been fabricated with a water-cooled copper nozzle. Two principal design parameters. a swirl angle and a recess length, have been investigated through hot firing tests for the understanding of their effects on high pressure combustion. Clearly, both parameters considerably affect the combustion efficiency, dynamics and hydraulic characteristics of an injector. Internal mixing of propellants in a recess region increases combustion efficiency along with the increase of a pressure drop required for flowing the same amount of mass flow rates. It is concluded that pressure buildup due to flame can be released by the increase of LOx flow axial momentum or the reduction of a recess length. Dynamic pressure measurements of the thrust chamber show varied dynamic behaviors depending on injector configurations.

• The KSFM Journal of Fluid Machinery
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• v.10 no.2 s.41
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• pp.41-45
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• 2007

The shutoff unit was designed to provide rapid insertion of neutron absorbing material into the reactor core to shutdown the reactor quickly and also to withdraw the absorber slowly to avoid a log-rate trip. Four shutoff units were installed on the HANARO reactor but the half-core test facility was equipped with one shutoff unit. The reactor trip or shutdown is accomplished by four shutoff units by insertion of the shutoff rods. The shutoff rod(SOR) is actuated by a directly linked hydraulic cylinder on the reactor chimney, which is pressurized by a hydraulic pump. The rod is released to drop by gravity, when triplicate solenoid valves are de-energized to vent the cylinder. The hydraulic pump, pipe and air supply system are provided to be similar with the HANARO reactor. The shutoff rod drops for 647mm stroke within 1.13 seconds to shut down the reactor and it is slowly inserted to the full down position, 700mm, with a damping. We have conducted the drop test of the shutoff rod in order to show the performance and the structural integrity of operating system of the shutoff unit. The present paper deals with the 647mm drop time and the withdrawal time according to variation of the pool water temperature, the water level and the core flow.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.2
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• pp.86-93
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• 2016

Performance tests of a 75-tonf liquid rocket engine turbopump were conducted. The performance of sub-components - two pumps and a turbine - and their power matching were measured and examined firstly near the design speed under the LN2 and kerosene environment. In the real propellant - LOX and kerosene - environment tests, design and off-design performance of turbopump were fully verified in regime of the rocket engine operation. During the off-design performance tests, turbopump running time was set longer than the engine operating time to verify the pump operability and set the pump inlet pressure close to design NPSHr to investigate pump suction capability in parallel. It has been found that developed-turbopump satisfied all of the engine required performances.

• Journal of Energy Engineering
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• v.25 no.4
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• pp.124-132
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• 2016

In order to estimate the effect of flow distributors connected to an upper nozzle of CMT(Core Makeup Tank) on the thermal-hydraulic characteristics in the tank, a simplified 2 inch Small Break Loss of Coolant Accident(SBLOCA) was simulated by skipping the decay power and Passive Residual Heat Removal System(PRHRS) actuation. The CMT is a part of safety injection systems in the SMART (System Integrated Modular Advanced Reactor). Each test was performed with reliable boundary conditions. It means that the pressure distribution is provided with repeatable and reproducible behavior during SBLOCA simulations. The maximum flow rates were achieved at around 350 seconds after the initial opening of the isolation valve installed in CMT. After a short period of decreased flow rate, it attained a steady injection flow rate after about 1,250 seconds. This unstable injection period of the CMT coolant is due to the condensation of steam injected into the upper part of CMT. The steady injection flow rate was about 8.4% higher with B-type distributor than that with A-type distributor. The gravity injection during hot condition tests were in good agreement with that during cold condition tests except for the early stages.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.120-128
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• 2019

It is very important to verify the seismic performance and stability of the power plant fixture in the domestic power plant, because earthquakes have increased in frequency around the world which resulted in the frequent occurrence of power plant damage caused by the failure of electric power facilities. In this study, through the on-site inspection of power plant fixation unit installed in domestic power plants, we carried out structural performance evaluation of the fixation unit anchor bolts installed on the concrete slabs. The field survey showed M12 J hook anchor bolts were used. Anchor bolt pullout and shear performance evaluation were performed based on ASTM E 488-96 standard. Moreover, artificial crack with the width of 0.5 mm was applied during the experiment based on ATM355.4 and ETAG 001. The comparison of M12 J hook anchor bolt pullout and shear test result to design value required in domestic and international design standard, show a satisfactory result. M12 J hook anchor pullout and shear performance was found to be about 35% and 7%, respectively, higher than the required design value.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.465-465
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• 2014

증식블랑켓모듈(TBM, Test Blanket Module)을 개발하여 왔다. 이 두 증식블랑켓모듈은 모두 헬륨냉각을 기반으로 개발 되어왔으며 이에 따라, 헬륨순환기, 헬륨히터 및 헬륨열교환기 등에 대한 기본적인 연구가 수행되었다. 이후 2012년 고체형 증식블랑켓모듈을 ITER TBM 개념으로 주도하기로 결정함에 따라, HCCR (Helium Cooled Ceramic Reflector) TBM의 보조계통인 하나인 헬륨냉각계통(HCS, Helium Cooling System)에 대한 개발이 본격적으로 이루어졌다. 한국원자력연구원에서는 HCCR TBM의 냉각성능을 만족하기 위하여 8 MPa, 1.5 kg/s 및 $300/500^{\circ}C$ (입구/출구 온도)의 운전조건을 갖는 헬륨냉각계통의 설계를 완료하였다. 설계된 헬륨냉각계통은 HCCR TBM에서 회수된 약 $450^{\circ}C$의 헬륨을 열회수기(recuperator)기와 냉각기를 통해 상온으로 냉각시킨 후, 필터를 통해 헬륨을 여과시킨다. 여과된 헬륨은 헬륨순환기에 의해 가압되어 열회수기를 다시 지나 $300^{\circ}C$ 이상으로 가열된다. 가열된 헬륨은 열회수기를 지나지 않는 상온의 헬륨과 혼합되어 최종적으로 HCCR TBM의 입구온도 조건인 $300^{\circ}C$로 맞추어 HCCR TBM에 공급된다. 이러한 열회수기 중심으로 '${\infty}$' 모양의 자가 교차로 설계된 헬륨냉각계통은 고온영역과 저온영역으로 냉각회로를 구분하여 순환기, 필터 및 각종 계측기의 운전온도 환경을 상온으로 유지시킬 수 있어 운전 및 유지보수 관점에서 이점이 있다. HCCR TBM의 헬륨냉각계통 설계 및 핵심 기기를 실증하고, 운전 경험을 쌓기 위하여 헬륨공급장치(HeSS, Helium Supply System)를 헬륨유량기준 1/3 규모(0.5 kg/s)로 구축하였으며, '14년까지 HeSS를 실증규모로 업그레이드 하기 위하여 80기압 환경에서 압축비 1.1, 유량 1.5 kg/s의 성능을 내는 헬륨순환기를 설치할 예정이다. 현재 구축된 1/3 규모 HeSS는 국내 구축된 전자빔 고열부하 시험 장비인 KoHLT-EB (Electron Beam)와 연계되어 HCCR TBM의 일차벽(플라즈마 대향부품)을 검증할 예정이며, 이를 통해 얻어진 열수력 DB는 현재 개발중인 핵융합로 안전해석코드인 GAMMA-FR 검증에 활용될 계획이다.

• International Journal of Highway Engineering
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• v.13 no.4
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• pp.159-166
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• 2011

Green house gas emissions are increasing as development of the industrial economy of the international community. Many countries in the world are endeavoring to reduce green house gas emissions under severe climate change. In order to protect grobal warming, government is trying to reduce green gas emissions under "Low Carbon Green Growth Policy" and investing climiate-firendly industries such as renewable energy harvesting. Renewable energy has been rapidly developing as a result of investment for development technology of using natural energy such as solar, wind, tidal, etc. There are lots of waste energy in the road space. However, nobody is not interested in waste energy from the road space. This paper present a fundamentally experimental study of energy harvesting technique to use waste energy in the road. The waste energy in the road is covered a pressure and impact of vehicles on the road, the radiant heat from asphalt pavement, road noise and vibration etc. In this study, an energy harvesting device using piezoelectric element is proposed and various tests are conducted to investigate a characteristic of this device as function of impact loading based on piezoelectric effect behavior. This paper shows the energy harvesting results of the device using domestic piezoelectirc element as a function of impact load size and pavement types.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2019.05a
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• pp.464-466
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• 2019

Controllers used in nuclear power plants require high reliability. A controller including a Field Programmable Gate Array (FPGA) and a Complex Programmable Logic Device (referred to hereinafter as FPGA) has been applied to many Nuclear Power Plants (NPP) in the past, including the APR1400 (Advanced Power Reactor 1400), a Korean digital nuclear power plant. Initially, the FPGA was considered as a general IC (Integrated Circuit) and verified only by device verification and performance testing. In the 1990s, research on FPGA verification began, and until the FPGA became a chip, it was regarded as software and the software Verification and Validation (V&V) using IEEE 1012-2004 was implemented. Currently, IEC 62566, which is a European standard, has been applied for a lot of verification. This method has been evaluated as the most sensible method to date. This is because the method of verifying the characteristics of SoC (System on Chip), which has been a problem in the existing verification method, is sufficiently applied. However, IEC 62566 is a European standard that has not yet been adopted in the United States and maintains the application of IEEE 1012 for FPGA. IEEE 1012-2004 or IEC 62566 is a technical standard. In practice, various methods are applied to meet technical standards. In this paper, we describe the procedure and important points of verification method of Nuclear Safety Class FPGA applying SoC verification method.