• Nuclear Engineering and Technology
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• 제49권5호
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• pp.979-988
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• 2017

The feasibility of cooling in a pressurized heavy water reactor after a large break loss-of-coolant accident has been analyzed using Multidimensional Analysis of Reactor Safety-KINS Standard code during the recirculation phase. Through evaluation of sensitivity of the fuel channel temperature to various effective recirculation flow areas, it is determined that proper cooling of the fuel channels in the broken loop is feasible if the effective flow area remains above approximately 70% of the nominal flow area. When the flow area is reduced by more than approximately 25% of the nominal value, however, incipience of boiling is expected, after which the thermal integrity of the fuel channel can be threatened. In addition, if a dramatic reduction of the recirculation flow occurs, excursions and frequent fluctuations of temperature in the fuel channels are likely to be unavoidable, and thus damage to the fuel channels would be anticipated. To resolve this, emergency coolant supply through the newly installed external injection path can be used as one alternative means of cooling, enabling fuel channel integrity to be maintained and permanently preventing severe accident conditions. Thus, the external injection flow required to guarantee fuel channel coolability has been estimated.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.269-274
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• 2011

A CFD analysis was performed to examine the inner channel blockage of dual-cooled fuel which has being developed for the power uprate of a pressurized water reactor (PWR). The dual-cooled fuel consists of an annular fuel pellet($UO_2$) and dual claddings as well as internal and external cooling channels. The dual-cooled annular fuel is different from a conventional solid 려el by employing an internal cooling channel for each fuel pellet as well as an external cooling channel. One of the key issues is the hypothetical event of inner channel blockage because the inner channel is an isolated flow channel without the coolant mixing between the neighboring flow channels. The inner channel blockage could cause the Departure from Nucleate Boiling (DNB) in the inner channel that eventually causes a fuel failure. This paper presents the CFD simulation of the flow through the side holes of the bottom end plug for the complete entrance blockage of the inner channel. Since the amount of coolant supply to the inner channel depends on largely the pressure loss at the side hole, the pressure loss coefficient of the side hole was estimated by the CFD analysis. The CFD prediction of the loss coefficient showed a reasonable agreement with an experimental data for the complete blockage of both the inner channel entrance and the outer channel. The CFD predictions also showed the decrease of the loss coefficient as the outer channel blockage increases.

• Nuclear Engineering and Technology
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• 제45권2호
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• pp.257-264
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• 2013

In Canada Deuterium Uranium (CANDU)-type nuclear power plants, the reactor is composed of 380 fuel channels and refueling is performed on one or two channels per day. At the time of refueling, the fluid force of the cooling water inside the channel is exploited. New fuel added upstream of the fuel channel is moved downstream by the fluid force of the cooling water, and the used fuel is pushed out. Through this process, refueling is completed. Among the 380 fuel channels, outer rows 1 and 2 (called the FARE channel) make the process of using only the internal fluid force impossible because of the low flow rate of the channel cooling water. Therefore, a Flow Assist Ram Extension (FARE) tool, a refueling aid, is used to refuel these channels in order to compensate for the insufficient fluid force. The FARE tool causes flow resistance, thus allowing the fuel to be moved down with the flow of cooling water. Although the existing FARE tool can perform refueling in Korean plants, the coolant flow rate is reduced to below 80% of the normal flow for some time during refueling. A Flow rate below 80% of the normal flow cause low flow rate alarm signal in the plant operation. A flow rate below 80% of the normal flow may cause difficulties in the plant operation because of the increase in the coolant temperature of the channel. A new and improved FARE tool is needed to address the limitations of the existing FARE tool. In this study, we identified the cause of the low flow phenomena of the existing FARE tool. A new and improved FARE tool has been designed and manufactured. The improved FARE tool has been tested many times using laboratory test apparatus and was redesigned until satisfactory results were obtained. In order to confirm the performance of the improved FARE tool in a real plant, the final design FARE tool was tested at Wolsong Nuclear Power Plant Unit 2. The test was carried out successfully and the low flow rate alarm signal was eliminated during refueling. Several additional improved FARE tools have been manufactured. These improved FARE tools are currently being used for Korean CANDU plant refueling.

• Nuclear Engineering and Technology
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• 제26권2호
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• pp.161-167
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• 1994

본 논문은 비상노심냉각계통을 필요로 하지 않는 압력관형 피동 수냉각로 개념을 제시한다. 여기서는 사고시 핵연료에서 생성되는 열을 감속재로 효과적으로 전달시키기 위해 금속 핵연료 매트릭스를 사용하는 핵연료 채널을 채택한다. 정상 운전시에는 보통의 냉각재가 핵연료를 냉각시키지만, 냉각재상실사고를 포함하여 정상적인 냉각계통의 작동이 이루어지지 않을 경우에는 피동 감속재냉각계통에 의해 핵연료가 냉각된다. 유한요소 코드를 이용한 해석 결과, 정상 상태 및 사고시 핵연료 온도를 허용 한도 이내로 유지할 수 있는 것으로 나타났다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.255-258
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• 2002

Liquid rocket engines using liquefied natural gas (LNG) or methane as a fuel is known to have several good characteristics, such as high specific impulse compared to other hydrocarbon fuels, environment-friendly exhaust gas, low production cost, and re-usability with low soot generation in the cooling channel. In this study, experimental combustion chambers capable of using LNC and $CH_{4}$ are being researched through experimental firing tests, and within easy range of eyes' inspection, there are the periodical existence of soot or discoloration in the chamber wall surface. This result means that mixture ratio of oxidizer and fuel fluctuates periodically between outer-row injectors in the mixing head in the circumferential direction. Therefore, based on this phenomenon, the variation of mixture ratio near the chamber wall caused by the spill pattern of a shear coaxial injector was analyzed quantitatively and the thermal heat flux Into the cooling channel is modified. Then, the calculated and modified results are compared with the measured ones.

• 한국추진공학회지
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• 제22권6호
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• pp.37-46
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• 2018

초음속 연소기에 대해 연료에 의한 연소기 재생 냉각을 가정하여 재생 냉각 유로 형상 설계를 수행하였다. 준일차원 모델을 사용하여 고온 측 및 저온 측 유동 계산을 수행하였으며 이 과정에서 양쪽 사이의 열전달을 계산하였다. 기준 형상에서 총 열교환량은 10.7 kW, 열유속은 $566kW/m^2$, 열교환기 입출구에서의 연료 온도 변화는 153 K으로 계산되었다. 7개의 열교환기 유로 형상에 대하여 열전달 성능을 비교하였다.

• 한국자동차공학회논문집
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• 제23권5호
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• pp.545-552
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• 2015

The heat generation in PEMFC is proportional to the electrical power output. Therefore, when the fuel cell produced the maximum output, the maximum heat was generated. In order to maintain the performance of the fuel cell, thermal management is as important as pressure and humidity conditions of the reactive gas. In this study, considering the thermal management for the maximum output operation, the optimal cooling channel design specifications of bipolar plate are found for the highest cooling performance. In the current bipolar plate research, many studies focused on analyzing various factors individually but there is no more study on the interaction between design factors. In this study, the heat transfer was simulated by COMSOL Multiphysics with the main design factors which are designated shape, width and rib length. One of the experimental design methods, general full factorial design method, was used to analyze the main factor and interaction on average temperature and maximum temperature for the design specification of fuel cell bipolar plate. When analysis result shows that all of these three factors are highly important, it can confirm that the interaction occurs between the factors.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제28회 춘계학술대회논문집
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• pp.148-151
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• 2007

동축 스월 인젝터 중에서 연료 인젝터의 스월 챔버 유무에 따른 인젝터 페이스의 냉각 특성을 알아보기 위해서 연료의 스월 챔버의 유무 조건만 다르고 모든 설계 조건이 같은 두 개의 인젝터를 만들었으며, 장시간 연소가 가능하도록 물을 이용한 재생 냉각 채널을 인젝터 페이스에 설치하였다. 두 개의 인젝터를 이용하여 연소 실험을 수행한 후 인젝터 페이스의 냉각 특성을 비교하였고, O/F ratio 2.0일 때와 O/F ratio 1.7일 때의 연소 특성 및 인젝터 페이스의 냉각 특성을 살펴보았다.

• 한국항공우주학회지
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• 제32권4호
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• pp.111-117
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• 2004

케로신과 액체산소를 추진제로 하며, 10톤을 설계 추력으로 하는 우주 발사체의 2단용 액체로켓엔진의 재생 냉각 특성에 대한 해석적 연구를 수행하였다. 또한 보조적인 냉각 방법으로서 노즐 확장부에는 대기로의 복사 방열에 의한 냉각을 적용하였다. 본 연구를 통해, 케로신을 연료로 하는 10톤 추력의 2단용 액체로켓엔진에서 재생냉각과 복사 냉각에 의한 냉각 기구만으로는 소재의 열 및 열구조적인 불안정성과 냉각채널에서의 과다한 압력강하에 의해 적합하지 않다는 것을 확인하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.643-646
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• 2017

탄화수소계열의 연료를 사용하는 액체로켓엔진에서 높은 열유속으로 인해 연소실 벽면이 구조적으로 손상 및 변형되는 것을 방지하기 위하여 연소실 벽면의 냉각은 필수적이다. 여러 가지 방법 중 연료를 냉각제로 사용 후 연소과정에 투입시키는 재생냉각 방식은 엔진 성능을 높여준다. 본 연구는 구리 단면적, 채널 내 유속, 채널에 가해지는 전류를 변화시켜 냉각제로 사용하는 케로신의 열전달 특성에 대해 알아보았다. 채널의 구리 단면적이 작을수록, 케로신의 유속이 빠를수록 대류 열전달이 빠르게 일어남을 알 수 있었다.