• 한국압력기기공학회 논문집
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• 제7권2호
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• pp.34-41
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• 2011

Wrought nickel-base superalloys are being considered as the structural materials in very-high temperature gas-cooled reactors. To understand the effects of impurities, especially oxygen, in helium coolant on the mechanical properties of Alloy 617, creep tests were performed in high temperature flowing He environments with varying $O_2$ contents at 800, 900, and $1000^{\circ}C$. Also, creep life in static He was measured to simulate the pseudo-inert environment. Creep life was the longest in static He, while the shortest in flowing helium. In static He, impurities like $O_2$ and moisture were quickly consumed by oxidation in the early stage of creep test, which prevented further oxidation during creep test. Without oxidation, microstructural change detrimental to creep such as decarburization and internal oxidation were prevented, which resulted in longer creep life. On the other hand, in flowing He environment, surface oxides were not stable enough to act as diffusion barriers for oxidation. Therefore, extensive decarburization and internal oxidation under tensile load contributed to premature failure resulting in short creep life. Limited test in flowing He+200ppm $O_2$ resulted in even shorter creep life. The oxidation samples showed extensive spallation which resulted in severe decarburization and internal oxidation in those environments. Further test and analysis are underway to clarify the relationship between oxidation and creep resistance.

• Nuclear Engineering and Technology
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• 제26권2호
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• pp.257-264
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• 1994

원자력발전소 중대사고시 용융된 노심과 잔류냉각수가 증기폭발을 일으켜 원자로 격납용기의 건전성을 위협할 수 있다. 본 연구에서는 증기폭발을 모사할 수 있는 실험 장치를 제작하고, 물과 프레온을 사용하여 증기폭발실험을 수행하였다. 이때 고속카메라를 사용하여 폭발현상을 관측하였고, 동압측정기와 압력분출관을 이용하여 생성되는 폭발압력과 기계적인 에너지를 계측하였다. 이를 토대로 증기폭발의 중요인자들(물의 온도, 물의 주입속도, 물의 주입 시간, 그리고 냉매의 깊이)에 대한 민감도 분석을 수행하였다. 그리고, 압력용기 바닥의 구조물이 용융/냉각재의 반응에 미치는 영향을 살펴보기위하여 실험용기 내부에 그리드를 설치하여 폭발실험을 실시하였다. 물/프레온의 폭발실험에서 계측된 기계적에너지를 이용한 에너지효율은 0.5∼l.6%인 것으로 계산되었다.

• 한국표면공학회지
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• 제49권4호
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• pp.389-394
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• 2016

The operation method of nuclear power plants is currently changing to high burn-up and long period that can enhance economics and efficiency of the plant. Since nuclear plant operation environment has been becoming severe, the amount of absorbed hydrogen also has increased. Absorbed hydrogen can be fatal securing safety of nuclear fuel cladding in case of Loss of Coolant Accidents(LOCA). In order to examine the impact of hydride on high-temperature oxidation, high-temperature oxidation experiment was performed on normal Zry-4 cladding and on Zry-4 cladding where hydrogen is charged in air pressure steam atmosphere under the $950^{\circ}C$ and $1000^{\circ}C$. According to the results, while oxidation acceleration due to charged hydrogen was not observed prior to breakaway oxidation creation, oxidation began to accelerate in cladding where hydrogens charged as soon as the breakaway oxidation started. If so much hydrogen are charged in the cladding, equiaxial monoclinic phase to unstable of stress is formed and it is presumed that oxidation is accelerated because nearby stress caused a crack in equiaxial phase, and that makes corrosion resistance decline sharply.

• Nuclear Engineering and Technology
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• 제18권4호
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• pp.273-280
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• 1986

이 연구의 목적은 가혹한 사고후 손상된 원자로심을 모의한 열을 발생하는 데브리층에서의 강제대류 드라이아웃 열유속을 실험적으로 얻고져 한 것이다. 이 연구에서 냉각재 순환장치를 사용하여 대기압하에서 냉각재가 상향 강제대류하는 유도 가열된 강구 입자층에서의 드라이아웃 열유속을 얻었다. 이 실험에서는 주로 강제대류 드라이아웃에 대한 질량유속.입자크기.입자층의 높이 및 냉각재의 서브클링의 영향이 관찰되었다. 실험은 입자직경이 1.5, 2.5, 3.0 및 4.0mm의 탄소강입자를 55mm 내경의 Pyrex 유리용기에 넣어 고주파유도 전류를 통해 가열하여 이루어졌다. 냉각재로서 증류수를 질량유속 0~3.5kg/$m^2$s로 변화시키어 공금하고 층의 높이는 55mm와 110mm, 냉각재 유입온도는 2$0^{\circ}C$와 8$0^{\circ}C$로 변화시켰다. 주요 실험결과는 다음과 같다. (1) 드라이아웃 열유속은 상향 강제 대류 질량유속과 입자크기내의 증가에 따라 증가한다. (2) 질량유속이 없는 경우 드라이아웃 열유속은 기존 연구결과와 같이 입자직경에 의존한다. (3) 얕은 입자층에서의 드라이아웃 열유속은 깊은 입자층의 것보다 얼마간 높다.

• 한국자동차공학회논문집
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• 제21권4호
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• pp.153-158
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• 2013

The purpose of this study is to investigate the performance characteristics of the counterflow exhaust heat recovery device for the applied gasoline engines. The EHRS device is installed behind the catalyst. This study investigates the engine warm-up characteristic, the exhaust noise characteristic, the back-pressure characteristic. The engine warm-up characteristics is (load 0%, load 10%, load 20%) in (idle, 1000rpm, 1500rpm, 2000rpm, 2500rpm) conditions by measuring the time it warmed up, coolant temperature ($25^{\circ}C{\sim}80^{\circ}C$) until the performance evaluation is performed. The wide open throttle and the coast down the exhaust noise and the back-pressure characteristic experiment repeated twice. The test conditions is 950rpm~6,050rpm proceed experiment repeated 3-5 times. Load 0% idle conditions except the results improved engine warm-up characteristics. The exhaust noise obtain similar results the BASE+EHRS W/O_FRT_MUFF with BASE and back-pressure to obtain similar results BASE+EHRS W/O_FRT_ MUFF with BASE+EHRS.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2305-2311
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• 2002

The pressure tube is a major component of the CANDU reactor, which supports nuclear fuel bundle and heavy water coolant. Pressure tubes are installed horizontally inside the reactor and only selected samples are periodically examined during in-service inspection. In this respect, a probabilistic safety assessment method is more appropriate fur the assessment of overall pressure tube safety. The failure behavior of CANDU pressure tubes, however, is governed by delayed hydride cracking which is the major difference from pipings and reactor pressure vessels. Since the delayed hydride cracking has more widely distributed governing parameters, it is impossible to apply a general PFM methodology directly. In this paper, a PFM methodology for the safety assessment of CANDU pressure tubes is introduced by applying Monte Carlo simulation in determining failure probability Initial hydrogen concentration, flaw shape and depth, axial and radial crack growth rate and fracture toughness were considered as probabilistic variables. Parametric study has been done under the base of pressure tube dimension and hydride precipitation temperature in calculating failure probability. Unstable fracture and plastic collapse are used for the failure assessment. The estimated failure probability showed about three-order difference with changing dimensions of pressure tube.

• Nuclear Engineering and Technology
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• 제26권3호
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• pp.389-400
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• 1994

FLECHT SEASET 실험 데이터를 사용하여 대형 냉각재 상실 사고시 재관수 첨두 피복재 온도에 대한 RELAP5 /MOD3/KAERI의 예측능력을 평가하였으며, 관련 불확실성을 통계적으로 정량화 하였다. 중력구동 재관수 실험및 광범위한 재관수율, 시스템 압력, 초기 피복재 온도, 연료봉 출력을 포괄하는 강제구동 재관수 실험들로 구성된 18개의 실험이 평가에 사용되었다. 평가 결과 재관수 첨두 피복재 온도에 대해 평균 7.56 K 낮게 예측하였으며 이를 포함한 관련 불확실성의 상한은 95% 신뢰도 수준에서 약 99 K로 정량화 되었다.

• Nuclear Engineering and Technology
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• 제55권7호
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• pp.2534-2546
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• 2023

Gas-cooled space reactor, which adopts He-Xe gas mixture as working fluid, is a better choice for megawatt power generation. In this paper, thermal-hydraulic characteristics of He-Xe gas mixture in 2×2 rod bundle wrapped with helical wires is numerically investigated. The velocity, pressure and temperature distribution of the coolant are obtained and analyzed. The results show that the existence of helical wires forms the vortexes and changes the velocity and temperature distribution. Hot spots are found at the contact corners between helical wires and fuel rods. The highest temperature of the hot spots reach 1600K, while the mainstream temperature is less than 400K. The helical wire structure increases the friction pressure drop by 20%-50%. The effect extent varies with the pitch and the number of helical wires. The helical wire structure leads to the reduction of Nusselt number. Comparing thermal-hydraulic performance ratios (THPR) of different structures, the THPR values are all less than 1. It means that gas-cooled space reactor adopting helical wires could not strengthen the core heat removal performance. This work provides the thermal-hydraulic design basis for He-Xe gas cooled space nuclear reactor.

• 한국정밀공학회지
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• 제25권3호
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• pp.115-125
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• 2008

Recently, Exhaust Gas Recirculation (EGR) system which re-flow a cooled exhaust gas from vehicles burning diesel as fuel to a combustion chamber of engine has been used to solve the serious air pollution. For the design and mass production of EGR system, it is essential to ensure structural integrity evaluation. The EGR system consisted of ten dimpled oval core rectangular tubes, two fix-plates, two coolant pipes, shell body and two flanges in this study. To confirm the safety of the designed system, finite element modeling about each component such as the dimpled oval core tube with the dimpled shape and others was carried out. The reliability of EGR system against exhaust gas flow with high temperature was investigated by flow and pressure analysis in the system. Also, thermal and strength analysis were verified the safety of EGR system against temperature change in the shell and tubes. Furthermore, modal analysis using ANSYS was also performed. From the results of FE analysis, there were confirmed that EGR system was safe against the flow of exhaust gas, temperature change in EGR system and vibration on operation condition, respectively.

• 한국결정성장학회지
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• 제8권1호
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• pp.1-9
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• 1998

본 연구에서는 냉각매체로서 물을 이용하는 수정된 열교환법을 이용하여 45$\times$45$\times$20(mm) 크기의 사각단면 형상의 sapphire 단결정의 제조가능 조건에 대하여 조사하였다. 온도에 따른 성장로 내의 압력 변화로부터 사파이어의 용융 및 응고 과정을 추적할 수 있었으며, 이로부터 sapphire 단결정은 1970~$1960^{\circ}C$에서 응고가 완료됨을 알 수 있었다. 도가니 성형시 이루어지는 '귀'의 형태는 도가니 벽면과 접촉되지 않는 '나선형태'이어야 한다. 열유출부는 융액 내의 온도구배를 지배하며 융액내의 열유속과 씨앗 결정의 흔적은 Mo 봉의 체적 변화로서 조절할 수 있었다. 기공 형성을 억제하기 위해서는 $0.2^{\circ}C$/min 이하의 발열체의 냉각속도가 요구되었다.