원전 피로 감시 시스템 개발 및 적용 현황

부명환,이경수,오창균,김현수,Boo, Myung Hwan,Lee, Kyoung Soo,Oh, Chang Kyun,Kim, Hyun Su 한국압력기기공학회 2017 한국압력기기공학회 논문집 Vol.13 No.2

세계적으로 원자력발전소의 안정적 운영 및 안전성 확보를 위해 수명기간 중 주요 기기 및 배관의 실제 운전 과도상태를 체계적으로 관리하고, 피로 손상의 정량적 평가 및 관리를 위한 체계적인 시스템이 요구되고 있는 실정이다. 이에 본 논문에서는 원자력발전소의 안전등급 1 설비에 대한 피로 평가요건을 분석하였고, 피로 감시방법 및 절차와 웹 기반으로 개발된 피로 감시 시스템인 NuFMS 개발 및 검증 내용을 기술하였다. NuFMS는 설계 시 고려한 과도상태 발생 횟수 대 비발전소의 특정 운전 시점에서의 실제 발생 횟수를 비교하여 안전 여유도의 정량적 확인이 가능하며, 누적피로사용계수 도출을 통해 정확한 피로영향 분석뿐만 아니라 손상 관리가 가능하다. 이와 같이 NuFMS의 적용을 통해 원자력발전소 기기 및 배관의 피로 건전성을 확인하고 운영 신뢰도를 향상시킬 수 있으며, 발전소의 안전성 유지 및 운영비용 절감 등의 효과를 기대할 수 있다. 따라서 향후 국내 전 원전에 NuFMS를 확대 적용할 예정이며, 이러한 기술의 해외 수출을 적극 추진 중이다. Metal fatigue is an important aging mechanism that material characteristics can be deteriorated when even a small load is applied repeatedly. An accurate fatigue evaluation is very important for component structural integrity and reliability. In the design stage of a nuclear power plant, the fatigue evaluations of the Class 1 components have to be performed. However, operating experience shows that the design evaluation can be very conservative due to conservatism in the transient severity and number of occurrence. Therefore, the fatigue monitoring system has been considered as a practical mean to ensure safe operation of the nuclear power plants. The fatigue monitoring system can quantify accumulated fatigue damage up to date for various plant conditions. The purpose of this paper is to describe the fatigue monitoring procedure and to introduce the fatigue monitoring program developed by the authors. The feasibility of the fatigue monitoring program is demonstrated by comparing with the actual operating data and finite element analysis results.

해수분위기에서 스테인리스강 배관 소켓 용접부의 선택적 부식

부명환,이장욱,이종훈 한국부식방식학회 2020 Corrosion Science and Technology Vol.19 No.4

Stainless steel has excellent corrosion resistance. The drawback is that pitting occurs easily due to the concentrationof chloride. In addition, corrosion of socket weld, which is structurally and chemically weaker than theother components of the pipe, occurs rapidly. Since these two phenomena overlap, pinhole leakage occursfrequently in the seawater pipe socket welds made of stainless steel at the power plants. To analyze thisspecific corrosion, a metallurgical analysis of the stainless steel socket welds, where the actual corrosionoccurred during the power plant operation, was performed. The micro-structure and chemical compositionof each socket weld were analyzed. In addition, selective corrosion of the specific micro-structure in a mixeddendrite structure comprising γ-austenite (gamma-phase iron) and δ-ferrite (iron at high temperature) wasinvestigated based on the characteristic micro-morphology and chemical composition of the corroded area. Finally, the different corrosion stages and characteristics of socket weld corrosion are summarized.

원전 냉각재환경이 주요기기 재료의 피로수명에 미치는 영향

부명환,이종훈 한국에너지학회 2019 한국에너지공학회 학술발표회 Vol.2019 No.10

Numerical simulation of temperature and thermal stress for nuclear piping by using computational fluid dynamics analysis and Green’s function

부명환,오창균,김현수,최청렬 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.5

Owing to the fact that thermal fatigue is a well-known damage mechanism in nuclear power plants, accurate stress and fatigue evaluation are highly important. Operating experience shows that the design condition is conservative compared to the actual one. Therefore, various fatigue monitoring methods have been extensively utilized to consider the actual operating data. However, defining the local temperature in the piping is difficult because temperature-measuring instruments are limited. The purpose of this paper is to define accurate local temperature in the piping and evaluate thermal stress using Green’s function (GF) by performing a series of computational fluid dynamics analyses considering the complex fluid conditions. Also, the thermal stress is determined by adopting GF and comparing it with that of the design condition. The fluid dynamics analysis result indicates that the fluid temperature slowly varies compared to the designed one even when the flow rate changes abruptly. In addition, the resulting thermal stress can significantly decrease when reflecting the actual temperature.

피로과정에서 S45C강의 반가폭과 잔류응력의 변화양상

부명환,박영철,김병수,이종문 한국비파괴검사학회 2002 한국비파괴검사학회지 Vol.22 No.5

기계구조물의 피로과정에 대한 손상정도를 평가하기 위하여 X선 회절을 이용하여 반가폭 및 하중방향과 수직방향에서의 2축에 대한 잔류응력의 변화를 측정하였다. 반가폭은 피로과정의 초기에는 큰 변화를 보이지만 피로수명비의 약10∼20%이후에는 큰 변화를 보이지 않았다. 2축 방향에 대한 잔류응력은 피로수명비의 40% 전후에서 길이방향의 경우는 감소와 증가를, 폭방향의 경우는 증가와 감소를 하였으며, 응력진폭이 클수록 잔류응력의 절대 값은 커지는 증가하는 경향을 나타내었다. The purpose of this study is to examine the change of full width half maximum(FWHM) and residual stress during fatigue process in S45C Steel by X-ray diffraction. For S45C Steel, the relationship between the change in fatigue damage of the specimen and the FWHM, and residual stress of X-ray diffraction profiles during the fatigue processes has been investigated. The FWHM decreases in the early period of fatigue cycle. The change of FWHM is associated with cyclic work hardening. The change of the FWHM is not significant in 10∼20% of ratio of fatigue life. The residual stress is changed with fatigue cycle increasing during the fatigue process.

S45C강의 피로과정에 대한 반가폭 및 잔류응력의 변화 ( The Change of Half Value Breadth and Residual Stress during Fatigue Process in S45C Steel )

부명환,구후택,정종현,박영철,김병수,김영석 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.1 No.1

X선 응력측정에 의한 복합재료의 3축 응력해석

부명환,박영철,광뢰행웅,Boo, Myung-Hwan,Park, Young-Chul,Hirose, Yukio 대한기계학회 1999 大韓機械學會論文集A Vol.23 No.7

In X-ray stress measurements for uni-directionally deformed surfaces such as grinding, a strongly curved $sin^2{\Psi} diagram, so called $\Psi-splitter, has been observed recently. It has been known that this is caused by the residual shear stress induced in the deformed layer by external forces. In this case it is necessary to consider this enough for ceramics and composite materials with tri-axial stress analysis. However, sufficient studies have not been done about the tri-axial stress analysis of the macro stress and micro. stress on each phase of the composite materials. The result of obtaining is as follows. 1. $\Psi-splitter does not appear in the vertical direction though $\Psi-splitter appears in grinding direction in WC-Co cemented carbides. The reversal of $\Psi-splitter to each phase does not appear. 2. $\Psi-splitter caused in WC-Co cemented carbides has a close relation in dislocation which accumulates in WC phase and phase transformation caused in Co phase. 3. The residual stress on the surface of grinding of each phase is in the state of the compression stress.

WC-Co합금의 X선 응력측정에 의한 탄성변형거동의 연구

夫明煥(Myung-Hwan Boo),吳世旭(Sae-Wook Oh),朴榮哲(Young-Chul Park),廣瀨幸雄(Yukio Hirose) 한국해양공학회 1994 韓國海洋工學會誌 Vol.8 No.2

초경합금은 기계적 성질이 다른 WC의 분산상과 Co의 결합상으로 구성되어 있다. 만일 이 합금이 거시적으로 균일하게 변형을 하면, 각 상들은 이들의 응력상태에 따라 다르게 변형될 것이다. 따라서 WC-Co 합금의 변형특성과 강화기구를 명확히 알기 위해서는 각상의 미시적 변형과 파괴기구를 검토할 필요가 있다.<br/> 본 연구에서는 시편에 굽힘하중을 가하여, X선 회절로 분산상인 WC상 및 결합상인 Co상의 X선적 탄성정수와 응력정수를 측정하였다. WC-Co합금중의 WC상과 Co상의 상응력은 WC(112)면과 Co(311)면의 회절로서 결정하였다. 그리고 이 상응력들을 복합법칙의 적용가능성에 대하여 검토하였다. Cemented carbides are composed of the dispersing phase of WC and biding phase of Co, which are very different from each other in mechanical properties. When the alloys are deformed uniformly in the macroscopic scale, each phase may be deformed differently under their own stress state. Therefore, in order to clarify the deformation characteristics and strengthening mechanism of the alloys, it is necessary to investigate microscopic deformation and fracture mechanism of each phase.<br/> In the present study, each phase of the X-ray elastic constant and the stress constant of the dispersing phase of WC and binding phase of Co, were measured by X-ray diffraction method during applied tensile elastic defromation. The phase stress of WC phase and Co phase within a WC-Co alloy was determined for diffraction from WC(112) plane and Co(311) plane. The phase stress was discussed on the basis of the law of mixture.

Zr-2.5Nb 압력관의 상온 수소취화

부명환(Myung-Hwan BOO),오동준(Dong-Jun OH),안창윤(Chang-Yun AN),김성수(Sung-Soo KIM),김영석(Young-Suk KIM) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8

The aim of his study is to investigate the effect of hydrogen embrittlement of Zr-2.5Nb CANDU pressure tube. The tests were performed at various of hydrogen contents for CCT specimens. The specimens were directly machined from the tube retaining original curvature using electric discharge machine. From the fracture toughness test, it was found that fracture toughness dJ/da was decreased with speedily increasing hydrogen content. And it observed constant value about 70-80ppm of hydrogen content. In fractography by SEM, we observed dimple fracture in AR materials, dimple and short fissure in 30ppm, and quesi-cleavage and large fissure in 80ppm. The decrease of fracture toughness with the addition of hydrogen is due the distribution of hydride and habit plane(10.7) of zirconium grain.

전산유체역학 해석을 이용한 열응력 평가의 보수성 저감방안 고찰

부명환(Myung Hwan Boo),오창균(Chang Kyun Oh),정성규(Sung Kyu Jung),최청열(Choeng Ryul Choi),김현수(Hyun Su Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.열공학 No.-