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Page : 12 - 23
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- 원자력 발전소 Alloy 600 부품의 PWSCC-Part 2
- Alloy 600재료는 가압 경수형 원자로의 증기발생기 전열관으로 사용되고 있는 것은 물론(최근에 내식성이 우수한 Alloy 690으로 교체되는 추세) control rod drive mechanisms (CRDMs), in-core instruments(ICIs), 열전대용 배관, 원자로 하부 관통관(reactor
vessel bottom head bottom mounted instruments(BMIs), 가압기 열소매(pressurizer heater sleeves)와 그 외 여러 계측기용 배관 재료로 널리 사용되고 있다.
Alloy 600은 Alloy 82와 Alloy 182등으로 압력용기강 재료(ferritic steel)와 용접되어 있으며 이러한 이종금속 용접부(Dissimilar metal weld, DMW)가 일차 계통수에 장기간 노출됨으로 인한 응력부식균열(Primary water stress corrosion cracking, PWSCC)이 발생하고 있다.
가동원전 부품에서 최초의 PWSCC는 1971년에 증기발생기 전열관에서 발생하였으며 그 후 세계 여러발전소의 배관 용접부에서 균열이 보고되었다. 국내 원전 증기발생기 Alloy 600재질의 배수노즐에서도 2007년과 2008년에 균열이 발생한 사례가 있는데 그 원인도 PWSCC로 밝혀졌다. 2010년과 2011년에는 각각 국내원전의 원자로 상부헤드 배기관에서
PWSCC가 발견되어 보수 조치한 바 있다. 또한 2012년에는 원자로 상부의 CRDM(Control rod drive mechanism)에서 균열이 발견되어 보수한 바 있다.
이와 같이 PWSCC는 부품의 가동연수가 길어짐에 따라 나타나는 경년열화(Aging degradation) 현상이므로 조기에 검출하고 필요시 보수, 교체하는 적극적인 관리 전략을 통해 원자력 발전소를 안전하게 운전하는 기준을 마련할 시점이다.
본 학술지(부식과 방식)에 ‘원자력 발전소 Alloy 600 부품의 PWSCC-Part 1’라는 제목으로 alloy 600 재료의 PWSCC의 개념, 그 발생과 전파에 미치는 미세조직, 온도, 응력, 수화학 환경등의 주요인자에 대해 본 저자가 저술한 바 있다. 본 논문에서는 PWSCC의 개시와 전파기구를 살펴보고 그 억제 기술 및 Alloy 600 부품 열화관리 전략을 소개하였다. - KEYWORDs : alloy 600,PWSCC,원자력발전소
- AUTHORs : 황성식식
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Page : 79 - 84
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- 배관감육관리에 활용되는 CHECWORKS 프로그램의 열수력해석 방법론 검증에 관한 연구
- In general, pipelines at nuclear power plants are affected by various types of degradation mechanisms and may be ruptured after gradually thinning. FAC (Flow-Accelerated Corrosion) is typical aging mechanism affecting the secondary side piping system. In Korea nuclear power plants, CHECWORKS program have
been used for management of wall thinning damages. However, sometimes, CHECWORKS program shows wrong results at the stage of NFA (Network Flow Analysis) in case of complex pipelines. This paper describes the calculation results of pressure drop in a complex pipeline and single line by using the CHECWORKS
program and the analysis results are compared with those of engineering calculation results including errors between them. - KEYWORDs : Flow-Accelerated Corrosion(FAC), CHECWORKS, Network Flow Analysis(NFA), Wear Rate Analysis(WRA), Wall Thinning
- AUTHORs : 서 혁 기†· 황 경 모
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Page : 85 - 92
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- 가압형 경수로 압력용기 재료인 저합금강의 동적 붕산 부식 실증 연구
- This work is concerned with an evaluation of dynamic boric acid corrosion (BAC) of low alloy steel for
reactor pressure vessel of a pressurized water reactor (PWR). Mockup test method was newly established
to investigate dynamic BAC of the low alloy steel under various conditions simulating a primary water
leakage incident. The average corrosion rate was measured from the weight loss of the low alloy steel
specimen, and the maximum corrosion rate was obtained by the surface profilometry after the mockup
test. The corrosion rates increased with the rise of the leakage rate of the primary water containing boric
acid, and the presence of oxygen dissolved in the primary water also accelerated the corrosion. From the
specimen surface analysis, it was found that typical flow-accelerated corrosion and jet-impingement occurred
under two-phase fluid of water droplet and steam environment. The maximum corrosion rate was determined
as 5.97 mm/year at the leakage rate of 20 cc/min of the primary water with a saturated content of oxygen
within the range of experimental condition of this work. - KEYWORDs : boric acid corrosion, flow-accelerated corrosion, low alloy steel, mockup test, reactor pressure vessel, primary water leakage
- AUTHORs : 김 성 우†·김 홍 표·황 성 식
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Page : 93 - 101
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- EN-DCPD 방법을 이용한 Alloy 600 재료의 국부부식균열 연구
- The object of this work is to establish an electrochemical noise(EN) measurement technique combined with a direct current potential drop(DCPD) method for monitoring of localized corrosion cracking of nickel-based alloy, and to analyze its mechanism. The electrochemical current and potential noises were measured under various conditions of applied stress to a compact tension specimen in a simulated primary water chemistry of a pressurized water reactor. The amplitude and frequency of the EN signals were evaluated in both time and frequency domains based on a shot noise theory, and then quantitatively analyzed using statistical Weibull distribution function. From the spectral analysis, the effect of the current application in DCPD
was found to be effectively excluded from the EN signals generated from the localized corrosion cracking. With the aid of a microstructural analysis, the relationship between EN signals and the localized corrosion cracking mechanism was investigated by comparing the shape parameter of Weibull distribution of a mean
time-to-failure. - KEYWORDs : corrosion fatigue, direct current potential drop method, electrochemical noise measurement,Nickel-base alloy, primary water stress corrosion cracking, Weibull distribution function
- AUTHORs : 이 연 주·김 성 우·김 홍 표†·황 성 식
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Page : 102 - 112
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- 초고온가스로용 Alloy 617의 불순물 함유 헬륨/공기 중에서 고온부식 특성
- A very high-temperature gas reactor (VHTR) is one of the next generation nuclear reactors owing to its
safety, high energy efficiency, and proliferation-resistance. Heat is transferred from the primary helium loop
to the secondary helium loop through an intermediate heat exchanger (IHX). Under VHTR environment
Alloy 617 is being considered a candidate Ni-based superalloy for the IHX of a VHTR, owing to its good
creep resistance, phase stability and corrosion resistance at high temperature. In this study, high-temperature
corrosion tests were carried out at 850 - 950oC in air and impure helium environments. Alloy 617 specimens
showed a parabolic oxidation behavior for all temperatures and environments. The activation energy for
oxidation was 154 kJ/mol in helium environment, and 261 kJ/mol in an air environment. The scanning
electron microscope (SEM) and energy-dispersive x-ray spectroscopy (EDS) results revealed that there were
a Cr-rich surface oxide layer, Al-rich internal oxides and depletion of grain boundary carbide after corrosion
test. The thickness and depths of degraded layers also showed a parabolic relationship with the time. A
corrosion rate of 950oC in impure helium was higher than that in an air environment, caused by difference
in the outer oxide morphology. - KEYWORDs : VHTR, Alloy 617, helium, high-temperature corrosion, oxidation
- AUTHORs : 정 수 진†·이 경 근·김 동 진·김 대 종
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Page : 119 - 124
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- High-temperature Oxidation of Nano-multilayered AlTiSiN Thin Films deposited on WC-based carbides
- Nano-multilayered, crystalline AlTiSiN thin films were deposited on WC-TiC-Co substrates by the
cathodic arc plasma deposition. The deposited film consisted of wurtzite-type AlN, NaCl-type TiN,
and tetragonal Ti2N phases. Their oxidation characteristics were studied at 800 and 900°C for up to
20 h in air. The WC-TiC-Co oxidized fast with large weight gains. By contrast, the AlTiSiN film
displayed superior oxidation resistance, due mainly to formation of the α-Al2O3-rich surface oxide
layer, below which an (Al2O3, TiO2, SiO2)-intermixed scale existed. Their oxidation progressed primarily by the outward diffusion of nitrogen, combined with the inward transport of oxygen that gradually reacted with Al, Ti, and Si in the film. - KEYWORDs : AlTiSiN thin films, WC carbides, oxidation, Al2O3 oxide
- AUTHORs : Yeon Sang Hwang and Dong Bok Lee†
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Page : 125 - 131
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- 액적충돌침식으로 인한 배관감육 예측체계 구축에 관한 연구
- The most common pipe wall thinning degradation mechanisms that can occur in the steam and feedwater systems are FAC (Flow Acceleration Corrosion), cavitation, flashing, and LDIE (Liquid Droplet Impingement Erosion). Among those degradation mechanisms, FAC has been investigated by many laboratories and industries. Cavitation and flashing are also protected on the piping design phase. LDIE has mainly investigated in aviation industry and turbine blade manufactures. On the other hand, LDIE has been little studied in NPP (Nuclear Power Plant) industry. This paper presents the development of prediction system for pipe wall thinning caused by LDIE in terms of erosion rate based on air-water ratio and material. Experiment is conducted in 3 cases of air-water ratio 0.79, 1.00, and 1.72 using the three types of the materials of A106B, SS400, and A6061. The main control parameter is the air-water ratio which is defined as the volumetric ratio of water to air (0.79, 1.00, 1.72). The experiments were performed for 15 days, and the surface morphology
and hardness of the materials were examined for every 5 days. Since the spraying velocity (v) of liquid droplets and their contact area (Ac) on specimens are changed according to the air-water ratio, we analyzed the behavior of LDIE for the materials. Finally, the prediction equations(i.e. erosion rate) for LDIE of the materials were determined in the range of the air-water ratio from 0 to 2%. - KEYWORDs : liquid droplet impingement erosion, two phase nozzle, air-water ratio, erosion rate
- AUTHORs : 김경훈†·조연수·황경모
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Page : 132 - 141
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- 실험 계획법 및 열역학 계산법을 이용한 초고온가스로용 니켈계 초합금 설계 방법론
- This work is concerning a methodology of Ni-base superalloy development for a very high temperature gas-cooled reactor(VHTR) using design of experiments(DOE) and thermodynamic calculations. Total 32 sets of the Ni-base superalloys with various chemical compositions were formulated based on a fractional factorial design of DOE, and the thermodynamic stability of topologically close-packed(TCP) phases of those alloys was calculated by using the THERMO-CALC software. From the statistical evaluation of the effect of the chemical composition on the formation of TCP phase up to a temperature of 950 oC, which should be suppressed for prolonged service life when it used as the structural components of VHTR, 16 sets were selected for further calculation of the mechanical properties. Considering the yield and ultimate tensile strengths of the selected alloys estimated by using the JMATPRO software, the optimized chemical composition of the alloys for VHTR application, especially intermediate heat exchanger, was proposed for a succeeding experimental study.
- KEYWORDs : design of experiments, intermediate heat exchanger, Ni-base superalloy, thermodynamic calculation, very high temperature gas-cooled reactor
- AUTHORs : 김성우†·김동진
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Page : 142 - 148
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- 원전 배관의 반복 측정 데이터에 대한 신뢰도 분석 방법
- Safety is a major concern in Nuclear Power Plants (NPPs). Piping systems in NPPs are very complex and composed of many components such as tees, elbows, expanders and straight pipes. The high pressure and high temperature water flows inside piping components. As high speed water flows inside piping, the pipe wall thinning occurs in various reasons such as FAC (Flow Accelerated Corrosion), LDIE (Liquid Droplet Impingement Erosion) and Flashing. To inspect the wall thinning phenomenon and protect the piping from damages, piping components are checked by UT measurement in every overhaul. During every overhaul, approximately 200~300 components (40,000~60,000 UT data) are examined in NPPs. There are some methods from EPRI for evaluating wear rate of components. However, only few studies have been conducted to find out the raw data reliability for the wear rate evaluation. Securing the reliable raw data is the key factor for a reasonable evaluation. This paper suggests the reliability analysis method for the repeatedly
measured data for wear rate evaluation. - KEYWORDs : UT measurement, repeated measurement, wall thinning, error, reliability, wear rate
- AUTHORs : 윤훈†·황경모
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Page : 149 - 157
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- 밀폐 박스거더형 무도장 내후성강 교량의 부식취약부에 대한 방식대책 연구(I)
- In corrosion-sensitive areas of exsisting unpainted weathering steel bridges with closed box girder structures. there are some serious local corrosion problems because of rain water or dew water which can not be solved by exsisting maintenance methods. These problems must be controled technically because of bad. influence on the safety of bridge. This study is the first stage of developing the economic corrosion control manual for these local corrosion problems. Through the injection of tar sealant into the crevice of mock-up equipment, it was prooved that the corrosive sealant can be useful to corrosion control at crevice of corrosion sensitive area.
- KEYWORDs : unpainted weathering steel, splice connection part, corrosion, corrosion sensitive area, multiunction sealant
- AUTHORs : 송창영†·이의호·이제현·박현출·최재석·노영태
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