초공간을 고려한 SA508강의 성능저하에 관한 시계열 신호의 카오스성 평가

권주경 忠南大學校 大學院 2002 국내석사

蒸氣發生器 傳熱管 曲管部의 渦電流檢査 複合信號 分析에 관한 硏究

김창수 忠南大學校 大學院 2009 국내박사

본 연구에서는 증기발생기 전열관 곡관부에 생성되는 기하학적 형상변화의 한 형태인 덴트(dent)와 응력부식균열 신호가 혼합되어 나타나는 복합신호에 대한 와전류신호의 특성을 분석하였다. 이를 위하여 덴트에 축방향 및 원주방향 노치를 가공한 시편의 와전류신호를 취득하여 신호 특성을 검토하였다. 본 연구를 통하여 얻은 결과를 요약하면 다음과 같다. 1. 증기발생기 전열관의 곡관부에서 덴트와 결함신호가 혼합된 복합신호는 전열관 굽힘공정에서 압축응력이 발생하는 곡관부의 곡률반경이 제일 작은 안쪽에서 생성된 것으로 확인되었다. 2. 증기발생기 전열관 곡관부에 생성된 복합신호는 굽힘공정으로 압축응력이 발생한 위치에서 덴트 신호가 먼저 생성되고, 이후에 응력집중으로 인하여 응력부식균열이 발생하였으며, 발생한 균열결함은 2차측 원주방향 응력부식균열인 것으로 판단된다. 3. 원주방향 노치와 덴트가 혼합된 복합신호에 대한 와전류신호 분석결과 40% 깊이 이상의 원주방향 노치신호는 덴트 신호와 구별이 가능하였고, 20% 깊이 이하의 원주방향 노치신호는 덴트 신호와 구분이 불가능하며 덴트 신호와 유사한 형태로 나타나고 있다. 4. 덴트와 원주방향 노치가 혼합된 복합신호에서 수직성분과 수평성분 간의 위상각은 원주방향 외경노치가 원주방향 내경노치 보다 상대적으로 크게 나타났다. 5. 축방향 노치와 덴트가 가공된 복합신호에서는 와전류신호의 형상이 왜곡되지 않으며, 단지 위상각이 작게 나타났다. 그리고 덴트와 축방향 외경노치가 혼합된 복합신호의 위상각은 내경 신호의 위상으로 바뀌는 것을 확인하였다. 6. 덴트와 원주방향 노치가 혼합된 복합신호에서 수직성분과 수평 성분간의 위상각 차이를 분석한 결과 내경노치의 위상은 M자 형태로 나타나며, 외경노치에서는 벨 형태로 나타난다. 그리고 수직성분과 수평성분 간의 위상각은 노치 깊이에 비례하여 증가하는 것으로 확인되었다. 7. 노치와 덴트가 혼합된 복합신호에서 수직성분의 진폭은 원주방향 외경 노치의 경우에는 노치 깊이에 반비례하지만, 나머지 경우에는 노치 깊이에 비례하여 증가하는 것으로 확인되었다. Steam generator tubes are critical boundary of the primary and secondary side in nuclear power plants. Eddy current testing is commonly used as the method of non-destructive testing for the safety and integrity of steam generator tubes in the nuclear power plants. Various damage mechanisms in the steam generator tubes occur. Changes in the geometric shape act as a stress concentration factor likel y to cause a defect during the steam generator operation. The mixedsignals with the geometric shape are distorted and attributes that are difficult to detect signals. An example is bending stress due to compression process at a U-bend occurring in the intrados region which has a small radius of curvature. The resulting change in the geometric shape may lead to a dent like occurrences. The dent can cause stress concentration and generates stress corrosion cracks. In this study, the steam generator tubes of nuclear power plant were selected to study for analysis of mixed-signal containing dent and stress corrosion cracks. Through this study, the following is a summary of the results. 1. The mixed signals at U-bend by compression process are analysed at the intrados region for the smallest radius of curvature. 2. The dent is first generated at U-bend in the steam generator due to bending stress and stress concentration on dent generates stress corrosion cracks. The stress corrosion cracks at U-bend are believed to be O.D circumferential cracks. 3. In the mixed signal compounded dent and circumferential notch, 40% depth or more of notches can be separated from the dent signal but less than 20% depth of notches are difficult to differentiate between dent and notch signal. 4. The eddy current signals compounded dent and axial notch aren't distorted but the eddy current signals compounded dent and circumferential notch are distorted in the form of bending in the middle. 5. In the eddy current signals compounded dent and circumferential notch, phase difference between vertical and horizontal elements for O.D notches is greater than for I.D notches.

고온 설비용 스테인리스강의 열기계적 피로 수명 예측에 관한 연구

최원두 忠南大學校 大學院 2009 국내박사

原子爐헤드 貫通管의 遠隔自動 表面檢査裝置 開發에 관한 硏究

김왕배 忠南大學校 大學院 2010 국내박사

경수로형 원자력발전소 원자로 상부헤드에는 제어봉구동장치 및 계측장치를 위한 관통관과 비 응축성 기체를 제거하기 위한 배기관이 설치되어 있다. 이 관통관 재질은 원자로 냉각재와 원자로 운전환경의 영향을 받아 응력부식균열 발생에 민감한 것으로 알려져 있다. 우리나라는 미국 원자력규제위원회 Order EA-03-009 및 발전사업자의 원자로헤드 관통관 검사계획에 따라 관통관과 주변 용접부의 건전성을 확인하고 있으며, 검사범위는 관통관 용접부 상하부 2“로 규정하고 있다. 그러나 한국 표준형 원자로헤드에 설치되어 있는 83개의 관통관 중 일부 관통관의 경우 기하학적 형상 및 깔데기 설치를 위한 나사산등의 영향으로 용접부 하부 2” 체적검사 요건을 충족시키지 못하고 있어, 액체침투탐상검사를 대체검사로 적용하고 있다. 그러나 검사 대상이 되는 원자로헤드 관통관의 경우 높은 선량의 방사선이 발생하는 위험지역인 동시에 설치 위치가 고소지역으로 수동 액체침투탐상검사를 하기에는 매우 열악한 환경을 가지고 있어 검사 결과의 신뢰도 저하 및 검사자의 방사선 피폭량 증가 등의 어려움이 있다. 본 연구에서는 이러한 열악한 환경 하에서 신뢰도 높은 검사를 통하여 원자로헤드관통관의 건전성을 명확히 확인함은 물론 검사자를 방사선 피폭으로부터 최대한 보호하고자 표면검사를 원격 자동으로 할 수 있는 검사장치 개발 하였다.

원전 배관의 정량적 非破壞診斷을 위한 超音波 검사 시스템 및 信號處理기술 개발

문균영 忠南大學校 大學院 2009 국내박사

蒸氣發生器 傳熱管 外面 슬러지 및 異物質 混入에 따른 渦電流 信號의 特性

신기석 忠南大學校 大學院 2010 국내박사

The accumulation of the sludge on the secondary side of the SG tube in NPP can result in developing SCC and even cause detrimental events such as tube rupture. As a proactive measures for the timely detection of those defects, SG tubes have been periodically diagnosed by employing ECT. While the signals influenced by the abnormal status of the sludge pile and non-ferromagnetic foreign materials with or without the sludge can lead miscall and confuse in determining whether they are defects or not. The objective of this study is to provide corrective methodology by characterization of the reproduced EC signals representing numerous non-ferromagnetic foreign materials in-flowed to the sludge pile and a void bearing sludge pile. Accordingly the derived methodology is assumed to be promptly applicable to the EC data analysis for the SG tubes. The main results obtained from this study are as follows 1) According to the review of the EC signals representing sludge pile mainly composed of iron oxide, those signals are assumed to be obviously separated from the normal or degraded condition of the SG tubes. Iron oxide bearing sludge pile, which is accumulated locally in the restricted area, i. e. TTS, tube support structure and abnormally neighboring tube-to-tube area, can create atmosphere to accelerate numerous degraded conditions of the SG tube, including SCC. 2) Comparing the phase angle of EC signals developed due to the influence of the foreign materials attached on the Alloy 600 and 690 tubes, the variation phase angle band of Alloy 600 is wider than that of Alloy 690. And the phase angle of foreign materials on those alloys showed their identical difference. However it has been found that the phase angle of the EC signals of sludge on Alloy 600 is similar to that of the EC signals of the CS on Alloy 690. In the process of EC data analysis especially on the foreign materials, these signal properties are to be noted. While the amplitude of the EC signals varies and is proportional to the electrical conductivity of the foreign materials on those alloys, the difference of the EC amplitude affected by foreign materials on which of the Alloy 600 and 690 shows little difference. 3) It is assumed that the abnormal VOL-like EC signals affected by the sludge pile does not result from the variation of the homogeneous state of sludge pile, but from the effects of the coexistence of in-flowed non-ferromagnetic materials and the sludge pile. The VOL-like EC signals are successfully reproduced by introducing NHM mock-up standard and it is found that the EC phase angle is changed with respect to the dimension of the materials. 4) By virtue of the experiments and data analysis of the abnormal EC signals generated by both the sludge pile which may develop SCC on the SG tubes and coexistence non-ferromagnetic materials and sludge pile, it has been confirmed that the methodology to discriminate VOL and VOL-like abnormal EC signal is assumed to be promptly applicable and dedicate to enhance the confidence level of the ECT for the SG tubes.

誘導超音波技術을 利用한 細管의 缺陷測定에 관한 硏究

주경문 忠南大學校 産業大學院 2010 국내석사

As a part of the measuring system, like a nervous system in human body, a mass of small tubes are installed in Nuclear Power Plants, an involved tubing system. Each of the tube is mostly less 1 inch in diameter, and extends over about 40m in total length. A visual inspection method has been mainly taken for the testing of integrity on the tubing system. However, it is a time-consuming method demanding lots of inspectors as well as extremely weak on radiation protection. Therefore, in an effort to find an alternative method, this study was undertaken aiming to test if guided wave technology is available in examining DN tubing of 3/8inch in Diameter installed in PHWRs. The guided wave method has never been used for the examination of 3/8inch tubing yet all over the world. In this study, DN tubing mockups with circumferential and axial direction cracks made by electrical discharge Machining(EDM) have been examined. During the study, the optimum frequency was set with analysis of S/N rate as per the variation of test frequency, and the signal sensitivity to the defect size and orientation was also interpreted in each frequency. Major findings of this study are summarized as follows 1. From the experimental results related to the S/N rate in 3/8inch tubing, the optimum frequency is observed at 100kHz. 2. The optimum frequency for axial flaws is observed at 100kHz. 3. Except for the 20% circumferential flaw, the optimum frequency for circumferential flaws is observed at 100kHz. 4. It was possible to approximately make a quantitative analysis for the detection of the defect and defect size at 100kHz.

重水爐型 原電의 原子爐 肉眼檢査 裝備 開發에 대한 硏究

이상훈 忠南大學校 大學院 2010 국내석사

Pressure tubes and Calandria tubes of Wolsong nuclear power plant unit 1 have been being replaced since they reach the design life of 30 year. During the replacement period, inspection equipment can access inside the calandria tubes through the removed calandria tubes. In order to inspect the inside of calandria tubes, anti-radioactive camera, hardness measurement instrument and 3-D scanner are required. The inspection of the calandria tube includes the measurement of the neutron irradiated brittleness, deformation and deflection of calandria and internals. In this study, an instrument for the measurement was developed. The development of the instrument and inspection for the pressure tubes had been depended on the foreign techniques. However, the instrument was developed and was successfully applied to the CANDU reactor through this study. The technique developed in this study can be applied to other non-destructive inspection area.

디지털 방사선을 이용한 강용접부 비파괴검사 기술 개발

박상기 忠南大學校 大學院 2010 국내박사

This study was projected to develop a CR(computed radiography) based NDE technology focusing on improving resolution and efficiency of radiography test to boiler tubing. In an effort to improve the image quality, all the factors that influence on radiography image quality were fully optimized, and digital radiography image enhancement algorithm and a new cassette applicable to boiler tubing inspection have been developed; as a result, the dramatically increased radiography resolution has been accomplished. The final results achieved from this study are as follows: 1. In this study, since Ir-192, which has been mainly used as a radiography source in industrial NDT, was known not to be proper energy to the boiler tube inspection, Se-75 was selected as a new radiation source for the use of digital radiography test to the boiler tube through energy adaptability tests, and theoretical and experimental results, 2. The conditions and parameters established in the medical CR imaging techniques were fully optimized for the industrial radiography test, mainly aiming to be used in boiler tube inspection. It was newly found in this study that 30% of the exposure time in CR imaging is enough compared to that of conventional film and the ASTM IP-2 and IP-3 are adaptable as an image plate, and 1.0mm and 2.0mm size of source should be used, that is smaller than 3.0mm of source used for film inspection. 3. A cassette applicable to the use of boiler tube inspection was newly built to minimize the radiation scattering. The cassette made SNR be enhanced up to 67% by using 0.5mm pb sheet that is thicker than 0.1mm pb sheet used in medical system. It was also verified that the thickness of PB sheet was not essential factor to consider in cassette inlet structure because there is little relation between the existence of PB sheet and SNR. 4. Due to the digital format, the image processing and enhancement can be applied on CR images of the boiler tubes. A noise filter was used to remove noise from the digital image. In addition, to restore the geometrical image distortion that is occurred during image acquisition, new method to devide domain inherent in CR image was built through the reasoning of the related factors from the nonlinear modeling which was performed to the incident radiation and transmitted radiation under the frame analysis for the incident radiation In the final CR imaging test by using where the all achievement of this study as described above applied to, it was verified that the resolution of CR image was distinctly increased as the line of image quality indicator was effectively detectable up to 0.16 mm in diameter, compared to 0.32 mm line which is detectable in film radiography. such an increased image resolution enables to improve detectability of the micro defects in the weld of boiler tube. As a result, it made a detection to the defects possible up to 0.5mm depth precision in CR images, which far exceeds the limit of maximum detectable dept of 2.0mm in existing film radiography. It also far reduces the time required for imaging to analysis within about 15 minutes with the advanced computed radiography test, which was established in this study, compared to about 52 minutes taken in conventional film radiography test. Consequently, it made a great contribution to the time efficiency of NDT. In conclusion, the significant results achieved in this study must cause to extend the use of CR imaging technology from medical field to industrial NDT, especially to the effective inspection of the boiler tube encouraging the wider use of CR in plant industries.

蒸氣發生器 傳熱管 外面 軸方向 균열의 定量的 平價에 관한 硏究

김인철 忠南大學校 大學院 2010 국내박사

Steam Generator (SG) tube, as a barrier isolating primary to the secondary coolant system of Nuclear Power Plants (NPP), shell maintain the structural integrity for the public safety and its efficient power generation capacity. And SG tubes bearing defects shell be timely detected and taken repair measures if needed. For the accomplishment of these objectives, SG tubes have been periodically examined by Eddy Current Testing(ECT) on the basis of administrative notices and intensified SG Management Program (SGMP). Stress Corrosion Cracking(SCC) on the SG tubes is not easily detected and even missed since it has lower signal amplitude and other disturbing factors against its detection. However once SCC is developed, that can cause detrimental affects to the SG tubes due to its rapid propagation rate. Accordingly SCC is categorized as prime damage mechanism challenging the soundness of the SG tubes. In this study, reproduced Electrical Discharge Machining(EDM) notch specimens are examined for the detectability and quantitative characterization of the axial Out Diameter SCC(ODSCC) by +Point MRPC probe, containing pancake, +Point and shielded pancake coils apart in a single plane around the circumference. Through this study, the following is a summary of the results. 1. The defect depth 25% where the defect length is below 4mm ODSCC can not detect both +Point and Pancake coil. Meanwhile the defect of above depth 25% 6mm can detect and sizing. Also, Expansion specimen was more difficult than Non-expansion specimen caused by geometry noise signal. 2. The defect depth 50% or more detect possible from +Point coil and Pancake coil irrespective crack length. +Point coil is good detection ability but is evaluated short at the long length or deep crack. 3. The start point Look-ahead and Look-behind can calculate and confirmed a past theory. 4. The results of profile signal amplitude appear three type. This research presented each type of measurement method about axial crack length. 5. The form which has a minimum amplitude value in the middle of ECT signal pulse profiles measures the length between the right highest point and left highest point. 6. The form which has a maximum amplitude value in the middle of ECT signal pulse profiles measures the length including between rise and drop transition point. (this study names landing and take off point) 7. The form which has a saturated amplitude value of ECT signal pulse profiles measures a saturation point in the both sides. 8. The results of this study are assumed to be applicable for providing key information of engineering evaluation of SCC and improvement of confidence level of ECT on SG tubes.