• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.4 no.2
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• pp.29-33
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• 2008

As the measures of nuclear power plant utilities and manufacturers to reduce the defects of tube expansion region during manufacturing steam generators, many types of NDEs(Non-Destructive Examinations) are conducted to inspect the expansion region. The expansion region of tube is subject to degrade because of stress concentration induced by tube expansion, sludge pile and high temperature. So the inspections for tube expansion region have been reinforced. Liquid penetrant test, helium leak test, Bobbin profile test and hydraulic test are performed to confirm the integrity of tube expanded by hydraulic expansion method. Liquid penetrant test and helium leak test are used to inspect seal weld region on tubesheet end part. Bobbin Profile test is used to inspect fully the expanded region of steam generator tube. Hydraulic test finally verifies the integrity of seal weld region on tubesheet end part.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.5
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• pp.510-517
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• 2001

This paper describes an initial study for the application of eddy current pattern recognition approaches to more realistic flaw characterization in steam generator tubes. For this purpose, finite-element model-based theoretical eddy current testing (ECT) signals are simulated from 5 types of OD flaws with the variation in flaw size parameters and testing frequency. In addition, three kinds of software are developed for the convenience in the application of steps in pattern recognition approaches such as feature extraction feature selection and classification by probabilistic neural networks (PNNs). The cross point of the ECT signals simulated from flaws with non-symmetric cross-sections shows the deviation from the origin of the impedance plane. New features taking advantages of this phenomenon are added to complete the feature set with a total of 18 features. Then, classification with PNNs are performed based on this feature set. The PNN classifiers show high performance for the identification of symmetry in the cross-section of a flaw. However, they show very limited success in the interrogation of the sharpness of flaw tips.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.4
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• pp.330-337
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• 2010

In this paper, 3-dimensional electromagnetic numerical analysis is performed about the eddy current(EC) array probe characteristic which is the next generation probe for accurate diagnosis of steam generator(SG) in nuclear power plants(NPPs). ASME(American Society of Mechanical Engineers) Standard and X-probe combo calibration standard tube are selected for acquisition of eddy current testing(ECT) signals and this result of compared with the real test signals for reasonability of result. Based on the analysis result of calibration standard tube, ECT signals that are about the defects of pitting, stress corrosion cracking(SCC), multiple SCC and wear is obtained. Material of specimen was Inconel 600 which is usually used for SG tubes in NPPs. The operation frequency of 300 kHz were used. The signal characteristics could be observed according to the various defects. The results in this paper can be helpful when the ECT signals from EC array probe are evaluated and analyzed.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.2
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• pp.137-144
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• 2009

In this paper, the signal analysis of eddy current array probe was performed to analyze the electromagnetic characteristics with the variation of FBH(flat bottomed hole) defects size on steam generator tube in NPP(nuclear power plants) using the electromagnetic finite element method. To obtain the electromagnetic characteristic of probes, the governing equation was derived from Maxwell's equations, and the individual problem was analyzed by using the 3-dimensional finite element method. For the simulation FBH defects were used. The depth of FBH defects were 20%, 40%, 60%, 80% and 100% of steam generator(SG) tube thickness, and it was assumed that the defects were located on the tube outside. And the operation frequencies of 100 kHz, 300 kHz and 400 kHz were used. Material of specimen was Inconel 600 which is usually used for SG tubes in NPP. The signal difference could be observed according to the size variation of depth of FBH defects and operation frequencies. The results in this paper can be helpful when the ECT(eddy current testing) signals from EC array probe are evaluated and analyzed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.5 s.236
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• pp.754-761
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• 2005

The 40\% of wall thickness criterion which has been used as a plugging rule of steam generator tubes is applicable only to a single cracked tube. In the previous studies performed by authors, several global failure prediction models were introduced to estimate the failure loads of steam generator tubes containing two adjacent parallel axial through-wall cracks. These models were applied for thin plates with two parallel cracks and the COD base model was selected as the optimum one. The objective of this study is to verify the applicability of the proposed optimum global failure prediction model for real steam generator tubes with two parallel axial through-wall cracks. For the sake of this, a series of plastic collapse tests and finite element analyses have been carried out fur the steam generator tubes with two machined parallel axial through-wall cracks. Thereby, it was proven that the proposed optimum failure prediction model can be used as the best one to estimate the failure load quite well. Also, interaction effects between two adjacent cracks were assessed through additional finite element analyses to investigate the effect on the global failure behavior.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.5
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• pp.383-392
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• 2007

In this paper, we study the prediction of depth and width of a defect in steam generator tube in nuclear power plant using neural network. To this end, we first generate eddy current testing (ECT) signals for 4 defect patterns of SG tube: I-In type, I-Out type, V-In type, and V-Out type. In particular, we generate 400 ECT signals for various widths and depths for each defect type by the numerical analysis program based on finite element modeling. From those generated ECT signals, we extract new feature vectors for the prediction of defect size, which include the angle between the two points where the maximum impedance and half the maximum impedance are achieved. Using the extracted feature vector, multi-layer perceptron with one hidden layer is used to predict the size of defects. Through the computer simulation study, it is shown that the proposed method achieves decent prediction performance in terms of maximum error and mean absolute percentage error (MAPE).

• Nuclear Engineering and Technology
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• v.27 no.4
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• pp.483-490
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• 1995

The objective of the PKL III A 4.4 experiment is to examine that the plant could be controlled by manually operative actions "after Steam Generator Tube Rupture under Offsite Power Available without Safety Injection". In order to verify the limitation and ability of the system code NLOOP in the expeiment simulation, the behaviors of the PKL III facility obtained in the experiment are compared with the results of NLOOP code. NLOOP code, which is originally developed to simulate the transients of the Westinghouse type PWRs by KAERI/SIEMENS, modified properly to simulate the PKL III facility. Particular attention is given to the RCS mass How rate of the natural circulation in loops and the termination behavior of the natural circulation in the isolated loop. The comparisons between the experimental and calculational results show the simulation ability and problems of the code. the code.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.4 no.2
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• pp.34-39
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• 2008

Steam Generator(SG) tubes are classified as one of the key components in nuclear power plants, and they should be periodically examined by the intensified management program for the assurance and diagnosis of their structural integrity. In this study, we use the optimum analysis technique to draw the detection and categorization of bowing(BOW) signals; abnormal tube-to-tube proximity in the SG upper bundle free span area. The locations in which BOW signals are detected likely have latent degradation of ODSCC(Outer Diameter Stress Corrosion Cracking). For the sake of timely and correct detection of BOW signals and diagnosis of ODSCC, we carried out the experimental demonstrations using a reduced mock-up. And we validated the MRPC(Motorized Rotating Pancake Coil) analysis technique is better than the bobbin. Hence, it comes to conclusion that the optimum analysis technique can be a good alternative for the reliable SG tube examination.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.101-104
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• 1996

In nuclear power plants, workers are reluctant of works in steam generator because of the high radiation environment and limited working space. It is strongly recommended that the examination and maintenance works be done by an automatic system for the protection of the operator from the radiation exposure. In this paper, it is proposed a new approach to the development of the automatic vision system to examine and repair the steam generator tubes at remote distance. Digital signal processors are used in implementing real time recognition and examination of steam generator holes in the proposed vision system. Performance of proposed digital vision system is illustrated by experiment for similar steam generator model.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.11a
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• pp.103-109
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• 1996

고리 원자력 1호기 14주기(‘95년도) 운전기간 중 증기발생기 세관 열전달 용량 저하로 전출력 운전 기간동안 정격출력보다 15% 감발 운전한 경험이 있었는데, 이 기간중 냉각재내 방사성 부식생성물(CRUD) 농도가 약 80% 감소됨을 발견하였다. 이때 출력감소 비율보다 많은 CRUD 감소현상 규명을 위해 냉각재 수질관리인자와 EPRI 피복재 부식모델인 PFCC코드를 사용한 피 복재 산화물 두께변화 등을 비교한 결과, 운전중 용출되는 방사성 부식생성물은 핵연료 표면의 피복재 산화물에 흡착된 Co핵종이 피복재 산화물 이탈시 함께 거동하는 것으로 확인되었으며, 피복재 산화물 이탈은 산화막 두께 및 열유속에 주로 의존함이 밝혀졌다. 따라서 냉각재내에서 방사성 부식 생성물의 생성률 저감을 위해서는 정상운전시 핵연료 표면의 산화막 증가를 억제할 수 있는 수질 조건을 도출하고 그에따른 운전을 통해 원전 작업자의 방사선 피폭량 저감 및 방사성폐기물의 발생을 줄일 수 있을 것으로 여겨진다.