Journal of the Korean Society for Nondestructive Testing (비파괴검사학회지)

The Korean Society for Nondestructive Testing (한국비파괴검사학회)
권호 표지

Quantitative EC Signal Analysis on the Axial Notch Cracks of the SG Tubes

SG Tube 축방향 노치 균열의 정량적 EC 신호평가

  • Published : 2009.08.30
Download PDF
⟨ Previous Next ⟩

Abstract

Steam generator(SG) tube, as a barrier isolating primary to the secondary coolant system of nuclear power plants(NPP), must maintain the structural integrity far the public safety and its efficient power generation capacity. And SG tubes bearing defects must 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 EDM notch specimens are examined for the detectability and quantitative characterization of the axial ODSCC by +PT MRPC probe, containing pancake, +PT and shielded pancake coils apart in a single plane around the circumference. The results of this study are assumed to be applicable fur providing key information of engineering evaluation of SCC and improvement of confidence level of ECT on SG tubes.

원자력발전소의 1차측 및 2차측 냉각계의 장벽 역할을 하는 핵심 설비중 하나인 증기발생기(steam generator, SG) 전열관은 공공의 사회적 안전성과 효율적인 발전 용량을 유지하기 위해 구조적 건전성을 유지하여야 한다. 또한 결함을 함유하고 있는 전열관은 해당결함을 조기에 검출, 정량적으로 결함을 평가하여 필요한 경우에는 보수조치를 수행하여야 한다. 이러한 결함의 검출 및 정량화를 위해서 검사관련 고시 및 강화된 SG 관리프로그램(SGMP)에 근거하여 와전류탐상검사법(eddy current testing, ECT)을 적용, 검사를 수행하고 있다. SG 전열관에서 검출되고 있는 결함중 응력부식균열(stress corrosion cracking, SCC)은 미세한 경우 결함의 검출이 어려울 뿐 아니라 생성된 결함의 성장속도가 빠르기 때문에 SG 전열관의 건전성을 위협하는 주요결함 기구중 하나로 분류하고 있다. 본 논문에서는 다양한 결함 깊이 및 길이별로 방전가공(electric discharge machining, EDM)된 축방향 ODSCC에 대해 pancake, +point 및 shielded pancake 코일 등이 탑재된 3 coil형태의 +PT MRPC(motorized rotating pancake coils)를 적용하여 결함의 검출가능 여부 및 크기 측정을 위한 검사를 수행하였으며 본 실험결과를 통해 SG 전열관의 건전성 및 원전 운전의 안전성을 진단하는 공학적 평가 자료로써의 활용 가능성 뿐 아니라 와전류탐상검사의 신뢰도 향상을 도모하고자 하였다.

Keywords

References

  1. H. P. Kim et. al., 'A state of the art on primary side stress corrosion cracking in nuclear power plant,' KAERI/ AR-556/2000, pp. 31-35, (2000)
  2. Zetec, Probe Catalog, pp. 6-10, (2007)
  3. Hugo L. Libby, 'Introduction to electromagnetic nondestructive test methods,' John Wiley & Sons, Inc., pp. 24-26, (1979)
  4. Zetec, Product Info. & User Guide, (1995)
  5. K. M. Min, J. A. Park, S. H. Kwon and H. S. Han, 'RPC data analysis development of reproduced SG tube cracks,' Proceedings of KHNP Nuclear Technology Workshop, pp . 347-353, (2008)
  6. V. S. Cecco, G. Van Drunen and F. L. Sharp, 'Advanced manual for eddy current test method,' CAN/CGSB-48.14-M86, pp. 77-78, (1986)
  7. Y. M. Cheong, et. al., 'Development of non-destructive testing technology for the crack of SG tubes', KAERI/RR-1183/92, pp. 40-41, (1992)
  8. K. M. Min, J. A. Park and D. J. Go, 'EC signal characteristics of materials and spacing of loose parts contacted on the SG tube secondary side,' Proceedings of 2008 KPVP Annual Conference, pp. 381-382, (2008)
  9. C. V. Dodd, W. E. Deeds, J. W. Luqire and W. G. Spoeri, 'Analysis of eddy current problems with a time-sharing computer,' Materials Evaluation, pp. 165-168, (1969)
  10. C. V. Dodd, W. E. Deeds, J. W. Luqire and W. G. Spoeri, 'Some eddy current problems and their integral solutions,' ORNL-4384, (1969)
  11. W. A. Simpson, C. V. Dodd, J. W. Luqire and W. G. Spoeri, 'Computer programs for some eddy current problems,' ORNL-TM-3295, (1971)