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A REVIEW OF CANDU FEEDER WALL THINNING

  • Chung, Han-Sub (Nuclear Power Generation Lab, Korea Electric Power Research Institute)
  • 투고 : 2010.04.01
  • 심사 : 2010.07.24
  • 발행 : 2010.10.31

초록

Flow Accelerated Corrosion is an active degradation mechanism of CANDU feeder. The tight bend downstream to Gray loc weld connection, close to reactor face, suffers significant wall thinning by FAC. Extensive in-service inspection of feeder wall thinning is very difficult because of the intense radiation field, complex geometry, and space restrictions. Development of a knowledge-based inspection program is important in order to guarantee that adequate wall thickness is maintained throughout the whole life of feeder. Research results and plant experiences are reviewed, and the plant inspection databases from Wolsong Units One to Four are analyzed in order to support developing such a knowledge-based inspection program. The initial thickness before wall thinning is highly non-uniform because of bending during manufacturing stage, and the thinning rate is non-uniform because of the mass transfer coefficient distributed non-uniformly depending on local hydraulics. It is obvious that the knowledge-based feeder inspection program should focus on both fastest thinning locations and thinnest locations. The feeder wall thinning rate is found to be correlated proportionately with QV of each channel. A statistical model is proposed to assess the remaining life of each feeder using the QV correlation and the measured thicknesses. W-1 feeder suffered significant thinning so that the shortest remaining life barely exceeded one year at the end of operation before replacement. W-2 feeder showed far slower thinning than W-1 feeder despite the faster coolant flow. It is believed that slower thinning in W-2 is because of higher chromium content in the carbon steel feeder material. The average Cr content of W-2 feeder is 0.051%, while that value is 0.02% for W-1 feeder. It is to be noted that FAC is reduced substantially even though the Cr content of W-2 feeder is still very low.

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참고문헌

  1. Bindi Chexal et al., Flow-Accelerated Corrosion in Power Plants, TR-106611-R1, Electric Power Research Institute, 1998
  2. Slade J P and Gendron T S, FAC and cracking of carbon steel piping in primary water-operating experience at the Point Lepreau Generating station, Proc. of the 12th International conf. on Environmental Degradation of materials in nuclear power systems-water reactors, Salt Lake City Utah USA, August 14-18, 2005, Ed. T R King, P J King and L Nelson, TMS 2005 p773-784.
  3. K.A. Burrill and E.L. Cheluget, Corrosion of CANDU Outlet Feeder Pipes, Proc. of the JAIF International Conference on Water Chemistry in Nuclear Power Plants, Kahiwaszaki, Japan, 1998, p699
  4. D.H. Lister et. al., The Accelerated Corrosion of CANDU Primary Piping, Proceedings of the JAIF International Conference on Water Chemistry in Nuclear Power Plants, Kahiwaszaki, Japan, 1998, p.442
  5. Z.H. Walker, Managing Flow Accelerated Corrosion in Carbon Steel Piping in Nuclear Plants, Proc. of ASME PVP: Pressure Vessels and Piping Conference, San Diego, USA, 2004
  6. O. De Bouvier, Effect of Redox Conditions on Flow Accelerated Corrosion: Influence of Hydrazine and Oxygen, Technical Report 1001768, Electric Power Research Institute, 2002
  7. F.H. Sweeton and C.F. Baes, J., The Solubility of Magnetite and Hydrolysis of Ferrous Ion in Aqueous Solutions at Elevated Temperatures, Chemical Thermodynamics 2, 479, 1970 https://doi.org/10.1016/0021-9614(70)90098-4
  8. S.E. Ziemniak, M.E. Jones, and K.E.S. Combs, Magnetite Solubility and Phase Stability in Alkaline Media at Elevated Temperatures, J. Solution Chemistry, Vol.24, No. 9, 837, 1995 https://doi.org/10.1007/BF00973442
  9. R.L. Scheaffer and J.T. McClave, Probability and Statistics for Engineers, 3rd edition, PWS-KENT Publishing Company, Boston MA USA, 1990