[논문]A REVIEW OF CANDU FEEDER WALL THINNING

Chung, Han-Sub

doi:10.5516/net.2010.42.5.568

A REVIEW OF CANDU FEEDER WALL THINNING 원문보기

Nuclear engineering and technology : an international journal of the Korean Nuclear Society, v.42 no.5, 2010년, pp.568 - 575

Chung, Han-Sub (Nuclear Power Generation Lab, Korea Electric Power Research Institute)

Abstract ▼ AI-Helper

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.

주제어

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가설 설정

1)The thinning rate is proportional to QV in each feeder.
3)There seems to be no systematic difference between the thinning rate of the first bend and the second bend. The amount of inspection data, however, may not be extensive enough to make a firm conclusion.
4)W-2 feeder suffers far slower thinning than W-1 feeder, despite the faster coolant flow rate. It is believed that the small amount of chromium content in the W-2 feeder, averaging 0.

제안 방법

The inspection was performed by manual ultrasonic test with point-to-point measurement. It was obvious that better inspection technology was needed in order to expand the inspection coverage into the extrados of the second bend, and then to the whole tight bend area and the downstream to the Gray loc weld. Currently, semi-automatic inspection tools are available, a 14 point bracelet for scanning thickness profile of whole tight bend location, and a Gray loc Area Inspection Tool for scanning thickness of area downstream to the weld.
The early stage inspections focused only on measurement of wall thickness in the extrados of the first bend. The inspection was performed by manual ultrasonic test with point-to-point measurement. It was obvious that better inspection technology was needed in order to expand the inspection coverage into the extrados of the second bend, and then to the whole tight bend area and the downstream to the Gray loc weld.

이론/모형

The solubility of magnetite can be calculated using the famous Sweeton & Baes equation, shown as equation (1) [7, 8].

성능/효과

2)The 2.5inch feeder shows faster thinning and shorter remaining life than that of the 2inch feeder, which can be understood by the thinning rate proportionate to QV.

참고문헌 (9)

Bindi Chexal et al., Flow-Accelerated Corrosion in Power Plants, TR-106611-R1, Electric Power Research Institute, 1998
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.
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
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
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
O. De Bouvier, Effect of Redox Conditions on Flow Accelerated Corrosion: Influence of Hydrazine and Oxygen, Technical Report 1001768, Electric Power Research Institute, 2002
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

상세보기
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

상세보기
R.L. Scheaffer and J.T. McClave, Probability and Statistics for Engineers, 3rd edition, PWS-KENT Publishing Company, Boston MA USA, 1990

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A REVIEW OF CANDU FEEDER WALL THINNING 원문보기

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A REVIEW OF CANDU FEEDER WALL THINNING 원문보기

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