Corrosion experience with the secondary side of steam generators in Japan
- Kansai Electric Power Co. Inc., Osaka (Japan)
- Mitsubishi Heavy Industries, Co., Kobe, Hyogo (Japan). Kobe Shipyard and Machinery Works
- Mitsubishi Heavy Industries, Co., Takasago, Hyogo (Japan). Takasago R and D Center
The authors have long years of experience with corrosion damage, on the secondary side of Steam Generator (SG) tubes. At first, this problem occurred as a result of wall thinning on the tubes owing to addition of sodium phosphate for water treatment in the secondary system in Pressurized Water Reactors (PWR). To prevent this problem, All Volatile Treatment (AVT) replaced sodium phosphate. In spite of this, Stress Corrosion Cracking (SCC) occurred at the crevices of the tube sheet owing to residual sodium phosphate, and Intergranular Attack (IGA) occurred at the Tube Support Plate (TSP) crevices even under an AVT environment. The possible cause of this problem seems to be a combination of an alkaline environment and an oxidizing condition. When the IGA was detected, it was difficult to find out the exact causative species from the operating data and examination of pulled tubes at that time. The only available working techniques for establishing the cause were evaluation of long-term water chemistry records and analysis of the oxide film on the IGA fracture surfaces. Once IGA occurs, improvements in water chemistry cannot be guaranteed to affect the inside of crevices, and thus the preventive measures may fail to provide the intended effect. IGA occurred in a greater magnitude, so that some SGs had to be replaced. Additionally, the authors also experienced pitting and circumferential SCC on the secondary side of SG tubes, though the number of cracked tubes was limited.
- OSTI ID:
- 409733
- Report Number(s):
- CONF-9510292--; ISBN 1-57570-008-4
- Country of Publication:
- United States
- Language:
- English
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