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Virginia Power's Surry units successfully used a combination of pressure pulses and chemical solvent to clean steam generators more effectively
The Electric Power Research Institute Steam Generator Owner's Group (EPRI SGOG) has been researching secondary-side chemical cleaning in an effort to reduce maintenance and outage costs at nuclear power plants. It identified a group of chemicals that proved to be effective, but prolonged exposure to high concentrations of these chemicals could result in excessive corrosion of steam generator components. A new, unique approach to steam generator cleaning combines the advantages of EPRrs chemical cleaning formulation with the benefits of Westinghouse's patented pressure pulse cleaning (PPC) techniques. This combination decreases the corrosive effect of the process while it increases the cleaning efficiency
Westinghouse Nuclear Services Division developed the patented PPC as part of an intensified, integrated outage program designed to reduce maintenance and outage costs while increasing the overall availability of nuclear power plants. The process, called pressure pulse chemical cleaning (PP/CC), was used successfully at Virginia Power's Surry Units 1 and 2. The process removed more than 38,000 lbs of deposits from both sites, with lower chemical and waste processing costs and less structural corrosion. An extensive video inspection conducted before, during and after completion of the process confirmed the success of the operation.
Derating problems
Westinghouse first used the PP/CC process on the Surry Unit 2 steam generators (Westinghouse model 51F, 3 loop). After 14 years of operation, the plant could only operate at approximately 85 percent of rated power because water level fluctuations in steam generator C required power reduction. Thermal-hydraulic analysis attributed the water level oscillations to the accumulation of corrosion products in the quatrefoil support plates, resulting in an excessive pressure drop. Engineers confirmed this blockage of the uppersupport plate quatrefoil flow holes through a specially designed visual inspection technique (steam generator in-bundle visual inspection) developed by Westinghouse and R. Brooks Associates.
For the 14 years the Surry Unit 2 steam generators were in service, operators performed tubesheet cleaning on a regular basis. However, they made no attempt to remove the deposits located in the upper bundle region. Initially, operators used the traditional PPC technique, mechanical cleaning without chemicals, in steam generator C...