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EDDY CURRENT SIGNAL ANALYSIS FROM NON-HOMOGENEOUS SLUDGE PILE

Steam generator tubes are the pressure boundary between the primary side and secondary side, which makes them critical for nuclear safety and tube integrity should be maintained with periodic inspection. Among various inspection method, eddy current testing has been applied for steam generator tubes domestically. As the operating time of nuclear power plant increases, not only damage mechanisms such as wear and stress corrosion cracking but also flaw masking signals like sludge and indications from some other inclusion in it has been becoming a challenging issue recently. These indications from other inclusion in the sludge pile tend to misguide eddy current data analysts because they look similar to volumetric indications on top of tubesheet which need to be repaired, in spite that they are not real defects. It seems to need to characterize these flawmasking indications specifically with experiment and understand what the differences are from the real volumetric indications. In this paper, a mock-up has been set up with various materials which could be included in steam generator sludge pile to simulate field indications. Through this experiment, it can be noted that titanium inclusion in the sludge pile behaves similar to the volumetric indications due to its electromagnetic characteristics. It is recommended that a chemical component analysis of sludge pile should be performed if volumetric indications are found in the sludge pile on top of tubesheet area to decide whether they are realistic.