Vibroacoustic methods for corrosion-state monitoring in nuclear power plant secondary piping structures
Stilson, Thomas Allen
Pipe wall corrosion in nuclear power plants has been identified as a critical cause of plant degradation. The application of risk-informed in-service inspection techniques has significantly improved the relative core damage frequency and the average capacity factor of the industry fleet, but the majority of inspection practices remain manual and point-wise in nature. Because nuclear power plant outages can cost as much as $2 million per day, time spent on inspection is expensive. Health-monitoring techniques using vibroacoustic sensor networks were investigated with the goal of developing an automatable and scalable degradation-state monitoring solution to reduce the amount of time spent during outages. Transmissibility function estimation between degrees of freedom was shown to have potential to detect mass change in pipe elbow fittings, and a damage index was developed to quantify the degree of damage based on this estimation. This index was shown to trend robustly between pipe elbows and remain stable over an 8-day operating period. Temperature, pressure, and gasket material were characterized for their impact on the damage index. Recently developed smart film technology was also evaluated for its ability to modulate the film’s complex shear modulus in correspondence to the level of chelation, or iron ion absorption, experienced by the film. In preliminary experimental characterization, this film was shown to have potential to indicate early-stage onset of corrosion with frequency response function estimation. Improving sensitivity to modulating film properties was identified as a major next step for development of the smart film approach to corrosion-onset detection.