Development and field validation of advanced array probes for steam generator inspection

Abstract

The aging of the steam generators at the nation`s nuclear power plants has led to the appearance of new forms of degradation in steam generator tubes and an increase in the frequency of forced outages due to major tube leak events. The eddy-current techniques currently being used for the inspection of steam generator tubing are no longer adequate to ensure that flaws will be detected before they lead to a shutdown of the plant. To meet the need for a fast and reliable method of inspection, ORNL has designed a 16-coil eddy-current array probe which combines an inspection speed similar to that of the bobbin coil with a sensitivity to cracks of any orientation similar to the rotating pancake coil. In addition, neural network and least square methods have been developed for the automatic analysis of the data acquired with the new probes. The probes and analysis software have been tested at two working steam generators where we have found an increase in the signal-to-noise ratio of a factor of five an increase in the inspection speed of a factor of 75 over the rotating pancake coil which maintaining similar detection and characterization capabilities.