Eddy Current Inspection of a 17-Year-Old Nuclear Steam Generator

Heavy water leaks from the Nuclear Power Demonstration steam generator led to a station shutdown for repairs early in 1979. Leak testing revealed several defective tubes. This prompted an extensive eddy current test program to establish the extent of damage to the generator. About 25 defective tubes were detected. All defects were located close to tube-sheets, in or near the ends of roll expanded areas in the tubes. Signal distortion from the tube expansion and by the ferromagnetic tubesheet made some defects difficult or impossible to detect with conventional eddy current probes (even in leaking tubes). This problem was solved by using a specially designed, spring-loaded, surface probe. Anomalous eddy current indications were encountered in areas away from defects. They were attributed to ferromagnetic inclusions and extensive copper deposits on tubes in the hot leg of the generator.