Robert Bienentreu; Westinghouse Electric Germany; Germany
Le, Q.; Westinghouse Electric Company LLC; USA
Cullen, B.; Westinghouse Electric Company LLC; USA
Session: Nuclear Industry 2
Time: 13:30 - 13:50
The eddy current examination of steam generator tubing continues to challenge outage schedules, outage risk evaluation, radiation protection, personnel dose, and overall outage costs. Localized geometric changes on steam generator tubes (such as the transition from expanded tube in tubesheet to unexpanded freespan tube regions above tubesheet) can complicate the detection of degradation at these locations using the bobbin eddy current inspection probe. Traditionally supplemental probe examination (such as the +POINT probe or X-PROBE ) has been used for identification of steam generator tube mechanical wear at these locations. If the bobbin probe can be used for the detection of mechanical wear at the top-of-tubesheet expansion transition region, significant savings in all of the above areas can be realized. Note that the initiation of stress corrosion cracking mechanisms at this location is not considered relevant for replacement Alloy 690TT tubed Steam Generators.
Due to known limitations of the conventional bobbin probe techniques to detect foreign object induced tube wear at the top-of-tubesheet expansion transition region supplemental probe examinations have been performed as a compensatory measure at locations where foreign object wear is most likely to occur. The extent of these supplemental examinations varies according to the individual conditions within each plant but typically involve 10 to 15% of the total tube count in each steam generator channel head plenum (inlet and outlet). The area where these supplemental inspections are performed are concentrated along the outer peripheral region of tubes which are exposed to the incoming feedwater.
Limiting the extent of these supplemental inspections through qualification of the bobbin probe to detect foreign object induced wear degradation can improve outage scheduling, reduce outage risk, reduce personnel dose, reduce the potential for personnel injury, reduce contaminated waste disposal cost, and reduce overall outage cost. This paper will discuss the methodology behind foreign object wear detection using the bobbin eddy current coil and the results of successful field implementation.