TABLE OF CONTENTS Full Text

Abstract Introduction Eddy current array probes Qualification using tubes removed from operating steam generators Validation using laboratory prepared samples Validation based on signal-to--noise comparisons Summary/conclusions References

ABSTRACT

A CANDU nuclear reactor was shut down for over one year because steam generator (SG) tubes had failed with outer diameter stress corrosion cracking (ODSCC) in the U-bend section. Novel, single-pass eddy current transmit-receive probes, denoted as C3, were successful in detecting all significant cracks so that the cracked tubes could be plugged and the unit restarted. Significant numbers of tubes with SCC were removed from a steam generator in order to validate the results of the new probe. Results from metallurgical examinations were used to obtain probability-ofdetection (POD) and sizing accuracy plots to quantify the performance of this new inspection technique.

Though effective, the above approach of relying on tubes removed from a reactor is expensive in terms of both economic and radiation exposure costs. This led to a search of more affordable methods to validate inspection techniques and procedures. Methods are presented for calculating POD curves based on signal-to-noise studies using field data. Results of eddy current scans of tubes with laboratory-induced ODSCC are presented with associated POD curves. These studies appear promising in predicting realistic POD curves for new inspection technologies. They are being used to qualify an improved eddy current array probe in preparation for field use.