Investigations of multi-frequency algorithms for detection of defects in FBR magnetic steam generators tubes covered with sodium

In the present paper it is presented the performance of multi-frequency eddy currents algorithms to cope with the eddy current signal from both sodium structures located on the outer surface of magnetic steam generator tubes surface as well as support plates of steam generator tubes. The algorithm improves the signal to noise ratio of defects detection even when these are located under steam generator support plates. Experimental measurements of defects signals using eddy currents, when there is or there is no sodium on the outer tube surface, are used to validate reliable computer simulation models in order to investigate and optimize the multi-frequency algorithms. The parameters of the most reliable multi-frequency algorithm, based on two or three excitation frequencies and using both simulated and experimental remote field eddy current signals, are found out for both cases when sodium adhere or not to the SG tube surface and a defect is placed or not under sodium bands or SG supports plates. (author)