Performance Improvement of High Temperature Electro-Magnetic Acoustic Transducer for In-service Inspection of Reactor Vessel in Sodium-cooled Fast Reactor

The performance of a previously developed high-temperature electro-magnetic acoustic transducer was improved to enhance its applicability to in-service inspection of a reactor vessel in a sodium-cooled fast reactor, which should be conducted in harsh conditions such as those of high temperature over 200°C, narrow access region, and prohibition of liquid couplant. The Halbach-type magnet array, which can offer a magnetic flux density higher than that from the PPM-type magnet array, was adopted, and the optimal size ratio of magnets that can provide a magnetic flux density higher than 1.4 times the one from the previous PPM-type array was selected through magnetic-field analyses. An improved electro-magnetic acoustic transducer was fabricated based on the optimal size ratio of magnets, and then, it was confirmed that an inner surface defect whose depth was 5% with respect to the thickness of the reactor vessel could be well detected by the improved electro-magnetic acoustic transducer at an increased lift-off, 33% higher than the one from the previous model, through performance demonstration tests