Vibrations of probe used for the defect detection of helical heating tubes in a fast breeder reactor. Part 1. Experimental results by using mock-up

This paper deals with the vibration and the sensor signal noise of the eddy current testing (ECT) probe used for a defect detection of helical heating tubes in the fast breeder reactor "Monju", developed in Japan. ECT probes are used for the detection of defects in a heating tube. The heating tube is composed of a helical tube and a straight tube because of their advantages of thermal efficiency and saving space. No vibrations of the ECT probe have been generated in usual straight heating tubes. However, vibrations of the ECT probe in the helical tube cause some noise and decrease the sensitivity of the ECT probe. The experiment was performed using a mock-up, and the noise characteristics of an ECT sensor mounted in an ECT probe were examined. The experimental results showed that the sensor signal noise during the insertion process of the ECT probe was higher than that of the return process, and vibrations of the insertion process had a certain emerging frequency. Attaching the long and flexible guide probe to the top of the ECT probe was an effective countermeasure against sensor signal noise.