Vibrations of probe used for the defect detection of helical heating tubes in a fast breeder reactor: Part 3. The mechanism of the vibration and the countermeasures

Abstract

An eddy current testing (ECT) probe is used for the diagnosis of helical heating tubes installed in the Japanese fast breeder reactor “Monju”. Vibrations of the ECT probe occur and make the diagnosis difficult. In our previous study, several characteristics of the vibrations were elucidated through some experiments, and we took some empirical countermeasures against the vibrations. Further, we showed that the vibrations were caused by Coulomb friction through some numerical simulations. In this paper, firstly, the return process of the ECT probe out of the heating tube is considered since only the insertion process of the ECT probe was considered in our previous study. Following this, the efficacy of the proposed vibration countermeasures is evaluated by way of numerical simulation. The mechanism of the vibration and the countermeasures are discussed on the basis of the entire behavior of the probe, which was obtained by a numerical simulation. Lastly, an improvement in the countermeasure is proposed. The validity of the improvement is demonstrated through a numerical simulation both in the insertion and the return processes.