Development of a technology for continuous acoustic emission monitoring of in-service damageability of metal in safety-related NPP equipment

Safe operation of the NPP main equipment whose design life has expired requires the development of new approaches to integrity diagnosis and monitoring due to high level of metal ageing. These approaches should be based on nondestructive testing methods which make it possible to inspect equipment not only during the period of repair, but also in conditions of operation when dangerous defects are initiating and growing. One of highly efficient present-day techniques for nondestructive testing suitable for use in the process of operation is acoustic emission method. The paper presents the results of the activities to develop a multi-parameter system for acoustic emission monitoring of the nuclear plant equipment damageability in the process of the unit operation with specific features of the NPP control taken into account. The stages of the activities are described with all factors of impacts on the developed system assessed and taken into account, namely the need for keeping the system serviceable during long-term operation in high-temperature conditions, a complicated geometry of the monitored item, and an increased level of noise, as well as the acquisition and transmission of monitoring data via intranet systems for being processed and displayed online. A series of system tuning experiments conducted in laboratory conditions to refine and validate the selected monitoring techniques are described.