Increasing Results Reliability for SG Tubes of NPPs with VVER based on Experimental Assessment of Human Factor

Problem of nuclear power plant (NPP) safe operation and risks reducing for nuclear power plants is one of the most actual ones. Taking into account the fact that NPP unit lifetimes are being extended beyond their design period, this problem becomes more and more important. One of the main and critical subsystems for NPP safe operation is steam generator (SG) consisting of (except other systems) about 11 thousands heat exchanging tubes, being the only boundary between primary and second circuits. During operation time the SG heat exchanging tubes are being affected with several degradation processes and mechanisms. This affects tubes integrity, NPP safety and economical effectiveness. Eddy current testing (ET) is the most effective, reliable and safe for personnel method of nondestructive testing (NDT). ET has the following advantages in comparison with other NDT methods that are also used at NPPs for detection of surface and subsurface flaws – visual, penetration and magnetic power: higher sensitivity in comparison with other surface methods; remotability and speed of ET performance that allow to reduce doses for personnel, performing NDT; and also possibility to detect not only surface flaws but also volume ones. Therefore ET is the most acceptable NDE method for SG tubing examination and ET results reliability enhancement is one of the most important problems.