Non-destructive evaluation (NDE) methods to be applied
Non-destructive methods for materials characterisation are based on physical principles that are correlated to macroscopic physical properties and microscopic effects. The non-destructive characterisation will be performed by means of micromagnetic, electrical and ultrasonic methods in various stages of material degradation caused by neutron irradiation. Micromagnetic techniques are used for the non-destructive characterisation of material properties of ferromagnetic materials (e.g. RPV steels). Micromagnetic materials characterisation is based on the correlation between the magnetic properties of ferromagnetic materials and their mechanical-technological characteristics, which depend on the microstructure. Generally, micromagnetic measuring devices contain a magnetisation unit, a probe to capture the magnetic response of the material and a unit for measurement control and data processing (usually a PC). Depending on the design of the magnetisation unit as well on the measurement parameters, different material depths and areas can be investigated. The Micromagnetic Inductive Response & Barkhausen Emission (MIRBE) method is based on the magnetic induction changes over time and the analysis of the magnetic Barkhausen noise signal together with other electromagnetic quantities in different measurement modes. Two modes of measurement will be used: fixed excitation and scanning intensity mode. Of particular interest is the latter one, where the applied magnetic field intensity increases and signals are measured at each step of the increasing field, creating a signal versus applied intensity curve. Increasing magnetisation field intensity allows obtaining the magnetic signature of the material at various points of the hysteresis curve, from near-coercivity to saturation regions.