Detection of irradiation effects on reactor-vessel steels by magneto-acoustic emission. Technical report 1987-1988

The irradiation effects of reactor-vessel steels were studied by magneto-acoustic emission (MAE). MAE is a new method of nondestructive evaluation. It is generated primarily by domain wall motions during magnetization of ferromagnetic materials in the alternating magnetic field. Since MAE activity is sensitive to the microstructural changes, it is applied to determine the status of steel samples exposed to neutron irradiation. Two commercial steels, A302B plate and A533B weld, and two model alloys were irradiated at four different conditions; high and low flux, two fluence levels, and three temperatures. For each material/condition and unirradiated control samples, MAE intensity in rms voltage with increasing magnetic field was measured. Direct and envelope-detected MAE waveforms were also recorded. Measurements were also made for the samples unirradiated but aged at 288 C up to 278 hours in order to separate the effects of thermal aging from irradiation effects. Barkhausen effects were also investigated using a surface probe. The results presented here show that MAE waveform analysis can be a promising nondestructive evaluation technique for monitoring the microscopic changes in the steel components subjected to neutron irradiation.