MONITORING NEUTRON EMBRITTLEMENT IN NUCLEAR PRESSURE-VESSEL STEELS USING MICROMAGNETIC BARKHAUSEN EMISSIONS

In nuclear power plants, neutron embrittlement of pressure vessel stee ls has been one of the main concerns. The use of micromagnetic Barkhau sen emissions is a promising method to monitor the variations in micro structural and subsurface stress states due to their influence on thes e emissions. Measurements of these emissions can reveal neutron irradi ation degradation in nuclear power plant components. Samples which wer e irradiated at different neutron fluences and annealed at different t emperatures were obtained from three reactor surveillance programs. Th e results of different neutron fluences and annealing procedures showe d noticeable fractional changes in the magnetic Barkhausen effect sign al parameter, DELTAMBE/MBE, and in the mechanical properties of these specimens. For example, increased intensity of neutron fluence decreas ed the DELTAMBE/MBE as well as impact energy and upper-shelf energy, b ut increased Rockwell hardness and yield strength. Typical changes in this parameter were in the range from -20% to -45% for fluences of up to 25 x 10(18) n cm-2.