Effect of Neutron Flux on Magnetic Hysteresis in Neutron-Irradiated Pressure Vessel Steels

The effect of neutron flux on magnetic minor hysteresis loops has been investigated on nuclear reactor pressure vessel steels, which were irradiated to a fluence of 3.3 × 10¹⁹ n/cm². A minor-loop coefficient, which is an indicator of internal stress, exhibits a local maximum at a fluence of ~1 × 10¹⁹ n/cm², whose position shifts to a low-fluence regime with decreasing neutron flux. Introducing an effective fluence, used to correct the flux effect of irradiation hardening, the data obtained by different flux were found to almost fall on single curve for some alloys. This implies that the flux effect on magnetic property is dominated by efficiency of radiation-enhanced diffusion of solute atoms, such as Cu, as in the case of irradiation hardening.