Neutron irradiation effects on magnetic minor hysteresis loops in nuclear reactor pressure vessel steels

Abstract

Magnetic minor hysteresis loops have been measured on A533B-type nuclear reactor pressure vessel steels with various combinations of Cu and Ni contents after neutron irradiation to a fluence up to 3.32 × 10¹⁹ n cm⁻². A strong compositional dependence of minor-loop properties, which are indicators of internal stress, was found. The properties of high-Cu and high-Ni steel show a large increase in the low fluence regime below 0.4 × 10¹⁹ n cm⁻², followed by a slow decrease, while those for low-Cu or low-Ni steel show a sudden decrease. The changes are roughly in linear proportion to the yield strength changes. The results were explained from the viewpoint of the formation and growth of Cu-rich precipitates and/or fine scale defects in the matrix and along pre-existing dislocations.

Keywords:

• magnetic hysteresis
• irradiation effects
• magnetic properties
• nanoscale precipitates
• neutron irradiation
• nuclear materials

Acknowledgements

This research project has been conducted under the research contract with the Japan Nuclear Safety Organization (JNES). We thank Mr. J. Smith, Dr. D. Gragg of UCSB for their assistance in magnetic measurements.