Using nonlinear ultrasound to measure microstructural changes due to radiation damage in steel

Abstract

This work demonstrates how nonlinear ultrasound (NLU) can be used to monitor radiation damage in nuclear reactor pressure vessel (RPV) steels. Radiation damage is a crucial concern in the nuclear industry since many nuclear plants throughout the United States are entering a period of life extension, meaning the RPV will be exposed to higher levels of neutron radiation than it was originally designed to withstand. Currently, there is no nondestructive evaluation (NDE) method to unambiguously characterize radiation damage in RPV steels, the development of which would enable the assessment of the integrity of the vessel, allowing operators to determine if they can continue to safely operate. NLU is an NDE technique that is sensitive to microstructural features in metallic materials. The physical effect monitored by NLU is the generation of higher harmonic frequencies in an initially monochromatic ultrasonic wave, arising from the interaction of the ultrasonic wave with microstructural features. Recent research has demonstrated that NLU is sensitive to the same microstructural changes that are produced in radiation damage, such as precipitate formation and changes in dislocation density. Current experimental and modeling results are presented that relate the nonlinear ultrasonic parameter to the amount of radiation damage in RPV steel materials.