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

Abstract

The planned life extension of nuclear reactors throughout the United States and abroad will cause reactor vessel and internals materials to be exposed to more neutron irradiation than was originally intended. A nondestructive evaluation (NDE) method to monitor radiation damage would enable safe and cost-effective continued operation of nuclear reactors. Nonlinear ultrasound is an NDE technique that is sensitive to microstructural changes in metallic materials, such as dislocations, precipitates, and their combinations, which are quantified by the measurable acoustic nonlinearity parameter. Recent research has shown the sensitivity of the acoustic nonlinearity parameter to increasing neutron fluence in representative Reactor Pressure Vessel (RPV) steels. The current work considers nonlinear ultrasonic experiments conducted on similar RPV steel samples that had a combination of irradiation, annealing, re-irradiation, and/or re-annealing to a total neutron fluence of 0.5–5 x 1019 n/cm2(E > 1 MeV) at an irradiation temperature of 290°C. The acoustic nonlinearity parameter generally increased with increasing neutron fluence, and consistently decreased from the irradiated to the annealed state over different levels of neutron fluence. This comprehensive set of results illustrates the dependence of the measured acoustic nonlinearity parameter on neutron fluence, material composition, irradiation temperature, and annealing.