Critical components for light water reactors (LWRs) evolve over decades in service, losing ductility and toughness due to thermaland irradiation aging. Destructive techniques to monitor their health may not always be applicable in the field, thus non-destructiveevaluation (NDE) methods are sought which can quickly and precisely identify the state of major LWR components such as corebarrels or primary coolant pipes. Here we demonstrate the use of gigahertz, non-contact ultrasonics to monitor and evaluate thehealth of cast austenitic stainless steels (CASS), used in some of the largest components in LWR primary systems. We do so bylinking changes in their surface acoustic wave (SAW) characteristics using transient grating spectroscopy (TGS) to transmissionelectron microscopy (TEM) verified evidence of spinodal decomposition and G-phase precipitation. Thermal aging is shown toinduce SAW peak splitting, correlated strongly with aging time-at-temperature and Charpy impact energy, and therefore increasedhardness, decreased toughness, and lower ductility. This case motivates looking at gigahertz ultrasonics as NDE techniques toindirectly detect other LWR material degradation modes, such as reactor pressure vessel (RPV) embrittlement. This would allowfor the greater use of NDE techniques to enable confident monitoring of LWR structural material health to 80 years and beyond.
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