Effects of long-term isothermal aging on microstructural and mechanical property evolution in ferritic-martensitic steels for sodium-cooled fast reactor applications

Abstract

In Generation IV sodium-cooled fast reactors, fuel cladding and core internals are expected to experience higher temperatures and higher burnup than in light water reactors. Knowledge of the long-term thermal and microstructural stability of materials used for such components is critical for safe and economical operation of these plants. Herein, candidate ferritic-martensitic cladding materials, G91 and G92, were isothermally aged between 360 °C and 700 °C for times of up to 50,000 hours. A combination of electron microscopy and mechanical testing was used to characterize thermodynamically and kinetically-induced evolution of both precipitate phases and the host matrix. Specifically, using high resolution, large-area scanning electron microscopy statistically relevant information was gathered on grain size, grain morphology, and grain boundary character. Such datasets fill the knowledge gap on exposure at extended temperature and time ranges of commercially available nuclear materials, and provide crucial information for lifetime prediction of components to be used in next-generation nuclear power applications.