Defect Evolution and Mechanical Degradation of Alloy 690 in Molten Glass Environment

Abstract

Alloy 690 is widely used in nuclear vitrification melters for its high-temperature strength and creep resistance. Operating temperatures of components can reach up to 1100 °C under corrosive molten glass environment. Thermal gradients and structural loads generate high interfacial stresses leading to localized corrosion and potential degradation of vessel life. In this work, the evolution of defect size, density and their distribution due to exposure of molten glass environment on Alloy 690 material have been studied. Tensile specimen has been designed and fabricated using 10 mm thick Alloy 690 plate that is used in fabrication of nuclear reprocessing plant components. These tensile specimens have been exposed to molten glass environment for different time durations, temperature and stress levels. The changes in mechanical properties under different operating conditions have been determined. It has been observed that there is significant reduction in ductility and strength of material after exposure to molten glass environment. Reason for such a change in mechanical properties have been investigated using the defect evolution in the Alloy 690 specimen. Microstructure analysis of tensile specimen has been carried out using optical microscopy to find the depth of defect developed on the surface after exposure to molten glass environment. Descriptive statistics has been used to summarize the key characteristics i.e., mean size, maximum size of defects and their standard deviations. These data shall be useful for life estimation of nuclear reprocessing components.