This study investigates the interaction between alloy 690 and two types of glasses: pristine borosilicate and P2O5-containing borosilicate glass, at typical glass pouring temperatures encountered during the vitrification of high-level radioactive waste in the back-end of Nuclear Fuel Cycle (NFC). Partial crystallization of both glasses was observed at the alloy 690/glass interface, with certain, though not entirely identical, crystalline phases forming at the interface. The density of these crystalline phases is significantly higher than that of the surrounding glass, which raises concerns about these reaction products settling at the bottom of the furnace. Such sedimentation could potentially obstruct the freeze valve, thereby halting the vitrification process. Additionally, intergranular grooves on the alloy surface exposed to P2O5-containing borosilicate glass were found to disappear with prolonged exposure. This phenomenon is attributed to the strong corrosive action of the highly basic and oxidizing P2O5-bearing glass, leading to the peeling away of the entire exposed surface of alloy 690.
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