| Abstract Scope |
The Hanford site in Washington State houses millions of gallons of high-level radioactive waste (HLW), designated for vitrification into a borosilicate glass waste form. However, upon cooling the HLW glass melt, nepheline (NaAlSiO₄) crystallization can occur, posing a significant challenge by compromising the chemical durability of the resulting waste form. Consequently, extensive efforts have been made to understand compositional factors influencing nepheline crystallization, including optical basicity and ionic field strength.
In this work, these concepts are employed to (1) elucidate the structural role of K in aluminoborosilicate glass systems and (2) establish its relationship with the kinetics of nepheline crystallization. Furthermore, (3) the underlying mechanism of the mixed alkali effect is investigated. Structural changes are probed using polarized Raman spectroscopy and 1B, 23Na, and 27Al MAS NMR spectroscopy. Property variations are assessed via Tg, viscosity, and Product Consistency Tests (PCT) to correlate structure, crystallization tendency, and corrosion behavior. |