Structure and Property Evaluation of Various Glass Matrices for Containment of Nuclear Waste

Borosilicate glass is used for the immobilization of high-level liquid waste (HLW). HLW originates in a reprocessing plant during the extraction of U and Pu from spent nuclear fuel. This waste contains high levels of α , β , and γ radioactivity, a wide range of elements, and salts. Its immobilization in a glass matrix helps in the containment of radioactivity. However, the stability of the glass network plays a vital role in determining how effectively the radioactivity can be contained without any release into the environment. The thermal, chemical, and mechanical stability of the product glass primarily depends on the additives present in the base glass. In this study, four sodium borosilicate base glass matrices were systematically investigated to evaluate the influence of CaO, K 2 O, Al 2 O 3 , and P 2 O 5 on their structural, thermal, and chemical properties. Raman spectroscopy, along with the Dell–Bray model, revealed significant changes in the distribution of silicon- and boron-based structural units with compositional variations. Glasses containing mixed modifiers (Na 2 O–CaO–K 2 O) exhibited superior performance and were found to be more suitable for the immobilization of high-sodium HLW compared with glasses containing only one modifier. The incorporation of mixed modifiers and Al 2 O 3 enhanced the chemical durability by approximately tenfold compared with the base composition. In contrast, the addition of 5 mol percent P 2 O 5 adversely affected the glass network, reducing the glass transition temperature ( Tg ) by approximately 45°C and decreasing the chemical durability by factors of 2–5. These findings provide valuable guidance for selecting and optimizing base glass matrices for the vitrification of diverse HLW streams.