Development and Characterization of Rare Earth-Rich Glassy Matrices Envisaged for the Immobilization of Concentrated Nuclear Waste Solutions

Abstract

New nuclear highly durable glass compositions, able to immobilize a higher concentration of high-level nuclear wastes than current borosilicate nuclear glasses, are being studied. Investigations are performed on rare earth (RE)-rich glasses, known as durable matrices. After a preliminary study on complex and simplified compositions, a basic glass composition was selected and studied (wt%): 51.0 SiO₂–8.5 B₂O₃–12.2 Na₂O–4.3 Al₂O₃–4.8 CaO–3.2 ZrO₂–16.0 RE₂O₃. Chemical durability, physical properties (viscosity, transformation temperature), and crystallization tendency of glasses containing either a mixture of RE (La + Ce + Pr + Nd) or only one RE were studied and compared. The local environment of RE (for RE = Nd) in the glass and its evolution according to Nd₂O₃ concentration (from 1.3 to 30 wt%) was also studied by coupling characterization methods such as extended X-ray absorption fine structure spectroscopy at the neodymium L_III-edge and optical absorption spectroscopy. ¹¹B, ²⁷Al magic angle spinning-nuclear magnetic resonance, and Raman spectroscopy were also used to study glass structure.