Immobilization of gadolinium in iron borophosphate glasses and iron borophosphate based glass-ceramics: Implications for the immobilization of plutonium(Ⅲ)

Immobilization of gadolinium (Gd), a nonradioactive surrogate for Pu³⁺, in iron borophosphate glasses/glass-ceramics (IBP glasses/glass-ceramics) has been investigated. The IBP glass containing 4 mol% Gd₂O₃ is homogeneously amorphous. At higher Gd₂O₃ concentrations, additional Gd is retained in the glasses as crystalline inclusions of monazite GdPO₄ crystalline phase detected with X-ray diffraction. Moreover, Gd₂O₃ addition increases the T_g of the IBP glasses in glass formation range, which is consistent with the structural modification of the glasses. The structure of the Gd₂O₃-loaded IBP glasses/glass-ceramics is mainly based on pyrophosphate units. The chemical durability of Gd₂O₃-loaded IBP glasses/glass-ceramics is comparable to widely used borosilicate glass waste forms and the existence of monazite GdPO₄ crystalline phase does not degrade the aqueous chemical durability of the IBP glasses/glass-ceramics. The Gd-loading results imply that the solubility should not be a limiting factor in processing nuclide Pu³⁺ if the formed crystalline phase(s) have high chemical durability. - Highlights: • Monazite GdPO₄ are identified in the IBP glasses containing up to 6 mol% Gd₂O₃. • R_L of the Gd₂O₃-loaded IBP glasses/glass-ceramics are about 10⁻² g m⁻² d⁻¹. • Existence of GdPO₄ does not degrade aqueous chemical durability of the IBP glass. • T_g increases with increasing Gd₂O₃ content in glass formation range. • IBP glasses are potential hosts for the immobilization of Pu³⁺ containing HLWs.