LnUO₄‐based glass–ceramic composites as waste forms for the immobilization of lanthanide‐bearing uranium wastes

Abstract

We report a comprehensive study on lanthanide monouranate-based glassceramic (GC) composites as potential waste forms for the immobilization of the lanthanide actinide fraction waste arising from the reprocessing of spent nuclear fuel (SNF). Although the crystalline LnUO 4 precursor prepared via a nitrate route can be well stabilized in a sodium aluminoborosilicate glass, the in situ crystallization of EuUO 4 in glass from oxide precursors (Eu 2 O 3 and U 3 O 8 ) is rather robust with regards to various processing conditions such as waste loadings, ceramic-to-glass ratios, and cooling rates. Scanning electron microscopy and transmission electron microscopy investigations revealed the detailed microstructures, where ∼1-5-μm spheres for NdUO 4 and EuUO 4 , and ∼1-5-μm rectangular crystals for DyUO 4 and HoUO 4 were observed in residual glasses. As designed, the pentavalent uranium has been confirmed by diffuse reflectance spectroscopy. Overall, LnUO 4 -based GC composite waste forms are chemically durable, offering flexible processing options with wide operating windows for SNF and process waste stream management.

A review of brannerite structured materials for nuclear waste management

“…With the presence of low valent fission products such as Cs + and Sr 2+ , it is possible to stabilize perovskite and hollandite together with brannerite in multiphase titanate GCs. In addition, Ln-doped U oxides such as LnUO4 can also be crystallized and stabilized in glass [127], making it a possible minor phase in some brannerite GCs if Ln as fission products are present.…”

Probing the Long- and Short-Range Structural Chemistry in the C-Type Bixbyite Oxides Th0.40Nd0.48Ce0.12O1.76, Th0.47Nd0.43Ce0.10O1.785, and Th0.45Nd0.37Ce0.18O1.815 via Synchrotron X-ray Diffraction and Absorption Spectroscopy

“…Oxygen-deficient fluorite compounds and their derivatives have been the focus of a plethora of solid-state materials science investigations across a wide variety of disciplines owing to the tremendous properties they can exhibit stemming from their subtle structural chemistries. − This is exemplified in applications pertaining to batteries, oxide ion conductors, and ferroelectrics, among others. Supporting the development of these materials, fundamental investigations on the solid-state chemistry of these compounds, particularly chemical changes including mechanisms that may lead to phase transformations or structural aberrations, have drawn protracted attention from material science communities. ,,− Core to this, fundamental chemical research is exploring and uncovering the unique individual roles and effects constituent elements of these compounds have upon chemical behavior at both the short and long ranges. Such bottom–up approaches have been successful in related materials including pyrochlore, , among other complex oxides, and promote their application toward more exotic material types, such as those stemming from nuclear energy and waste compounds.…”

“…Considering the relevance of the quaternary (Th 1– x – y Nd x Ce y )­O 2– x 0.5 system in exploring the structural behavior and chemistry of SNF-related materials, ,, among the broader field of fluorite and actinide structure solid-state chemistry, it is salient to understand the structural and redox chemistry of C-type bixbyite phases that can form in this family of oxides. Accordingly, the present investigation has examined the C-type bixbyite oxides Th 0.40 Nd 0.48 Ce 0.12 O 1.76 , Th 0.47 Nd 0.43 Ce 0.10 O 1.785 , and Th 0.45 Nd 0.37 Ce 0.18 O 1.815 via high-resolution short- and long-range techniques including synchrotron X-ray powder diffraction, high-energy resolution fluorescence detection X-ray near edge structure and extended X-ray absorption fine structure spectroscopy measurements.…”