Hydrothermal synthesis of homogenous and size-controlled uranium-thorium oxide micro-particles for nuclear safeguards

Particle analysis is one of the key-techniques used in the field of nuclear safeguards. Beyond traditional uranium isotopy measurement, other methodologies are implemented to better characterize nuclear ma-terials. Among them, age dating at the particle scale enables to determine the time elapsed since the last chemical step of separation/purification or enrichment. The 230Th-234U couple being one of the most common radiochronometer, there is a need for morphology and size controlled uranium-thorium mixed oxides particles that could be used as reference materials during isotopic measurements. With this aim, uranium-thorium mixed oxide microspheres were synthesized using a wet chemistry route. The hy-drothermal conversion of aspartate precursors at T = 433 K led to mixed dioxide micro-particles with controlled spherical morphology and size, up to 5 mol% in thorium. In order to remove impurities, den-sify the micro-particles, and control the chemical form of the final compounds, heat treatments were per-formed under various atmospheres. Nearly stoichiometric (U,Th)O2 dioxides were obtained under reduc-ing conditions (Ar-4%H2) while U3O8-based samples were formed under air, with thorium incorporated in the structure up to 2 mol%. Last, the homogeneity of the cation distribution in the samples was evaluated by various methods, including PERALS a-scintillation counting, as well as X-EDS and LG-SIMS analyzes of individual particles, leading to consistent results. Particularly, the relative external reproducibility (2 a) of the 232Th+/238U+ ion ratios measured at the particle scale remained below 10%, paving the way to use these mixed oxide particles in the field of nuclear safeguards.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

Particle analysis is a key technique in the field of nuclear safeguards. Apart from traditional uranium isotopic measurement, age dating at the particle scale is implemented to better characterize nuclear materials. This study synthesized uranium-thorium mixed oxide microspheres with controlled spherical morphology and size using a wet chemistry route, and evaluated the homogeneity of the cation distribution in the samples. The results suggest the potential use of these mixed oxide particles in the field of nuclear safeguards.