Safely probing the chemistry of Chernobyl nuclear fuel using micro-focus X-ray analysis

Abstract

Detailed chemical analysis of the solidified molten fuel still residing in the stricken Chernobyl reactor unit 4 are inferred using multi-modal micro-focus x-ray analysis of a low-radioactivity proxy. A fascinating...

Chemical state mapping of simulant Chernobyl lava-like fuel containing material using micro-focused synchrotron X-ray spectroscopy

“…The excitation energy was set to 18000 eV, which is sufficient to stimulate emission of Zr K characteristic X-rays. The correlation of U and Zr distributions are in excellent agreement with the previous study of phase assemblages obtained by a combination of m-XRD and m-XRF analysis (Ding et al, 2021). High U and Zr contents were observed in regions where the dominant observed phases included (U,Zr)O 2 and (U,Zr)SiO 4 .…”

“…Maps of Ca abundances show that it was associated with the glass matrix, where the concentrations of U and Zr were significantly lower, compared with regions dominated by crystalline phases. The distribution of Fe and Ni was concentrated in Fe-Ni alloy particles, as observed in a previous study (Ding et al, 2021); an example is shown in the approximate centre of the m-XRF maps shown in Fig. 2, between the edges of two neighbouring crystallites.…”

“…In common with the selected reference compounds, for which m-XANES and corresponding difference spectrum are shown in Fig. 1(b), these contain UO 8 polyhedra (Ding et al, 2021).…”

“…In this contribution, we describe the development of methods to quantitatively estimate U oxidation states, in micrometre-sized pixels, within m-XRF maps collected at multiple energies over the U L 3 absorption edge. For the purpose of method development, we apply these methods to investigate representative low-activity simulant Chernobyl LFCMs, that closely approximate the composition and microstructure of the core melt down product formed in the Chernobyl nuclear accident (Kiselev & Checherov, 2001;Ushakov et al, 1996;Burakov et al, 1997;Borovoi et al, 1998), but without the inclusion of short-lived fission product nuclides (Barlow et al, 2017(Barlow et al, , 2020Ding et al, 2021). Previous investigation of simulant LFCMs by analysis of bulk U L 3 XANES demonstrated a narrow range of average oxidation states of 4.0-4.5+ (Barlow et al, 2017(Barlow et al, , 2020.…”

Thermodynamic non-ideality and disorder heterogeneity in actinide silicate solid solutions

“…How the mixing of various actinides impacts the structural and thermodynamic stabilities is essential to the understanding of behaviors of Pu in the zircon structure type. On the other hand, coffinite is known to be one of the key alternation phases of uraninite (UO 2 in nature) or UO 2 in the spent nuclear fuel (SNF) in a geologic repository [23][24][25][26][27][28][29][30] due to the contact with groundwater under anoxic and silica-enriched conditions 31,32 . However, whether uranothorite or other actinide silicate solid solutions can be more important sinks for U, Pu, and other minor actinides that control the dissolution and distribution of radionuclides is unknown and requires a fundamental thermodynamic assessment.…”