X-ray absorption spectroscopy and actinide electrochemistry: a setup dedicated to radioactive samples applied to neptunium chemistry

Abstract

A spectroelectrochemical setup has been developed to investigate radioactive elements in small volumes (0.7 to 2 ml) under oxidation–reduction (redox) controlled conditions by X-ray absorption spectroscopy (XAS). The cell design is presented together with in situ XAS measurements performed during neptunium redox reactions. Cycling experiments on the NpO2 2+/NpO2 + redox couple were applied to qualify the cell electrodynamics using XANES measurements and its ability to probe modifications in the neptunyl hydration shell in a 1 mol l−1 HNO3 solution. The XAS results are in agreement with previous structural studies and the NpO2 2+/NpO2 + standard potential, determined using Nernst methods, is consistent with measurements based on other techniques. Subsequently, the NpO2 +, NpO2 2+ and Np4+ ion structures in solution were stabilized and measured using EXAFS. The resulting fit parameters are again compared with other results from the literature and with theoretical models in order to evaluate how this spectroelectrochemistry experiment succeeds or fails to stabilize the oxidation states of actinides. The experiment succeeded in: (i) implementing a robust and safe XAS device to investigate unstable radioactive species, (ii) evaluate in a reproducible manner the NpO2 2+/NpO2 + standard potential under dilute conditions and (iii) clarify mechanistic aspects of the actinyl hydration sphere in solution. In contrast, a detailed comparison of EXAFS fit parameters shows that this method is less appropriate than the majority of the previously reported chemical methods for the stabilization of the Np4+ ion.

Advancing the Am Extractant Design through the Interplay among Planarity, Preorganization, and Substitution Effects

“…Previous experimental and theoretical studies suggest that for the three actinyl ions, UO 2 2+ , NpO 2 2+ , and PuO 2 2+ , the most prevalent form in liquid water is in the form of the penta-aquo complex, AnO 2 (H 2 O) 5 2+ . − Figure shows selected optimized structures of representative UO 2 2+ compounds. The structures of NpO 2 2+ and PuO 2 2+ compounds are very similar to the analogous UO 2 2+ compounds.…”

From Molecular Oxo-Hydroxo Ce Clusters to Crystalline CeO2

“…The cerium oxidation state in the reactive media was fixed at IV by electro-oxidation in galvanometric conditions ( I = 1 mA) and maintained during HERFD-XAS measurements using an in situ electrochemistry setup. The setup is similar to the one already described by Bengio and Husar except that only the inner part of the cell was used for this experiment to provide a better HERFD-XAS signal/noise ratio. , (The second confinement previously used for radioactive samples and the dry ionic liquid was of no use for cerium aqueous electro-oxidation. )…”

“…The setup is similar to the one already described by Bengio and Husar except that only the inner part of the cell was used for this experiment to provide a better HERFD-XAS signal/noise ratio. 61,62 (The second confinement previously used for radioactive samples and the dry ionic liquid was of no use for cerium aqueous electro-oxidation. )…”

Synchrotron Radiation Techniques and their Application to Actinide Materials

“…Besides the scientific importance, actinide speciation studies are key to understanding extraction mechanisms and separation processes in fuel reprocessing (Dressler et al, 2022;Moeyaert et al, 2021;Pruessmann et al, 2022), the corrosion and the reduction-oxidation behavior of nuclear waste forms in storage facilities (Glasauer et al, 2022;Husar et al, 2022), the mechanisms by which actinides can contaminate the biosphere (Cot-Auriol et al, 2021;Estevenon et al, 2021;Pidchenko et al, 2020;Vitova et al, 2020), their mobility in contaminated sites and how best they can be removed from the environment (Dumas et al, 2022;Jegou et al, 2022;Le Pape et al, 2020). The clean up of the Rocky Flats Nuclear Weapons Plant, near Denver, is exemplary of the practical importance of these studies (Clark et al, 2006).…”