Quantitative Microstructural Characterization of Plutonium Oxalate Auto‐Degradation and Evidence for PuO₂ Nanocrystal Formation

Abstract

It has been known since the 1950s that plutonium oxalate powders change color and lose mass over time when stored at room temperature in air. Despite several studies monitoring these changes, there are still discrepancies in the literature regarding the speciation of intermediate and final products that result from this decomposition. Presented here for the first time is a comprehensive series of time-resolved powder X-ray diffraction experiments coupled with solid-state optical spectro-scopy and electron microscopy of aged plutonium (III) and (IV) oxalate powders. These data provide fresh insight into the chemical and structural changes that occur in these solids over time at room temperature and represent new evidence suggesting both plutonium (III) and plutonium (IV) oxalates auto-decompose to form nanocrystalline plutonium oxide in the solid state.

Biodegradable Methane Sulfonic Acid-Based Nonaqueous Dissolution, Estimation, and Recovery: Toward Development of a Simplified Scheme for Plutonium-Bearing Fuel Matrices

“…The precipitate was subjected to powder XRD (Figure ). The pattern obtained was consistent with the literature and database − for Pu­(IV) oxalate. However, Pu oxalates have been reported to lose water of hydration as well as crystallinity with time and temperature , which may lead to anomalies in the XRD pattern.…”

Synthesis and multi-scale properties of PuO2 nanoparticles: recent advances and open questions

“…105 FTIR spectra recently acquired on PuO 2 nanoparticles prepared by auto-radiolytic decomposition of Pu(IV) and Pu(III) oxalates in the air atmosphere were also suggested to be possibly associated with carbonate moieties. 120 Computational calculations allowed the estimation of the surface energy and predicted that the (111) surface is the most stable surface for PuO 2 in comparison to the (110) and (100) indexed ones. It is expected that the selective adsorption of ligands on the desired surface would also control the morphology of nanocrystals that are formed.…”

“…Recently, PuO 2 nanoparticles obtained by auto-radiolytic decomposition of Pu oxalate compounds were found to exhibit a variety of colors despite evidence of similar preparation and storage conditions for the precursors (room temperature in air) and similar properties for the obtained nanocrystals (FTIR, XRD, UV-vis spectroscopy). 20,120 It is noteworthy that the authors reported the formation of PuO 2 nanocrystals from both Pu(III) and Pu(IV) oxalates. The few examples related to the variability of powder colors strongly suggest that nanosizing PuO 2 causes a signicant impact on the electronic transitions responsible for optical absorption which is most probably related to surface characteristics.…”

“…The hydrated oxalate precursors were stored in air for several years at room temperature and pressure. 120 …”

“…In analogy with the recent report on oxalate ligands by Corbey et al , the observed radiolysis effect on ligands potentially complexing Pu aqueous species but also PuO 2 nanoparticles under environmental conditions appears relevant. 120 Size-dependent crystallographic properties of PuO 2 , or AnO 2 nanoparticles to a large extent therefore represent a complex topic requiring a detailed understanding and more rationalized investigations.…”