Isolation and Reactivity of Uranyl Superoxide

Abstract

The high radiation field associated with spent nuclear fuel (UIVO2) pellets produces an array of reactive radical species that impact the corrosion and formation of secondary alteration phases. Dioxygen radicals are important as radiolysis products, but the interaction between these reactive oxygen species and UVIO22+ and its effects on the resultant alteration phases is unclear. We report the first example of a UVI superoxide compound and explore its reactivity in the environments relevant to the storage of spent nuclear fuel. We utilized X‐ray diffraction and Raman scattering techniques to demonstrate that the uranyl superoxide reacts with CO2 in air to afford a mixed uranyl peroxide/carbonate within 3 days, both in solution and under atmospheric conditions. An additional transformation occurs over the course of 3 months to form a potassium UVI carbonate (grimselite), which also occurs as an alteration product on Chernobyl corium. Our results demonstrate the presence and significance of the superoxide anion in the alteration of spent nuclear fuel and indicate the impact of uranyl superoxide chemistry on high prevalence of carbonate in the secondary phases of spent nuclear fuel.

From Adsorption to Precipitation of U(VI): What is the Role of pH and Natural Organic Matter?

“…Our findings suggest that at 0.5 h, the adsorption of U onto POM is the primary reaction between NOM and U–KCl, while the precipitation of U–K-bearing crystalline solids is evident after 24 h of reaction. Carbonation reactions in the presence of U­(VI) have been previously observed within these time scales, and the surface of the POM could facilitate heterogeneous nucleation of U–K-bearing crystals as the reaction time progresses from 0.5 to 24 h. Our results are unique given that other studies only focused on the adsorption of U onto organic material . However, other investigations have shown that other metal ions adsorbed to POM can lead to the growth of metal–NOM crystalline phases .…”

“…The dioxygen radicals can invoke further mineralization processes and have previously been shown by Kravchuk and Forbes to degrade phosphonate molecules to the inorganic phosphate by breaking a C–P bond . In addition, Kravchuk et al also demonstrated that U­(VI) can stabilize superoxide radicals and promote carbonation processes that specifically resulted in the formation of uranyl peroxide carbonate complexes and the grimselite phase through a solid-state transformation . Both Kravchuk et al and Blanes Díaz et al also noted that photochemical degradation of U­(VI) organic materials can take place in the solid state, and so these mineralization reactions may indeed occur following adsorption to the POM phase …”

“…65 In addition, Kravchuk et al also demonstrated that U(VI) can stabilize superoxide radicals and promote carbonation processes that specifically resulted in the formation of uranyl peroxide carbonate complexes and the grimselite phase through a solid-state transformation. 66 Both Kravchuk et al and Blanes Di ́az et al also noted that photochemical degradation of U(VI) organic materials can take place in the solid state, and so these mineralization reactions may indeed occur following adsorption to the POM phase. 67 In experiments at pH 7 in the absence of NOM, we identified a U(VI) solid phase.…”

Theoretical prediction of a graphene-like 2D uranyl material with p-orbital antiferromagnetism

“…The O–O bond length of the superoxido ligand in the 2D uranyl sheet is 1.34 Å, close to that of the naked one (1.33 Å) as well as that of a recently reported uranyl superoxide compound (1.39 Å). 79 …”

Research progress of SERS on uranyl ions and uranyl compounds: a review

“…Besides, the aforementioned techniques are unable to reveal chemical information on speciation or bonding, hence it is difficult for them to identify the structural information of uranyl compounds. As reported in the studies, many techniques, including FTIR, 9,10 Raman, 11,12 electrospray ionization mass spectrometry, 13,14 and X-ray absorption fine structure spectroscopy (XAFS), 15,16 have been utilized to reveal the chemical information of uranyl compounds. Electrospray ionization mass spectrometry can provide coordination information through dissecting the fragment ion peaks of pyrolysis products, and thus speculating the chemical structures of uranyl compounds.…”