The effects of radiation chemistry on radiochemistry: when unpaired electrons defy great expectations

Impacts of trace level chromium on formation of superoxide within uranyl triperoxide complexes

U(VI) peroxides are important within the nuclear fuel cycle, but reactive oxygen species (ROS) can form upon oxidation. Herein, we identified the spectral signatures of a U(VI) diperoxosuperoxide complex (KUPS-1) and observed that the transformation of U(VI) triperoxide (KUT-1) to superoxide forms occurred with trace-level Cr. U(VI) superoxide complexes were identified in EPR solution spectra without the use of spin-traps.

Radiation-Induced Defects in Uranyl Trinitrate Solids

Actinides are inherently radioactive; thus, ionizing radiation is emitted by these elements can have profound effects on its surrounding chemical environment through the formation of free radical species. While previous work has noted that the presence of free radicals in the system impacts the redox state of the actinides, there is little atomistic understanding of how these metal cations interact with free radicals. Herein, we explore the effects of radiation (UV and γ) on three U(VI) trinitrate complexes, M[UO2(NO3)3] (where M=K+, Rb+, Cs+), and their respective nitrate salts in the solid state via electron paramagnetic resonance (EPR) and Raman spectroscopy paired with Density Functional Theory (DFT) methods. We find that the alkali salts form nitrate radicals under UV and γ irradiation, but also note the presence of additional degradation products. M[UO2(NO3)3] solids also form nitrate radicals and additional DFT calculations indicate the species corresponds to a change from the bidentate bound nitrate anion into a monodentate NO3 • radical. Computational studies also highlight the need to include the second sphere coordination environment around the [UO2(NO3)3]0,1 species to gain agreement between the experimental and predicted EPR signatures.

An experimental and computational look at the radiolytic degradation of TODGA and the effect on metal complexation

A combination of Fukui function calculations with experimental characterization gives an improved understanding of the behaviour of TODGA solutions after radiolysis.

Stability studies of GANEX system under different irradiation conditions

To demonstrate the robustness of extraction systems against radiolytic degradation is nowadays one of the limiting points to ensure a safe and stable operation for advanced nuclear fuel strategies. In this paper, is addressed the stability of one of most promising extractants (TODGA, N,N,N′,N′-tetraoctyldiglycolamide) but also the importance of designing realistic model to simulate and study the degradation of the systems. For that, new irradiations experiments were carried out where mixture between phases and the oxygen content have been taken into account. Extraction behaviour and composition of the organic phases after γ-irradiation have been measured and compared. Although TODGA studies are applicable to many processes currently under development, this work is focus on Grouped Actinides Extraction (GANEX) process development.

Exploring crown-ether functionalization on the stabilization of hexavalent neptunium

Crown-ether molecules are used in radiochemical separations due to their high selectivity for a range of metal cations. Previous investigations regarding the interactions of 18-crown-6 (18C6) with ²³⁷Np suggested the formation of a Np(v) inclusion complex, but also reported rapid reduction of Np(vi) to Np(v) in the presence of the ether molecule. Herein, we investigate the impact of crown ether functionalization by exploring the Np(v) and Np(vi) dicyclohexano-18-crown-6 (DCH-18C6) systems. Two [X(DCH-18C6)]₂[Np(vi)O₂Cl₄] compounds (X = K (1) and Na (2)) were crystallized and characterized by single crystal X-ray diffraction and Raman spectroscopy. Additional studies of Np(vi), Np(v), and Np(v)/Np(vi) in solution indicated redox stability in the presence of functionalized crowns and preferential crystallization of Np(vi) DCH-18C6 solids. These results indicate that functionalization of the crown can lead to higher resistance to radiolysis and increased stability of the Np(vi) oxidation state in solution.