Environmental modeling of uranium interstitial compositions of non-stoichiometric oxides: experimental and theoretical analysis

Abstract

Study of uranium interstitial compositions of non-stoichiometric oxides UO2+x (x ∈ 0.1-0.02) in gas and condense phases has been presented, using various soft-ionization mass spectrometric methods such as ESI-, APCI-, and MALDI-MS at a wide dynamic temperature gradient (∈ 25-300 °C). Linearly polarized vibrational spectroscopy has been utilized in order to assign unambiguously, the vibrational frequencies of uranium non-stoichiometric oxides. Experimental design has involved xUO2.66·yUO2.33, xUO2.66·yUO2.33/SiO2, xUO2.66·yUO2.33/SiO2 (NaOH) and SiO2/x'NaOH·y'UO2(NO3)2·6H2O, multicomponent systems (x = 1, y ∈ 0.1-1.0 and x' = 1, y' ∈ 0.1-0.6) as well as phase transitions UO2(NO3)2·6H2O → {U4O9(UO2.25)} → U3O7(UO2.33) → U3O8(UO2.66) → {UO3}, thus ensuring a maximal representativeness to real environmental conditions, where diverse chemical, geochemical and biochemical reactions, including complexation and sorption onto minerals have occurred. Experimental factors such as UV-irradiation, pH, temperature, concentration levels, solvent types and ion strength have been taken into consideration, too. As far as uranium speciation represents a challenging analytical task in terms of chemical identification diverse coordination species, mechanistic aspects relating incorporation of oxygen into UO 2+x form the shown full methods validation significantly impacts the field of environmental radioanalytical chemistry. UO2 is the most commonly used fuel in nuclear reactors around the globe; however, a large non-stoichiometric range ∈ UO1.65-UO2.25 has occurred due to radiolysis of water on UO2 surface yielding to H2O2, OH(·), and more. Each of those compositions has different oxygen diffusion. And in this respect enormous effort has been concentrated to study the potential impact of hazardous radionuclide on the environment, encompassing from the reprocessing to the disposal stages of the fuel waste, including the waste itself, the processes in the waste containers, the clay around the containers, and geological processes. In a broader sense, thereby, this study contributes to field of environmental analysis highlighting the great ability of various soft-ionization MS methods, particularly, MALDI-MS one, for direct assay of complex multicomponent heterogeneous mixtures at fmol-attomol concentration ranges, along with it the great instrumental features allowing, not only meaningful quantitative, but also structural information of the analytes, thus making the method indispensable for environmental speciation of radionuclides, generally.

Hyperstoichiometric Uranium Dioxides: Rapid Synthesis and Irradiation-Induced Structural Changes

“…28,29 In turn, these changes in fuel properties impact its performance, storage, and potentially during geologic disposal. 30,31 An in-depth understanding of such hyperstoichiometric surface phases is essential because nanoscale features could lead to considerable deviations from their bulk counterparts. However, the radiation-induced structure transformations of the UO 2.12 surface phase and its relationships to fuel bulk properties are yet to be investigated.…”

“…Uranium dioxide (UO 2 ) with a cubic fluorite structure is the primary fuel for commercial light-water nuclear reactors. − UO 2 accommodates excess oxygen atoms as interstitial defects and forms a series of hyperstoichiometric phases with a general formula of UO 2+ x (0 > x > 0.25). − These phases readily form on a single crystalline UO 2 surface at relatively low temperatures. , The diffusion-controlled filling of oxygen in UO 2 lattice positions occurs until the unit cell reaches a composition of UO 2.25 without noticeable alteration to the cubic structure. ,− The most energetically favorable defect structure is UO 2.12 . − This oxide phase forms on fuel pellet surfaces, influencing thermal conductivity, fission product diffusion, high-burnup structure, , and corrosion behavior. , In turn, these changes in fuel properties impact its performance, storage, and potentially during geologic disposal. , An in-depth understanding of such hyperstoichiometric surface phases is essential because nanoscale features could lead to considerable deviations from their bulk counterparts. However, the radiation-induced structure transformations of the UO 2.12 surface phase and its relationships to fuel bulk properties are yet to be investigated.…”

Relativistic DFT Probe for Reaction Energies and Electronic/Bonding Properties of Polypyrrolic Hetero-Bimetallic Actinide Complexes: Effects of Uranylendo-Oxo Functionalization

“…The reported results are crucial in quality control and monitoring programs for the assessment of radionuclide migration. The impact of the study significantly evaluated the risks associated with radioactive contamination. , The environmental modeling of uranium interstitial compositions of nonstoichiometric oxides is maximal representative of real environmental biogeochemical reactions of uranium sorption onto sediments. , …”

“…8,9 The environmental modeling of uranium interstitial compositions of nonstoichiometric oxides is maximal representative of real environmental biogeochemical reactions of uranium sorption onto sediments. 10,11 In solution and the solid state, the hexavalent uranyl is able to interact with actinyl or actinide to form cation−cationinteraction (CCI) complexes. For instance, the CCI complexes have been constructed previously in cases of uranyl(VI) with either actinyl or actinide ion in solution and the solid state.…”