The pentavalent actinide solution chemistry in the environment

Uranium contamination of bivalve Mytilus galloprovincialis, speciation and localization

Uranium is a natural radioelement (also a model for heavier actinides), but may be released through anthropogenic activities. In order to assess its environmental impact in a given ecosystem, such as the marine system, it is essential to understand its distribution and speciation, and also to quantify its bioaccumulation. Our objective was to improve our understanding of the transfer and accumulation of uranium in marine biota with mussels taken here as sentinel species because of their sedentary nature and ability to filter seawater. We report here on the investigation of uranium accumulation, speciation, and localization in Mytilus galloprovincialis using a combination of several analytical (Inductively Coupled Plasma Mass Spectrometry, ICP-MS), spectroscopic (X ray Absorption Spectroscopy, XAS, Time Resolved Laser Induced Fluorescence Spectroscopy, TRLIFS), and imaging (Transmission Electron Microscopy, TEM, μ-XAS, Secondary Ion Mass Spectrometry, SIMS) techniques. Two cohorts of mussels from the Toulon Naval Base and the Villefranche-sur-Mer location were studied. The measurement of uranium Concentration Factor (CF) values show a clear trend in the organs of M. galloprovincialis: hepatopancreas ≫ gill > body ≥ mantle > foot. Although CF values for the entire mussel are comparable for TNB and VFM, hepatopancreas values show a significant increase in those from Toulon versus Villefranche-sur-Mer. Two organs of interest were selected for further spectroscopic investigations: the byssus and the hepatopancreas. In both cases, U(VI) (uranyl) is accumulated in a diffuse pattern, most probably linked to protein complexing functions, with the absence of a condensed phase. While such speciation studies on marine organisms can be challenging, they are an essential step for deciphering the impact of metallic radionuclides on the marine biota in the case of accidental release. Following our assumptions on uranyl speciation in both byssus and hepatopancreas, further steps will include the inventory and identification of the proteins or metabolites involved.

Aquatic Chemistry of Pentavalent Plutonium: Determination of the First Hydrolysis Constant

Up to now, no recommendations have been made by the Organisation for Economic Co-operation and Development Nuclear Energy Agency (OECD-NEA) for the first two hydrolysis constants of pentavalent plutonium. We have determined them, as well as those of Np(V), by means of capillary electrophoresis coupled with inductively coupled plasma mass spectrometry (CE-ICP-MS) in 0.1 M NaCl at 25 °C. The hydrolysis constants of Pu(V) were compared to those of Np(V), for which consensual values have been proposed by the OECD-NEA. The first hydrolysis stability constant for Pu(V) extrapolated at zero ionic strength (log⁡β10*=-(11.50±0.12)) is, as expected, close to that of Np(V) (log⁡β10*=-(11.36±0.13)). We have obtained an excellent agreement with the OECD-NEA value for Np(V) [log⁡β10*=-(11.3±0.7)]. Based on eight independent values including our own, we propose a new, robust value for the first hydrolysis of Np(V): log⁡β10*=-(11.22±0.20). The determination of the second hydrolysis constant for Np(V) by CE-ICP-MS [⁢log⁡β20*=-(24.40±0.33)] deviates from the value adopted by the OECD-NEA [⁢log⁡β20*=-(23.6±0.5)]. This discrepancy might be explained by the association of a sodium counter cation with the species [NpO2(OH)2]-. A stability constant is proposed at zero ionic strength and 25 °C for this association: log⁡KNa[NpO2(OH)2]0=(1.6±0.5). As a result, it is considered that the second hydrolysis constant for Pu(V), [⁢log⁡β20*=-(24.24±0.26)], is also a mixed constant, taking into account both the hydrolysis and the association with a sodium cation.

Synthesis of Silica-Based Quaternized Adsorption Material and Study on Its Adsorption Behavior for Pu(IV)

In this research, we explored the synthesis optimization of the silica-based quaternized adsorption material (SG-VTS-VPQ) and its adsorption behavior for Pu(IV). By optimizing the synthesis process, the grafting amount of 4-vinylpyridine reached 1.25 mmol·g⁻¹. According to the analysis of NMR and XPS, the quaternization rate of pyridine groups reached 91.13%. In the adsorption experiments, the thermodynamic experiment results show that the adsorption of Pu(IV) by SG-VTS-VPQ is more in line with the Langmuir adsorption model and the adsorption type is a typical chemical adsorption; the kinetic results show that adsorption process is more in line with the pseudo first-order kinetic model, and the larger specific surface area of SG-VTS-VPQ plays an important role in the adsorption. The results of the adsorption mechanism show that the adsorption of Pu(IV) by SG-VTS-VPQ is mainly complex anion Pu(NO₃)₆²⁻ and Pu(NO₃)₅⁻. This research provides in-depth and detailed ideas for the surface modification and application of porous silica gel, and at the same time provides a new way to develop the direction of the analysis of pretreatment materials in the spent fuel reprocessing field.

A Review of Environmental and Economic Implications of Closing the Nuclear Fuel Cycle—Part One: Wastes and Environmental Impacts

Globally, around half a million tonnes of spent nuclear fuel (SNF) will be in dry or wet storage by around 2050. Continued storage is not sustainable, and this SNF must eventually either be disposed (the open nuclear fuel cycle) or recycled (the closed fuel cycle). Many international studies have addressed the advantages and disadvantages of these options. To inform this debate, a detailed survey of the available literature related to environmental assessments of closed and open cycles has been undertaken. Environmental impacts are one of the three pillars that, alongside economic and societal impacts, must be considered for sustainable development. The aims are to provide a critical review of the open literature in order to determine what generic conclusions can be drawn from the broad base of international studies. This review covers the results of life cycle assessments and studies on waste arisings, showing how the management of spent fuels in the open and closed cycles impact the environment, including the use of natural resources, radioactive waste characteristics (heat loading, radiotoxicity and volume) and the size of the geological repository. In the framework of sustainable development, the next part of this review will consider economic impacts.

Determination of the stability constants of Pu(VI) carbonate complexes by capillary electrophoresis coupled with inductively coupled plasma mass spectrometer

New determination of the stability constants related to the Pu(VI)/carbonate chemical system has been obtained by coupling capillary electrophoresis and ICP-MS at the ionic strength of 0.202 m in NaClO4 and for a temperature of 25°C. The following values have been obtained: log 10 β PuO 2 CO 3 = 8.12 ± 0.02 , ${\log _{10}}{\beta _{{\rm{Pu}}{{\rm{O}}_2}{\rm{C}}{{\rm{O}}_3}}} = 8.12 \pm 0.02,$ log 10 β PuO 2 ( CO 3 ) 2 2 − = 13.96 ± 0.04 , ${\log _{10}}{\beta _{{\rm{Pu}}{{\rm{O}}_2}({\rm{C}}{{\rm{O}}_3})_2^{2 - }}} = 13.96 \pm 0.04,$ and log 10 β PuO 2 ( CO 3 ) 3 4 − = 18.10 ± 0.03. ${\log _{10}}{\beta _{{\rm{Pu}}{{\rm{O}}_2}({\rm{C}}{{\rm{O}}_3})_3^{4 - }}} = 18.10 \pm 0.03.$ Based on the values selected by AEN/OECD, the interaction coefficients have been re-evaluated as follows: ε PuO 2 CO 3 = 0.02 ± 0.21 , ${\varepsilon _{{\rm{Pu}}{{\rm{O}}_2}{\rm{C}}{{\rm{O}}_3}}} = 0.02 \pm 0.21,$ ε PuO 2 ( CO 3 ) 2 2 − , Na + = 0.12 ± 0.08 , ${\varepsilon _{{\rm{Pu}}{{\rm{O}}_2}({\rm{C}}{{\rm{O}}_3})_2^{2 - },{\rm{N}}{{\rm{a}}^ + }}} = 0.12 \pm 0.08,$ ε PuO 2 ( CO 3 ) 3 4 − , Na + = 0.14 ± 0.18  kg ⋅ mol − 1 . ${\varepsilon _{{\rm{Pu}}{{\rm{O}}_2}({\rm{C}}{{\rm{O}}_3})_3^{4 - },{\rm{N}}{{\rm{a}}^ + }}} = 0.14 \pm 0.18{\rm{ kg}} \cdot {\rm{mo}}{{\rm{l}}^{ - 1}}.$

Focus on speciation assessment in marine radiochemistry using X-ray absorption spectroscopy

We review the state-of-the-art and recent advances in the determination of radionuclide speciation in seawater.

Structural and magnetic susceptibility characterization of Pu(v) aqua ion using sonochemistry as a facile synthesis method

The facile sonochemical preparation of pure, stable and concentrated Pu(v) aqueous solutions allowed to investigate its solvation environment and magnetic properties.

Stability, speciation and spectral properties of NpO2+ complexes with pyridine monocarboxylates in aqueous solution

Neptunyl ion as NpO₂⁺ is the least reacting and most mobile radioactive species among all the actinides. The picolinic acid used for decontamination is co-disposed along with the radioactive waste. Thus, in long term storage of HLW, there is high possibility of interaction of actinides and long lived fission products with the picolinate and can cause migration. The complexation of NpO₂⁺ with the three structural isomers of pyridine monocarboxylates provides an insight to explore the role of hetero atom (nitrogen) with respect to key binding moiety (carboxylate). In the present study, the log β values, speciation and spectral properties of NpO₂⁺ complexes with pyridine monocarboxylates viz. picolinate, nicotinate and isonicotinate, have been studied at 298K in 0.1M NaClO₄ medium using spectrophotometry. The complexation reactions involving protonated ligands are always accompanied by protonation/deprotonation process; thus, the protonation constants of all the three pyridine monocarboxylates under same conditions were also determined by potentiometry. The spectrophotometric data analysis for complexation of NpO₂⁺ with pyridine monocarboxylates indicated the presence of ML and ML₂ complexes with log β values of 2.96±0.04, 5.67±0.08 for picolinate, 1.34±0.09, 1.65±0.12 for nicotinate and 1.52±0.04, 2.39±0.06 for isonicotinate. The higher values of log β for picolinate were attributed to chelation while in other two isomers, the binding is through carboxylate group only. Density Functional Theory (DFT) calculations were carried out to get optimized geometries and electrostatic charges on various atoms of the complexes and free pyridine monocarboxylates to support the experimental data. The higher stability of NpO₂⁺ nicotinate and isonicotinate complexes compared to simple carboxylates and the difference in log β between the two is due to the charge polarization from unbound nitrogen to the bound carboxylate oxygen atoms.