Speciation Of Plutonium Research Articles

Plutonium Speciation and Oxidation State Distributions in the Presence of Citrate.

We explored the speciation and kinetics of the Pu(VI)-citrate and Pu(III)-citrate systems (pHm = 2.5-11.0, I = 0.1 M NaCl, T = 23 °C, O2(g) < 2 ppm) using ultraviolet-visible-near-infrared (UV-vis-NIR) spectrophotometry, solvent extraction, and PHREEQC modeling. Formation constants were determined for PuO2(HcitH)(aq) (log K°1,1 = 1.09 ± 0.05) and PuO2(HcitH)(citH)3- (log K°1,2 = -0.20 ± 0.07), and evidence for (PuO2)m(citH-k)n(OH)x2m(3+k)n-x was identified under alkaline conditions. Pu(VI) species were found to be less stable in the presence of citrate than in the absence of citrate (t ≤ 168 days); the rate of reduction increased with increasing pH. The direct reduction of Pu(VI) to Pu(IV) was required to fit experimental data in the presence of citrate but did not improve the fit for Pu in the absence of citrate. We also observed increased Pu(III) stability in the presence of citrate (t ≤ 293 days), with higher concentrations of Pu(III) favored at lower pH. Finally, we provide evidence of a radiolysis-driven mechanism for the citrate-mediated reduction of plutonium that involves electron transfer from the oxidative breakdown of citrate. Our work highlights the need to investigate the redox effect of organic ligands on plutonium oxidation states under repository-relevant conditions.

Speciation of plutonium and some chemical elements in the bottom sediments of the Laptev sea and the Kara sea

The comparison of the speciation forms of 239Pu and chemical elements, including rare earth elements (REE), in the bottom sediments of the Kara Sea and the Laptev Sea is given. The speciation forms were investigated by three different methods of selective leaching. Data were obtained on the content of chemical elements and 239Pu in the composition of complexes with different lability: easily soluble, bound to organic matter, including groups of humic acids (HA) and fulvic acids (FC), as well as with amorphous oxides of Fe and Mn. It is shown that humic and low molecular weight organic acids and their compounds with chemical elements can influence the behavior of plutonium in the seawater-bottom sediments system in the waters of the Arctic seas. The possibility of using a number of REE as a marker for predicting the migration behavior of plutonium is evaluated.

Efficient Plutonium Extraction and Electrochemical Insights in a Hydrophobic Deep Eutectic Solvent for Radioactive Waste Management

In this study, we explore the extraction and electrochemical characteristics of Plutonium using a hydrophobic deep eutectic solvent (DES) consisting of tetra-Butyl Ammonium Bromide(TBABr) as the hydrogen bond acceptor and Decanoic acid (DA) as the hydrogen bond donor in a 1:2 ratio composition. Hydrophobic DES possesses unique attributes, such as low volatility and a high affinity for metal ions, making it a promising choice for Plutonium extraction. We systematically investigate the influence of various parameters, including DES composition, acid concentration, and extraction duration. Our extraction experiments reveal that the hydrophobic DES exhibits its maximum Plutonium extraction efficiency (95%) at a 4 M HNO3 concentration, with a distribution coefficient (D) reaching nearly 71. To gain insights into the electrochemical behavior of Plutonium within the hydrophobic DES, we conduct cyclic voltammetry experiments. The resulting voltammograms offer valuable insights into the redox properties and stability of Plutonium species within the DES. Furthermore, we analyze the impact of potential scan rate on the electrochemical response, shedding light on the kinetics and mechanisms underlying Plutonium electrochemistry within the hydrophobic DES. These findings underscore the considerable potential of hydrophobic DES for efficient Plutonium extraction and electrochemical separation. This research contributes to the development of sustainable and environmentally friendly approaches for managing Plutonium, particularly in the context of nuclear waste disposal

Speciation of Plutonium and Some Chemical Elements in the Bottom Sediments of the Laptev Sea and the Kara Sea

Speciation of Plutonium and Some Chemical Elements in the Bottom Sediments of the Laptev Sea and the Kara Sea

The impact of nuclear data uncertainty on identifying plutonium diversion in liquid-fueled Molten Salt Reactors

Molten salt-fueled reactors (MSRs) have gained popularity recently, but there are challenges in accounting for nuclear material due to the inability to count discrete items (e.g., fuel assemblies). The focus of this work is to calculate what changes would occur due to diversion of fissile material, and to evaluate the effect of nuclear data uncertainties on these quantities. The impact of other sources of uncertainty (e.g., measurement error) is out of the scope. A thermal-spectrum MSR was modeled using Serpent 2 and SCALE 6.3.b12 (beta), including plutonium diversion scenarios. The feed and removal capabilities were recently added into the depletion schemes of these codes. Protracted and abrupt diversion scenarios were developed for the removal of 1 and 10 significant quantities (SQs) of plutonium. The SCALE module Sampler was used to perform nuclear data uncertainty propagation along the depletion interval from neutron cross-sections, fission product yield and decay data. Results showed that along with plutonium species, other actinides and fission products presented significant changes between the reference scenario (i.e., no diversion) and the 10 SQ plutonium protracted diversion scenario. Considering their propagated nuclear data uncertainty from Sampler simulations, some actinides such Am and Cm showed changes higher than their nuclear data uncertainty, which goes from 2.23% for 241Am up to 4.88% for 242mAm. Some fission products also presented notable changes, Sr and Y isotopes are examples with positive changes, while Cd, Eu and Sm isotopes showed more prominent changes on the negative side, with uncertainties in the range of 1.89% for 149Sm to 3.31% for 113Cd. The analysis extended to nuclides regularly moved to other modeled inventories, showing that 105,106Ru can be good candidates given their low uncertainty that stands within the 1% range. Many other isotopes with considerable changes presented high uncertainty values and methods to improve their nuclear data uncertainty estimation will be sought in future work.

Investigation of the Plutonium(IV) Interactions with Two Variants of the EF-Hand Ca-Binding Site I of Calmodulin.

Due to its presence in the nuclear industry and its strong radiotoxicity, plutonium is an actinide of major interest in the event of internal contamination. To improve the understanding of its mechanisms of transport and accumulation in the body, the complexation of Pu(IV) to the most common protein calcium-binding motif found in cells, the EF-hand motif of calmodulin, was investigated. Visible and X-ray absorption spectroscopies (XAS) in solution made it possible to investigate the speciation of plutonium at physiological pH (pH 7.4) and pH 6 in two variants of the calmodulin Ca-binding site I and using Pu(IV) in different media: carbonate, chloride, or nitrate solutions. Three different species of Pu were identified in the samples, with formation of 1:1 Pu(IV):calmodulin peptide complexes, Pu(IV) reduction, and formation of peptide-mediated Pu(IV) hexanuclear cluster.

Experimental Test of a Process Upset in the EURO-GANEX Process and Spectroscopic Study of the Product

ABSTRACT EURO-GANEX is an innovative hydrometallurgical process for the group separation of transuranic actinides from future spent nuclear fuels. A flowsheet test of a process upset (or ‘maloperation’) has been carried out involving the reduction in the concentration of the scrub acid feed to the extract-scrub contactors. The experimental test was completed in two stages. First, the extract-scrub contactors were run under normal flowsheet conditions before initiating the process upset by reducing the scrub acidity from 0.5 to 0.05 mol/L HNO3. At low acidity, a change in the online UV-Vis spectra of the solvent phase indicated the formation of hydrolyzed plutonium species or plutonium colloid formation. Surprisingly, however, this did not lead to the recycle and accumulation of plutonium in the extract-scrub contactors as expected indicating that the EURO-GANEX process is quite robust towards this process upset. Further spectroscopic investigations of the organic-phase species were also performed to characterize the conditions under which the hydrolyzed plutonium species form in the EURO-GANEX solvent as well as separate TODGA and DMDOHEMA phases. The spectroscopic studies supported the view that Pu(IV) hydrolyses at low acidity but the hydrolysis is limited by the organic ligands and is consequently reversible on raising the acidity again. The hydrolysis was also observed in separate TODGA and DMDOHEMA phases.

Aqueous Speciation of Tetravalent Actinides in the Presence of Chloride and Nitrate Ligands.

Speciation of hexachloride tetravalent uranium, neptunium, and plutonium species in aqueous media has been investigated using density functional theory in the presence of inner sphere ligands such as chloride, nitrate, and solvent molecules. All possible structures with the formula [AnIV(Cl)x(H2O)y(NO3)z]4-x-z (An = U, Np, and Pu; x = 0-6, y = 0-8, and z = 0-6) were considered to explore the speciation chemical space of each actinide. The nature of the mixed-ligand complexes present in solution is controlled by the concentration of free ligands in solution. A low chloride concentration is suitable to drive the speciation away from the highly thermodynamically stable hexachloride species. Furthermore, the formation of dimeric species can proceed through both olation and oxolation mechanisms. Oxolation is preferred for monomers that contain fewer water ligands, while olation becomes favorable for complexes with more water ligands.

Thermodynamic modeling of Pu(IV) and nitric acid extraction by 1.1 M tri-iso-amyl phosphate in n-dodecane

A thermodynamic model for the liquid–liquid extraction of tetravalent plutonium (Pu(IV)) by 1.1 M Tri iso Amyl Phosphate (TiAP) in n-dodecane was developed. The activity coefficients of species in the aqueous phase were estimated using eUNIQUAC activity coefficient model. The plutonium speciation in the aqueous nitric acid solution of 1–6 M concentration region was modelled by taking account of mono nitrate (Pu(NO3)3+), di nitrate $$({\text{Pu}}({\text{NO}}_{3} )_{2}^{2 + } )$$ , tetra nitrate (Pu(NO3)4) and hexa nitrate $$({\text{Pu}}({\text{NO}}_{3} )_{6}^{2 - } )$$ complexes. The eUNIQUAC activity coefficient model parameter and stability constant of tetra and hexa nitrate complexes were determined using the experimental water activity as well as extraction data. The distribution coefficient of nitric acid and Pu(IV) in the 1.1 M TiAP was estimated by accounting HNO3·TiAP, HNO3·2TiAP and Pu(NO3)4·2TiAP complexes in the organic phase. A good correlation between the estimated and experimental organic phase concentration of nitric acid and plutonium nitrate was obtained.

Speciation of Uranium and Plutonium From Nuclear Legacy Sites to the Environment: A Mini Review.

The row of 15 chemical elements from Ac to Lr with atomic numbers from 89 to 103 are known as the actinides, which are all radioactive. Among them, uranium and plutonium are the most important as they are used in the nuclear fuel cycle and nuclear weapon production. Since the beginning of national nuclear programs and nuclear tests, many radioactively contaminated nuclear legacy sites, have been formed. This mini review covers the latest experimental, modeling, and case studies of plutonium and uranium migration in the environment, including the speciation of these elements and the chemical reactions that control their migration pathways.

Unified Framework for Modeling Reactive Extraction of Metals: Illustration on Plutonium(IV) Extraction with Tri-n-butyl Phosphate

Reactive extraction of nuclear elements from aqueous nitric acid solutions using an organic solvent is an important process operation. A thermodynamic model to predict the equilibrium compositions of the two phases will be useful in optimizing the performance of such processes. A general framework is presented in this work for modeling such systems by dividing the complex reactive metal extraction system into appropriate subsystems, whose models are combined to derive the overall model. This approach reduced the number of parameters to be estimated at each stage, making the framework reliable and accurate. The procedure is illustrated for extraction of plutonium (Pu4+) using tri-n-butyl phosphate (TBP) as the organic solvent. This model for Pu extraction correctly accounts for free TBP, the dissociation of nitric acid in concentrated solutions, and formation of hydrolyzed species of plutonium to predict the distribution coefficient of Pu(IV) accurately over the practical range of nitric acid concentration...

High effectiveness of pure polydopamine in extraction of uranium and plutonium from groundwater and seawater

Sorption properties of polydopamine (PDA) for uranium and plutonium from an aqueous environment are reported at three different pH values (2, 4 and 6.5–7). In addition to deionized (DI) water, artificial groundwater (GW) and seawater (SW) were used with U uptake close to 100% in each case. PDA polymer has been identified as a material with extremely high sorption capacity Qmax ∼500 mg g−1 of the polymer at pH 6.5 and high selectivity for uranium. Similar high sorption properties are revealed for plutonium uptake. PDA-uranyl and PDA-plutonium interactions responsible for the observed adsorption processes have been addressed with a set of experimental techniques including FTIR spectroscopy, electron microscopy and cyclic voltammetry.

Experimental Speciation of Plutonium(IV) in Natural Seawater

AbstractSolubility, migration, and bioavailability of plutonium is lacunar because experimental evidences are missing. We report here on X‐ray Absorption Spectroscopy of plutonium in natural seawater. The observed valence state is +IV and its speciation corresponds to PuO2 type colloids. Furthermore, aging of the solution shows a gradient of ordering from hydroxide colloidal species to more crystalline PuO2 colloids.

Topological speciation of actinide-transferrin complexes by capillary isoelectric focusing coupled with inductively coupled plasma mass spectrometry: evidence of the non-closure of the lobes.

The determination of the binding constant between transferrin and thorium and the conformational changes of the protein upon metal complexation (thorium and plutonium) have been studied by both capillary electrophoresis (CE) and capillary isoelectric focusing (cIEF) coupled with inductively coupled plasma mass spectrometry (ICP-MS). This method allows the use of both the separation power of the cIEF and the low detection limit of ICP-MS which is critical when working with highly radioactive elements. To our knowledge, this is the first time a method coupling cIEF and ICP-MS is reported in the literature. Nitrilotriacetate was used to prevent from actinide hydrolysis and as a competitive ligand with transferrin. The binding constant for the complexation of transferrin and thorium, in the absence of bicarbonate at pH 7, was found to be log K = 18.65 ± 0.19. This value, close to that of transferrin with iron, evidenced the high affinity of the protein for thorium. The results obtained by the newly developed method, cIEF-ICPMS, showed no pI change after the addition of thorium or plutonium, whereas a pI shift (linked to conformational changes) occurred for the transferrin-indium complex. This suggests that, despite the high affinity towards the actinides, the protein does not undergo a significant structure change upon complexation. The important ionic radius of the cations Th4+ (1.05 Å, CN = 8) and Pu4+ (0.96 Å, CN = 8) with respect to Fe3+ (0.645 Å, CN = 6) and to a lesser extent to In3+ (0.800 Å, CN = 6) suggests that the transferrin lobe does not close completely after complexation. However, mixed indium-actinide complexes showed structural changes even at high concentrations of apotransferrin. The conformational change is not governed by the actinide but by the other metals present.

Laser ablation absorption spectroscopy for isotopic analysis of plutonium: Spectroscopic properties and analytical performance

Spectroscopic properties of atomic species of plutonium were investigated by combining laser ablation and resonance absorption techniques for the analysis of a plutonium oxide sample. For 17 transitions of Pu atoms and ions, the absorbance, isotope shift, and hyperfine splitting were determined via Voigt profile fitting of the recorded absorption spectra. Three transitions were selected as candidates for analytical use. Using these transitions, we investigated the analytical performance that was attainable and determined a correlation coefficient R2 between the absorbance and plutonium concentration of 0.9999, a limit of detection of 30–130ppm, and a relative standard deviation of approximately 6% for an abundance of 240Pu of 2.4%. These results demonstrate that laser ablation absorption spectroscopy is applicable to the remote isotopic analysis of highly radioactive nuclear fuels and waste materials containing multiple actinide elements.

Plutonium interaction studies with the Mont Terri Opalinus Clay isolate Sporomusa sp. MT-2.99: changes in the plutonium speciation by solvent extractions

Since plutonium could be released from nuclear waste disposal sites, the exploration of the complex interaction processes between plutonium and bacteria is necessary for an improved understanding of the fate of plutonium in the vicinity of such a nuclear waste disposal site. In this basic study, the interaction of plutonium with cells of the bacterium, Sporomusa sp. MT-2.99, isolated from Mont Terri Opalinus Clay, was investigated anaerobically (in 0.1M NaClO4) with or without adding Na-pyruvate as an electron donor. The cells displayed a strong pH-dependent affinity for Pu. In the absence of Na-pyruvate, a strong enrichment of stable Pu(V) in the supernatants was discovered, whereas Pu(IV) polymers dominated the Pu oxidation state distribution on the biomass at pH 6.1. A pH-dependent enrichment of the lower Pu oxidation states (e.g., Pu(III) at pH 6.1 which is considered to be more mobile than Pu(IV) formed at pH 4) was observed in the presence of up to 10mM Na-pyruvate. In all cases, the presence of bacterial cells enhanced removal of Pu from solution and accelerated Pu interaction reactions, e.g., biosorption and bioreduction.

Sorption and redox speciation of plutonium at the illite surface under highly saline conditions

Natural groundwater may contain high salt concentrations, such as those occurring at several potential deep geological nuclear waste repository sites. Actinide sorption to clays (e.g. illite) under saline conditions has, however, been rarely studied. Furthermore, both illite surface and ionic strength may affect redox speciation of actinides like plutonium. In the present study, Pu sorption to illite is investigated under anaerobic conditions for 3<pHm (=−log mH+)<10andmNaCl=1.0and3.2 molal (m). Results are compared with previous data for mNaCl=0.1m. According to redox potential measurements and based on Eu(III)-illite sorption data (taken as analogue of Pu(III)), the strong effect of mNaCl on overall Pu uptake observed for pHm<6 is mainly attributed to the presence of Pu(III) and its competition with Na+ for ion exchange sites. For pHm>6, overall Pu uptake is largely insensitive to mNaCl due to the prevalence of strongly adsorbed Pu(IV). By applying appropriate corrections to the activity coefficients of dissolved ions and using the 2-site protolysis non-electrostatic surface complexation and cation exchange (2 SPNE SC/CE) model, experimental data on Pu sorption to illite as a function of pH, Eh and mNaCl can be very well reproduced.

Photoreduction of Pu(V,VI) by TiO2

Abstract In this study, the effect of light on the kinetics and speciation of plutonium at its interaction with particles of TiO2 under different light conditions is shown for the first time. It was found that sorption was followed by reduction of the plutonium to Pu(IV). In this, the reduction reaction and sorption in conditions of the presence of light proceed significantly more rapidly due to the photocatalytic activity of titanium dioxide, providing a source of electrons for the reaction. Spectral methods (XAFS and TEM) showed that plutonium forms nanoclusters with the structure of PuO2, which decorate the surface of the solid phase.

Sorption and Redox Speciation of Plutonium at the Illite Surface.

The geochemical behavior of Pu strongly depends on its redox speciation. In this study, we investigated Pu sorption onto Na-illite, a relevant component of potential host rocks for high-level nuclear waste repositories, under anaerobic conditions. When contacting Pu (85% Pu(IV), 11% Pu(V), and 4% Pu(III); 8 × 10(-11) < [Pu]tot/M < 10(-8)) with illite in 0.1 M NaCl at pH between 3 and 10, Pu uptake was characterized by log Rd > 4 (Rd: distribution coefficient in L kg(-1)). Small amounts of aqueous Pu(V) were detected in solution on contact with illite after 1 week, which is not expected to be stable at the measured redox potentials (Eh) in our experiments. This observation suggests time-dependent reduction of Pu(V) to Pu(IV). After one year, log Rd values had increased compared to those after 1 week due to the reduction of weakly adsorbing Pu(V). For pH < 5, Pu(IV) and Pu(III) coexisted in solution under our experimental conditions, showing that Pu(IV) reduction to Pu(III) occurred in the illite suspension. Taking (i) surface complexation constants determined for Eu(III)-illite interaction (with redox-insensitive Eu(III) as a chemical analogue to Pu(III)), (ii) the known constant for Pu(III)-Pu(IV) redox transition, and (iii) measured Eh and pH, overall Pu uptake was well-predicted.

Sensitive redox speciation of iron, neptunium, and plutonium by capillary electrophoresis hyphenated to inductively coupled plasma sector field mass spectrometry.

The long-term safety assessment for nuclear waste repositories requires a detailed understanding of actinide (geo)chemistry. Advanced analytical tools are required to gain insight into actinide speciation in a given system. The geochemical conditions in the vicinity of a nuclear repository control the redox state of radionuclides, which in turn has a strong impact on their mobility. Besides the long-lived radionuclides plutonium (Pu) and neptunium (Np), which are key elements in high level nuclear waste, iron (Fe) represents a main component in natural systems controlling redox-related geochemical processes. Measuring the oxidation state distribution for redox sensitive radionuclides and other metal ions is challenging at trace concentrations below the detection limit of most available spectroscopic methods (≥10(-6) M). Consequently, ultrasensitive new analytical techniques are required. Capillary electrophoresis (CE) is a suitable separation method for metal cations. CE hyphenated to inductively coupled plasma sector field mass spectrometry (CE-ICP-SF-MS) was used to measure the redox speciation of Pu (III, IV, V, VI), Np (IV, V, VI), and Fe (II, III) at concentrations lower than 10(-7) M. CE coupling and separation parameters such as sample gas pressure, make up flow rate, capillary position, auxiliary gas flow, as well as the electrolyte system were optimized to obtain the maximum sensitivity. We obtain detection limits of 10(-12) M for Np and Pu. The various oxidation state species of Pu and Np in different samples were separated by application of an acetate-based electrolyte system. The separation of Fe (II) and Fe (III) was investigated using different organic complexing ligands, EDTA, and o-phenanthroline. For the Fe redox system, a limit of detection of 10(-8) M was calculated. By applying this analytical system to sorption studies, we were able to underline previously published results for the sorption behavior of Np in highly diluted concentrations, and we monitored the time-dependent reduction of Pu(VI) by Fe(II). This study clearly shows that CE-ICP-SF-MS is a suitable separation method for the redox states of Pu, Np, and Fe.