Electrodeposition Of Uranium Research Articles

Uranium electrodeposition at boron-doped diamond electrodes

Uranium electrodeposition at boron-doped diamond electrodes

Phase-Field Modelling and Morphological Classification of Uranium Dendrites for the Electrorefining of Used Nuclear Fuel

Electrorefining is an important unit operation for the pyroprocessing of used nuclear fuel; however, the uncontrolled growth of uranium dendrites on the cathode is hindering its engineering application. In this study, the phase-field modelling is applied to the study of the growth of uranium dendrites using the finite element method, and the fractal dimension and the perimeter-to-area ratio are employed to classify quantitatively the morphologies of uranium dendrites. It is shown that uranium dendrites can form sprout-like, fishbone-like, and tree-like morphologies, and the effects of anisotropic strength, symmetry index, overpotential, and temperature to the morphologies of uranium dendrites are discussed. It is concluded that the diffusion of uranium cations (diffusion rate-controlling) in molten salt and the electrode kinetics (kinetic rate-controlling) are the two rate-controlling steps for the electrodeposition of uranium, and the diffusion rate-controlling mechanism is responsible for the growth of complicated dendritic morphologies.

The Application of Low-Melting LiCl-KCl-CsCl Eutectic to Electrodeposit Uranium Metal

The aim of this work is to explore the electrodeposition of uranium in low-melting LiCl-KCl-CsCl eutectic. A variety of conventional electrochemical techniques, including cyclic voltammetry (CV), chronopotentiometry (CP), and chronoamperometry (CA), were employed to study the electrochemical and kinetic properties of uranium at different temperatures ranging from 573 to 872 K. First, the electrochemical behaviors and diffusion coefficients of uranium species in the melts were investigated and compared to the published results. The temperature significantly affects the cathodic current response of the U4+/U3+ couple within the low temperature range. Moreover, the nucleation mechanisms of uranium in the electrodeposition process were evaluated, and the results indicated that nucleation and growth tend to occur via the same instantaneous mode at all applied temperatures and overpotential ranges. Finally, metallic uranium was deposited by potentiostatic electrolysis at an overpotential of −100 mV vs. U3+/U at different temperatures, and their morphologies and compositions were characterized by SEM-EDS and XRD, respectively. The results show that from 573 to 773 K, uranium deposits evolve form one-dimensional needle-like to multidimensional dendritic structures. No dendrite-free uranium deposits were obtained in the CsCl-containing melts regardless of the temperature.

Purification of LiCl–KCl eutectic waste salt containing rare earth chlorides delivered from the pyrochemical process of used nuclear fuel using a reactive distillation process

In the pyrochemical process of used nuclear fuel, the purification of waste salts containing radioactive nuclides can greatly contribute to a radioactive waste reduction. For this reason, the purification of LiCl–KCl eutectic salt containing rare earth chlorides was performed using a series of the phosphorylation process and the distillation process. LiCl–KCl eutectic salt recovered from the purification had a very low concentration (<1 ppm) for the rare earth chlorides. The recycling feasibility of the recovered salt was verified through a uranium electro-deposition test using LiCl–KCl eutectic salt as the electrolyte. Based on these results, one body type of reactive distillation equipment with two top covers was designed.

Thorium-234 Electrodeposition Using Ionic and Aqueous Uranyl Solutions

The isotope 234Th is daughter from 238U natural decay, with a half-life of 24.1 days. Then, 234Th produces 234Pa/234mPa pair, which decay to 234U, with a half-life of 6.70 h, emitting an intense beta radiation in the order of 2.2 MeV [1]. This short-lived thorium isotope has been used as a tracer for a variety of transport processes in aquatic systems [2,3]. Pourbaix diagram for aqueous solution of thorium and uranyl, as presented in Figure 1, shows that Th4+ has pref-erential hydroxide formation if compared to (UO2)2+ in pHs greater than 3. For this, some beta/alpha ratio increase is fore-seen during uranyl electrodeposition. Considering lower pHs, there is a prevalence of ionic state for either cations Th4+ or (UO2)2+. [Figure 1 – Pourbaix Diagram for uranyl solution containing thorium in low concentration.] The present work made an extensive experimentation to obtain thorium precipitation as 234Th, which happens during uranyl reduction or hydroxyl precipitation. The experimental process was as indicated below:1. Acidic solutions of 50mM [U] in UO2(NO3)2 in 2˗propanol (ionic solution: 140 experiments) and 50mM [U] UO2(NO3)2 in bidistilled water (aqueous solution: 98 experiments) with pH~1; 2. Direct cathodic polarization galvanostatic set at ˗100mA (110 experiments); 3. Pulsed cathodic polarization galvanostatic set at ˗100mA during 70 ms (“on”-stage) followed by 10 ms (“off”-stage) with a frequency of 12.5 Hz (128 experiments). The 4-graph set in Figure 2 shows the main results of the 234Th electrodeposition by means of radioactive alpha and beta emission counting. From these results, it is re-markable that the direct polarization and aqueous solu-tion has no great effect in changing the beta/alpha ratio. The level of this ratio stayed under 10, which could be a sign of preferential electrodeposition of thorium as indi-cated in Pourbaix diagram. However, when 2˗propanol uranyl electrolyte was used associated with pulse polari-zation, the results showed drastic increase of beta/alpha ratio. It reached ratio levels above 100. [Figure 2 – Results of ratio, varying with pH, from electrodeposi-tion experiments taking into account the solution type (aqueous and ionic) and the electrodeposition method (direct and pulsed). Experiments: 238 in total; 98 aqueous and 140 ionic; 110 using direct polarization and 128 using pulsed polarization.] This association of pulse polarization and ionic electro-lyte under high cathodic polarization imposed variables that are important to build up the 234Th content obtained from uranyl-solution electrodeposition in very acidic 2-propanol media, under higher cathodic polarization. This occurrence might be linked to restrictions imposed by non-protonated process by using 2-propanol solution, hindrance of water electrolysis to produce hydroxyl near the cathode and H2 evolution4,5, which promotes very acidic media around the cathode and probable hydride formation in absence of hydroxyl. As a general idea, there is a likely co-reduction of Th4+ and U4+ co-reduction, forming hydride species. The co-reduction from uranium-VI (uranyl) to uranium-IV has a feasible condition under high acidic condition, low water electrolysis and non-equilibrium of high imposed cathodic polarization4,5. When there is an exhaustion of thorium deposition in the same solution, noticed by beta-counting decreasing, it is observed that uranium electrodeposition starts more promptly, discernible by alpha-counting increasing.

Uranium Electrodeposition Using Direct Potential Technique in Less Acidic Aqueous Media

Electrodeposition of uranium is a common practice to create samples for alpha spectrometry and it could be an alternative way to produce irradiation LEU targets to fabricate radiopharmaceuticals as 99Mo used for cancer diagnosis. Usually electrodeposition of uranium uses ionic or aqueous solutions to produce uranium deposits in less acidic electrolytes (pH>2.5). During uranium electrodeposition, there is a high competition with H2 evolution, once cathodic potentials are very high. In less acidic electrolyte the electrodeposition is uranyl hydroxyl and uranium oxides compounds, formed directly from uranyl (U-VI) structure. A reliable regression equation (R2=0.836) for alpha emission activity of uranium deposition was obtained, based on cell temperature and electrodeposition time. The deposition has oxide/hydroxide nature, acting as insulator during electrochemical process. The maximum level of deposited uranium, in terms of alpha activity, was around 34 Bq.cm-2 (-1.8 VAg/AgCl, 2000 s, 60°C). In this condition, the inferred maximum amount of uranium was ~5.4 mg [U] /cm2, which might be interesting to build probe samples to simulate irradiation targets.

Uranium Electrodeposition Using Direct Potential Technique in Less Acidic Aqueous Media

Electrodeposition of uranium is a common practice to create samples for alpha spectrometry [1] and this methodology could be an alternative way to produce irradiation LEU targets [3, 4] to fabricate radiopharmaceuticals as 99Mo used for cancer diagnosis [5]. Many workers [6] studied the uranium deposition at high temperature (>200ºC) using salt baths and producing metallic uranium and alloys. The low temperature electrodeposition in ionic solutions is an ongoing investigation, mainly using RTIL way with moderate success as accounted in recent papers in the literature [7].The aqueous route to produce metallic uranium appeared to have a marginal success, using high acidity (pH <1) [8, 9]. At pH>2, it is possible to deposit the oxidized uranium compound UO2(OH)2.H2O as shown in the equilibrium diagram of molar fraction against pH presented in Figure 1.Figure 1 - Equilibrium fraction diagram of UO2(NO3)2 .6H2O solution with 50mM [U] against pH at 25°C, calculated by Medusa [2].Experimental . Aqueous solution of UO2(NO3)2 .6H2O with 50mM [U] (pH = 2.6); temperature at levels: 30°C and 60°C; electrodeposition times: 600, 1000, 1500 and 2000 s; cathodic potential of -1.80 VAg/AgCl; reference electrode: Ag/AgCl; substrate: electrodeposited Ni over an AA6061 plate.Results and Discussion. After using an aqueous solution with pH > 3, we got a precipitate which was a loose yellowish oxidized substance. Below this pH level, using the range of 2.5<pH<3, we succeeded to get a solid grayish deposit, adherent to the substrate, with . In this work, we aimed to achieve higher uranium deposition amount in a shorter time. This is crucial for technological reasons to produce commercial targets.Figure 2 – Curves representing the experimental uranium electrodeposition at two levels of temperature 30 and 60°C, along process duration.Figure 2 displays the experimental results of the uranium deposition experimentation. An equation, following an exponential decay, consistently modeled the electrodeposition rate (Radj >0.85). The alpha-emission is directed related to 238U+235U amount. The gradient of alpha activity in DPS (Bq/cm2) by time was found to be represented by:dDPS/dt=A+B.exp(-t/Q)The fitted parameters were: A-parameter varying from 38.7 (30°C) to 75.8 (60°C); B from -52.2 (30°C) to -41.7 (60°C) and Q from 723.4 (30°C) to 2640.8 (60°C). B and Q, with proper units, represent the driving force parameters given by the temperature increase. An apparent deceleration of the process seems to occur, probably due to the properties of deposited uranium compound as insulator.Acknowledgement. Thanks are due to FAPESP for granting this research by the project PJ2013/08614-3.

Pulse Electrodeposition of Natural Uranium in 2-Propanol Acidic Ionic Solution

A regular way to produce samples for alpha-spectrometry and other nuclear emissions could be by means of electrodeposition. Uranium electrodeposition may also be used to fabricate irradiation targets for radiopharmaceutical production. In this work, the electrodeposition of natural uranium was made by pulsed potential in galvanostatic state over nickel substrate, having a cathodic area of 2 cm2. The samples have been exposed to UO2(NO3)2 acidic concentrated solution diluted 1:20 in 2-propanol, having final concentration at 50 mM [U] with pH<1. The pulsed potential varied between two levels, from 0 V to −10 V and from 0 V to −15 V, inside a tubular electrochemical cell made of quartz. The pulsed electrodeposition had a rectangular potential wave with duty cycle of 75% and a frequency of 25 Hz, with a constant duration of 1400 s. The higher alpha emission activity that was obtained from the oxide/hydroxide electrodeposit reached the level of 30 Bq/cm2 for a cathodic potential polarization at 0V/-15V during 1400 s of pulsed electrodeposition. Explanation of uranium electrodeposition at lower pHs was based on potential migration of polarity at the cathode during pulsing potential, allowing production of OH- and nascent oxygen in anodic microregions.

Production of double-sided targets by electrodeposition: initial evaluation and optimization of performance

The Detector for Advanced Neutron Capture Experiments (DANCE) located at the Los Alamos Neutron Science Center is used to perform neutron capture cross-section measurements on radioactive and non-radioactive isotopes. Thin actinide targets for the DANCE detector are typically prepared by molecular deposition on thin titanium foils. For the preparation of double-sided deposits, a Teflon electrodeposition cell was constructed with two liquid chambers with a foil substrate in between, allowing electrodeposition on both sides of the foil. We have been studying the electrodeposition of uranium from isopropyl alcohol solutions using this cell. Effects of acid composition, uranium concentration, current, and deposition time will be described.

A phase-field simulation of uranium dendrite growth on the cathode in the electrorefining process

The uranium dendrite growth on the cathode during the pyroprocessing of uranium is investigated using a novel phase-field model, in which electrodeposition of uranium and zirconium from the molten-salt is taken into account. The threshold concentration of zirconium in the molten salt demarcating the dendritic and planar growth is then estimated as a function of the current density. Moreover, the growth process of both the dendritic and planar electrodeposits has been demonstrated by way of varying the mobility of the phase field, which consists of the effect of attachment kinetics and diffusion.

Performance of the mesh-type liquid cadmium cathode structure for the electrodeposition of uranium from the molten salt

Abstract A mesh-type liquid cadmium cathode (LCC) structure has been devised to improve the performance of the electro-winning process for the recovery of actinides in a molten chloride system. For the verification of its performance, electrodeposition experiments of uranium from the molten LiCl-KCl-UCl3 salt were conducted at 773 K for different current densities using the mesh-type LCC structure. Uranium was successfully collected over 5ߙwt.ߙ% in the LCC without growing uranium dendrites. The mesh-type LCC structure prevented the uncontrolled growth of uranium dendrites into the electrolyte phase above the cadmium surface and caused the LCC deposit to accumulate at the higher in the cadmium phase over uranium solubility in cadmium. After cooling the LCC crucible, its solid deposits were identified as an intermetallic compound UCd11 by EPMA and XRD analysis. The cathode potential profiles from the electrochemical experiments and the chemical structure of the LCC deposits showed that it could be applied practically to recover the actinides above their solubility in cadmium.

Nanoscopic study of chemical species during uranium electrodeposition for alpha spectrometry sources

High resolution alpha spectrometry (AS) is commonly applied for the determination of actinides and other alpha-emitting nuclides in many applications. Electrodeposition is the standard procedure for preparing α-particle sources usually made of a thin and uniform radioactive deposit onto a metallic substrate. Natural U sources prepared by the Hallstadius method are known to contain co-deposited Pt from the anode. In this sense, the main aim of this work is to conclusively review the behaviour of Pt and U in the electrodeposition process and their distribution in the resulting deposit, factors that are responsible for the thickness and uniformity of the sources. In addition to new scanning electron microscopy/energy dispersive spectroscopy (SEM–EDX) and X-ray absorption fine structure (XAFS) data, the electrodeposited surface has been analyzed using both atomic force microscopy (AFM) and synchrotron radiation Grazing Incidence X-ray diffraction (GI-XRD). The results concerning morphology of the deposit, surface roughness, topography and surface structure obtained from sources prepared at different electrodeposition times agree with the AS results concerning electrodeposition yield and spectral resolution.

Electrochemical behaviour of uranium (IV) in DMF at vitreous carbon

The electrochemical behaviour of UCl 4 (0.01 mol L −1 up to 0.05 mol L −1) in 0.1 mol L −1 TBAPF 6/DMF solution at vitreous carbon was studied, at room temperature, by cyclic voltammetry and potentiostatic techniques. The electrolytic solutions were analyzed by UV spectroscopy (UV), and the electrodeposited films were characterized by Rutherford Backscattering Spectroscopy (RBS) and X-ray diffraction (XRD). The cyclic voltammetric results, at low UCl 4 concentrations (0.01 mol L −1), point that the reduction of U(IV) to U(0) occurs in two steps involving mainly U(IV) and U(III) species. The first electron transfer reaction is quasi-reversible and the second irreversible. The diffusion coefficient of U(IV) in DMF and the charge rate constant were determined to be 4.78 × 10 −7 cm 2 s −1 and 1.93 × 10 −3 cm s −1 (at 0.02 V s −1), respectively. RBS data obtained from samples prepared at constant potential (−3.10 V) during 3 h at room temperature, indicated the presence of uranium particles deposited all over the vitreous carbon surface with aggregates in some places, confirming that the second reduction step corresponds to uranium electrodeposition. No crystallographic ordering could be seen by XRD, pointing to an amorphous character of the uranium films.

Evolution of chemical species during electrodeposition of uranium for alpha spectrometry by the Hallstadius method

The morphology and composition of uranium alpha sources with co-deposited platinum have been investigated by scanning electron microscopy (SEM) with energy dispersive X-ray fluorescence analysis (EDX), X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) studies. Combined SEM and EDX measurements reveal the effect of porous platinum on the morphology of the sources which in turn affects their alpha-spectral resolution. The XPS analysis suggests that the presence of platinum initially increases the concentration of hydroxyl species in the deposits, which then act as centres for subsequent preferential uranium precipitation. XPS and XAFS analysis also provide for first time an indication of oxidation states of uranium present in the sources prepared by the Hallstadius method. These results are in line with Hansen's theory of electrodeposition of actinides.

Studies on applications of room temperature ionic liquids

Room temperature ionic liquids (RTILs) have many potential applications in nuclear fuel cycle, especially actinide and fission product separations. This paper outlines the results of work in our Centre directed towards identifying specific applications with respect to recovery of uranium and palladium from nitric acid media. The use of RTILs as diluents for extraction processes as well as electrolysis media have been explored. The extraction of uranium(VI) and palladium(II) from nitric acid medium by tri- n-butyl phosphate solution in RTIL has been studied. Voltammetric investigations on the suitability of RTIL as electrolytic medium for the electrodeposition of uranium and palladium at near ambient conditions are reported. The feasibility of electrodeposition of uranium as uranium oxide (UO 2) and palladium(II) as metallic palladium from the loaded organic phase has been demonstrated.

Determination of 234U/238U isotope ratios in environmental waters by quadrupole ICP-MS after U stripping from alpha-spectrometry counting sources

The 234U/238U isotope ratio has been widely used as a tracer for geochemical processes in underground aquifers. Quadrupole-based inductively coupled plasma mass spectrometry (ICP-MS) equipped with a high-efficiency nebulizer and a membrane desolvator was employed for the determination of 234U/238U isotope ratios in natural water samples. The instrumental limit of detection for 234U was at the low pg L(-1) level with very low sample consumption. Measurement precision (234U/238U) was 3-5% for bottled mineral water with elevated uranium concentration (>1 microg L(-1)). For the analysis of groundwater samples from the Almonte-Marisma underground aquifer (Huelva, Spain), uranium was stripped from stainless steel planchets that had previously been used as radiometric counting sources for alpha-particle spectrometry. Potential spectral interferences from other metals introduced during the dissolution were investigated. Matrix-matched blank solutions were needed to subtract the background on 234U due to the formation of platinum argides, and to allow for mass bias correction and background correction. The Pt appears to be an impurity present in the stainless steel, either as a minor component by itself or after extraction from the anode and a subsequent uranium electrodeposition. The 234U/238U isotope ratio data were in very good agreement with those of alpha spectrometry, while precision was improved by a factor of up to 10 and counting time was reduced down to approximately 20 min (10 replicate measurements).

Electrodeposition of uranium in dimethyl sulfoxide and its inhibition by acetylacetone as studied by EQCM

In the study of the all-uranium redox-flow battery with a high efficiency, electrochemical investigations of the negative electrode reaction, i.e. U(IV)/U(III) of uranium β-diketone complexes, is necessary in aprotic solvents. In our recent studies, the uranium(IV) acelylacetonate, known to show the simplest voltammograms due to a quasi-reversible U(IV)/U(III) reaction at −2.6 V versus Fc/Fc + in the solvent with the small donor number, shows more complicated voltammograms in the solvents with the larger donor numbers such as dimethyl sulfoxide (DMSO). For U 4+ ion without acetylacetone in such solvents, several researchers reported an electrodeposition at around −1.6 to −2 V versus Fc/Fc +, whereas its details have not known at all. Therefore in this study, the electrode reactions of the U(IV)/U(III) and the U(III)/U(0) reaction of U(dmso) 8(ClO 4) 4 were investigated by direct monitoring of weight changes of a Au electrode during potential sweeps by using the EQCM, as well as the HMDE. Also, an inhibition of the uranium electrodeposition by an addition of the acetylacetone was investigated.

Metal Electrodeposition and Electron Transfer Studies of Uranium Compounds in Room Temperature Ionic Liquids

Room temperature ionic liquids (RTIL's) comprised of 1,3-dialkylimidazolium or quaternary ammonium cations and one of several anions such as PF{sub 6}{sup -}, BF{sub 4}{sup -}, or {sup -}N(SO{sub 2}CF{sub 3}){sub 2}, represent a class of solvents that possess great potential for use in applications employing electrochemical procedures. Part of the intrigue with RTIL's stems from some of their inherent solvent properties including negligible vapor pressure, good conductivity, high chemical and thermal stability, and non-flammability. Additionally, a substantial number of RTIL's can be envisioned simply by combining different cation and anion pairs, thereby making them attractive for specific application needs. We are interested in learning more about the possible use of RTIL's within the nuclear industry. In this regard our research team has been exploring the electron transfer behavior of simple metal ions in addition to coordination and organometallic complexes in these novel solvents. Results from our research have also provided us with insight into the bonding interactions between our current anion of choice, bis(trifluoromethylsulfonyl)imide = NTf{sub 2}, and open coordination sites on actinide and transition metal fragments. This presentation will focus on recent results in two areas: the electrodeposition of electropositive metal ions from RTIL solutions and the electron transfermore » behavior for several uranium complexes. Details concerning the cathodic electrodeposition and anodic stripping of alkali metals (Na, K) from various working electrode surfaces (Pt, Au, W, Glassy Carbon) will be discussed. Figure 1 displays typical behavior for the electrodeposition of potassium metal from an RTIL containing potassium ions produced through the reaction of KH with H[NTf{sub 2}]. Our efforts with other metal ions, including our results to date with uranium electrodeposition, will be covered during the presentation. The electron transfer behavior for a number of uranium complexes have been studied with various electrochemical methods including cyclic and square-wave voltammetry, chronoamperometry, and bulk coulometry. Results from these studies will be presented to show the general electron transfer behavior of metal complexes in the RTIL's. As an example, Figure 2 shows the difference in chemical stability of an electrogenerated U(V) anion for two uranyl (U(VI)O{sub 2}{sup 2+}) complexes due to the difference in ancillary ligands about the uranyl moiety. Figure 2a shows a cyclic voltammogram (CV) for the U(VI)/U(V) couple of a uranyl complex containing a multi-dentate chelating nitrogen/oxygen ligand (inset in figure). The couple is both chemically and electrochemically reversible. The CV in Figure 2b is that of [UO{sub 2}Cl{sub 4}]{sup 2-} in which the electrogenerated U(V) derivative is unstable yielding a chemically irreversible wave. For the compound giving rise to the CV in Figure 2a its electrochemical behavior in a conventional nonaqueous electrolyte medium is very similar to that obtained in the RTIL. While this result does not illustrate a distinct advantage for employing the RTIL solvent in this particular case, we believe it effectively demonstrates the ability of the RTIL to be utilized as a solvent/electrolyte medium for detailed electrochemical studies without severe limitations.« less

Electrodeposition of Uranium and Transuranic Elements onto Solid Cathode in LiCl-KCl/Cd System for Pyrometallurgical Partitioning

A pyrometallurgical partitioning process is being developed for recovering transuranic elements (TRUs) from high-level liquid waste. In the process, actinides are separated from fission product, especially rare earth elements (REs), by means of an electrorefining technique or a reductive-extraction technique. In this study, electrorefining experiments were carried out in LiClKCl/Cd system to recover actinides from salt bath containing actinides and REs. Uranium and neptunium could be depleted from the salt bath and recovered onto a solid cathode with high collection efficiency and high selectivity. Plutonium and americium, however, were difficult to be recovered at high current efficiency because reduction of Nd3+ to Nd2+ at about—1.7V consumed cathodic current prior to the deposition of Pu or Am. The rotation of the cathode had rather negative effect against deposition of Am and Pu in case of coexistence of much amount of Nd because Nd2+ was removed from the cathode surface quickly and the reaction of Nd3+ to Nd2+ was promoted. At higher current density, Pu and Am could be recovered onto solid cathode but current efficiency became too low. The result indicated that electrorefining technique in the pyro-partitioning was effective for U and Np but not for Pu and Am.

Electrodeposition of Uranium and Transuranic Elements onto Solid Cathode in LiCl-KCl/Cd System for Pyrometallurgical Partitioning

Electrodeposition of Uranium and Transuranic Elements onto Solid Cathode in LiCl-KCl/Cd System for Pyrometallurgical Partitioning