Electrorefining Cell Research Articles

Electrorefining of un-irradiated and irradiated U-6 wt. % Zr metal fuel for deposition of uranium

The present paper reports the data on electrorefining of un-irradiated and irradiated U-6 wt. % Zr (U-Zr) fuel carried out at 773 K in LiCl-KCl-UCl3 electrolyte in an augmented hot cell facility. The electrorefining cell and electrode handling system were specially designed, fabricated, and installed inside the hot cell. Potentiostatic electrorefining was employed for the selective deposition of uranium. About 61 % and 36 % of initial uranium feed was deposited during the electrorefining of un-irradiated and irradiated U-Zr fuel respectively. Current efficiencies of about 96 % and 80 % were obtained for un-irradiated and irradiated runs respectively. No significant change in concentration of uranium in the electrolyte was observed before and after the electrorefining. The co-deposition of other fission products was negligible and zirconium content in the uranium product was found to be 3 mg/g of uranium.

Ionic Mass Transfer at Point Electrodes Located at Cathode Support Plate in an Electrorefining Cell in Presence of Rectangular Turbulent Promoters

Current density plays a major role in deciding the plant size, current efficiency, and energy consumption in electrorefining cells. In general, operating current density will be 40% of the limiting current density. Forced circulation of the electrolyte in the presence of promoters improves the mass transfer coefficient. In the present study, rectangular turbulence promoters are fitted at the bottom side of the cell to improve the mass transfer coefficient at the cathode support plate. The limiting current density technique is used to measure the mass transfer coefficient. The variables covered in the present study are the effects of flow rate, promoter height, and spacing among the promoters. The electrolyte consists of copper sulfate and sulphuric acid. At a regulated flow rate, the electrolyte is pumped from the recirculation tank to the cell through an intermediate overhead tank. The limiting current density increased with an increasing flow rate in the presence of promoters, and thus the overall mass transfer coefficient on the cathode support plate also improved. With an increase in the flow rate of the electrolyte from 6.67 × 10−6 to 153.33 m3/s, limiting current density increased from 356.8 to 488.8 A/m2 for spacing of 0.30 m, with a promoter height of 0.01 m. However, it is noteworthy that when the promoter height is increased from 0.01 to 0.07 m, the overall mass transfer coefficient is found to increase up to 60%, but with the further increase in the promoter height to 0.30 m the mass transfer coefficient starts to decrease. Therefore, the optimized cell parameters are established in this work. The current sustainable concept of employing rectangular turbulence promoters will bring benefits to any precious metal refining or electrowinning tank house electrolytes.

Development of small-scale plutonium electrorefining in molten CaCl2

Molten salt extraction and electrorefining of plutonium were successfully conducted with only a 200-g initial charge. Due to this small scale, the electrorefining cell components were redesigned relative to conventional, multi-kg standards. The efficiency and yield of this small-scale process are comparable to those of larger-scale exemplars. Chemical analysis of the plutonium product and the anode heel is presented. The product was 99.8% pure. The anode heel was able to be depleted beyond the expected freezing point without significant impurity carryover.

Development and Prospect of Liquid Metal Battery: A Bidirectional Electrorefining Cell

Development and Prospect of Liquid Metal Battery: A Bidirectional Electrorefining Cell

Evaluation of flow behavior in copper electro-refining cell with different inlet arrangements

Abstract The arrangement of electrolyte inlet in the copper electro-refining (ER) cell has a great influence on the local flow field, which affects the distribution of electrical current density in consequence. In order to understand the complicated phenomena of electrolyte flow behavior in vertical counter electrodes in full-scale copper ER cell, the three-dimensional computational fluid dynamics (CFD) models with four different arrangements of electrolyte inlets, i.e., single inlet (SI), central bottom inlets (CBI), top side interlaced inlets (TII), and bottom side interlaced inlets (BII), were established to simulate the flow behavior. Simulation results have revealed that the parallel injection devices help to improve the electrolyte velocity between electrodes, and while the relative range of electrolyte velocity in CBI exceeds that of TII and BII, which is more than 4 times, indicating its severer unequal flow distribution. Meanwhile, the average velocity of electrolyte in BII is 4 times larger than that of SI due to its higher turbulence intensity. Generally, one of the efficient ways to supply fresh copper solution rapidly and uniformly into the inter-electrode space is to adapt the arrangement of BII. By utilizing such an arrangement, the electro-refining under high electrical current density is possible, and the productivity can be increased in sequence.

Two-Phase Flow Modeling of Copper Electrorefining Involving Impurity Particles

Impurity particles (slime particles) play a vital role in copper electrorefining, as they are a major source of cathodic contamination. Their behavior and transport in electrorefining cells are largely affected by electrolyte flows. Therefore, it is significant to study the fluid flow field in copper electrorefining with the consideration of impurity particles. A two-phase flow model of copper electrorefining was developed with one liquid phase of electrolyte and one dispersed phase of impurity particles. Copper electrorefining in a lab-scale cell was then simulated for two different impurity particle releasing scenarios. With impurity particle released only from the inlet, dispersed phase particles can be transported to the inter-electrode domain by electrolyte inflows through its sides rather than its bottom. Thus, the side parts of the cathode encounter more impurity particles than the center part in this scenario. With impurity particles released from both the inlet and the anode, dispersed phase particles fill up the electrorefining cell much faster, and the cathode is exposed to significant volume fractions of the dispersed phase much earlier. A large amount of impurity particles from the anode are settled on the cell bottom. The dispersed phase particles are distributed almost uniformly in front of the cathode after initial stages.

Simulation Study of Electrolyte Flow and Slime Particle Transport in a Newly Designed Copper Electrorefining Cell

A model based in COMSOL Multiphysics (a finite element analysis software) consisting of a specially designed electrorefining cell was developed to simulate copper electrorefining. This cell has its inlet on the side wall near the cell top and its outlet on the opposite side wall near the cell bottom. Copper concentration profile was acquired as electrochemical simulation results. Electrolyte flow velocity field and slime particle trajectory were obtained as fluid flow and particle transport simulation results. Features of the copper concentration profile, the electrolyte flow field, and the slime particle transport are discussed. The simulation results of this cell are compared with those of a lab-scale conventional cell, and some advantages of this cell can be found: cupric ions in the cell are more uniformly distributed with better convection in the inter-electrode domain; slime particles are more likely to settle to the cell bottom without affecting the cathode purity.

Simulation Study of Electrolyte Flow and Slime Particle Transport in a Newly Designed Copper Electrorefining Cell

A model based in COMSOL Multiphysics (a finite element analysis software) consisting of a specially designed electrorefining cell was developed to simulate copper electrorefining. This cell has its inlet on the side wall near the cell top and its outlet on the opposite side wall near the cell bottom. The electrolyte enters from the inlet, flows directly into the gap between electrodes, and exits the cell from the bottom outlet. Unlike the flow field in conventional electrorefining cells that have inlets near the cell bottom and outlets near the cell top, the natural convection between electrodes in this cell can be suppressed by the inlet flow, which leads to concurrent downward flows along both the anode and the cathode. Copper concentration profile and fluid density profile were acquired as electrochemical simulation results. Electrolyte flow velocity field, slime particle trajectory, and slime particle distribution were obtained as fluid flow and particle transport simulation results. Features of the copper concentration profile, the electrolyte flow field, and the slime particle transport are discussed. The simulation results of this cell were compared with those of a conventional cell, and some advantages of this cell can be found: copper ions in the cell are more uniformly distributed between electrodes by the strong forced convection; electrode reactions can reach steady state at higher current densities and lower electrolyte copper concentrations; slime particles are more likely to settle to the cell bottom without affecting the cathode purity.

Experimental and Simulation Studies of Electrolyte Flow and Slime Particle Transport in a Pilot Scale Copper Electrorefining Cell

Copper electrorefining tests were conducted in a pilot scale cell made of transparent cell walls, allowing direct observation and microscopic video recording of the electrolyte flow. Fluid flow velocities in the gaps between adjacent anodes and cathodes were measured by analyzing the recorded video using a video analysis and modeling software. Modeling and simulation of copper electrorefining in this cell were performed using COMSOL Multiphysics, a finite element method simulation software. The flow velocity field results from modeling agree reasonably well with the measured electrolyte velocities. The transport of slime particle in electrolyte flow was also simulated and the appearance frequencies of slime particles in the domain within 200 microns from cathode surface at different positions of cathodes were compared with impurity levels in the copper cathodes harvested from experimental tests. The results show good correlation especially with the total concentration of major impurities. Thus the cathodic contamination can be predicted by the slime particle appearance frequency in front of the cathode.

Simulation and Validation Studies of Impurity Particle Behavior in Copper Electrorefining

A model based in COMSOL Multiphysics consisting of an electrorefining cell was utilized to simulate copper electrorefining. Concentration and electrolyte density profiles were generated as electrochemical simulation results. Fluid velocity field, particle trajectories, and particle distribution maps were generated to study impurity particle behavior in electrolyte. A three factor designed set of boundary conditions was used to determine the effects of inlet flow rate, temperature, and current density on impurity particle behavior in electrolyte and the associated distribution on the cross section (slice) 100 microns away from the front surface of the cathode during copper electrorefining. The number of impurity particles on the cross section was counted for each set of boundary conditions. The model data for impurity particle distribution was compared with measured impurity particle contamination at the cathode surface, and the results show a very good correlation, which suggests the model is reasonable. The model results show the three factors have significant effects on the number of impurity particles on the cross section. The impurity particle counts at the corner positions of the slice are much higher than those at the center position of the slice. Possible explanations for the simulation results are proposed.

CFD modelling and simulation of industrial-scale copper electrorefining process

Both electrolyte flow and cupric ion concentration fields have been numerically calculated with the computational fluid dynamics (CFD) model in an industrial-scale copper electrorefining cell. In this CFD model, both of the natural convection induced by the electrochemical reactions and the forced convection caused by the electrolyte circulation are taken into account. In order to examine how the difference in the ways of the electrolyte circulation affects the electrolyte flow pattern associated with the concentration field, three different ways of the electrolyte circulation, “bottom inlet to top outlet”, “top inlet to bottom outlet”, and “side inlet to top outlet”, have been modeled.Calculation results have revealed that both “bottom inlet to top outlet” and “top inlet to bottom outlet” circulations have characteristic flow patterns that are locally formed near the inlet. On the other hand, “side inlet to top outlet” circulation forms the inherent two vortex tubes in the space below the electrodes. It is also found that the electrolyte flow patterns in the inter-electrode spaces are formed mainly by the natural convection, and they are insensitive to kinds of the electrolyte circulation way.

CFD modeling of the electrolyte flow in the copper electrorefining cell of Sarcheshmeh copper complex

Electrolytic refining is the principal method of mass producing high-purity copper in an industrial scale. In this study, a three dimensional computational fluid dynamics simulation together with experimental field measurements was applied to optimize the performance of industrial electrolysis cell in the Sarcheshmeh copper complex, Iran. The continuity, momentum equations with inclusion of buoyancy force and the copper mass concentration equation were solved by finite volume method. In order to calculate the velocity distribution in the cell, the k–ω turbulence flow model has been used. There was a good agreement between the simulation results and the experimental data of the electrolysis cell. After the validation of the model, the effects of flow pattern, copper mass concentration distribution, current density, volumetric flow rate of feed and the distance between the electrodes on the performance of the cell using CFD were studied. The results of CFD modeling show that along the cathode and anode surfaces, there were a down flow and an up flow due to natural convection, respectively. Increasing the current density caused an increase of copper mass concentration near the anodes and a decrease near the cathodes; that is in accordance with Faraday's law. Increasing the volumetric flow rate of feed caused an increase of vertical velocity near the anodes and cathodes. Decreasing the distance between electrodes caused a decrease of the natural convection between the anodes and the cathodes and increasing of copper mass concentration near the anodes.

Electro-fluid analysis of a molten-salt electrorefiner with rotating cruciform anode baskets

A computational fluid dynamics (CFD)-based multiphysics model of a molten-salt electrorefiner is presented for the computational electro-fluid analysis. A target model of the electrorefining cell presented here has a structure arranged concentrically with the cathode annulus surrounding a rotating cruciform anode inside it. This comprehensive approach of a multiphysics model solves the convective and diffusive transport of ionic uranium and allows for a prediction of the concentration present in the LiCl–KCl eutectic electrolyte between the electrodes at a current driven condition. The coupling of the local overpotential distribution and uranium concentration gradient makes it possible to predict the local current density distribution at the electrode surfaces.

Computational analysis of a molten-salt electrochemical system for nuclear waste treatment

This paper describes ongoing research into the multi-physics model development of an electrorefining process for the treatment of spent nuclear fuel. A forced convection of molten eutectic (LiCl–KCl) electrolyte in an electrorefining cell is considered to establish an appropriate electro-fluid model within the 3-dimensional framework of a conventional computational fluid dynamic model. This computational platform includes the electrochemical reaction rate of charge transfer kinetics which is described by a Butler–Volmer equation, while mass transport is considered using an ionic transport equation. The coupling of the local overpotential distribution and uranium concentration gradient makes it possible to predict the local current density distribution at the electrode surfaces.

Cathodic refining in molten salts: Removal of oxygen, sulfur and selenium from static and flowing molten copper

The removal of nonmetallic impurities, including oxygen, sulfur and selenium, from molten copper (cathode) was achieved by constant voltage electrolysis in molten BaCl2 and CaCl2 alone, or the eutectic mixture of the two at temperatures slightly higher than the melting point of copper. At the applied voltages (2.1 ∼ 2.9 V), the cathodic refining occurred without provoking the decomposition of the chloride salts, demonstrating the cathodic ionization of impurities to be responsible. Further evidence supporting this mechanism came from SEM, EDX and preliminary voltammetric studies. To increase the mass transfer of the impurities in the molten copper during the refining process, a novel recessed channel electrode (RCE) was used. The results have demonstrated the feasibility and efficiency of using this technology in terms of space, time and yield of product, offering considerable advantages over a simple electrorefining cell.

Thermochemical modelling of electrotransport of uranium and plutonium in an electrorefiner

Electrotransport behaviour of U and Pu in a molten salt electrorefining cell has been numerically simulated with an improved thermochemical model. Depending upon saturated or unsaturated states of the liquid Cd electrodes with respect to U or Pu or with both U and Pu, 16 conditions of electrorefiner cell operation have been categorised and electrotransport simulated for all the realistic conditions. Algebraic equations for determining the compositions of the salt phase and the two electrodes under each condition of electrotransport are derived. Fractional mass transport coefficients and relative fractional mass transport coefficients are derived for each condition to illustrate the electrotransport behaviour. Comparison is made between modeling with concentration dependent and concentration independent activity coefficients for U and Pu in liquid Cd. The electrotransport to a solid cathode and anodic dissolution have also been simulated. Application of the model to reprocessing of spent metallic fuel is discussed with respect to U recovery, Pu enrichment and reconstitution of the spent fuel with desired fuel composition.

Some Computations in Planning Reconstitution of a 500-MW(electric) Fast Breeder Reactor (Metallic) Fuel by Electrorefining

To compare and evaluate various fuel cycle options for a 500-MW(electric) fast breeder reactor, the electrorefining process has been examined for reprocessing spent fuel. Making use of an improved thermochemical model, optimum process conditions for electrorefining have been worked out. These conditions are the following: capacity of the electrorefining cell, number of cells, batch size, feed adjustments, sequential operations for recovery of uranium and co-recovery of uranium and plutonium, number of cycles, and timeframe to meet the refueling schedule. The spent fuel is envisaged to undergo reprocessing in three campaigns: (a) the inner core campaign, (b) the outer core campaign, and (c) the blanket and the leftover campaign. Feed adjustments are done by mixing either the spent inner core or the outer core fuels with the blankets. Three product streams with required fuel composition for direct refabrication of the inner core, the outer core, and the blanket fuel subassemblies, respectively, are obtained by certain sequential electrorefining operations. These calculations made for a mixed-oxide fuel core can be easily extended to the metallic core.

An application of confocal scanning beam laser microscopy (CSBLM) to the electrodeposition of copper

Structural characteristics of copper electrodeposition in a laboratory-scale copper electrorefining cell, studied by confocal scanning beam laser microscopy (CSBLM), are presented. Quantitative description of the roughness of the surface is provided by three-dimensional reconstructed images, and sectional depth profiles of the surface via digital image processing are shown along with surface roughness distribution. Quantitative information about the effect of current density on surface roughness is of direct interest to industrial copper electrorefining.

Investigation of Cell Resistance for Molten Salt Electrorefining of Spent Nuclear Fuel

Cell resistance for molten salt electrorefining of spent nuclear fuel under various electrode configurations was investigated by using the two-dimensional finite element method. Three electrorefining cell configurations were evaluated; (1) a liquid Cd anode and a solid cathode made of low carbon steel with or without a ceramic plate at the bottom, (2) a liquid Cd anode and a liquid Cd cathode, and (3) two anodes in the form of a perforated steel basket filled with spent nuclear fuel and two solid cathodes, in two different arrangements. The calculated results agreed reasonably well with previously obtained experimental data. The effect of polarization on the cell resistance was found to be small for a typical uranium concentration in the molten salt electrolyte and the liquid Cd anode. The calculation results are helpful in interpreting experimental data, and a correlation formula was developed that may be useful in estimating the cell resistance of new cell designs.

Investigation of Cell Resistance for Molten Salt Electrorefining of Spent Nuclear Fuel.

Cell resistance for molten salt electrorefining of spent nuclear fuel under various electrode configurations was investigated by using the two-dimensional finite element method. Three electrorefining cell configurations were evaluated; (1) a liquid Cd anode and a solid cathode made of low carbon steel with or without a ceramic plate at the bottom, (2) a liquid Cd anode and a liquid Cd cathode, and (3) two anodes in the form of a perforated steel basket filled with spent nuclear fuel and two solid cathodes, in two different arrangements. The calculated results agreed reasonably well with previously obtained experimental data. The effect of polarization on the cell resistance was found to be small for a typical uranium concentration in the molten salt electrolyte and the liquid Cd anode. The calculation results are helpful in interpreting experimental data, and a correlation formula was developed that may be useful in estimating the cell resistance of new cell designs.