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The thermodynamic and transport properties of high-temperature chloride molten salt systems are of great significance for spent fuel reprocessing in the field of nuclear energy engineering. Here, by using machine learning based deep potential (DP) method, we train a high-precision force field model for the LiCl-KCl-LiF system. During force field training, adding new dataset through multiple iterations improves the accuracy of the force field model and its applicability to more configurations. The comparison of density functional theory (DFT) and DP results for the test dataset indicates that our trained DP model has the same accuracy as DFT. Then, we comprehensively investigate the local structure, thermophysical properties, and transport properties of the LiCl-KCl and LiCl-KCl-LiF molten salt systems using the trained DP model. The effects of temperature and LiF concentration on the above properties are analyzed. This work provides guidance for the training of machine learning force fields in molten salt systems and the study of basic physical properties of high-temperature chloride molten salt systems.

The electrorefining of spent metallic fuels is conducted in LiCl–KCl eutectic–based salt to recycle U, Pu, and minor actinides when chemically active fission products of rare earth, alkali, and alkaline-earth metals accumulate in the salt. For removing the fission products from the salt, a batchwise multistage countercurrent extraction technique using a liquid Cd solvent and a Li reductant was investigated and found to achieve both a high recovery ratio of actinides and a sufficient degree of separation from rare earths. Vessels containing salt were prepared in accordance with the number of stages, and a smaller vessel containing liquid Cd was immersed in them sequentially to extract actinides from the salt. This operation is simple and reliable. The results calculated using the equilibrium separation factors reported in the literature suggested that four-stage extraction offers satisfactory performance for the separation of actinides from rare earths: more than 80% of Nd remained in the salt when 99.9% of Pu was recovered. Moreover, demonstration tests were conducted using Nd and Dy as surrogates of actinides and rare earths, respectively. The separation factor between Dy and Nd was determined to be 21, which was approximately equal to that between Nd and Pu reported in the literature. It was shown that the experimental results of extracting Nd while leaving Dy in the salt were in good agreement with the calculated results. In conclusion, batchwise multistage countercurrent extraction was proved to be a promising actinide separation method. [ABSTRACT FROM AUTHOR]

This work concerns the electrochemical behaviors of La3+ on W electrodes in the LiCl-KCl-LaCl3 molten salt at 723-813 K. The results show that La3+ is reduced at about -2.04 V(vs. Ag/AgCl) on inert W electrode, which is a one-step three-electron transfer process. The redox potential, Gibbs free energy and activity coefficient of La3+/La are calculated by open circuit chronopotentiometry on W electrode in LiCl-KCl-LaCl3 molten salt. Potentiometric titration was used to study the reaction of lanthanum chloride with oxide ions. The titration curve shows that the precipitate of oxide is LaOCl. According to the experimental apparent electrode potential, activity coefficient and relevant thermodynamic data, the phase diagram of La-O stability was drawn. The stable phase diagram of E-pO2- shows that LaOCl is the most stable compound in the range of higher O2- concentration at 723 K.

In this work, EIS was applied to characterize the temporal recovery of uranium from UCl4 onto a tungsten electrode in molten LiCl-KCl salt between sets of pulse reverse-pulse (PRP) deposition steps. Impedance measurements were fitted to an equivalent circuit (EC) model of the electrode interface using Simplex optimization to calculate the double layer capacitance, charge transfer resistance, Warburg impedance, and CPE-restricted diffusion. Diffusion of uranium towards the electrode surface dominated the surface interactions for the first 80 cycles, followed by a transition to kinetic control for the remaining 520 cycles. A decrease in the Warburg impedance showed depletion of uranium from the bulk melt, which was confirmed to be a 52.5% reduction through ICP-OES. Reduction in the phasance from CPE-restricted diffusion suggested the formation of pores in the uranium deposits, which was confirmed through SEM characterization.

High temperature molten salt corrosion is of utmost importance for selecting and qualifying structural materials for critical applications. Pyrochemical reprocessing of spent metallic fuels of the future fast breeder reactors in India is widely considered. One of the main processes of pyrochemical reprocessing is electrorefining. Electrorefining is generally conducted in LiCl–KCl molten salt at 500–600 °C under an inert atmosphere. Research groups worldwide are involved in developing corrosion resistant materials and investigating the corrosion behaviour of various structural materials for LiCl–KCl applications under different environments. A wide variety of materials, including metals, alloys, intermetallics, single crystals, glass and ceramics, have been investigated in molten LiCl–KCl salt. This review focuses mainly on the corrosion assessment of materials for LiCl–KCl application; a complete literature review with emphasis on the corrosion issues of materials is provided. This paper reviews the corrosion issues of metals and alloys in molten salts and the selection criteria of corrosion-resistant materials for molten salts. Understanding the molten salt corrosion mechanisms and future research scope are also discussed. [ABSTRACT FROM AUTHOR]

The chlorination of UO2 in presence of Nd2O3, Pr6O11, CeO2 and La2O3 in LiCl–KCl melt using AlCl3 and Al metal at 773 K is studied here. All the oxides were chlorinated and the extent of conversion of UO2, Nd2O3 and Pr6O11 was quantified through UV–Vis spectroscopy whereas for quantification of CeO2 and La2O3, inductively coupled plasma optical emission spectroscopy (ICP-OES) was employed. Conversion of ~ 92% for UO2 and ~ 95% for lanthanide (Nd, Pr) oxide was achieved when each of them was chlorinated independently. The results showed that the presence of even a single lanthanide oxide reduces the conversion efficiency of UO2. The conversion efficiency of UO2 in presence of all the lanthanide oxides studied here decreased by nearly 12%. The effect of lanthanide oxides on the chlorination of UO2 using AlCl3 and Al metal and their quantification by UV–Vis spectrophotometry is reported in the present study. [ABSTRACT FROM AUTHOR]

In this paper, the reaction kinetic mechanism of La3+ was studied in the LiCl-KCl eutectic salt at various temperatures. First, the diffusion coefficient of La3+(D) measured by cyclic voltammetry(CV) increases from 3.06×10-5 cm2/s to 6.08×10-5 cm2/s with the temperature ranging from 723 K to 873 K, and the activation energy of La3+ diffusion(ED) in the molten salts is 34.51 kJ/mol calculated by the Arrhenius equation. Subsequently, the kinetic parameters of La3+ on the W electrode were studied by the electrochemical impedance spectroscopy(EIS). In the temperature range of 723-873 K, the exchange current density(i0) is measured to be 0.48-1.39 A/cm2, and the reaction rate constant(k0) is determined as 2.04×10-4-5.90×10-4 cm/s. Moreover, the corresponding reaction activation energy(Ea) is found to be 35.04 kJ/mol. The Nyquist plots and the fitted circuit diagrams explored the reaction kinetic mechanism of La3+ on a W electrode. It was illustrated that the electrochemical reduction rate of La3+ in the LiCl-KCl eutectic salt is controlled by diffusion and charge transfer, and it is positively correlated with temperature.

Pyroprocessing of spent nuclear fuels uses the LiCl–KCl molten salt as an electrolyte, which contains dissolved fission products and can be very corrosive to the structural alloys. This study investigates the effect of EuCl3 on the corrosion behavior of four commercial alloys: Haynes C276, Inconel 600, Incoloy 800, and 316L stainless steel. Static immersion tests and electrochemical polarization measurements were carried out in molten LiCl–KCl salts with and without EuCl3 additives at 500°C. The results showed that the presence of EuCl3 caused the severe dissolution of Ni, Fe, and Cr from alloys, accompanied by the cathodic reduction of EuCl3 to EuCl2. All alloys suffered from intergranular dissolution and cracking, with additional pitting and void attacks for Incoloy 800 and 316L stainless steel.

The kinetic and thermodynamic properties of La(III) in LiCl–KCl–LaCl3 melts on inert electrode (Mo) were investigated by different electrochemical methods. The reduction of La(III) into metallic La on the Mo electrode is a quasi-reversible process that can transfer three electrons in a single step. In the temperature range of 723–848 K, the diffusion coefficient and reaction activation energy of La(III) in LiCl–KCl–LaCl3 melts were calculated using Cyclic voltammetry (CV) and Chronopotentiometry (CP). Moreover, relationships between the diffusion coefficient with temperature were formulated as follows: lnD0 = − 3.32/T + 5.27 (CV) and lnD0 = − 4.7/T − 5.89 (CP). The dependence of exchange current density of La(III)/La(0) on the experimental temperatures was constructed by Tafel (lnj0 = − 2.04/T − 1.93) and Linear polarization (LP) (lnj0 = − 2.74/T − 0.912). The apparent electrode potentials, Gibbs free energy, and activity coefficient of La(III)/La(0) were estimated using Open-circuit chronopotentiometry (OCP). Different LaCl3 concentrations were added to LiCl–KCl melts, and the ion concentration of La(III) in the melts was determined using Normal Pulse Voltammetry (NPV). The obtained results had a relative error of less than 10% when compared to the ICP results. It shows that the results obtained by NPV detection are accurate and reliable.Graphical abstract: The kinetic and thermodynamic properties of La(III) in LiCl–KCl–LaCl3 melts on inert electrode (Mo) were investigated by different electrochemical methods. The reduction of La(III) into metallic La on the Mo electrode is a quasi-reversible process that can transfer three electrons in a single step. In the temperature range of 723–848 K, the diffusion coefficient and reaction activation energy of La(III) in LiCl–KCl–LaCl3 melts were calculated using Cyclic voltammetry (CV) and Chronopotentiometry (CP). Moreover, relationships between the diffusion coefficient with temperature were formulated as follows: lnD0 = − 3.32/T + 5.27 (CV) and lnD0 = − 4.7/T − 5.89 (CP). The dependence of exchange current density of La(III)/La(0) on the experimental temperatures was constructed by Tafel (lnj0 = − 2.04/T − 1.93) and Linear polarization (LP) (lnj0 = − 2.74/T − 0.912). The apparent electrode potentials, Gibbs free energy, and activity coefficient of La(III)/La(0) were estimated using Open-circuit chronopotentiometry (OCP). Different LaCl3 concentrations were added to LiCl–KCl melts, and the ion concentration of La(III) in the melts was determined using Normal Pulse Voltammetry (NPV). The obtained results had a relative error of less than 10% when compared to the ICP results. It shows that the results obtained by NPV detection are accurate and reliable. [ABSTRACT FROM AUTHOR]

The electrochemical behavior of Yb(III) was studied at a W electrode in LiCl–KCl–ZnCl2 molten salt system. Cyclic voltammetry, square wave voltammetry, open circuit chronopotentiometry, and chronopotentiometry were used to investigate the electrochemical co-deposition of Yb(III) and Zn(II) in LiCl–KCl melt. Extraction efficiency of Yb(III) from LiCl–KCl–ZnCl2 melt was calculated to be 99.49% after potentiostatic electrolysis for 40 h. Zn–Yb alloys were prepared by galvanostatic electrolysis through co-deposition of Zn(II) and Yb(III) for 3 h. XRD and SEM–EDS were used to analyze the components and morphology. YbZn2 intermetallic compound is the most stable product under the experimental electrolysis conditions. [ABSTRACT FROM AUTHOR]

In situ energy-dispersive X-ray diffraction was employed to investigate electrochemical Dy–Ni alloying in molten LiCl–KCl at 723 K. This enabled the determination of the crystal structures and orientations of the products formed during molten salt electrolysis, while also eliminating the effects of the post-electrolysis processes (such as cooling and washing) that are necessary in ex situ measurements. The diffraction peak intensities of DyNi2 generally increased during potentiostatic electrolysis at 0.50 V vs. Li+/Li, whereas the Ni diffraction peak intensities gradually decreased. Furthermore, the intensity of the X-ray fluorescence peak of Dy gradually increased. Thus, DyNi2 could be directly formed from Ni via electrolysis, as no diffraction peaks corresponding to materials other than Ni and DyNi2 were observed. Moreover, (022)-oriented DyNi2 grew preferentially on the (200)-oriented Ni substrate.

In this paper, the electrochemical behaviors of Pb(II) and Pr(III) were investigated on W electrode in LiCl–KCl melts, respectively. The results illustrated that the reduction of Pb(II) and Pr(III) was a one step process. When the PbCl2 and PrCl3 co-existed in the molten salt, the cyclic voltammetry, square wave voltammetry and open circuit chronopotentiometry illustrated that four kinds of Pb-Pr intermetallic compounds were formed at 773 K. Whereafter, the electrochemical behavior of Pr(III) on liquid Pb cathode was studied by cyclic voltammetry in LiCl–KCl melts, and the result showed that only one kind of Pb-Pr intermetallic compound was formed at 773 K. The Pr element was extracted by galvanostatic and potentiostatic electrolysis with the assistance of Pb cathode in LiCl–KCl–PrCl3 melts, respectively. Finally, the obtained alloys were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), and the result illustrated that the prepared intermetallic compound mainly is Pb3Pr. [ABSTRACT FROM AUTHOR]

In this work, laser induced breakdown spectroscopic (LIBS) technique is utilized to estimate U in presence of large excess of lithium and potassium chloride (LiCl–KCl) or Cd mixtures. Colloidal solution of hydroxides of U, produced by adding NaOH was spread over filter paper and subjected to LIBS analysis after drying in air. Nearly 50 times enhancement in the LIBS signal was found as compared to normal solution. Using Er as an internal standard, emission line of U(II) at 385.957 nm shows linearity from 50 to 600 ppm. The detection limit of U was found to be 21 ppm. The presence of 5% LiCl–KCl salt or 3% Cd does not alter the calibration plot significantly. The estimations of U in synthetic samples agree well with the values measured by spectrophotometric method. [ABSTRACT FROM AUTHOR]

This study presents an experimental investigation on Zr separation from Zr-2.5Nb by anode potentiostatic electrorefining in LiCl-KCl-ZrCl4 0.5 wt. % at 773 K for irradiated CANDU pressure tube decontamination. By the ORIGEN-2 code calculation, radioactive characteristics were investigated to show that Nb-94 was the most significant radionuclide with an aspect of waste level reduction by electrorefining. Three electrorefining tests were performed by fixing the applied potential as −0.9 V (vs. Ag/AgCl 1 wt. %) at the anode to dissolve only Zr. A cathode basket was installed to collect detached deposits from the cathode. Electrorefining results showed Zr was deposited on the cathode with a small amount of Nb and other alloying elements. The chemical form of the cathode deposits was shown to be only Zr metal or a mixture of Zr metal and ZrCl, depending on the experimental conditions related to the surface area ratio of the cathode to the anode. It was determined that the Zr metal reduction at the cathode was attributed to the two-step reduction reaction of Zr4+/ZrCl and ZrCl/Zr. [ABSTRACT FROM AUTHOR]

The distillation behaviors of some fission product fluorides in LiCl–KCl system were investigated. For rare earth element, the corresponding decontamination factors (DFs) of Ce in 5 wt% CeF3–LiCl–KCl salts were over 100 at 1040 K and 13 Pa. For SrF2, the very poor DFs was deduced for the presence of more volatile SrClF, while Zr4+ was observed to complex easily with F− and Cl−, which affected its evaporation rate and the separation efficiency. F ion concentration in condensate salt was 1–2 level higher than the metal ion due to the stronger covalent band. [ABSTRACT FROM AUTHOR]

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-UCl 3 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. [ABSTRACT FROM AUTHOR]

This paper reports the hygroscopic properties of eutectic LiCl-KCl after absorption into zeolite-4A, up to salt loadings of 75 wt%. Samples of the salt occluded zeolite were hydrated in a humidity chamber at constant temperature and relative humidity for up to 100 h. At up to 45 wt% salt loading, the un-occluded phase of salt consisted primarily of NaCl, which forms when the Na+ ions present in the zeolite framework exchange with Li+ and K+ ions from the eutectic LiCl-KCl. This results in minimal water absorption and corrosion of contacted stainless steel. At greater than 45 wt% salt loading, water absorption and corrosion progressively worsened. The mixture has a significant amount of excess LiCl-KCl, making it highly hygroscopic. This study reveals an option for the intermediate treatment of waste salt from spent nuclear fuel electrorefiners that could facilitate it to be stored in a non-inert atmosphere for extended periods of time before final conversion into a permanent waste form. [ABSTRACT FROM AUTHOR]

This study presents an experimental investigation on Zr separation from Zr-2.5Nb by anode potentiostatic electrorefining in LiCl-KCl-ZrCl4 0.5 wt. % at 773 K for irradiated CANDU pressure tube decontamination. By the ORIGEN-2 code calculation, radioactive characteristics were investigated to show that Nb-94 was the most significant radionuclide with an aspect of waste level reduction by electrorefining. Three electrorefining tests were performed by fixing the applied potential as −0.9 V (vs. Ag/AgCl 1 wt. %) at the anode to dissolve only Zr. A cathode basket was installed to collect detached deposits from the cathode. Electrorefining results showed Zr was deposited on the cathode with a small amount of Nb and other alloying elements. The chemical form of the cathode deposits was shown to be only Zr metal or a mixture of Zr metal and ZrCl, depending on the experimental conditions related to the surface area ratio of the cathode to the anode. It was determined that the Zr metal reduction at the cathode was attributed to the two-step reduction reaction of Zr4+/ZrCl and ZrCl/Zr.

Electrochemical and kinetic properties of samarium (Sm) in LiCl–KCl eutectic salt were investigated at various concentrations and temperatures. Cyclic voltammetry (CV) were performed to determine diffusion coefficient and the rate constant (k0). In addition, electrochemical impedance spectroscopy (EIS) was conducted for further understandings on the kinetic behaviors of Sm(III)/Sm(II) couple. The values of the diffusion coefficients were in the range of 3.54 × 10−6 to 9.58 × 10−5 cm2 s−1 and the values of k0 were estimated to be in the range of 0.63 × 10−2 to 1.11 × 10−2 cm s−1. The values of i0 for Sm(III)/Sm(II) were computed by obtaining the charge transfer resistance from the curve fitting analysis, ranging from 1.04 × 10−3 to 2.97 × 10−3 A cm−2. [ABSTRACT FROM AUTHOR]

In this study, the electrochemical behaviors of niobium were examined with 1.0 wt% of NbCl 5 in the molten LiCl–KCl at 450 °C via different electrochemical techniques. A chronoamperometry was performed to prepare solutions containing the selected oxidation state of the Nb ion, and the color of the solution was compared to the literature data. Cyclic voltammetries were performed with a combination of different scan ranges and scan rates using an electrochemical cell prepared by LiCl–KCl–NbCl 5 salt mixture and an inert tungsten electrode. Five oxidation and four reduction peaks were found, and possible redox reactions attributing to each peak were identified based on the rate of change of the current density as a function of the scan rate. It was found that Nb(V) can be deposited as a metallic Nb via Nb(IV), Nb(III), and Nb(II), and the deposition of the metallic Nb is perturbed by the formation of insoluble nonstoichiometric Nb chloride compounds on the electrode surface. Three irreversible oxidation peaks were caused by the oxidation of metallic Nb and insoluble Nb chlorides, which competed with each other, but the dissolution of metallic Nb became dominant as the scan rate increased. X-ray diffraction analysis was performed to examine the possibility of a chemical reduction of Nb(V) to Nb(IV), but no evidence was found, which indicated the initial concentration of Nb(V) was preserved in all the experiments. It was also found that the different pyrochemical processes would desirable to separate Nb for the purpose of salt purification as well as volume reduction of radioactive waste, depending on the electrochemical behaviors for other elements that can be simultaneously dissolved with Nb. • Electrochemical behaviors of Nb in LiCl–KCl were identified by cyclic voltammetry. • Apparent potentials for redox reactions of Nb are verified with literature. • Pyrochemical decontamination processes for Nb-containing wastes are proposed. [ABSTRACT FROM AUTHOR]

A fast, precise and simple spectrophotometric method was developed for the estimation of uranium in LiCl–KCl salt matrix using phosphoric acid as a complexing agent. The 421 nm absorbance peak of uranium was found to be spectral interference free and area of this peak was used for the quantitative analysis. Linearity over 100–7000 ppm with a detection limit of 25 ppm of uranium in 10% LiCl–KCl matrix was obtained by this method. The present method was successfully applied for the quantitative estimation of uranium in synthetic salt mixtures and the results were found to be more accurate than the values measured by ICP-OES. [ABSTRACT FROM AUTHOR]

Abstract The electrochemical behavior of Yb(III) in LiCl–KCl–YbCl 3 melts on W and liquid Zn electrodes was studied at 813 K. On the W electrode, the diffusion coefficient of Yb(III) was determined to be 3.38 × 10−5 cm2 s−1. The apparent standard Gibbs energy of the reaction: YbCl 2 + 1 / 2 Cl 2 → YbCl 3 in LiCl–KCl melts was calculated. On the liquid Zn electrode, the results from cyclic voltammetry, square wave voltammetry and open circuit chronopotentiometry indicated that two electrochemical signals corresponding to the formation of two kinds of Zn–Yb intermetallic compounds were observed. Ytterbium was extracted in the form of Zn–Yb alloys by galvanostatic electrolysis on liquid Zn electrode. The results from XRD show that three kinds of Zn-Yb intermetallic compounds were formed. Moreover, the different phases of Zn–Yb alloys could be controlled by adjusting the concentrations of YbCl 3. [ABSTRACT FROM AUTHOR]

Highlights • The reduction peaks of Th(IV)/Th(0) and Ce(III)/Ce(0) in the respective ternary melt were same with those in the quaternary melt. • The separation rate of Th reached up to 98.9%. • The cathode product contained Th metal and ThO 2. • The onset reduction potential of Ce(III)/Ce negative-shifted of about 40 mV after electrolysis. Abstract The extraction and recycle of thorium is an essential step in the thorium-uranium closed fuel cycle designed for Thorium-based Molten Salt Reactor system (TMSR), and the separation of thorium from FPs especially lanthanides is a key issue in the thorium recovery. In this paper, the electrochemical behaviors of Th(IV) and Ce(III) on Mo electrode were studied by cyclic voltammetry (CV) and chronopotentiometry (CP) techniques at 773 K in ThF 4 (3 wt%)/CeF 3 (0.3 wt%)-LiCl-KCl ternary melt and CeF 3 (0.3 wt%)-ThF 4 (3 wt%)-LiCl-KCl quaternary melt, respectively. The reduction peaks of Th(IV)/Th(0) and Ce(III)/Ce(0) were at −1.83 V and −2.21 V (vs. Ag/AgCl) in the respective ternary melt, respectively, which were same with the values in the quaternary melt; however, the oxidation peaks in the CeF 3 -ThF 4 -LiCl-KCl melt shifted negatively about 0.1 V. Pulsed potential electrolysis of quaternary melt revealed that 98.9% of Th(IV) can be electrochemical separated from the melt with almost all cerium remaining in the melt, based on the inductively coupled plasma atomic emission spectrometer (ICP-AES) results. [ABSTRACT FROM AUTHOR]

Abstract The intermetallic compound formations of Ce-Bi on an inert W electrode in the molten LiCl-KCl eutectic with CeCl 3 and BiCl 3 for an electrolytic reduction process was investigated with various electrochemical techniques of cyclic voltammetry, square wave voltammetry, and open circuit chronopotentiometry. The electrochemical reduction of Ce3+ on the inert electrode at 773 K was observed at more positive potential with Bi3+ than that without Bi3+ due to lowering activity of Ce by intermetallic compound formations. Cyclic voltammogram and square wave voltammogram exhibited four reduction peaks with overlapping signals. Application of peak separation technique allow five intermetallic compounds of BiCe 1/2 , BiCe, BiCe 4/3 , BiCe 5/3 , BiCe 2 to be determined. Intermetallic compound formations of Ce-Bi were confirmed with open circuit chronopotentiogram which exhibited five plateau corresponding to a state in which two phases of intermetallic compounds coexist on the electrode surface. Analysis of cyclic voltammograms according to molar ratio of Bi to Ce showed that the amount of CeBi 2 and CeBi at the reduction potential above −1.5 V were increased at the higher molar ratio of Bi to Ce. The experimental results indicated that intermetallic compounds of Ce-Bi could be formed on the inert electrode in LiCl-KCl-CeCl 3 -BiCl 3 melt by electrolytic reduction and the type and amount of the resulting intermetallic compound on the inert electrode by electrolytic reduction could be varied depending on the applied potential and molar ratio of Bi to Ce, respectively. Highlights • Co-reduction of Bi and Ce ions on inert electrode in molten LiCl-KCl eutectic. • Application of peak separation technique to analyze voltammograms. • Identification of intermetallic compound formations of Bi-Ce by electrolytic reduction. [ABSTRACT FROM AUTHOR]

In this report, the electrochemical behaviors of Pr(III) and Ni(II) ions on a W electrode were investigated in LiCl‐KCl eutectic by cyclic voltammetry (CV), square wave voltammetry (SWV), chronopotentiometry (CP) and open‐circuit chronopotentiometry (OCP) techniques. From the results of electrochemical methods, different signals corresponding to seven kinds of intermetallic compounds in the phase diagram of Pr−Ni were observed. The thermodynamic properties of intermetallic compounds in the temperature range of 823–923 K were investigated by open‐circuit chronopotentiometry. With the evaluated apparent standard potentials of Pr−Ni intermetallic compounds, the Gibbs energies, enthalpies and entropies of formation were also calculated. The co‐reduction products by galvanostatic and potentiostatic electrolysis were characterized based on X‐ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive X‐ray spectroscopy (EDS). The shape of the alloy obviously changes from granular to bulk, and the alloy phase changes from Pr‐rich to Ni‐rich. The co‐reduction products of PrNi5, PrNi2 and PrNi were identified. The thermodynamic properties of Pr−Ni alloys in a molten salt are investigated by using electrochemical techniques. The alloy phase and shape are found to change depending on the electrolysis conditions. [ABSTRACT FROM AUTHOR]

In this study, UCl4 was prepared by the reaction of HCl gas with UO2 in the LiCl-KCl eutectic. Then, the electrochemical behavior of U4+ and U3+ on a Mo cathode was investigated by various electrochemical techniques. The reduction process of U4+ was regarded as two steps: U4++e=U3+; U3++3e=U. Diffusion coefficients of U4+ and U3+, the apparent standard potential of U4+/U3+, U3+/U as well as U4+/U in the LiCl-KCl molten salt on the Mo electrode was determined by numerous electrochemical methods. The thermodynamic functions of formation of Gibbs free energy of UCl4 and UCl3 are calculated as well. [ABSTRACT FROM AUTHOR]

In this study, UCl4 was prepared by the reaction of HCl gas with UO2 in the LiCl-KCl eutectic. Then, the electrochemical behavior of U4+ and U3+ on a Mo cathode was investigated by various electrochemical techniques. The reduction process of U4+ was regarded as two steps: U4+ + e = U3+; U3+ + 3e = U. Diffusion coefficients of U4+ and U3+, the apparent standard potential of U4+/U3+, U3+/U as well as U4+/U in the LiCl-KCl molten salt on the Mo electrode was determined by numerous electrochemical methods. The thermodynamic functions of formation of Gibbs free energy of UCl4 and UCl3 are calculated as well. [ABSTRACT FROM AUTHOR]

Electrowinning process was investigated for extracting actinides from molten salts used for the pyrochemical reprocessing of spent nuclear fuels. The separation of actinides from lanthanides is expected to be enhanced by employing inert solid cathodes due to larger potential differences on these cathodes. In this study, the co-deposition behavior of Pu and U metals onto an inert solid cathode made of tungsten was examined in LiCl-KCl eutectic melts containing UCl 3 and PuCl 3 at 773 K. The standard potential of U 3+ /U is 0.31 V more positive than that of Pu 3+ /Pu. The U 3+ concentration was varied in the range of 0.11–0.66 wt%, while the Pu 3+ concentration was maintained at approximately 2.9 wt%. When the U 3+ concentration was not sufficiently low, the deposited U metal readily grew outward from the electrode surface and the electrode surface area rapidly increased, which facilitated only the deposition of U metal. It was estimated that metallic Pu can be efficiently collected along with U at U 3+ concentrations lower than ∼0.2 wt%. [ABSTRACT FROM AUTHOR]

During pyrochemical reprocessing of spent nuclear fuel, complex melts based on LiCl-KCl eutectic are formed, but their properties are still not well studied. We measured the electrical conductivity of (LiCl-KCl) eut. − CeCl 3 , (LiCl-KCl) eut. − NdCl 3 and (LiCl-KCl) eut. − UCl 3 quasi-binary melts was up to 40 mol.% CeCl 3 , 40 mol.% NdCl 3 and 10.45 mol.% UCl 3 in a wide temperature span. In addition the electrical conductivity of several compositions, such as (LiCl-KCl) eut. − CeCl 3 + NdCl 3 and (LiCl-KCl) eut. − CeCl 3 + NdCl 3 + UCl 3 was measured. The measurements were carried out in quartz cells of the capillary type. When the total concentration of trivalent ions is less than 12 mol.%, we found that the conductivity of mixtures of arbitrary composition is almost a linear function of CeCl 3 , NdCl 3 , and UCl 3 the overall concentration. [ABSTRACT FROM AUTHOR]

Electrochemical impedance spectroscopy (EIS), linear polarization (LP), Tafel and cyclic voltammetry (CV) were performed to investigate the exchange current density (i 0 ) of U/U 3+ reaction in LiCl-KCl eutectic salt under different UCl 3 concentrations (0.5 wt%–4 wt%) and temperature conditions (723 K–798 K). The EIS spectra were measured by applying minimum overpotential from equilibrium potential and fitted to the proposed equivalent circuit. From the EIS experiments, the calculated values of i 0 were varied from 0.0054 A cm −2 to 0.102 A cm −2 . For the LP and Tafel methods, i 0 values were determined from the linear fitting at small and large overpotential ranges of the current-potential curves. The measurement for i 0 via CV was done analogously to the LP method. All i 0 values have the linear trend with the change of concentration and temperature; however, these values measured by LP, Tafel, and CV methods are greatly influenced by the change in electrode surface area. Overall, i 0 agreed within 33% relative error range with the EIS method being the most consistent and accurate in comparison to reported literature values. Dimensionless analysis was done on the EIS data sets providing insightful correlations for prediction of i 0 under various experimental conditions. [ABSTRACT FROM AUTHOR]

This work presents a comprehensive study for the electrochemical behaviors of zirconium in LiCl-KCl eutectic. The effects of stirring, temperature and Zr concentration on the electrode reactions, the ZrCl4 sublimation from the melt, microcosmic morphologies of Zr deposits (ZrCl and Zr) obtained at different potential and temperature have been investigated. The behaviors of Zr(IV), on a large concentration range from 0.13% to 2.28% in melt, show a multiple-step reaction involving Zr(IV), Zr(II), ZrCl and Zr species. Temperature plays a crucial role on the changes of Zr(IV) reduction behavior on the solid electrode. The Zr(IV)/ZrCl couple is more easily observed at lower temperature and gradually diminishes with the increase of temperature. The Zr(IV)/Zr(II) and Zr(II)/Zr reactions are predominant on the W electrode at higher temperatures. At 673 K, a layered structure of insoluble ZrCl formed by potentiostatic electrolyses at 1.1 V was visualized by scanning electron microscopy-energy dispersive X-ray (SEM-EDS), while only Zr metal particles was observed at higher temperature than 773 K. An evolution of the Zr-based structure and size corresponding to the ZrCl and Zr metal based on different potentiostatic electrolysis was observed. The average particle size of the Zr metalparticles increases with the increase of temperature. [ABSTRACT FROM AUTHOR]

A novel spectroscopic furnace has been developed for the in situ acquisition of UV-visible absorption spectra in high temperature molten salts. The furnace has been used to obtain spectra of neodymium(III) and praseodymium(III) trichloride in LiCl-KCl eutectic at 450°C over various Ln(III) concentrations. The major absorption peaks for both for Nd(III) and Pr(III) in the UV-visible region of the spectrum have been identified and the molar absorbances quantified for each of these absorption maxima. The neodymium and praseodymium were then precipitated by adding respectively, Li 2 CO 3 and Li 2 O to the salt and monitored using UV-visible spectroscopy. In both cases the precipitate has been identified as the relevant LnOCl by powder XRD. [ABSTRACT FROM AUTHOR]

This paper presents experimental results of cyclic voltammetry on CeCl 3 in LiCl-KCl using tungsten electrode and Bi coated electrode respectively at 703K. Using tungsten electrode at low concentration of CeCl 3 , the redox reaction has been shown to be reversible. Diffusion coefficient and apparent standard potential of Ce(III) in LiCl-KCl were 0.42×10 -5 (cm 2 /s) and -3.153 (V vs. Cl 2 /Cl − ) under 50mV/s. In order to obtain Bi coated electrode, cyclic voltammetry was carried out on eutectic salt including BiCl 3 . The redox reaction of Ce on Bi coated electrode has been shown to be reversible and apparent standard potential on Bi coated electrode moved 782mV compared with tungsten cathode. [ABSTRACT FROM AUTHOR]

The electrochemical behavior of Th(IV) ion on molybdenum (Mo) electrode was studied by cyclic voltammetry (CV) and square wave voltammetry (SWV) technologies at 773 K in ThF 4 -LiCl-KCl melt. The reduction of Th(IV) to metal Th at −1.67 V ( vs. Ag/AgCl) is a four-electron exchange process, which is quasi-reversible and diffusion-controlled. The diffusion coefficient (D) and activation energy of diffusion process for Th(IV) were determined to be 3.77 × 10 −5 cm 2 s −1 and 59.2 kJ mol −1 . The pulse potential electrolysis of ThF 4 -LiCl-KCl melt revealed that 86.8% of Th(IV) can be separated from the melt based on the inductively coupled plasma atomic emission spectrometer (ICP-AES) results. [ABSTRACT FROM AUTHOR]

The electrode reactions of Nd (III)/Nd couple at liquid Zn and Zn-coated W electrodes in LiCl-KCl melt were investigated in the temperature range of 707–784 K. In the both cases, the electrochemical reduction of Nd (III) was observed at a more positive potential than that on an inert W electrode, due to the low activity of Nd in the metal phase. Cyclic voltammetry (CV) recorded at the liquid Zn electrode suggests the existence of a quasi-reversible reaction. The activity coefficient and apparent standard potential have been obtained. On the Zn-coated W electrode, the formation of five obvious non-homogeneous Nd-Zn intermetallic compounds could be observed through CV and open circuit chronopotentiometry (OCP) measurements and the thermodynamics of these intermetallic compounds was also investigated. Electromotive force (emf) measurements for the Nd-Zn intermetallic compounds in two-phase coexisting states were also carried out in the temperature range of 707–784 K. Moreover, the standard formation Gibbs energies and the standard equilibrium constant of each Nd-Zn intermetallic compound were also calculated and the thermodynamic stabilities of these compounds at our experimental temperatures were evaluated. [ABSTRACT FROM AUTHOR]

Thermochemical conversion of UO 2 to UCl 3 using AlCl 3 and Al metal in LiCl–KCl melt at 773 K is reported here. The reaction product was assessed qualitatively by UV–Vis spectroscopy, cyclic voltammetry (CV) and square wave voltammetry (SWV). The extent of conversion efficiency was quantified through UV–Vis spectroscopy by measuring the absorbance of U(VI) at 420 nm after dissolving the reaction product in 1 M HNO 3 + 1 M H 3 PO 4 medium. The conversion process was optimized by varying concentrations of AlCl 3 (stoichiometric × 1 to 4) and the duration of reactions (45 min–5 h). About 93% conversion of UO 2 was achieved by doubling the stoichiometric requirement of AlCl 3 in 50 g of LiCl–KCl salt in 2.5 h. • The conversion of UO 2 to UCl 3 is achieved using AlCl 3 and Al metal in LiCl–KCl. • Cyclic and square wave voltammetry ascertain the conversion through redox peaks. • UV–Vis spectrophotometry is used to quantify the conversion of UO 2 to UCl 3. • More than 92% conversion is achieved at optimized experimental conditions. [ABSTRACT FROM AUTHOR]

The electrical conductivity of (LiCl-KCl) eut. - CdCl 2 quasi-binary melts was measured over entire concentrations range and in a wide temperature span. The liquidus line of the system was plotted based on conductivity data. The equivalent conductivity and its activation energy were calculated. The results were interpreted in terms of coexistence and mutual influence of the complexes formed by the Li + and Cd 2+ cations. [ABSTRACT FROM AUTHOR]

Electrorefining of irradiated metallic fuels was successfully demonstrated: Actinides (U, Pu, Np, Am and Cm) in the fuels were dissolved in LiCl–KCl melts with high dissolution ratios, while U was selectively deposited on a solid cathode and the simultaneous recovery of actinides in a liquid Cd cathode was confirmed. The behavior of actinides, the fuel matrix stabilizer Zr and fission products such as lanthanide, alkaline, alkaline earth and noble metal, at the electrorefining is discussed based on the ICP-MS analysis of the samples taken from molten salt electrolyte, anode fuel residues and cathode deposits. [ABSTRACT FROM AUTHOR]

Molten salts technology is of significant interest for nuclear, solar, and other energy systems. In this work, first-principles molecular dynamics (FPMD) was used to model the solute behavior in eutectic LiCl–KCl and FLiBe (Li 2 BeF 4 ) melts at 773 K and 973 K, respectively. The thermo-kinetic properties for solute systems such as the redox potential, solute diffusion coefficients and structural information surrounding the solute were predicted from FPMD modeling and the calculated properties are generally in agreement with the experiments. In particular, we formulate an approach to model redox energetics vs. chlorine (or fluorine) potential from first-principles approaches. This study develops approaches for, and demonstrates the capabilities of, FPMD to model solute properties in molten salts. [ABSTRACT FROM AUTHOR]