LiCl-KCl Eutectic Melt Research Articles

Oxygen Electrode Reaction in a LiCl–KCl Eutectic Melt

Oxygen electrode reaction was investigated on a boron-doped diamond electrode in a LiCl–KCl eutectic melt. The standard formal potential of decreases with the elevation of temperature. The potential at is vs . The standard formal free energy change increases with the temperature elevation, calculated to be at . The standard formal entropy and enthalpy changes are determined to be and , respectively, at .

Electronic absorption spectra of Sm(II) and Yb(II) ions in a LiCl–KCl eutectic melt at 450 °C

We have measured the absorption spectra of Sm(II) and Yb(II) ions in LiCl–KCl eutectic at 450 °C. The UV spectra of Sm(II) and Yb(II) exhibited intense and broad peaks at around ∼260 nm, which is attributable to the 4 f–5 d transitions. With the aid of the UV–vis spectroscopic method, in-situ identification of spontaneous reduction of trivalent Sm and Yb ions to divalent ions was achieved.

A Quartz Tube Based Ag/Ag+Reference Electrode with a Tungsten Tip Junction for an Electrochemical Study in Molten Salts

reference electrode (Py-REF). The results of the electrochemical potential measurements with the W-tip-Quartz- REF and the Py-REF in the LiCl-KCl eutectic melts for a wide temperature range proved that the oxide layer on the surface of the tungsten metal tip provided a high ionic conduction. Stability of our newly designed W-tip- Quartz-REF was tested by measuring a junction potential for 12 hours at 700

Electrolysis of AmN in LiCl-KCl Eutectic Melts and Renitridation of Am Recovered in Liquid Cd Cathode

R&D of the nitride fuel cycle technology is underway at Japan Atomic Energy Agency (JAEA). Behavior of americium (Am) in the pyrochemical process, which includes anodic dissolution of AmN and recovery of Am into a liquid cadmium (Cd) cathode by electrolysis in LiCl-KCl eutectic melts, and nitride formation of Am recovered in liquid Cd, is presented.

Anodic Dissolution and Chemical Reduction of Noble Metals in LiCl-KCl Melt

The anodic behaviors of Pd, Pt and Au have been investigated in LiCl-KCl eutectic melt at 683 K. Chemical reduction of the dissolved noble metal ions by H2 and CH4 has been also carried out. It was shown that Pd and Au could be dissolved anodically with a large dissolution rate, and that the dissolution rate of Pt was limited because of its passivation behavior. Fine particles of these noble metals were obtained by H2 or CH4 reduction though they combined together.

XAFS Study on Chlorination of Y2O3 in LiCl-KCl-ZrCl4 Melt

The chlorination reaction of Y2O3 with ZrCl4 in LiCl-KCl eutectic melt was investigated by X-ray absorption fine structure (XAFS) technique. The chlorination reaction was observed between 773 K and 823 K as the 1st peak shift of the Fourier transform magnitude function |FT(k3χ(k))|. The peak corresponding to the nearest Y3+-Cl− correlation was observed in the XAFS analysis at 823 K as the result of the chlorination. It was confirmed that the mixture melts after the reaction is almost equivalent to a molten 5% YCl3 -(LiCl-KCl eutectic) mixture.

Electrochemical Behavior of Zr on a Liquid Cd Electrode in LiCl–KCl Eutectic Melts

The electrochemical behavior of zirconium on a liquid cadmium electrode was studied in LiCl–KCl melts containing at 773 K. In a cyclic voltammogram of the liquid cadmium electrode, a cathodic peak was observed at around (vs ) as well as at attributed to zirconium metal deposition. Because the deposit obtained by potentiostatic electrolysis at was confirmed to be from X-ray diffraction analysis, the cathodic peak at corresponded to formation. The open-circut-potential of the liquid cadmium electrode with was measured to calculate thermodynamic properties such as relative partial molar Gibbs energies of zirconium in . The quantity of zirconium recovered in the liquid cadmium electrode by the potentiostatic electrolysis at was measured by inductively coupled plasma-atomic emission spectroscopy. The result indicated of the zirconium recovery efficiency, which was defined as the quantity of electricity corresponding to the recovered zirconium divided by the total quantity of passed electricity.

EPR Investigation on a Quantitative Analysis of Eu(II) and Eu(III) in LiCl/KCl Eutectic Molten Salt

EPR spectroscopic technique was applied for a quantitative analysis of Eu(II) for a speciation of europium in a LiCl-KCl eutectic melt. By adopting the first absorption line of each isotopes (151Eu and 153Eu), a calibration plot was obtained. The calibration of the EPR intensity shows a good linearity according to the amount of Eu(II). The EPR intensity was identified to increase proportionally with a decrease of the attenuation parameter for EPR microwave power. The fluorescence technique was used qualitatively to find whether either of Eu(II) or Eu(III) ions exists in a molten salt sample. The ICP-AES technique was also adopted to determine the total concentration of europium in the sample, since EPR is only sensitive for detecting the Eu(II) ion. The extent of the reduction of Eu(III) in the LiCl-KCl eutectic melt at 723 K was determined by using this technique.

Spectroelectrochemical Study of Neptunium in Molten LiCl-KCl Eutectic

Neptunium behaviour in an LiCl-KCl eutectic melt at 723 K was studied using spectroelectrochemistry. Cathodic reduction of neptunium(IV)-containing melts led to the formation of Np(III) ions and then neptunium metal. Electronic absorption spectra of Np(IV) and Np(III) chloro species in LiCl-KCl melt were recorded and resolved into individual Gaussian bands. The nature of neptunium complex ions in the melt is discussed.

Anodic Behaviors of Noble Metals in Eutectic LiCl-KCl Melt

The anodic behaviors of some noble metals and their alloys in dehydrated LiCl-KCl eutectic melt have been studied as a basic study on a new reprocessing process of spent UO2 nuclear fuel by an electrorefining technique. Palladium and Ru dissolved anodically as Pd2+ and Ru3+, respectively. Rhodium dissolved as Rh3+, and was passivated by surface film formation. The potentials where the steady dissolution current density was 10-3 A/cm2 were 3.02V for Pd, 3.08V for Rh and 3.12V for Ru, These values were more positive than the reported value of UO2. The anodic behaviors of Pt-Rh and Pd-Ru alloys were explained from those of each component, and no peculiar influence by alloying was seen. These results indicate that the noble metals and alloys can be separated from UO2 by leaving them in the anode by the control of the anode potential.

EPR and luminescence studies of Eu(II) magnetically diluted in LiCl–KCl salt

High-temperature LiCl–KCl molten salt medium provides an efficient way to produce the paramagnetic Eu(II) ion to be magnetically diluted into a diamagnetic host medium. Eu(II) was formed by a dissolution and an auto-reduction processes in a high-temperature LiCl–KCl eutectic melt at 723 K by using Eu 2O 3 as a starting material. By using EPR and luminescence spectroscopic method, we studied the nature of the magnetically isolated paramagnetic Eu(II) ion diluted in a LiCl–KCl medium. With the aid of these spectroscopic tools, it was found that stable Eu(II) species was formed spontaneously at 723 K under anaerobic conditions. EPR and luminescence spectroscopy provided detailed information regarding the nature of the europium ion in a molten salt.

Electrode Reaction of the U3+/U Couple at Liquid Cd and Bi Electrodes in LiCl-KCl Eutectic Melts

The electrode reactions of the Np3+/Np couple at liquid Cd and Bi electrodes were investigated by cyclic voltammetry at 723, 773 and 823 K in the LiCl–KCl eutectic melt. It was found that the diffusion of Np3+ in the salt phase was the rate-determining step in the cathodic reaction when the concentration of NpCl3 was less than about 1 wt % and the liquid Cd or Bi phase was not saturated with Np. The redox potentials of the Np3+/Np couple at the liquid Cd electrode at 723, 773 and 823 K were observed to be more positive than those at the Mo electrode by 0.158, 0.140 and 0.126 V, respectively. The potential shift results from a lowering of the activity of Np in the Cd phase according to the formation of the NpCd11 alloy at 723 K and NpCd6 at 773 and 823 K. The redox potentials of the Np3+/Np couple at the liquid Bi electrode at 723, 773 and 823 K were more positive than those at the Mo electrode by 0.427, 0.419 and 0.410 V, respectively, which is attributable to a lowering of the activity of Np in the Bi phase due to the formation of NpBi2.

Electrochemical properties of the Ag +|Ag and other reference electrodes in the LiCl–KCl eutectic melts

Thermochemical properties of the Ag +|Ag reference electrode were investigated by comparison with those of the Cl −|Cl 2 reference electrode in the LiCl–KCl eutectic melt at 673–873 K, and the influence of the AgCl concentration on the equilibrium potential was also studied. The potential difference between the Ag +|Ag electrode and the Cl −|Cl 2 reference electrode varied in nearly linear proportion to the concentration of AgCl ranging from 0.01 to 20 mol%. When the AgCl concentration in the inner solution of the Ag +|Ag electrode was 1.02 mol%, the equilibrium potential, E, of the Ag +|Ag electrode versus the Cl −|Cl 2 reference electrode at 673–873 K is described as following: E = −1.061 (±0.005) + 0.0000649 (±0.0000010) T, where T is the temperature in K. Since the density increased with an increase of the AgCl content, the mole number of electrolytes in a given volume increased. Accordingly, the standard redox potential, E A g + | Ag 0 , could be corrected by the equation: E A g + | Ag 0 = − 1.080 ( ± 0.005 ) + 0.000346 ( ± 0.000005 ) T . Furthermore, characteristics of other reference electrodes such as the Al 3+|Al and Li +|Li (Li–Al and Li–Sb alloys) electrodes were investigated. The standard redox potential, E A l 3 + | Al 0 , of the Al 3+|Al couple at 673–873 K is described as following: E A l 3 + | Al 0 = − 2.289 ( ± 0.005 ) + 0.000405 ( ± 0.000005 ) T . The equilibrium potential between the Li–Al (Li:Al = 42:58 in mol%) and the Cl −|Cl 2 reference electrode, E L i + | Li ( Li – Al ) and that between the Li–Sb (Li:Sb = 59:41 in mol%) alloys electrode and the Cl −|Cl 2 reference electrode, E L i + | Li ( Li – Sb ) , were obtained at the temperature range from 673 to 873 K ( E L i + | Li ( Li – Al ) = − 3.923 ( ± 0.005 ) + 0.000860 ( ± 0.000005 ) T and E L i + | Li ( Li – Sb ) = − 2.960 ( ± 0.005 ) + 0.000313 ( ± 0.000005 ) T .

Investigation of electrorefining of metallic alloy fuel onto solid Al cathodes

This work concerned the electrorefining of UZr and UPuZr alloys on a solid aluminium cathode, in the LiCl–KCl eutectic melt containing U3+, Pu3+, Np3+, Zr2+ or Zr4+, Am3+, Nd3+, Y3+, Ce3+ and Gd3+ chlorides. During constant current electrolyses, the use of a cathodic cut-off potential (−1.25V versus Ag/AgCl) allowed to selectively deposit actinides (mainly U), while lanthanides remained in the salt. The aim was to determine the maximal load achievable on a single aluminium electrode. The total exchange charge was 4300C, which represents the deposition of 3.72g of actinides in 4.17g Al, yielding a composition of 44.6wt% An in Al. It was shown that the melting of the cathode contributed to increase the total amount of actinides deposited on the aluminium.

Electrochemical transient techniques for determination of uranium and rare-earth metal separation coefficients in molten salts

The main step in the pyrometallurgical recycling process of spent nuclear fuel is a molten salt electrorefining. The knowledge of separation coefficients of actinides (U, Np, Pu and Am) and rare-earth metals (Y, La, Ce, Nd and Gd) is very important for this step. Usually the separation coefficients are evaluated from the formal standard potentials of metals in melts containing their own ions, i.e. values obtained by potentiometric method. Electrochemical experiments were carried out at 723–823 K in order to estimate separation coefficients in LiCl–KCl eutectic melt containing uranium and lanthanum trichlorides. The electrochemical behaviour of UCl 3 in LiCl–KCl melt was studied by different electrochemical methods. The diffusion coefficients of U(III) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry. The standard rate constants of charge transfer for electroreduction of uranium, U(III) + 3e − → U, were calculated by the impedance spectroscopy method. The values of constants testify that electroreduction of U(III) to U is mainly controlled by the rate of charge transfer. La(III) discharge on uranium electrode was also investigated. It was shown that for the calculation of uranium and lanthanum separation coefficients it is necessary to determine the voltammetric peak potentials of U(III) and La(III), their concentration in the melt and the kinetic parameters relating to U(III) discharge such as transfer and diffusion coefficients, and standard rate constants of charge transfer.

Fabrication and electrochemical behavior of nitride fuel for future applications

Mononitride is the first candidate of fuel material in the accelerator driven system (ADS) for minor actinide (MA) transmutation designed by JAERI, being coupled with pyrochemical process for treatment of spent fuel. This paper summarizes recent R&D on the fabrication and electrochemical behavior of nitride fuel carried out in JAERI. Mononitride of U, Np, Pu, Am, Cm and their solid solutions have been prepared by carbothermic reduction from their dioxides. Mononitride containing diluent material such as ZrN also has been prepared and characterized. Electrode behavior of nitride fuel in the LiCl–KCl eutectic melt has been investigated by electrochemical measurements in order to apply pyrochemical process to nitride fuel cycle for MA transmutation.

Determination of uranium and rare-earth metals separation coefficients in LiCl–KCl melt by electrochemical transient techniques

The main step in the pyrometallurgical process of spent nuclear fuel recycling is a molten salt electrorefining. The knowledge of separation coefficients of actinides (U, Np, Pu and Am) and rare-earth metals (Y, La, Ce, Nd and Gd) is very important for this step. Usually the separation coefficients are evaluated from the formal standard potentials of metals in melts containing their own ions, values obtained by potentiometric method. Electrochemical experiments were carried out at 723–823 K in order to estimate separation coefficients in LiCl–KCl eutectic melt containing uranium and lanthanum trichlorides. It was shown that for the calculation of uranium and lanthanum separation coefficients it is necessary to determine the voltammetric peak potentials of U(III) and La(III), their concentration in the melt and the kinetic parameters relating to U(III) discharge such as transfer and diffusion coefficients, and standard rate constants of charge transfer.

Thermochemical properties of the intermetallic compounds in the lanthanum–cadmium system

Thermochemical properties on the intermetallic compounds in the lanthanum–cadmium (La–Cd) system were investigated electrochemically. The redox reactions of the La 3+/La couple at the Cd-coated W electrodes, which were prepared by the electrodeposition of Cd at the W electrode, were studied by cyclic voltammetry and chronopotentiometry at 673, 723, 773, 823 and 873 K in the LiCl–KCl eutectic melts containing 1.2 wt% LaCl 3. There were several cathodic and anodic peaks corresponding to the formation and the decomposition of the intermetallic compounds, LaCd x , respectively, in the cyclic voltammograms. Since the amount of Cd adsorbed on the W electrode could be evaluated during the electrochemical measurement, the compositions of all LaCd x could be analyzed exactly from the accumulated coulomb numbers of every anodic peak, which was attributed to the decomposition of each LaCd x . The formation energy of each LaCd x could be also estimated by chronopotentiometry.

Electrochemical behavior of actinides and actinide nitrides in LiCl–KCl eutectic melts

The redox potentials of the U 3+/U, Np 3+/Np and Pu 3+/Pu couples at Mo, Cd and Bi electrodes in LiCl–KCl eutectic melt containing UCl 3, NpCl 3 and PuCl 3, respectively, were evaluated by electrochemical measurements at the temperature range between 723 and 823 K. The standard potentials of the U 3+/U, Np 3+/Np and Pu 3+/Pu couples versus the Ag +/Ag (1 wt.% AgCl) reference electrode were given by the following equations: E U 3 + / U 0 = − 1.8647 + 0.000798 × T , E N p 3 + / Np 0 = − 2.0298 + 0.000706 × T and E P u 3 + / Pu 0 = − 2.232 + 0.00094 × T , where E values are in volts, T in kelvin. The differences between the redox potentials at Mo electrode and those at liquid metal electrodes were attributable to the lowering in the activities of U, Pu and Np in liquid metal phases according to the alloy formation. Similarly, the anodic dissolutions of UN, NpN and PuN were observed at about 0.7 V more positive potential than those of U, Np and Pu, respectively, since the stabilization of U, Np and Pu by nitriding lowered the activities of U, Np and Pu, respectively, in the solid phase.

Electrochemistry of Uranium in Molten LiCl-KCl Eutectic

The Institute for Transuranium Elements (ITU) is building up an accurate database of actinide behavior in chloride melts in support of its nuclear fuel reprocessing development program. The electrochemical properties of uranium, dissolved in LiCl-KCl eutectic melt, were investigated by transient electrochemical techniques, such as cyclic voltammetry (CV) and chronopotentiometry on an inert tungsten electrode. It was shown that is reduced to by a two-step mechanism corresponding to and transitions. In the range, the diffusion coefficients of and were similar and equal to: and . The apparent standard potentials of and redox systems were vs. and vs. , respectively. Some thermochemical properties of uranium solutions were also derived from the electrochemical measurements. The Gibbs free energies of dilute solution of and in the LiCl-KCl were determined to be: and in kJ , respectively. In the range, the activity coefficients γ of and range between and , respectively.