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The application of the rotating cylinder electrode (RCE) to molten LiCl-KCl eutectic mixtures for electroanalytical measurements is presented. This enabled the measurement of the limiting current which was observed to follow a linear trend with the rotational rate raised to 0.64–0.65 power on average, which closely agrees with existing RCE mass-transfer correlations. This is the first publication of electroanalytical RCE measurements in LiCl-KCl eutectic based molten salt mixtures, to our knowledge. These measurements were made in mixtures of molten LiCl-KCl eutectic containing UCl 3 and MgCl 2 . Kinetic parameters were calculated for Mg 2+ in LiCl-KCl eutectic. The exchange current density ( i o ) of Mg 2+ deposition varied with mole fraction ( x ) according to i o (A cm −2 ) = 1.64 x 0.689 . The parameters from RCE measurements were also applied in an electrochemical co-deposition model entitled DREP to detect and predict the deposition rate of U and Mg. DREP succeeded in detecting the co-deposition of U and Mg, even when Mg constituted less than 0.5 wt% of the deposit. [ABSTRACT FROM AUTHOR]

The thermodynamic behavior of lanthanides in molten salt systems is of significant scientific interest for the spent fuel reprocessing of Generation IV reactors. In this study, the apparent standard reduction potential (apparent potential) and activity coefficient of LaCl 3 were determined in a molten salt solution of eutectic LiCl-KCl as a function of concentration of LaCl 3 . The effect of adding up to 1.40 mol % CsCl was also investigated. These properties were determined by measuring the open circuit potential of the La—La(III) redox couple in a high temperature molten salt electrochemical cell. Both the apparent potential and activity coefficient exhibited a strong dependence on concentration. A low concentration (0.69 mol %) of CsCl had no significant effect on the measured properties, while a higher concentration (1.40 mol %) of CsCl caused an increase (become more positive) in the apparent potential and activity coefficient at the higher range of LaCl 3 concentrations. [ABSTRACT FROM AUTHOR]

Direct electrolytic reduction of UO 2 in LiCl-Li 2 O was performed with a platinum anode surrounded by a mesh shroud. The anode shroud was comprised of three pieces; shaft, cage and screen. The shaft and cage were made of Haynes C2000 and the screen was made of Hastelloy C276. Five reduction tests were performed sequentially with the same anode/shroud set, while two other reduction tests did not use an anode shroud. Based on mass measurements, the average rate of platinum loss from corrosion was determined to be 1.69 µm/hr. It was confirmed with X-ray diffraction that a layer of lithium platinate forms on the surface of the anode. The anode shroud was found to increase the anodic potential by 0.25 V. After each test, a corrosion coupon was removed from the Haynes C2000 anode shroud and analyzed via scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). Salt samples were taken after each test and analyzed using inductively coupled plasma mass spectrometry. The results indicated that nickel, chromium, and molybdenum were all depleted from the Hastelloy C276 shroud and accumulated in the molten salt. SEM-EDS line scans were used to estimate linear corrosion rates. Based on nickel, chromium, and molybdenum, the shroud corrosion rates were determined to be 0.36, 0.49, and 0.51 µm/hr, respectively. [ABSTRACT FROM AUTHOR]

The drawdown of actinides is an important unit operation to enable the recycling of electrorefiner salt and minimization of waste. A new method for the drawdown of actinide chlorides from LiCl-KCl molten salt has been demonstrated here. Using the galvanic interaction between the Gd/Gd(III) and U/U(III) redox reactions, it is shown that UCl 3 concentration in eutectic LiCl-KCl can be reduced from 8.06 wt.% (1.39 mol %) to 0.72 wt.% (0.12 mol %) in about an hour via plating U metal onto a steel basket. This is a simple process for returning actinides to the electrorefiner and minimizing their loss to the salt waste stream. [ABSTRACT FROM AUTHOR]

Options for reducing purified metal chlorides to metallic form were evaluated in support of the development of a metal purification process based on the conversion of impure metal via hydriding followed by chlorination. Metallothermic reduction of CeCl 3 was tested using Li, Ca, and Na as reductant metals with and without a molten salt solvent in MgO and Y 2 O 3 -coated MgO crucibles. The effects of added reductant metal form, crucible material and dimensions, and mixture hold times above Ce melting temperature were studied. Direct contact of Li and CeCl 3 was ineffective due to their immiscibility. A low-density alloy was formed between Li and Ce using Li in a LiCl solvent. Na was ineffective at reducing CeCl 3 to any measurable degree. The highest percent recovery (71.4 %) and consolidation of Ce was achieved when using Ca in a CaCl 2 -NaCl solvent with 99.8 % removal of CeCl 3 from the salt. Side reaction with MgO crucibles was found to be at least partially responsible for reduced Ce recovery. [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]

Conducting research experiments on plutonium electrorefining is difficult due to the significant hazards and regulations associated with nuclear materials. Finding a surrogate for plutonium electrorefining studies would enable more fundamental research to be conducted. Potential surrogates were first identified by determining the physical properties required to conduct electrorefining at the same conditions commonly used in plutonium electrorefining, a molten metal and molten CaCl 2 at 1123 K. Ce-CeCl 3, In-InCl 3, and Pb-PbCl 2 were the only potential surrogates identified using these constraints. Sn-SnCl 2 was also tested at these same conditions. More potential surrogates were identified by changing the matrix salt and operating temperature. This expanded the potential surrogate list to also include Zn-ZnCl 2 , Sn-SnCl 2 , and Bi-BiCl 3. Zn-ZnCl 2 was used with the LiCl-CaCl 2 (65:35 mol%) eutectic at 773 K. Sn-SnCl 2 and Bi-BiCl 3 were used with the LiCl-KCl-CaCl 2 (50.5:44.2:5.3 mol%) eutectic at 673–773 K. Ce electrorefining in molten CaCl 2 resulted in a difficult to separate colloid mixture of Ce, Ca and Cl. Electrorefining rates for In in molten CaCl 2 were too slow due to InCl 3 volatilizing out of the molten salt. Only trace amounts of SnCl 2 was retained in the CaCl 2 at 1123 K resulting in impractical electrorefining rates. Zn metal product was successfully collected in the LiCl-CaCl 2 eutectic molten salt, but the metal obtained did not coalesce into one piece. Sn and Bi were successfully electrorefined in the LiCl-KCl-CaCl 2 eutectic molten salt and coalesced into product rings with high yields and coulombic efficiencies. While a surrogate could not be identified using the same conditions as plutonium electrorefining, two possible surrogates, Sn-SnCl 2 and Bi-BiCl 3, were found that could imitate the physical configuration (i.e., molten salt on top of molten metal) of plutonium electrorefining at a reduced temperature using the eutectic LiCl-KCl-CaCl 2 salt at 673–773 K in place of CaCl 2 at 1123 K. [ABSTRACT FROM AUTHOR]

Abstract Direct electrolytic reduction (DER) of UO 2 utilizes a molten LiCl-Li 2 O electrolyte operating at 650 °C.Productive processes at the cathode are UO 2 and Li 2 O reduction (followed by metallothermic reduction of UO 2 by Li metal). Non-productive reduction current has been observed that could be attributed to impurities produced from interaction of the salt with water. Cyclic voltammetry (CV) scans of molten mixtures of LiCl containing Li 2 O, LiOH, and/or Li 2 O 2 indicate that LiOH is the primary cause of reduction current preceding UO 2 and Li 2 O reduction. LiOH reduction appears as a broad soluble-soluble transition and forms a pre-reduction plateau characteristic of micro-electrode reactions. Electrochemical response to LiOH in the salt is reduced with addition of Li0, providing a practical approach to eliminating LiOH from LiCl-Li 2 O salt before the DER process. Generation of H 2 gas was detected while heating Li0 with LiCl-Li 2 O-LiOH, consistent with a reaction mechanism where LiOH reduction causes formation of Li 2 O and H 2. [ABSTRACT FROM AUTHOR]

Improvements in the galvanic reduction of UCl 3 from LiCl-KCl- UCl 3 molten salts are reported. This process has potential application for drawdown operations for electrorefiner salt. Short circuiting a gadolinium rod to a stainless steel basket causes a galvanic reaction which results in simultaneous reduction of UCl 3 to U(0) and oxidation of Gd(0) to GdCl 3 . Two galvanic cell configurations were tested: one with the gadolinium metal inserted into the stainless steel basket, and one with the gadolinium metal separated from the stainless steel basket. When using a rotating basket and a physically separated gadolinium metal rod, concentration of uranium decreased from 0.168 to < 0.00004 mol % within 105 min, representing over 99.97% removal from salt. Electrochemical potential measurements were recorded for the galvanic couple, and it was found that the potential became more negative during reduction process and leveled off when all of the UCl 3 was reduced. In experiments in which MgCl 2 was added to the salt as a surrogate for PuCl 3 , it was observed to co-deposit with the UCl 3 . Other rare earth chlorides ( LaCl 3 , NdCl 3 , and CeCl 3 ) were not removed from the salt during the reduction process. [ABSTRACT FROM AUTHOR]

The electrochemical behavior of MgCl 2 in molten LiCl-KCl eutectic was investigated to evaluate its suitability as a surrogate for PuCl 3 in studies related to the eletrorefining of used nuclear fuel. The reduction of Mg 2+ was found to be electrochemically reversible up to 300 mV s −1 at 773 K. The diffusion coefficient for Mg 2+ was calculated to be 1.74 and 2.17 × 10 −5 cm 2 s −1 with and without U 3+ present, respectively, at 773 K using cyclic voltammetry (CV). Upon comparison to literature data, the diffusion coefficient of Mg 2+ differs by only 8.8% (with U 3+ present) from that of Pu 3+ and the difference in peak potentials was only 79 mV. Binary-analyte mixtures of UCl 3 and MgCl 2 in eutectic LiCl-KCl were further investigated using CV, normal pulse voltammetry (NPV), chronoamperometry (CA) and open-circuit potential (OCP) measurements for the purpose of comparing each technique's accuracy in measuring U 3+ and Mg 2+ concentrations. Of all the techniques tested, NPV resulted in the lowest error which was, on average, 11.4% and 9.81% for U 3+ and Mg 2+ , respectively. [ABSTRACT FROM AUTHOR]

Understanding the electrochemical properties of rare earth elements is important for developing efficient techniques for separating rare earth elements from actinides recovered during the electrodeposition process. In this study the cyclic voltammetry for lanthanum in molten LiClKCl eutectic was recorded at 773 K for different scan rates and different bulk concentrations. A model accounting for mass transport, kinetics and adsorption was applied to analyze the experimental data via performing a nonlinear least squares fit. The results of the simulation are compared against the results of a conventional analysis of the cyclic voltammograms and against the existing literature. At the scan rates used, the reduction/oxidation process is quasi-reversible. The values of diffusivities derived from simulation were larger than the ones derived commonly using equations for diffusion-limited processes. However, those equations were derived based on an assumption of reversibility. This simulation-based approach may provide a more accurate option for analyzing systems that do not exhibit reversibility. [ABSTRACT FROM AUTHOR]

Abstract: This study examines how much cell potential changes with five differently assumed real anode surface area cases. Determining real anode surface area is a significant issue to be resolved for precisely modeling molten salt electrorefining. Based on a three-dimensional electrorefining model, calculated cell potentials compare with an experimental cell potential variation over 80h of operation of the Mark-IV electrorefiner with driver fuel from the Experimental Breeder Reactor II. We succeeded to achieve a good agreement with an overall trend of the experimental data with appropriate selection of a mode for real anode surface area, but there are still local inconsistencies between theoretical calculation and experimental observation. In addition, the results were validated and compared with two-dimensional results to identify possible uncertainty factors that had to be further considered in a computational electrorefining analysis. These uncertainty factors include material properties, heterogeneous material distribution, surface roughness, and current efficiency. Zirconium’s abundance and complex behavior have more impact on uncertainty towards the latter period of electrorefining at given batch of fuel. The benchmark results found that anode materials would be dissolved from both axial and radial directions at least for low burn-up metallic fuels after active liquid sodium bonding was dissolved. [Copyright &y& Elsevier]

Abstract: The reaction kinetics of ZrN and HfN immersed in a quaternary salt of composition of 28.5% LiCl–36.3% KCl–29.4% NaCl–5.8% UCl3 (in weight percent) were assessed. Coupons of ZrN and HfN were exposed to the quaternary salt at 525–900°C for 4–485h. The reaction kinetics of the salt-refractory interactions were assessed through physical and microstructural characterization including scanning electron microscopy, X-ray diffraction and mass spectrometry. The results indicated that ZrN and HfN lose weight under all conditions investigated. While multiple mechanisms were evident, it is proposed that dissolution and oxidation were the dominant reactions that influence the weight loss. For the overall reaction, negative apparent activation energy values of −46 and −28kJ/mol were observed in ZrN and HfN, respectively. These seemingly anomalous activation energies were associated with the simultaneous occurrence of electrochemical dissolution and surface oxide formation. [ABSTRACT FROM AUTHOR]

The properties of a dehalogenated salt waste form (DSWF) were investigated for the immobilization of electrorefiner salt waste from the pyrometallurgical reprocessing of used nuclear fuel. Dehalogenation of salt through reaction with hydrogen-Y zeolite provides a viable means of decreasing solid waste volume prior to immobilization. The presence of residual salt (from insufficient dehalogenation reaction time or inefficient operation) on waste form properties is also evaluated via hot stage X-ray diffraction and leach testing. Residual salt appears to volatilize during sintering, producing a secondary waste stream. The kinetic dissolution rates of DSWFs show evidence of congruent dissolution and exhibit lower dissolution rates compared to the baseline GBS advanced ceramic waste form. Additional characterization is required to determine behavior due to saturation effects. [ABSTRACT FROM AUTHOR]

A purification process involving simultaneous chlorination and volatilization is reported using aluminum, iron, gallium, and uranium separation from cerium metal as the demonstration system. Anhydrous Cl 2 gas was reacted with the metal after it had been converted to small particles of hydride at temperatures ranging from 523 to 973 K. Each of the impurities should form chlorides with relatively high saturated vapor pressures. The objective of the process was to volatilize these chlorides after first achieving near-complete conversion of the metals to hydride and then chlorides. Complete conversion of hydrides to chlorides could not be achieved using relatively low-grade (99.5%) Cl 2. High decontamination factors for all of the metal impurities required near complete conversion to chloride. It was concluded that oxygen contamination of the feed gas stream likely limits the conversion to chlorides by forming oxides instead, which then limits the volatilization of contaminants. Uranium was particularly challenging to remove in experiments suspected of having high oxygen contamination in the feed gas stream. After switching to ultra-high purity (99.999%) Cl 2 , complete conversion to chlorides within the measurement error was possible for the entire temperature range studied. Decontamination factors for aluminum, iron, gallium, and uranium were found to have average values of 1.9, 9.8, 14, and 5, respectively, at 973 K. While the process was most extensively studied using a once-through gas flow, recycling unreacted Cl 2 gas succeeded at minimizing waste while still maintaining complete conversion and similar decontamination factors. [ABSTRACT FROM AUTHOR]

Hydriding and chlorination of buttons of metallic cerium have been tested as a head-end step to separating metal impurities from actinides. The objective was to achieve complete conversion to chlorides while maintaining high surface area via small particles and open porosity. Hydriding by reaction with 100% H 2 gas at 573 K was successful at reducing cm-scale metal buttons into small particles/fragments. This step was followed by reaction with flowing 99.5% anhydrous Cl 2 gas at temperatures ranging from 423 to 573 K for 60 min. In experiments reported here, up to 92% conversion to cerium chloride was achieved from reacting with the anhydrous chlorine gas. The final chloride product has high porosity coupled with small particle sizes (microns to 1600 μm), which makes it suitable for subsequent purification processes. Higher chlorine concentrations in the gas favor higher conversion to chloride. The optimal temperature to achieve high chlorination is 523 K. Oxygen is a minor impurity in the chlorine gas which appears to prevent complete chlorination from being achieved. [ABSTRACT FROM AUTHOR]

Molten salt mixtures containing LiCl-KCl-UCl 3 -CeCl 3 were used as surrogates for molten salt reactor fuel in a study of electrochemical concentration analysis. Current responses to low concentration CeCl 3 (0.5 wt% Ce) in molten eutectic LiCl-KCl with high concentration UCl 3 (5 and 10 wt% U) were measured using cyclic voltammetry (CV) and square wave voltammetry (SWV). CV peaks associated with CeCl 3 were impossible to quantify because of dominant reducing current contribution from UCl 3. SWV results featured peaks from UCl 4 , UCl 3 , and CeCl 3 with minimal baseline interference. A potential hold at −1.5 V for 100 s was effective at cleaning the working electrode in between each SWV scan, which enabled generating reproducible (with ±1.10% average error) peak current results for CeCl 3 over a period of 2 h. The peak current density for CeCl 3 increased by 8.3% from doubling the U concentration from 5 to 10 wt%, thus indicating that this method is promising for measuring minor metal ion concentrations in molten salt reactor fuel with high U concentrations. [ABSTRACT FROM AUTHOR]