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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]

One of the major sources of error for electroanalytical measurements in high-temperature molten salts is from the measurement of the working electrode (WE) area. A glass sealed working electrode (GSWE) was developed in order to set the exposed area of tungsten and reduce the error associated with WE area. The insulating property of the glass while in contact with molten salt was verified by observing the independence of electrochemical signals with adjustments in the WE position. The integrity of the glass coating was also confirmed by observing the stability of electrochemical signals (±1.9%) over several hours. Cyclic voltammetry (CV) and normal pulse voltammetry (NPV) were applied at 10 different concentrations of UCl 3 . Above 0.17 mol dm −3 UCl 3 , the electrochemical signals from CV and NPV deviate significantly from linearity with concentration, but in opposite directions. A shift from reversible to quasi-reversible behavior and migration are theorized to cause the non-linearity for CV and NPV, respectively. A model is proposed to account for migration in NPV resulting in a significant error reduction in the electrochemical concentration measurement. [ABSTRACT FROM AUTHOR]

Transparent system experimental studies have been performed to provide measurement and analysis of oxygen bubble distributions at different sparging rates in LiCl-KCl molten salt at 500°C using a high-speed digital camera and an oxygen sensor. The results reveal that bubble sizes and rise velocities increased with an increase in oxygen sparging rate. The bubbles observed were ellipsoidal in shape, and an equivalent diameter based on the ellipsoid volume was calculated, ranging from 0.00263 m to 0.00407 m. Results also show that the bubble equivalent diameters are normally distributed. A Fanning friction factor correlation was used to predict a bubble's rise velocity. The oxygen mass transfer coefficients were calculated using the oxygenation model; these values were on the order of 10-4 m/s and followed a decreasing trend corresponding to an increasing bubble size and sparging rate. The diffusivities were calculated based on two different approaches--one based on physics of the bubbles and the other on systematic properties. The diffusivity values calculated from bubble physics are 1.65 x 10-9 m²/s to 8.40 x 10-4 m²/s, which are within the range suggested by literature for gases in liquids of a similar viscosity. [ABSTRACT FROM AUTHOR]

Abstract: A parametric study has been conducted to identify the effects of several parameters on the separation of CsCl from molten LiCl–KCl salt via a melt crystallization process. A reverse vertical Bridgman technique was used to grow the salt ingots. The investigated parameters were: (1) the advancement rate, (2) the crucible lid configuration, (3) the amount of salt mixture, (4) the initial composition of CsCl, and (5) the temperature difference between the high and low furnace zones. From each grown salt ingot, samples were taken axially and analyzed using inductively coupled plasma mass spectrometry. Results show that CsCl concentrations at the top of the ingots were low and increased to a maximum at the bottom of the salt. Salt (LiCl–KCl) recycle percentages for the experiments ranged from 50% to 75% and the CsCl composition in the waste salt was low. To increase the recycle percentage and the concentration of CsCl in the waste form, multiple crystallization stages were explored showing that they were practical under the optimal experimental conditions at 5.0mm/h rate with a lid configuration and temperature difference of 200°C for a total of five crystallization stages. Up to 88% of the LiCl–KCl salt can be recycled under these proposed conditions. [Copyright &y& Elsevier]

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]