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Our previous work ("Method Development for Quantitative Analysis of Actinides in Molten Salts" 2015) 1 demonstrated that by following a set of developed procedures and a refined data analysis method, cyclic voltammetry can be used for very precise, real-time quantitative concentration measurements of actinides in molten salts. This work examines the suitability of the established procedures over a wider range of concentrations comparable to those expected in the normal operation of an electrorefiner used in the pyrochemical processing of used nuclear fuel. We found that electrochemical methods can be used for very precise concentration measurements up to approximately 2 wt%. For higher actinide concentrations, the value of the diffusion coefficient decreases and these variations have to be taken into consideration. We also investigated the application of voltammetry for analyzing systems containing multiple elements (U 3+ and Pu 3+ ) and found that a zero current baseline determination of the second or succeeding peak in the voltammogram is not a correct approach, since that peak is affected by the tail from the peak that preceded it. We then used a different method of data analysis that allows for an accurate baseline determination and can be used to analyze systems involving more than one component. Pyrochemical reprocessing technology represents a promising alternative to aqueous processes for separating actinides from the remaining irradiated fuel by employing electrolytic methods in a molten salt media.2-8 The electrorefiner is the centerpiece of the process, in which uranium (U) and transuranic elements are separated from the bulk of the fission product elements by electrotransport onto a solid or liquid cathode. High-precision, real-time concentration measurements of actinides in molten salts are required to monitor the progress of the process and could be used for material control and accountability measurements. The development of these measurements is essential for implementing and operating a commercial fuel reprocessing facility.9-11 Electrochemical techniques are very well-suited for this purpose since they allow rapid real-time measurements, do not require the use of standards, and are compatible with remote handling operations.1,11-13 Unlike other chemical methods, they do not require the collection and preparation of representative samples, so they avoid problems that can result from contaminating the sample and its degradation. Also, the equipment is not affected by the high radiation field present in a fuel processing operation, and the analytical results can be received in a relatively short time (e.g., less than 2 minutes).In our previous work, 1 we investigated the applicability of electrochemical methods for quantitative measurements of actinide concentrations in molten salts. We demonstrated that by following a particular set of procedures, and refining data analysis and experimental methods, very precise and reproducible measurements could be achieved. The concentrations of uranium (U) a...

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This paper describes how electrochemical techniques have been used to develop a method for high-precision, real-time quantitative measurements of the concentration of actinides, present in in molten salts as actinide chlorides, for pyrochemical process monitoring applications. Possible reasons for discrepancies between reported measurements obtained with electrochemical techniques have been investigated and a combination of methods to improve their precision has been established. The combination of methods consists of selecting a suitable electroanalytical measurement technique, experimentally verifying assumptions used in its theoretical analysis, ensuring reproducible conditions at the electrode/electrolyte interface, and using an improved method to eliminate the need to know the electrode surface area. By following the developed procedures and refining both experimental techniques and data analysis methods, precise and reproducible measurements were obtained for U and Pu in LiCl/KCl eutectic at 773 K. Preliminary results showed that cyclic voltammetry, along with a method of standard area addition, are very promising tools for in situ quantitative measurements with a degree of precision comparable to destructive analysis techniques. Electrorefining is the main step in pyrochemical reprocessing. During this process, actinides are separated from the bulk of the fission product elements by electrochemical dissolution and electrotransport onto a solid or liquid cathode. The goal of the process is to maximize the separation and recovery of actinides from chlorinated fission products so that minimal amounts of actinides are lost to the process waste stream. [1][2][3][4][5] In addition to efficient actinide recovery, there is a need to address the safeguarding the recycle system. 5 Highprecision, real-time concentration measurements of actinides, present as actinide chlorides, in molten salts are required for process monitoring and control and could be used to support traditional material control and accountability techniques. Development of these measurements is essential to implement and operate a commercial fuel reprocessing facility. [6][7][8][9][10] Electrochemical techniques are well suited for in situ monitoring because they allow rapid, real-time measurements, are compatible with remote handling operations, and do not require the use of standards. Also, the equipment is not affected by the high radiation field present in a fuel processing operation.9,10 Unlike offline destructive analysis techniques, in situ methods do not require representative sample collection and preparation, and therefore avoid problems with sample contamination and degradation. In addition, analytical results can be received in a relatively short period (for example, less than 2 minutes).In an electrochemical cell, the measured potential (E), current (i), or charge (Q) is related to the quantity of the analyte in the solution; therefore, it can serve as an analytical signal for concentration measurements. 11,12 Depending on the applied...

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