Several radioactive iodine isotopes are formed as fission products in the nuclear fuel, and retained within the fuel matrix by the fuel cladding as containment. During reprocessing of the used fuels by the pyroprocessing route, a significant fraction of iodine is reported to be retained in the molten salt as iodide (I -). The oxidation of Iis strongly influenced by the Cl -. When Clconcentration is in excess of I -, the iodide oxidizes to [ICl2]in two single electron steps via an [I2Cl]intermediate. The presence of chloride leads to oxidation of I3to occur at less positive potentials. Chemla effect of type 1 has been observed in the LiCl-KCl molten salt systems wherein the mobility of the K + is larger than that of Li + when the fraction of KCl is higher than 0.325 at 723 K. The Chemla effect could lead to accumulation of KCl near the cathode and adversely influence the electrolytic parameters.
Practical information is provided on electrochemical measurements in molten salt systems. The emphasis is on chloride and fluoride systems, but the principles are applicable to any high-temperature molten salt or molten oxide electrolyte system. Considerations are given to topics such as the functionality of electrochemical measurement equipment, reference electrodes, materials selection and chemical compatibility, interpretation of electrochemical measurement signals, molten salt properties, and laboratory practices.
Reprocessing and/or waste management issues are of concern to the "back end" of the nuclear fuel cycle. Of course, there are a great many "nuclear fuel cycle" scenarios to consider; if not in practice, then at least in theory. The simplest conceptually is the "once through" fuel cycle in which the spent fuel is discarded. The more complex fuel cycle scenarios involve reprocessing spent nuclear fuels and a family of nuclear reactor technologies to accommodate burning and breeding for various military and commercial needs. Therefore, the selection of a specific "fuel cycle" is what ultimately imposes the engineering requirements of the reprocessing and waste management technologies. No one part is independent of the other parts in a fuel cycle flowsheet; all parts should be fully integrated. This paper presents a summary of nuclear chemistry processes, nuclear reactor technologies, associated nuclear fuel types, and the reprocessing technologies that serve the different nuclear fuel types. Comprehending how this series of topics are related to each other is a prerequisite to understanding the requirements of any reprocessing strategy. The summary materials presented here are selective, as opposed to comprehensive. More detailed information on any one subject can be found in the reference materials.
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