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Abstract  

The calorimetric glass transition and dielectric dynamics of -relaxation in propylene glycol (PG) and its five oligomers (polypropylene glycol, PPG) have been investigated by the modulated differential scanning calorimetry (MDSC) and the broadband dielectric spectroscopy. From the temperature dependence of heat capacity of PPGs, it is clarified that the glass transition temperature (T g) and the glass transition region are affected by the heating rate. The kinetic changes of PG and PPGs near T g strongly depend on the underlying heating rate. With increasing the molecular mass of PPGs, the fragility derived from the relaxation time against temperature also increases. The PG monomer is stronger than its oligomers, PPGs, because of the larger number density of the —OH end group which tends to construct the intermolecular network structure. Adam-Gibbs (AG) theory could still hold for MDSC results due to the fact that the dielectric relaxation time can be related to the configurational entropy.

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Abstract  

In order to determine the operating conditions of an uranium reduction process with U3O8-Li-LiCl system, the operating conditions have been evaluated in thermodynamic aspects and the results were experimentally confirmed in this study. All the reduction experiments were conducted in an argon atmospheric glove box, and the resultant degree of reduction was determined by analyzing the product using XRD and TGA. In the results of this study, a reduction yield greater than 95% is achieved within about 3 hours of reaction. The effects of the added quantity of Li and LiCl to the reduction yield of U3O8 and the preferential removal of several metal oxides accompanying U3O8 in the course of reduction were discussed. For a greater reduction of U3O8, an additional 20% of Li is required when compared to the stoichiometric composition. The proper composition of LiCl is about 75% based on the weight of U3O8 charged.

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Abstract  

In order to determine the operating condition of an uranium chlorination process with U3O8-C-Cl2 system, the experimental conditions have been evaluated preliminarily by the thermochemical analysis and experimentally confirmed in this study. The dry-type chlorination of U3O8 occurs as irreversible and exothermic reaction and produces many kinds of chloride compounds such as UCl3, UCl4, UCl5 and UCl6 in the air and humidity controlled argon environment. Taking account of Gibbs free energy and vapor pressure for various chloride compounds, the proper temperature range of chlorination appears to be 863 to 953 K in aspects of increasing reaction rate and the yield of nonvolatile product. In the course of the experimental confirmation the powder of U3O8 is perfectly converted into uranium chlorides within 4 hours above 863K, and then the maximum fraction of uranium chloride remaining in the reactor is about 30% of total conversion mass.

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Abstract  

In order to determine the operating conditions of an electrolyzer to recover lithium metal from molten salt wastes composed of LiCl, Li2O, Cs2O, and SrO, electrolytic reduction experiments have been carried out in a single compartment electrochemical reactor with a mono-polar connection. All the combinative experiments were conducted in an argon atmospheric glove box, and each applied potential-current value was synchronously measured and analyzed in aspects of the preferentially recovering probability of lithium in mixed phases. The effect of the electrode surface area on the current was also observed. Based on our experimental results compared with electrochemical thermodynamic evaluation, it is revealed that Li2O can be preferentially reduced to lithium by controlled LiCl concentration and applied potential.

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Abstract  

This paper describes ongoing research into the multi-physics model development of an electrorefining process for the treatment of spent nuclear fuel. A forced convection of molten eutectic (LiCl–KCl) electrolyte in an electrorefining cell is considered to establish an appropriate electro-fluid model within the 3-dimensional framework of a conventional computational fluid dynamic model. This computational platform includes the electrochemical reaction rate of charge transfer kinetics which is described by a Butler–Volmer equation, while mass transport is considered using an ionic transport equation. The coupling of the local overpotential distribution and uranium concentration gradient makes it possible to predict the local current density distribution at the electrode surfaces.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: K. Kim, J. Bae, B. Park, D. Ahn, S. Paek, S. Kwon, J. Shim, S. Kim, H. Lee, E. Kim, and I. Hwang

Abstract  

A pyrochemical processing has become one of the potential technologies for a future nuclear fuel cycle. An integrated multi-physics simulation and electrotransport model of a molten-salt electrolytic process are proposed and discussed with respect to the recovery of pure uranium when using thermochemical data. This study has been performed to provide information for diffusion boundary layers between the molten salt (KCl-LiCl) and electrode. The diffusion-controlled electrochemical model demonstrate a prediction of the electrotransport behaviors of LWR spent fuel as a function of the time up to the corresponding electrotransport satisfying a given applied current based on a galvanostatic electrolysis.

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