Title: Thermodynamics of Molten Salts for Nuclear Applications - JRC-ITU-TN-2008/40
Authors: BENES Ondrej
Publisher: European Commission - Joint Research Centre - Institute for Transuranium Elements
Publication Year: 2008
JRC N°: JRC50490
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC50490
Type: PhD Theses
Abstract: The molten salt reactor (MSR) is one of the six reactor concepts of the Generation IV initiative, an international collaboration to study the next generation nuclear power reactors. The fuel of the MSR is based on the dissolution of the fissile material (235U, 233U or 239Pu) in a matrix of a molten salt that must fulfill several requirements with respect to its physical properties. These requirements are very well satisfied by the various systems containing alkali metal and alkali earth fluorides. In this study in total 32 binary fluoride systems have been thermodynamically assessed in order to predict the fuel properties in terms of the melting behaviour, the vapour pressure and the solubility of the actinides in the fuel matrix. Based on these properties, in total eight fuel compositions for the MSR have been proposed. As part of the experimental study, two gas tight crucibles have been developped in order to measure the fluoride samples up to high temperatures. One is designed for a drop calorimeter used to measure the heat capacity of the (Li,Na)F liquid solution, whereas the other one is designed for a Differential Scanning Calorimeter (DSC) which was used to determine the equilibrium data points of the NaNO3-KNO3, RbF-CsF and CaF2-ThF4 binary systems. The data of the two latter systems were used to improve our thermodynamic database. The Schottky contributions of the UPd3 sample were measured by the drop calorimeter and a very good correlation to the theoretical curve has been obtained. This measurement also confirmed that the drop calorimetry is in general a very sensitive method to determine relatively small energies. An approach of obtaining the excess Gibbs energies of the solutions ab initio has been demonstrated in the case of (Rb,Cs)F solid solution and a very good correlation with the measured solidus and liquidus data has been observed.
JRC Directorate:Nuclear Safety and Security

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