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This chapter will briefly describe the current state-of-the-art of molten salt reactor research and describe various concepts studied worldwide. A variety of fuel salts will be identified and their chemical aspects discussed with an emphasis on the importance of chemical behavior on smooth operation of the reactor in the context of performance and safety. As there is much more data on actinoid-containing fluoride systems, the current chapter mainly addresses fluoride-based fuels, but where appropriate comparisons to chloride systems are made as well as halides. It will address the relevance of various thermophysical properties on the performance of the molten salt reactor with insight on the fission product chemistry and its influence on the fuel behavior.

WOS: 000345253800025, A laser heating approach combined with fast pyrometry in a thermal arrest method was used to provide new data for the melting/solidification phase transition in mixed (PuO2 + ThO2) at high temperature. At low concentration of ThO2 in PuO2 a minimum in the solidification temperature in the pseudo binary (PuO2 + ThO2) was observed. The minimum was found around a composition with 5 mol% ThO2. Phase transition temperatures of other compositions are closer to an ideal solution behaviour. To detect changes in the material a complete investigation with electron microscopy, Raman spectroscopy and powder X-ray diffraction was done. Raman vibration modes were found, that are characteristic for materials containing PuO2, and high temperature segregation effects during solidification were described. The results obtained in the present work are compared to other mixed actinide dioxides and compared to the ideal solution case for this system. The presented results show the importance of the high-temperature oxygen chemistry in this actinide oxide phase. (C) 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license., European CommissionEuropean Commission Joint Research Centre; E.ON Kernkraft GmbH [32920], The Authors are indebted to the JRC - ITU members G. Pagliosa, D. Bouexire, B. Cremer, A. Janssen and O.S. Valu for their precious help in the sample characterisation and P. Raison and A.L. Smith for the helpful discussions and valuable suggestions. This work is funded by the European Commission and partly supported by E.ON Kernkraft GmbH via contract No. 32920.

In this chapter, the properties of the actinide (5f) elements are discussed. These elements are unstable and undergo radioactive decay. Because handling them is complex and their availability is limited, it is difficult to experimentally investigate their (bulk) properties and most of the data presented here are given for the major actinides, uranium and plutonium, which have been studied extensively because they are fissile and are used as fuel in nuclear reactors.