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Experimental measurements of the basic physical properties of the melt NaF-LiF-BeF 2 are presented as validation of the concept of a molten-salt reactor for burning actinides from spent fuel from light-water reactors. Compositions which are characterized by the minimal molar fraction LiF 15-17% and BeF 2 25-27% and meet the special requirements for a fuel salt for the concept under study are found. The melts of the fluorides of three metals have an acceptable melting temperature (<500°C), permit dissolution of actinide and lanthanide trifluorides to molar fraction 2% and higher at 600°C, possess good neutronphysical (even without enrichment with respect to 7 Li) and thermophysical properties, are compatible with nickel-molybdenum alloys to temperature 750°C, are inexpensive and are not strongly activated by neutrons so that they do not present a long-term disposal risk.The handling of spent nuclear fuel and radioactive wastes imposes additional requirements on nuclear power and its infrastructure and technology. Closure of the nuclear fuel cycle makes it desirable to examine a three-component structure of nuclear power where, together with solid-fuel thermal and fast reactors, special reactors with liquid circulating fuel based on metal fluorides for burning plutonium and transplutonium actinides with a degraded composition from spent fuel of solidfuel reactors will operate. The integrated system of conversion of these actinides into molten-salt reactors (reactor + reprocessing unit) can be implemented on the basis of one fuel carrier, bypassing the fabrication and transport state with repeated recycling of the fuel.In this concept of a 2400 MW(t) molten-salt burner reactor with a hollow core, the ternary system NaF-LiF-BeF 2 was chosen as the fuel carrier [1]. The system considered is loaded only with trifluorides of plutonium and transplutonium actinides of spent fuel from light-water reactors and has a high efficiency in burning actinides due to the possibility of operating without additional neutron sources. The fraction of burner reactors of this type required to close the fuel cycle being considered can be about 25%.The optimal neutron spectrum for this reactor is an intermediate spectrum, so that the core does not contain an internal graphite moderator [1]. It is surrounded only with an external reflector, which is made of graphite. In such a system, the specific power density with respect to fuel salt is ~47 W/cm 3 . It is supposed that the inert gases will be automatically removed (in 30 sec) by flushing with helium and noble metals (in 2.5 h) from the core. For the chosen scenarios of the fuel load with

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