Properties of liquid-salt nuclear fuel and its reprocessing technology

The chemical processes taking place in Molten Salt Reactor and in fuel reprocessing are determined by the physical-chemical properties of salt composition essentially and considered to be the basical in the ADTT - ATW facility serviceability. At present the composition of molten salt and the range of fuel involved in molten salt have been determined practically. Some fuel compositions of solvent-melt corresponding to their eutectic contents (taking into consideration their nuclear and physical properties) can incorporate LiF, NaF, BeF₂ and ZrF₄. One of the important equilibrium properties of fluoride fuel systems is solubility. Solubility of some REE (La, Nd, Sm) as well as actinides (Pu) was studied experimentally when developing the MSRE project. Noble and semi-noble metals Mo, Te, Ru and Ag were not assumed to form stable fluorides and to precipitate on the metallic surfaces. The solubility of PuF3 in molten LiF-BeF₂-ZrF₄ did not exceed 0.19-0.24 mole%. Thus, the solubility of plutonium trifluoride is sufficient for the burner reactor serviceability to be achieved. Knowing electrochemical behavior of REE, actinides and noble metals (Ru, Ag, etc.) in fluoride melts, it is possible to develop methods for their isolation from fuel salt compositions. Eectrochemical deposition of these metals in complicated by high reduction ability of actinides and especially lanthanides. The range of standard potential values of actinide and fission products elements in the fuel salt was estimated, from the values of conventional standard potential (E*). The unknown values E°,E*,E** were estimated using ratio describing the difference between E° and E* through ionic moments dissolved salt and solvent cations. On the base of this ratio the conventional standard potentials (E**) were calculated for comprising thorium, uranium, plutonium and lanthane with liquid bismuth that can be used for electrochemical separation of actinides and lanthanides in liquid salt fuel reprocessing . The fuel cycle of ADTT - ATW plant is considered taking account of fuel composition, its plutonium content, general volume of fuel salt and its reprocessing possibility. According to our version, the technological process was based on three operations of melt treatment. Inert gas treatment of molten salt fuel to remove gaseous fission products; to remove noble and seminoble fission products with-active metal; chemical fuel reprocessing to remove actinides and residual fission products; the fuel decontamination factor from impurities is about 100-500.