A. Sagara

O. Motojima

S. Tanaka

T. Terai

National Institute for Fusion Science (NIFS-Repository)

§3. Chemical Aspects in Molten-salt FLIBE System Design for FFH R Tanaka, S., Terai, T. (Univ. Tokyo), Sagara, A., Motojima, 0. Liquid tritium breeding materials have m<my advantages such as no irradiation dcunage, easy control of chemical composition, and continuous replacement in the blanket. Among liquid breeder e<mdid.:'ltes, the molten mixture of lithium fluoride and beryllium fluoride (60(~LiF-40c?(,BeF:-! denoted as FLIBE) is a promising material for the blanket in FFHR because of its chemical stability, large fluidity and low electric conductivity to reduce ~1HD pressure drop. The applicability of FLIBE molten-salt as the tritium breeding material for FFHR was discussed to design the most suitable and adv<mced blanket. \Ye investigated some chemical aspects such as material compatibility, tritium breeding <md tritium recovery to point out the insufficiencies of basic studies for FLIBE. The FLIBE temperatures at the inlet and the outlet of the blanket were determined to be 723 K and 823 K, respectively, based on the melting point of FLIBE and the creep behavior of .TFL-1 considered as a structural material. It is considered that beryllium loaded inside the FLIBE flow in the blanket for high TBR reduce TF produced by the nuclear reaction of LiF with neutron. By the reduction of HF, the corrosion for the structural material may become moderate, but tllis means the corrosion of beryllium metal proceeds. Thus, we should not only predict the corrosion behavior from the thermodynamic point of view, but investigate the dis sol uti on of beryllium and corrosion behavior of beryllium and structural materials by experiment. From the viewpoint of tritium inventory and corrosion behavior T2 or I-IT is more favorable than TF, and TF concentration should be kept as lovv as possible in the blanket system. Because the rate of the chemical reaction of TF with H2 dissolving in FLIBE to produce m· is not enough high to keep TF concentration low, experiments on the reaction rate of TF with beryllium are very important. HT and T 2 having a large release rate coefficient to the gas phase arc considered to penneate easily through the structural material to the enviromnent, whlch should be prevented for safety cu1d lligh efficiency of tritium recovery. Because the tubing walls for FLIBE should be the first barrier for tritium penneation, it is necessary to use a chemical barrier between the first and the second tubing \Valls of a doublc-\vall tube . For excunple, if He + 0 2 gas is used as a chenlical getter, chemical fonn of tritium penneating through the first tubing wall changes from T :-! to T 20 , which hardly penneates through the second tubing wall at all. The heat exchanger wall must also have a chemical barrier to reduce hitium penneation to the secondary loop . The chemical bcuTicr for the heat exchange wall must transfer heat at an enough large rate with small tritium penneation rate . Rowing liquid metal or pressurized gas is considered as the tritium penneation barrier having a lligh heat transfer coefficient, but further investigations are required. In order to increase the rele~se rate of HT cu1d T2 from FLIBE, it is useful to make liquid FLIBE spray with a lot of nozzles of a small diruneter to increase the surface area of FLIBE droplets . With the advantage of tllis concept, we can design a FLIBE blanket loop system, whose tritium inventory is less than 0.1 g in 500 ton of FLIBE. However, we must note that <Ul investigation about the interfacial energy of FLIBE are necessary to discuss about the possibility of producing such small droplets. The diffusivity ru1d solubility in RLIBE in well -characterized conditions are essential parameters for design of the tritium recovery system. 267 

Chemical Aspects in Molten-salt FLIBE System Design for FFH R

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