Advanced study of tritium recovery from molten salt Flibe blanket in fusion reactor

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Flibe (2LiF+BeF_2 mixed molten salt) is expected to be an advanced liquid blanket fluid for a helical-type DEMO fusion reactor called FFHR-2 because it has an ability of good thermal conductance and high tritium breeding ratio under high magnetic field and high-density neutron flux. However, it has disadvantages that it is difficult to handle tritium in the molten salt because of generation of tritium fluoride and the recovery and enclosure of tritium are difficult. Therefore, there was less application to conceptual design of fusion reactors and therefore less experimental studies on Flibe/tritium chemistry. In the present study, we investigated experimentally the permeability of hydrogen isotopes through Flibe and reduction-oxidation (redox) control by Be rods immersed in Flibe that will provide important data to design fusion reactors. The main purpose of the present study is to propose a new blanket circulation loop system composed of Flibe ducts, a tritium extraction system and a … More heat exchanger that can control to a rate lower than 10 Ci/day of acceptable tritium leak rate and a tritium concentration lower than 1 ppm of acceptable tritium inventory. The following findings were obtained from the experiment and analysis of the present study :1.We determined the permeability of deuterium through molten Flibe enclosed in a dual-tube Ni permeation vessel. Judging from the permeability, diffusivity and solubility of deuterium in Flibe, hydrogen isotopes are resent as a H^+ ion in Flibe. Therefore strong interaction between H^+ and F^- ions was observed, and HF (DF or TF) is a main species diffusing in non-redox controlled Flibe.2.We determined hydrogen H_2 through Flinak (a LiF+NaF+KF mixed molten salt), and hydrogen was present as a molecular form in it. This is because there is no tetragonal network of BeF_4^<2-> different from the Flibe case. F^- ions in Flinak were localized in the vicinity of Li^+, K^+ and Na^+ ions. In other words, there are much less free F^- ions in Flinak, and therefore Flinak corresponds to the well redox-controlled Flibe.3.Flibe was successfully redox-controlled by Be immersed in it. This is because free F- ions that were present in non-controlled Flibe were changed to BeF_2 by the reaction with Be dissolved in Flibe physically. The free F^- ions were consumed by the redox reaction and hydrogen in Flibe was present in a molecular form. Consequently, tritium will be present in a molecular form in well redox-controlled fusion reactor blankets when Be is used as a neutron multiplier.4.In order to maintain the tritium leak rate in a 1GW fusion reactor lower than the acceptable level (10 Ci/day), we need a sophisticated tritium recovery system made of low permeable materials. We provided design equations for tritium permeable window, bubbling tower and spray tower for high tritium recovery, and each apparatus was designed using the equations. Less