Exploration of Potential Material - Coolant System in Application to A First Wall Structure of Fusion Reactors

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To develop a first wall structure of fusion reactors, which separates plasma and energy conversion system, solutions for material-related issues, such as irradiation induced degradation and compatibility with environments, are required. In this project, a new design concept was proposed to give a potential solution for this problem, where pressurized superheated steam is used as coolant. An experimental evaluation was carried out of the compatibility of several candidate fusion structural materials using pressurized superheated steam (up to 70℃, 100 bar) as test environment. The tested candidate materials include (1) low-activation ferritic-martensitic steel F82H, (2) vanadium alloys, and (3) TiAl-based intermetallic compounds. Based on the oxidation rates and results of oxide scale analysis, following conclusions were drawn;1. TiAl-based alloys showed the highest oxidation resistance in superheated steam environment. Steam oxidation property of F82H was equivalent to that of advanced … More heat-resistant steels for USC boiler application. Both the TiAl-based alloys and F82H have sufficient compatibility with superheated steam environment from an oxidation rate point of view.2. In particular, Ti-Al-V alloy, which has about 8% ductility at room temperature, showed excellent oxidation resistance in superheated steam.3. AlィイD22ィエD2OィイD23ィエD2 did not form as a continuous layer both for TiAl and Ti-Al-V in superheated steam, where oxidation potential of the environment was not high, and hence, AlィイD22ィエD2OィイD23ィエD2 did not work as a diffusion barrier. However, the relatively low oxidation potential of the environment does not allow to form VィイD22ィエD2OィイD25ィエD2. Therefore, accelerated oxidation did not occur for Ti-Al-V. The excellent oxidation resistance of Ti-Al-V was explained that substitutional solid solution of V in the oxide scale TiOィイD22ィエD2 lowered concentration of oxygen vacancy in the oxide scale due to smaller atomic radius of V compared with Ti and, as a result, diffusion rate of oxygen decreased. Less