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Status of research and development of advanced tritium breeder in broader approach activities

幅広いアプローチ活動における先進トリチウム増殖材料に関する研究開発の現状

星野 毅

Hoshino, Tsuyoshi

日本と欧州で核融合エネルギー開発の早期実現をはかることを目的として行う研究開発である幅広いアプローチ(BA)活動の一環として、水素により還元されにくく、Liの蒸発及び核的燃焼に対する耐久性の高い先進トリチウム増殖材料として、Li$$_{2}$$TiO$$_{3}$$よりLi/Ti比が大きく、しかもLi$$_{2}$$TiO$$_{3}$$の結晶構造を持つ先進トリチウム増殖材料であるLi添加型Li$$_{2}$$TiO$$_{3}$$(Li$$_{2+x}$$TiO$$_{3+y}$$)の研究開発を行った。始発原料に水酸化リチウム一水和物とメタチタン酸を用いることで、高温・長時間使用時においても化学的に安定な単一相の結晶構造を有するLi添加型Li$$_{2}$$TiO$$_{3}$$が合成可能となることを初めて明らかにした。さらに、このLi添加型Li$$_{2}$$TiO$$_{3}$$粉末を用い、核融合炉に装荷する際の形状である微小球を湿式造粒法により試作試験を行ったところ、約1mmのLi添加型Li$$_{2}$$TiO$$_{3}$$微小球の試作に成功した。

Lithium titanate (Li$$_{2}$$TiO$$_{3}$$) is one of the most promising candidates among tritium breeding materials because of its good tritium release. However, the mass of Li$$_{2}$$TiO$$_{3}$$ was decreased with time in the hydrogen atmosphere. It is assumed that the mass decrease indicates the loss of the oxygen contained in the sample caused by the change from Ti $$^{4+}$$ to Ti $$^{3+}$$, and that the partial pressures of Li-containing species were increased in the hydrogen atmosphere. In order to decrease the mass-change at high temperature, advanced tritium breeder with added Li should be developed to improve the physical and chemical stability in hydrogen atmosphere. In the case of the Li$$_{2+x}$$TiO$$_{3+y}$$ samples used by the present study, LiOHH$$_{2}$$O and H$$_{2}$$TiO$$_{3}$$ were proportionally mixed with the molar ratio Li/Ti of 2.2. The results of XRD measurement showed that this sample existed as non-stoichiometric compound Li$$_{2+x}$$TiO$$_{3+y}$$. Then, trial fabrication tests of advanced breeder pebbles were carried out by sol-gel method.

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