Novel granulation process of beryllide as advanced neutron multipliers

先進中性子増倍材としてのベリライドの新造粒プロセス

中道 勝; 金 宰煥; 米原 和男

Nakamichi, Masaru; Kim, Jae-Hwan; Yonehara, Kazuo

核融合原型炉の早期実現を目指した幅広いアプローチ(BA)活動において、高温下の安定性に優れたベリリウム金属間化合物(ベリライド)の製造技術開発の一環として、ベリライドの微小球製造プロセスを新たに開発した。ベリライド合成手法としては、従来法である熱間等方加圧法や鋳造法などでは、均質な材料が得られず、工程も複雑であり、ベリライドの合成すら困難であった。今回は、ベリライド合成にプラズマ焼結法を適用することにより、簡便に脆くないベリライドを合成することに成功した。プラズマ焼結法は、原料粉末にパルス電流を負荷することによって材料表面を活性化(清浄)し、焼結性を向上させる手法であり、これにより表面酸化層などの不純物を除去でき、脆くない焼結体を形成できる手法である。そして、プラズマ焼結製のベリライドを用いて、回転電極法により目標形状である直径1mmの微小球製造にも成功した。

Advanced neutron multipliers with lower swelling and higher stability at high temperature are desired in pebble-bed blankets, which would have a big impact on the design of a DEMO reactor, especially on the blanket operating temperature. Development of advanced neutron multipliers has been started by Japan and EU in the DEMO R&D as a part of the Broader Approach (BA) activities. Beryllium intermetallic compounds (beryllides) such as BeTi are one of the most promising advanced neutron multipliers. In order to fabricate the beryllide pebbles, beryllide with shapes of block and/or rod is necessary when a melting granulation process is applied such as a rotating electrode method. However, beryllide is too brittle for the fabrication of blocks or rods by these methods. A plasma sintering method has been proposed as new technique which uses a non conventional consolidation process, because this method is simple, and is easy to control. It was clarified that the beryllide could be simultaneously synthesized and jointed by the plasma sintering method in the insert material region between two beryllide blocks, with no variation of the phase and hardness. Beryllide rod of BeTi with 10 mm in diameter and 60 mm in length has been successfully fabricated by the plasma sintering method. Using this plasma-sintered beryllide rod, prototype pebble of beryllide was performed by a rotating electrode method. The prototype pebbles of BeTi with 1 mm in average diameter were successfully fabricated. The present paper describes novel granulation process of beryllide using these methods including fabrication and granulation techniques.