IFMIFターゲットアセンブリ構造設計検討

Investigation of IFMIF target assembly structure design

井田 瑞穂; 中村 博雄; 山村 外志夫*; 杉本 昌義

Ida, Mizuho; Nakamura, Hiroo; Yamamura, Toshio*; Sugimoto, Masayoshi

国際核融合材料照射施設(IFMIF)のターゲットアセンブリの背面壁は強い中性子照射を受けるため、アセンブリとの接合部をリップ構造として溶接により交換する構造となっている。中性子照射下での背面壁の熱応力と変形を低減するうえで重要である背面壁の押し付け圧力を、限られた配置スペース内で機械式クランプによりどれだけ実現できるか検討し、背面壁の内外圧力差0.4MPaまで可能であることを明らかにした。また、液体リチウムが装荷時に凝固しないようにアセンブリの温度を維持するための保温材として熱伝導が小さいものを調査し、その保温材がアセンブリ温度300C程度まで熱伝導率0.008W/mKを維持できるとすると、必要な保温材厚さは8.2mm,重量は32kgで済むことを明らかにした。保温材が施工できない背面壁の温度維持のための高発熱密度ヒーターも調査し、配置・施工を検討した結果、窒化珪素ヒーターを用いて必要発熱量8.4kWを達成できることを明らかにした。さらに、アセンブリをリチウムループから分離・結合する際の揺れ止めと位置決めのための遠隔操作機器の構造も検討した。

In the International Fusion Materials Irradiation Facility (IFMIF), the back-wall of target assembly is the part suffered the highest neutron-flux. The back-wall and the assembly are designed to have lips for cutting/welding at the back-wall replacement. To reduce thermal stress and deformation of the back-wall under neutron irradiation, contact pressure between the back-wall and the assembly is one of dominant factors. Therefore, an investigation was performed for feasible clamping pressure of a mechanical clamp set in limited space around the back-wall. It was clarified that the clamp can give a pressure difference up to 0.4 MPa between the contact pressure and atmosphere pressure in the test cell room. Also a research was performed for the dissimilar metal welding in the back-wall. Use of 309 steel was found adequate as the intermediate filler metal through the research of previous welding. Maintaining a temperature of the target assembly so as to avoid a freezing of liquid lithium is needed at the lithium charge into the loop before the beam injection. The assembly is covered with thermal insulation. Therefore, a research and an investigation were performed for compact and light thermal-insulation effective even under helium (i.e. high heat-conduction) condition of the test cell room. The result was as follows; in the case that a thermal conductivity 0.008 W/mK of one of found insulation materials is available in the temperature range up to 300C of the IFMIF target assembly, needed thickness and weight of the insulation were respectively only 8.2 mm and 32 kg. Also a research was performed for high-heat-density heaters to maintain temperature of the back-wall which can not be cover with insulation due to limited space. A heater made of silicon-nitride was found to be adequate. Total heat of 8.4kW on the back-wall was found to be achievable through an investigations of heater arrange.