Application of SMAs to pipe connections, mechanical connections, vacuum seals and jack systems

The simplification of maintenance procedures for reactor structures is one of the important items for operating D-T fusion reactors. Remote maintenance applications using shape memory alloys (SMA) for fusion reactors is proposed and their feasibility discussed. Four types of SMA components have been fabricated and tested: pipe connector for primary coolant lines instead of welding/cutting, C-shaped mechanical quick connectors for segment connections instead of bolting, metal packing for vacuum seals instead of lip seal welding or metal O-rings, and jack systems for lifting heavy reactor components. For the pipe connectors, a flange-type was tested. A flange-type connector consists of two pipe flanges (SUS304, diameter 200) and twelve Ni-Ti SMA bolts (M6Xl50). A helium leak of less than 1x10-7 Pa·l/s was not detected. For the C-shaped connectors, a pair of interlocking C-shaped plates is connected by eight Ni-Ti bolts (M8Xl84) and the SMA bolt recovery force is used as the connector force. A force of 4x104N was obtained at 0.86% of the given strain. The metal packing is made by bonding SMA wire to an O-ring. A welding test of the SMA was done. Two SMA rods of 8 mm in dia. were bonded by CO2 laser welding. The shape memory effect was not lost after welding. The jack systems consist of two oblique keys connected by SMA bolts (M9Xl260). A lifting force of 2.7x104N was obtained at 1.9% of the given strain. From the results of these experiments, it was found that applications using SMAs, especially Ni-Ti alloys, is feasible for fusion reactors. (author). 7 refs, figs