Development of Welding Technique for Double Wall Tube

A helical-coil-type double wall tube with wire mesh interlayer, is proposed for a steam generator of the new-type small reactor 4S. The 4S, Super-Safe, Small and Simple is a small-sized sodium cooled fast reactor. It is necessary to make a tube-to-tube joint of an independent inner-to-inner and outer-to-outer way without bonding inner and outer walls. So we have been developing the welding techniques to satisfy this requirement. A keyhole type laser welding technique was selected and a small laser welding head, which can weld from the inside the inner tube, was developed. Using this welding head, welding conditions, such as welding speed and laser power were surveyed. As a result of the test, the welding condition, which did not make the inner and outer tubes bonding, was obtained. There was no non-adequate phase change. Tensile strength was satisfied the specification for the base metal. (author)