Overview of challenges and developments in joining tungsten and steel for future fusion reactors

In future fusion reactors, the blanket is foreseen to remove heat from the reactor and enclose material to breed tritium. While the blanket structure is made of steel, for a successful operation its first wall (FW) needs to be armoured by a tungsten layer. Joining tungsten and steel is currently a key issue in engineering nuclear fusion reactors beyond ITER as will be shown in this publication. This manuscript firstly presents the influence of the joining procedure on stress and strain fields in the FW. Secondly, general aspects that need to be considered in realizing the joint are introduced and, lastly, an overview of current approaches to realize tungsten-armoured steel is given. A comparison of the challenges and approaches leads to the conclusion that all joining techniques require much more research, and that the field currently suffers from a missing programmatic research approach.