Safety aspects of joints and coatings for plasma facing components with composite structures

Abstract

Silicon carbide fibres silicon carbide matrix (SiC/SiC) composites are among the most promising materials for high temperature applications, but they cannot be joined by traditional ways because they do not melt and the typical mechanical joints (rivets, bolts, etc.) are ineffective with these new materials: this is a problem for the preparation of complex structures, such as those of plasma-facing components (PFCs) for fusion reactors. Furthermore, these composites show a poor resistance towards the oxidation, they are porous and permeable to fluids. PFCs made of composite materials and in which joints and coatings are made with advanced materials pose some new problems regarding their safety. In particular, the following aspects have been addressed in this paper: (a) tritium inventory; (b) activated dust in plasma chamber; (c) accident-relevant low-activation properties; and (d) long-term relevant low-activation properties. As a result of all the above mentioned aspects, some safety-relevant guidelines for the choice of joining and coating materials for PFCs are finally discussed.