Potential of Copper Alloys using a Divertor Heat Sink in the Helical Reactor FFHR-d1 and their Brazing Properties with Tungsten Armor by using the Typical Candidate Filler Materials*)

Abstract

A tungsten block is supposed to be used as a divertor armor material on the helical reactor FFHR-d1. On the other hand, material selection of the heat sink and bonding technique between armor and heat sink are currently under investigation. On the material selection, copper alloy has a large advantage for the thermal conductivity, but its material properties such as toughness and thermal conductivity, are dramatically decreased due to the neutron irradiation. However, from the assessment of the neutronics environment on the divertor region of the FFHRd1, copper alloys could be used for a heat sink especially at the outer divertor. In the ITER case, copper alloy (CuCrZr) pipes are joined by a brazing technique with Nicuman37 filler material. This combination has not been optimized for the FFHR-d1, because the toughness of the CuCrZr at high temperature over 450◦C is dramatically decreased with increasing the temperature. As such, another candidate is an oxide dispersion-strengthened copper alloy (ODS-Cu) such as GlidCop ®. For the bonding technique, a reliable brazing combination between “two kinds of copper alloys” and “three kinds of filler materials (MBF-20, BNi-6, Nicuman37)” were investigated from a viewpoint of mechanical strength. The most superior fracture strength among the three filler materials was BNi-6 with GlidCop ®.