AbstractTensile and fracture behaviour of two copper alloys i.e. CuAl25 IG0 and CuCrZr and their joints with 316L(N) IG stainless steel produced by hot isostatic pressing (HIP) have been determined in unirradiated and neutron irradiated conditions. The experimental results and the numerical calculations indicate that tensile properties and fracture toughness values of the Cu/SS HIP joint specimens are reduced with respect to those of the corresponding copper base alloys. The properties of the joints are dominated by the strength mismatch between the copper alloys and stainless steel.