This work was carried out to obtain sound welds and to select the most suitable binary metal joint among three different dissimilar metal combinations such as Zr-4/Ta, Mo/Ta and Ti/Ta (seal tube/sensor sheath) joints for an instrumented nuclear fuel irradiation test. To do this, the Taguchi experimental method was employed to optimize the experimental data. In addition, metallography, micro-focus x-ray radiography and a hardness test were conducted to examine the welds. From the weld bead appearance, penetration depth and bead width as well as the weld defects standpoint, the Zr-4/Ta joint is suggested for a circumferential joining between a seal tube and a sensor sheath. The optimized welding parameters based on the Zr-4/Ta joint are suggested as well.