[en] The microfission chambers (MFCs) provide time-resolved measurements of the global neutron source strength and fusion power from ITER. In the previous work, the MFC for low power operations (measurement range: fusion power of 100 W - 1 kW) has been designed and developed together with the MFC for high power operation (measurement range : fusion power of 1 kW - 1 GW). Combination of two types of the MFC almost covers the target measurement requirements of ITER. Signals from the MFCs are transferred by double coaxial mineral Insulated (MI) cables. The MFCs will be installed in the vacuum vessel, so that the MI cables should be placed in the vacuum vessel. In this design work, the placing route of the MI cables from the installation position of the MFC to the feed-through in the upper port is designed. As far placing of the MI cable, since the MI cable is filled with Ar gas at 14.6 atom, the double pipe structure, in which the outer pipe covers the MI cable, is going to be adopted in order to prevent the gas leak into the vacuum vessel. The exhaust system of the double pipe is also designed for detection and exhaust of the leaked Ar gas. Further, we design that copper flanges with 7 mm width for heat conductance will be installed between the MI cable and the outer pipe at interval of 300 mm, in order that the maximum temperature of the MI cable due to temperature rise by the nuclear heating doesn't exceed the operating temperature (400degC) of the MI cable in a light-water reactor. As a result, it is found that the temperature of the MI cable can be suppressed less than 340degC. (author)