The Japanese design of HFTM, so-called HFTM-H, aims to be used for high temperature irradiation test up to 1000°C for SiC/SiCf composite and refractory materials. During irradiation test periods in the IFMIF, irradiated materials must be maintained at constant temperatures. It is confirmed that the conceptual design of HFTM-H can satisfy the requirement for displacement per atom (dpa). The gas production rate to dpa ratio, which is important requirement for the design of HFTM-H as well as dpa is calculated. Nuclear heating distribution in HFTM-H is also predicted, which is served to temperature control design and structural analysis.