1. Nuclear Hydrogen and Heat Application Research Center, Japan Atomic Energy Agency (JAEA), 4002 Narita-cho, Oarai-machi, Higashi-ibaraki-gun, Ibaraki 311-1393, Japan
2. HTR Project Group, Corporate R&D Headquarters, Fuji Electric Co., Ltd., 1-1 Tanabeshinden, Kawasaki-ku, Kanagawa 210-9530, Japan