1. Ship Research Institute, Nuclear Ship Division 6-38-1 Shinkawa, Mitaka, Tokyo 181, Japan
2. Institute of Plasma Physics Nagoya University, Furo-Cho, Chikusa-Ku, Nagoya 464, Japan
3. Kyoto University, Department of Nuclear Engineering Yoshida-Honmachi, Sakyo-Ku, Kyoto 606, Japan