1. Graduate School of Engineering, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo 060-8628, Japan
2. Research Reactor Institute, Kyoto University, Asashiro-Nishi, Kumatori, Osaka 590-0494, Japan
3. Research Institute of Nuclear Engineering, University of Fukui, Tetsuwa-cho, Tsuruga, Fukui 914-0055, Japan
4. Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan