1. Japan Atomic Energy Research Institute, Tokai Research Establishment Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
2. Nagoya University Department of Energy Engineering and Science, Furo-cho, Chikusa-ku Nagoya 464-8603, Japan
3. Kyoto University Research Reactor Institute, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan