1. Department of Chemical Science and Engineering, Kobe University, 1‐1 Rokkodai, Nada, Kobe 657‐8501 (Japan), Fax: (+81) 78‐803‐6181
2. Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2‐12‐1 O‐okayama, Meguro‐ku, Tokyo 152‐8550 (Japan)