1. FBR Safety Unit, Advanced Nuclear System R&D Directorate, Japan Atomic Energy Agency, 4002 Narita-cho, O-arai, Ibaraki 311-1393, Japan
2. Research and Development Department, Japan Atomic Power Company, 1-1 Kanda-Mitoshiro, Chiyoda-ku, Tokyo 101-0053, Japan
3. Reactor Core and Safety Design Department, Mitsubishi FBR Systems, Inc., 2-34-17, Jingumae, Shibuya-ku, Tokyo 150-0001, Japan