1. Toshiba Corporation Nuclear Engineering Laboratory 8 Shin-Sugita, Isogo-ku, Yokohama 235, Japan
2. Toshiba Corporation Isogo Engineering Center 8 Shin-Sugita, Isogo-ku, Yokohama 235, Japan
3. Tokyo Institute of Technology Department of Mechanical Engineering, Ookayama, Meguro-ku, Tokyo 152, Japan