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. Power Reactor and Nuclear Fuel Development Corporation O-arai Engineering Center, 4002 Narita O-araimachi, Ibaraki-ken 311-13, Japan
4. Tokyo Institute of Technology Department of Mechanical Engineering, Ookayama Meguro-ku, Tokyo 152, Japan