1. Kyoto University, Research Reactor Institute, Kumatori-cho, Sennan-gun, Osaka 590-04, Japan
2. Osaka University, Department of Nuclear Engineering, Yamada-oka 2-1, Suita, Osaka 565, Japan
3. Oak Ridge National Laboratory, P.O. Box 2008, Bldg. 6025, Oak Ridge, Tennessee 37831-6364