1. Office of Biospheric Assessment for Waste Disposal, National Institute of Radiological Sciences; 4-9-1 Anagawa Inage-ku Chiba 263-8555 Japan
2. Dep. of Radioecology; Institute for Environmental Sciences; 1-7 Ienomae, Obuchi Rokkasho-mura, Kamikita-gun Aomori 039-3212 Japan
3. Noriyoshi Tsuchiya Graduate School of Environmental Studies, Tohoku Univ.; 6-6-20 Aramaki-aza-Aoba Aoba-ku, Sendai 980-8579 Japan