1. Nuclear Fuel Cycle Engineering Laboratories, Japan Atomic Energy Agency, 4-33 Muramatsu, Tokai, Ibaraki 319-1194, Japan
2. Materials Sciences Research Center, Japan Atomic Energy Agency, 1-1 Koto, Sayo, Hyogo 679-5148, Japan
3. Environmental Geology Laboratory, Faculty of Engineering, Hokkaido University, Kita 13 Nishi 8, Sapporo, Hokkaido 060-8628, Japan