1. Japan Atomic Energy Agency; Horonobe Underground Research Center; 432-2, Hokushin, Horonobe-cho, Hokkaido 098-3224 Japan
2. Northern Advancement Center for Science & Technology; Horonobe Research Institute for the Subsurface Environment; 5-3, Sakae-machi, Horonobe-cho, Hokkaido 098-3221 Japan
3. Division of Sustainable Resources Engineering, Faculty of Engineering; Hokkaido University; North 13 West 8, Kita-ku, Sapporo Hokkaido 060-8628 Japan