JAEA is developing two off-site underground research laboratory projects in Japan: one in sedimentary rock (Horonobe, Hokkaido) and the other in crystalline rock (Mizunami, Gifu). Horonobe’s URL project consists of three phases: (i) surface-based investigation (Phase I); (ii) construction (Phase II); and, (iii) operation (Phase III). At present, Phase II has been started. In parallel, predictions of potential changes in the geological environment prevailing around the URL are in progress. Future plans after Phase II are briefly introduced as well.


Two off-site underground research laboratory (URL) projects are under construction by JAEA (Japan Atomic Energy Agency), one in sedimentary rock (Horonobe, Hokkaido) and the other in crystalline rock (Mizunami, Gifu) (Fig.1). The technical aims of the Horonobe URL project are to study the geological environment as an example of a sedimentary formation in Japan; confirming the reliability of technologies for geological disposal of High-Level Radioactive Waste (HLW). Meanwhile, the URL also has an important social aim to provide opportunities for the general public to experience an actual deep underground environment and to become familiar with the R&D activities conducted there. Research and development activities are planned over three partly overlapping phases that will span a total duration of about 20 years: the 1st surfacebased investigation phase (5 years), the 2nd URL construction phase (8 years) and the 3rd operation phase (12 years). The field investigations in Phase I started in 2001 and ended in 2006. Phase II stated in 2005 and the ventilation shaft and the east access shaft will be excavated approximately 50m in depth at the end of March of 2007.


2.1 Geological environment Geology in and around the URL area of 3000 × 3000m consists of Neogene formations shown in Figure 2 and 3.

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