The Horonobe Underground Research Laboratory (URL) project has been being pursued to develop the geological disposal technology of HLW intended for a sedimentary rock (mudstone) and saline groundwater distributing in the Horonobe area, north part of Hokkaido, Japan, as an off-site URL, since 2001. This project, extended over a period of about 20 years as a whole, has been being advanced divided into 3 phases; surface-based investigation phase (Phase I), construction phase (Phase II) and operation phase (Phase III). Phase I was completed in March, 2006 and Phase II initiated in November, 2005. In Phase I, the geological environment model (geology/geological structure, hydrology, groundwater chemistry and rock mechanics) was constructed based on the results of geophysical survey and deep borehole investigation, etc., and design of underground facilities and decision of the construction plan were carried out. The underground facilities consist of a ventilation shaft (the Ventilation shaft), 2 access shafts (the East and the West access shafts) and several horizontal drifts (140m, 250m, 350m and 500m in depth). By the first half of FY2010, both of the Ventilation shaft and the East access shaft were excavated up to 250m in depth and the 140m depth gallery was completed. The 250m depth drift was additionally connected between the Ventilation shaft and the East access shaft. The geological formation in the URL area consists of mainly the Koetoi Formation (shallower formation) and the Wakkanai Formation (deeper formation). During construction, so far, in-situ experiments and investigations for the geological environment and engineering technology such as measurements for EDZ/EdZ (Mine-by experiment, seismic tomography, hydraulic investigations, etc.), cross-hole hydraulic tests, initial rock stress measurements, in-situ construction test of shotcrete by low alkaline cement, etc. were carried out in the 140m depth gallery. Presently, monitoring of groundwater chemistry, measurements for EDZ/EdZ, etc. are on-going. Phase III will start from the latter half of FY2010 in parallel with investigations in Phase II. Various in-situ experiments such as performance test of EBS, corrosion test of overpack material, backfilling test of a tunnel, etc. are planned in the underground facilities. This paper reports status of in-situ experiments carried out so far and outline of construction plan of the underground facilities in the JAEA's 2nd midterm plan (FY2010-2014) and in-situ investigation and experiment plan in the underground facilities in Phase III.
