Current status and future prospects of the Horonobe International Project, 3; Task B: Systematic integration of repository technology options

Hayano, Akira  

In the design and construction of a repository for high-level radioactive waste, it is considered to set criteria for the rational locating of disposal tunnels and holes, taking into account the effects of faults and fractures distributed in the host rock at the tunnel to pit scale and excavation damaged zones (EDZs) that occur after tunnel excavation on the workability of the disposal tunnels and the long-term stability of the engineered barriers. In addition, tunnel sealing technologies such as tunnel backfilling and hydraulic plugs will be considered to prevent short-circuit flow of radionuclides through the excavated tunnels and the surrounding EDZs. In Task B of the HIP, we will attempt to establish criteria for the layout of disposal tunnels and holes, and the systematic integration of technical options related to the design, construction, operation and closure of the repository, using the investigation and construction at the Horonobe URL for Neogene sedimentary rocks as a case study. Based on information provided by the participating organisations and existing case studies from Japan and overseas, the current focus is on the reduction of the mechanical strength of the rock mass, the effects of water inflow on disposal tunnels and holes, or the effects on engineered barriers, in relation to the locating of disposal tunnels and boreholes and the emplacement of engineered barriers, and is currently working on analyses to predict features associated with these. Investigation, construction and testing of the 500 m niches No. 8 and No. 9 to confirm the validity of these predictions, and full-scale tunnel backfilling and hydraulic plug installation test in the 350 m Niche No. 6, will be carried out in Phase 2 of the HIP.