Synthesis report on the R&D for the Horonobe Underground Research Laboratory Project carried out between fiscal years 2020-2024

Nakayama, Masashi ; Ishii, Eiichi   ; Aoyagi, Kazuhei  ; Hayano, Akira  ; Ono, Hirokazu ; Ozaki, Yusuke  ; Mochizuki, Akihito  ; Takeda, Masaki ; Kimura, Shun  

The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA). The main aim of the project is to enhance the reliability of relevant technologies for the geological disposal of high-level radioactive waste by investigating the deep geological environment within the host sedimentary rocks at Horonobe in Hokkaido, northern Japan. These investigations have been conducted in three phases: "Phase 1: Surface-based investigation", "Phase 2: Construction" (investigation during tunnel excavation) and "Phase 3: Operation" (investigation in subsurface facilities). Since the fiscal year 2020, we have been conducting R&D based on the Horonobe Underground Research Plan for the Fiscal Year 2020 Onwards, which was approved by Hokkaido Prefecture and Horonobe Town. In particular, we are working on the following key tasks with the aim of completing JAEA's 3rd and 4th Mid- and Long-Term Plans: "Study on near-field system performance in geological environments", "Demonstration of repository design options" and "Understanding of buffering behaviour of sedimentary rocks to natural perturbations". This report summarizes the R&D activities on the three above-mentioned key tasks, the goals of which were achieved between fiscal years 2020 and 2024. The results obtained from these tasks will be systematically organized as part of the "Systematic integration of technologies towards EBS emplacement" which has been in progress since fiscal year 2024. This task includes concepts related to the layout of galleries and pits, installation methods for engineered barrier materials, and methods for evaluating their containment performance.