NEA Horonobe International Project - HIP Interim report for Phase 1 (February 2023 - March 2025)

Tachi, Yukio  ; Aoyagi, Kazuhei  ; Ozaki, Yusuke  ; Hayano, Akira  ; Ono, Hirokazu ; Takeda, Masaki ; Mochizuki, Akihito  ; Dei, Shuntaro  ; Minaka, Jumpei; Murakami, Hiroaki  ; Kimura, Shun  ; Sato, Naomi ; Tamura, Tomonori ; Fairat, K.; Hama, Katsuhiro ; Mikake, Shinichiro ; Ota, Kunio ; Sugita, Yutaka ; Taniguchi, Naoki ; Ishii, Eiichi   ; 66 of others*

This interim report summarises the research activity which was carried out in the Phase 1 (February 2023 to March 2025) of the Horonobe International Project (HIP), which utilises an underground facility for the research and development of geological disposal at the town of Horonobe in Hokkaido. The aims of this project are to develop and demonstrate advanced technologies to be used in repository design, operation, closure, and a realistic safety assessment in deep geological disposal. In Task A (Solute transport experiment with model testing), the fracture distribution, transmissivity, and connectivity were evaluated prior to the in situ tracer test at a depth of 250 m. Then, two types of in situ tracer tests were successfully carried out and breakthrough curves using sorbing and non-sorbing tracers were successfully obtained. In Task B (Systematic integration of repository technology options), the distribution of fractures or faults, development of the excavation damaged zone, and water inflow from fracture during excavation were predicted prior to the excavation of the gallery at 500 m depth. In Task C (Full-scale engineered barrier system dismantling experiment), data acquisition of the full-scale engineered barrier system experiment performed at 350 m depth was continued. The research results in this interim report will contribute to the further development of preliminary safety assessments of the geological disposal project.