Influence of heterogeneity on ions and HDO diffusion in pre-Neogene sedimentary rocks

Hou, L.*; 岡本 駿一*; 戸田 賀奈子*; 深津 勇太  ; 石寺 孝充 ; 斉藤 拓巳*

Hou, L.*; Okamoto, Shunichi*; Toda, Kanako*; Fukatsu, Yuta; Ishidera, Takamitsu; Saito, Takumi*

This study examines pre-Neogene sedimentary rocks, prevalent in the Japanese basement and considered potential host rocks for high-level radioactive waste (HLW) repositories. These rocks, characterized by their block-in matrix structures, present unique challenges in understanding the diffusion behaviors of radionuclides. Given their lithofacies, vein patterns, and fracture characteristics, an approach is required to clarify diffusion behaviors, based on their structural characteristics. The research employs through-diffusion experiments with Cs, I, and HDO to address this. The obtained breakthrough curves are modeled with the help of X-ray Computed Tomography (X-ray CT) scanning data. These investigations are pivotal in assessing the barrier performance of pre-Neogene sedimentary rocks for effective long-term containment of HLW.