Diffusion of Cs, I and HDO onto pre-Neogene sedimentary rocks

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

This study investigates the diffusion behaviors of Cs, I, and HDO in a pre-Neogene sedimentary rock as a potential host rock for high-level radioactive waste (HLW) disposal in Japan. Through-diffusion experiments were conducted to reveal distinct patterns in their breakthrough curves. Cs exhibited the fastest diffusion among the tracers, significantly influenced by fractures, surface diffusion mechanisms, and aragonite formation. In contrast, the anion exclusion effect notably hindered the diffusion behavior of I. The results highlight the diverse diffusion and retardation properties of pre-Neogene sedimentary rocks, showing that the effective diffusion coefficient of HDO is more similar to that of crystalline rocks. These findings contribute to the understanding of the suitability of pre-Neogene sedimentary rocks as a potential natural barrier for HLW repositories.