Pore connectivity of clay materials implicated in fluid flow and chemical diffusion

Hu, Q.*; Wang, Q.*; Zhao, C.*; Tachi, Yukio  ; Fukatsu, Yuta  

A low aqueous-phase diffusion in low-permeable clay barrier materials has been accepted as a critical process in the long-term performance evaluation of nuclear waste repository. Low-permeable clay materials whose pores are poorly interconnected are known to have anomalous diffusion properties that strongly impact long-term net diffusion. Related research works with mudrocks of Wakkanai formation of Horonobe URL in Japan, Opalinus clay of Mt. Terri URL in Switzerland, as well as various shale and clay mineral, utilizes a complementary suite of pore structure characterization approaches (e.g., mercury intrusion porosimetry, small angle neutron scattering) and tracer experiments followed with micro-scale mapping with laser ablation-ICP-MS. These results presents the relationship between pore connectivity and anomalous diffusion in clay materials. Pore size is not the major contributor to slow fluid flow and radionuclide transport, the anomalous behavior appears to be caused by low pore connectivity.