Diffusion and sorption behavior of HTO, Cs, I and U in mortar

Due to the accident of Fukushima Daiichi Nuclear Power Plant (NPP), a large amount of contaminated water has been generated in such as the reactor building. Concrete materials of the building have been in contact with contaminated water for a long time, therefore radionuclides in contaminated water may be penetrating into these concrete materials. For developing the plans of decommissioning of NPP and waste management including decontamination and disposal, it is important to estimate radionuclides inventory and concentration distribution in the concrete materials. For this purpose, the present study focuses on understanding the sorption and diffusion behavior and related mechanisms in the ordinary Portland cement (OPC) mortar. Effective diffusion coefficients (D_e) and sorption distribution coefficients (K_d) in OPC mortar for HTO, Cs, I and U as key radionuclides were measured by the through-diffusion and batch sorption experiments. As a result, D_e values of tracers derived were in the sequence of HTO ≈ I > Cs > U, implying that cation exclusion effects may be important mechanisms in OPC mortar. K_d values derived from diffusion and sorption experiments were consistently in the sequence of U > Cs > I, however, the near-surface disturbance in diffusion samples and crushed effect in batch sorption samples must be considered for K_d evaluation for high-sorbing radionuclides such as U. (author)