Estimation of sorption reduction by organic ligands in actinide-cement systems

Ochs, M.*; Dolder, F.*; Tachi, Yukio  

The clean-up activities related to the accident at the Fukushima nuclear power plant give rise to several types of wastes containing cementitious materials as well as substances that can influence radionuclide migration, especially organic complexing substances. Complexation by dissolved organic ligands will compete with sorption reactions between radionuclides and cementitious materials and therefore lead to a decrease of sorption. This paper focuses on a more systematic and broad-ranging evaluation of estimating sorption reduction factors (SRF) and maximum no-effect concentrations (NEC) on the basis of calculated aqueous radionuclide speciation and, where available, on the comparison with SRF/NEC calculated from experimental data. It can be concluded that experimental data from ternary systems (radionuclide-ligand-cement) are clearly most reliable for the determination of SRF by organic ligands. The quality of SRF estimates on the basis of modelled aqueous speciation is very heterogeneous at this point and is hampered especially in the actinide-ISA systems by uncertainties regarding the nature of relevant species at highly alkaline pH.