Retention of uranium in cement systems. Effects of cement degradation and complexing ligands

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, boron, and chloride salts. The present study focuses on a methodology, based on available literature information, for quantifying the retention behavior of uranium (VI) in cement materials of different degradation states and in the presence of organics, boron, and salts. To account for the many variables defining uranium uptake in cement systems a stepwise approach is proposed and illustrated: 1) definition of conditions and U speciation in each relevant degradation state, 2) assessment of U(VI) uptake processes based on a critical review of literature information, 3) K_d setting on the basis of original experimental data that are consistent with the identified processes and speciation, 4) assessment of ligand effects based on data preferably from ternary systems, or from speciation and analogue information. (author)