Sorption parameter setting approaches for radioactive waste disposal considering perturbation effects: sorption reduction factors for organics

Various types of post-accident radioactive waste have been generated from cleanup and decommissioning activities at the Fukushima Daiichi nuclear power plant. Perturbation effects resulting from co-existing substances may influence radionuclide sorption. For the disposal of these wastes, perturbation effects on sorption parameters must be critically evaluated for the safety assessment of the disposal systems. The present study focuses on developing a methodology to quantify sorption parameters in the presence of such perturbation effects and on illustrating example calculations regarding sorption reduction factors (SRFs) due to the presence of organic ligands (ISA; isosaccharinic acid) for cement systems. Three approaches for the derivation of SRFs; 1) semi-quantitative estimation based on analogy with solubility enhancement factors (SEFs) derived from measured solubility, 2) prediction based on radionuclide speciation calculation, and 3) quantification from experimental sorption data in ternary systems were coupled and tested for the Am-ISA-cement system. Our approach allows to critically evaluate the dependence of sorption reduction factors for various perturbed systems on the chosen method of quantification, in accordance with the data availability for a given perturbation.