In the framework of the French deep geological repository for radioactive waste, cement-based materials are envisaged to immobilize radionuclides and/or provide protection from radiation to the environment. Superplasticisers (SPs) are added to these materials to increase their workability. SPs will undergo degradation by coupled radiolytic and hydrolytic effects in the pore solution leading to the formation of potentially complexing degradation products. The objective was to study the potential effect of radiolyzed superplasticizers contained in cement-based materials on radionuclide uptake. The Eu speciation and solubility with organic ligands resulting from the degradation of SPs were studied for the two solutions and the results were compared. Two different SPs were selected, a polycarboxylate ether and a polynapthalene sulfonate. Two different protocols were followed: direct irradiation of the solution containing the superplasticizer, and irradiation of the compacted cement sample followed by extraction of the pore water. Solubility enhancements observed in artificial cement waters are not representative of real cement pore water interactions, in agreement with other studies. Finally, the effects of alkaline hydrolysis and radiolysis of SPs on Eu solubility in pore water are limited.
Keywords: Complexation; Degradation; Europium; Hydrolysis; Radiolysis; Solubility; Speciation; Superplasticizers.
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