Retention and diffusion of radioactive and toxic species on cementitious systems: Main outcome of the CEBAMA project

Abstract Cement-based materials are key components in repository barrier systems. To improve the available knowledge base, the CEBAMA (Cement-based materials) project aimed to provide insight on general processes and phenomena than can be easily transferred to different applications. A bottom up approach was used to study radionuclide retention by cementitious materials in the European CEBAMA project, encompassing both individual cement mineral phases and hardened cement pastes. Solubility experiments were conducted with Be, Mo and Se under high pH conditions to provide realistic solubility limits and radionuclide speciation schemes as a prerequisite for meaningful adsorption studies. A number of retention mechanisms were addressed including adsorption, solid solution formation and precipitation of radionuclides within new solid phases formed during cement hydration and evolution. Sorption/desorption experiments were carried out on several anionic radionuclides and/or toxic elements which have received less attention than metals to date, namely: Be, Mo, Tc, I, Se, Cl, Ra and 14C. Solid solution formation between radionuclides in a range of oxidation states (Se, I and Mo) and the main components (OH−, SO4−2, Cl−) of cementitious phases (AFm, Ca4Al2(OH)12·SO4·6H2O) were also investigated.