Resumen de Determination of key master variables and radionuclide behavior in the swedish final repository environmen
Maria Rosa González Siso Sampedro
This PhD thesis investigates the key processes controlling de mobility of some of the redox sensitive radionuclides present in the waste (U, Pu and Tc) and Ni as a critical radionuclide, in the Swedish Final Repository (SFR) used for the disposal of low-and intermediate level radioactive waste (L/ILW) in Sweden.
According to previous modeling work performed by Amphos 21 (Duro et al, 2014), the presence of cement and cementitious materials (used for the construction and for the waste stabilization) will impose highly alkaline and strongly reducing conditions in the vicinity of the repository due to the ingress of groundwater in the SFR repository. These extreme conditions will have an impact on the chemical behavior of the redox sensitive radionuclides present in the waste, as well as in the presence of the organic ligands contained in the wastes in SFR repository, like Isosaccharinic Acid (ISA), which could affect the mobility of radionuclides.
In order to have an exhaustive study, this thesis presents an experimental determination and thermodynamic modelling of the key processes in SFR repository evolution of the Fe(II)/Fe3O4(s) redox system and the solubility equilibria of Fe3O4(s) under high pH and strongly reducing conditions. Moreover, a study of the effect of these redox conditions on the redox state and mobility of key redox sensitive radionuclides: Pu, U and Tc is presented. And finally, a determination of the solubility of Ni(II) under alkaline and the reducing conditions imposed by the magnetite/Fe(II), including the effect of isosaccharinic acid (ISA) as the main degradation product of the cellulose under alkaline and reducing conditions.
