Evaluation of the mobility behavior of radionuclides in highly saline and alkaline conditions is a major concern for performance assessment of radioactive waste disposal. The aim of this study is to determine the effect of up to 2.8 mol/kgsolution content of NaNO3, onto the solubility and the sorption of U(VI) in a hardened cement-paste (HCP) prepared from an ordinary Portland cement (CEM I). To avoid the interference of the high salt concentration (and ionic strength) and because of expected low solubility of uranium under such alkaline conditions, the time-resolved laser fluorescence (TRLFS) was selected to measured accurate U(VI) concentration in solution using the standard addition method in 85% H3PO4 to limit dilution and matrix effects and allows determining of resulting [U(VI)] in solution with acceptable precision for distribution factor (Rd) both in sorption and desorption experiments. The operational solubility limit measured at high ionic strength is lowered by a factor 3 compared to the reference cementitious condition, with the Rd values decrease by ca. a factor 4. Sorption of U(VI) appears to be reversible under these conditions.