Determination and uncertainties of radioelement solubility limits to be used by SKB in the SR 97' performance assessment exercise

The Swedish Fuel and Waste Management Co, SKB, is at present preparing a Pe rformance Assessment (PA) exercise of its HLNW repository concept. The dete rmination of solubility limits of the main radioelements contained in the s pent nuclear fuel is a necessary work to understand their potential migrati on in both the near and far fields. The calculated solubilities are compared to experimental data from relevant spent nuclear fuel dissolution tests and field observations from natural s ystems, particularly Natural Analogue study sites. This work discusses the main uncertainties associated to the calculated solubilities, particularly those related to the variability of groundwater composition, redox conditio ns and temperature of the system. The results of the sensivity analysis indicate that although the solubility of some radioelements, such as Th, is not dramatically affected by the unc ertainty in the determination of the physico-chemical parameters mentioned above, most of the elements are strongly influenced by this variability, sp ecially Am, U, Np, Pu and Tc.