The retardation of radionuclides in the near- and far-field of radioactive waste repositories is largely dominated by two processes:
- Solubility limitation by precipitation of radionuclide-bearing minerals
- Sorption of radionuclides on minerals
Quantifying the extent of these processes lies at the heart of geochemical modeling in support of safety analyses; and the preparation of thermodynamic databases for establishing solubility limits and sorption databases is a core-competence of LES.
The critical evaluation of thermodynamic data has a long tradition at LES, beginning with the Nagra Thermochemical Data Base 05/92, followed by the Nagra/PSI Chemical Thermodynamic Data Base 01/01 and finally the PSI/Nagra Chemical Thermodynamic Database 12/07. The elements considered in these databases can be broadly grouped into radiotoxic elements, chemotoxic elements and elements constituting groundwaters.
Currently, LES is engaged in updating thermodynamic data of elements already considered in previous editions of the database and in evaluating thermodynamic data of new elements (Ti, Cu, Ag, Sm, Ho, Hg, Pb, Po, Ac, Pa, Cf and possibly Cr, Zn, Cd, Sb, and Tl).
The chemical thermodynamic databases prepared by LES are officially released with GEMS, the Gibbs energy minimization software for geochemical modeling developed at LES.
