The iron phases formed during the corrosion of the waste containers strongly influence the geochemical environment in the vicinity of the waste. In particular, the redox conditions are strongly determined by iron species. Knowledge of the processes taking place and the reaction products formed in the aqueous and solid phases helps to reliably estimate the source term for the release of redox-sensitive radionuclides in particular from the vicinity of the waste. The planned project thus makes an important contribution to the further development of our understanding of the chemical processes taking place in the repository system. The results from earlier projects and from the literature on a chemical, thermodynamic (Pitzer) activity model for the chemistry of iron in the near-field of a repository will be summarized. Existing data gaps are to be filled by additional experiments using modern, complementary techniques.

In particular, where necessary, the calculation of activity coefficients of complex iron species should be made possible. The work, i.e. the developed thermodynamic data and Pitzer model parameters, can be implemented in the German thermodynamic reference database THEREDA (www.thereda.de) in a second step. The work enables significantly improved modeling of Fe chemistry in systems with high ionic strength, which require the use of the thermodynamic Pitzer model. This applies, of course, to the description of Fe chemistry in saline solutions in the context of final disposal in the host rock salt, but also explicitly for solutions of high ionic strength (> 2M), which may occur in the context of possible final disposal in northern German clay formations.