Aqueous thermodynamic data

Starting point for the development of the database was the selection of mineral phases and elements most relevant for safety assessment studies presently discussed in Germany. The selection of the mineral phases was mainly based on reports of thepetrography from a number of different drill cores obtained from the Gorleben site and their relevance for sorption or influence on geochemical conditions. As most critical solid phases quartz, feldspar, muscovite, gibbsite, goethite, calcite, kaolinite and illite were determined. For the elements three groups were distinguished:

Elements occurring as radionuclides,

Elements acting as competing cations, and

Elements constituting complexing ligands.

The selection of the first group was based on their relevance for long-term safety, on the question whether they are sorbing at all, and on the availability of comprehensive and reliable thermodynamic data. For those elements occurring in different oxidation states the ones representative under oxidizing conditions were chosen as the major target of the project is an improved description of the far-field of a repository. For the second and third group the ones with highest impact and high probability of occurrence in the natural system or released from the repository have been included. As a result Ni, Se, Cs, Cm, Am, Pu, U, Th, Np, Ra, Ca, Fe, Al, CO32-, SO42- and SiO32- have been selected for the calculations.