THEREDA – Thermodynamic Reference Database for Nuclear Waste Disposal in Germany

The disposal of radioactive waste including the assessment of long-term safety is an open question in Germany. In addition to the choice of the repository host rock (salt, granite, clay) the basic necessity of a consistent and bindingly used reference database exists. Only by means of such a database it is possible to assess potential failure scenarios accurately and to make well-founded predictions about the long-term safety. Specific needs for waste repository and remediation projects in Germany are comprehensive datasets also covering high temperatures and high salinities. Against this background, available databases (NEA-TDB, IUPAC, NAGRA-PSI) do not suffice all these requests and are limited in their use, partly because of high restrictions and resulting incompleteness of thermodynamic datasets. Other databases rely on heterogeneous and therefore inconsistent data yielding in inadequately reproducible and plausible model calculations. Due to these deficiencies THEREDA, a joint project of institutions leading in the field of safety research for nuclear waste disposal in Germany, was started. It will provide consistent thermodynamic datasets and enhance the transparency and reliability of safety analyses.
Within the project THEREDA we seek to compile data of high quality, accordance and traceability, mainly from existing databases, and to complement this basis particularly with datasets for high saline systems (Pitzer and SIT parameters) and systems at elevated temperatures. Persistent data gaps are closed via estimated values. The identification of such gaps can also aid decisions about the scheduling of experimental programs. Each dataset included in THEREDA is documented in detail and gets a grade of quality attached. Higher grades of quality are allocated to thermodynamic parameters derived from experimental data, namely from non-thermochemical experiments, whereas estimated values determined from systematic trends in thermodynamical behavior or from studies of chemical analogs get lower ratings. Furthermore, numerical data uncertainties and the quality of data sources (primary or secondary literature, peer-reviewed or non-certified) are categorized.
THEREDA will represent a source of information on thermodynamic data that will be publicly accessible and free of charge via Internet (www.thereda.de) and set up on a SQL-database. A broad use of the database is ensured by export functions tailored to important geochemical codes such as EQ3/6, PHREEQC, GWB and ChemApp.