THEREDA: Providing quality-assured thermodynamic data for waste management assessment

The THEREDA project develops a consistent and quality assured thermodynamic reference database for modeling geochemical processes in waste disposal sites. It offers evaluated thermodynamic data for all relevant elements, covering both radioactive waste and chemo-toxic substances, see table 1 for a detailed list. All host rocks currently discussed as candidates for waste repositories in Germany are considered. Thus, parameters for a variety of models describing interactions in mixed phases are included. Here, namely the Pitzer- and SIT-formalisms to describe activity coefficients of hydrated ions and molecules are supported. Provision is made to include parameters for solid solution models and non-ideal gas models at a later stage. Both thermodynamic and interaction parameters can be described by (flexible) temperature functions.
An essential topic in the context of nuclear waste is public confidence building on scientific responsibility. This is addressed by a detailed scheme of quality assurance (QA), incorporating elements such as data categorization (review quality, original publication type, experimental category, and uncertainty level), validity limits, full bibliographic tracking, formalized data evaluation procedures, internal consistency checks (coupled to the concepts of dependent data sets and alternatives), data audits, benchmark test cases, and finally external feedback enabled through free access (www.thereda.de) combined with a variety of communication tools. Each part of THEREDA and its accompanying QA, as well as all technologic details, are fully documented.
Another important topic is that THEREDA strives for a broad coverage of all relevant reactions and species by making use of estimation methods, ranging from chemical analogy to LFER and fractional group algorithms. Such values are clearly labeled, also carry uncertainties, and have validity limits assigned.
To ease the use of the THEREDA data pool both “fixed” complete and consistent databases (updated twice a year) as well as user-specified ones can be downloaded directly form the project’s webpage. Available formats are a generic ASCII type, and formats as required by the geochemical speciation codes PhreeqC, EQ3/6, ChemApp and Geochemist’s workbench.