THEREDA – Recent, present, and future developments

INTRODUCTION

The thermodynamic reference database THEREDA is maintained within the frame of a collaborative project aiming at the calculation of solubilities in high-saline solutions. The database is designed for applications in the context of the disposal of radioactive waste in rock salt formations and clay formations featuring solutions with a higher ionic strength. The project provides an internally consistent set of data, formatted for the use by several widely used geochemical codes. With the focus on high ionic strength systems, THEREDA complements other database projects focusing on low-saline solutions, such as THERMOCHIMIE or the PSI Chemical Thermodynamic Database. Users can access data and application examples, as well as download parameter files for their own use, from the website www.thereda.de.

RECENT DEVELOPMENTS

New project phase
In 2020, the core project entered its 4th phase scheduled to run until 31st of January 2025. Parallel to the core project, coordinated and supported by it, other projects are running dedicated to the extension of THEREDA in specific fields.

Maintenance
Efforts are constantly taken to facilitate maintenance and future development of THEREDA. This includes databank structure, further development of graphical user interface to promote networking on the database, measures for knowledge preservation, and processes and quality management for future releases.

Data release
In 2022 new data were released. Apart from adding and updating datasets released before this was the first cumulative release where all system data sets were combined into one parameter file for each supported code.
The following elements are part of the present release:

• actinides and their chemical analogues: Th, U, Np, Pu, Am, Cm & Nd,
• fission products: Se, Sr, Tc & Cs,
• matrix elements: Na, K, Mg, Ca, Al, Si - Cl, SO4, CO3, PO4,
• heavy metals: Pb.

Supported codes
After having abandoned the support for EQ3/6, TOUGH-REACT hast been added to the existing support of PHREEQC, ChemApp and Geochemist’s Workbench.

PRESENT AND FUTURE DEVELOPMENTS

Data release planned in 2023
A new data release is planned for the last quarter of this year. Updates and extensions will include:

• Zn – Na, K, Mg, Ca – Cl, SO4, CO3 – H2O(l) (also alkaline systems),
• U(+IV) hydrolysis in NaCl, MgCl2 and CaCl2 systems,
• Solubility of carbonates up to 100°C,
• Si, Al – Na, K, Mg, Ca – Cl, SO4, CO3 – H2O(l) (aqueous species only, polythermal, also alkaline systems),
• Na, K, Mg, Ca – Cl, SO4 – H2O(l) (alkaline systems, T ≤ 40°C),
• H2S(g), HS- – Na, K, Mg – Cl, SO4 – H2O(l) (partially polythermal),
• Na, K, Mg, Ca – Cl, SO4, NO3 – H2O(l),
• molar volumes for selected mineral phases.

Application examples
Altogether 505 application examples were created, on display on our website (www.thereda.de). They demonstrate the capabilities of THEREDA and indicate fields of future improvement. Two application example calculations of the data release planned in 2023 are shown in Figure 1 and Figure 2.
Archiving and assessment of exp. data for the system of oceanic salts
The polythermal dataset is based on the evaluation of about 16,000 solubility data points. Since the beginning of the 4th project phase their bibliographic origin is captured in the databank. Previous application examples are reproduced, or new ones created in the process. At present, binary subsystems are completed and ternary subsystems are in the process of revision. Altogether more than 400 primary data files and more than 100 application examples were created.

ACKNOWLEDGEMENTS

THEREDA is funded by the German “Bundesgesellschaft für Endlagerung (BGE)”, contract number 45181017.