Databases and Codes
Safety analysis for a geological repository for radioactive waste, underground disposal of chemotoxic waste and the remediation of abandoned uranium mines share a common aspect: It is essential that any potential migration of toxic constituents into the biosphere has to be predictable reliably. Important input for the various computational codes are generic, i.e. non-site-specific, thermodynamic data concerning speciation and solubility. Once such data are available – and provided an understanding of the related physico-chemical processes – a coupling of restrictive models to long-term safety assessment codes comes into reach. There, a balance between model details and computational performance is still challenging.
Thermodynamic Reference Database THEREDA
The main objective of joint project THEREDA (Thermodynamic Reference Database, click partners logos on right) is the establishment of a comprehensive and internally consistent thermodynamic reference database for the geochemical modeling of near-field and far-field processes occurring in the different rock formations currently under discussion in Germany to host a repository for radioactive waste.
THEREDA offers evaluated thermodynamic data for all compounds of elements, which according to the present state of research are dose relevant.
Actinides, Fission and Activation Products:
- Pa, Th, U, Np, Pu, Am, Cm
- Rb, Sr, Tc, Cs, Sm, Ra
- System of oceanic salts: Na+, K+, H+, OH−, Mg2+, Ca2+, Cl−, SO42−, CO32−/HCO3−/CO2(aq) - H2O containing the elements Na, K, Mg, Ca, Cl, S, C
- Hydrated cement phases (including Al, Si)
The website www.thereda.de shall serve users as a portal to the database and as an information and discussion platform on issues concerning the database. The quality management is not restricted to providing a quality assured database, the user ought to be enabled to understand correctly and to apply the quality criteria of the thermodynamic reference database by accompanying information.
Sorption Database RES³T
RES³T (Rossendorf Expert System for Surface and Sorption Thermodynamics)  is a digitized version of a thermodynamic sorption database as required for the parametrization of Surface Complexation Models (SCM). It is mineral-specific and can therefore also be used for additive models of more complex solid phases such as rocks or soils.
A user interface (www.hzdr.de/res3t) helps to access selected mineral and sorption data, to convert parameter units, to extract internally consistent data sets for sorption modeling. Data records comprise of mineral properties, specific surface area values, characteristics of surface binding sites and their protolysis, sorption ligand information, and surface complexation reactions.
Implementation of Thermodynamic Data into Codes
Within the joint project with GRS ESTRAL (Realistic Integration of Sorption Processes in Transport Programs for long-term Safety Analysis) the existing 3D transport program r³t  is extended towards a more realistic description of the sorption of radionuclides under changing geochemical conditions. As application case for a proof-of-concept, the Gorleben site, a potential repository site in Germany has been selected. The sorption of radionuclides on mineral surfaces is described by Kd values based on SCM data from RES³T, calculated in PHREEQC  as a function of important environmental parameters. Parameter variation and assembling of Kd matrices is performed by UCODE .
Most of these individual parameters are not available in r³t so far. Therefore, the code is to be modified.
For coupling the transport and chemistry the calculated smart Kd values have to be accessible from within r³t at each time-space point for the correct geochemical conditions. The main challenge here is finding a fast and robust algorithm for search in multidimensional matrices.
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 Brendler, V. et al. (2003) J. Contam. Hydrol. 61, 281-291.
 Richter, A. et al. (2008) in: Adsorption of Metals by Geomedia II, Amsterdam: Elsevier, 267-291.
 Fein, E. (2004) Report GRS-192.
 Parkhurst, D.L.; Appelo, C.A.J. (1999) U.S.G.S. Report 99-425.
 Poeter, E.P. et al. (2005) U.S.G.S. Techniques and Methods 6-A11.