## 3 Evaluation and Application of a Thermodynamic Database (TDB) in Geochemical Models  
### Evaluation of a Thermodynamic Database (TDB)  
The geochemical models are shipped with thermodynamic databases, and each equilibrium constant of the TDBs for a chemical reaction can be separated from the simulation model. This means that the equilibrium constant is not rigidly embedded in the simulation model. Users can easily change the equilibrium constant value and add/delete chemical reactions without affecting the code function in the database. The geochemical models used in this study (such as PHREEQC and EQ3/6) allow users to modify the equilibrium constants in input files or databases with internal consistency. The required data of the equilibrium constant or standard Gibbs free energy can be found in the thermodynamics database of the geochemical model. We should check whether the database contains the thermodynamic and kinetic parameters of the species involved in the model. At the same time, we should focus on whether the data in the thermodynamic database have internal consistency; for example, the enthalpy of formation (\(\Delta_{f}H^{0}\)), standard Gibbs energy of formation (\(\Delta_{f}G^{0}\)), and entropy (\(\Delta_{f}S^{0}\)) for the chemical species x may come from different sources. The value (i.e., equilibrium constant or standard Gibbs free energy) of thermodynamics database may be obtained through the statistical regression analysis of experimental data at the beginning of the derivation; however, the value may not be consistent with the relationship of the formula (\(\Delta_{f}G^{0}_{X}=\Delta_{f}H^{0}_{X}-T\Delta_{f}S^{0}_{X}\)). Achieving the consistency of these parameters is an important task that is still in progress in the establishment of geochemical models and chemical thermodynamics databases [30; 31]. The widely used PHREEQC geochemical model already has an internal TDB. In addition to the databases in the PHREEQC, WATEQ4F and MINTEQ models, Lawrence Livermore National Laboratory in the United States developed a database of chemical the modynamics. The database comes with EQ3/6, which can be used in the PHREEQC model. Andra/RWM, France, developed a chemical TDB named ThermoChimie-TDB [32]. To date, the format of the ThermoChimie database has been employed by other models, including PHREEQC, CHESS [33], Crunch [34] and Toughreact [35]. The compatibility of the TDBs can be extended to other models, including Medusa [36] and Geochemist's workbench [37], according to the demand for databases. Other research institutions have also developed various chemical TDBs. Examples include the Thermochemical Database Project developed by the Nuclear Energy Agency (NEA) [38; 39; 40]; the Thermodynamic Reference Database (THEREDA) focusing on transuranic elements, which was developed by various German institutions [41]; Japanese JNC TDB [42]; British HATCHES [43]; Nagra/PSI chemical TDB, developed by the Swiss Radioactive Waste Management Agency [44]; and MOLDATA [45] TDB, which is under compilation by SCK.CEN at Mol (Belgium) for use in a framework of safety case development by ONDRAF/NIRAS. These TDBs have been developed to support the geochemical modeling required for the safety and performance assessment of radioactive waste repositories. Together, they provide good coverage of geochemical reaction data for the hydrogeochemical simulation of radioactive waste disposal. Three TDBs--ThermoChimie-TDB, THEREDA and NEA TDB--are described as follows. The latest release of ThermoChimie (V10a) can be downloaded using the \"Download\" table. The database contains the basic major elements, numerous nuclides and toxic chemical elements. The main elements include C, N, O, F, Na, Mg, Al, Si, P, S, Cl, K, CA, Fe and Ba.