## 3 Results  
The solubility values of various radionuclides in natural groundwater system estimated by using PHREEQC to derive the source term of exposure dose are represented in Table 3. In most cases, the solubility data calculated with two different chemical thermodynamic databases, i.e., JAEA-TDB and updated TDB, were largely consistent with each other, except for the case of, U which showed a slightly increased aqueous solubility. According to thermodynamic calculation, the predominant presence of oxides (e.g., Ce, Fe, Nb, Pu, and Tc), carbonates (e.g., Co and Ni), and ternary carbonate hydroxide solid phases (e.g., Am and Cm) were identified as the solubility limiting phase under the given groundwater system. In all cases, no changes in the solubility limiting phase were observed for both thermodynamic database cases, which also match well with the behavior of the solubility data of each radionuclide in terms of the selection of the thermodynamic database. By using the solubility data of various radionuclides as the source term, exposure dose expected from the waste repository was predicted with the RESRAD-OFFSETE code as represented in Figure 1. The authors note that the exposure dose result obtained in this work does not represent that of Gyeongju repository but of the default model of RESRAD-OFFSETE code, since all the input parameters were set to be the default values of RESRAD-OFFSETE code, except for radionuclide inventory and aqueous solubility. The obtained \begin{table}
\begin{tabular}{l l} \hline
**Parameter** & **Value** \\ \hline pH & 7.4 \(\pm\) 0.9 \\ E\({}_{\text{h}}\) & 155 \(\pm\) 31 mV \\ Ionic strength & 8.3 \(\times\) 10\({}^{-2}\) mol/kg\({}_{\text{w}}\) \\ \hline
**Constituent** & **Concentration (mol/kg\({}_{\text{w}}\))** \\ \hline Na & 3.8 \(\times\) 10\({}^{-2}\) \\ K & 1.0 \(\times\) 10\({}^{-3}\) \\ Ca & 7.9 \(\times\) 10\({}^{-3}\) \\ Mg & 5.8 \(\times\) 10\({}^{-3}\) \\ SiO\({}_{2}\) & 6.0 \(\times\) 10\({}^{-4}\) \\ Cl\({}^{-}\) & 5.7 \(\times\) 10\({}^{-2}\) \\ SO\({}_{4}\)\({}^{2-}\) & 3.5 \(\times\) 10\({}^{-3}\) \\ Alkalinity as HCO\({}_{3}\)\({}^{-}\) & 1.5 \(\times\) 10\({}^{-3}\) \\ Br\({}^{-}\) & 1.7 \(\times\) 10\({}^{-4}\) \\ Fe & 8.5 \(\times\) 10\({}^{-5}\) \\ Mn & 4.3 \(\times\) 10\({}^{-5}\) \\ Sr & 1.4 \(\times\) 10\({}^{-5}\) \\ \hline \end{tabular}
\end{table} 
Table 2: Geochemical parameters of the natural groundwater system employed in this work. \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Radionuclide**} & \multicolumn{2}{c}{**Solubility at pH 7.4 (mol/kg\({}_{\text{w}}\))**} & \multirow{2}{*}{**Solubility Limiting Phase**} \\ \cline{2-3}  & **JAEA-TDB** & **Updated TDB** & \\ \hline Am & 1.54 \(\times\) 10\({}^{-7}\) & 1.57 \(\times\) 10\({}^{-7}\) & AmCO\({}_{3}\)OH-0.5H\({}_{2}\)O(cr) \\ Ce & 1.46 \(\times\) 10\({}^{-10}\) & 1.42 \(\times\) 10\({}^{-10}\) & CeO\({}_{2}\)(cr) \\ Cm & 1.54 \(\times\) 10\({}^{-7}\) & 1.54 \(\times\) 10\({}^{-7}\) & CmCO\({}_{3}\)OH-0.5H\({}_{2}\)O(cr) \\ Co & 9.51 \(\times\) 10\({}^{-5}\) & 9.45 \(\times\) 10\({}^{-5}\) & CoCO\({}_{3}\)(cr) \\ Fe & 3.61 \(\times\) 10\({}^{-12}\) & 3.57 \(\times\) 10\({}^{-12}\) & Fe\({}_{2}\)O\({}_{3}\)(s) \\ Nb & 1.42 \(\times\) 10\({}^{-7}\) & 1.42 \(\times\) 10\({}^{-7}\) & Nb\({}_{2}\)O\({}_{5}\)(s) \\ Ni & 9.54 \(\times\) 10\({}^{-5}\) & 9.43 \(\times\) 10\({}^{-5}\) & NiO\({}_{3}\)(cr) \\ Pu & 7.40 \(\times\) 10\({}^{-17}\) & 7.20 \(\times\) 10\({}^{-17}\) & PuO\({}_{2}\)(cr) \\ Sr & 7.32 \(\times\) 10\({}^{-4}\) & 7.29 \(\times\) 10\({}^{-4}\) & SrSO\({}_{4}\)(s) \\ Tc & 8.40 \(\times\) 10\({}^{-5}\) & 8.37 \(\times\) 10\({}^{-5}\) & TcO\({}_{2}\)(cr) \\ U & 3.24 \(\times\) 10\({}^{-6}\) & 8.42 \(\times\) 10\({}^{-6}\) & CaUO\({}_{4}\)(cr) \\ \hline \end{tabular}
\end{table} 
Table 3: Solubility data of various radionuclides in a natural groundwater system estimated using JAEA-TDB and updated TDB. result represented similar or negligibly changed exposure doses between the JAEA-TDB and the updated TDB due to the remarkable similarity between the solubility data.