Solubility of neptunium oxide in the KURT (KAERI Underground Research Tunnel) groundwater

Effect of Carbonate on the Solubility of Neptunium in Natural Granitic Groundwater

“…However, as can be seen in Fig. 5, the solubility values reported by Kim et al [26] are higher than those calculated based on the OECD-NEA TDB. Moreover, the wide range of scatters of the Np(IV) solubility data has been attributed particularly to the different carbonate concentrations (Fig.…”

“…For a comparison of the neptunium solubility with that from various experimental results, the calculation of solubility and the neptunium species was performed with the YS-1-7 groundwater [26]. The geochemical properties of YS-1-7 are analogous to other experimental conditions in the literature [19,21,22,26,27]. The Eh value of the YS-1-7 groundwater, with a higher carbonate concentration of 78.4 mg/L at a depth of 140 m to 150 m, is -200 mV.…”

“…In the YS-1 groundwater, the total carbonate concentration is much lower the experimental value reported in the literature [19,21,22,26,27]. For the purpose of comparison between calculated and experimental solubility, the YS-1-7 groundwater, which has the highest carbonate concentration of all the groundwater samples, was used for the solubility calculation.…”

“…Due to the high ionic strength of the solution, the experimental data shown in M at pH of 8 to 12.5 [22]. Kim et al performed the experiment with NpO2 powder put into the groundwater; the activity of 237 Np in a filtered sample solution was measured at pH 9.5, 10.2, and 11.1 at a controlled Eh = -0.2 V [26]. The calculation of solubility was made under the same groundwater conditions as those of YS-1-7 performed by Kim et al, based on the formation constants selected in OECD-NEA TDB.…”

“…-or both at a pH value of less than 10, and Np(OH)4(CO3) 2- [26]. Therefore, these two studies were not considered for the calculation of the formation constants of the Np(IV) ternary complexes in this study.…”