Solubilities of actinides in a domestic groundwater and a bentonite porewater calculated by using PHREEQC

This study presents the solubilities and speciations of actinides, calculated by the PHREEQC (V.2) code in a granitic groundwater and a Ca-bentonite porewater under a reducing condition. The respective solubilities for the amorphous U, Am, Th, Np and Pu compounds in the groundwater were 2.2 × 10−5, 1.2 × 10−7, 3.1 × 10−9, 3.4 × 10−9 and 6.3 × 10−11 mole/L, and these values are comparable to the results calculated by the MUGREM and EQ3/6 codes. The major dissolved species for U, Am, Th, Np and Pu were UO2(OH)3−, Am(OH)2+, Th(OH)4(aq), Np(OH)3CO3− and Pu(OH)3CO3−, respectively. However, carbonate complex ions were anticipated as the major species in the porewater except for thorium due to an increase of the carbonate concentration and a decrease of the pH.