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

Abstract 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 UO 2 (OH) 3 − , Am(OH) 2 + , Th(OH) 4 (aq), Np(OH) 3 CO 3 − and Pu(OH) 3 CO 3 − , 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.