Safety assessment in the disposal of high-level radioactive wastes (HLWs): a geochemical study of uranium complexes in deep groundwater in granites from Beishan, China

To clarify the species of uranium and its effect on the safety assessment in the disposal of high-level radioactive wastes (HLWs), we presented geochemical simulations of Beishan deep groundwater in Gansu Province, China. The Ca–UO2–CO3 complexes are the main species. They can decrease the blocking of granites on uranium, which is unfavorable for the long-term and safe disposal of HLWs. The Ca2+ may become the critical factor that determines the uranium species when the formation of Ca2UO2(CO3)3(aq) increases with Ca2+ concentrations. Our study provides an important basis and reference for future safety assessment in the geological disposal of HLWs.