Development Of Geochemical Software SSCS And Application Of Groundwater System

In order to solve the environmental pollution problem caused by the migration of nuclides out of the repository in the process of deep geological burial of high-level radioactive waste,it is necessary to obtain the chemical form distribution of nuclides in the groundwater environment and at the mineral-water interface.A geochemical software-SSCS is developed to calculate the chemical form distribution of elements（taking Neptunium as an example）in complex water environment under the support of the project“Compilation of Neptunium Chemical Speciation Simulation Calculation Program Code and Software System Debugging in Environmental Water”.Importantly,SSCS is employed to study the speciation distribution of Np in Tamusu groundwater and the effects of p H,Eh,different ions and various concentrations.Results indicate that neptunium mainly exists as Np O₂⁺in Tamusu groundwater.Under acidic,neutral or weak alkaline conditions,neptunium mainly exists as Np O₂⁺,while in strong alkaline conditions,the main species is Np O₂（OH）₃^-.Meanwhile when Eh<33 m V,Np（OH）₄is the dominant species;when Eh>33 m V,Np（Ⅴ）is more stable and Np O₂⁺becomes the main species.Different anions also have influence on the speciation distribution of neptunium in the order of HCO₃^->SO₄^2-≈F^->Cl^-。The hydrolysis ability of Np with different valences is Np（Ⅴ）<Np（Ⅲ）<Np（Ⅵ）<Np（Ⅳ）;the complexing ability of Np with different valences with HCO₃^-,SO₄^2-and F^-is:Np（Ⅲ）<Np（Ⅴ）<Np（Ⅵ）<Np（Ⅳ）.It shows that Np mainly exists as Np O₂⁺,which has the characteristics of low hydrolysis ability and weak complexation ability.This result provides theoretical guidance for the subsequent study of mineral adsorption.In order to further study the morphological distribution of Np at the mineral-water interface,the adsorption behavior of Np（Ⅴ）on goethite and hematite in tamusu groundwater is calculated by PHREEQC.When Np（Ⅴ）is adsorbed on goethite and hematite,its total adsorption capacity increases rapidly with p H changes and then remains unchanged,and is weakly affected by ionic strength.The remaining non-adsorbed Np in the system exists as low-mobility Np（OH）₄,indicating that the migration of Np（Ⅴ）in a changing and complex environment can be stably and effectively blocked.The results show that the calculation program-SSCS owning China’s national intellectual property rights,which is jointly developed by this research group and the China Institute of Atomic Energy,can provide a detailed basis for the study of nuclide diffusion and migration behavior in the underground environment.This work provides theoretical guidance and experimental basis for the safe disposal of radioactive waste.It is of great significance to the sustainable development of the nuclear energy industry.