Development of Simulation Software on Chemical Species(SSCS) About Nuclide in Groundwater System

It is critical to develop the methods and technologies of studying the species and concentration in the processing of adsorption, and diffusion of some important radionuclides in spent fuel waste processing such as Beishan granites in domestic institutions and universities for the geological disposal of high-level radioactive wastes. Enrich the models used or constructed and the calculation procedures developed in the past two decades in this field. In order to evaluate the safety of the repository, chemical speciation analysis of nuclides is the premise of research to accurately predict the migration behavior of nuclides. In view of the rapid development of China's nuclear energy industry and the need to establish the identification of nuclides in the environment, it is of great significance to carry out the study of the chemical forms of nuclides around the repository in China. Aiming at the research requirements of element speciation distribution in the environment, a set of B/S architecture element speciation distribution simulation software is developed with JAVA as the development tool, MySQL as the database, and Tomcat as the container. In order to solve the convergence problem of chemical reaction equilibrium nonlinear equations encountered in simulation calculation, the method based on chemical reaction potential energy is introduced to solve the chemical reaction nonlinear equations quickly, and the multi-phase equilibrium calculation can be expanded. SSCS was used to study the species of U in groundwater and the effects of Eh, pH, different ions and concentrations. The calculation results indicate that neptunium mainly exists as NpO2CO-3(aq) in groundwater. Under strong acidic conditions, neptunium maily exists as NpO+2(aq), while in weak acidic, neutral or weak alkaline conditions, the main species are NpO+2(aq) and NpO2OH.When the solution is in strong alkaline conditions, the species are complicated most of neptunium exists as NpO2(CO3)-3(aq), with the possible generation of NpO2(CO3)3-2 or NpO2(CO3)5-3. Np(Ⅴ) is stable in the reduction condition, while Np(Ⅳ) and Np(Ⅵ) are the possible generation. Comparing the neptunium calculation results of the software in the environment with the PHREEQC calculation results, the relative error is within 10 %. For the distribution of trace elements in the environment, a theoretical calculation solution is provided.