Computer Modelling of the Interaction between Water and Complex Solid Phases

Sammanfattning: In this work the program package PASSIPHIC is described. The program has been developed to calculate the equilibrium for an aqueous phase in contact with a complex solid. The complex solid is considered as consisting of pure minerals and /or solid solutions. Cement has been used as an example.

Cementitious materials are likely to be present in large quantities in repositories for radioactive waste. The chemistry in the vicinity of such a repository will hence be influenced by the cement. Cement has been shown to serve as an immobiliser of many elements due to its high internal pH (> 12.5), large surface area and the ability of the hydrated phases in the cement matrix to incorporate radionuclides. Thus, the modelling of the evolution of cement-water interaction is an important factor in determining the release rates of radionuclides from a repository for radioactive waste.

The PASSIPHIC program has been used to simulate leaching of cement with non-saline groundwater and the result is compared to experimental data. The agreement between experimental and calculated data has been found to be good.