Abstract / Project Outlining

The main objective of this project is to improve the scientific basis for performance and safety assessment of various waste management strategies. The goal is to provide fundamental knowledge about the behaviour of actinides and fission products in solution and solid phases. The research programme is focused on understanding the phenomena that are of key importance for modelling of the chemical processes that i) control the integrity of waste canisters; ii) control the dissolution of the waste form (source term); and iii) determine the rate and extent of radionuclide transport in dissolved or particle form from the repository to the biosphere. This project follows out of the findings of a concerted action entitled "Joint European Thermodynamic Database for Environmental Modelling - JETDEM", published in the Nuclear Science and Technology series under EUR 1913 1EN. For more details, please refer to the JETDEM WWW-page.

The project is structured into three work packages:

• Thermodynamics of aquatic actinides
  To eliminate the most serious deficiencies in the thermodynamic database for the actinides in aqueous systems, the following chemical reactions will be studied: complexation of tetravalent ions, formation of ternary complexes, complexation with phosphate, and their redox behaviour. To tackle these problems, classical wet-chemistry methods will be combined with state-of-the-art laser spectroscopic tools. In addition semi-empirical and more direct theory-based methods will be developed for predictions of chemical data for the actinide system.
• Thermodynamics of the solid-water interface reactions
  The underlying goal of the experimental/modelling programme is to understand the processes controlling the uptake and release of safety relevant radionuclides on materials and minerals important in radioactive waste management. The work is directed toward understanding of sorption mechanisms and the development of models to predict sorption in real systems.
• Thermodynamic properties of secondary solid phases
  The formation of secondary solid phases is considered to be one of the key processes controlling the mobility of radionuclides in the environment. Classical wet-chemical experiments will be coupled to modern microscopic and spectroscopic techniques, to link empirical macroscopic parameters to well-defined molecular-level processes.

Duration: September 2000 - August 2003