Is the thermodynamic approach appropriate to describe natural dynamic systems? (Status and limitations)

The long-term performance assessment of a nuclear waste repository entails sound knowledge on the migration behaviour of radionuclides in a given aquifer system, which can in principle be appraised by a well-founded thermodynamic approach. For various reasons, in such an endeavour, a number of uncertainties are involved, which cause difficulties in the application of a thermodynamic approach to natural dynamic systems. This paper summarises the present state of the thermodynamic approach being applied to the assessment of various geochemical reactions of radionuclides and discusses the limitations involved in application to laboratory systems as well as dynamic natural systems.