Determining redox properties of clay-rich sedimentary deposits in the context of performance assessment of radioactive waste repositories: Conceptual and practical aspects

The aim of the report is to provide an assessment of different approaches to determine redox conditions in subsurface environment regarding their strength and limitations in view of using the determined values to predict the redox speciation of radionuclides in clay-rich host rocks of nuclear waste repositories. First, the redox sensitivity of radionuclides in the anticipated waste will be evaluated. In the following, general aspects regarding redox equilibrium in clay-rich sediments and the kinetics of redox processes will be presented. In the third chapter, the relevance of the main redox couples for controlling the redox properties of clay-rich sediments and their interaction with radionuclides will be discussed. This chapter also provides an overview about studies on clay-rich formations which are investigated in the context of nuclear waste disposal. Finally, different approaches for assessing the Eh in clay-rich sedimentary deposits will be reviewed and evaluated in terms of the goal to predict the redox speciation of radionuclides.