Behavior of anionic radionuclides in the rhizosphere state of the art and experimental approach.

A. Martin-Garin, S. Roussel-Debet, L. Février Wokshop IUR-Andra - 3-5 avril 2002 - Palais des Congrès, Nancy - Proceedings - 17/32

In soil, radionuclide speciation and bio-availability are controlled by many processes in solution (pH, redox potential) and at the liquid solid interface (sorption, precipitation, etc.). The in-situ physico-chemical parameters depend mostly on the intrinsic properties of the soil. In surface horizons, biological processes, induced and/or activated by the plant roots and the micro-organisms also play a key role. Long live radionuclides such as 99Tc and 79Se are known to be directly or indirectly affected by these microbiological effects. The main processes involved are reviewed and their consequences on migration and/or root transfer are discussed. Actually, if each individual process is rather known, the global resulting effect on the behavior of these radionuclides (increasing or decreasing the mobility) is still uncertain. Thereafter experiments and modelling are performed to better understand the fate of radionuclides in a biologically active soil. The objectives are to determine the influence of microbial effects on radionuclide behavior and, therefore, on the variability of the common assessing Kd and Ft parameters. An experimental approach coupling bio-physico-geochemical processes in described. It consists in quantifying the importance of radionuclide migration through surface soils, under steady state hydrodynamic conditions and characterized microbiological environment. First experimental results for Tc will be presented.