The objective of the present work is to determine the global effect of microbial presence on the mobility of radionuclides supposedly immobilized in the near field (clay or cement).
Micro-organisms can produce organic or mineral acids that can promote corrosion and complexing agents that can modify the characteristics of the repository. So, radionuclides that have been immobilized by cement or bitumen embedding matrix can be leached either as soluble ions or soluble complexes (effects of the corrosion of the matrix). This leads to an increase of their mobility.
On the other hand, micro-organisms can decrease the mobility of initially soluble species by sorption on the cell membrane or on polymers (especially polysaccharides) produced by cells, and also by bioaccumulation in the cell.
The experiments are carried out on cylindrical samples of pure cement or on fine mote of clay, containing U (introduced as Uranyl nitrate) or Cs (introduced as Cesium chloride). The organic acid producing microorganisms growth on cellulose, one carbon source that can be found in nuclear waste.
The main headings of interest can be broken down to:
Pilot plant design and realization, hydraulic tests, choice of working conditions
Metabolism study of cellulolytic microorganisms
Leaching of U and Cs contained in cementitious or clay matrix by the culture medium containing microorganisms
Study of the different effects of direct and indirect microbial action on radionuclide mobility or retardation