Microbial processes in nuclear waste repositories – microbial transformation of bentonite and microbial-induced corrosion of container material
Prof. Dr. Thorsten Stumpf, Dr. Johannes Raff, Dr. Andrea Cherkouk (HZDR)
A safe and long-term storage of highly radioactive waste in deep geological layers should be achieved by a multi-barrier concept consisting of geological, geotechnical and technical barriers. Possible materials for a geotechnical barrier are the so-called bentonites. These are clay minerals, which due to their mineralogical composition, have a high swelling capacity and a low solvent permeability and are therefore particularly suitable as a geotechnical barrier.1
Like all natural materials, bentonites also contain different microorganisms. The aim of this work is to investigate to which extend these microorganisms can influence the conditions in a nuclear repository by the microbial transformation of the bentonite and the corrosion of the container material.
Therefore, it should be investigated, which microorganisms are present in bentonite and how these microbial communities will be evolving in dependence on different temperatures.
Furthermore it will be investigated, to which extend the present microorganisms are able to reduce Fe(III) to Fe(II) and how this process affects the retention of radionuclides such as uranium and technetium. For this purpose, sorption experiments with microbial transformed bentonite and the corresponding radionuclides are carried out, and the proportion of sorbed radionuclides is determined by inductively coupled plasma – mass spectrometry (ICP-MS). Furthermore, the samples can be further analysed using time-resolved laser-induced fluorescence spectroscopy (TRLFS).
In addition, we will investigate how the microorganisms, inhabiting bentonite, influence the corrosion of the container material. Therefore, in lab experiments the corrosion of steel coupons embedded in bentonite will be investigated under different conditions.
1Sellin P. & Leupin, O. (2013). The Use of Clay as an Engineered Barrier in Radioactive-Waste Management – A Review, Clays and Clay Minerals, 61, (6), 477-498.