Microbial and vegetal life in the near- and far-field of a nuclear waste repository

One of the so far unanswered question related to a nuclear waste repositiory is how big is the influence of biosystems on the safety of such a repository. Although this question can not be answered at this time, ongoing researches adress the questions of who lives in the possible host rocks, how do these organisms interact with radionuclides and what is their impact on the geochemical conditions there during the operation of a repository. This includes also researches on the microbial diversity in backfill materials such as bentonite and the microbial influence on their properties, e.g. swelling capacity and hydraulic conductivity. In addition, various procaryotic and eucaryotic organisms in the far-field of a repository, namely bacteria, fungi and plants, are currently being investigated for their interaction with radionuclides and their influence on radionuclide migration. The latter includes also a possible radionuclide entry into the food chain. The goal is to identify dominant processes and to understand them on a molecular level. Ultimately, this will allow to derive biological parameters which are suitable to be included in the radionuclide transport modeling. Identified processes will also be considered for the development of remediation concepts for the purification of contaminated water and soil.
In the second part of the talk, the interaction of uranium and neptunium with bacteriogenic iron oxides precipitates, formed by the ferrous oxidizing and stalk-forming bacterium Gallionella ferruginea from a granitic host rock, is presented in more detail. This work shows that bacteriogenic iron oxides have a high potential to immobilize radionuclides in nuclear waste repositories.