Progress in the Geomicrobiology of Radioactive Waste Disposal
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Progress in the Geomicrobiology of Radioactive Waste Disposal J. M. West1 and I. G. McKinley2 1 British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK 2 NAGRA, Hardstrasse 73, CH-5430 Wettingen, Switzerland ABSTRACT Over the past 20 years, radioactive waste microbiology has included a variety of analyses of disposal options for High Level (HLW) and Low/Intermediate Level (L/ILW) waste. Projects have covered a wide range of areas including: fundamental microbiology of geological formations; microbial tolerance to extreme conditions; biodegradation of repository materials and the interaction of radionuclides with microbes and their by-products. The work has included field sampling, laboratory studies, natural analogue investigations and development of mathematical models. Progress in the topic is considered by evaluating each part of the repository system in terms of microbial presence, possible microbial influence on the performance of the engineered and natural barriers, and how such influences can be quantified. From this perspective, priorities for future work in this area are identified. INTRODUCTION Radioactive waste microbiology started with the realization that microbes could exist in formations relevant to the disposal of waste and that the effects of microbial activity could have profound influences on waste containment [1]. Since then the subject has expanded to include analyses of microbiological influences on specific disposal options for HLW and L/ILW. This paper summarizes overall progress in the topic and makes recommendations for future R and D activities. MICROBIOLOGY OF RELEVANT GEOLOGICAL FORMATIONS Many national programs have studied the microbes present in geological formations that were being considered as host rocks for repositories [2, 3, 4, 5]. The rationale for this work seems that if no indigenous populations exist then microbes may not be viable in the environment selected and hence not be a problem. A selection of some of these analyses is given in Table I and, apart from Asse in Germany, microbial populations clearly are present in all potential host rocks. Table I also shows that the composition of microbial populations varies with site. However, it is now increasingly recognized that the analysis of ambient microbial populations is part of site characterization and may be more critical to understanding the hydrogeochemistry of the site than to assessing the role of microbes on repository performance. Given that geochemistry and isotope hydrology are key factors for determining the suitability of low permeability host rocks, the role of microbes in establishing site characteristics needs to be evaluated. Thus it is important to determine the activity levels of all relevant microbial groups even if counting total numbers of cells at family or species level is recognized to be a purely academic pursuit.
Table I. Bacterial populations in deep groundwater environments [after 6, 7] Location
Geology
Depth (mbgl)
Bacterial Count
Canada
Granite
350 - 400
Total counts 103–105 cel
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