The Impact of Microbial Biofilms on the Performance of Materials Relevant to the Nuclear Fuel Cycle

The proposed strategy for long-term storage of nuclear waste within the UK involves emplacement within geological disposal facilities (GDF). Highly alkaline and anoxic conditions expected to develop will result in the chemical degradation of cellulosic content present within intermediate level waste facilities (ILW-GDF). The major constituents of cellulose degradation products (CDP)will be isosaccharinic acid (ISA), the a and b forms of which can form soluble complexes with a range of radionuclides subsequently altering the sorption capacity of materials engineered to contain radioactive contaminants.

Migrating radionuclides that are able to transport out of the GDF to the far-field environment through complexation processes may be controlled by sorption processes and pore water chemistry that surrounds the host rock at a pH that is milder than the near-field. Biofilm communities that are able to survive under the alkaline and anaerobic conditions could aid in the retention of radiological species by utilising ISA as a carbon source.

By using flow-cell systems which in corporate sand as a substrate for sorption, the behaviour of natural analogues and radionuclides was studied to understand how they would behave if they were present within the far-field. Ni(II), Eu(II) and Th(IV) were found to adsorb to sand under the relevant conditions, however the presence of ISA as a complexing agent only influenced Ni(II) migration through the system. Microbes capable of biofilm formation on the sand surface were capable of the degradation of CDPs through fermentation processes which resulted in Ni(II) movement being hindered via removal of the complexed ISA. Contrastingly, the transport of soluble U(VI) was not restricted through adsorption to sand. Microbial reduction induced by the introduction of biofilm-forming microbes lead to a decrease in measured U(VI) within effluent samples due to its reduction to insoluble U(IV).

Microscopy and molecular techniques investigated for the analysis of biofilms on complex surfaces allowed the elemental, extra polymeric substance (EPS), and community composition of microbial biofilms grown within sand columns to be studied.