MICROBIOLOGY OF SPENT NUCLEAR-FUEL STORAGE BASINS

Microbiological studies of spent nuclear fuel storage basins at Savann ah River Site (SRS) were performed as a preliminary step to elucidate the potential for microbial-influenced corrosion (MIC) in these facili ties. Total direct counts and culturable counts performed during a 2-y ear period indicated microbial densities of 10(4) to 10(7) cells/ml in water samples and on submerged metal coupons collected from these bas ins. Bacterial communities present in the basin transformed between 15 % and 89% of the compounds present in Biolog(TM) plates. Additionally, the presence of several biocorrosion-relevant microbial groups (i.e., sulfate-reducing bacteria and acid-producing bacteria) was detected w ith commercially available test kits. Scanning electron microscopy and X-ray spectra analysis of osmium tetroxide-stained coupons demonstrat ed the development of microbial biofilm communities on some metal coup ons submerged for 3 weeks in storage basins. After 12 months, coupons were fully covered by biofilms, with some deterioration of the coupon surface evident at the microscopical level. These results suggest that , despite the oligotrophic and radiological environment of the SRS sto rage basins and the active water deionization treatments commonly appl ied to prevent electrochemical corrosion in these facilities, these co nditions do not prevent microbial colonization and survival. Such micr obial densities and wide diversity of carbon source utilization reflec t the ability of the microbial populations to adapt to these environme nts. The presumptive presence of sulfate-reducing bacteria and acid-pr oducing bacteria and the development of biofilms on submerged coupons indicated that an environment for MIC of metal components in the stora ge basins may occur. However, to date, there has been no indication or evidence of MIC in the basins. Basin chemistry control and corrosion surveillance programs instituted several years ago have substantially abated all corrosion mechanisms.