Development of a carbon-14 bioseparation technique for cleanup of nuclear graphite

A preliminary study on the bioseparation of Carbon-14 was carried out using a mixed-culture of microorganisms obtained from the Pebble Bed Modular Reactor Company (PBMR). The culture demonstrated the ability to bio-accumulate radiocarbon-14 (C-14) from solution. The experiment consisting of a growth vessel and a bio-filter connected in a closed loop. The bio-filter was not installed for the purpose of treatment but rather as a method of isolation of microorganisms for further processing. Significant amounts of C-14 were detected in the trapped cells in the bio-filter, significantly higher than in controls taken before adding carbon sources containing C-14. The microorganisms were grown under micro-aerobic conditions with graphite carbon and commercially purchased powdered carbon as the predominant supplied carbon sources. Small amounts of sucrose (500 mg/L) were added at 48 hour intervals to promote the growth of heterotrophic microorganisms. Additional work is required to determine the amount of C-14 escaping through gases produced as a product of metabolism (CO2 and CO) and the total carbon metabolized by the microorganisms in order to report with accuracy the degree of separation of C-14 from the C-14/C-12 mixture. A proof of concept study is underway to determine the C-14 mass balance, characterize the microorganisms in the reactor, and establish the presence or absence of processes that might have affected the preliminary observations. (authors)