Radionuclide sorption to a mixture of anaerobic bacteria in the repository environment

Abstract

The sorption of the radionuclides, Pu, Np, Pa, Sr and Cs, to a mixture of anaerobic bacteria activated under specific conditions of temperature, pH and depleted nutrients after a long dormant period has been investigated. For Pu, after 4 hours at neutral pH, the distribution coefficient (Kd) between bacteria and aqueous phase at 308 and 278 K was around 103'4 (ml g"1). Over 5 days, however, the Kd at 308 K increased to over 105. Sterilized (dead) and dormant anaerobic bacteria adsorbed Pu to the same extent. Kd for Np at 308 K after 5 days had a low value around 102. After 10 days, however, Kd was > 100-fold higher. On the other hand, Kd for Np at 278 K remained low, without any significant increase over time. The interaction between Pa and bacteria was found to be stronger than that for Np, with Kd for Pa about 100 times higher. For Sr and Ca, significant Kd change was not seen through 120 d. The value for Sr is a few times larger than that for Cs due to the different electrostatic interaction with the bacteria based on the charge of ion.