Potential microbial influence on the performance of subsurface, salt-based nuclear waste repositories

Abstract Microorganisms can influence the performance of nuclear waste repositories through activities or processes that affect radionuclide migration. In the case of subterranean salt-based repositories, the influence of microorganisms may be limited by the unique constraints of such sites (e.g., high ionic strength, low water activity, nutrient supply) coupled with the conditions of the repositories themselves (e.g., anoxia, radioactivity, high temperatures). Indigenous extremely halophilic archaea can survive long term at high ionic strength and may remain viable throughout a repository’s lifetime. However, their ability to affect repository performance through waste and radionuclide transformation is uncertain, as they are mostly aerobic and repositories are projected to be anoxic. Microorganisms introduced with waste may contribute to transformation within drums but may not survive high-salt concentrations once drums have been breached and inundated with brine. However, both indigenous and introduced organisms may associate with radionuclides and enhance or mitigate radionuclide migration in this capacity.