Heat and Radiation Greatly Reduce Microbe Survival in Deep Underground Storage

Greg Howard
12th July, 2024

Heat and Radiation Greatly Reduce Microbe Survival in Deep Underground Storage

Simulating the early hot phase of a deep geological repository, this experimental setup of bentonite exposed to varying heat, radiation, and saturation levels ultimately demonstrated that prolonged high temperatures (90–150 °C) are the primary driver of dramatic microbial viability loss, irrespective of the radiation dose or bentonite form.

Image adapted from: Bartak et al. / CC BY (Source)

Key Findings

  • The study by the Technical University of Liberec examined how heat and irradiation affect microorganisms in bentonite used in deep geological repositories (DGRs) for nuclear waste
  • High temperatures (90°C and 150°C) significantly reduced microbial viability in bentonite, more so than irradiation
  • Microbial recovery was observed in bentonite powder samples heated to 90°C for up to six months, but not after 12 months or at 150°C
Understanding how microorganisms in bentonite react to the conditions in deep geological repositories (DGRs) for nuclear waste is crucial for the long-term stability of these storage systems. A recent study by the Technical University of Liberec[1] delves into this issue by examining the effects of heat and irradiation on microbial activity in bentonite, a key component of the engineered barrier system (EBS) in DGRs. Bentonite's role in DGRs is to provide a stable barrier that isolates radioactive waste from the environment. However, the presence of indigenous microorganisms in bentonite could potentially compromise its integrity over time. To predict how these microorganisms will behave during the early hot phase of DGR evolution, the study subjected two types of bentonite (BCV and MX-80) to varying conditions of heat (90–150°C) and irradiation (0.4 Gy.h−1) over a period of up to 18 months. The study utilized a combination of molecular-genetic, microscopic, and cultivation-based techniques to assess microbial survivability. The results showed that exposure to high temperatures (90°C and 150°C) significantly reduced microbial viability in both types of bentonite, regardless of the bentonite/water ratio or saturation level. This suggests that temperature is a more critical factor than irradiation in influencing microbial activity in bentonite. Interestingly, bentonite powder samples exhibited some microbial recovery after being heated to 90°C for up to six months, but this recovery was not observed after 12 months. Exposure to 150°C had an even more pronounced effect, with minimal microbial recovery observed. These findings align with earlier studies that have demonstrated the impact of temperature on microbial activity in bentonite. For instance, a study focusing on the Cerny Vrch bentonite found that microbial activity decreased with increasing temperature, with 90°C proving to be a limiting factor for microbial proliferation[2]. The recent study also complements previous research on gas generation in DGRs due to microbial activity. A study conducted over seven years found that microbial degradation of cellulosic material can produce gases like methane, which can increase rock cavity pressure and affect the mobility of radionuclides[3]. This highlights the importance of understanding microbial activity not just in terms of bentonite integrity but also in the broader context of DGR stability. Moreover, the study's findings on the negligible impact of irradiation on microbial activity are consistent with earlier research that showed biogeochemical processes are not significantly restricted by radiation dose rates. For example, a study on sediment microcosms revealed that even high radiation levels did not inhibit microbial processes like Fe(III) reduction[4]. The Technical University of Liberec's study recommends further long-term experiments at additional temperatures, combined with mathematical predictions of temperature evolution in DGRs. This approach aims to validate the potential development of microbially depleted zones in the bentonite buffer around waste canisters, thereby refining predictions of microbial effects over time in DGRs. In summary, this study provides valuable insights into the factors influencing microbial activity in bentonite under DGR-relevant conditions. By highlighting the critical role of temperature and the limited impact of irradiation, it offers a clearer understanding of how to maintain the long-term stability and safety of deep geological repositories for nuclear waste.

EnvironmentSustainabilityBiotech

References

Main Study

1) Dramatic loss of microbial viability in bentonite exposed to heat and gamma radiation: implications for deep geological repository

Published 11th July, 2024

https://doi.org/10.1007/s11274-024-04069-w

Related Studies

2) Survivability and proliferation of microorganisms in bentonite with implication to radioactive waste geological disposal: strong effect of temperature and negligible effect of pressure.

https://doi.org/10.1007/s11274-023-03849-0

3) Microbial Degradation of Cellulosic Material and Gas Generation: Implications for the Management of Low- and Intermediate-Level Radioactive Waste.

https://doi.org/10.3389/fmicb.2019.00204

4) The impact of gamma radiation on sediment microbial processes.

https://doi.org/10.1128/AEM.00590-15


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