Alkali-resistant bacteria can enhance the reliability of underground nuclear waste storage facilities. The byproducts of their life processes are capable of sealing cracks in cement, which helps maintain the integrity of protective structures.

The Challenge of Cement Barrier Longevity

One of the safest methods for storing nuclear waste is to bury it underground in special containers placed in tunnels hundreds of meters deep. Cement is widely used in the construction of such storage sites: it serves both as a structural material and for sealing containers and filling gaps.

However, over time, even durable cement can deteriorate due to groundwater, as well as mechanical and chemical factors. This leads to the formation of microcracks and pores in the material, which can result in radioactive leaks. High alkalinity of cement (pH 10–12) adds another layer of complexity: while this property gives the material longevity and resistance to corrosion, it can also weaken adjacent protective layers, threatening the overall integrity of the storage facility.

A Biotechnological Approach to Cement Restoration

A team of British scientists has proposed using bacteria that thrive in alkaline environments to restore concrete. This method is known as microbially induced carbonate precipitation (MICP). Details of the research were published in the journal ACS Omega.

The chemists studied how concrete changes over time in the presence of such bacteria. They hypothesized that the metabolic byproducts of these microorganisms could help concrete self-heal its cracks.

The Experiment and Its Results

Over six months, researchers conducted experiments with slabs made from low-alkaline cement (pH 10–11), which is less prone to corrosion yet strong enough for long-term use. Bacteria capable of surviving in alkaline conditions were collected from a natural site with high pH and placed in a laboratory solution simulating groundwater. Cement slabs were immersed in this solution, and the amount of organic material available to the bacteria was varied.

The crack-sealing mechanism works as follows: bacteria process organic matter and, in the course of their life, release carbon dioxide. This gas reacts with calcium and magnesium leached from the cement, forming calcite and other carbonate minerals that fill the cracks.

The experiment showed that the effectiveness of self-healing depends on the amount of organic material available to the bacteria. In environments rich in carbon, the bacteria were highly active, producing more carbon dioxide, which lowered the pH of the surrounding water and promoted the formation of more calcite crystals. This allowed cracks to be sealed efficiently and reduced the porosity of the cement. However, when the concentration of organic matter was insufficient, the self-healing process became less effective.

Application Prospects

The researchers note that despite the promising experimental results, further studies are needed to assess the potential of MICP technology over longer timescales and under the complex, real-world conditions of nuclear waste storage facilities.