Microbes can help low-pH cement protect nuclear waste, Pg13

Key Highlights:

• Nuclear activities globally produce about 2,00,000 m3 of radioactive waste annually, with 10,000 m3 requiring long-term geological storage.
• Geological disposal facilities (GDFs) are constructed hundreds of meters underground to store waste containers within cement backfill.
• A low-pH cement formulation, CEBAMA, is being considered in Europe for GDFs due to its structural performance and chemical compatibility.
• Research indicates that microbes in low-pH cements can facilitate microbially induced carbonate precipitation (MICP), which can seal cracks, given sufficient organic carbon and nitrate ions.

Detailed Insights:

• GDFs rely on cement to secure waste, support tunnels, and impede the movement of radioactive materials in groundwater.
• CEBAMA's lower pH is advantageous as it reduces the risk of steel corrosion caused by alkaline water, but its long-term evolution is under investigation.
• MICP is a process where bacteria induce the precipitation of calcium carbonate, which can seal cracks and pores in concrete, enhancing durability.
• The University of Manchester study simulated GDF conditions to assess whether alkaliphilic, anaerobic microbes could drive MICP in low-pH cement.
• The study found that MICP in low-pH cements depends on the availability of organic carbon and electron acceptors like nitrate ions.
• In high-carbon conditions, microbial metabolism leads to carbonate deposits that seal cracks; conversely, carbon scarcity results in calcium leaching and low MICP rates.
• While MICP can seal cracks, it may also lead to the accumulation of hydrogen and methane, potentially affecting the mechanical stability of the repository.
• Over extended periods, cement alteration will create cracks beyond the capacity of MICP, providing escape routes for generated gases.

Key Concepts Involved:

• Radioactive Waste: Materials contaminated with radioactive substances, posing risks to health and the environment.
• Geological Disposal Facilities (GDFs): Purpose-built caverns for the long-term storage of high-level radioactive waste.
• Microbially Induced Carbonate Precipitation (MICP): A process where microbes facilitate the precipitation of carbonate minerals, like calcium carbonate.