Investigating the microbiology of proposed nuclear waste storage systems

Tuesday, April 12, 2022

Rachel Beaver first became interested in microbiology during her undergraduate degree at Waterloo, when taking Fundamentals of Microbiology, taught by Professor Josh Neufeld. She was inspired to continue along this path, completing three co-op terms, her undergraduate thesis, and master’s degree in the Neufeld lab.

Now pursuing her PhD in the same lab, Beaver is currently investigating the microbial impact on the safety of long-term underground storage sites for nuclear waste materials, known as deep geological repositories (DGRs).

Rachel Beaver pipetting a sample in the lab

“Something I really enjoy about this project is how the results that I generate will be used to address an important and applied challenge,” says Beaver.

In her latest work, Beaver studied the microorganisms that might exist in DGRs, particularly in the materials proposed to encase the nuclear waste.

It’s important to study these barrier materials because this is where microorganisms are most likely to grow in a DGR. One major concern with microorganisms is their potential to cause corrosion of the metal containers that isolate the nuclear waste. “Certain microorganisms create compounds that can corrode the metal components of the DGR. One particular group, the sulfate-reducing bacteria, can turn sulfate into sulfide, which can potentially corrode the copper coating of waste containers.”

In particular, one of the materials Beaver is looking at is bentonite clay, a material that expands when wet and is being considered to encase DGRs because it could act as a sealant to keep the waste containers from interacting with the environment.

“Bentonite clay is a good material for this application because it swells when water is added, creating a tight sealing system,” says Beaver. “This reduces both the growth of microorganisms and flow rates of groundwater that might be carrying corrosive compounds through the DGR.”

A sample of rock being prepared for analysisTo study the possible microbiology of DGRs and bentonite clay, the researchers took samples from natural sites that are analogous to the barrier materials. These samples were from the Tsukinuno bentonite deposit in Japan that formed about 10 million years ago, the Opalinus Clay formation in Switzerland that formed about 174 million years ago and the Canadian shield crystalline rock from Northern Ontario that formed about 2.7 billion years ago.

They found few microorganisms in samples from all three natural sites. Sulfate-reducing bacteria were only found in samples from the Tsukinuno bentonite deposit and there was no conclusive data from the other two sites. Nevertheless, they show that not every sample from the same site had the same microorganisms.

“An important challenge with analyzing environmental samples that have so few microorganisms is distinguishing between rock-associated bacteria and background ‘noise’ that our sensitive techniques can also detect," says Professor Neufeld. “This research demonstrates how confidence in results increases when stringent lab protocols are coupled with rigorous comparison of sample results to those of controls.”

Looking ahead, Beaver is continuing this research, where she plans to use pressure vessels to study bentonite clay and determine the density, time, and oxygen conditions required to suppress microbial growth.