Confidence in Safety report revisited, CLC learns more about local geology

·6 min read

SOUTH BRUCE – The Community Liaison Committee (CLC) received a more in-depth presentation about the Nuclear Waste Management Organization’s (NWMO) Confidence in Safety report released in June 2022.

Paul Gierszewski, the NWMO’s director of safety and technical research, is “personally responsible for a group at NWMO that leads the safety assessment and the technical research,” he told CLC members at its Sept. 1 meeting.

Gierszewski summarized where the NWMO is currently “with respect to our perspectives on confidence in safety at the South Bruce site,” highlighting what the report said and what they are seeing.

“It’s important, though, first, to be very clear that we are at a point along the process of developing increasing confidence in the site,” he said.

Outlining that there are other things to be done in the future along with what has already been done or is in progress, Gierszewski added, “What we’re seeing right now is whether we have sufficient confidence in the likely outcome to want to proceed to the next steps to proceed with this site.

“We’re not saying that we have enough information at this point to proceed with a license to construct, or license to operate, but what we’re seeing is that we’ve learned enough from completing studies, such as the two deep boreholes as an example of things that we’ve done.”

He said that additional confidence would come from the work currently underway or planned in the future.

“Our confidence in the site is based on the deep geological repository with multiple barriers,” he said, reiterating that this “internationally accepted approach” is being applied in South Bruce.

“But what’s different now…is the evidence of the suitability of the rock at the South Bruce site,” Gierszewski said. “Up until now, we’ve had regional information that we thought would look good, we’ve got that additional confidence coming in now from our studies.”

The borehole studies completed so far show that the rock buried deep in the earth of Southern Ontario and around the Great Lakes represents some of the oldest sedimentary rocks in North America. They are around 400 million years old.

“This area was originally, four or five hundred million years ago, under an ocean,” he said. “So, it was deposits of sand, silt and shells over millions of years to the ocean bed that formed these layers. And then over millions of years, as the ocean dried and was buried and compressed, those layers of material were all compressed into the sedimentary rock formations that we see now.”

Regional studies, like the 90 boreholes that the Ontario Power Generation (OPG) conducted at the Bruce Nuclear site when they were trying to gain approval for a low- to intermediate-level nuclear waste DGR, provide additional data for comparison, confirming that southern Ontario rock is good rock for a DGR.

Gierszewski explained how the consistency of the rock formations’ layers from Lake Huron’s shores to the potential site in South Bruce was an important factor in the studies. As a result, they were not surprised that they were similar to what they expected.

“We’re finding the rock formations at about the depths and about the thicknesses,” he said. “And they’re looking at this point, like what we’d expect them to be based on the regional information. So that’s a really important piece of information to us that we’ve learned.”

Geology structure at the South Bruce site

The Cobourg Formation, at 650 metres deep, is the target location for the underground nuclear waste storage facility. This formation is 40 metres thick and below hundreds of metres of permeable limestone, dolostone, and shale.

“It’s deep, it’s thick, it covers a large area so there’s enough space to put the repository in, and it’s a strong and low permeability rock, below it is another 200 metres of low permeability rock, and then we get down to what geologists call the Precambrian bedrock,” Gierszewski said. “This is a nice, granite-based rock that’s essentially the base of the continent. Elsewhere, that rock comes up to the surface, and we call it the Canadian Shield. Here, it’s about 900 metres below the surface.”

Another discovery was what they didn’t find – no water-bearing Cambrian Formation above the bedrock. Gierszewski explained why this is important and how it affects their confidence in safety thought process.

“Elsewhere in southern Ontario, there is a sandstone formation, called the Cambrian Formation, that usually exists just above that Precambrian crystalline bedrock. It’s water bearing, and its high pressure. We know that it stops at some point, we weren’t sure whether it was or was not at the South Bruce site. Evidence shows, it’s not there.”

Also not found in the South Bruce area were any natural resources, like oil or gas, which Gierszewski said is good “because it reduces the incentive for anyone to want to dig into the repository.”

Seismic activity is being monitored by five “micro seismic stations,” so sensitive they are picking up rock blasting in Owen Sound. These stations and maps of recorded earthquakes in southern Ontario show that there has not been any seismic activity in the South Bruce area.

“The last point is that there’s not even any potable water below about 200 metres, it’s too salty,” Gierszewski said, “So that means there’ll be no incentive for anyone to drill a well down to the repository level to try to extract water from that location.”

He talked about future testing and studies that would lead up to any application for the construction of the DGR, explaining that many of these studies provide a baseline for the NWMO.

“So, I’ve described where we have detailed site characterization planned should this site be selected,” he added. “However, we feel that the uncertainties that remain are less about the suitability of the rock, and more about developing a quantitative understanding of the site.”

Looking at the salinity of the host rock, which he said is “a favourable indicator for the stability of the geology,” and its effects on the engineered materials is one of the things that require further analysis.

Environmental testing, groundwater monitoring, and rock core sample analysis are ongoing; he said.

“And all of this will be put together into a variety of site-specific analyses to then support decisions on licensing applications and detail design, and so on.”

Gierszewski finished his presentation by saying, “Overall, based on the assessment results to date, the NWMO is confident that a deep geologic repository could be constructed at the South Bruce site in a manner that would provide safe long term management for Canada’s used nuclear fuel.”

Cory Bilyea, Local Journalism Initiative Reporter, Wingham Advance Times