Queen's University Queen's University

Mark Diederichs and the GeoEngineering Centre

[Mark Diederichs]

Waste Wise

People can argue endlessly about whether nuclear power is desirable. But they can’t dispute the fact that, like it or not, it’s a part of society – and that society needs to find a safe way to dispose of nuclear waste.

Hundreds of scientists around the world are grappling with this issue, and Dr.Mark Diederichs is in the thick of it. Diederichs, a professor of geological engineering at Queen’sand a member of the GeoEngineering Centre at Queen’s– RMC (see sidebar), is part of a Canadian research group that’s designing massive underground chambers where nuclear waste can be stored safely long term. Diederichs’ expertise is in figuring out how the geology and characteristics of the surrounding rock interact with shafts or tunnels excavated within it. Does the rock fracture or disintegrate? How does the tunnelling affect water flow? Will a major geological event in the distant future compromise the stability of the excavation?

There are different types of nuclear waste. The kind that captures the most public attention consists of bundled uranium fuel rods from the cores of nuclear reactors. Spent fuel, known as high-level waste, remains radioactive and is toxic to humans. It takes thousands of years to degrade to a harmless state. Used nuclear fuel destined for long-term storage is typically encased in thick jackets of copper or lead and concrete and stored in secure facilities at the site of the nuclear reactor that produced them.

Though it’s less hazardous, low- and intermediate-level nuclear waste – such as nuclear plant maintenance tools and equipment, machine parts and some types of medical waste – must also be safely stored. In Ontario, contaminated material from the Darlington, Pickering and Bruce nuclear generating stations is currently stored in secure canisters at the Western Waste Management Facility near the Bruce generating station near Kincardine.

With Diederichs’ assistance, the Nuclear Waste Management Organization (NWMO), a government mandated, industry supported organization for which Diederichs is a technical adviser, has designed a Deep Geologic Repository, or DGR, to be built under the Bruce site. The mine-like facility, now in the licensing phase, will be bored out of limestone 680 metres underground and below a 200-metre thick shale deposit, and be large enough to contain all the low- and intermediate-level waste produced by Ontario’s 20 nuclear reactors through the rest of their life cycle.

To determine the geological suitability of a potential excavation site, other geologists and engineers like Diederichs study the chemistry and physics of underground water to estimate how long it’s been since it experienced a major geological transformation. In the case of the Bruce site, for instance, it’s been hundreds of millions of years. While this is no guarantee that the rock will remain stable forever, it does provide a comforting outlook from a human safety perspective. Diederichs, himself, studies the physical response characteristics of the various geological units and simulates the mechanical behavior of the rock around the facility during construction and for up to a million years after closure. The point of the testing is to ensure that no radioactivity will reach the layers of water above it if the underground site is somehow compromised. All indications are that the geology at the Bruce site provides this safety barrier.

Diederichs is also involved with NWMO’s other big research project: a deep-storage facility for Canada’s high-level nuclear waste. Because the stakes are so high, it will take at least a decade to choose a location for the facility and another 20 to 30 years before it’s actually built. The public must be satisfied that it will be safe – the exhaustive consultation process is called Adaptive Phase Management – and accomplishing this can be even tougher than the engineering and construction of the site. In fact, in the 1990s, the Canadian government was considering a deep-storage facility dug out of the Canadian Shield. The project was shelved not because of complex technical issues but, as one scientist observed, “because of public dread.”

“Nuclear waste is all about communication,” says Diederichs. “We can work on the technical issues as geologists and engineers, but at the end of the day our work in that area has to be communicated to the public. That’s hard to do, because the time scales we’re dealing with are very challenging. How do you persuade someone that something will be safe for basically forever? This is where geology and geological engineering become as much about the future as it is about the past.”

The GeoEngineering Centre

The GeoEngineering Centre consists of professors and graduate students from four different engineering departments at Queen ’s and the Royal Military College (RMC). Together, the colleagues bring new knowledge and techniques to the fields of geotechnical, geohydrological, geochemical, geomechanical and geosynthetics engineering.

For instance, at Queen ’s, Dr. Ian Moore leads a team of students that designs stronger and more durable culverts, those arched metal, concrete and polymer tubes that are buried under roads and rail lines to allow streams and rivers, or people, cars and trains, to pass through.

At RMC, civil engineering professor Dr. Richard Bathurst designs earthquake -resistant retaining walls – vertical or near-vertical “earth structures” used to contain rocks and soil behind highway overpasses, reservoirs and buildings. Bathurst ’s laboratory includes a ”shaking table,” a nine -metre square solid-steel platform on which he constructs small-scale retaining walls, then activates to mimic the violent back-and-forth motion of an earthquake.

Also at Queen’s, Dr. Kerry Rowe is a world leader in landfill design whose work is helping to prevent toxic leachate in dumps from polluting nearby soil and groundwater.

Since 2001, the GeoEngineering Centre ’s innovative research on wall and bridge strength, groundwater flow, landfill liners, tunnel and mine design, and the long-term stability of mine tailings – to name but a few of the Centre ’s multiple areas of expertise – has been applied across Canada and around the world.

Profile by Alec Ross
(e)Affect Issue 3, Spring 2013