Small modular reactors will generate more radioactive waste than their larger, existing cousins, and its chemical complexity will make it more difficult to manage, a new study says.
Published in the peer-reviewed journal of the National Academy of Sciences, the study compared designs for three small modular reactors (SMRs) with a standard pressurized-water reactor. (One of the new designs studied was the Integral Molten Salt Reactor (IMSR) from Oakville, Ont.-based Terrestrial Energy.) It concluded that most SMR designs will “entail a significant net disadvantage for nuclear waste disposal” and will produce wastes that aren’t compatible with existing disposal practices and facilities.
“We’re trying to say: ‘Put a pin in this,’ ” said Allison Macfarlane, director of the University of British Columbia School of Public Policy and Global Affairs and a former chair of the U.S. Nuclear Regulatory Commission. (Her co-authors included two post-doctoral researchers who now work for an organization charged with establishing an underground nuclear waste facility in Sweden.)
“You need to account for how much of this material there’s going to be, and think about what kind of disposal facility you’ll need,” Prof. Macfarlane said.
Nuclear reactors produce radioactive wastes that include spent fuel, contaminated coolant and worn-out components. The composition of those wastes depends on factors such as the fuel used, and the physical design and materials used to make the reactor. The wastes often throw off hazardous radioactivity and heat, which makes managing them costly and difficult.
Reactors that generate larger quantities of waste, or wastes that are unusual or require new disposal methods, can face formidable competitive disadvantages relative to those producing wastes that can be managed with existing practices. Waste must be considered when comparing nuclear generation with alternatives such as hydropower, wind or solar.
Traditional reactors have been capable of generating up to 1,000 or more megawatts of electricity, and are water-cooled; their spent fuel is highly radioactive and must be isolated from the environment for hundreds of thousands of years. SMRs by definition produce less than 300 megawatts, and would be cooled by novel substances such as molten salt or helium, producing different wastes.
Prof. Macfarlane said the smaller a reactor is, the more neutrons tend to escape the core and affect other components. “That will create more radioactivity in the materials used in the reactor vessel,” she said, which will “have to be accounted for as a waste product.” The researchers also determined that fuels from some SMRs would likely need processing to make them suitable for underground disposal.
The researchers found the studied SMRs would produce between double and 30-fold the volumes of waste arising from a typical reactor. They estimated spent fuel from Terrestrial’s IMSR would contain higher concentrations of fissile materials than that from traditional reactors. That means the fuel could be at risk of renewed fission chain reactions if stored in high concentrations, meaning it would need to occupy more space underground.
Such assertions contradict marketing claims from many SMR vendors. For instance, Terrestrial Energy has said on its website that its IMSR would produce “40 per cent less waste than conventional nuclear power plants.” (In a statement to The Globe and Mail, Terrestrial said passages in the study pertaining to the IMSR contained “numerous inaccuracies.” It added that its reactor is 50 per cent more efficient than a conventional reactor, “so clearly it produces less radioactive waste or activity per unit power.”) Several other vendors say their reactors can recycle spent fuel from existing nuclear stations.
It’s unclear how SMR wastes would be disposed of in Canada.
With the exception of Finland, most countries that have operated nuclear power plants, including Canada and the United States, have failed to establish underground repositories (known as deep geologic repositories, or DGRs) for spent fuel. The Nuclear Waste Management Organization (NWMO), which seeks to establish a repository in Ontario, is nearing the end of its site selection process. The Nuclear Fuel Waste Act requires the NWMO to provide services for managing SMR fuels “over the long-term at a fair and reasonable cost.” The organization’s criteria for accepting wastes, which are not yet complete, require durable, solid materials that will not react chemically or release radionuclides.
A year ago, the Union of Concerned Scientists published a report that concluded many proposed SMRs would require new facilities to manage their wastes. It called claims that SMRs could burn existing waste “a misleading oversimplification.” The report found that reactors can consume only a fraction of spent fuel as new fuel – and that requires reprocessing to extract plutonium and other materials that could be used in weapons, thus raising what the organization described as an “unacceptable” risk.
“The most important takeaway is that you really need to plan carefully for the back end of the fuel cycle,” Prof. Macfarlane said. “And too often, the back end of the fuel cycle gets ignored in talking about new technologies, or existing technologies.”
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Matthew McClearn