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Spent fuel bundles stored in closed water pools at Pickering Nuclear Generating Station near Toronto in 1975, in the early years of Canada's nuclear power industry. As of last summer, Canada had accumulated 3.1 million used fuel bundles, stored temporarily at Pickering and other nuclear plants.Barrie Davis/The Globe and Mail

Both of the final candidate sites for a proposed underground disposal facility for Canada’s spent nuclear fuel – Ignace and South Bruce, Ontario – are geologically suitable, the Nuclear Waste Management Organization announced Thursday.

The two reports (one for each site) were the culmination of a decade of study. The findings were based primarily on data from boreholes roughly one kilometre deep – six at the Revell site roughly 40 kilometres northwest of Ignace, and two in South Bruce – as well as seismic surveys. The NWMO said it found no nasty surprises at either location, and that neither site was measurably superior to the other.

“We’ve looked at the rock in our hands, so to speak, at repository depth, and above and below it,” said Paul Gierszewski, the NWMO’s director of safety and technical research.

“The sites are looking to be what we thought they ought to be from the nature of the rock.”

The NWMO concluded that the ancient rock formations would be capable of dissipating heat from the highly radioactive fuel bundles. It found no indications of unfavourable geology such as faults nearby. Neither site contains oil, natural gas or other deposits that might attract prospectors to dig in the area. Groundwater flows very slowly at both locations and the infrastructure required to operate the facilities, including highways and power lines, are in close proximity.

Nearly all of Canada’s spent fuel is solid uranium dioxide, which has been pressed into ceramic pellets and sealed inside bundles of fuel rods. Upon removal from a reactor, it gives off heat and dangerous levels of gamma and neutron radiation. It will remain harmful to humans for hundreds of thousands of years.

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As of last summer, Canada’s spent nuclear fuel inventory amounted to 3.1 million fuel bundles, currently stored at nuclear power plants in Ontario, Quebec and New Brunswick. After removal from reactors, it’s kept in specially designed water pools for approximately a decade, during which radioactivity levels drops precipitously. Afterward, it’s sealed in concrete storage containers. But with containers lasting only a few decades, these are decidedly temporary arrangements

The idea behind a deep geological repository (DGR) is to store that hazardous waste underground permanently, at sufficient depth that the gamma and neutron radiation does not reach the surface. Late last year, the NWMO said it expects to begin transporting waste to its DGR beginning in the 2040s; it would take half a century to move it all, likely by road, rail, or a combination of both.

The NWMO plans to choose between the two locations by the end of next year, and is seeking partnership agreements with local municipalities and First Nations; the reports are intended to facilitate those discussions. Further site studies will be needed, it added, along with more advanced designs and safety analyses. These would be presented to regulators such as the Canadian Nuclear Safety Commission for an impact assessment, and multiple licensing applications.

Several other countries with nuclear power reactors also have plans to establish DGRs: among them, Finland and Sweden have already approved sites for that purpose.

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