Uranium mining and milling

Amara's first assignment for Hana is a site visit report. Meridian has been asked to review the environmental performance monitoring for a utility that buys uranium from northern Saskatchewan. "Before you look at a single number," Amara says, "understand why the Athabasca Basin is unique. Most uranium mines in the world move hundreds of tonnes of rock for each tonne of uranium. Some mines in Saskatchewan move only a few. That changes the engineering, the radiation protection and the environmental footprint completely."

Where uranium comes from

Uranium is a common element in the Earth's crust, about as abundant as tin, but it is usually spread too thinly to recover economically. Ore deposits form where geological processes have concentrated it, typically where oxidizing groundwater carried dissolved uranium until it met a reducing environment and precipitated. The main deposit types include unconformity-related deposits, where uranium collected at the boundary between ancient sandstones and the older basement rock beneath; sandstone-hosted deposits, where it is spread through porous sandstone along old groundwater fronts; breccia complexes such as Olympic Dam in Australia, where uranium is a by-product of copper and gold; and others found in volcanic and granitic rocks.

World production is concentrated in a few countries. Kazakhstan, Canada, Namibia and Australia have together produced most of the world's uranium in recent years, with Uzbekistan, Russia, Niger and China also significant. Uranium is traded internationally, so a reactor in Ontario or Tennessee may burn fuel made from uranium mined on another continent. The grade of an ore, the fraction of uranium it contains, varies by more than a thousand times between deposits, and grade is the single most important factor in the economics and environmental footprint of a mine.

# From ore to yellowcake: how much rock is moved for one tonne of uranium.
# Grades are illustrative of the ranges reported for different deposit types.
deposits = [("very high grade (Athabasca-type)", 0.15),
            ("high grade", 0.02),
            ("typical conventional", 0.002),
            ("low grade", 0.0005)]
recovery = 0.95          # fraction of uranium recovered in the mill
for name, grade in deposits:
    ore_t = 1.0 / (grade * recovery)
    print(f"{name:34s} grade {grade*100:6.2f} % U   ore per tonne U: {ore_t:9.0f} t")
U3O8_per_U = 842.08 / (3 * 238.03)      # mass ratio of U3O8 to the uranium it contains
print(f"one tonne of uranium is shipped as about {U3O8_per_U:.3f} t of U3O8 concentrate")
lb_per_kg = 2.20462
print(f"which is {U3O8_per_U*1000*lb_per_kg:,.0f} lb of U3O8")

very high grade (Athabasca-type)   grade  15.00 % U   ore per tonne U:         7 t
high grade                         grade   2.00 % U   ore per tonne U:        53 t
typical conventional               grade   0.20 % U   ore per tonne U:       526 t
low grade                          grade   0.05 % U   ore per tonne U:      2105 t
one tonne of uranium is shipped as about 1.179 t of U3O8 concentrate
which is 2,600 lb of U3O8

The program makes the scale difference concrete. A very high grade Athabasca ore needs only a few tonnes of rock for a tonne of uranium; a conventional ore at 0.2 percent needs more than five hundred tonnes, with all the energy, water and waste rock that implies. The high grades bring their own challenge, however: the ore is intensely radioactive, so it cannot be handled by workers in the usual way, and the radon it releases must be controlled carefully.

Mining in Saskatchewan's Athabasca Basin

Canada's uranium comes almost entirely from the Athabasca Basin in northern Saskatchewan. Cameco operates the McArthur River mine and the Key Lake mill, which processes its ore, and the Cigar Lake mine, whose ore is processed at the McClean Lake mill operated by Orano. In 2025 McArthur River and Key Lake produced about 15 million pounds of uranium oxide concentrate and Cigar Lake about 19 million pounds, on a 100 percent basis, according to the companies' reports. Ore at these mines is among the richest in the world, with average grades of several percent and, in places, far higher.

The high grade and difficult ground have led to unusual mining methods. At Cigar Lake the ore lies in water-saturated sandstone, so the ground around it is frozen with brine pipes to keep water out and to stabilize the rock. The ore is then cut by high-pressure water jets directed remotely from inside a shielded tunnel, so that miners never approach the ore face. The slurry is pumped to the surface, thickened and trucked in shielded containers to the mill. At McArthur River, freezing and raise boring are used for similar reasons. Ventilation is very high to keep radon progeny concentrations low, and workers wear dosimeters that track exposure to both gamma radiation and radon decay products.

In-situ recovery

Not all uranium is mined by digging. In in-situ recovery, sometimes called in-situ leaching, a solution is pumped down injection wells into a permeable sandstone ore body, where it dissolves the uranium, and is pumped back up through recovery wells. The uranium is then taken out of solution at a surface plant. The method is used where the ore is in a permeable aquifer bounded above and below by impermeable layers, which keep the solution contained. It produces little waste rock and no tailings pile, but it needs careful monitoring of the surrounding groundwater and restoration of the aquifer afterwards. Kazakhstan produces most of its large output this way. Canada's deposits are not suited to the method, but in-situ recovery is common in Wyoming and Texas.

Milling: from ore to concentrate

A uranium mill crushes and grinds the ore, then dissolves the uranium in an acid or alkaline leach. The uranium is separated from the leach solution by solvent extraction or ion exchange, precipitated, and dried and calcined to a concentrate called yellowcake, a mixture of uranium oxides usually reported as U₃O₈. The concentrate is packed in steel drums and shipped to a refinery. Almost everything else in the ore, more than 99 percent of the mass for conventional ores, remains as tailings: finely ground rock and process residue that still contains most of the original radioactivity, because the long decay chain of uranium-238 includes radium-226 and thorium-230, which are not removed with the uranium.

Tailings management is the main long-term environmental issue of uranium milling. Older North American mills placed tailings in surface ponds behind dams, some of which have needed expensive remediation. Modern Saskatchewan practice places tailings in mined-out pits below the water table, with a permeable envelope that lets groundwater flow around rather than through the tailings, reducing the release of contaminants. The CNSC and the Province of Saskatchewan regulate the mines and mills, which must hold financial assurances to pay for decommissioning.

Radiation protection in mines and mills

Uranium miners face three main radiation pathways: external gamma radiation from the ore, inhalation of radon progeny, and inhalation or ingestion of long-lived dust. Historically, radon was the most serious, and miners in the mid-twentieth century who worked in poorly ventilated mines had greatly increased rates of lung cancer. Modern mines control radon with high ventilation rates, sealing of exposed ore, and monitoring of the working level, a measure of the potential alpha energy of short-lived radon progeny in air. Dose limits for workers are the same as in other nuclear facilities, and typical modern doses in well-run mines are a small fraction of the limit.

Environmental monitoring and closure

Every operating mine and mill runs an environmental monitoring program that samples air, surface water, groundwater, sediments, fish and vegetation around the site, and compares the results with predictions and with regulatory limits. The results are reported to regulators and, increasingly, published. Closure planning starts before the mine opens: the operator must describe how the site will be decommissioned, how tailings and waste rock will be stabilized, and how long monitoring will continue, and must post financial assurance large enough for the work to be done even if the company no longer exists. The aim is a site that can be released for other uses or left in a stable condition needing minimal care.

Engagement with nearby communities, including Indigenous communities whose traditional territory includes the mine sites, has become a central part of uranium mining. Agreements on employment, business opportunities, environmental monitoring and benefit sharing are now common, and communities increasingly take part in monitoring directly. These relationships matter to regulators as well as to operators, because trust in the monitoring results depends on the people who live nearby being able to see and question them.

Environmental assessment and closure of mines

A modern uranium mine is planned from the start with its closure in mind. Before a mine is licensed, an environmental assessment examines its effects on water, air, wildlife and people, including Indigenous communities whose lands and traditional uses may be affected. The operator must prepare a decommissioning plan and provide a financial guarantee large enough to pay for closure if the company cannot. During operation, the operator monitors water quality in nearby lakes and streams, radon and dust levels, and the radiation doses received by workers. After mining ends, pits are backfilled or flooded, buildings are removed, tailings are covered and the site is monitored until it can be returned to public use or placed under long-term institutional control.

In Saskatchewan, mines are licensed by the CNSC and regulated jointly with the provincial government. Environmental assessments are carried out under federal and provincial laws, and the CNSC holds financial guarantees for decommissioning. Legacy sites from the early industry, such as the Gunnar and Lorado mines near Lake Athabasca, abandoned in the 1960s, are being remediated by the Saskatchewan Research Council under a program funded by the federal and provincial governments. Elliot Lake in Ontario, once the largest uranium mining centre in the world, has had its tailings areas covered with water and monitored since the 1990s.

Worker protection in mines and mills

The main radiation risks for uranium miners are inhalation of radon progeny and of long-lived dust, together with external gamma radiation near high-grade ore. Early miners in the 1940s and 1950s worked in poorly ventilated mines and suffered high rates of lung cancer, which led to modern radiation protection standards for mining. Today, mines control radon with powerful ventilation systems, monitor every worker's exposure with personal dosimeters and air samplers, and use remote equipment for the richest ores. In the very high-grade deposits of the Athabasca Basin, ore is mined by methods in which no person enters the ore body: at Cigar Lake, the ground is frozen and the ore is cut by high-pressure water jets controlled from a distance, then pumped as a slurry to the surface.

As a result, average doses to uranium miners in North America are now a few millisieverts a year, well below the regulatory limit of 50 mSv in any one year and 100 mSv over five years for nuclear energy workers in Canada, and the corresponding occupational limits in the United States. Mill workers are protected from dust and from the yellowcake product, which is mainly a chemical rather than a radiological hazard, by enclosed processes, ventilation and protective equipment.