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Canada's historical role in developing nuclear weapons

May 28, 2012

Chalk River Laboratories, February 1954
Chalk River Laboratories, February 1954. Located about 200 km north of Ottawa, Ontario, Chalk River Laboratories buildings contained the ZEEP, NRX and NRU reactors (under construction). Originally part of an effort to produce plutonium for nuclear weapons, the ZEEP reactor was designed by a team of Canadian, British and French scientists and engineers during the Second World War.

The extraction and processing of uranium as well as research into the production of nuclear materials for military purposes are part of Canada's history. The better-known chapter of that history is probably Canada's participation in the Manhattan Project during the Second World War (WWII), when our country supplied and refined uranium for use in U.S. facilities. Canada continued to be a supplier of uranium for military purposes for two decades after the war.

Less well known to most, perhaps, is our involvement in research to produce and extract plutonium as part of the Manhattan Project, which ended in 1946. Canada also sold irradiated (used) nuclear fuel, from which plutonium was extracted, to the U.S. between 1959 and 1964. All transfers of nuclear materials for non-peaceful purposes were halted the following year.

C.D. Howe
C.D. Howe, Canada's wartime cabinet minister who formally entered Canada into the nuclear age.

A wartime decision

It was in the midst of WWII, on August 17, 1942, that Canada formally decided to enter the nuclear age. The British government was looking for a partner to relocate its Cambridge-based nuclear laboratory during the war to facilitate collaboration with the U.S. in developing nuclear weapons. After negotiations between the United Kingdom and Canada, agreement was reached. C.D. Howe, Minister of Canada's wartime Department of Munitions and Supply, famously gave the go ahead for the Montreal Laboratory (forerunner of the Chalk River Laboratories) with the simple words “Okay, let's go." The laboratory would become associated with the U.S. Manhattan Project, which would build a nuclear bomb.

A year later, the Québec Agreement between the UK and the U.S. was signed by Winston Churchill and Franklin Delano Roosevelt. This multinational agreement sealed the general terms which would later define Canada's role in the Manhattan Project and the nuclear weapons programs of the Allies.


The early expansion of Canada's uranium industry was driven by the military's interest in the development and production of nuclear weapons. During WWII, a Canadian company, Eldorado Gold Mining Company, reopened a recently closed radium mine, (the presence of radium is closely associated with that of uranium) to supply the U.S. military with the uranium needed to produce the nuclear bomb.

From the mine, located near Great Bear Lake in the Northwest Territories, uranium-bearing ore was extracted and shipped thousands of kilometres to Eldorado's milling and refining facility in Port Hope, Ontario. In 1942, the federal government purchased and nationalized Eldorado's uranium-related assets.

For the duration of WWII, Eldorado's Port Hope facility refined ore from many countries, including the U.S. and what is now the Democratic Republic of Congo, in response to the overwhelming demand for uranium driven by the Manhattan Project.

Miner hauling a car of uranium-bearing ore
A miner hauling a car of uranium-bearing ore at Eldorado Mine of Great Bear Lake, NWT, c. 1930. Radium mining ended at the mine in 1939. In 1941, the private mine was reopened to supply the U.S. with the uranium needed to develop the nuclear bomb. Because of its strategic importance, the Canadian government bought the company one year after.


During WWII, Canada joined the U.S. and the UK in their efforts to produce a nuclear bomb. The fission of uranium, the method used to harness the energy found within the atom, was discovered in 1939. By the end of 1942, the UK and Canada had established the Montreal Laboratory to develop nuclear weapons. Scientists from both nations and from France collaborated to design the ZEEP (zero energy experimental pile) reactor.

The ZEEP, housed in Chalk River, Ontario, was a small prototype reactor constructed to prove that natural uranium and heavy water could be used to create and sustain nuclear fission (also known as achieving “criticality"). The reactor was also used to demonstrate the design's potential to generate plutonium – an artificially created fissile material that can be extracted chemically from irradiated uranium fuel – for the Allies' military programs. The first reactor to achieve criticality outside the U.S. (in September 1945), the ZEEP served as the basis for the design of the NRX (National Research Experimental) reactor.

Heavy water production – Cominco, in Trail, British Columbia, produced and supplied heavy water for the Manhattan Project, mainly to U.S. military facilities. It sold the product until 1956.

Post-WWII period

Following the war, the global demand for uranium continued to be driven by military uses.

Many Canadian communities experienced rapid growth in the post-war period as a result of the burgeoning mining industry. Uranium City, in Northern Saskatchewan, hosted a number of mining operations comprising several mines and two mills. Two Ontario areas – Bancroft and Elliot Lake – also experienced a boom in uranium mining activities. Elliot Lake would come to be recognized as the “Uranium Capital" of the world, with over 12 mines and several nearby mills, operated by Denison Mines and Rio Algom.

Canada's nuclear history
Check out our interactive timeline to learn about Canada's nuclear history  

By 1959, the U.S. military's demand for uranium had slowed. Canada officially stopped exporting uranium for weapon production in 1965. Unfortunately, this led to the abandonment of some uranium mines leaving sites that were not cleaned up to today's standards. The Canadian Nuclear Safety Commission (CNSC) has been actively working to ensure that such legacy sites are remediated to limit environmental impacts.

After the Manhattan Project was terminated in 1946, Chalk River Laboratories focused its efforts on medical and industrial applications of nuclear technology. A laboratory to extract plutonium from irradiated fuel rods from the NRX was developed and operated until 1954.

Between 1959 and 1964, about 252 kg of plutonium contained in used nuclear fuel was exported to the U.S. The material was transferred from Chalk River Laboratories to the Savannah River Site in South Carolina, where it was processed and blended with the remaining U.S. nuclear weapons program inventories.

Canada's role in nuclear non-proliferation

In 1965, the Canadian government decided that all exports of uranium and all other nuclear materials would be for peaceful purposes only. Canada was the first country with significant nuclear capability to reject nuclear weapons and has since been actively involved in promoting the peaceful use of nuclear energy around the world. This policy was reinforced in 1970 when Canada signed the United Nations Nuclear Non-Proliferation Treaty.

The CNSC's non-proliferation mandate

Fulfilling Canada's international commitments on non-proliferation has been a CNSC responsibility since the Atomic Energy Control Act was passed in 1946. The CNSC works with Foreign Affairs, Trade and Development Canada to implement key elements of Canada's international non-proliferation policy, which include the peaceful use of nuclear energy, as well as obligations related to safeguards and security.

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