The History and Current State of Canada's CANDU Nuclear Reactor

Chelsea Liekhus-Schmaltz
February 26, 2013

Submitted as coursework for PH241, Stanford University, Winter 2013

Fig. 1: Nuclear energy makes a significant contribution to the total electricity in Canada. (Data from Statistics Canada. [3])


It's funny to think that a single decision during war time can completely change the post-war industry of a country, but this is exactly the story of Canada and its CANDU technology. CANDU stands for "CANadian Deuterium Uranium" nuclear reactor, and it is a unique piece of nuclear technology that was developed during WWII. The CANDU reactor is special because it uses heavy water as its regulator therefore allowing natural uranium to be used as fuel. This is in contrast with its light water cousin which requires enriched uranium. [1] The CANDU reactor also has a flexible fuel-cycle so that it can use waste from light water reactors to power the CANDU reactor using the DUPIC (Direct Use of Spent Pressurized Water Reactor Fuel in CANDUs) process. [2] Canada currently uses the CANDU technology to supply 17% of its electricity needs by use of three plants in Ontario and one in New Brunswick. [3,4]

While the CANDU reactor has historically been considered a hallmark of Canadian industry, the technology currently faces uncertain times. This is a result of its role in nuclear proliferation and the weakened state of the crown company that oversaw the growth of the technology. While the future of the technology is now uncertain, studying its development provides interesting insight into Canada's place in today's nuclear world.


The story of the CANDU reactor begins in WWII. In 1940 under the threat of the German invasion of Norway, a Russian-born scientist by the name of Lew Kowarski escaped to British soil with almost the entire world's supply of heavy water. He and his colleague Hans von Halban had been developing a new type of reactor that would use heavy water as its regulator. This was particularly important during the war because it would allow for the production of plutonium without the expense of refining uranium. [5]

In the fall of 1942 Kowarski's group of British scientists were denied access to the USA due to tensions over security and patents issues, so the National Research Council of Canada accepted the group onto Canadian soil to continue working on the heavy water reactor. This decision would turn out to be crucial for development of the CANDU reactor in Canada. [5]

The group set about creating a laboratory at the University of Montreal to develop the technology. Later, they would move to Chalk River, Ontario where Kowarski lead a team to create the ZEEP (Zero Energy Experimental Pile) reactor which went critical in 1945. [5,6] Following this, the National Research Experimental (NRX) and National Research Universal (NRU) reactors were built at the Chalk River site as well and went critical in 1947 and 1957 respectively. [5,6]

Between the creation of NRX and NRU, a new crown company AECL (Atomic Energy of Canada Limited) came to control the research site and was responsible for promoting nuclear power in Canada. However, AECL faced a major problem while trying to develop nuclear power. Canada was not a particularly industrial country compared to its neighbors across the ocean or south of the border. Therefore, the nation could not build the giant steel pressure vessels required for scaled versions of NRX and NRU for power generation, nor could the country spare the expense required for refining uranium. Therefore AECL decided to create smaller reactors that would be heavy water regulated so as to make use of their expansive natural uranium resources and their expertise in heavy water reactors. In 1962 the Nuclear Power Demonstration reactor presented the necessary technology for generating power and initiated the beginning of Canada's nuclear energy industry and introduced the CANDU reactor. [6,7]

India and Its Bomb

During the 60s, Canada continued to build its CANDU reactors within its borders and started to supply reactors abroad by building the CIRUS (Canadian-Indian Reactor, U.S.) research reactor in India. While this was not strictly a CANDU type reactor, it is in fact based off of the NRX reactor, it is nonetheless a heavy water reactor. Unfortunately, the consequences of this exchange would not be fully realized until 1974 when India tested its first nuclear bomb. Although India had signed treaties with Canada to limit its use of the reactor for peaceful means, it is generally accepted that the plutonium used in this test was manufactured in the CIRUS. [4,8,9]

This caused a major uproar amongst the international community against the heavy water design. Three aspects of heavy water reactors came under scrutiny including 1) allowance for use of natural uranium so that fuel can be more easily obtained, 2) plutonium can be created more frequently per kilowatt of electricity in heavy water reactors, and 3) new fuel can be added to the reactor while it is running - allowing for more covert activities to go undetected. [10] Although Canada immediately discontinued any exchange of nuclear intelligence with India after the nuclear test, the implications of their initial technology exchange did not end there.

Later in 1998, the Indian government would conduct a thermonuclear test which could have possibly used plutonium from the CIRUS reactor as well as tritium, a by-product of the heavy water regulator, from CANDU clone designs based on other CANDU reactors supplied by Canada. Again, there was immediate backlash against the Canadian government for selling its nuclear technology. [4,8]

Trouble Within AECL

In addition to the mishaps abroad, trouble was brewing within the crown company AECL. Reports of poor management were widely distributed. There were also growing worries that the reactors were more complicated to operate than once thought, and installments and refurbishments seemed to always go over budget and over time. [11] This was most recently demonstrated when AECL tried to construct two new nuclear reactors at Chalk River Laboratories called MAPLE I and MAPLE II. After eight years and $600-million, the project was canceled due to safety concerns. [12]

Eventually, the Canada's conservative government decided that the crown company was bleeding too much money and sold the power generation portion to SNC-Lavalin Group Inc. for $15-million in June, 2012. [13] The new company is called Candu Energy. The transition was not an easy one. The purchase resulted in the loss of over 200 engineers and scientists, weakening the intellectual strength of the company. The new company's start was further slowed by a strike of the nuclear workers and soft international markets. [14]

The Future of the CANDU

While Candu Energy is trying to entice Jordan and China to purchase CANDU reactors, within Canada it is unsure whether the newest nuclear plant to be built in Ontario will be a CANDU reactor. [15,16] In addition, in Ontario's latest 20-year energy plan published in 2012, where most nuclear plants are located, more emphasis has been put on moving to natural gas. [17] It would therefore seem as though Canada is moving away from the CANDU technology as well as nuclear power in general, and it is unclear if the Canadian government will provide much more support in the future for the CANDU reactor. So the question becomes, what should be done with the CANDU technology?

The prospects of the CANDU reactor looks bleak considering the trials it has endured; however there is a possible trajectory for its future. The CANDU's flexible fuel-cycle allows for a potential route for removing waste using the DUPIC process. Countries could therefore install CANDU reactors as waste disposal sites. [2] Since this possibility would require some development, the direction would have to come from AECL. Considering the state of AECL at the moment, it is not clear whether either path will be taken.


The CANDU reactor technology has come quite far from is quiet beginnings in Chalk River, ON. While it has endured a troubled past, it now seems to faces an uncertain future due to its contribution to possible proliferation risk. This story could change soon though if the CANDU reactor is used to dispose nuclear waste from light water reactors.

© Chelsea Liekhus-Schmaltz. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] P. Bordia, "CANDU Reactors," Physics 241, Winter 2012.

[2] T. Hamilton, "Chalk River Should Consider Nuclear Waste as a Business Opportunity," Toronto Star, 30 Mar 12.

[3] "Energy Statistics Handbook: First Quarter 2012," Statistics Canada, Catalogue No. 57-601-X, August 2012.

[4] R. G. Steed, Nuclear Power in Canada and Beyond (General Store Publishing House, 2007).

[5] J. Whitlock, "Entering the Nuclear Age," Legion Magazine, 1 Sep 03.

[6] D. Durant and G. F. Johnson, Nuclear Waste Management in Canada: Critical Issues, Critical Perspectives (U. British Columbia Press, 2009).

[7] M. Ivanco, "Hard-Won Nuclear Expertise Should Not Be Thrown Away," Toronto Star, 22 Jun 09.

[8] R. Silver and M. Hibbs. "Opponents Say South Asian Tests Show All CANDU Exports Should End." Nucleonics Week 25 Jun 98, p. 17. - Can't find this reference. Please provide link. - RBL

[9] S. Nawaz, India's Nuclear Weapons Programme (Progressive Publishers, 1985).

[10] M. M. Miller, "Heavy Water and Nonproliferation: Topical Report," MIT Energy Laboratory Report No. MIT-EL 80-009, May 1980.

[11] A. DePalma, "Canadians Export A Type Of Reactor They Closed Down," New York Times, 3 Dec 97.

[12] P. White, "Canada's Nuclear Know-How in Accelerated Decay," Toronto Globe and Mail, 10 Aug 09.

[13] S. McCarthy, "SNC Got a Deal, But Candu Profits Not Guaranteed," Toronto Globe and Mail, 30 Jun 11.

[14] J. Spears, "Candu Energy Grapples With Strike and Soft Markets," Toronto Star, 20 Jun 12.

[15] S. McCarthy, "Candu Pursues New Reactor Sales in China," Toronto Globe and Mail, 2 Aug 12.

[16] T. Hamilton, "McKinsey to Report on Reactor Options," Toronto Star, 1 Jun 07.

[17] D. McKinnion, "Ontario's Long-Term Energy Plan: The Good, the Bad and the Ugly," Toronto Globe and Mail, 5 Feb 11.