The CANDU Reactor

Einstein's famous equation E=mc2 tells us that matter and energy are equivalent. In principle, matter can change into energy and vice versa. Physicists working in laboratories around the world in the first half of the 20th century were able to demonstrate Einstein's law by "splitting" atoms of uranium. When they fired neutrons at uranium atoms, the uranium atoms split into two atoms of lesser mass, producing heat energy equivalent to the missing mass. The idea of turning this reaction into a new way to generate electricity occurred to scientists and other people almost immediately.

The idea was actually quite simple. The energy produced from a splitting uranium atom (nuclear fission) could be used to heat up water inside a reactor. The heated water turns to steam that spins turbines. The turbines drive generators, producing electricity. The water also cools the uranium fuel and slows down the neutrons that fly out from the splitting atoms. This slowing down of the neutrons is important, because slow neutrons split atoms more efficiently than fast ones.

During World War II, as part of the Allied war effort, a team of Canadian and British scientists gathered secretly in Montreal. It was 1942 and their job was to design a nuclear reactor. Though the basic design is actually quite simple, the engineering is not easy. When uranium atoms split, they release heat energy and fast-moving neutrons. These neutrons can split other uranium atoms. The trick is to produce enough neutrons to sustain the reaction without it going too fast and getting out of hand. Other teams of scientists and engineers working in Europe and the U.S. were using enriched uranium and water in their reactors. Enriched uranium produces more neutrons than ordinary uranium. This was important, because water absorbs too many neutrons to allow a reaction with ordinary uranium to sustain itself. The problem was that enriched uranium is very expensive. The Canadian team had the smart idea of replacing ordinary water with "heavy water", which has an extra neutron. Then they could use ordinary uranium in their nuclear reactor.

In 1944 the Canadian and British team got the official go-ahead to develop a small experimental nuclear reactor called ZEEP (for Zero Energy Experimental Pile). ZEEP was switched on in September 1945 at the National Research Council's new laboratories in Chalk River, Ontario. It was the first self-sustained nuclear reaction outside the United States, launching Canada as one of the world's leaders in nuclear energy research.

In 1952, the Canadian government created a crown corporation, Atomic Energy of Canada Ltd. (AECL), to develop peaceful uses of nuclear energy. One of the first tasks assigned to AECL scientists and engineers was to develop a reactor that could produce electricity on a large scale. AECL, Ontario Hydro and Canadian General Electric teamed up to build Canada's first nuclear power plant, using the Canadian-developed heavy-water design. By June 1962, they were able to feed nuclear-generated power into the Canadian electricity grid for the first time, successfully demonstrating the feasibility of the CANDU concept.

Ontario Hydro now owns and operates most of the CANDUs that have been built. About one-half of Ontario's electricity is generated from nuclear fission. Outside Ontario, there are two other nuclear power plants in Canada. One is located at Point Lepreau, N.B., the other at Gentilly, Que. Canada has also sold CANDU reactor units to Argentina, Romania, Republic of Korea, People's Republic of China, India and Pakistan.

For information, visit the Atom Energy of Canada Ltd. Website at www.aecl.ca.