The CANDU reactor (Canadian deuterium uranium) uses uranium, bundled in the form of uranium oxide fuel pellets, to produce electricity. (A comparison between CANDU reactors and other types of reactors would be an interesting optional extension topic.)

Saskatchewan has abundant deposits of uranium ore which is refined for use in nuclear reactors.

The refined uranium oxide fuel pellets are stacked into cylindrical rods. The rods are arranged into a fuel bundle which is then ready to be placed in special pressure tubes inside the reactor.

The reactor vessel is called the calandria.

Nuclear reactors can not explode like a nuclear bomb. Even under a worst-case scenario, with a core meltdown, a critical mass of fuel would not be present and the fuel would burn into the ground. (This, of course, would lead to very serious consequences, including possible loss of life and environmental damage.)

Refuelling can be done by removing fuel bundles from the pressure tubes and replacing them with new bundles. In a CANDU reactor this can be done without having to shut the reactor down.

Heavy water is used as the moderator in a CANDU reactor. Heavy water contains deuterium, an isotope of hydrogen having one neutron in the nucleus. Heavy water also transfers heat from the fuel into a heat exchanger which heats ordinary water to produce steam.

The steam produced is used to turn turbines which are connected to electric generators.

Condensers change the steam back into water so it can be cycled back to the steam generator.

Some experts believe that the design of the CANDU reactor makes them safer than other types of nuclear reactors.

If excess heat builds up in the calandria, the heavy water can be drained out. This causes the chain reaction to stop, because the moderator is no longer present.

Supporters of the use of nuclear energy feel that it is a safe and effective way to produce energy. With the demand for energy increasing, and the problems associated with burning fossil fuels, such as acid precipitation and the greenhouse effect, they regard the use of nuclear energy as being necessary.

Nuclear energy avoids some of the problems of generating hydro-electric power. Flooding land to build dams creates environmental and social problems.

The use of nuclear energy may avoid the need for long transmission lines. Nuclear plants can be built in relatively close proximity to where the power is needed.

Nuclear energy produces very small amounts of waste by volume. The radioactive materials can be concentrated for storage and monitoring in one place. Poisonous metals (such as arsenic, lead, and mercury), toxic gases, carbon dioxide, and fly ash are not released into the atmosphere.

Critics of the use of nuclear energy cite various problems with its use. The opposition to the use of nuclear energy has grown so strong in recent years, that some reactors have been shut down. Other reactors scheduled for development have been delayed or were never completed because of the social and political pressure exerted by the antinuclear lobby. The debate continues.

The Chernobyl nuclear accident lead to a justifiable scepticism about any claims of the safety of nuclear reactors, particularly if those claims come from spokespersons of the industry, who often cite the strict controls and regulations faced by the industry.

CANDU reactors need to be built near a large body of water. Fresh water is circulated through the condensers. Excess heat is returned to the source. Raising the temperature reduces the oxygen content of the water, creating an environmental stress on many kinds of living organisms. The heated water does, however, offer some possibilities for commercial aquaculture, allowing for warm-water species to be harvested in colder regions. The excess heat can also be used for commercial greenhouses or other applications. Air cooling is possible.

Critics also suggest that mining safety is an issue with the use of nuclear energy. The ore is slightly radioactive. Radon gas is often present at the mine site. The disposed tailings contain trace amounts of uranium. Unless they can be disposed of properly, they can cause ground water contamination and environmental damage to the land on which they are dumped.

The entire cycle, from mining the fuel to its eventual disposal after use, is called the nuclear fuel cycle.

Used nuclear fuel is both hot and radioactive. It is stored under water in large cooling pools for up to two years after use, until it cools. Some of the used fuel will still remain radioactive for up to several thousand years. This concerns many people.

The storage of used fuel is a contentious issue for those concerned about the protection of the environment. No ideal solution has yet been developed to dispose the waste. Current proposals for waste management merely offer temporary storage solutions until better methods become available.

Storage of waste in underground salt mines offers one possible solution. Formations in the Canadian Shield offer other possibilities. The area being considered as a storage site must be dry and relatively free of earthquake and volcanic activity.

Decommissioning of nuclear reactors, once they have completed their useful service, is another issue frequently raised by opponents to the use of nuclear energy.

One of the waste materials from a nuclear reactor is plutonium. It is known to cause cancer in extremely small quantities. It is also used to make nuclear weapons. Some argue against the use of nuclear reactors because they provide a country with the potential to build a nuclear weapons arsenal. (An interesting anecdote is that of the development of India's first atomic bomb, which occurred partially as a result of their having purchased the rights to the CANDU technology from Canada. This occurred in spite of India having been under a contractual obligation not to exploit CANDU reactor technology for anything other than peaceful uses.)

The use of nuclear energy is controversial. Individuals need to have a solid knowledge base before taking a stand on the issue. One needs to weigh the risks against the benefits involved. Once an individual has taken a position regarding the use of nuclear energy, responsible action is needed to persuade other citizens to adopt a similar position.

Arguments for or against the use of nuclear energy should be based on reason -- not emotion. One needs to remain open-minded, listening carefully to the arguments presented by those who hold a different position.

If one examines the uses of energy since before the Industrial Revolution, it becomes apparent that the major source used has changed throughout time, based on economics, the development of new technologies, and a variety of other factors. Some of these same factors are at work today, determining which sources of energy will be most advantageous to use in the future.

A concern for the protection of the environment needs to play a prominent role whenever decisions which might have an adverse affect on the environment are being considered. Alternative solutions to problems need to be examined with regard to their environmental impact.

One very important strategy is to promote conservation. Instead of demanding more and more energy, at the expense of the environment and our resources, individuals, institutions, and government all have to search for ways to conserve energy. If everyone strives to use energy wisely, existing resources will last longer. Less damage to the environment will occur. Can we reach sustainable development?

Learning Outcomes

Students will increase their abilities to:

1. Describe how a nuclear reactor works.
2. Identify the type of fuel used in a nuclear reactor.
3. Outline the nuclear fuel cycle, from the initial mining of raw materials to the final storage of waste material.
4. Recognize the role that Saskatchewan and Canada play in nuclear technology.
5. Explain why a nuclear explosion is not possible in a nuclear reactor.
6. Identify some of the main features of the CANDU nuclear reactor.
7. Explain the purpose of using heavy water in CANDU reactors.
8. Identify some of the safety features that have been designed into the CANDU nuclear reactor system.
   
9. State some of the facts that supporters of the use of nuclear energy use to substantiate their position
10. State some of the concerns that critics raise regarding the use of nuclear energy.
11. Suggest what concerns regarding the environment emerge as a result of the use of nuclear energy.
12. Suggest how environmental concerns regarding the use of non-nuclear methods of electrical generation might be alleviated with the use of nuclear energy.
13. Using a solid knowledge base of all of the previous outcomes, develop a position which either supports or rejects the use of nuclear energy for peaceful purposes.
14. Defend a position which either supports or rejects the use of nuclear energy for peaceful purposes.
15. Defend a position which either supports or rejects the use of nuclear energy for military purposes.

Information provided by: http://www.sasked.gov.sk.ca