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Gentilly-2 nuclear reactor

Gentilly-2 nuclear reactor (Axel Drainville [CC BY-NC 2.0], flickr)

STEM in Context

Cleaning Up Nuclear Waste After Decommissioning

Karen Cholmondeley

Summary

When a nuclear reactor is no longer in use, the radioactivity in its materials remains. That’s why it’s important to safely deal with the radioactive waste those plants leave behind.

Governments across the globe are examining ways to decommission (shut down) older nuclear power plants and deal with the dangerous radioactive waste those plants leave behind. Canada is no exception. In 2012, it closed one of its reactors: the Quebec Gentilly-2 nuclear reactor. Decommissioning nuclear power plants is challenging work. Let’s find out why.

How do nuclear reactors work?

The key ingredient in nearly all current nuclear reactors is uranium-235. This is a radioactive isotope of uranium, which is packaged in long columns called fuel rods. When the rods are bombarded with a controlled stream of neutrons, the atoms that make up uranium-235 actually split apart. This happens through a process called nuclear fission. Fission produces an enormous amount of heat, which is transferred to the surrounding water. The heated water produces steam with enough force to spin a turbine and generate electricity.

A typical fuel bundle used in a power reactor
A typical fuel bundle used in a power reactor measures about 50 cm and weighs about 24 kg (Source: Canadian Nuclear Safety Commission).

The water used in many nuclear reactors is called heavy water. That’s because the hydrogen in the H20 molecule contains an extra neutron. Heavy water helps to moderate (slow down) the fission reaction and cool down fuel rods. Regular water would absorb the neutrons released from the uranium. But heavy water already has an extra neutron, so it can’t absorb any more neutrons.

Did you know?

Nuclear power generates about 15% of Canada’s total electricity

Why do nuclear reactors have to shut down? 

Unfortunately, uranium-235 atoms will not keep splitting apart forever. Eventually, they will no longer be useful for energy production. But the fuel rods remain extremely hot and radioactive. This means they continue to emit high-energy particles such as electrons or gamma rays. These particles can cause significant damage to cells in living organisms, including humans. 

The radioactivity of uranium-235 does decrease over time. Eventually, it becomes harmless. However, this process can take over a thousand years!  So what can be done with these hazardous fuel rods until then?

How is a nuclear power plant decommissioned?

The first step is to slowly cool the fuel rods in a storage pond that looks like a giant swimming pool. The water also helps prevent radiation from being emitted. The used fuel rods have to stay in this pond for at least 10 years! After that, rods can be transferred to dry storage containers, usually made of stainless steel or ceramic. The containers are sealed tightly and the rods are stored inside for another 50 years or more.

Did you know?

Each year, a total of 34 000 cubic metres of high-level nuclear waste is produced worldwide. That’s enough to fill almost 14 Olympic-sized swimming pools

Fuel pool at the Bruce Nuclear Generating Station
Fuel pool at the Bruce Nuclear Generating Station, Kincardine, Ontario (Source: Canadian Nuclear Safety Commission).

Are there any decommissioned nuclear reactors in Canada?

In 2012, the Government of Quebec decided to close its Gentilly-2 nuclear reactor because it was expensive to operate. All of the most dangerous waste, including the fuel rods, were removed and stored in the ponds you just read about. The building that housed the nuclear reactor and all of its contents was sealed airtight. No one will be able to enter or exit the building for about 50 years. This process has already been done for Gentilly-1, an earlier reactor built at the same power station. 

There are also 4 decommissioned nuclear reactors in Ontario.

Did you know?

Some countries use a special type of nuclear reactor called a breeder reactor, which uses the radioactive waste from a regular reactor as fuel.

Summing up

Overall, nuclear reactors are a relatively safe and powerful method of generating electricity. In particular, they emit much less pollution than burning fossil fuels. However, the question of how to manage and dispose of nuclear waste remains a major challenge. As you have just learned, nuclear waste is a problem that remains for decades after a nuclear power plant has been decommissioned.
 

Starting Points

Connecting and Relating
  • Do you live in the vicinity of a nuclear power plant? If so, which plant? What is the status of the reactors at the nuclear power plant? 
  • Imagine it is the year 2065 and the land at the Gentilly-2 site in Quebec has been developed into a residential area. You have been searching for a house in the same general area; would you live at the Gentilly-2 site? Why or why not?
     
Connecting and Relating
  • Do you live in the vicinity of a nuclear power plant? If so, which plant? What is the status of the reactors at the nuclear power plant? 
  • Imagine it is the year 2065 and the land at the Gentilly-2 site in Quebec has been developed into a residential area. You have been searching for a house in the same general area; would you live at the Gentilly-2 site? Why or why not?
     
Relating Science and Technology to Society and the Environment
  • The cost of decommissioning Quebec’s nuclear power plant, Gentilly-2, is estimated to be 1.2 billion dollars and will take about 50 years.  Why do you think  decommissioning is so expensive and time-intensive?
  • Find out what organization in Canada regulates the entire life-cycle of nuclear power plants, from construction to decommissioning. 
  • How do the current methods of dealing with nuclear waste demonstrate the link between science, technology, society and the environment? Explain.
     
Relating Science and Technology to Society and the Environment
  • The cost of decommissioning Quebec’s nuclear power plant, Gentilly-2, is estimated to be 1.2 billion dollars and will take about 50 years.  Why do you think  decommissioning is so expensive and time-intensive?
  • Find out what organization in Canada regulates the entire life-cycle of nuclear power plants, from construction to decommissioning. 
  • How do the current methods of dealing with nuclear waste demonstrate the link between science, technology, society and the environment? Explain.
     
Exploring Concepts
  • The process inside nuclear reactors involves a controlled reaction with Uranium-235. Explore the reaction further and describe the process in detail, including the chemical equation associated with the nuclear reaction.
  • Research the different ways of disposing of or storing nuclear waste. What are the possible pros and cons of each method? Which method do you think is best? Explain your reasoning.
  • Some of the principal components of a nuclear reactor are control rods, uranium fuel rods and a graphite block which acts as a moderator. The function of the moderator is to slow down the neutrons produced in a reaction.  Why is it necessary to slow down the neutrons? (Note: This question may require additional research)
     
Exploring Concepts
  • The process inside nuclear reactors involves a controlled reaction with Uranium-235. Explore the reaction further and describe the process in detail, including the chemical equation associated with the nuclear reaction.
  • Research the different ways of disposing of or storing nuclear waste. What are the possible pros and cons of each method? Which method do you think is best? Explain your reasoning.
  • Some of the principal components of a nuclear reactor are control rods, uranium fuel rods and a graphite block which acts as a moderator. The function of the moderator is to slow down the neutrons produced in a reaction.  Why is it necessary to slow down the neutrons? (Note: This question may require additional research)
     
Media Literacy
  • Explore how popular media portrays nuclear reactors. Compare that to scientific literature found online. Is the media portrayal of nuclear reactors accurate or sensationalized? Explain.
     
Media Literacy
  • Explore how popular media portrays nuclear reactors. Compare that to scientific literature found online. Is the media portrayal of nuclear reactors accurate or sensationalized? Explain.
     
Teaching Suggestions
  • This article can be used for Earth & Environment and Chemistry teaching and learning related to nuclear, radioactivity, fission & fusion, and energy impacts. Concepts introduced include nuclear power plants, decommission, radioactive isotope, Uranium-235, nuclear fission, fuel rods, neutrons, heavy water, electrons and gamma rays. 
  • Before reading this article, teachers could have students complete a Vocabulary Preview learning strategy to introduce and reinforce new terminology. Ready-to-use Vocabulary Preview reproducibles are available in [Google doc] and [PDF] formats. 
  • After reading the article, teachers could have students, look at the issues surrounding decommissioning a nuclear power plant from different stakeholder perspectives by conducting an Issues and Stakeholders learning strategy. The students could first engage in a full-class discussion to identify a few key issues associated with decommissioning Nuclear Power plants to use in conducting the learning strategy. Ready-to-use Issues & Stakeholders reproducibles are available in [Google doc] and [PDF] formats. A completed Issues and Stakeholders sample of possible student responses to this article is also available as a [PDF]. 
  • To consolidate an understanding of the steps of nuclear decommissioning and timeframes for each step, students could summarize the steps that are outlined in the article in a visual format, such as a graphic organizer or infographic. 
     
Teaching Suggestions
  • This article can be used for Earth & Environment and Chemistry teaching and learning related to nuclear, radioactivity, fission & fusion, and energy impacts. Concepts introduced include nuclear power plants, decommission, radioactive isotope, Uranium-235, nuclear fission, fuel rods, neutrons, heavy water, electrons and gamma rays. 
  • Before reading this article, teachers could have students complete a Vocabulary Preview learning strategy to introduce and reinforce new terminology. Ready-to-use Vocabulary Preview reproducibles are available in [Google doc] and [PDF] formats. 
  • After reading the article, teachers could have students, look at the issues surrounding decommissioning a nuclear power plant from different stakeholder perspectives by conducting an Issues and Stakeholders learning strategy. The students could first engage in a full-class discussion to identify a few key issues associated with decommissioning Nuclear Power plants to use in conducting the learning strategy. Ready-to-use Issues & Stakeholders reproducibles are available in [Google doc] and [PDF] formats. A completed Issues and Stakeholders sample of possible student responses to this article is also available as a [PDF]. 
  • To consolidate an understanding of the steps of nuclear decommissioning and timeframes for each step, students could summarize the steps that are outlined in the article in a visual format, such as a graphic organizer or infographic. 
     

Learn more

Nuclear Energy Explained (Video) (2015)

This video (5:17 min.) by Kurzgesagt discusses where nuclear technology is today, and how technology evolved to get to the point it's at.

How do fast breeder reactors differ from regular nuclear power plants?

For Scientific American, P. Andrew Karam discusses the differences between fast breeder and regular nuclear power plants.

Chernobyl Nuclear Accident: The Aftermath of a Disaster (2019)

This entry for the Encyclopaedia Britannica gives an overview on the history of the Chernobyl nuclear accident in 1986.
 

References

Canadian Nuclear Association. (n.d.). Waste management.

Canadian Nuclear Safety Comission. (2019). Nuclear power plants.

International Atomic Energy Agency. (2016). Nuclear power reactors in the world.

Nuclear Energy Institute. (n.d.). How a nuclear reactor works.

United States Nuclear Regulatory Commission. (2015). NRC: Backgrounder on radioactive waste.

World Nuclear Association. (2017). Radioactive waste - Myths and realities.

Karen Cholmondeley

Karen Cholmondeley recently completed my MSc. and isnow actively seeking her next adventure! Karen loves science because it helps offer explanations to so many different questions affecting all aspects of our lives, from health to nature to technology. In Karen's free time she loves to read, travel, and be outside (unless it's cold!).