Cleaning Up Nuclear Waste After Decommissioning

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.

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

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.