Lesson video

Hello, my name's Dr.

George, and this lesson is all about nuclear power.

It's part of the unit nuclear physics.

The outcome of the lesson is I can compare the pros and cons of the generation of electricity using nuclear power.

Here are the key words for the lesson.

I'll introduce them as we go along, but this slide's here in case you want to come back anytime to remind yourself of the meanings.

The lessons divided into three parts.

They're called nuclear waste and contamination, pros and cons of nuclear power, and power from nuclear fusion.

Nuclear power stations use nuclear fuels, such as uranium and plutonium, to generate heat by nuclear fission and produce electricity.

The fission process produces radiation and radioactive materials.

Fission of the nuclear fuel produces daughter nuclei, so fission involves a large nucleus breaking up into two smaller nuclei and some neutrons.

And even from the same parent nucleus, there can be many different daughter nuclei, and some of these will be unstable, so they'll be radioactive isotopes.

Large numbers of free neutrons are also produced, and these can be absorbed by more nuclei in the fuel, causing further fission in a chain reaction.

Gamma radiation is also released from the core, so fission releases gamma radiation, and this will cause irradiation of the surroundings.

The surroundings will be exposed to that radiation.

The radioactive material produced in a nuclear power station is known as nuclear waste.

There are three main categories of nuclear waste based on how much radiation they emit per kilogramme.

There's low-level waste called LLW for short, intermediate-level waste, ILW, and high-level waste, HLW.

As nuclear waste contains unstable nuclei, a radioactive material, it can cause radioactive contamination if it leaks.

And contamination is different from irradiation.

Contamination is where radioactive material gets onto or into something.

Low-level nuclear waste is the least radioactive category, and it makes up over 90% of nuclear waste from power stations.

It consists of materials that have been slightly contaminated by other waste, and so it gives off low-levels of harmful radiation.

Examples include gloves and clothing worn by workers in hospitals who work with radioactive materials, or nuclear power stations, and some materials used in construction.

An example in this photo are these gloves, which will be contaminated from touching the uranium sample shown there.

Low-level waste is stored in steel containers, which are buried underground in remote and secure locations away from people and other life.

Now, is this true or false? Exposure to gamma radiation causes clothing to become contaminated.

And choose A, B or C to justify your choice of answer.

When I ask a question, I'll wait five seconds, but you may well need longer, in which case press pause and press play when you have your answer ready.

And this statement is false, and that's because contamination is the transfer of radioactive particles, and that doesn't happen by exposure to radiation.

Exposure to radiation can be harmful or damaging, but exposure to gamma radiation wouldn't introduce radioactive material into something, and it wouldn't turn the atoms of something into being unstable.

Intermediate-level nuclear waste is more active than low-level waste.

It makes up around 7% of the waste produced by nuclear power stations.

It doesn't emit enough radiation to become hot, so it can still be stored without the need for cooling.

It needs to be stored carefully in sealed containers at designated sites around the country.

These sites are usually near the power stations that produce the waste.

Which of the following is the most suitable for storing intermediate-level nuclear waste that emits gamma radiation? And the correct answer is lead-lined steel boxes, because lead is a good absorber of gamma radiation.

It's a dense metal.

High-level nuclear waste is very radioactive.

It makes up less than 1% of the waste produced by nuclear power stations.

The high activity of this type of waste raises its temperature, so it's emitting so much radiation that that raises the temperature, and so it needs to be cooled as well as kept far away from people.

Waste from used nuclear fuel rods is so active that it needs to be kept in deep pools of water for several years to prevent it from melting.

Once it's cooled down enough, high-level nuclear waste is added to other materials, and then the mixture is made into glass for storage.

We say that the material is vitrified.

This makes a very stable solid.

It doesn't leak over time, it doesn't corrode.

This solidified waste is stored in steel canisters, and it will be stored in secure facilities for up to 150 years, before being transferred to a permanent storage site called a repository.

But the location of the final repository in the UK hasn't been decided yet, although we've been using nuclear power for years.

Now, which of these three is a source of high-level nuclear waste? The only one of these that's a source of high-level nuclear waste is used nuclear fuel rods.

And now here's a longer written task for you.

Have a go at answering these questions.

Press pause when you do, and when you press play, I'll show you some example answers.

So here are some example answers.

A source of low-level waste could be clothing that's been contaminated, and how that needs to be stored is it'll be compacted and stored in metal containers, which are buried.

Then an example of high-level nuclear waste would be spent, that is used, nuclear fuel rods.

Why it needs to be cooled is because it's so active, it continuously heats itself up, increasing its own temperature.

It needs to be cooled to prevent it from melting.

And why cooling isn't needed after several years have passed is because over time, the activity of the waste will fall, and so it's temperature will increase less and less quickly.

After a few years, the activity will be low enough for the sample to stop heating itself up.

And now let's go on to the second part of the lesson, pros and cons of nuclear power.

Over 30 countries operate nuclear power stations to generate electricity.

Some countries only have a small number of stations.

For example, the Netherlands has just a single nuclear power station, which produces about 4% of its needs.

Other countries have a large number of stations.

France generates over 60% of its electricity from nuclear power, using over 15 nuclear power stations.

The UK has nine stations, producing 13% of its needs, with another two under construction.

Nuclear power stations are very expensive to commission.

They take many years to plan and get approval for.

And most of the public don't want to live near a nuclear power station.

Once a power station is approved, it's built to very high standards, which costs a lot of money.

The construction involves a large scale use of concrete and steel, and that produces significant carbon emissions, as with any construction.

Most nuclear power stations are designed to operate for 20 to 30 years, and during this time, they don't release carbon dioxide gas into the atmosphere, unlike fossil fuel power stations.

They do produce small amounts of nuclear waste as they operate.

And many nuclear power stations have actually operated for far longer than their original specification because they're so expensive to replace.

Germany, by the way, has recently decommissioned, shut down, the last of its nuclear power plants.

What are waste products of nuclear power stations? And the correct answers are carbon dioxide as they're being built because of the construction, and nuclear waste, while they're generating electricity.

Nuclear power stations are designed to operate continuously.

The power station operates in all weather conditions, many running every day of the year.

They can be refuelled while they're operating, with spent fuel removed and new fuel rods inserted a few at a time.

The power stations occasionally shut down for maintenance, but shutting down and restarting takes several days, so it's not done often.

In what ways are nuclear power stations better than wind turbines? A is true, they can generate electricity more reliably.

They don't depend on whether it's windy or not.

And they can generate electricity in all types of weather.

After a nuclear power station has reached the end of its useful life, it's decommissioned.

In the short term, this involves permanently shutting down the reactor core, removal of all the spent and unspent fuel, and in the long term, the non-radioactive parts of the station are taken apart over a few years, and the radioactive parts are taken apart over many years, producing substantial amounts of nuclear waste.

Nuclear power plants have a good safety record, but accidents can have serious consequences.

The probability of an accident is low, but if one does happen, it can be very severe.

If a reactor is not cooled properly for some reason, it can undergo meltdown.

This means that the core overheats and parts of it begin to melt.

It can lead to an increase in nuclear reaction rate, faster heating, and an increase in the pressure of the coolant in the core, which could rupture, burst the containment vessel that surrounds the core.

If this happened, radioactive material can escape and contaminate the environment.

This is not a nuclear explosion, not like a nuclear bomb, but the rupture of the containment vessel by the pressure inside is a kind of explosion.

In 1986, there was a serious nuclear accident in Chernobyl in Ukraine.

A reactor meltdown destroyed the containment building and released large quantities of radioactive material into the atmosphere.

Large areas of land around the power plant were contaminated by radioactive material, and some are still abandoned today because they're not considered safe for people to live in.

In 2011, the Fukushima power station in Japan suffered damage to its electrical systems because of an earthquake and a tsunami, a tidal wave.

Some of the reactors couldn't be cooled properly and there was a buildup of pressure which damaged the containment systems, releasing radioactive materials into the environment.

Many people are worried about the use of nuclear power.

When people are asked, they tend to quickly recall the danger of nuclear accidents and nuclear waste, but they don't remember so easily the benefits of nuclear power.

This means there are usually high-levels of opposition to constructing new power stations.

What happens during the meltdown of a nuclear reactor? B is correct.

A buildup of pressure may cause an explosion, although not a nuclear explosion.

And also C, the temperature of the core increases too quickly.

And if the containment vessel gets ruptured, radioactive particles may escape from the core.

Now here's a written task for you.

Imagine that the construction of a new nuclear fission power station has been proposed in your region.

Write a short letter to your local member of parliament outlining your views on the construction of the power station.

I'd like you to address arguments both for and against the construction, and these can be scientific, economic and social arguments.

Press pause while you do this, and press play when you're finished.

Here are some examples of things you could have included.

Some of the arguments for are that it doesn't release carbon dioxide while it's in use, which would contribute to the greenhouse effect.

It has a high power output.

It offers a continuous supply of electricity, which isn't weather dependent.

There are highly paid jobs in the construction, operation and later decommissioning of the plant.

It only produces small volumes of waste over its lifetime.

And we're going to need new sources of electricity for electric cars.

Some of the arguments against are that it's very expensive to build and later to decommission a nuclear power plant.

There is a chance of a nuclear accident.

Nuclear waste can be very dangerous and need storage for thousands of years.

Nuclear fuel needs to be imported.

Nuclear fuel is mined, but not in this country.

Renewable alternative energy resources are cheaper.

And the power station may be considered ugly and have a negative impact on the landscape.

Well done if you included some of these points in your answers.

And now let's learn about power from nuclear fusion.

Remember, so far, we've been looking at nuclear fission power plants.

Nuclear fusion is a joining of two small nuclei together to make a larger one.

Here's an example, and there is energy release in this process because the mass of the particles produced is actually slightly less than the mass of the original particles, and that causes a release of energy.

Nuclear fusion is the process that powers stars, such as our sun.

An example fusion process would be a hydrogen-2 nucleus and a hydrogen-1 nucleus, as shown here.

And when these two nuclei fuse, they form helium-3.

This equation shows a nuclear fusion reaction, but two of the numbers have been replaced by the letters X and Y.

What are the values of these? And the correct answer is C, X is seven and Y is two.

And that's because the total number of nucleons on the left is four plus three, which is seven, so there'll be seven nucleons on the right.

And there are four protons on the right, so it'll be four altogether on the left.

Well done if you picked that one.

Protons in the nucleus are positively charged, and so there are large repulsive forces between them, which only increase as they get closer together.

These forces make it difficult for nuclei which contain protons to collide.

But at the centre of a star in its core, the temperature and pressure are very high.

That's because gravitational forces pulling the mass together compress the material inside the star, forcing the nuclei closer together.

The high temperatures inside the core strip the electrons off their atoms, and this forms a type of matter called a plasma, consisting of bare nuclei and free moving electrons.

So inside the core, there are very fast moving nuclei travelling in all directions.

Fusion happens in the core of stars because the temperature and pressure are so high.

The nuclei moving so quickly that they can collide with each other before the repulsive forces, between them, can slow them down.

The high pressure means there are many nuclei close together and that increases the chances of nuclei colliding.

So, why is it difficult to cause hydrogen nuclei to collide with each other? And the only correct statement here is D, because there are strong repulsive forces between them, electrostatic repulsion between the positively charged protons.

If we could produce controlled nuclear fusion on earth, we could use that as a power source, but it turns out it's very difficult.

There are three main issues.

Very high temperatures needed to make the nuclei move quickly enough, so that they overcome their electrostatic repulsion and actually collide.

And enough nuclei need to collide, they need to collide at a high enough rate to produce a useful fusion reaction, which releases lots of energy.

If energy is only released very slowly, it's not worth doing.

And the energy needs to be able to be extracted from the core where the fusion is happening without stopping the nuclear fusion reactions from continuing.

Experimental reactors have managed to produce some controlled nuclear fusion.

What happens is hydrogen isotopes get ionised, and they're spun around a donut shaped container called a torus using magnetic forces.

This collection of hydrogen ions is heated by electromagnetic fields, until they're moving fast enough that fusion happens.

Fusion reactions and experiments have gone on for several seconds, but not long enough for commercial use.

Not enough that you could actually run a power station this way.

So research into nuclear fusion continues.

If it can be made to work, it will have advantages over nuclear fission because the fuels needed for nuclear fusion are hydrogen isotopes, which are available from water.

They're very readily available.

Fusion produces much less radioactive waste, does produce some, but much less than nuclear fission.

And there's no risk of meltdown or large scale contamination.

Nuclear fusion isn't a chain reaction.

It can't spin out of control.

Which of the following are advantages of nuclear fusion power compared to nuclear fission power? And A is true, nuclear fusion produces less radioactive waste.

And C is also true, nuclear fusion reactors cannot melt down.

At this stage, we can't say that nuclear fusion is a more reliable technology.

We haven't fully made the technology work yet.

And nuclear fusion reactors are difficult to build.

Now, can you write a short discussion about whether scientists and engineers should continue to try to develop a nuclear fusion reactor? It does cost money, of course, to continue this research.

Your discussion should include reasons why the development of working fusion reactors would be useful, some of the issues making development difficult, and alternatives to developing this new type of nuclear reactor, other ways we could generate electricity.

Press pause when you do this, and press play when you've finished.

I'll show you some of the points that you could have included.

Usefulness, it would provide a reliable source of energy, doesn't depend on the weather or the seasons.

Fusion reactors would have a high power output.

They produce less nuclear waste than nuclear fission reactors, and they're safer than nuclear fission reactors, and they have low or no carbon emissions.

Difficulties, it's hard to produce the very high temperature and pressure needed.

They're very expensive to develop.

They still do produce a little nuclear waste.

And they require specific isotopes of hydrogen, which could become rare over time.

Alternatives, you could say that there are some renewable power resources that are simpler and less expensive, such as wind power and solar power.

Well done if you included some of these points in your answers, and you may have come up with some other ones too.

Now we're at the end of the lesson, so here's a summary.

Operational nuclear power stations are based on nuclear fission, which involves splitting large nuclei into smaller ones.

Fission power stations produce nuclear waste.

The high-level waste from fuel rods is very dangerous and difficult to manage over long periods.

Waste leaks and nuclear accidents can cause contamination of the environment.

Decommissioning, shutting down a nuclear power plant is difficult and expensive.

Nuclear fusion involves merging small nuclei to release energy.

This requires very high temperatures and pressures.

Fusion technology has been in development for over 50 years, but it's not yet fully functional.

Well done for working through this lesson, which contained a lot of new information.

I hope you found it interesting and useful to know.

Bye for now.