How does nuclear power work and why is the UK investing more money in it?

The government has announced the biggest nuclear programme in a generation, which includes £14.2bn to build the Sizewell C nuclear power station in Suffolk.

It has also confirmed that Rolls Royce will build the UK's first small modular reactors (SMRs).

In non-military reactors, nuclear power is generated by bombarding uranium atoms with much smaller neutron particles.

This causes the atoms to split in a process called nuclear fission, which releases huge amounts of energy as heat.

The heat is used to boil water and produce steam which drives turbines and generates electricity.

In November 2024, the UK and 30 other countries signed a global pledge to triple their nuclear capacity by 2050.

Like fossil fuels, nuclear power uses non-renewable energy resources, but unlike coal and gas power stations, nuclear plants do not produce greenhouse gases such as carbon dioxide or methane during their operation.

Building new nuclear power stations does create emissions as a result of manufacturing the steel and other materials needed. But the total amount of emissions generated across the lifecycle of a plant is still relatively low.

Expanding the use of nuclear power therefore helps the government meet its future climate change targets - although neither Sizewell C nor any SMRs are likely to be operational before its target for almost completely clean power by 2030.

The UK has nine nuclear reactors in operation - some sites have more than one reactor - but they're ageing, and eight of them are due to close by the end of the decade.

The other nuclear plant under construction - Hinkley Point C in Somerset - is not due to switch on until the early 2030s.

The existing nuclear power stations were responsible for just more than 14% of the electricity generated in the UK in 2024.

But crucially, nuclear provides "baseload" power - a steady supply of reliable electricity that can meet continuous demands on the grid, alongside more weather-dependent renewable sources, like wind and solar.

• What is climate change?
• What is net zero and how are the UK and other countries doing?
• Where does the UK get its energy?

The government says the Sizewell C project will create 10,000 direct jobs in construction, welding, and hospitality as well as thousands more in companies supplying additional goods and services.

Once operational, ministers say the plant will generate enough energy to power the equivalent of six million homes and should last for 60 years.

The power station - which is being built by the French energy company EDF - will sit right next to the Sizewell B nuclear plant that has been operating since 1995, and not far from the decommissioned Sizewell A site, which first opened in 1967.

Prime Minister Sir Keir Starmer insists that the project will not be given "a blank cheque". However, the £14.2bn figure only covers the next four years.

Construction is expected to cost about £20bn in total, and will take at least a decade to complete.

In January, EDF denied claims that the final budget could be closer to £40bn.

However, the firm did accept that its Hinkley Point C plant in Somerset would cost more than £40bn compared to a 2022 estimate of £26bn. It is expected to go live more than a decade later than planned.

SMRs work on the same principle as large power plants, using a nuclear reaction to generate heat that in turn produces electricity.

However, SMRs are a fraction of the size of a typical large reactor, and can generate up to a third of the same amount of power.

They can be built to order in factories and then transported and fitted together on location, which could make them faster and cheaper to build.

However, the cost savings are not expected to materialise until large quantities of SMRs are being built, so the first plants are likely to be very expensive.

It is not clear how much it will cost to deal with the nuclear waste generated by SMRs.

Sellafield in Cumbria deals with most of the country's nuclear waste, but it is already running out of space and running costs have increased sharply.

Rolls Royce was chosen after a two-year competition, five months after Sir Keir said he would reform planning rules to make it easier to build SMRs across the UK.

The government is investing more than £2.5bn for the overall SMR programme in the period covered by the latest Spending Review.

It says the project could potentially support up to 3,000 new skilled jobs and provide power for the equivalent of around three million homes.

Great British Nuclear - which is responsible for delivering the government's policy - is expected to announce the location of the first SMR by the end of 2025, with projects due to be connected to the power grid in the mid-2030s.

No sites will be approved close to airports, military sites or pipelines. Sites at risk of flooding or which are valuable to nature will also be ruled out.

Although many countries are considering SMRs, only Russia and China have operational plants.

In 2024, a number of big tech firms including Amazon, Microsoft and Google said SMRs could be extremely useful to provide energy for their power-hungry data centres and servers.

The International Atomic Energy Agency says nuclear power plants are among "the safest and most secure facilities in the world".

They are subject to stringent international safety standards.

However, there have been a number of high-profile accidents which released large amounts of radioactive material into the environment.

The worst nuclear accident in history was caused by an explosion at the Chernobyl nuclear power plant in Ukraine in 1986.

More recently an enormous earthquake caused a tsunami which flooded the Fukushima nuclear plant in Japan in 2011, triggering a partial meltdown of the reactor cores.

However, even under normal conditions, the hazardous radioactive waste which is produced by generating nuclear power needs to be safely managed and stored for hundreds of years.