What is nuclear energy (and why is it considered a clean energy)?

The power of the atom has been at the heart of electricity generation for more than half a century. Now nuclear fission – the process by which nuclear energy is used to generate electricity – looks set to support the future of clean, net zero energy systems globally.

Nuclear energy has been part of the global energy mix since nuclear reactors first started producing power in the late 1950s. From its heyday in the 1960s to the late 1980s, nuclear power’s popularity has risen and fallen – and often been a source of controversy.

Today it plays a role in helping to provide clean, low-carbon electricity and could be pivotal in our efforts to reach net zero by 2050.

How does nuclear energy work?

Nuclear power stations work in a very similar way to coal- and gas-fired power stations, but the science behind the nuclear production process is much more advanced.

In a nuclear reactor, a reaction is driven by the splitting of atoms – a process called nuclear fission – where a particle is fired at an atom to split it into two smaller atoms (and some additional neutrons). The neutrons released hit other atoms, causing them to divide and release more neutrons. This is called a chain reaction and the whole process creates masses of heat.

Nuclear reactors generate heat, which is removed by a circulating fluid, such as water, and turned into pressurised steam. This steam is then forced through turbines that turn electrical generators to produce electricity.

What are the benefits of nuclear energy?

  • Unlike many renewable energy sources, power from nuclear energy can be generated 24 hours a day and isn’t dependent on the weather, like wind and solar power tend to be.

  • Because of this, nuclear power is more readily available to meet energy demands, which helps to lower the carbon intensity of the electricity supply during times when other renewable energy sources might not be as readily available.

  • Some new-generation nuclear power stations are now certified for 80 years of operation – far longer than a gas- or coal-fired power stations and many renewable installations. However, there are a number of significant expenses to consider, including upfront expense, decommissioning costs and storage costs of depleted fuel and other materials. They also require a lot of maintenance over their lifespan.

Poppy fields with pylons and overhead lines and Sizewell A and B nuclear power stations in the background

Is nuclear energy clean?

In an emissions sense, nuclear power is considered to be clean. It produces zero carbon emissions and doesn’t produce other noxious greenhouse gases through its operation.

The lifecycle emissions of nuclear energy (emissions resulting from every stage of the production process) are also significantly lower than in fossil fuel-based generation.1

Is nuclear energy renewable?

Nuclear fuels, such as the element uranium, are not considered renewable as they are a finite material mined from the ground and can only be found in certain locations. But nuclear power stations use a miniscule amount of fuel to generate the same amount of electricity that a coal or gas power station would (1 kg of uranium = 2.7 million kg of coal), so they’re considered a reliable source of energy for decades to come.

There are concerns around what to do with spent fuel from reactors, as there’s still no definitive way to dispose of it indefinitely without risk. However, although the reactors and housing remain untouchable for considerable lengths of time when a nuclear site is decommissioned, a new reactor can be built on the site itself.

How much is nuclear energy currently used?

The first commercial nuclear power station was Calder Hall in Great Britain; two small 65MW dual purpose reactors that came online in 1956. Including Calder Hall, the UK has had 19 nuclear power stations on- and offline over the past 66 years.

As of 2021, there are now only six active power stations across the UK, which house 11 operational reactors in total. The station with the largest operating capacity is Sizewell B in Suffolk, with a capacity of 1,198MWe.2

In 2020, the share of UK electricity generation from nuclear was 16.1%. Only natural gas and wind power generate more electricity annually, but nuclear has remained consistent in this level of contribution over the past 25 years.3

The US is the world's largest producer of nuclear power, generating more than 30% of the world’s total nuclear capacity.4 There are 93 operational reactors across 55 nuclear power plants in the country, offering a combined generational capacity of 95.4GW. This makes up 20% of the US’ current electricity mix.5

France is also a notable consumer of nuclear energy, with about 70% of its electricity derived from this source due to a long-standing policy based on energy security.6


What is the future of nuclear electricity generation?

As the UK and US aim for net zero by 2050, the mix of electricity generation will change. Nuclear energy is likely to play a role globally in helping nuclear-capable nations achieve these goals.

In the UK, the construction of Hinkley Point C in Somerset has marked the current government’s intention to have nuclear as a pillar of its energy mix. Sizewell C – a sister plant to the active B station – is currently under consultation, with a proposed generation of 3.2GW. As of 2021 in the US, there are plans to ‘uprate’ existing reactors to increase their generation capacity, while two new reactors in Vogtle, Georgia, are expected to come online in 2023.

Small modular reactors

The future may also see the introduction of Small Modular Reactors (SMRs). These are smaller version of nuclear power plants, similar to those that power nuclear submarines and ships.

While SMRs’ power output is substantially less than a full-scale nuclear power station (they generate as little as a fifth of current-generation reactors), they can be more easily manufactured and transported to where they’re needed, before being dismantled and returned at the end of their operating life.

Nuclear fusion

Nuclear fusion has often been talked about to generate electricity. The basic premise is that two nuclei of a light atom, such as hydrogen, fuse in a process that gives off massive amounts of energy – an estimated four times the amount of nuclear fission, using far less the amount of resources. The sun itself is a huge, self-regulating nuclear fusion reactor!

Nuclear fusion can’t be achieved on any commercial scale yet and has only happened in lab conditions for seconds. However, scientists have been closely studying this technology since the 1930s and believe a breakthrough is imminent. The assembly of ITER in France, the world’s largest international fusion facility, commenced in 2020.7

Last updated: 8 Aug 2022
The information in this article is intended as a factual explainer and does not necessarily reflect National Grid's strategic direction or current business activities.