With the expected closure of JET in 2024, what does this mean for the future of nuclear fusion energy?

Fusion energy has the potential to unlock a vast amount of clean power, several times the amount available from nuclear fission (the reaction used in the nuclear power plants of today). For this reason, fusion energy is expected to hold a major role in the future energy mix for a zero-carbon grid.

As things stand, however, fusion is not yet commercially viable and colossal challenges still face its successful implementation into the grid. Before it can be integrated into our everyday lives, fusion is expected to be one of the major engineering challenges of the century.

Despite the large amount of research that goes into fusion, there is still a lack of public understanding of how it actually works and where it currently stands as an energy source.

How Nuclear Fusion Works

Sometimes described as the “opposite” of nuclear fission, fusion is the process of building heavier atomic nuclei from lighter ones. This process releases energy from the conversion of mass according to Albert Einstein’s famous equation: E= mc2.

Nuclear fusion releases nearly four million times more energy than using coal, oil or gas. The replacement of carbon-intensive fossil fuels with fusion would therefore make a huge contribution to reducing carbon emissions.

Fusion already takes place at the core of all stars and is constantly occurring in our own Sun. The majority of the sun’s energy is produced through the fusion of hydrogen isotopes into helium.

To recreate the conditions in which these reactions are feasible, extremely high temperatures and pressures are required. The temperatures in the Sun can reach up to 15 million ˚C but due to its vast size and the abundance of hydrogen isotopes, fusion is much more likely to occur in the Sun than on Earth. This means that to successfully fuse atomic nuclei on Earth temperatures in excess of 100 million ˚C are required.

These enormous temperatures lead to substantial energy demand for fusion to occur. Beyond the sheer cost of such high energy intensity, significant design challenges have to be overcome to build a reactor that can withstand the heat.

Attempting to solve the problem of fusion on Earth are several research facilities, including JET and ITER. Their aim is to not only achieve fusion, but to demonstrate its viability as a controlled energy source for future grids.


The Joint European Torus (JET) is located in the Culham Centre for Fusion Energy in Oxfordshire, UK. The main purpose of JET is to be able to conduct fusion experiments and investigate the future possibility of nuclear fusion grid energy.

With over 100,000 experiments conducted since its commissioning 40 years ago, huge progress has been made. In 2022, a breakthrough for fusion energy occurred at JET, with the production of 59 megajoules of energy for over five seconds.

The energy produced by fusion is often expressed as an energy gain; due to the large amount of energy required to start the fusion reaction, making enough energy to be “net positive” — where more energy is produced than is put into the reaction — is needed for fusion to become beneficial.

Even with the successful production of 59 megajoules at JET, this was still only circa breaking even in energy terms. Later in the same year, however, the first net positive fusion experiment occurred at the National Ignition Facility (NIF), California, US. The production of net positive energy from fusion is promising for the future. With these successful experiments, fusion will likely be on the grid within the next 30 years, but what would a grid with fusion energy look like?

Will fusion work like nuclear fission?

Nuclear fission is a well-established and self-sustaining energy source that is commonly used on varying scales globally. In 2023, nuclear fission provides around 15 % of the UK’s total energy for the national grid at any given time. This value only varies slightly (~1 %) because nuclear fission is defined as a “base load” energy plant.

The base load of the national grid is the minimum electricity demand that requires a steady supply of energy to be met. Due to the continuous supply, reliability, low operating cost, high capacity factor and low carbon emissions, nuclear fission is well suited to supplying the base load for the national grid. Indeed, nuclear fission can operate 24 hours a day for up to 2 years with no refuelling or maintenance.

So, does nuclear fusion hold the same potential?

Other base load infrastructures typically used in the UK include coal and gas-fired power plants. With the UK’s goal of phasing out unabated coal by 2024 and the requirement for carbon capture and storage (CCS) for the continuation of gas post-2050, what does this mean for base load energy supply? What type of energy plants will be able to supply this energy? Could it be 100% nuclear fission?

The answer currently is no. The UK is developing renewable energy sources such as offshore wind and solar very fast. Although this is promising for a low-carbon grid, the intermittency of these energy sources poses a problem. Without energy storage, it is hard to match the supply and demand of electricity. This, alongside the large amount of offshore wind expected in 2050 from Scotland (11 GW by 2030), will also put a large strain on the transmission system to transport the electricity to other regions in the UK.

The Role of Fusion in the Future

At a recent tour around the JET fusion site it was made clear that they do not expect fusion to be connected to the grid before 2050. They do, however, expect that fusion will play a role in sustaining the (hopefully) zero carbon grid.

However, with JET now set to close in 2024, could fusion’s integration into the UK grid be delayed further?

Well, according to the UK Atomic Energy Authority, this represents the “first-of-a-kind decommissioning of a tritiated fusion reactor and ancillary buildings”. For fusion to be developed the environmental impacts and safety of the decommissioning stages needs to be understood. This puts the UK and its European partners at an advantage.

And this is not the end of fusion experiments, either. Quite the opposite. For example, ITER (meaning “The Way” in Latin), a collaboration between 35 nations in Southern France, is an even larger research facility. Once completed, the project will seek to achieve a fusion energy gain of 10, holding promise for the future of the technology. ITER was expected to be operational by 2023 but delays have pushed this back to 2025.

Fusion is expected to be on the UK national grid post-2050 either as a base load plant or in cycles of 8 hour bursts. Either way, it offers an almost boundless energy source that can be scheduled and controlled, unlike the conventional intermittent renewables used now. In short, the future of fusion is a bright one.