04 June 2026 , 19:29
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Britain’s attempts to harness fusion energy could trigger a nuclear disaster, official documents reveal.
A prototype reactor that works as a "mini-Sun" is being developed in Nottinghamshire to create huge amounts of energy by smashing atoms together.
Fusion energy is seen as a panacea for the energy crisis and for sustainable, long-term net zero energy generation.
But official documents reveal concerns that a disaster at the site could contaminate 15,000 hectares of surrounding land, costing farmers £80m in lost profits, and result in thousands of cases of cancer in civilians and workers.
A worst-case event, such as an explosion of the reactor itself, could lead to millions of pounds of damage, with the costs borne by the taxpayer.
Fusion involves smashing two types of hydrogen together at high temperature to release the energy trapped within. It is extremely hard to carry out and so far has created only small amounts of energy.
Stars use fusion to create energy and the process requires huge pressure and temperature. Replicating that on Earth is an engineering and scientific hurdle yet to be accomplished anywhere.
Britain hopes to lead the world in fusion energy.
The Government hopes STEP will be operational by 2040 and provide energy to the power grid in Britain.
It would be the first functional nuclear fusion power plant in the world and is planned to be operational for 30 years.
Pound for pound, fusion makes four million times more energy than coal and creates none of the emissions or problematic waste of current energy generation methods.
It is seen as a key route for the UK and the world to reach net zero in the long term as it produces no greenhouse gas emissions.
Officials at DESNZ modelled the annual likelihood of 13 possible disasters for a government contingency liability document which acts as an insurance policy for the project. It is backed by the taxpayer because no company will insure the project because it is an unprecedented endeavor on this scale.
The official verdict warns a nuclear incident at the STEP fusion project in Nottinghamshire could lead to "contamination of farmland" and to "many years of farming profit losses". Models suggest there is a 2.9 per cent chance of a serious incident over the plant’s lifetime.
The documents warn that 15,000 hectares would be exposed to radiation and lead to an annual profit loss of £4m for 20 years.
Another risk of a nuclear accident at STEP is radiation exposure to the site’s 500 workers. About 50 would be exposed to a plume of radiation, modeling suggests, and five of these "in the immediate vicinity" would suffer direct exposure to high doses.
But there is a wider risk of radiation particles in the local area, the unredacted documents reveal, specifically small villages and the town of Gainsborough, with 22,000 residents.
The Government refused to disclose how many residents within the 0.6-mile risk zone could be killed by an accident at STEP.
The Telegraph understands councils and health organisations have not been made aware of such a risk.
The Chernobyl disaster in 1986 led to an exclusion zone with an 18.6-mile radius following the meltdown of the fission reactor. These reactors, such as Sizewell and Hinckley as well as Chernobyl and Fukushima, are capable of runaway chain reactions if not kept in check.
This is impossible for fusion, which is inherently safer as a process despite being harder to achieve. Fusion also generates no nuclear waste.
However, there are still risks associated with the extreme temperatures and using radioactive material.
A financial worst-case scenario of a disaster at STEP could see the taxpayer liable for up to £190m in damages, the documents state.
The government audit reveals this could rise to an "unlimited" fee because of uncertainty about the site, the process and the fallout.
Assessed issues include a vacuum failure inside the reactor that could trigger a hydrogen explosion, an earthquake and planes crashing into the site.
Six of the 13 events modelled were accidental aircraft crashes, which have a one in 3.2 million chance of happening in a given year.
These would lead to "instant fatalities, most of which may not be due to radiological consequences".
Four scenarios involved a fault to the tokamak, the spherical arena where the fusion takes place, which will be subjected to temperatures hotter than the Sun at 100 million degrees Celsius.
The odds of this happening in a year are estimated at either one in 1,250 or one in 200 for the eventuality of a tokamak vacuum failure triggering a hydrogen explosion.
Two scenarios focused on a fuel process fault, which was deemed the most likely at 1 in 250 per year. The final scenario is an earthquake, which has a one-in-seven-million likelihood annually.
The Government modelled the costs of death caused by irradiating the local area, but refused to disclose how many people would be expected to die and how much this would cost.
Cost and impact of how many staff would die and the treatment of cancer in affected people were also modelled, but not disclosed.
£1m in damages
Calculations also reveal the Government expects a disaster would lead to a payment of more than £1m for suffering, harm and medical costs to on-site workers.
Radiation exposure could trigger cancer in workers and the public, with victims able to claim compensation for up to 30 years after any incident.
Officials initially tried to keep the accident scenarios secret, citing national security, but were forced to reveal them after a Telegraph challenge.
The UK Atomic Energy Authority (UKAEA) insisted the chance of any serious incident during the plant’s entire lifetime was only 2.9 per cent, and that fusion was far safer than conventional nuclear power.
Fusion energy is less risky than fission energy as a runaway reaction, such as what happened at Chernobyl, is impossible.
The Government has made fusion energy a long-term priority and has recently deployed £2.5bn in funding to further the industry. This includes £1.3bn for STEP.
A further £180m has been earmarked for building LIBRTI, a facility to develop fusion fuel technology for power plants such as STEP.
Engineers designing STEP intend for it to be a 22-meter-tall (72ft) spherical tokamak where the two forms of hydrogen – deuterium and tritium – will merge to make helium and release huge amounts of harnessable energy.
The subsequent plasma ball of around 100 million degrees Celsius will have a radius of 3.6m (1ft), designs show, and be controlled by magnets.
Engineers are hopeful that STEP will generate 1.6GW of power – about half as much as Hinkley Point C – which equates to a net output of up to 200 MWe.
STEP is being built on the same site as the former coal power station West Burton A near Retford and it was recently announced the project would be built by the ILIOS consortium, led by construction firms Kier and Nuvia.
The consortium also consists of A_AL architects, Aecom, and Turner and Townsend.
Government sources claim the risk shown in the documents is in line with conventional power plants and lower than a nuclear fission facility.
A DESNZ spokesman said: "This is sensationalist reporting. These documents only outline the worst-case scenario and the risk is extremely low."
A spokesman for the UKAEA added: "Fusion energy has the potential to provide reliable, low-carbon and baseload power while supporting thousands of skilled jobs and we believe represents a big opportunity for the UK."
They added that STEP is being designed with "multiple layers of safety systems and robust measures".
"The process of fusion energy is fundamentally different from conventional nuclear fission," they said.
"It does not involve a chain reaction and cannot ’runaway’ or ’melt down’. Fusion does not produce high-level radioactive waste and does not carry a risk of large-scale nuclear accidents as seen in historical fission events.
"The fusion process stops almost instantly if the necessary conditions are not maintained."
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