TL;DR:

  • The UK’s Rolls-Royce SMR programme is targeting first power delivery in the mid-2030s from a 470 MWe modular reactor design
  • Great British Nuclear has shortlisted SMR technologies for deployment at multiple sites; Wylfa and Sizewell are the leading candidates
  • SMRs won’t replace renewables — but they address the intermittency gap that solar and wind cannot solve alone

Nuclear power barely features in most UK household energy conversations, which is understandable: the last reactor to come online was Hinkley Point C’s first unit, still years away from full operation. But small modular reactors — a genuinely different approach to nuclear generation — have moved from a government aspiration to a funded, contracted programme. If the timelines hold, SMRs will be generating electricity into British homes by the late 2030s.

Understanding what SMRs are, how they differ from conventional nuclear, and what the UK programme actually looks like helps make sense of where Britain’s energy mix is headed.

What Makes a Reactor “Small” and “Modular”

Conventional nuclear plants like Hinkley Point C are enormous. The two EPR reactors there will each generate 1,650 megawatts — enough for about 5 million homes — but the project costs have exceeded £32 billion and taken over a decade to build. The scale that makes them productive also makes them expensive and slow.

Small modular reactors flip this equation. A typical SMR design generates between 100 and 500 megawatts — roughly a quarter to a third of a large conventional reactor. The key word is modular: major components are factory-manufactured and shipped to site for assembly, rather than being built from scratch at the construction location.

The argument for modularity is essentially the same as for prefabricated housing: factory production is more consistent, faster, and cheaper than bespoke on-site construction. You build the first unit to learn the system, the second unit more efficiently, and by the tenth unit you’re approaching genuinely competitive costs.

The Rolls-Royce SMR Design

The UK’s most advanced SMR programme is led by Rolls-Royce SMR Ltd, a consortium that includes BNF Resources UK, Exelon Generation, and the UK government (which holds a stake). Their design is a 470 MWe pressurised water reactor — familiar technology at smaller scale — built primarily in factories and assembled on site in modules.

The target: a first-of-a-kind (FOAK) plant generating electricity by the mid-2030s. The Generic Design Assessment (GDA), the UK regulatory process for approving reactor designs, is underway with the Office for Nuclear Regulation and the Environment Agency. Approval is expected before 2028.

Rolls-Royce projects the FOAK cost at around £2.5 billion per unit, with subsequent units coming down toward £1.8 billion as the supply chain matures. At scale, the levelised cost of electricity would be competitive with offshore wind. That last claim is contested — critics note that nuclear costs have historically increased rather than decreased — but the modular manufacturing approach does provide a structural mechanism for cost reduction that conventional builds lack.

Great British Nuclear and Site Selection

The government body overseeing the SMR programme is Great British Nuclear (GBN), established in 2023 as a delivery vehicle for new nuclear investment. GBN ran a competitive selection process that resulted in a shortlist of SMR technologies for potential UK deployment, with Rolls-Royce SMR as the leading domestic candidate.

Site selection is in progress. The leading candidates for SMR deployment are:

Wylfa, Anglesey — a former Magnox site with existing nuclear licensing, grid connections, and community familiarity with nuclear employment. North Wales has strongly supported nuclear development. Wylfa is the frontrunner for the first SMR site.

Sizewell, Suffolk — the site of Sizewell C, the large-scale EDF project, but with potential capacity for SMR development alongside or instead of the megaproject.

Oldbury and Bradwell — former reactor sites with infrastructure in place, both on the GBN longlist.

The planning and site consent process for new nuclear in England runs through the Infrastructure Planning Commission, with decisions ultimately made by the Secretary of State for Energy Security and Net Zero. For a mid-2030s first power date, site selection and planning consent need to be substantially complete by 2028.

Why SMRs and Not Just More Wind and Solar

The question is fair. Offshore wind costs have fallen dramatically, the UK has world-class wind resources, and solar is now cheap enough to deploy at scale. Why invest in nuclear at all?

The honest answer is that the National Grid has a problem with dispatchable low-carbon power — generation that can be turned on when the sun isn’t shining and the wind isn’t blowing. Currently that gap is filled by gas, which is neither low-carbon nor domestically produced. Interconnectors with France and Norway help, but they have physical limits and are subject to geopolitical risk.

Nuclear is dispatchable. It runs continuously, independent of weather, and produces no carbon during operation. Battery storage can cover short gaps (hours), but multi-day “dunkelflaute” events — the low-wind, low-sun periods that every renewable system faces in winter — require something nuclear or gas can provide and batteries cannot.

SMRs are also being positioned as industrial heat sources for net-zero manufacturing — aluminium smelting, hydrogen production, and chemical processes that need consistent high-temperature heat and can’t wait for the wind to blow.

What the Timelines Actually Look Like

The mid-2030s is the optimistic scenario. Nuclear projects have a consistent track record of delays, and the SMR programme still has substantial regulatory and planning work ahead. A realistic planning horizon looks like:

  • 2026–2027: GDA completion for Rolls-Royce SMR design
  • 2027–2028: Site selection finalised, planning applications submitted
  • 2029–2031: Planning consent, land acquisition, supply chain contracts
  • 2031–2034: Construction of first unit
  • 2035–2036: First power, possibly 2037–2038 for full operation

This is not imminent electricity. Anyone making energy decisions for their home in the next decade should not be factoring SMRs into their planning.

The Cost and Subsidy Question

New nuclear in the UK has historically relied on Contracts for Difference — government-backed strike prices that guarantee generators a fixed return per megawatt-hour. Hinkley Point C negotiated a strike price of around £92/MWh in 2013 money, which looked expensive against the gas prices of the time but looks more reasonable after the 2022 energy crisis.

The GBN SMR programme is expected to use a similar mechanism, with a strike price negotiated between the government and Rolls-Royce SMR. Critics argue this represents a subsidy that could otherwise go to scaling renewables faster. Supporters argue that the firm dispatchable capacity nuclear provides is worth paying a premium for.

What’s clear is that SMRs won’t happen without government support. The economics of first-of-a-kind nuclear construction don’t work without some form of guaranteed revenue.

The Bottom Line for UK Energy Consumers

SMRs won’t appear on your electricity bill as a distinct line item, but they’ll influence the energy mix your supplier buys from. If the programme delivers — and that’s a significant “if” — they’ll reduce the gas dependence that has driven electricity price volatility, provide a floor of low-carbon baseload capacity, and support industrial decarbonisation in sectors that renewables can’t directly serve.

For homeowners making decisions about heat pumps, solar, and battery storage today: none of that changes. Those investments pay back on current and near-future grid economics. SMRs are a 2035 story at the earliest, and the most important thing they offer is reducing the risk that a renewables-heavy grid hits a structural problem in the 2040s. That’s worth having — but it’s not a reason to delay the investments that make sense right now.