Nuclear domain

Why is the nuclear capacity cliff a problem?

Nuclear provides around 15 per cent of GB electricity from a fleet of ageing reactors, most of which will close by 2030. Hinkley Point C is under construction and Sizewell C has been approved, but the gap between retirements and replacement is real and growing. Small modular reactors could change the long-run picture, but they are still years from deployment.

Heat → CCUS Interconnectors
~15%
of GB electricity (2024)
~6 GW
current operating capacity
3.2 GW
under construction (HPC)
24 GW
government target by 2050

What remains of the nuclear fleet?

Britain built the world's first commercial nuclear power station (Calder Hall, 1956) and once had 26 operating reactors. Five stations remain operational, all operated by EDF Energy.

Operating (AGR) Operating (PWR) Under construction Planned Torness1,185 MW AGR | closes 2030 Hartlepool1,185 MW AGR | closes 2026 Heysham 1 and 21,150 + 1,230 MW AGRboth close 2028 Sizewell B1,198 MW PWR | closes 2035 Sizewell C (planned)3,260 MW EPR | RAB funded Hinkley Point C3,260 MW EPRunder construction | ~2030 CAPACITY TRAJECTORY 2024: ~6 GW2029: ~1.2 GW (minimum)2050 target: 24 GW

By 2029-2030, only Sizewell B (1.2 GW) will be operating. Lowest nuclear capacity since the 1960s. Hinkley Point C is expected to begin generating around 2030.

What AGR reactors are and why they are closing

Advanced Gas-Cooled Reactors (AGRs) are a uniquely British design using carbon dioxide gas as a coolant and graphite as a moderator. The graphite moderator blocks degrade over decades of neutron bombardment, developing cracks that eventually limit safe operation. When inspections show cracks have progressed beyond safety case limits, the station must close.

When does each station close?

The AGR fleet is closing in rapid succession. Each closure removes approximately 1 GW of reliable, low-carbon baseload capacity. The diagram below shows the capacity gap between retirements and new build.

Nuclear Capacity: Closures, New Build, and the Gap (GW) 8 7 6 5 4 3 2 1 0 2020 2025 2030 2035 2040 2045 2050 Capacity gap Dungeness B Hunterston + Hinkley B Hartlepool Heysham 1+2 Torness Sizewell B only (1.2 GW) HPC Unit 1 HPC Unit 2 SZC Unit 1 SZC Unit 2 SMR fleet (if ordered) 24 GW target Existing fleet closures New large reactors (HPC + SZC) SMR fleet (indicative) Capacity gap
Dungeness B closed (2021)
Two AGR reactors, 1,040 MW. Closed early due to graphite core deterioration.
Hunterston B closed (2022)
Two AGR reactors, 965 MW. Closed after graphite cracking investigations.
Hinkley Point B closed (2022)
Two AGR reactors, 965 MW. Closed on schedule after life extensions.
Hartlepool to close (2026)
Two AGR reactors, 1,185 MW. Subject to ONR safety case.
Heysham 1 and 2 to close (2028)
Four AGR reactors, 2,380 MW combined. Multiple life extensions granted.
Torness to close (2030)
Two AGR reactors, 1,185 MW. Last of the AGR fleet.
Nuclear capacity minimum (2029-2030)
Only Sizewell B (1.2 GW) operating. Lowest capacity since the 1960s.
Hinkley Point C Unit 1 expected (~2030)
First EPR unit, 1,630 MW. Begins to close the capacity gap.

What large nuclear projects are in the pipeline?

Two large EPR projects are the centrepiece of the UK's nuclear replacement strategy, using the same reactor design but different funding models.

Hinkley Point C

Two EPR reactors, 3.2 GW total. Under construction in Somerset. Strike price of 92.50 pounds/MWh (2012 prices). Cost risen from 18 billion to over 35 billion. First unit expected around 2030.

Developer: EDF / CGN  |  Capacity: 3,260 MW  |  Cost: 35bn+

Sizewell C

Replica of HPC, 3.2 GW. Approved 2022 with Regulated Asset Base funding. UK government has 50 per cent equity stake through Great British Nuclear.

Developer: SZC Co (50% UK govt)  |  Capacity: 3,260 MW  |  Funding: RAB
Why the RAB model should be cheaper than HPC's CfD

The RAB model allows construction costs to be passed through to consumer bills during construction, reducing the developer's financing cost. Because nuclear projects are capital-intensive with long construction periods, financing cost is a significant portion of total cost. RAB reduces the risk premium, which should translate to lower electricity cost. The trade-off is that consumers start paying before the station generates any power.

Can small modular reactors change the picture?

SMRs are factory-manufactured reactors with capacity up to 470 MW per unit. Standardised, modular construction should reduce costs and construction times. The UK government launched the SMR competition through Great British Nuclear in 2023.

Rolls-Royce SMR

470 MW pressurised water reactor. Modular construction with factory-built components. Target cost 1.8 billion per unit with series build.

Capacity: 470 MW  |  Status: GBN selected, GDA in progress

GE Hitachi BWRX-300

300 MW boiling water reactor. Simplified safety systems. Under construction in Ontario, Canada.

Capacity: 300 MW  |  Status: GBN selected

Holtec SMR-160

160 MW pressurised water reactor with passive safety. Underground reactor design. Targeting existing sites.

Capacity: 160 MW  |  Status: GBN consideration

Advanced Modular Reactors

Generation IV designs using alternative coolants. UK allocated 385 million for AMR demonstration. Likely post-2035.

Status: R&D stage  |  Timeline: Post-2035
Why fleet ordering matters more than single-unit cost

The economic case for SMRs depends on building enough units to amortise the factory investment. A single SMR will be more expensive per MW than a large reactor. The cost advantage materialises with a fleet order of 10-15 units. South Korea's APR-1400 fleet demonstrates that repeated construction of identical designs is the proven route to cost reduction.

Methodology and sources

Last reviewed: 17 March 2026

Content sourced from the React page component at commit e19c4d6. Operating fleet data from EDF Energy and ONR assessments. HPC cost from EDF project updates. Nuclear generation share from DESNZ DUKES Table 5.1.

SourceRolls-Royce SMR selected - SMR programme and delivery context.
SourceSizewell C final investment decision - Large new-build commitment.
SourceOffice for Nuclear Regulation - Regulatory and safety context.
SourceCivil Nuclear Roadmap to 2050 - Strategic framework and targets.
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