Choosing where to site nuclear reactors has always been emotive and contentious. As significant pieces of energy or defence infrastructure, government policy has always mandated the choice of sites for new reactors. In the past concerns over safety and public uncertainty around the health effects of nuclear power stations drove government and its advisers to exercise caution by choosing remote sites along the country’s coastline with one notable exception at Trawsfynydd.
Consequences of a Legacy Siting Policy
Remote locations may have allayed unfounded fears around health but have had unintended consequences to the electrical grid, with large generating stations often sited a considerable distance from large electrical consumers. This problem has been exacerbated as the country’s energy mix has changed with the abolition of coal as a fuel source. Many renewable replacements are equally remote from high density centres of population or industrial activity. Likewise, interconnectors to European countries by their very nature must land in coastal areas.
An increasing imbalance in the grid combined with volatility in both generation and consumers have led to a sharp rise in balancing costs as the National Energy System Operator faces new challenges to continued stability of the electrical transmission network.
The UK’s EN-6 siting framework has played a pivotal role in shaping nuclear energy deployment since it was published in 2011. EN-6 set out the Government’s siting policy for nuclear power stations deployable before the end of 2025, identifying eight suitable sites in England and Wales. EN-7, while never formally published, was developed in parallel as a set of technical siting criteria intended to support government and industry in the early-stage screening of potential nuclear sites beyond those listed in EN-6. Among those criteria, the semi-urban population density threshold—designed to avoid development in areas of moderate or high population concentration—has become increasingly outdated. While it originally aimed to reflect the safety case requirements of large-scale reactors, it now risks acting as a rigid constraint on emerging, lower-risk nuclear technologies, limiting the flexibility needed to meet the UK’s future energy and decarbonisation goals.
EN-7 and the Transition to Flexible Siting
The draft EN-7 published in 2023—and subject to renewed consultation in 2025—establishes a technology-neutral framework for assessing new nuclear sites. Unlike EN-6, it no longer prescribes specific locations nor limits deployment to a particular timeframe. It is designed to accommodate both traditional large-scale reactors and newer designs, including Gen III+ SMRs and Gen IV AMRs.
This shift recognises the need for more distributed, adaptable, and integrated nuclear infrastructure. But despite this intent, EN-7 still retains siting criteria that were originally devised with large pressurised water reactors (PWRs) in mind—most notably the guidance to avoid siting in semi-urban areas.
Why the Semi-Urban Criterion Is Outdated
1. It fails to differentiate between reactor classes
The semi-urban exclusion threshold was based on risk profiles for gigawatt-scale reactors—where offsite consequences from worst-case scenarios could be significant. But the emerging UK fleet will likely include:
- Gen III+ SMRs, which are evolutionary designs derived from proven PWR technologies, but at a smaller scale (approximately 300–470 MWe). They feature passive safety systems, simplified construction, and in some cases, underground containment.
- Gen IV AMRs, which depart more radically from conventional designs, using advanced fuels, coolants (such as molten salt or gas), and configurations that aim to eliminate high-consequence failure modes entirely.
While neither design class is exempt from regulatory scrutiny—and AMRs in particular remain under development—their risk profiles and safety case architecture are fundamentally different from legacy GW-scale reactors. EN-7 acknowledges the technology shift, but does not yet translate that recognition into a differentiated approach to population density.
2. It blocks viable brownfield and grid-connected sites
By advising against siting near semi-urban areas, the draft EN-7 risks excluding many of the very sites that are most suitable for modular deployment—particularly those with:
- Existing grid infrastructure or substations
- Historical energy use or industrial footprints
- Proximity to heat loads, transport links, or hydrogen production demand
These are not remote greenfield sites—they are technically capable, strategically located parcels of land that, with a modern reactor design, could support clean, dispatchable energy. The current criterion creates a false constraint, based not on updated risk modelling but on a static spatial filter.
3. It undermines design-informed siting policy
The principle behind the Planning Act 2008 and its associated NPS framework is that nationally significant infrastructure projects (NSIPs) should be assessed on their merits, using evidence-based criteria. Applying an undifferentiated exclusion to all nuclear designs—without accounting for the containment strategy, accident scenario modelling, or passive safety performance—is inconsistent with that ethos.
A more robust, risk-informed approach would allow for site-specific evaluation, supported by detailed safety cases, rather than applying a blanket presumption against any development near moderate population zones.
What Should Replace It?
The final version of EN-7 should maintain the UK’s high bar for nuclear safety and planning rigour—but it must evolve the tools used to enforce it. Specifically:
- Replace the semi-urban threshold with a graded assessment model linked to the reactor technology and specific design characteristics
- Enable brownfield and industrial site reuse, where ALARP arguments demonstrate that risks can be managed
- Align spatial guidance with the capabilities of Gen III+ and Gen IV systems, allowing for context-specific trade-offs between proximity, risk, and system value
Rather than imposing design-specific exclusions at the policy level, EN-7 should adopt technology-specific criteria that reflect known mitigation potential prior to DCO assessment. These would allow siting flexibility to be assessed fairly and consistently, while ensuring that project-level design details are properly interrogated during the DCO process.
Conclusion
The publication of EN-7 as a formal draft National Policy Statement marks a long-overdue modernisation of the UK’s nuclear siting framework. But if it simply reasserts outdated planning constraints—like the semi-urban criterion—without adapting to the reality of new reactor technologies, it risks undermining the very flexibility and innovation it aims to support.
A modern nuclear policy must be both technology-aware and system-integrated. That means giving developers the tools—and the regulatory space—to develop new reactor sites where they make sense, not just in remote locations that often cause as many problems as they avoid.
Next Steps
Nuclear Consulting is working with reactor vendors, developers and site owners to create safe and sustainable energy systems with nuclear at their core. While safety will always remain the primary concern, our analysts have developed novel techniques to identify new sites throughout England and Wales that have a high probability of gaining development consent when assessed against EN-7.
We are working with government and industry bodies to ensure that the final published version of the NPS takes note of the fast pace of development around small and advanced nuclear thus ensuring that we have planning policy that is fit for the coming decade or longer. Our focus is to ensure a level playing field that does not artificially penalise innovation through lack of vision or backwards-looking technophobia.
Contact Us to discuss siting and planning issues around new nuclear.
