New nuclear power stations: assessing reactor designs
Source: gov.uk (2025-12-11)

The Environment Agency’s Generic Design Assessment (GDA) of new nuclear power station designs and how we engage with others during the process.

The Environment Agency, Office for Nuclear Regulation (ONR) and Natural Resources Wales are working together to make sure that any new nuclear power stations built in the UK meet high standards for:
- safety
- security
- environmental protection
- waste management
- nuclear safeguards (https://www.onr.org.uk/safeguards/index.htm)
Latest news

The Environment Agency has:
- completed Step 1 and Step 2 of the GDA on GE Vernova Hitachi Nuclear Energy’s BWRX-300 small modular reactor on 11 December 2025
- completed Step 1 and started Step 2 of the GDA on Holtec International’s small modular reactor SMR-300 on 1 August 2024
- completed Step 2 and started Step 3 of the GDA on Rolls-Royce SMR Limited’s 470MWe small modular reactor on 30 July 2024
- published a blog post about the Holtec SMR GDA (https://environmentagency.blog.gov.uk/2025/02/05/how-the-environment-agency-is-assessing-new-nuclear-power-station-designs/)
- published a blog post about the GE Vernova Hitachi SMR GDA
- published a blog post about the Rolls-Royce SMR GDA
- published a blog post on ensuring nuclear reactor designs meet high standards of environmental protection (https://environmentagency.blog.gov.uk/2024/08/01/ensuring-nuclear-reactor-designs-meet-high-standards-of-environmental-protection/)
Generic Design Assessment

Government has stated that nuclear power plays an important role as part of a mix of different energy sources. In 2007 the UK government asked the regulators to work together to introduce a new process for assessing designs for new nuclear power stations.

The Environment Agency and ONR developed a process called Generic Design Assessment (GDA). They use this process to scrutinise new nuclear power stations at an early stage. This is before a developer has formed detailed proposals for building at a specific site or applied for licences or permits. This means that the regulators can identify potential design or technical concerns early on and ask the designer to resolve them.

The process has up to 3 steps, with the assessment becoming increasingly more detailed. If the design company still has significant issues to resolve after the regulators have completed their planned assessments, further steps can be added to the process.

It takes around 4 years to complete the 3 steps of the GDA process.

Initiation

Fundamental assessment

Detailed assessment

The design company must provide detailed information to make the environment case for their nuclear power station design. The regulators will carefully examine the information and will ask questions. They will request further information if necessary and identify if changes to the design might be needed.

At the end of each step, the regulators issue statements and reports about their findings. What they issue will depend on the scope of the GDA they agreed with the design company during Step 1.

If the agreed scope is sufficiently broad and detailed, with the potential to achieve a ‘Statement of Design Acceptability’ (SoDA), then we will consider issuing one. We will only issue a SoDA if we judge that the design is acceptable. Similarly ONR will consider issuing a ‘Design Acceptance Confirmation’ (DAC).

Issuing a SoDA and DAC means that the regulators consider that if a new nuclear power station were built using that design, it should be capable of meeting the UK’s high standards of safety, security and environmental protection.

Before a site operator can build a new nuclear power station, they must apply for and obtain all of the site specific approvals they need. These include:
- environmental permits for construction and operation
- a development consent order (planning permission) from the Secretary of State for Energy Security and Net Zero
- a nuclear site licence and other safety and security consents from ONR
When making decisions about an operator’s environmental permit applications for a proposed site, the Environment Agency will take account of all the work it has done during GDA.

More information about GDA

The regulators have produced some infographics about GDA (https://www.gov.uk/government/publications/regulating-new-nuclear-power-stations-infographics).

Modernised GDA process and updated guidance

In 2019 the regulators modernised the GDA process, using their learning from previous assessments. They have made the process more flexible to help with the assessment of small modular reactors and less mature designs. This includes providing other options for other GDA outcomes, in addition to the current option of issuing (or not) a DAC and SoDA.

The Environment Agency has produced updated guidance for organisations who want to submit a design for assessment (https://www.gov.uk/government/publications/new-nuclear-power-plants-generic-design-assessment-guidance-for-requesting-parties). We refer to these organisations as ‘requesting parties’ because they can be made up of a number of companies, including nuclear power station designers and operators. The guidance explains the GDA process and the information they must provide.

In developing the modernised GDA process the regulators have been careful to make sure that a requesting party still has to meet the same requirements and expectations to achieve a SoDA and DAC.

GDAs started before 2019 followed earlier versions of the assessment of candidate nuclear power plant designs (https://www.gov.uk/government/publications/assessment-of-candidate-nuclear-power-plant-designs) produced by the Environment Agency and ONR.

The regulators will be using the updated guidance for all future GDAs.

During 2024, the regulators published new joint guidance for developers and designers of new nuclear power stations seeking early engagement (https://www.onr.org.uk/generic-design-assessment/early-regulatory-engagement-on-new-nuclear-projects/) before entering GDA and permitting. Additional guidance was published in 2025 to support organisations undertaking a tier 3 preliminary design review (PDR) (https://view.officeapps.live.com/op/view.aspx?src=https%3A%2F%2Fwww.onr.org.uk%2Fmedia%2Ftjyhwhyy%2Fnew-nuclear-power-plants-early-engagement-preliminary-design-review-guide.docx&wdOrigin=BROWSELINK).

The following companies have entered the early engagement process:
- Last Energy (Tier 3 completed PDR)
- Moltex Flex (Tier 1 completed)
- Newcleo (Tier 1 completed)
- X-Energy (Tier 1 completed, Tier 2 ongoing)
- TerraPower (Tier 2 completed)
The Environment Agency is currently reviewing its guidance following the announcement of a new collaborative initiative with the Office for Nuclear Regulation and the US Nuclear Regulatory Commission (https://www.onr.org.uk/news/all-news/2025/09/nuclear-regulators-renew-transatlantic-agreement).

Public and stakeholder engagement

GDA is an open and transparent process. The nuclear regulators worked with Sciencewise to understand how the public wants to be informed and consulted about assessing new nuclear power station designs (https://sciencewise.org.uk/projects/new-nuclear-power-stations-improving-public-involvement-in-reactor-design-assessments/?portfolioCats=43%2C44%2C45%2C46%2C15).

The nuclear regulators also worked with partners and Sciencewise to explore public views toward the siting and deployment of advanced nuclear technologies (https://sciencewise.org.uk/projects/advanced-nuclear-technologies/?portfolioCats=43%2C44%2C45%2C46%2C15), to support policy development and inform future engagement.

There are a number of ways the public and other stakeholders can get involved in GDA.

GDA comments process

A nuclear power station design company going through GDA must set up a website to:
- publish information about the design
- invite the public to ask questions and make comments
The design company must respond to any comments or questions they receive.

The regulators will see the comments and questions and the responses provided. They can also use this information to help inform their assessment work.

The Environment Agency and ONR have set up a joint programme office to help administer the GDA process. During GDA, the joint programme office acts as a single point of contact between the regulators and the design company. The public and stakeholders can also send their comments to the joint programme office.

The comments process is open throughout a GDA. It closes about 4 months before the regulators issue statements at the end of steps 2 and 3, or make decisions about issuing a SoDA or DAC.

The comments process document on the ONR website (https://www.onr.org.uk/generic-design-assessment/get-involved/) has more information about how it works.

Consulting on GDA findings

During Step 3, the Environment Agency will consult on its preliminary GDA findings from the detailed assessment if the scope agreed with the requesting party is sufficient to consider issuing a SoDA. This follows the same approach as the original GDA process. If the agreed scope is not sufficient to consider issuing a SoDA, the Environment Agency will not consult.

The Environment Agency will carefully consider all the comments we receive during the consultation on our preliminary findings. We will use the comments to help inform our assessment and decision about whether to issue a SoDA for a particular design.

Meetings and events

You can talk to the Environment Agency about assessing new nuclear power station designs at:
- site stakeholder groups
- local community liaison councils
- industry conferences
- public events
To find out when these will take place, email the Environment Agency: xxx@xxx.xx (mailto:xxx@xxx.xx).

Ongoing and completed GDAs

Information about GDAs that are in progress or have ended.

GE Vernova Hitachi Nuclear Energy – BWRX-300 small modular reactor

The regulators began a 2 step GDA for the GE Vernova Hitachi Nuclear Energy BWRX-300 on 25 January 2024. This followed a request from the Department for Energy Security and Net Zero to carry out the GDA after it had completed its review of GE-Hitachi’s application for a 2 step GDA.

The BWRX-300 small modular reactor design uses boiling water reactor technology.

GE Vernova Hitachi Nuclear Energy International LLC (UK Branch) is the requesting party for the GDA. The requesting party is a branch office of GE Vernova Hitachi Nuclear Energy International LLC (GVHI). The BWRX-300 is designed by GE Vernova Hitachi Nuclear Energy Americas LLC (GVHA), a sister company of GVHI.

The regulators completed GDA Step 1 of the BWRX-300 small modular reactor in December 2024 (https://www.gov.uk/government/publications/gda-step-1-of-the-ge-hitachi-smr-statement-of-findings).

The regulators completed GDA Step 2 of the BWRX-300 small modular reactor in December 2025 (https://www.gov.uk/government/publications/gda-step-2-of-the-ge-vernova-hitachi-smr-fundamental-assessment).

This GDA ended in December 2025. The regulators were not asked to carry out Step 3 of GDA, ‘Detailed Assessment’. The Step 2 conclusion is subject to carrying out a detailed assessment and any future developer gaining the necessary site-specific permissions.

The comments process for this GDA opened in December 2024 and closed in August 2025. You can read about the comments process or look at information about the design on GE Vernova Hitachi website (https://www.gevernova.com/nuclear/uk-smr).

Find out more about the GDA for the GE-Hitachi BWRX-300 on the joint regulators’ website (https://www.onr.org.uk/generic-design-assessment/assessment-of-reactors/ge-hitachi-bwrx-300).

Holtec International – SMR-300 small modular reactor

The regulators began a 2 step GDA for the Holtec SMR-300 design on 18 October 2023. This follows a request from the Department for Energy Security and Net Zero to carry out the GDA following a review of Holtec’s application.

The SMR-300 design is a small modular reactor and uses pressurised water reactor technology.

The requesting party is Holtec International. The GDA will be managed by Holtec Britain Limited. Holtec has applied for a 2 step GDA.

The regulators completed GDA Step 1 of the Holtec SMR (https://www.gov.uk/government/publications/gda-step-1-of-the-holtec-smr-statement-of-findings) in August 2024.

The regulators are now carrying out Step 2 of GDA. Step 2 is the first major technical assessment and focuses on the environmental protection features of this design. Step 2 is currently planned to take 15 months.

The comments process for this GDA opened in August 2024 and closed in November 2025. You can read about the comments process or look at information about the design on the Holtec Britain GDA website (https://gda.holtecbritain.com/).

Find out more about the GDA for the Holtec International SMR on the joint regulators website (https://www.onr.org.uk/generic-design-assessment/assessment-of-reactors/holtec-international-smr-300/).

Rolls-Royce SMR Limited – 470MWe small modular reactor

The regulators began assessing the Rolls-Royce SMR in April 2022. This follows a request from the Department for Business, Energy and Industrial Strategy on 3 March 2022, to carry out the GDA following a review of Rolls-Royce SMR Limited’s application.

The 470MWe small modular reactor uses pressurised water reactor technology. This GDA is the first on a design developed in the UK.

The requesting party is Rolls-Royce SMR Limited.

The regulators completed GDA Step 1 in April 2023. Read the GDA Step 1 of the Rolls-Royce SMR: statement of findings (https://www.gov.uk/government/publications/gda-step-1-of-the-rolls-royce-smr-statement-of-findings).

The regulators completed GDA Step 2 in July 2024. Read the GDA Step 2 of the Rolls-Royce SMR: statement of findings (https://www.gov.uk/government/publications/gda-step-2-of-the-rolls-royce-smr-fundamental-assessment).

The regulators are now carrying out Step 3 of GDA. Step 3 is the detailed assessment and, for the Environment Agency and Natural Resources Wales, it focuses on the environment case and includes a public consultation on the preliminary findings. The Rolls-Royce SMR design has been selected by Great British Energy-Nuclear (GBE-N) for deployment at Wylfa in Wales (subject to contract). We will continue to engage with both Rolls-Royce SMR and GBE-N to ensure all parties get the maximum benefit from the GDA as the plan to deploy this reactor design moves into this next phase.

The comments process for this GDA opened in April 2023. It will stay open until around 4 months before the regulators make their final decision.

You can make comments or ask a question about this design on the Rolls-Royce SMR website (https://gda.rolls-royce-smr.com/).

You can also send comments through the joint programme office by emailing xxx@xxx.xx (mailto:xxx@xxx.xx).

Find out more about the GDA for Rolls-Royce SMR on the joint regulators website (https://www.onr.org.uk/new-reactors/rolls-royce/index.htm).

General Nuclear System Ltd – UK HPR1000

The regulators began assessing the UK HPR1000 in January 2017. The requesting party consists of China General Nuclear Power Corporation, Électricité de France S.A. and General Nuclear International Limited, with General Nuclear System Ltd acting on behalf of the requesting parties. They moved to Step 2 of the GDA in November 2017 and completed the initial, high level technical assessment in November 2018.

Read the summary report for the initial assessment of the UK HPR1000 design (https://www.gov.uk/government/publications/new-nuclear-power-stations-initial-assessment-of-general-nuclear-systems-uk-hpr1000-design).

The Environment Agency consulted on their findings from their environmental assessment from 11 January 2021 to 4 April 2021.

The comments process for this GDA opened in November 2017 and closed in September 2021. You can read about the comments process or look at the information about the design on the UK HPR1000 (https://www.ukhpr1000.co.uk/make-a-comment/) website.

In January 2022 the regulators completed their GDA for this design and concluded that it should be capable of meeting UK safety, security and environment protection requirements.

Read the Environment Agency’s documents about the GDA for the UK HPR1000 design (https://www.gov.uk/government/collections/gda-uk-hpr1000-new-nuclear-power-station-design).

EDF and Areva – UK EPR

The regulators began assessing EDF and Areva’s UK EPR nuclear power station design in 2007.

The Environment Agency consulted on its findings from its environmental assessment from 28 June to 18 October 2010 and published its decision and interim SoDA in December 2011.

In December 2012, the regulators completed their GDA of this design and concluded that it should be capable of meeting UK safety, security and environment protection requirements.

EDF Energy is building this reactor design at Hinkley Point in Somerset and Sizewell in Suffolk (https://www.edfenergy.com/energy/nuclear-new-build-projects/hinkley-point-c).

Find out more about the Environment Agency’s regulation of Hinkley Point nuclear power station (https://www.gov.uk/guidance/hinkley-point-nuclear-regulation).

Find out more about the Environment Agency’s regulation of Sizewell in Suffolk (https://www.gov.uk/guidance/sizewell-nuclear-regulation).

Read the regulator’s documents about the GDA for EDF and Areva’s UK EPR nuclear power station design (https://www.gov.uk/government/collections/gda-edf-and-areva-uk-epr-new-nuclear-power-station-design).

Read information about this design on the EDF website (https://www.edfenergy.com/energy/nuclear-new-build-projects/hinkley-point-c/reactor/uk-epr-generic-design-assessment).

Hitachi GE UK Advanced Boiling Water Reactor (ABWR)

The regulators began assessing Hitachi GE’s UK ABWR nuclear power station design in January 2014.

The Environment Agency and Natural Resources Wales consulted on their findings from their environmental assessment from 12 December 2016 to 3 March 2017.

In December 2017 the regulators completed their GDA of this design and concluded that it should be capable of meeting UK safety, security and environment protection requirements.

Read the regulators’ documents about the GDA for Hitachi GE’s UK ABWR nuclear power station design (https://www.gov.uk/government/collections/gda-hitachi-ge-uk-abwr-new-nuclear-power-station-design).

You can also read information about the UK ABWR design on the Hitachi GE website (http://www.hitachi-hgne-uk-abwr.co.uk/).

Westinghouse Electric Company AP1000

The regulators began assessing Westinghouse Electric Company’s AP1000 nuclear power station design in 2007.

The Environment Agency consulted on its findings from its environmental assessment from 28 June to 18 October 2010. It published its decision and an interim SoDA in December 2011.

In March 2017 the regulators completed their GDA of this design and concluded that it should be capable of meeting UK safety, security and environment protection requirements.

Read the regulators’ documents about the GDA for the Westinghouse Electric Company’s AP1000 nuclear power station design (https://www.gov.uk/government/collections/gda-westinghouse-electric-company-ap1000-new-nuclear-power-station-design).

You can also read information about this design on the Westinghouse website (https://westinghousenuclear.com/energy-systems/ap1000-pwr/overview).

Contacts

Email the Environment Agency: xxx@xxx.xx (mailto:xxx@xxx.xx).

Email the ONR: xxx@xxx.xx (mailto:xxx@xxx.xx).

To sign up for the Environment Agency’s nuclear regulation e-bulletin, email: xxx@xxx.xx (mailto:xxx@xxx.xx).

More information

Read the government’s National Policy Statement for nuclear power generation (https://www.gov.uk/government/collections/national-policy-statements-for-energy-infrastructure).

Read the government’s information on Advanced Nuclear Technologies (https://www.gov.uk/government/publications/advanced-nuclear-technologies).

Read the government’s information about how to apply for GDA (https://www.gov.uk/government/publications/entry-to-the-generic-design-assessment-for-advanced-nuclear-reactors).

Read about how the Environment Agency, ONR and Natural Resources Wales work together on GDA (https://www.onr.org.uk/generic-design-assessment/).

Read about ONR’s work on nuclear new build (https://www.onr.org.uk/our-work/what-we-regulate/new-reactors/).

Read about Natural Resources Wales’s work on nuclear new build (https://naturalresourceswales.gov.uk/about-us/what-we-do/how-we-regulate-you/our-role-in-nuclear-regulation).