Decision

GDA Step 2 of the GE Vernova Hitachi SMR: Fundamental Assessment public summary

Published 11 December 2025

Applies to England and Wales

Executive summary

Nuclear energy has an essential role to play in the government’s mission to make Britain a clean energy superpower. As a source of clean, stable and reliable power, it offers significant opportunities to achieve energy security and climate security, by providing low carbon, dispatchable energy.

As regulators of the nuclear industry, the Environment Agency, Natural Resources Wales (NRW) and the Office for Nuclear Regulation (ONR) are working together to make sure that any new nuclear power stations built in the UK meet high standards of safety, security, environmental protection and waste management.

The generic design assessment (GDA) process allows the UK’s nuclear regulators to assess new nuclear power station designs at an early stage of the regulatory process and to provide confidence that these new designs can be constructed, operated and decommissioned in the UK. Early assessment of the design allows us to identify any potential regulatory concerns or design issues and ask the reactor design company to address them. This will help to avoid potentially costly and time-consuming changes arising from resolving regulatory concerns that are identified after construction of the nuclear power station has begun.

GE Vernova Hitachi Nuclear Energy International LLC, UK Branch (known as the Requesting Party or RP) submitted the BWRX-300 small modular reactor (SMR) design to the UK government for entry into GDA in December 2022. The government decided that the RP was ready to enter GDA and asked the regulators (the Environment Agency, ONR and NRW) to begin a 2-step assessment process which started on 25 January 2024.

The RP is a branch office of GE Vernova Hitachi Nuclear Energy International LLC (GVHI). The design being assessed is the BWRX-300, which is designed by GE Vernova Hitachi Nuclear Energy Americas LLC (GVHA), a sister company of GVHI.

The entity names listed above are slightly different to those used in our Step 1 documents. This is a name change only, and the company number and the legal identity of the RP has not changed.

The BWRX-300 design is a SMR based on boiling water reactor (BWR) technology. It is being designed to generate 300 megawatts of electricity. This would be enough to power over 500,000 homes.

GE Vernova Hitachi Nuclear Energy International took part in Great British Energy‑Nuclear’s competition to select an SMR to be operated in the UK but it was not selected as the preferred bidder to build the country’s first SMRs. However, this does not prevent GHVI, UK Branch from proposing to develop BWRX-300 reactors in the UK.

Ontario Power Generation is developing the BWRX-300 at Darlington, near Toronto Canada, and Tennessee Valley Authority is developing the BWRX-300 at Clinch River nuclear site in the USA.

We completed Step 1, ‘Initiation’, of GDA on the GE Vernova Hitachi BWRX-300 design on 12 December 2024. We have now completed Step 2, ‘Fundamental Assessment’, of the GDA and concluded that there are no fundamental shortfalls in environmental protection in the BWRX-300 at this stage of assessment. We have not been asked to carry out Step 3 of GDA, ‘Detailed Assessment’, and so this conclusion is subject to carrying out of a detailed assessment and any future developer gaining the necessary site-specific permissions. The detailed assessment work would include the further work that we have identified in Step 2 to demonstrate that the proposal not to sort and segregate waste ion exchange resins and liquid effluents meets the UK requirement to use the best available techniques (BAT) to minimise waste and select the optimal disposal route. There is an open Regulatory Observation (RO) on this topic which will be closed when the work is completed during any future UK development. Our conclusion is without prejudice to us identifying further regulatory concerns and shortfalls during a future detailed assessment, which could be carried out in an extension of GDA or in site-specific pre-application and permitting activities.

This document summarises our main report and provides background on the GDA process, consents, our public engagement and next steps.

Illustration of BWRX-300 SMR. Copyright GE Vernova Hitachi Nuclear Energy International LLC.

1. New nuclear power stations – government policy

UK energy policy, including the use of nuclear power, is a matter for government. The previous government’s policy was set out in the energy white papers that it published, including ‘Powering our Net Zero Future’ in 2020. This set out the need for nuclear power, among other measures, to help the UK achieve net zero by 2050.

In 2022, the then government published the British energy security strategy. This states an aim that by 2050, up to 24 gigawatts or a quarter of the electricity used in Great Britain will be from nuclear. This ambition was reinforced through the Civil nuclear roadmap, published in January 2024, which sets out the vision for the sector and important enabling policies to achieve this.

In 2024, the current government was elected and confirmed in its consultation in February 2025 on the proposed new national planning statement for new nuclear power stations (EN7), that

nuclear has an essential role to play in our mission to make Britain a clean energy superpower. As a source of clean, stable and reliable power, it offers huge opportunities to deliver energy security and climate security, as well as economic security for workers and communities across the country.

2. New nuclear power stations – the environment agencies

The Environment Agency has published its own strategy EA2030 change for a better environment to guide its activities.

The 5-year strategy (EA2030) sets out how the Environment Agency will fulfil its responsibilities over the next 5 years against its long-term goals for England. These are:

• healthy air, land and water supporting nature’s recovery
• sustainable growth
• a nation resilient to climate change

NRW has published a corporate plan to 2030, with a vision of nature and people thriving together. This will be achieved through collective action towards:

• nature’s recovery
• resilience to climate change
• minimising pollution

As enabling regulators, we will continue to engage with the government, regulatory partners, industry and others on nuclear energy matters, including policies, proposals and projects. We will make sure that people and the environment are properly protected.

Our processes align with the goals in EA2030 because they help make sure that new nuclear power stations are designed, constructed and operated in ways that would minimise waste, consider sustainability and properly protect the environment.

3. Regulating nuclear power stations

The Environment Agency and NRW regulate the potential impacts of nuclear sites in England and Wales on people and the environment. We do this by issuing environmental permits which cover activities required for:

• preparing the site and constructing the power station
• operating and decommissioning the power station

The Environment Agency and NRW also regulate other new and existing nuclear facilities in England and Wales. These can include fuel manufacturing sites, uranium enrichment plants, and waste management and disposal facilities.

We work closely with ONR, which regulates nuclear safety, conventional health and safety, security and safeguards at nuclear licensed sites.

Our process for assessing new power station designs and permitting new nuclear sites has several possible stages, including early engagement, GDA and environmental permitting.

3.1 Generic design assessment (GDA)

GDA is where we assess the environmental protection aspects of a power station design that would be relevant to any site. This is based on a ‘generic site’ with characteristics defined by the RP. Later, when we assess applications for environmental permits, we use the actual characteristics of the specific site where the developer proposes building the power station. The site-specific characteristics may be different from those of the GDA generic site.

The Environment Agency and ONR developed the GDA process. NRW participates in GDA where the company designing the nuclear power station advises that its design might be proposed for construction in Wales.

The GDA of a new design is not a mandatory requirement. Developers of nuclear power stations may choose to apply to the government to enter GDA to get an early view from regulators on their design. This helps to reduce risks to the developer over an entire project and enables the regulators to identify regulatory concerns and issues early so that these can be resolved before construction begins. The government asks the regulators to start a GDA if it decides that the nuclear power station design company is ready to enter GDA.

We’ve designed GDA as a flexible process with up to 3 steps. The assessment becomes increasingly more detailed with each step. At the end of each step, we will issue statements and reports about our findings. If the reactor design company still has significant issues to resolve after we have completed our planned assessments, we can add further steps to the process for resolving those remaining issues.

Step 1: Initiation

This is the preparatory part of the design assessment process when we make agreements with the reactor design company and agree the scope and the information it needs to provide. As part of this step, we carry out a readiness review and confirm that the reactor design company has put in place the arrangements and resources needed for the GDA process.

GE Vernova Hitachi Nuclear Energy International LLC, UK Branch completed Step 1 in December 2024.

Step 2: Fundamental Assessment

This is when the first technical assessments begin. It focuses on the environmental protection features of the design. The regulators will issue a Step 2 Statement at the end of the step. A Requesting Party may wish to stop the GDA at the end of Step 2 or proceed to Step 3. Getting to the end of Step 2 normally takes around 2 years.

This is the step that we have just completed for GE Vernova Hitachi Nuclear Energy International LLC, UK Branch. The company applied for a 2-step GDA only and no detailed assessment of the BWRX-300 has been requested. Options for carrying out detailed assessment are available if requested by GE Vernova Hitachi Nuclear Energy International LLC.

Step 3: Detailed Assessment

This is a detailed assessment of the environment case. Where a full GDA is being carried out, we will run a public consultation, where we ask for comments on our assessment in Step 3. We consider all relevant responses before completing our assessments and making our decision on whether to issue a Statement of Design Acceptability (SoDA). If a full Step 3 is not being carried out, we will issue a Step 3 Statement. Getting to the end of Step 3 takes around 4 years.

Where a full Step 3 is being carried out (including public consultation), we will publish a decision document that sets out our decision on the design. Potential outcomes include:

Issuing a Statement of Design Acceptability (SoDA)

We will issue a SoDA if the design is acceptable. This means we:

• have not found any GDA Issues
• consider that the design is capable of being constructed, operated and decommissioned in a way that complies with our regulatory requirements and expectations
• believe that people and the environment will be properly protected

Issuing an interim Statement of Design Acceptability (iSoDA)

We will issue an iSoDA if we are broadly content with the environmental protection aspects, but there are still issues to be resolved and the RP has provided credible plans for addressing them. Normally, once it addresses these issues, we will issue a full SoDA.

Not issuing a SoDA or iSoDA

We will not issue a SoDA or iSoDA if the design is unsuitable and would not provide the right levels of environmental protection. This could also be because there are GDA Issues but no credible plan to resolve them. We would issue a Step 3 Statement if this was the case. Also, we issue a Step 3 Statement if we have not carried out a public consultation.

Our GDA guidance for the reactor design company sets out in detail the process that we follow.

Completed GDAs

We have carried out generic design assessment on these reactor designs:

• EDF-Areva’s UK EPR, completed a 3-step GDA in December 2012, and there are 2 reactors currently under construction at Hinkley Point C in Somerset and 2 at Sizewell C in Suffolk
• Westinghouse’s AP1000, completed a 3-step GDA in March 2017
• Hitachi-GE’s Advanced Boiling Water Reactor (ABWR), completed a 3-step GDA in December 2017
• General Nuclear System Limited’s UK HPR1000, completed a 3-step GDA in February 2022
• GE Vernova Hitachi’s BWRX-300, completed a 2-step GDA in December 2025

Current GDAs

We are currently assessing the following reactor designs:

• Rolls-Royce SMR Limited’s small modular reactor (3-step GDA)
• Holtec International’s SMR-300 small modular reactor (2-step GDA)

Westinghouse and TerraPower have submitted applications to enter GDA.

Early engagement process

The regulators have introduced a new additional process that enables early engagement with reactor vendors where their designs are not yet ready to enter GDA. We are engaging with several companies in this process:

• Last Energy (Preliminary Design Review completed July 2025)
• Moltex Flex
• Newcleo
• TerraPower
• X-Energy

3.2 Environmental permits

In order to build and operate a new power station at a specific site, a company must apply for environmental permits from the Environment Agency in England or NRW if the site is in Wales.

These permits cover site investigation and preparation, construction works and associated developments such as workers’ accommodation, operation and decommissioning.

Site preparation and construction-related permits include activities such as:

• drilling boreholes
• abstracting groundwater (such as from dewatering of excavations)
• discharging effluents (including groundwater and concrete batching plant waters)
• using mobile diesel electricity generators
• flood risk activity permits (for work near rivers and flood defence assets)

Operational permits are needed to:

• dispose of and discharge radioactive waste
• operate standby power supply systems using diesel generators
• discharge returned abstracted water (from the cooling water system and fish recovery and returns system) and other liquid trade effluents (including treated sewage effluent) to the sea or inland water body

If we receive permit applications, we will decide whether or not to grant the permits and, if so, what conditions we should apply. When making decisions about site-specific permit applications, we will take account of matters relevant to the specific site as well as the GDA for the design proposed for the site.

We will also carry out a public consultation before deciding whether to grant permits for a specific site. We will make our decision once we have considered the comments we receive in the consultation. We may also receive applications for changes (variations) to the environmental permits and, where appropriate, we will consult on these.

4. The BWRX-300

There are currently over 400 nuclear reactors operating around the world. The BWR is a common type of reactor in operation, with 43 operating worldwide. There are also 2 BWRs under construction, 17 BWRs not generating currently, and 53 in permanent shutdown.

There are a range of sizes and potential uses for BWRs, but all operating BWRs are used for power generation.

The BWRX-300 is a BWR which is being designed to generate 300 megawatts of electricity (MWe). This would be enough to power over 500,000 homes.

The BWRX-300 is still being designed and not yet in operation. The design has completed the vendor design review process with the Canadian Nuclear Safety Commission (CNSC) and it has now received an application for a licence to construct in Canada. Certain aspects of the design have also been reviewed by the United States Nuclear Regulatory Commission (US NRC) as part of pre-licensing activities. GE Vernova Hitachi Nuclear Energy submitted a construction permit to the US NRC in 2024 for the Tennessee Valley Authority’s Clinch River site. GE Vernova Hitachi Nuclear Energy is also progressing early regulatory activities in Poland and the Czech Republic.

How does a BWR reactor work?

When a uranium-235 atom absorbs a neutron, it can split into 2 or more smaller atoms, release energy and emit several neutrons. This is the fission process. In a reactor, these fissions happen in a controlled process called a chain reaction, which provides a continuous heat source.

This heat is removed from the reactor core by circulating water through it. The water boils into steam which is dried in the ‘stream drier’ at the top of the reactor vessel. The steam is then used to power a turbine which drives a generator to produce electricity. After passing through the turbine, the steam is condensed back to water, using a separate cooling water circuit. This cooling water system is the same as for any power station. The cooling water circuit can use seawater, freshwater or circulating water through cooling towers. The water from the condensed steam is returned to the reactor core to start the heat removal process again.

In a BWR the heat removal process takes place in a single circuit, unlike in pressurised water reactors (PWRs) where the water is kept in a liquid phase under pressure and heat is exchanged to a secondary circuit via a steam generator before passing through a turbine. BWRs do not have steam generators or a pressuriser as found in PWRs.

The GE Vernova Hitachi BWRX-300 has features in common with most other types of nuclear power station, including:

• a spent (used) fuel storage pond
• spent fuel dry store (not in GDA scope)
• water treatment systems for maintaining water circuits and their chemistry in good condition
• radioactive waste treatment and storage facilities
• back-up systems for providing power in the event of a loss of electrical supply from the grid

The BWRX-300 would be mostly constructed and assembled in factory-built modules.

Find out more on the GE Vernova Hitachi Nuclear Energy website.

5. About Step 1 (initiation) and our decision

We began GDA on the BWRX-300 in January 2024. We completed Step 1, the initiation stage and published our report in December 2024.

6. About Step 2 (Fundamental Assessment) and our decision

We began Step 2 in December 2024. We have now completed Step 2, the Fundamental Assessment stage and published our Step 2 Statement and our assessment report.

The objectives of Step 2 were:

• for the Environment Agency to carry out an assessment to identify any fundamental environmental protection shortfalls in the design
• for the RP to complete the submissions needed for Step 2 (and Step 3, if necessary)
• to confirm if the RP has understood the regulatory approach used in the UK and whether the design can comply with UK regulations and Environment Agency guidance
• to identify the additional work the RP may need to carry out as part of a future assessment stage

During Step 2, we continued the joint assessment with ONR of the GDA project management arrangements to give us confidence in the quality of the GDA submissions.

With the RP we:

• provided feedback on the content and structure of its submissions
• raised Regulatory Queries (RQ) where we needed clarification on content

The RP captured these clarifications in the final versions of the Preliminary Environmental Report (PER) and Preliminary Safety Report (PSR) uploaded to the RP’s GDA website in August 2025.

Our Step 2 assessment concluded that there were no ‘fundamental’ environmental protection shortfalls in the design, but we did identify one ‘potential’ environmental protection shortfall relating to waste segregation that the RP will need to resolve. Further work will be needed by the RP to prove that its decision not to sort and segregated waste ion exchange resins and liquid effluents demonstrates BAT.

We raised a RO (RO-BWRX300-002) to highlight our concerns and to determine what the RP proposed to do to substantiate this decision. This would have to be addressed in detailed assessment as part of a pre-application or application for a site-specific permit. RO actions 1 and 2 were closed in GDA Step 2 through amendments made to the PER and PSR. RO actions 3 to 9 remain open at the end of GDA Step 2, as the work would be completed during any future UK development. If the RP cannot demonstrate that its proposals on waste segregation are BAT, then design changes may be required.

Overall, there were no aspects of the design that we identified to be unacceptable. Below are some additional judgements following our fundamental assessment.

We recommend continued consideration of decommissioning throughout the RP’s detailed design work to ensure there is sufficient information for any future permit application.

We are satisfied that the RP has a systematic optimisation process and that the structure of the demonstration of BAT provides a suitable basis to be taken forward by any future developer. The design at this stage is likely to be consistent with the application of BAT for minimising the impact of radioactive waste disposals on people and the environment, subject to the completion of the further work identified in RO-BWRX300-002.

The estimates for gaseous and liquid discharges presented in the RP’s submissions adopt a worst case and are considered representative of discharge limits rather than realistic estimates of the expected discharges. Further work is required to specify expected discharges, including addressing improvement of the overly conservative source term, contribution from expected events and alignment with 2004/2/Euratom.

The RP has made indicative estimates for low activity and higher activity solid wastes from operation of the BWRX-300 and for decommissioning wastes. The RP has also demonstrated that all radioactive waste streams expected to be generated by the BWRX-300 would have a disposal route. 

An independent review by Nuclear Waste Services (NWS) of the future disposal of spent fuel and certain solid radioactive waste streams has concluded that they are likely to be able to be disposed of in a future geological facility. We agree with this view. NWS also noted that the source term was overly conservative and would need to be improved.

Sampling and monitoring provision is still in the early stages of development. However, we would recommend (for both gaseous and aqueous discharges) that approximate positioning requirements for sample extraction and flow monitoring are considered as soon as possible. This will ensure that a suitable zone will remain available where the equipment can be installed, allowing for the requirements for representative sampling/monitoring to be met.

We agree that the radiation dose to public and wildlife from radioactive waste discharges and disposals is likely to be below relevant dose limits and dose constraints during normal operations based on bounding case discharge data. However, refinement of the discharges will be needed to be able to draw specific conclusions (such as dominant radionuclide contributions or plant environmental performance) based on the subsequent radiological assessment.

Two standby diesel generators are required to provide power during any loss of off-site power events. The BWRX-300 will likely require a permit under the Medium Combustion Plant Directive (MCPD) as the thermal input is above 1 MWth and below 50 MWth but will not require a large combustion plant (LCP) permit.

We agree that the RP is applying relevant legislation, regulatory requirements and relevant good practice in its design decisions.

We have not been asked to carry out Step 3 of GDA, Detailed Assessment, and so this conclusion is subject to carrying out of that assessment (in an extension of GDA or as part of site-specific work) and any future developer gaining the necessary site-specific permissions. The detailed assessment work would include the further work from the FAPs and that identified in the open RO, which will be closed when the work is completed during any future UK development. Our conclusion is without prejudice to us identifying further regulatory concerns and shortfalls during a future detailed assessment.

Our Step 2 Fundamental Assessment Report provides more detail. [link to main report]

7. Permissions and consents for a nuclear power station

Any company that wants to build and operate a new nuclear power station must obtain several site-specific permissions. These include:

• environmental permits from the Environment Agency or NRW
• a nuclear site licence and relevant consents from ONR
• planning permissions from the Planning Inspectorate

GE Vernova Hitachi was not selected by Great British Energy-Nuclear as its technology partner for further development. Currently, no developers have identified a site and applied for environmental permits to use the BWRX-300 in the UK.

7.1 Environmental permits

We provide information on these in section 3.2.

7.2 Nuclear site licence

ONR regulates the nuclear safety, conventional health and safety, security and safeguards at nuclear sites. Any organisation that wants to carry out nuclear activities must apply to ONR for, and obtain, a nuclear site licence. It must do this before it starts building a new nuclear power station. Granting a nuclear site licence is a significant step, but, on its own, it does not give an organisation permission to start nuclear-related construction. For that, it must get further regulatory permission from ONR.

7.2 Planning permission

A developer using the BWRX-300 needs a Development Consent Order from the Secretary of State for the Department for Energy Security and Net Zero. The Secretary of State makes a decision having received recommendations from the Planning Inspectorate.

The environment agencies are consultees in this process and provide advice throughout.

7.3 Electricity generation licence

An operator would need an electricity generation licence from Ofgem, the regulator for the gas and electricity markets.

7.4 Regulatory justification

Regulatory justification is required for any process involving radiation exposure. In essence, regulatory justification requires that the net benefits of that process exceed health detriments. This is not a site-specific requirement but is carried out for new nuclear power station designs. The justifying authority for new nuclear power stations is the Secretary of State for the Department for Environment, Food and Rural Affairs (Defra). No application for regulatory justification has yet been made for the BWRX-300.

7.5 Other permissions

An operator will also need approval from the government for a Funded Decommissioning and Waste Management Plan for its site. This is to ensure that there are funds to decommission and dispose of the waste from a site at the end of its life.

Other regulatory permissions can also be required depending on the location and local environment of a site and a developer’s proposals. This could include marine licences from the Marine Management Organisation (England), species licences from Natural England (England) and the equivalent permissions in Wales from NRW.

8. Public and stakeholder engagement for this GDA

We designed our GDA process to be open and transparent.

We expect nuclear reactor design companies to set up a GDA website, publish the information they send to us as part of the assessment process (its safety, security and environmental submissions), and update it as new information becomes available.

We ask the company to set up and manage a public comments process so that stakeholders and the public can look at the published information, provide comments and receive a response from the company to relevant questions.

Regulators see the questions and the responses, and, where relevant, use these to help inform our assessments. Comments can also be made to the nuclear regulators’ Joint Programme Office.

Our process guidance for public engagement is shared and discussed with the company and its communications team.

8.1 Public comments process review

The RP set up an accessible, bilingual (English-Welsh) GDA website and comments process, published design information on it, and updated it as new information became available.

GE Vernova Hitachi was asked to promote the website, the documents and comments process when it was launched (at the start of Step 2 on 12 December 2024) and throughout Step 2. We noted that publicity of the process by the company was limited. There was also a delay in uploading documents.

GE Vernova Hitachi Nuclear Energy was required to respond to questions and comments about its design. The comments process closed on 31 August 2025 after receiving 7 comments.

We considered any comments received up to 31 August 2025, and GE Vernova Hitachi Nuclear Energy’s responses to those comments, during the Step 2 assessments.

The comments received covered:

• 2 offers to support GVHI in achieving their development goals
• missing documents not on the website at the start of Step 2
• requests for names of individuals in the company
• using nuclear for hydrogen generation
• a statement noting that there are points in the operational cycle of the BWRX-300 where coolant circulation is not solely driven by natural circulation, which the RP acknowledged

None of the comments directly impacted our assessment of the BWRX-300 or our GDA process.

As part of their joint communications plan the nuclear regulators publicised the second step of GDA and the comments process being available through the media and directly to stakeholders.

Information about GDA and the comments process is widely available on:

• the joint regulators’ webpage
• the ‘get involved’ webpage
• the Environment Agency webpage on assessing reactor designs for new nuclear power stations
• ONR’s webpage on new reactors
• NRW’s webpage on how it regulates the nuclear industry

8.2 Get involved

This GDA has now ended. You can continue to get involved by:

• taking part in engagement and consultations should this BWRX-300 reactor design be taken forward by a developer at a site in England or Wales
• talking to us at public, stakeholder and industry events
• engaging in our other new nuclear build work, including any other GDAs

The regulators published an approach to engagement for this GDA on their joint webpages.

9. GDA timetable and next steps

The planned duration of the GDA of the BWRX-300 overall was 24 months.

Step 1 (Initiation) started on 25 January 2024 and finished on 12 December 2024.

Step 2 (Fundamental Assessment) started on 12 December 2024 and ended on 11 December 2025.

In addition to this public summary, we have published a Step 2 Statement and a Fundamental Assessment report. This is the end of the GDA process for the BWRX-300.

10. Contact us

You can feed back on this document or our work on assessing this design.

Environment Agency

Email: nuclear@environment-agency.gov.uk

Natural Resources Wales

Email: enquiries@naturalresourcewales.gov.uk