Decision

GDA Step 2 of the Holtec SMR-300: Statement of findings

Published 31 March 2026

Applies to England and Wales

The Environment Agency and Natural Resources Wales have issued this Step 2 Statement to Holtec International (the Requesting Party), on its successful completion of Step 2 of the generic design assessment (GDA) of the Holtec SMR-300 reactor design. This is a twin unit, pressurised water reactor with each reactor unit providing a power of approximately 1,050 megawatts (MW) (thermal) and a generating capacity of approximately 320 MW (electrical).

The assessment has been carried out in line with our published guidance for Requesting Parties.

The Environment Agency in partnership with Natural Resources Wales have assessed the fundamental aspects of the Holtec SMR-300 design related to environmental protection and waste management. This statement provides a summary of our position following completion of the assessment.

1. Overall conclusion

Overall, the SMR-300 design appears to be capable of meeting relevant environmental regulatory requirements, provided that the Requesting Party (RP) delivers on its commitments and resolves identified gaps post GDA and at the site-specific permitting stage. While the design is still evolving, the frameworks and approaches presented give us confidence that environmental protection objectives can be achieved. Based on our assessment across all topic areas, we have found no fundamental environmental protection shortfalls at this stage in the development of the SMR-300 that could prevent the design from being acceptable for future deployment in England or Wales.

2. Our Step 2 assessment

The assessment was against the GDA scope, which was agreed with the RP in Step 1 (HOLTEC BRITAIN, 2024), and set out in the Preliminary Safety Report Part A Chapter 1 (HOLTEC BRITAIN, 2025b) and Part A Chapter 2 (HOLTEC BRITAIN, 2025c), Design Reference Point (HOLTEC BRITAIN, 2025a), and Master Document Submission List (HOLTEC BRITAIN, 2025d). We have assessed submissions across all environmental protection topics relevant to GDA, including structures, systems and components (SSCs) of the reactor design, which are applicable to safety, environmental protection or security. Where there are aspects of the design which have been excluded from the GDA scope, we are satisfied that the RP has captured any relevant assumptions and GDA commitments in an appropriate project register. These aspects will be assessed at a future stage, during the environmental permitting process, when more information becomes available.

This statement and its conclusions are based on the findings of our assessment made on the final versions of the RP’s safety, security, safeguards and environment case (SSEC) and supporting documents submitted for GDA, provided to us in July 2025. We have set out our detailed findings and conclusions in our Step 2 Fundamental Assessment Report (Environment Agency, 2026).

The RP has demonstrated an understanding of the relevant regulatory requirements and provided sufficient information to enable a meaningful assessment. Our main findings are described in this section.

The RP has established robust governance and quality management systems, ensuring control over design development and GDA submissions. We are satisfied these arrangements are adequate for this stage of GDA.

The RP’s methodology and approach to the demonstration of best available techniques (BAT) and its radioactive waste management strategy meet our expectations for Step 2. 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. While some evidence gaps remain due to design immaturity, the RP has committed to addressing these through GDA commitments and future evidence.

The RP has presented sufficient information about the management of solid wastes and spent fuel to satisfy the requirements of Step 2 of GDA. Further work is required at the pre-application and site-specific permitting stage to provide a full disposability case. We recommend continued consideration of decommissioning throughout the detailed design work to ensure there is sufficient information for any future permit application.

Calculation of discharges and proposed limits for gaseous and liquid discharges presented in GDA is thorough, systematic and appropriate for this stage, subject to refinement as the design matures. GDA commitments and future evidence are in place to address aspects that will need to be reviewed when reactor-specific design values and site-specific considerations are available.

Sampling and monitoring provision is still in the early stages of development. However, we are satisfied that the RP understands the requirements associated with sampling and monitoring and that its considerations are adequate for this stage of GDA.

Methods presented for calculating dose impacts for members of the public and wildlife are adequate for this stage of GDA, and we found no fundamental shortfalls in the RP’s submissions. The initial assessment undertaken using the preliminary discharge limits resulted in doses to people and dose rates to wildlife that were all below the relevant dose limits and source and site dose constraints. The assessments presented by the RP were carried out for a single SMR-300 unit and will therefore be higher for the design reference of a twin-unit deployment. However, the RP stated that doubling the doses presented in the preliminary environmental report (PER) would be bounding. Noting that the initial assessment is used as a conservative screening tool, our assessment findings are not changed by doubling the doses to the public and wildlife. A refined radiological impact assessment will be required at the pre-application and site-specific permitting stage, and we are satisfied with the RP’s approach.

The twin-unit SMR-300 will require 4 diesel generators and one auxiliary boiler and will therefore likely require an environmental permit under the Medium Combustion Plant Directive (MCPD) as the thermal input is above one MWth and below 50 MWth. Further specification of conventional environmental systems, chemical inventories and combustion plant details will be required at the site-specific permitting stage.

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

We have not been requested to carry out Step 3 of GDA (Detailed Assessment) and so these conclusions are subject to carrying out a detailed assessment and any future developer gaining the necessary site-specific permissions. The detailed assessment work would include the further work identified in the RP’s commitments, assumptions and requirements register. Our conclusions are without prejudice to us identifying any further regulatory concerns and shortfalls during any future detailed assessment.

3. References

Environment Agency, 2026. Generic Design Assessment of the Holtec SMR-300 design. Step 2 - Fundamental Assessment Report (FAR), March 2026.

HOLTEC BRITAIN, 2024. SMR-300 UK Generic Design Assessment Scope, HI-2240121, Revision 1, May 2024.

HOLTEC BRITAIN, 2025a. GDA Design Reference Point, HI-2240648, Revision 2, May 2025.

HOLTEC BRITAIN, 2025b. Holtec SMR-300 GDA PSR Part A Chapter 1 Introduction, HI-2240332, Revision 1, July 2025.

HOLTEC BRITAIN, 2025c. Holtec SMR-300 GDA PSR Part A Chapter 2 General Design Aspects and Site Characteristics, HI-2240333, Revision 1, July 2025.

HOLTEC BRITAIN, 2025d. SMR-300 GDA Master Document Submission List for GDA, HI-2240061, Revision 16, September 2025.