Decision

GDA Step 2 of the GE Vernova Hitachi SMR: Statement of Findings public summary

Published 11 December 2025

Applies to England and Wales

The Environment Agency and Natural Resources Wales have issued this Step 2 Statement to GE Vernova Hitachi Nuclear Energy LLC, UK Branch, on its successful completion of Step 2 of the generic design assessment (GDA) of the BWRX-300 reactor design, a 300 MWe boiling water reactor.

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 BWRX-300 design related to environmental protection and waste management. This statement provides a summary of our position following completion of the assessment.

Overall conclusion

Our Step 2 assessment has concluded that no fundamental environmental protection shortfalls in the design have been identified so far. However, we have identified one potential environmental protection shortfall. We think that further work will be needed to prove that the decision not to sort and segregate waste ion exchange resins demonstrates the best available techniques (BAT).

We raised a Regulatory Observation (RO) (RO-BWRX300-002) to highlight our concerns and to determine what the Requesting Party (RP) proposed to do to substantiate this decision. This information would be required as part of a site-specific permit application. Actions 1 and 2 of the RO were closed in GDA Step 2 through amendments made to the Preliminary Environmental Report (PER) and Preliminary Safety Report (PSR). Actions 3 to 9 of the RO remain open at the end of GDA Step 2, as the work would be completed during any future UK development.

Our Step 2 assessment

We agreed a scope of assessment with the RP in Step 1 (GE-Hitachi, 2024). The agreed GDA scope is comprehensive with regards to environmental protection from radioactive substances and contains all the systems, structures and components that have a bearing on the generation and management of radioactive waste for the life cycle of the plant. The life cycle encompasses design through operations to decommissioning and site clearance.

This statement and its conclusions are based on the findings of our assessment made on the PER and PSR updated in July 2025 and supporting documents GE Vernova Hitachi Nuclear Energy LLC, UK Branch submitted for the GDA.

The submissions assessed are identified in the Master Document Submission List, Revision 19 (GE-Hitachi, 2025a). The BWRX-300 design that we assessed in Step 2 was set out in the Design Reference Report (GE-Hitachi, 2025b).

We have set out our detailed findings and conclusions in our Step 2 Fundamental Assessment Report (Environment Agency 2025).

Overall, there were no aspects of the design that we identified to be unacceptable, based on the information provided. Our fundamental assessment has resulted in the following conclusions:

1. The RP has adequate management arrangements in place to implement GDA. There is a mature design process and an appropriate integrated management system in place for staff capability, document delivery, document control and quality surveillance, such that we can be confident in the submissions received for this GDA.

2. There is a clear integrated waste management strategy that considers radioactive waste and conventional solid wastes, which is considered good practice. We recommend that decommissioning continues to be considered throughout the detailed design to ensure there is enough information for any future permit application.

3. 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 Regulatory Observation RO-BWRX300-002.

4. The estimates for gaseous and liquid discharges presented in GDA adopt a bounding case and are considered representative of discharge limits rather than realistic estimates of the expected discharges. Further work is required around source term refinement, contribution from expected events and alignment with 2004/2/Euratom [EU, 2004].

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

6. An expert view by Nuclear Waste Services (NWS) on the future disposal of spent fuel and certain solid radioactive waste streams has concluded that it is likely that the wastes could be disposed of in a future geological facility. We agree with this view.

7. One of the important points NWS raised is the lack of a reliable radiological source term on which to base realistic estimates. This aligns with our concerns in relation to overly conservative solid radioactive waste estimates, discharge estimates and dose impacts.

8. Sampling and monitoring provision is still in the early stages of development. However, the necessary work identified through Forward Actions Plans (FAPs) for sampling and monitoring are adequate for Step 2 of a GDA. 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 be available where the equipment can be installed, allowing for the requirements for representative sampling/monitoring to be met.

9. We agree that the radiation dose to the 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, source term refinement will be needed to draw specific conclusions (such as dominant radionuclide contributions or plant environmental performance) based on the subsequent radiological assessment.

10. Two standby diesel generators are required to provide power during any loss of off-site power events. The BWRX-300 will likely require an environmental permit under the Medium Combustion Plant Directive Permit as the thermal input is above 1 MWth and below 50 MWth but will not require a Large Combustion Plant permit.

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 this conclusion is subject to carrying out that detailed assessment and any future developer gaining the necessary site-specific permissions. The detailed assessment would include the further work from the FAPs and the work we have identified in the open RO, which will be closed when this work is completed during any future UK development. Our conclusion is without prejudice to us identifying further regulatory concerns and shortfalls during any future detailed assessment.

References

GE-Hitachi, 2024. Scope of Generic Design Assessment, NEDC-34148P Revision 2, October 2024.

GE-Hitachi, 2025a. Master Document Submission List, NEDO-34087 Revision 19, November 2025.

GE-Hitachi, 2025b. Design Reference Report, NEDC-34154P Revision 3, April 2025.

Environment Agency, 2025. Generic Design Assessment of the BWRX-300 design. Step 2 - Fundamental Assessment Report (FAR), December 2025.