Executive summary
This report presents the findings from the Preliminary Design Review (PDR) assessment conducted by the Office for Nuclear Regulation and the Environment Agency (collectively referred to as ‘the regulators’) of Last Energy’s PWR-20 concept. The review was carried out under the early engagement framework for new nuclear projects, described in ‘New nuclear power plants – Early regulatory engagement for new nuclear projects’ ONR-GDA-GD-009. The Environment Agency participated in the PDR as the environmental regulator for England and on behalf of Natural Resources Wales (NRW). Therefore, the conclusions of this report should be considered for any proposed developments in both England and Wales.
Last Energy and the regulators held three multi-day technical workshops between May 2024 and October 2024 under the early engagement framework before the regulators’ review of PDR submissions began in February 2025. Last Energy selected three topics for review: organisational plans and arrangements, environment and decommissioning, and safety analysis process and maturity. The PDR was completed in June 2025.
As part of the PDR, the regulators reviewed the three submissions provided by Last Energy and held two technical convergence workshops. The aim was to identify potentially significant gaps against regulatory expectations in the selected topic areas, provide advice on options for resolving those gaps, and help Last Energy better understand project risks on the pathway to nuclear site licensing and environmental permitting. The PDR enabled the regulators to examine and discuss aspects of the PWR-20 design, safety and environmental case, waste management, and decommissioning philosophy. For example, through PDR:
- Last Energy has progressed its organisational plans, incorporating feedback from the regulators on role definitions for environmental and security matters, and has committed to establishing a Design Authority presence in the UK at an earlier stage. This showed understanding and responsiveness towards alignment with regulatory expectations on business models/ activities, organisational baseline and management systems.
- The regulators identified that a suitable disposal route for certain reactor materials will be a key issue for Last Energy to resolve, as some materials may not be compatible with UK nuclear waste repositories. Last Energy has committed to addressing this issue through engagement with relevant stakeholders as the PWR-20 design is developed further.
- Last Energy shared the safety philosophy and first iteration application of the safety analysis framework to characterise nuclear safety risks associated with the PWR-20. Regulatory advice covered the extent and depth of safety analysis planned, expectations for safety classification and qualification of components, demonstration of passive systems reliability and overall approach to demonstrating defence-in-depth. ONR advised that it is philosophically possible to rely entirely on two passive safety systems, providing there is adequate defence in depth (multiple independent barriers to fault progression), and a robust body of evidence would be required to substantiate the claims. ONR has identified potential for technical challenges in these areas to be significant but there are grounds to expect that they could be resolved in future.
In parallel with the PDR, ONR developed and established the cornerstone intervention framework for assessment of the prospective nuclear site licence application related to the Llynfi site. ONR noted that Last Energy’s aspiration to receive a nuclear site licence decision by December 2027 could be achieved if Last Energy delivers the necessary submissions to the required standard and according to schedule.
Based on the focused review of the three topics during PDR, Last Energy has built confidence in the regulators that it understands regulatory expectations in those areas and is planning to address them as its design, safety, and environmental cases progress. Interactions with Last Energy throughout the PDR have been professional and constructive, laying foundations for future engagement and assessment during licensing and permitting. PDR has identified areas of novelty, provided advice on them and delivered focus for future regulatory assessment.
Prior to initiating the PDR, Last Energy informed the regulators that it did not intend to complete a Generic Design Assessment (GDA), but would instead apply directly for nuclear site licensing and environmental permitting for the Llynfi site in Wales. It is important to note that PDR is not a substitute for generic or site-specific design assessment, nuclear site licensing, or environmental permitting. Further regulatory assessment of the design, safety, security, and environmental cases by ONR and the environmental regulators will therefore be required.
