Office for Nuclear Regulation

Sizewell C

On 30 June 2020, ONR received an application from NNB Generation Company (SZC) Ltd for a nuclear site licence to construct and operate a twin EPR™ power station at Sizewell in Suffolk, adjacent to the existing Sizewell B station. We expect the design of the power station to be closely based on that currently under construction at Hinkley Point C.

In addition to a nuclear site licence, before it can start construction, the applicant must obtain a number of site-specific permissions from other regulators and Government, including environmental permits and planning permission in the form of a Development Consent Order (DCO) from the Secretary of State. NNB Generation Company (SZC) Ltd has submitted applications for environmental permits to the Environment Agency  and for a DCO to the Planning Inspectorate .

ONR's regulatory responsibility starts at the point of granting of a nuclear site licence. If we decide to grant the licence, after our assessment of the application, we will use the powers available under the site licence to require the licensee to request our permission for starting nuclear safety related construction at Sizewell C. Similarly, the licensee will be required to seek ONR’s permission to proceed to subsequent, key construction and commissioning stages up to the start of commercial operation.

Our assessment of the site licence application will culminate, if successful, in a recommendation to the ONR Chief Nuclear Inspector on granting the licence. Our publication Licensing Nuclear Installations provides guidance on the licensing process and the factors that we may take into account when reviewing an application for a nuclear site licence.

We will undertake our assessment activities in accordance with the guidance provided in the Licensing of Nuclear Installations document and ONR's Safety Assessment PrinciplesTechnical Assessment Guides and Technical Inspection Guides.

The overall outcome of our assessment will be a Project Assessment Report that will draw together the views of ONR's technical specialists on the applicant’s readiness to become a nuclear site licensee. NNB Generation Company (SZC) Ltd is targeting a licence grant by mid-2022, and we plan to complete our assessment of the application within this timescale. 

Progress statement – September 2021

On 30th June 2020, NNB GenCo (SZC) Limited (‘NNB GenCo’) applied to ONR for a nuclear site licence to permit the construction and operation of two EPR™ reactors at the Sizewell C (SZC) site. 

To progress its assessment of the licence application, ONR is implementing a programme of interventions and engagements aimed at gathering evidence to form a judgement on the capability of NNB GenCo and the effectiveness of its management arrangements to:

Our current views on the progress on each of these themes is summarised below.

Organisational capability

ONR has set out its expectations in Licensing Nuclear Installations that a prospective licensee should establish an organisation capable of managing matters relating to nuclear safety and security and discharging the obligations associated with holding a nuclear site licence. ONR expects this capability to be comprised in arrangements covering several key components including:

NNB GenCo has been progressively developing its organisational capability since nuclear site licence application. Progress is broadly in-line with expectations. NNB GenCo is intelligently adopting the arrangements from Hinkley Point C (HPC) to underpin its quality management system. NNB GenCo has established processes to ensure this adoption is considered and systematic, and where appropriate learning is identified.

NNB GenCo is working with HPC and Nuclear Generation Limited to establish a common nuclear competency framework across EDF Energy; this framework should provide the foundation for NNB GenCo to demonstrate the competency of its organisation. NNB GenCo continues to mature its governance arrangements, informed by its stakeholders.

Shadow working for Sizewell C is currently planned to commence in early 2022; this is a period where NNB GenCo will work to its organisational and management arrangements as if it was a nuclear site licensee, to demonstrate the adequacy of its organisation. ONR will seek confidence in the adequacy of all elements of its organisational capability throughout this shadow working period to inform our assessment.     

Licence Condition compliance

ONR does not expect NNB GenCo to produce fully developed site management and compliance arrangements for all 36 standard licence conditions at the point of licence grant as some are only relevant to activities that will take place as the project progresses through construction and commissioning.  However, fully developed arrangements must be in place for more than half of the standard licence conditions before licence grant.

ONR and NNB GenCo have developed and agreed a programme of Licence Condition compliance targeted discussions, to ensure appropriate development is maintained to support ONR’s licensing assessment.  NNB GenCo has set up a targeted working group involving representatives from Sizewell C and Hinkley Point C, with the aim of transferring learning from the Hinkley Point C experience into the Sizewell C compliance arrangements. 

Safety report

For site licencing, ONR does not expect NNB GenCo to have produced a specific safety case, however, ONR is engaging with NNB GenCo to understand how the safety case will be produced, and what processes etc will be used post licencing.

ONR understands the safety case will follow closely both the process and content of the HPC safety case for the areas that are to be replicated, with a key section of the future safety case justifying the replication strategy.

Site Suitability

A key element of ONR’s site licensing assessment is the suitability of the site. In accordance with our published guidance (Licensing Nuclear Installations), before a nuclear site licence is granted the prospective licensee will need to satisfy ONR that:

We are satisfied that the requirements of the first two bullets are satisfactorily met. With regard to external hazards, engagement is still ongoing with NNB GenCo in order for ONR to gain confidence in the characterisation of the hazards and to ensure there is no challenge to the suitability of the site.

Conventional health & safety

In accordance with the requirements of the Construction (Design and Management) Regulations 2015 (CDM), ONR seeks assurance that NNB GenCo (SZC) Ltd (NNB) has established management arrangements to secure the health, safety and welfare of persons who will work on the construction site.

NNB GenCo has been developing its organisational capability and is replicating arrangements from Hinkley Point C (HPC), in line with its strategy document “Sizewell C Project: Overarching CDM Strategy” which aims to gather and apply lessons from HPC (and elsewhere).  A significant difference from HPC is that it is proposed that the principal contractor will be a Civil Works Alliance (an alliance of 5 companies including NNB GenCo). A Project Delivery Organisation sits below the Client to provide integration across the project. ONRs focus has been on ensuring that appropriate appointments are being made in line with CDM.

NNB GenCo is engaging with other regulators including HSE. Work has been on-going to clarify the extent of the new nuclear build site and the vires of ONR, HSE and other regulators with an interest in aspects of the proposed development.

As the project progresses ONR will seek assurance regarding the constructability of the two EPR units at SZC in relation to conventional health and safety issues.

Nuclear security

NNB GenCo SZC Security staff will continue to develop the SZC Nuclear Site Security Plan (NSSP) and the current schedule for submission of the NSSP to ONR for approval is early 2022. In addition to detailing the security standards, arrangements and procedures during the construction phase of the project, the NSSP should also demonstrate to ONR that NNB GenCo has a comprehensive understanding of what the security regime will be when the facility is operational and how the arrangements will meet regulatory expectations. It is acknowledged that specific details of the security arrangements during the later stages of the project will not yet be confirmed but these will be included in future iterations of the NSSP. In order to benefit from the operational experience gained at Hinkley Point C (HPC), it is anticipated that NNB GenCo will use the principles of ‘intelligent replication’ and adopt and adapt some of the security arrangements currently employed at HPC. 


Overall, ONR is satisfied with the progress made towards the target of completing its licensing assessment by mid-2022.

Publication of reports

ONR is committed to being an open and transparent body, and will publish on this website the following material:


What is in a Nuclear Site Licence application?

The application is organised into a portfolio of high-level documents, covering a number of technical topic areas, and includes a summary document.

Should it be granted, a site licence puts the licence holder under strict legal obligations and, importantly, gives wider and deeper regulatory powers to ONR to ensure the safe construction, commissioning, operation and eventual decommissioning of a nuclear site.

What is ONR's role?

ONR is the independent regulator for nuclear safety and security for the UK. Our duty is to ensure that the nuclear industry controls its hazards effectively, has a culture of continuous improvement and maintains high standards.

We are responsible for licensing companies that wish to construct and operate new nuclear power stations at sites in Great Britain.

What does ONR look at during the assessment?

We will assess this application, partly informed by our previous assessment of the EPRTM at Hinkley Point C - including using the relevant lessons from that assessment, while focusing on aspects specifically relevant to Sizewell C.

We will request more detail on the areas for assessment and produce inspection reports, the areas for assessment for a nuclear site licence are - organisational capability, site suitability & safe design, licence condition compliance arrangements, emergency preparedness & response, conventional & fire safety, security, safeguards, and licensing & legal aspects.

We need to be satisfied that the applicant's choice of site is suitable; that it understands the hazards and risks of the activities that it proposes to carry out; and that it has a suitable schedule of safety submissions leading through to a pre-construction safety case. 

We place particular emphasis on the need to gain confidence that the applicant has the organisational capability to lead and manage for safety. This means that we must be satisfied with the applicant's governance arrangements, resources, competencies and management processes before we can consider recommending that the Chief Inspector grants a licence.

How long does it take to do the assessment?

The duration of ONR's assessment is dependent on a number of factors, including quality and timeliness of the submissions, but we anticipate being ready to make a decision by mid-2022.

What happens next?

The overall outcome of our activities during the assessment phase will be a Project Assessment Report that will draw together the views of ONR's technical specialists on NNB Generation Company (SZC) Limited readiness to become a nuclear site licence holder.  

Does this mean they can start to build at Sizewell?

No. The assessment of a nuclear site licence is a significant step, but is not itself permission to start nuclear-related construction. That requires a separate regulatory permission from ONR.

Who else has to give permission for construction to start?

In addition to a nuclear site licence and permission to start nuclear-related construction, before it can start construction, the applicant must obtain a number of site-specific permissions from other regulators and Government, including environmental permits and planning permission in the form of a Development Consent Order (DCO) from the Secretary of State. NNB Generation Company (SZC) Ltd has submitted applications for environmental permits to the Environment Agency and for a DCO to the Planning Inspectorate. The Planning Inspectorate’s examination of the DCO application began in April 2021 and is expected to end in October 2021, with a recommendation to the Secretary of State anticipated in early 2022.