Erosion at the North end of the Sizewell C site and (version 6)  Site Data Summary Report

• Date released: 21 January 2026
• Request number: FOI202511049
• Release of information under: FOIA

Information requested

1. Advise whether Sizewell C Ltd has advised ONR of the recent erosion of the coast at the northern end of the Sizewell C site and, if so, does this have implications for the safety of workers during the construction of Sizewell C and/or for the project's site safety case for its full lifetime till all spent fuel is removed from the site, now admitted by SZC Ltd to be 2160, not 2140 in the approved DCO.

2. Advise whether ONR has received the data arising from the 2024 survey of the Sizewell coast and, if so, please supply copies of the relevant documentation and correspondence with the developer and Environment Agency.

3. Confirm what arrangements are in place for ONR to keep appraised of the erosion and flood risk affecting the SZC site.

4. Provide a copy of the latest Site Data Summary Report submitted by SZC Ltd (TASC already have a copy of revision 4 of the SDSR should that remain the latest version).

Information released

We confirm that under s.1 of the FOIA, we hold some of the information you have requested. Under Parts 1 and 2 of your request, we can confirm ONR has not received any recent erosion data. Previous Sizewell C (SZC) As Low As Reasonably Practicable (ALARP) studies have considered long term erosion, and ONR’s assessment reports (ONR 2022 and 2024) have further highlighted the need for SZC to consider long term erosion (Platform Observations 1, 6, 13 and 14 of ONR 2022).  Coastal erosion will continue to remain a subject of focus through our routine, ongoing, regulatory interaction.

We expect to agree Relevant Good Practice with the dutyholder in relation to coastal erosion analysis and expect related risks, e.g. flooding, to be reduced as low as reasonably practical (see ONR Safety Assessment Principle EHA.12, and related narrative).  We anticipate this will be evident within future safety case reports. (see ONR 2022 and 2024).

Under Part 3 of your request, we can confirm that through its RITE policy, ONR engages with SZC on a frequent basis to discuss management of risks arising across a series of technical areas. Previous ONR assessment reports have identified the need to define “trigger points” to ensure adequate measures to reduce risk ALARP are in place, in sufficient time prior to the impact of significant climate change effects such as the effects of long-term erosion (Platform Observation 14).  ONR will continue to engage with SZC in relation to risks arising from erosion and flooding, as the analysis develops in support of safety demonstrations such as the pre-construction and pre-commissioning safety reports (PCSR).

We confirm that under s.1 of the FOIA, we hold some the document described in Part 4 of your request. We are releasing the version of the Sizewell C Site Data Summary Report (SDSR) we hold with redactions, as set out below, and this is attached to this response.

Exemptions applied

• S.24, Safeguarding national security
• S.40, Personal information
• S.41, Information provided in confidence
• S.43, Commercial interests

Further guidance on these can be found on the ICO website.

Absolute exemptions

Section 41 FOIA – Information provided in confidence

S.41 sets out an exemption from the right to know where the information was provided to the public authority in confidence. This applies to information which was obtained by ONR from any other person, and its disclosure would constitute a breach of confidence, or a legal person could bring a court action for that breach of confidence and that court action would be likely to succeed.

We consider that information in relation to the potential commercial operation of SZC which is not in the public domain has the necessary quality of confidence and given to ONR in circumstances imparting an obligation of confidence.

In addition, we consider that disclosure of this type of information has the potential to be harmful to EDF and SZC’s commercial interests and therefore should not be disclosed.

This includes information in relation to seismic spectra frequencies which no longer represents the seismic design basis being adopted at SZC, based on recent agreements with ONR. As work is still ongoing to fully converge between SZC and ONR, this particular information is incomplete, and it would therefore provide an erroneous picture to anyone receiving the information.

This is an absolute exemption and so does not require the public interest test.

Section 40 FOIA – Personal information

We have also removed some information from the SDSR as it is personal data. This consists of names and job titles. Release of each of this type of information could identify the individual either directly or indirectly. The personal data has been withheld using the exemption S.40(2) of the FOIA.

Release of the information would breach principle (a) of GDPR (lawfulness, fairness and transparency) on the grounds that there is no lawful basis to process this data. In addition, releasing this personal data would also breach principle (b) of GDPR (purpose limitation) as the data was provided for the purposes of document control.

Qualified exemptions

In our previous correspondence to you, dated 19 December 2025, we set out that we were considering the Public Interest Test in relation to the following qualified exemptions:

• S.24, Safeguarding national security
• S.43, Commercial interests

Section 24 FOIA – Safeguarding national security

S.24 sets out the exemption from the right to know where the information requested is required for the purposes of safeguarding national security. It works to protect national security, which includes protection of potential targets. It allows a public authority not to disclose information if it considers releasing the information would make the UK or its citizens more vulnerable to a national security threat.

Section 43 FOIA – Commercial interests

S.43(2) exempts information where disclosure would, or would be likely to, prejudice the commercial interests of any person (an individual, a company, the public authority itself or any other legal entity).

As these are qualified exemptions, we are required to balance the public interest between disclosure and non-disclosure. We have therefore applied the Public Interest Test, as set out below.

Public Interest Test

Factors for disclosure (s.24 and s.43)

• We are committed to being an open and transparent regulator. We will use openness and transparency to achieve our objective of developing and maintaining stakeholder trust in ONR as an effective independent regulator;
• Issues related to the nuclear industry are subject to close scrutiny and debate, there is a public interest in information related to nuclear activities and the release of such information. The information may provide reassurance to the public about the safety of nuclear sites; and,
• e recognise that there is considerable public interest relating to the location suitability of a proposed new nuclear site and how site-specific external hazards are considered in site suitability. This is particularly significant in the context of increasing public discourse and focus on climate change and its impact on weather patterns, flooding risks, and the environment.

Factors against disclosure (s.24 – Safeguarding national security)

• Information that relates to the purposes of safeguarding national security and which may be of use to terrorists and other hostile actors is exempt from disclosure. Disclosure of the locations of key nuclear safety important facilities, and descriptions of building locations and activities could provide an adversary with information that enables them to develop intelligence which may help in the planning of malicious attacks and help them defeat security arrangements;
• Disclosure of information relating to the emergency preparedness and arrangements at nuclear sites, in conjunction with providing details of proposed key specific building locations at SZC, would not be in the public interest as this would reveal where personnel would be physically placed in the event of an emergency taking place at the site. Releasing this information into the public domain may assist hostile or malicious actors assist in carrying out threats or attacks against ONR’s dutyholders and the nuclear industry;
• Similarly, releasing information regarding turbine missile risks is strongly not in the public interest as this could disclose security vulnerabilities for both Sizewell B and SZC. This information shows areas that are potentially vulnerable to an impact from a missile and would be of particular use to an insider threat;
• Paragraph 13 of s.24(1) makes it clear that there need be no evidence that an attack is imminent for this exemption to be applied; and,
• Adversaries or hostile actors can be highly motivated and may go to great lengths to gather separate pieces of intelligence to attempt to expose vulnerabilities.

Conclusion

After careful consideration of the factors set out above, we have concluded that the specific information relating to locations and descriptions of building locations and activities, emergency preparedness and arrangements, and turbine missile strike risks should be withheld. There is a strong public interest in safeguarding national security. The interests of national security should be given significant weight in the above factors against disclosure and outweigh the need for openness in terms of these specific types of information.

Factors against disclosure (s.43(2) – Prejudice to commercial interests)

• Disclosure of information relating to reactor trip frequencies would prejudice EDF and SZC’s commercial interests. This information pertains to commercial output and the potential commercial operation of SZC which is not in the public domain. Releasing this commercially sensitive information could therefore impact upon the commercial case for the site; and,
• Information relating to extreme high sea temperatures and extreme high air temperatures should not be disclosed as these parameters could impact how SZC operates the site in the future and potentially affect plant output. In addition, this information is still the subject of ongoing research. If taken out of context release of this information could damage business confidence and thereby cause prejudice to EDF and SZC’s commercial interests.

Conclusion

There is a strong public interest in protecting the commercial interests of individual companies and organisations, and ensuring they are able to compete in the market fairly. In addition, some of the information described was provided in confidence to ONR. As a result it is in the public interest to withhold the information related to reactor trip frequencies, extreme high sea temperatures and extreme high air temperatures on the basis that publication of that information would be likely to prejudice the possible future commercial operations and commercial case for SZC.

Overall conclusion on the SDSR

We recognise there is significant public interest in providing information that would enable further understanding of the underpinning arguments and evidence regarding the justification of site suitability of the proposed SZC site. As part of the Nuclear Site Licence (NSL) application, it must be shown that the proposed site represents a suitable location from a nuclear safety point of view. The SDSR has been produced at an appropriate and proportionate depth to demonstrate this at the NSL application stage. Based on our assessment of the factors set out above, we have concluded that it is in the public interest to disclose the version of the SDSR we hold, with the caveat this is subject to the limited types of information relating to safeguarding national security, commercial interests, provided in confidence, and personal data being redacted.

Exemptions applied

s.24, s.40, s.41, s43

Public Interest Test (PIT)

Yes, included above.