Executive summary
Date(s) of inspection
- November 2025
Aim of inspection
The aim of this reactive inspection was to inspect and gain assurance on the adequacy of arrangements for the installation of primary circuit components into the Unit 1 and Unit 2 reactor buildings at the HPC site, with a particular focus on installation of the Pressuriser into Unit 1 HR. This was to provide confidence that learning from previous events during installation of the steam generators had been captured and acted upon to prevent further events from occurring.
Subject(s) of inspection
- CDM 15 - Rating: GREEN
- LC19 - Construction or installation of new plant - Rating: GREEN
Key findings, inspector's opinions and reasons for judgement made
This was a reactive inspection to enable ONR to gain confidence that there were adequate arrangements in place to install the Unit 1 Pressuriser and that these arrangements were also adequate for the installation of future primary circuit and other large nuclear safety significant plant and equipment.
There have been three incidents during installation activities that have resulted in damage to primary circuit components. Whilst this damage has been repaired, the inspection considered the adequacy of NNB GenCo (HPC) Ltd (NNB's) investigations into these incidents, to assess whether arrangements for the Pressuriser installation have been amended to reflect the lessons learned.
The inspection included a series of presentations from NNB and its Tier 1 installation contractor Framatome, together with a site visit to the location where the Pressuriser will be installed. A number of documents detailing the arrangements for Pressuriser installation were provided and these were discussed during two subsequent meetings.
My inspection found that, in relation to the sample undertaken, NNB has carried out adequate investigations into the first two incidents, the investigation for the third incident being ongoing. I judged that the investigations have identified suitable action plans and that these actions are being progressed. Framatome has produced an adequate improvement plan and this is subject to surveillance and oversight by NNB using a quality plan. I acknowledged that in some areas, such as improving the use of human performance tools, the embedding of learning will take time and will extend beyond Pressuriser installation.
I gained assurance that NNB has adequate arrangements for the installation of the Pressuriser and that improvements are planned to provide an enhanced level of assurance for the installation of further primary circuit components into Unit 1 and Unit 2 reactor buildings.
Regarding the specific arrangements for Pressuriser installation, I gave advice and guidance that the arrangement of documents was overly complex and that it was challenging to establish the key points of the lift plan for ease of briefing to site personnel undertaking the task. Although I received adequate assurance that this activity will be subject to enhanced oversight and supervision by both Framatome and NNB, arrangements for future installation of key items should be reviewed to see if they can be simplified. No regulatory issue was raised, however ONR may choose to sample arrangements for future installation activities to gain assurance that improvement plans have been fully implemented and learning has been embedded.
Conclusion
Following my inspection, I have made the following judgements:
- I considered the investigations carried out into the incidents involving the MCP3 Casing (INF-4924) and Steam Generator 3 (INF-5448) to be adequate, with appropriate action plans.
- The investigation into the incident involving Steam Generator 2 (INF-5642) is ongoing, however I judged that some common learning has been made available and has been taken into account in the development of a Framatome Improvement plan.
- I judged that the Framatome Improvement Plan has used the learning from the three incidents to develop appropriate time-bound actions and is adequate.
NNB has considered, within the actions arising out of the investigations, where it can make its own improvements. A quality plan has been developed specifically to enhance oversight of Framatome primary circuit installation activities, and I judge it to adequately identify appropriate areas of focus. For other key installation activities involving other contractors, NNB is going to implement a HAZOP type approach to identify the most sensitive activities where enhanced NNB oversight will be required. Overall, I judge that NNB has taken into account the lessons learned from these incidents and is enhancing its governance and oversight arrangements to mitigate the risk of a repeat event.
With respect to the readiness for Pressuriser installation, I judged that the documentation supporting the safe execution of the installation was unduly complex, partly generic and contained in multiple documents. I considered that there was too much reliance placed on the pre-job brief to address any gaps in the documentation.
The following items require follow-up by ONR with NNB. This will be done during future planned engagements:
There is a significant training programme proposed to improve the use of human performance tools in the Framatome team. This will take time to embed and ONR should assess its effectiveness at a future inspection.
For future installation of components important to safety, ONR should consider inspecting arrangements to judge whether improvements have been made to simplify the lift plan so that there is an appropriate focus on command and control, critical activities and key risks.
Although there were some deficiencies in compliance arrangements, in particular the overall coherence of the lift plan, I have rated this inspection GREEN in accordance with NS-INSP-GD-064, because relevant good practice was generally met and suitably enhanced oversight and supervision is proposed for the Pressuriser installation.