Executive summary
Date(s) of inspection:
March 2025
Aim of inspection
Licence Condition (LC) compliance inspections are an essential element of ONR's intervention strategy on any nuclear site and consist of a series of inspections, each of which is intended to establish whether NNB Generation Company (HPC) Ltd and it’s supporting services (hereafter referred to as the licensee), have adequate arrangements in place, and are adequately implementing these arrangements, for compliance with a specific LC.
LC19 requires that: ‘Where the licensee proposes to construct or install any new plant which may affect safety the licensee shall make and implement adequate arrangements to control the construction or installation.’
Site welding of the HPC primary circuit entails connecting the main coolant line (MCL) pipework to the primary circuit vessels (reactor pressure vessel, steam generators and main coolant pumps). The licensee has classed most of the primary circuit as high integrity which requires a high level of demonstration of structural reliability and commensurate attention to quality.
Therefore, the aim of this inspection was to gain assurance that the licensee is adequately implementing its arrangements for compliance with LC19, in relation to high integrity component (HIC) welding of the MCL onsite at HPC.
The inspection was carried out over one day at HPC site. The licensee provided an agenda prior to the intervention (WIRED: ONRW-932509302-19281).
Subject(s) of inspection
- LC19 - Construction or installation of new plant - Rating: Green
Key findings, inspector's opinions and reasons for judgement made
This inspection was undertaken as part of a series of planned interventions in accordance with the Hinkley Point C (HPC) Intervention Strategy for 2024/2025.
During my inspection, I sampled non-destructive testing (NDT) and Destructive testing results, the applicable follow-up document (FUD), including a sample check of associated weld records, and implementation the licensee’s arrangements in relation to the welding consumables store used for MCL welding. I sampled welding procedure specification compliance and care and maintenance of the MCL in the HR building. I also sampled the welder’s and NDT inspectors qualifications and observed MCL welding, including a visual inspection of deposited weld.
At the time of this intervention, welding of Loop 3 welds C1 and C2 were ongoing. These are the first HIC welds onsite. Welding commenced on 24 March 2025.
I am satisfied that the licensee’s LC19 arrangements, and implementation of those arrangements, in relation to joint preparation weld repairs are adequate from a Structural Integrity perspective.
I was able to see that the welding parameters complied with the applicable welding procedure, and that the welding procedure was adequate. I noted that the MCL appeared to be adequately wrapped which gave me confidence from a care and maintenance perspective.
I noted that temperature and humidity readings in the consumable store had been checked and were compliant with the welding consumable control procedure, and that the procedure was adequate. I could see that the consumable had been logged out and that the batch had been approved.
I provided regulatory advise that future welding production tests should be sufficiently representative of any access restrictions the welders may encounter during site welding.
Conclusion
At the time of my intervention, and from the information I have sampled, I am content that the licensee has adequate LC19 arrangements in place for HIC welding and NDT of the MCL at HPC site, and that these arrangements are being adequately implemented.
I have identified some minor shortfalls in relation to charpy impact testing temperature, surveillance barriers and surveillance inspector access which I will address via Level 4 Regulatory Issue RI-12523. I will also monitor NDT results via this regulatory issue.
Overall, I consider that, in accordance with ONR guidance on the application of inspection ratings, a GREEN rating is appropriate for this inspection.