In February 2025, the UK Office for Nuclear Regulation (ONR) carried out an inspection relating to tanks and vessels manufactured by Groupe ADF for Hinkley Point C (HPC). The inspection was triggered by previous operating experience where quality issues had been identified in welding and radiography.

The tanks and vessels were considered important to nuclear safety. Therefore, ONR’s concern was not only whether the completed items appeared visually acceptable, but whether the welding and inspection activities had been properly controlled, reviewed, documented and accepted by competent personnel.

From a welding engineering perspective, the issue was not simply one isolated weld defect. The findings pointed to weaknesses in the wider welding quality assurance system, including welding procedure control, welding inspection competence, consumable control, radiography of weld repairs and licensee oversight.

Why Welding Control Matters in Nuclear Fabrication

In nuclear and other safety-significant industries, weld quality is not proven only by final visual inspection or by the presence of an NDT report. It must be demonstrated through a traceable chain of control from design, procedure qualification and production welding through to inspection, repair, documentation and final acceptance.

For tanks and vessels, welded joints such as shell seams, nozzle welds and attachment welds can be critical to pressure boundary integrity, containment, leak-tightness and long-term structural performance. If welding activities are not properly controlled, the risk is not limited to visible weld defects. It can also include hidden flaws, incomplete repairs, poor traceability, unsuitable inspection coverage and weak technical justification for acceptance.

Key Welding-Related Findings from the ONR Inspection

1. Consequences of Nozzle Weld Failure Were Not Substantiated

One important finding was that the licensee and responsible designer could not substantiate the consequences of nozzle weld failure.

This is significant because nozzle welds can be critical areas in tanks and vessels. They often introduce stress concentration, geometric discontinuity and possible leakage paths. If the consequence of nozzle weld failure is not clearly understood, it becomes difficult to justify the required level of inspection, NDT coverage, acceptance criteria and repair control.

In high-integrity fabrication, the consequence of weld failure should influence the inspection strategy. For example, a safety-significant nozzle weld may require enhanced NDT, additional review, stricter hold points and clearer repair acceptance requirements.

2. WPS and PQR Review by Competent Personnel Was Not Demonstrated

Another key welding-related issue was that ADF welding procedures had not been demonstrably reviewed and accepted by suitably qualified and experienced persons on behalf of the licensee.

In safety-significant fabrication, it is not enough for a Welding Procedure Specification (WPS) and Procedure Qualification Record (PQR) to exist. The project must also show that the WPS and PQR were technically reviewed, accepted and authorised by competent welding personnel acting for the licensee.

This is an important point for welding engineers and QA/QC professionals. A WPS controls essential production welding variables such as process, filler metal, preheat, interpass temperature, heat input, shielding gas, joint preparation and welding position. If the WPS has not been properly reviewed against the project requirements, the welding work may proceed without adequate technical assurance.

3. Welding Inspector Qualification Requirements Were Not Specified

ONR also identified that welding inspector qualification requirements had not been specified.

This means there was insufficient clarity on what level of certification, experience and authorisation was required for personnel inspecting the welds. In high-integrity fabrication, welding inspection sign-off must be performed by personnel who are demonstrably competent for the specific welding activity, material, product form and inspection duty.

For example, it should be clear whether the welding inspector requires CSWIP, PCN, ISO 9712, EN ISO 14731-related welding coordination competence, or other project-recognised qualifications and experience. The important point is that competence must be defined before the work is performed, not assumed after inspection records have been signed.

4. Welding Inspection Surveillance Checks Were Not Specified

A further concern was that surveillance checks for welding inspection were not specified.

This suggests weakness in the Inspection and Test Plan (ITP) or surveillance arrangements. For safety-related tanks and vessels, the ITP should define the welding inspection stages, hold points, witness points, acceptance criteria and records required before work can proceed.

Typical welding surveillance points may include:

• material identification and traceability before fabrication;
• joint preparation and fit-up before welding;
• confirmation of approved WPS before welding starts;
• welder qualification verification;
• preheat and interpass temperature checks;
• welding consumable issue and batch traceability;
• in-process welding surveillance;
• visual inspection after welding;
• NDT completion and acceptance;
• repair approval and re-examination;
• final documentation review before release.

Where these surveillance checks are not specified, there is a risk that welding activities may be accepted without adequate evidence that the required controls were applied.

5. Welding Consumable Control Was Inadequate

The report also identified lack of welding consumable control at ADF.

This is a fundamental welding quality issue. Welding consumables must be controlled from receipt through storage, baking, issue, use and traceability to the specific weld. Poor consumable control can affect weld integrity, mechanical properties, hydrogen control and compliance with the qualified welding procedure.

For controlled fabrication, a welding consumable management system should include:

• consumable receipt inspection;
• batch and heat number traceability;
• storage temperature and humidity control;
• baking and holding oven records where required;
• issue logs linked to welder and weld number;
• return and re-drying rules;
• segregation of damaged, expired or uncontrolled consumables.

If consumables are not properly controlled, it becomes difficult to prove that the weld was made using the correct filler material under the conditions required by the approved WPS.

6. Radiography Shortfalls Were Identified for Weld Repairs

Radiography was another area of concern, particularly in relation to weld repairs.

Repaired welds require strong control because the repair process can introduce new defects or leave original defects insufficiently removed. The radiographic examination of weld repairs must therefore be clearly specified, properly performed, reviewed by competent personnel and traceable to the repaired weld area.

For weld repairs, the quality system should define:

• how the defect is excavated and verified before repair welding;
• which repair WPS is applicable;
• who approves the repair;
• what NDT method is required after repair;
• the required extent of re-examination;
• how radiographs are reviewed and accepted;
• how the repair history is recorded in the weld dossier.

Without this level of control, there is a risk that repaired welds may be accepted without adequate evidence that the defect was fully removed and the repair weld is acceptable.

7. Radiograph Delivery Timeframe to HPC Was Not Specified

ONR also noted that the timeframe for radiographs to be sent to Hinkley Point C had not been specified.

Although this may appear administrative, it has technical importance. Without timely delivery of radiographs, the licensee may not be able to review, accept, challenge or trend NDT evidence before later manufacturing or installation activities continue.

For safety-significant fabrication, radiographic records are not just paperwork. They are part of the weld acceptance evidence. Late delivery can weaken oversight, delay technical review and reduce the opportunity to identify repeated defects or repair trends early.

The Main Welding Quality Lesson

The main lesson from the Hinkley Point C ADF tanks and vessels inspection is that weld quality must be demonstrated through a complete and traceable system of control.

That system should include:

• approved WPS and PQR records;
• competent welders, welding inspectors and NDT personnel;
• defined welding inspection hold and witness points;
• controlled welding consumables;
• clear repair welding procedures;
• complete radiographic and NDT records;
• timely review of inspection evidence;
• effective licensee oversight of supplier welding activities.

Overall, the welding-related findings show that the issue was not simply weld appearance or individual radiographic quality. The deeper concern was whether the complete welding quality chain was under control.

For welding and fabrication professionals, the key lesson is clear: in nuclear and other safety-significant projects, weld quality is not proven only by final inspection. It is proven by a traceable system of control from procedure qualification, through production welding, inspection, NDT, repair, documentation and final acceptance.

This article discusses the February 2025 ONR inspection findings for Hinkley Point C ADF tanks and vessels. It should be read as a welding quality assurance case study, not as a statement on the current status of the project.

Common Questions on the ONR Welding Findings: Welding Quality Issues Identified in the HPC ADF Tanks and Vessels Inspection

1. What was the Hinkley Point C ADF tanks and vessels inspection about?

The inspection was carried out by the UK Office for Nuclear Regulation in February 2025. It focused on tanks and vessels manufactured by Groupe ADF for Hinkley Point C. The inspection was triggered by previous operating experience where quality issues had been identified in welding and radiography.

2. Why were the ADF tanks and vessels important?

The tanks and vessels were considered important to nuclear safety. This meant ONR needed confidence that the items were structurally sound and that welding, inspection, radiography, documentation and oversight had been properly controlled.

3. What were the main welding quality issues identified?

The main welding-related issues included weaknesses in nozzle weld consequence assessment, WPS and PQR review, welding inspector qualification requirements, welding inspection surveillance, consumable control, radiography of weld repairs, radiograph delivery timing and licensee oversight.

4. Did ONR identify one specific weld defect?

The concern was broader than a single weld defect. ONR’s findings pointed to weaknesses in the overall welding quality assurance system. The issue was whether the complete welding quality chain was properly controlled and evidenced.

5. Why was nozzle weld failure considered important?

Nozzle welds can be critical areas in tanks and vessels because they may involve stress concentration, geometric discontinuity and potential leakage paths. If the consequence of nozzle weld failure is not understood, it becomes difficult to justify the required inspection level, NDT coverage, acceptance criteria and repair control.

6. What is the importance of WPS and PQR review?

A Welding Procedure Specification and Procedure Qualification Record are central to welding control. However, for safety-significant fabrication, it is not enough for these documents to exist. They must also be reviewed and accepted by suitably qualified and experienced personnel acting on behalf of the licensee.

7. Why does welding inspector competence matter?

Welding inspection sign-off is only reliable if the inspector is competent and authorised for the specific work being inspected. ONR identified that welding inspector qualification requirements had not been specified, which created uncertainty over the basis for inspection acceptance.

8. What does welding inspection surveillance mean?

Welding inspection surveillance means planned checks during fabrication to confirm that welding activities are being carried out correctly. This may include checks on material traceability, fit-up, WPS use, welder qualification, consumables, welding parameters, visual inspection, NDT and repair control.

9. Why is welding consumable control important?

Welding consumables can directly affect weld quality, mechanical properties, hydrogen control and compliance with the approved welding procedure. If consumables are not properly controlled and traceable, it becomes difficult to prove that the correct filler material was used under the required conditions.

10. Why were radiography and weld repairs a concern?

Weld repairs require strong control because repair welding can introduce new defects or leave original defects insufficiently removed. Radiography of repaired welds must therefore be properly specified, performed, reviewed and linked to the repaired weld area.

11. Why does radiograph delivery time matter?

Radiographs form part of the weld acceptance evidence. If the timeframe for sending radiographs to Hinkley Point C is not specified, the licensee may not be able to review, accept, challenge or trend NDT evidence before later manufacturing or installation activities continue.

12. What role does the licensee play?

The licensee is the organisation legally responsible for nuclear site safety. For Hinkley Point C, the licensee is NNB Generation Company (HPC) Ltd. Even where fabrication is performed by suppliers such as Groupe ADF, the licensee remains responsible for ensuring adequate control, oversight and acceptance of work that may affect nuclear safety.

13. How does EDF relate to the licensee?

Hinkley Point C is an EDF-led nuclear new-build project. The formal nuclear site licence holder is NNB Generation Company (HPC) Ltd, EDF’s Hinkley Point C project company. ONR therefore refers to NNB GenCo as the licensee in its regulatory inspection reports.

14. What rating did ONR give the inspection?

ONR rated both LC12, relating to suitably qualified and experienced persons, and LC19, relating to construction or installation control, as Amber. This reflected significant shortfalls requiring improvement.

15. What is the main welding lesson from this inspection?

The main lesson is that weld quality in nuclear and other safety-significant fabrication is not proven only by final inspection or by the existence of an NDT report. It must be demonstrated through a traceable system covering procedure qualification, production welding, inspection, consumable control, NDT, repair, documentation and oversight.

16. Is this article a statement on the current status of the project?

No. This article discusses the February 2025 ONR inspection findings as a welding quality assurance case study. It should not be read as a statement on the current status of Hinkley Point C or Groupe ADF’s present arrangements.