Office for Nuclear Regulation

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Wood Group (Birchwood) - NNB Generation Company (HPC) Ltd LC17 inspection

Executive summary

Purpose of Intervention

The purpose of the intervention was to form a judgment on the adequacy of the fracture toughness testing (FTT), analysis and recommendations in advance of the final Fracture Mechanic Assessments (FMAs) of the Hinkley Point C pressure circuits and welds, and to provide assurance that the fracture toughness recommendations that the licensee uses in its assessments are soundly based.

Interventions carried out by ONR

The Office for Nuclear Regulation (ONR) carried out a one day inspection at Wood Group Birchwood facility through observation of fracture toughness testing activities and discussions with relevant NNB Generation Company (HPC) Limited (NNB GenCo), Framatome and Wood personnel.

The intervention is relevant to Licence Condition (LC) 17 which requires the licensee to make and implement adequate quality management arrangements in respect of all matters which may affect safety.

The intervention covered the following topics relating to fracture toughness testing:

Explanation of judgment if safety system not judged to be adequate

Not applicable; this was not a system-based inspection.

Key findings, inspector's opinions and reasons for judgments made

The licensee and Wood Group presented their approach to specimen tracking. Wood Group appeared to have adequate control over specimen tracking, and the licensee appeared to have adequate control and oversight of Wood Group's process for specimen tracking. Following the observation, I am content that Wood Group is competent and capable of performing adequate fracture toughness testing. 

The licensee had not taken into consideration the minimum and maximum heat inputs permitted by the welding procedure when producing welded mock-ups for fracture toughness testing. Therefore, in my opinion, the specimens produced to date do not appear to be sufficiently representative. An action has been placed on the licensee to resolve this finding which will be monitored via a Regulatory Issue.

The licensee had not taken into consideration repeat repairs to High Integrity Component (HIC) welds. Therefore, the licensee’s FTT strategy and programme does not appear to be sufficiently representative.  An action has been placed on the licensee to resolve this finding which will be monitored via a Regulatory Issue.

The surveillance arrangements in place for FTT appeared to be adequate, and I am content that the licensee has adequate oversight of the FTT programme.

Conclusion of Intervention

I am content that the licensee has adequate control and oversight of Wood Group's process for specimen tracking. I am also content that the licensee has adequate arrangements in place for surveillance of fracture toughness testing.

However, the licensee’s fracture toughness testing programme does not provide confidence that adequate fracture toughness will be achieved for HIC welds which have been produced at minimum and maximum heat inputs permitted by the welding procedure, nor does it provide confidence that adequate fracture toughness will be achieved for repeat repairs to HIC welds. Therefore, an inspection rating of AMBER is appropriate for LC 17 (implementation of adequate quality management arrangements).