Office for Nuclear Regulation

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Hunterston B Planned Intervention

Executive summary

Purpose of intervention

This was a planned inspection of EDF Energy Nuclear Generation Ltd’s (NGL’s) Hunterston B power station, undertaken as part of the planned intervention strategy for the Civil Nuclear Reactor Programme (CNRP) of the Office for Nuclear Regulation (ONR).

The work was carried out in line with the planned inspection programme contained in the Hunterston B Integrated Intervention Strategy (IIS).

Interventions Carried Out by ONR

The nominated site inspector for Hunterston B and I (Specialist Electrical Inspector) carried out a System Based Inspection (SBI) of the turbine over speed protection system and the Back-Up Cooling System (BUCS).

The intervention was performed in line with ONR’s guidance requirements (as described in our technical inspection guides) in the areas inspected.

Explanation of Judgement if Safety System Not Judged to be Adequate

The turbine over speed protection system and Back-up Cooling System (BUCS) were judged to meet the requirements of the safety case and were adequate.

Key Findings, Inspector's Opinions and Reasons for Judgements Made

The ONR team carried out a system based inspection of the turbine over speed protection system and the BUCS  and concluded that:

LC10 (training) – IIS Rating 3 (adequate).  We were satisfied that training and development of staff was effectively controlled and that operations were overseen by suitably qualified and experienced person and that there are arrangements in place for succession planning.

LC23 (operating rules) – IIS Rating 3 (adequate).  Station were unable to immediately demonstrate the provenance of key safety case limits and conditions associated with plant’s installed turbines, although an adequate audit trail was demonstrated through existing company technical standards.  The recently installed BUCS was described and we were satisfied that safety case limits and conditions were consistent within the underlying safety case and the safety functional requirements document. We were further satisfied that the operating rules had been duly updated to reflect changes to the plant. We provided advice to Hunterston B in improving the visibility of the turbine overspeed safety case, consistent with observations made across other stations.

LC24 (operating instructions) – IIS Rating 3 (adequate).  We were satisfied that adequate operating instructions were in place to support plant operations and that these were to the required format and suitably illustrated.

LC27 (safety mechanisms, devices and circuits (SMDC)) – IIS Rating 4 (below standard).  For the turbine overspeed protection system we found that fundamental requirements were met but examples were seen of failure to follow procedures in the reporting of plant condition, leading to unreported physical degradation of SMDCs related to turbine overspeed protection being identified during the inspection. We were satisfied that the BUCS system was regarded as SMDC and was being managed accordingly.

LC28 (examination, maintenance, inspection and testing) – IIS Rating 4 (below standard).  Shortcomings found during the inspection and examination of SMDC were observed on elements of the turbine overspeed protection systems of both turbines.  It was not apparent that the site was aware of these before the inspection, but immediate actions were taken to begin repairs in light of our observations.  Two ONR Issues have been raised against which regulatory follow-up will be ensured.

Conclusion of Intervention

In order to inform our judgement we have considered the evidence observed in relation to good practices and areas where we consider there to be minor shortfalls in compliance.  To conclude, based upon balance of evidence presented by NGL during this inspection, we consider that the requirements of the safety case have been adequately implemented at Hunterston B.

There are no findings from this inspection that could significantly undermine nuclear safety.