Office for Nuclear Regulation

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Systems Based Inspection (SBI) 09 - Transformers, grid systems and main electrical systems

Executive summary

Purpose of Intervention

The primary focus of this intervention was a planned system based inspection (SBI) of EDF Energy Nuclear Generation Ltd (EDF NGL) Hunterston B (HNB) power station transformers, grid systems and main electrical systems, which was undertaken as part of the planned intervention strategy for the Operating Facilities Division (OFD) of the Office for Nuclear Regulation (ONR).

The work was carried out by an ONR Electrical Inspector and an ONR Control and Instrumentation (C&I) Inspector, and in line with the planned inspection programme contained in the HNB Integrated Intervention Strategy (IIS).

Interventions Carried Out by ONR

During this intervention we performed a SBI of the transformers, grid systems and main electrical systems to establish whether they are able to adequately fulfil their safety functional requirements in line with the safety case; the overall safety requirement of which is to ensure that electrical power is distributed to safety systems and plant (e.g. gas circulators and reactor cooling water pumps) under normal and abnormal operating conditions. The main items of equipment that contribute to this safety requirement are:

A sampled based examination of the aforementioned was performed against the following Licence Conditions (LC), which are applicable provisions of the Energy Act 2013:

In addition we undertook a progress review of ONR regulatory issue (RI) 4349, which covers a number of EDF NGL HNB periodic safety review (PSR) 3 electrical related action requests (AR).

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

Not applicable.

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

The key findings of our SBI of the transformers, grid systems and main electrical systems are:

In relation to ONR RI 4349, we were satisfied that the associated ARs have been adequately addressed. RI 4349 will be updated to reflect this progress.

Conclusion of Intervention

From the evidence sampled during this SBI against LCs 10, 23, 24, 27 and 28, we judged that the transformers, grid systems and main electrical systems fulfil their associated safety case requirements and are adequate.

We consider that the action requests raised as part of ONR’s assessment of the HNB periodic safety review (PSR) 3 have been adequately addressed. RI 4349 will be updated to reflect this progress.

There are no findings from this intervention that could significantly undermine nuclear safety at HNB. At present, no additional regulatory action is needed over and above the planned interventions at HNB power station, as set out in the HNB IIS, which will continue as planned.