Office for Nuclear Regulation

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Hinkley Point B – SBI09 Electrical Systems

Executive summary

Purpose of Intervention

The purpose of this intervention was to undertake a system based inspection (SBI) of EDF Energy Nuclear Generation Ltd.’s (NGL’s) Hinkley Point B Power Station specifically the transformers, grid systems, and main electrical system. This was undertaken as part of the planned intervention strategy for the Operating Facilities Division (OFD) of the Office for Nuclear Regulation (ONR).

The intervention was carried out by an electrical specialist inspector supported by the outgoing and incoming nominated site inspectors.

Interventions Carried Out by ONR

We performed a safety case informed SBI of the transformers, grid systems, and main electrical system to judge the systems’ performance against its safety function. The functions of these systems are to provide the infrastructure for electricity export to the national electrical transmission grid and for electrical supplies to the entire site. At Hinkley Point B this is achieved through the 400kV and the 275kV systems. Electricity from the station’s generator transformers is exported to national electrical transmission grid at 400kV whilst the units are at power. The 400kV system also provides electrical supplies at voltages at and below 11kV, for appropriate distribution around the site to plant and equipment which are required to be resilient to a fault on the national electrical transmission grid. The 275kV system is the means, by which electricity is imported, from the national electricity transmission grid, for the purposes of providing electrical supplies at voltages at and below 11kV, for appropriate distribution around the site to plant and equipment that do not require to be resilient to a fault on the national electrical transmission grid. The 400KV and 275kV systems are not interconnected at the highest voltage levels. Through examination of these systems, compliance inspections were performed against the following Licence Conditions (LC) which are provisions of the Energy Act 2013:

The inspections were based on sampling the implementation of the licensee’s arrangements at Hinkley Point B against the LCs. The objective of the inspection was to determine whether the licensee’s arrangements were adequately implemented and in accordance with the systems’ safety case requirements.

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

During this intervention, the following key activities were also undertaken:

Explanation of Judgement if Safety System Not Judged to be Adequate

From the inspection, we judged that the implementation of the arrangements for the transformers, grid systems, and main electrical system met the requirements of the safety case and was adequate.

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

During the course of this SBI, it was found that Hinkley Point B has arrangements to ensure that the transformers, grid systems, and main electrical system is inspected, maintained and, as necessary, operated in accordance with the safety case. The arrangements examined complied with the licensee’s legal duties on the areas sampled during the inspection. The inspection identified a number of areas for potential improvement, and although none gave rise to significant concern, the station has agreed to take action to address them. These observations were minor in nature and none were judged to be compliance issues, hence no regulatory follow-up is considered necessary.

In summary, the SBI of transformers, grid systems, and main electrical system, inspected for LCs 10, 23, 24, 27, and 28, is rated as green on the basis that relevant good practice was met and any identified deficiencies in compliance arrangements were of minor significance. No intervention rating has been assigned to LC 34 as this LC was not deemed applicable to this SBI.

Conclusion of Intervention

From the evidence sampled during this SBI 09 inspection against LCs 10, 23, 24, 27, and 28, we consider that the implementation of the arrangements for the transformers, grid systems, and main electrical system met the requirements of the safety case.

The electrical specialist Inspector followed up a regulatory issue associated with the electrical systems arising from the last periodic safety review. Based on discussions with the licensee staff, the inspector was satisfied that adequate progress was being made and no additional regulatory action was necessary.

 A number of familiarisation sessions (para. 6) were undertaken in support of the handover of the ONR site inspection duties during the intervention. Based on attendance at the HESAC, and engagements with the safety representatives, emergency planning engineer and regulatory issues follow-up the incoming nominated site inspector was satisfied that the site based handover had been satisfactorily completed.

There are no findings from this inspection that could significantly undermine nuclear safety.  At present, no additional regulatory action is needed over and above the planned interventions at Hinkley Point B  Power Station as set out in the Integrated Intervention Strategy, which will continue as planned.