Office for Nuclear Regulation

Heysham 1 - Transformers, Grid Systems, and Main Electrical System (SBI 09)

Executive summary

Purpose of Intervention

The purpose of this intervention was to conduct a system based inspection (SBI) of EDF Energy Nuclear Generation Ltd.’s (NGL’s) Heysham A 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 nominated site inspector and a control and instrumentation associate inspector.

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 power for export to the national electricity transmission grid and to provide power supplies to the entire site. At Heysham A this is achieved through the 23kV system where electricity from the turbo generators is transformed up to 400kV for export to grid through a distribution network. The 23kV is also transformed down to a number of voltages levels at and below 11kV, for appropriate distribution around the site. Whilst the reactor is off load these systems provide the sole means for importing electricity from the national electricity transmission grid. In the event of a fault on the national electricity transmission grid, these systems provide the means for the appropriate distribution of electricity from the site’s emergency generation systems. 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 Heysham A 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 transformers, grid systems, and main electrical system met the requirements of the safety case and was adequate. We did, however, consider a LC28 shortfall against the technical specifications relating to an incorrectly completed maintenance instruction. We considered this deficiency to be minor and did not judge it to significantly affect the ability of the transformers, grid systems, and main electrical system met the requirements of the safety case.

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

In general, during the course of this SBI, it was found that Heysham A 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.

We did observe, however, an error in a LC28 related maintenance instruction which had the potential to cause noncompliance with Heysham A’s written arrangements. The licensee subsequently advised us that the component was appropriate, suitable and available for service. We requested that the licensee review the extent of condition of other similar components to ensure that they were appropriate, suitable and available for service and review maintenance documentation associated with this type of component for suitability in order to remove any error traps and add appropriate pass/fail criterion. A level 4 regulatory issue (6267) was raised to address our concerns.  

During the plant walkdown, we noted that the housekeeping arrangements met the standards and expectations the licensee aspires to.

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 transformers, grid systems, and main electrical system met the requirements of the safety case.

Regarding the Heysham A / Hartlepool steam release safety case information gathering meeting, we were satisfied with the advice, discussions and explanations given at this point. We were also content that there is no need for any regulatory action at this point.

From the ONR issues review meeting 102, the station are generally progressing the ONR issues with a number being closed out since the previous review.  There are some longstanding issues in PSA/ DBA area that should be reviewed and civil issues that are substantially completed.  However no concerns of significance that requires issues to be escalated at this time.

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 Heysham A Power Station as set out in the Integrated Intervention Strategy, which will continue as planned.